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Long-term annual burning of grassland increases CO 2 emissions from soils
Abstract
Grasslands have potential to mitigate against climate change because of their large capacity to store soil organic carbon (SOC). However, the long-term impact of grassland management such as burning, which is still common in many areas of the world, on SOC is still a matter of debate. The objective of this study was to quantify the long-term effects of annual burning on CO 2 output from soils and SOC stocks. The study was performed on a 62 years old field trial comparing annual burning (AB) to no burning associated with tree encroachment (NB), and to annual mowing (AM) with all treatments laid out in randomized block design with three replicates per treatment. CO 2 emissions from soil were continuously measured over two years and were correlated to soil chemical and physical properties. AB and AM produced 30 and 34% greater CO 2 emissions from soil than NB (1.80 ± 0.13 vs. 2.34 ± 0.18 and 2.41 ± 0.17 g C-CO 2 m −2 d −1 for NB, AB and AM respectively). AB and AM also produced greater CO 2 emissions from soil and per gram of soil carbon (1.32 ± 0.1 and 1.35 ± 0.1 mg C-CO 2 g C −1 d −1 , respectively) than NB (1.05 ± 0.07 mg C-CO 2 g C −1 d −1), which corresponded to significant differences of respectively 26% and 29%. Overall, CO 2 emissions from soil (per m 2) significantly increased with soil water content (r = 0.72) followed by SOC stocks (r = 0.59), SOC content (r = 0.50), soil bulk density (r = 0.49), soil temperature (r = 0.47), C:N ratio (r = 0.46) and mean weight diameter (r = 0.38). These findings suggest that long-term annual burning increases CO 2 output from soils. Additional greenhouse gases emissions from burning itself and alternative grassland management techniques were finally discussed.
... Burning of grass is a traditional grassland management practice that has long been used to enhance grass productivity and prevent bush encroachment (Montané et al., 2007;Trollope, 1980). However, burning of grasslands was found to increase soil C losses Abdalla et al., 2016;Xu & Wan, 2008). Abdalla et al. (2016) found that long-term (62-year) annual burning increased soil CO 2 by 30% compared with unburned grass in South Africa. ...
... However, burning of grasslands was found to increase soil C losses Abdalla et al., 2016;Xu & Wan, 2008). Abdalla et al. (2016) found that long-term (62-year) annual burning increased soil CO 2 by 30% compared with unburned grass in South Africa. Such an increase in CO 2 emissions from burned grassland soil was explained by soil aggregate instability . ...
... The higher aboveground biomass production is associated with a higher soil C sequestration rate (Table 3), implying that high soil cover by grass reduces soil water losses via evaporation and topsoil temperature fluctuations (e.g. Abdalla et al., 2016;Bahn et al., 2008;Guntiñas et al., 2012). Soil temperature, which correlated positively to CO 2 emission (Table 3, Figure 5), is an accurate proxy for estimating soil respiration in the absence of water stress (Bahn et al., 2008). ...
Restoration of degraded grasslands through improved management is among the
possible sustainable solutions to compensate for anthropogenic soil carbon (C)
emissions. While several studies have shown a positive effect of rehabilitation on
soil C, the impact on soil CO2 emissions is still uncertain. Therefore, this study
aimed at quantifying the impact of grassland rehabilitation on soil CO2 emissions
in a degraded grassland, South Africa. Commonly used rehabilitation practices
were considered, that is rotational grazing (RG), livestock exclosure with
fertilizer application (EF) and annual burning (AB), all being compared with
traditional free grazing (FG). A total of 2880 in situ measurements of CO2 emissions
were performed over 2.5 years under field conditions simultaneously with
aboveground biomass, soil temperature, water content and soil organic C (SOC)
to understand the changes in C fluxes. The RG performed the best under degraded
grasslands by decreasing net CO2 emissions (per g of C) by 17% compared
to FG, while EF increased emissions by 76% and AB had similar emissions to FG.
The lower net emission under RG is associated with an increase in SOC stocks
by 50% and aboveground biomass by 93%, after three years of implementation.
Soil CO2 emissions were correlated positively to aboveground biomass and topsoil
temperature (r = 0.91 and 0.60, respectively), implying a high effect of grass
cover on soil microclimate and microbial activity. These results suggested RG as
a potential cost-effective
nature-based
soil management strategy to increase SOC
stocks into degraded grassland. However, long-term
trials replicated in different
environments are still required.
... The C is mainly stabilized in the soil aggregates, with the level of stabilization depending on the soil aggregation controlled, mainly by the management practices (Egan et al., 2018;Six et al., 2002). Management practices such as grassland burning and mowing can strongly affect soil aggregation and soil CO 2 emissions, thus alter the soil C stocks of managed grasslands (Abdalla et al., 2016;Shimoda & Takahashi, 2009;Soong & Cotrufo, 2015). ...
... Therefore, the present study investigated the proportion of aggregate fractions and the SOC and N content associated with these fractions in a long-term grassland experiment established in 1950 at the Ukulinga research farm in South Africa. The obtained SOC data were correlated to soil CO 2 emissions measured at the same site by Abdalla et al. (2016) to address the potential effect of SOC in different aggregate fractions on soil CO 2 emissions. The study hypothesized that first, long-term annual burning would decrease aggregate stability, and C and N pools in the soils compared to annual mowing and undisturbed grassland because the combustion of aboveground biomass and litter reduces fresh C input to soils. ...
... The soils are derived from colluvium shale with dolerite intrusions and are classified as Plinthic Acrisols (IIUS-WRB, 2014). Soil depth is shallow, ranging from 5 cm in the upslope to a maximum of 60 cm depth in the downslope (Abdalla et al., 2016). ...
ABSTRACT
Burning has commonly been used to increase forage production and nutrients cycling in grasslands. However, its long-term effects on soil organic carbon (SOC) and nitrogen (N) pools within the aggregates and the relation between aggregates-associated SOC and soil CO2 emissions need further appraisal. This study evaluated the effects
of 64 years of annual burning on SOC and N dynamics compared to annual mowing and undisturbed treatments in a grassland experiment established in 1950. Soils were sampled from four depths representing the upper 30 cm layer and fractionated into macroaggregates, microaggregates and silt + clay fractions. The macroaggregates
were further fractionated into three occluded fractions. The SOC in the bulk soil and aggregates were correlated to soil CO2 effluxes measured under field conditions. Compared to the undisturbed treatment, annual burning decreased aggregates stability,
SOC and N in the upper 30 cm layer by 8%, 5% and 12%, respectively. Grassland mowing induced greater aggregates stability than burning only in the upper 5 cm. Burning also decreased SOC in the large macroaggregates (e.g., 0–5 cm) compared to mowing and the undisturbed grasslands but proportionally increased the microaggregates and their associated SOC. Soil N associated with aggregates decreased largely following grassland burning, for example, by 8.8-fold in the microaggregates within the large macroaggregates at 20–30 cm compared to the undisturbed grassland. Burning also increased soil CO2 emissions by 33 and 16% compared to undisturbed and mowing, respectively. The combustion of fresh C and soil organic matter by fire is likely responsible for the low soil aggregation, high SOC and N losses under burned grassland. These results suggested a direct link between grass burning and
SOC losses, a key component for escalating climate change severity. Therefore, less frequent burning or a rotation of burning and mowing should be investigated for sustainable grasslands management.
KEYWORDS
annual mowing, climate change, grassland sustainability, soil aggregates, soil respiration, South
Africa
... Burning of grass is a traditional grassland management practice that has long been used to enhance grass productivity and prevent bush encroachment (Montané et al., 2007;Trollope, 1980). However, burning of grasslands was found to increase soil C losses Abdalla et al., 2016;Xu & Wan, 2008). Abdalla et al. (2016) found that long-term (62-year) annual burning increased soil CO 2 by 30% compared with unburned grass in South Africa. ...
... However, burning of grasslands was found to increase soil C losses Abdalla et al., 2016;Xu & Wan, 2008). Abdalla et al. (2016) found that long-term (62-year) annual burning increased soil CO 2 by 30% compared with unburned grass in South Africa. Such an increase in CO 2 emissions from burned grassland soil was explained by soil aggregate instability . ...
... The higher aboveground biomass production is associated with a higher soil C sequestration rate (Table 3), implying that high soil cover by grass reduces soil water losses via evaporation and topsoil temperature fluctuations (e.g. Abdalla et al., 2016;Bahn et al., 2008;Guntiñas et al., 2012). Soil temperature, which correlated positively to CO 2 emission (Table 3, Figure 5), is an accurate proxy for estimating soil respiration in the absence of water stress (Bahn et al., 2008). ...
Restoration of degraded grasslands through improved management is among the possible sustainable solutions to compensate for anthropogenic soil carbon (C) emissions. While several studies have shown a positive effect of rehabilitation on soil C, the impact on soil CO2 emissions is still uncertain. Therefore, this study aimed at quantifying the impact of grassland rehabilitation on soil CO2 emissions in a degraded grassland, South Africa. Commonly used rehabilitation practices were considered, i.e., rotational grazing (RG), livestock exclosure with fertilization (EF) and annual burning (AB), all being compared to traditional free grazing (FG). A total of 2880 in‐situ measurements of CO2 emissions were performed over 2.5 years under field conditions simultaneously with aboveground biomass, soil temperature, water content, and soil organic C (SOC) to understand the changes in C fluxes. The RG performed the best under degraded grasslands by decreasing net CO2 emissions (per g of C) by 17% compared to FG, while EF increased emissions by 76% and AB had similar emissions to FG. The lower net emission under RG is associated with an increase in SOC stocks by 50% and aboveground biomass by 93%, after three years of implementation. Soil CO2 emissions were correlated positively to aboveground biomass and topsoil temperature (r = 0.91 and 0.60, respectively), implying a high effect of grass cover on soil microclimate and microbial activity. These results suggested RG as a potential cost‐effective nature‐based soil management strategy to increase SOC stocks into degraded grassland. However, long‐term trials replicated in different environments are still required.
... Grasslands, which are natural ecosystems with grass as the dominant vegetation, occupy about 40% of the earth's land surface area and 70% of all agricultural land (FAO, 2015). Despite being mostly found under the arid to semi-arid climates of Africa, Asia and America where net primary production is significantly lower than the worldwide average (Abdalla et al., 2016), grassland soils store about 10% of the global soil organic C (SOC) stocks, which is nearly 50% more than is stored in forests worldwide (FAO, 2015). Previous work established that grassland soil C stocks are sensitive to changes in land use and management. ...
... It was also learned from Abdalla et al. (2016) that when grazing intensity rises above carrying capacity, SOC stocks decrease at an average rate of − 0.9% per year, which can be attributed to a net loss of grass and/or inability of frequently grazed plants to build root C reserves, thus unable to sustain atmospheric C allocation to soils (Savory and Parsons, 1980). On the other hand, Conant et al. (2017) reported that only 49% of worldwide studies on improved grassland management practices such as low stocking rates, exclusion of grazing livestock and planned rotational grazing enhanced SOC stocks, thus pointing to the absence of consensus on the grassland management strategies to promote for increasing SOC stocks. ...
... There is also no consensus on the impact of practices that do not involve livestock such as burning, which is a common practice for increasing fodder production and quality, whilst avoiding bush encroachments (Tainton, 1999). For instance, Abdalla et al. (2016) reported that SOC stocks increased from 1.4 to 1.6 kg C m − 2 (i.e. by 14%) in the 0-0.2 m soil depth of a long-term (70 years) annual burning trial in sub-tropical humid South Africa. However, Granged et al. (2011) reported a decrease of 35% for a site in Spain, and Nardoto and Bustamante (2003) reported a 13% decline for another site in Brasil. ...
Grasslands occupy 70% of whole agricultural land and hold significant amounts of carbon, a key element in the regulation of Earth's soils fertility, biomass production and climate. Previous work has shown that carbon stocks of grassland soils have been largely depleted worldwide due to missuse or mismanagement but that shifts in management could also potentially increase soil carbon stocks and mitigate against the degradation of natural ecosystems. However, the existing literature points to large discrepancies in the impact of grassland management practices on soil carbon, which the present study investigated. Here we considered 235 experimental sites in 18 countries across the world where shifts in grassland management involved different grazing strategies (free, F vs controlled, C; high, H vs low, L density grazers), grazers exclusion (E), mowing (M) and burning (B). The best performing practice was controlled grazing with high density of grazers (CHG) with an average soil organic carbon content (SOCC) increase of 21% and with 100% of the studies pointing to a SOCC increase. This was followed by E (14.9%; 60%) and FLG (13.3%; 80%). On average, burning grasslands, decreases SOCC by 9.3% but 31% of the studies pointed to an increase, thus indicating discrepancies in the impact of grassland management. CLG and mowing did not significantly impact SOCC. These results also indicated that B decreased SOCC the most under moist to humid climates (−10.9% vs −1.7% under arid to semi-arid), while that E was only beneficial in arid to semi-arid grasslands. Adoption of rotational high-intensity grazing in place of free grazing grasslands, should be seriously considered by policy and decision makers to mitigate against climate change while fostering economic and social development.
... The C is mainly stabilized in the soil aggregates, with the level of stabilization depending on the soil aggregation controlled, mainly by the management practices (Egan et al., 2018;Six et al., 2002). Management practices such as grassland burning and mowing can strongly affect soil aggregation and soil CO 2 emissions, thus alter the soil C stocks of managed grasslands (Abdalla et al., 2016;Shimoda & Takahashi, 2009;Soong & Cotrufo, 2015). ...
... Therefore, the present study investigated the proportion of aggregate fractions and the SOC and N content associated with these fractions in a long-term grassland experiment established in 1950 at the Ukulinga research farm in South Africa. The obtained SOC data were correlated to soil CO 2 emissions measured at the same site by Abdalla et al. (2016) to address the potential effect of SOC in different aggregate fractions on soil CO 2 emissions. The study hypothesized that first, long-term annual burning would decrease aggregate stability, and C and N pools in the soils compared to annual mowing and undisturbed grassland because the combustion of aboveground biomass and litter reduces fresh C input to soils. ...
... The soils are derived from colluvium shale with dolerite intrusions and are classified as Plinthic Acrisols (IIUS-WRB, 2014). Soil depth is shallow, ranging from 5 cm in the upslope to a maximum of 60 cm depth in the downslope (Abdalla et al., 2016). ...
Burning has commonly been used to increase forage production and nutrients cycling in grasslands. However, its long-term effects on soil organic carbon (SOC) and nitrogen (N) pools within the aggregates and the relation between aggregates-associated SOC and soil CO2 emissions needs further appraisal. This study evaluated the effects of 64-years of annual burning on SOC and N dynamics compared to annual mowing and undisturbed treatments in a grassland experiment established in 1950. Soils were sampled from four depths representing the upper 30 cm layer and fractionated into; macroaggregates, microaggregates, and silt+clay fractions. The macroaggregates were further fractionated into three occluded fractions. The SOC in the bulk soil and aggregates were correlated to soil CO2 effluxes measured under field conditions. Compared to the undisturbed treatment, annual burning decreased aggregates stability, SOC and N in the upper 30 cm layer by 8, 5 and 12%, respectively. Grassland mowing induced greater aggregates stability than burning only in the upper 5 cm. Burning also decreased SOC in the large macroaggregates (e.g., 0-5 cm) compared to mowing and the undisturbed grasslands but proportionally increased the microaggregates and their associated SOC. Soil N associated with aggregates decreased largely following grassland burning, e.g., by 8.8-fold in the microaggregates within the large macroaggregates at 20-30 cm compared to the undisturbed grassland. Burning also increased soil CO2 emissions by 33 and 16% compared to undisturbed and mowing, respectively. The combustion of fresh C and soil organic matter by fire is likely responsible for the low soil aggregation, high SOC and N losses under burned grassland. These results suggested a direct link between grass burning and SOC losses, a key component for escalating climate change severity. Therefore, less frequent burning or a rotation of burning and mowing should be investigated for sustainable grasslands management.
... The use of prescribed fire as a key management tool in grasslands is still debated, as evidenced by historical fire suppression initiatives (Bond, 2016;Tilman et al., 2000). Regular and more frequent fires reduce SOC over time in arid to semi-arid grasslands and savannas (Abdalla et al., 2016;Knicker, 2007). A recent study in Kruger National Park long-term burning trails showed that whilst a fire-excluded closed savanna had higher long-term total C, annual burning led to an immediate, short-term increase in total C attributed to post-fire pyrogenic C input (Strydom et al., 2024). ...
... However, in humid regions, studies suggest that fire exclusion and the resulting afforestation decrease SOC storage (Jackson et al., 2002;Mureva et al., 2018). In a long-term burning experiment, although fire increased CO 2 emissions from soils, SOC was 13% higher in annually burnt mesic grasslands than in unburnt woody-encroached grasslands, suggesting that fire resulted in long-term SOC storage because of increased productivity post-fire (Abdalla et al., 2016). ...
Despite the importance of South Africa's Afromontane grasslands for ecosystem services (water supply and biodiversity), soil organic carbon (SOC) research remains limited. These grasslands evolved with fire, and fire exclusion leads to native plant afforestation. This study investigated SOC fractions and origin to understand the impact of fire‐exclusion‐driven afforestation and aspect on SOC storage in Afromontane grasslands. This study in Cathedral Peak Research Catchments, initiated in the 1940s, compared an afforested fire‐excluded site (AF) to a periodically burnt (accidental fires, 2–5 years interval) grassland (PB) within the same catchment (Catchment‐IX). Additionally, it compared a south‐facing periodically burnt grassland (Catchment‐IX) to a north‐facing biennially burnt grassland (Catchment‐VI). Soil samples collected at soil‐depth increments (0–5, 5–10, 10–15, 15–20, 20–30, 30–60 and 60–100 cm) revealed that, within Catchment IX, PB had more topsoil SOC stocks and microbial activity than AF but similar active carbon (C) concentrations. As expected, δ ¹³ C values revealed that SOC in PB originates from C 4 grasses, whilst it mostly originates from C 3 plants in AF. The south‐facing slope (Catchment‐IX) had more SOC stocks, microbial activity and active C compared to the north‐facing slope (Catchment‐VI). Fire‐exclusion‐driven afforestation changed SOC input from roots to litter, thus reducing SOC storage. Cooler south‐facing slopes are better C reservoirs. Afromontane grasslands show greater potential for C sequestration than afforested systems.
... About 70% of agriculture land lies mostly in arid and semiarid regions of Africa, Asia, and America. These regions have very low primary productivity in comparison to world average production (Abdalla et al. 2016). Although these regions store only about 10% of the global SOC stocks, it is nearly half of that is sequestered in forests worldwide (FAO 2015). ...
... Another intensive meta-analysis of 628 soil profiles showed that decreasing quality of grasslands resulted in on average 9% decline in SOC (Dlamini et al. 2016). Also decrease in SOC is associated with rise in frequency of grazing due to net loss of vegetation and poor root development of grasses (Abdalla et al. 2016). ...
The carbon (C) problem and its impact on climate have been attracting attention for
many decades. The last few decades have seen tremendous changes in agriculture
and the world’s food chain. New and modern agriculture techniques result in more
depletion of C from the soil and cause a remarkable increase in C concentration in
the atmosphere. Increased demand for food and energy is the two main anthropogenic factors affecting soil organic carbon (SOC) status in a climate change era.
While global trade in agricultural commodities has increased interconnectivity
among food resources in developed and developing countries, it has also contributed
to and exacerbated the challenges related to malnutrition, food security, environmental degradation, and large-scale soil sustainability, making it harder to achieve
the targets of Sustainable Development Goals (SDGs) of eliminating poverty and
hunger. Different technologies, programs, and policies should be adopted for
enhancing SOC in the soil of various agroecosystems. Soil C levels have reduced
over decades of conversion of pristine ecosystems into agricultural landscapes,
which now offers the opportunity to store C from the air into the soil. C stabilization
into agricultural soils is a novel research approach and offers a promising reduction
in atmospheric carbon dioxide (CO2) levels. This book brings together all aspects of
plans and policies for SOC management in agriculture, with a special focus on the
diversity of management practices of soil in agricultural systems. The book offers
broad ideas of new plans and policies for improving SOC in the agricultural
production system. It will be suitable for teachers, researchers, policymakers, and
undergraduate and graduate students of soil science, microbiology, agronomy,
ecology, and environmental sciences.
... About 70% of agriculture land lies mostly in arid and semiarid regions of Africa, Asia, and America. These regions have very low primary productivity in comparison to world average production (Abdalla et al. 2016). Although these regions store only about 10% of the global SOC stocks, it is nearly half of that is sequestered in forests worldwide (FAO 2015). ...
... Another intensive meta-analysis of 628 soil profiles showed that decreasing quality of grasslands resulted in on average 9% decline in SOC (Dlamini et al. 2016). Also decrease in SOC is associated with rise in frequency of grazing due to net loss of vegetation and poor root development of grasses (Abdalla et al. 2016). ...
Environmental management and its sustainability are a key concern today. Anthropogenic CO2 emission and its related negative consequences on environment were observed due to industrial development, mining, deforestation, and intensive agricultural practices. This unstoppable rising CO2 concentration impairs key environmental services and its sustainability. Recently, NOAA-based Mauna Loa Atmospheric Baseline Observatory has reported CO2 concentration of about 419 ppm in 2021 along with 40 billion MT of CO2 pollution every year in the environment. This figures enough to represent unstoppable CO2 emissions which need global concern urgently. GHGs including CO2 emissions raised global temperature are under the discussion table of IPCC and at global policy platforms during Paris Agreement and COP-21. However, many countries have participated in Paris Agreement and COP-21 for reducing emissions and set a target to reduce 2 °C global temperature identified by IPCC. Similarly, the target of zero emission is also discussed in several climate policy papers including IPCC and during Paris Agreement and COP-21. Introducing recent and updated climate-resilient technologies, viz. carbon dioxide capture, and storage (CCS), reduces excessive emission and performs C sequestration and storage for long term in various environmental components such as lithosphere (soil/geology), hydrosphere (ocean), and biosphere. Similarly, forest-based CO2 removal (CDR) policy emphasized sustainable forest management (SFM) practices for greater CO2 sink and storage in terrestrial forest ecosystem. Monitoring CO2 concentration in environment through remote sensing is an effective tool that helps to assess CO2 sequestration at global level. An effective policy, research, and favorable political situation are needed for greater potential of CO2 removal and storage into the vegetation, ocean, and underground geological formation. Thus, a hawk eye remains constant on rising CO2 in atmosphere and its sequestration through better research technologies for sustainable environment which becomes global agenda for climate policy makers.KeywordsCO2 sequestrationCCSEnvironmental managementSustainabilityClimate policy
... Contudo, as emissões provenientes das queimadas anuais para manejo de PN, podem influenciar na qualidade do ar na região, contribuindo para a poluição atmosférica. As pastagens manejadas com a queima, apresentam maiores teores de emissão de CO2 para a atmosfera do que o manejo sem queima (SOUZA et al., 2015;ABDALLA et al., 2016). No entanto, a exposição a altos níveis de poluentes atmosféricos emitidos por queimadas, podem causar uma variedade de danos à saúde humana (CARMO et al., 2013). ...
... Todavia, as pastagens manejadas com a prática da queimada, causam impactos ao solo, e emitem gases poluentes para a atmosfera (CHRISTOPHERSON, 2012;CARMO et al., 2013;SOUZA et al., 2015;ABDALLA et al., 2016). Diante do exposto, o objetivo do presente trabalho é avaliar o comportamento das Cada um dos pontos fora amostrado três vezes, cujos poluentes atmosféricos medidos foram: dióxido de carbono (CO2), monóxido de carbono (CO), monóxido de nitrogênio (NO), dióxido de nitrogênio (NO2) e dióxido de enxofre (SO2), além das variáveis temperatura ambiente e umidade relativa ambiente. ...
No município de Lages-SC, a queima de campo para manejo do solo ainda é muito praticada pelos produtores e pecuaristas. Contudo, apesar de liberadas em algumas situações, estas ações podem afetar a qualidade do solo e da vegetação e serem fontes emissoras de poluentes potencializando a poluição atmosférica e o aumento das concentrações dos gases de efeito estufa. Diante disso, objetivou-se com este estudo, verificar o comportamento dos gases emitidos na queima de uma pastagem natural e apresentar os possíveis impactos provenientes desta prática. As coletas foram efetuadas em um ponto controle sem presença de queima e em três pontos com a presença de queima, nas fases de chama e fumaça, mediante a equipamentos de medição portáteis e de resultados instantâneos. As coletas foram realizadas no período vespertino em setembro de 2020. Os gases amostrados foram o CO, CO2, NO, NO2 e SO2, além da temperatura e umidade relativa do ambiente. As concentrações dos pontos de coleta na fase de chama foram menores do que as concentrações nos pontos de coleta na fase de fumaça. Verificou-se que as concentrações dos compostos foram influenciadas pelos fatores meteorológicos, as características da vegetação predominante em cada ponto de coleta e pela dispersão destes por meio do vapor d’água. Diante da importância da manutenção das pastagens naturais e os impactos que as emissões provenientes das queimadas causam ao meio ambiente e à saúde humana, se fazem necessários mais estudos que venham a contribuir para o entendimento da relação deste com a presença do fogo. Em busca de manejo adequado, eficiente e de baixo impacto, que mantenham as pastagens naturais, proporcione qualidade ao solo e vegetação, bem como baixas emissões para a atmosfera. No entanto, estes conhecimentos devem ser dissipados, servindo de base para a criação de políticas eficientes e capazes de mitigar os impactos ao meio.
... (1) (Abdalla et al., 2016) where Xi is the mean diameter for each fraction size, Wi is the proportional weight of the fraction from the total dry weight of soil used, and n is the number of aggregate classes separated. Organic C in water-stable soil aggregate fractions and bulk soil was analyzed using the Walkley-Black dichromate oxidation method (Walkley and Black, 1934). ...
... Location of the long-term grassland study site in South Africa.(Abdalla et al., 2016). ...
... Additionally, it can improve coverage and biodiversity [56]. This combination of factors may contribute to the observed increases in soil C and N stocks, as reported by Abdalla et al. [57] and Manson et al. [58], in pasture areas. ...
This study aimed to analyze the carbon (C) stock and stabilization of soil organic matter in particulate- and mineral-associated fractions across different land use systems after 32 years of experimentation in the Brazilian Cerrado. The experiment was established in 1991 and was performed in Planaltina-DF. The treatments evaluated included continuous pasture with monoculture grasses; integrated crop–livestock systems under no tillage; continuous cropping under no tillage; minimum tillage; and the preservation of the native Cerrado biome in its original condition. Soil sampling was performed to a depth of 30 cm. Carbon and nitrogen (N) stocks were quantified for the years 2001, 2009, 2013, and 2023, with soil organic matter fractionation performed on samples from 2023. Land use change resulted in significant losses of soil C and N in areas managed with conventional soil preparation practices. Systems that promote plant diversity, such as integrated crop–livestock systems, enhanced soil C and N stocks (72.8 and 5.5 Mg ha−1, respectively) and increased both particulate organic matter and mineral-associated fractions, most of which were in more stabilized forms. Integrated crop–livestock systems are management practices that offer an effective alternative to present methods in terms of combating climate change and supporting ecosystem sustainability.
... Therefore, the interaction between warming and N addition on GHG fluxes requires comprehensive analysis. Furthermore, previous studies generally do not consider the impacts of changes in edaphic factors, including SOC, dissolved organic carbon (DOC), microbial biomass carbon (MBC), NH 4 + , nitrate (NO 3 − ), total nitrogen (TN), and microbial biomass nitrogen (MBN), on GHG fluxes under both warming and N addition ( Abdalla et al., 2016 ;Iqbal et al., 2010 ;Nelissen et al., 2012 ;Zhou et al., 2016a ). Therefore, a comprehensive understanding of warming and N addition on GHG fluxes can help to predict terrestrial ecosystem C and N cycling under global change. ...
... Low-severity fires often result in C accumulation due to partly burned and slash fragments that enter the soil, whereas high-severity fires lead to significant C loss (Alcañiz et al., 2018), particularly in forests compared with grasslands Zhou et al., 2022). While studies have shown that fire severity can increase the magnitude of the declines of R s , R h and R a (Cooperdock et al., 2020;Dooley & Treseder, 2012;Hu et al., 2021;Wang et al., 2012) due to increased plant and microbial mortality, other studies (particularly short-term) have reported positive or neutral impacts (Abdalla et al., 2016;Fierro et al., 2007;Hu et al., 2020;Martínez-García et al., 2017). Inconsistent responses for larger spatiotemporal scales might be attributed to the differences in fire characteristics, sampling times, vegetation restoration processes, biomes and management practices Song et al., 2019). ...
The impact of fire on above‐ground biomass has significant consequences on soil carbon (C) dynamics, which is essential in predicting the global C budget during the Anthropocene. However, there is considerable spatiotemporal variability in the directions and magnitudes of fire effects on soil respiration, and the drivers associated with these effects are not well understood.
Here, we conducted a global meta‐analysis of 1327 individual observations from 170 studies to determine the extent to which fire influenced soil total respiration (Rs), heterotrophic respiration (Rh) and autotrophic respiration (Ra).
We found fires reduced Rs, Rh and Ra, with an average effect of −11.0%, −17.5% and −40.6%, compared with unburnt sites. Specifically, wildfires significantly reduced Rs and Rh (−20.4% and −25.0%, respectively), and prescribed fire significantly decreased Ra (−74.8%). The influences of fire on Rs and its components were moderated by fire severity, season, type, climate zones and biomes. After several years from the time of the fire, the negative effects of fire on Rs diminished and then recovered to a state not significantly different from unburnt sites; Rh exhibited a similar but decayed temporal response. Similarly, the negative effects on Ra disappeared after 3 years following the latest fire. The magnitude of the effect on Rs was strongly associated with soil temperature, cation exchange capacity, total nitrogen (N) content and N‐acquiring enzyme activity. In contrast, the magnitude of the effect on Rh significantly changed with pH, bulk density, texture, soil C and nutrient contents, and C‐acquiring enzyme activity.
Our findings advance the understanding of the inhibition and associated mechanisms of fire on Rs and its components, highlighting the need for new research efforts to predict the spatial‐temporal shifts in underground C‐cycling induced by fire.
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... The grasslands cover approximately 40% of the Earth's land surface (Le Cain et al., 2002;Wang and Fang, 2009) and provide livelihoods for nearly 800 million people, as well as forage for livestock, wildlife habitat, valuable ecosystem services and locations for recreation and tourism (White et al., 2000;Zhang, 2006;Stromberg et al., 2013). Grassland ecosystems serve important economic and ecological functions, such as material production, climate regulation, soil and water conservation, sand stabilization, soil improvement and biodiversity preservation (Liu et al., 2011;Abdalla et al., 2016;Trepekli et al., 2016). However, grassland ecosystems are easily susceptible to disturbances and highly vulnerable to climate change and human activities (Li et al., 2007;Yan et al., 2013;Davis et al., 2014;Eichelmann et al., 2016). ...
Grasslands form an important component of forests in Kashmir Himalaya and form subsistence basis for the local as well as nomadic farm families. They support livestock species which in turn play very important economic and socio-cultural roles for the wellbeing of rural households in the form of food, income, asset saving, transport, and sustainable agricultural production. However, overgrazing coupled with improper management of grasslands is gradually impairing their regenerative potential. The overgrazing in grasslands results in a deleterious change in floristic composition, productivity, and palatability. We investigated the effect of grazing on the productivity of herbaceous vegetation in grasslands of Kashmir Himalaya by a comparative analysis of protected and unprotected plots. The plant species occurring in the study area were listed and their biomass (above-ground and below-ground) was estimated by clippings. The study revealed low values for biomass in unprotected plots and vice-versa was true for protected plots. The low biomass is attributed to the removal of an appreciable quantity of herbage cover by grazing animals. The species richness and the floristic composition modified significantly with grazing intensification.
... For instance, Li et al. (2017b) reported that continued grazing all the year round significantly decreased the aboveground biomass, diversity and ecosystem C storage in an alpine meadow on the Qinghai-Tibet degradation on soil organic C storage globally by a meta-analysis, and found that the soil organic C storage decreased by 16% and 23.7% in dry climates and Asia, respectively. In addition, Abdalla et al. (2016) reported that annual burning and annual mowing of grassland significantly increased soil CO 2 emissions by 30% and 34% respectively, in South Africa. Therefore, it is important to explore a scientific grassland management strategy for improving the production and ecological function of grasslands. ...
Grazing exclusion has been widely used to restore degraded grasslands worldwide. Total soil respiration (Rs) (consisting of heterotrophic respiration (Rh, microbes and soil fauna respiration) and autotrophic respiration (Ra, plant root and their symbionts respiration)) play a critical role in the global carbon (C) balance. Quantifying Rs, Rh and Ra in relation to different grazing exclusion durations is vital to better understanding the impact of grassland management on global C cycling. However, how Rs and its components respond to different grazing exclusion durations remain unclear. Therefore, in this study, a trenching method was used to separate the Ra and Rh in an alpine meadow with different grazing exclusion durations (0, 4, 7, 10 and 12 years) on the north-eastern Qinghai-Tibet Plateau. Our results demonstrated that the growing season Rs, Rh and Ra showed nonlinear (hump-shaped) response patterns with the length of grazing exclusion, with a peak point at the 7-year grazing exclusion. Meanwhile, grazing exclusion treatments significantly increased the Rs, Rh and Ra compared to the grazed site. Grazing exclusion substantially increased the soil respiration temperature sensitivity (Q10) values of Rs, Rh and Ra. Moreover, the Q10 values of Ra and Rh showed hump-shaped response patterns with the length of grazing exclusion, with a threshold of 7 years grazing exclusion. The annual Ra/Rs ratio ranged from 53% to 69% during the growing season, indicating that changes in soil respiration were mainly determined by changes in autotrophic respiration. In addition, soil temperature could better explain Rh (R² = 0.89–0.94) than Ra (R² = 0.84–0.9). Our research highlights the nonlinear response of Rs, Rh and Ra to the length of grazing exclusion, and suggests that different grazing exclusion durations should be considered for better evaluating the impact of grassland management on global C cycling on the north-eastern Qinghai-Tibet Plateau.
... For instance, Li et al. (2017b) reported that continued grazing all the year round significantly decreased the aboveground biomass, diversity and ecosystem C storage in an alpine meadow on the Qinghai-Tibet degradation on soil organic C storage globally by a meta-analysis, and found that the soil organic C storage decreased by 16% and 23.7% in dry climates and Asia, respectively. In addition, Abdalla et al. (2016) reported that annual burning and annual mowing of grassland significantly increased soil CO 2 emissions by 30% and 34% respectively, in South Africa. Therefore, it is important to explore a scientific grassland management strategy for improving the production and ecological function of grasslands. ...
... Harris et al. (2007) suggested that burning grasslands might only affect superficial root system, with no marked effect in deeper soil layers. In fact, the actual impact of grassland burning on SOC (and GHG) is complex and sometimes controversial (Soong and Cotrufo, 2015;Abdalla et al., 2016). There are few studies of effect of burning in the Campos region: Potes et al. (2009Potes et al. ( , 2012 and Knicker et al. (2012) observed larger stocks of SOC in areas with occasional removal of aboveground biomass by burning and concluded that plant growth could be promoted by removal of senescent biomass. ...
Agricultural expansion on pristine woodlands and grasslands in Brazil usually causes major changes in soil organic C (SOC) stocks. Quantitative assessment of these stocks, their regional distribution and variability in rural landscapes are key scientific issues related to the Brazilian commitment to pursue climate-friendly agriculture. The aim of this research was to refine existing SOC stocks estimates in the Campos de Cima da Serra (temperate highlands) of Rio Grande do Sul state. Our approach included soil sampling campaigns to obtain primary SOC data, complemented by secondary data sources (published surveys and research projects). The field study sampled surface soil layers (to 30 cm depth) stratified by the predominant soil classes and agricultural land uses: primary grasslands with and without fire management, grasslands overseeded with legume forages, and fields fallowed after intensive annual horticultural crops or Pinus plantations (secondary grasslands). Large SOC stocks (0–30 cm depth) were measured in Ultisols (244.4 Mg C ha ⁻¹ ) and Inceptisols (191.1 Mg C ha ⁻¹ ) under grasslands without burning, whereas lower stocks were found in Inceptisols under agricultural crops. SOC stocks in this study were generally larger than those calculated using IPCC global reference SOC stocks, those estimated in SOC maps of Brazil − 70% higher in Inceptisols and 120% higher in Ultisols. Our estimates were 75% higher than those estimated for the study region in a state SOC map. Soils in this region store large C stocks, which had been generally underestimated in previous smaller scale inventory. Additionally, the SOC stock map obtained allows more detailed visualization of the spatial distribution of SOC than previously possible. This information can be used to define public policies for conservation agriculture and support the update and refinement of national inventories of SOC greenhouse gases.
... However, grassland ecosystems, resource-limited by nature, are fragile and highly vulnerable to climate change and human activities because of continuously increasing livestock grazing intensity (GI) and the widespread degradation of rangelands and grasslands (Eichelmann et al. 2016;Li et al. 2007; Davis et al. 2014;Yan et al. 2013;Steinfeld et al. 2006). Grassland net primary production (NPP) is the main way in which herbivore forage consumption can be determined in semiarid ecosystems; calculating this variable, however, assumes knowledge of important economic and ecological functions including material production, climate regulation, and soil and water conservation (Abdalla et al. 2016;Trepekli et al. 2016;Liu et al. 2011). ...
Remote sensing (RS) technologies provide robust techniques for quantifying net primary productivity (NPP) which is a key component of ecosystem production management. Applying RS, the confounding effects of carbon consumed by livestock grazing were neglected by previous studies, which created uncertainties and underestimation of NPP for the grazed lands. The grasslands in Xinjiang were selected as a case study to improve the RS based NPP estimation. A defoliation formulation model (DFM) based on RS is developed to evaluate the extent of underestimated NPP between 1982 and 2011. The estimates were then used to examine the spatiotemporal patterns of the calculated NPP. Results show that average annual underestimated NPP was 55.74 gC·m⁻²yr⁻¹ over the time period understudied, accounting for 29.06% of the total NPP for the Xinjiang grasslands. The spatial distribution of underestimated NPP is related to both grazing intensity and time. Data for the Xinjiang grasslands show that the average annual NPP was 179.41 gC·m⁻²yr⁻¹, the annual NPP with an increasing trend was observed at a rate of 1.04 gC·m⁻²yr⁻¹ between 1982 and 2011. The spatial distribution of NPP reveals distinct variations from high to low encompassing the geolocations of the Tianshan Mountains, northern and southern Xinjiang Province and corresponding with mid-mountain meadow, typical grassland, desert grassland, alpine meadow, and saline meadow grassland types. This study contributes to improving RS-based NPP estimations for grazed land and provides a more accurate data to support the scientific management of fragile grassland ecosystems in Xinjiang.
... Soil aggregation contributes to the increase in aggregate diameter, and C and N stocks in the soil; and minimizes the changes in the carbon cycle that are influenced by the availability of nitrogen from soil (Zhu et al., 2017), because the greater the aggregation, the lower the flow of CO 2 from the soil (Abdalla et al., 2016). ...
Sustainable agricultural production systems can improve physical attributes of soil as well as increase carbon and nitrogen stocks in soils. The objective of this study was to evaluate changes in the stability of soil aggregates and contents and stocks of carbon and nitrogen after the conversion of native forest to crop-livestock-forest integration systems in the region of Western Pará. Soil samples from five management systems (including a control) were collected at three depths in a randomized block design, with five replications. The stability of the aggregates, soil density, particle density, and total soil porosity, as well as total carbon and nitrogen and their respective stocks were evaluated. The native forest had the highest percentages of macroaggregates, followed by the integration system with African mahogany. At a depth of 0-0.10 m, the contents and stocks of carbon were higher in the agricultural area and in the integration system with cumaru, whereas nitrogen contents and stocks were higher in the native forest, followed by the integration systems with mahogany and cumaru. Compared to the other systems, the pasture area stored more carbon at depths of 0-0.10 and 0.10-0.20 m.
... However, top-soil C:N ratio correlated positively with gross soil CO 2 emission, which agreed with findings by several previous studies (e.g. Whitaker et al., 2014;Spohn, 2015;Abdalla et al., 2016). Spohn (2015) explained such positive correlation in terms of three microbial mechanisms; nitrogen mining, overflow respiration, and enzyme inhibition. ...
Grassland degradation reduces net primary production and, subsequently, soil fertility and soil organic carbon stocks (SOCs); however, little is known about its impact on soil CO2 emissions, particularly the emissions relative to SOCs and biomass produced. The main objective of this study, performed in KwaZulu-Natal province of South Africa, was to quantify the impact of grass basal cover, as main indicator of grassland degradation, on soil CO2 emissions. The soil CO2 emissions were measured from three grass cover levels (non-degraded, with 100% grass cover; moderately degraded: 25 < grass cover < 50%; and highly degraded: 0 < grass cover < 5%) using a LI-COR 6400XT. The measurements were done at three randomly selected positions in each grass cover level, from January 2013 to April 2015. At each position, measurements were done once during winter months and twice during summer months, resulting in a total of 1053 measurements for the entire study period. The measured average gross soil CO2 emission was significantly higher (1.78 ± 0.013 g CO2-C m⁻² day⁻¹) in non-degraded than moderately (1.60 ± 0.12 g CO2-C m⁻² day⁻¹) and highly degraded grasslands (0.68 ± 0.10 g CO2-C m⁻² day⁻¹). However, when expressed relative to SOCs and aboveground biomass produced, the trends were opposite. Average soil CO2 emission relative to SOCs was lowest in the non-degraded grassland (0.034 ± 0.01 g CO2-C g⁻¹C day⁻¹) and highest in the moderately degraded grassland (0.058 ± 0.02 g CO2-C g⁻¹C day⁻¹) with the highly degraded grassland being intermediate (0.04 ± 0.00 g CO2 g⁻¹C day⁻¹). Similarly, soil CO2 emission relative to aboveground biomass produced was lowest in the non-degraded grassland at 0.15 ± 0.02 kg CO2-C kg⁻¹ biomass year⁻¹, which was almost 5 fold lower than 0.73 ± 0.01 kg CO2-C kg⁻¹ biomass year⁻¹ in the highly degraded grassland. Gross soil CO2 emission correlated significantly and positively with SOC (r = 0.83 and 0.82 for SOC content and stocks, respectively), SON (0.67 and 0.53 for content and stocks, respectively), C:N ration (0.62), and soil water content (0.75) but negatively with clay content (−0.89). Soil CO2 emission relative to SOCs correlated significantly and negatively with both SOC (−0.50 and −0.51 for content and stocks, respectively) and SON (−0.45 and −0.42 for content and stocks, respectively). While gross CO2 emissions decreased with grassland degradation, CO2 emission relative to both SOCs and aboveground biomass increased with grassland degradation. These results point to direct links between grassland degradation and global warming because CO2 is one of the key greenhouse gases. Therefore, strategies for rehabilitating degraded grasslands need to aim at reducing soil CO2 emission in order to mitigate climate change.
... Para o caso das sementes certificadas, em Chibuto, os agricultores são assistidos por extensionistas, que além de treiná-los, fazem o acompanhamento do processo produtivo, sendo solicitados pelos agricultores sempre que for necessário. No entanto, a insuficiência de extensionistas aliada a precárias condições de trabalho e a fraca organização dos agricultores, não permitem que número considerável de beneficiários seja abrangido, reduzindo a adoção e o conhecimento dos procedimentos necessários para determinada tecnologia disseminada.Contudo, quando questionados sobre as práticas realizadas durante a produção de hortícolas utilizando-se sementes melhoradas, constatou-se entre outros, a queima de restos de plantas existentes na área de produção, durante a preparação do solo, o que poderia ser evitado, de forma a conferir maior estabilidade ao solo(COWAN, SMITH & FITZGERALD, 2016;ABDALLA et al., 2016;LEÓN et al., 2015;SHAKESBY et al., 2015;BADÍA-VILLAS et al., 2014;TURRIÓN et al., 2012).Os resultados deste estudo referentes a dinâmica do uso de sementes certificadas devido aos elevados preços e a insuficiência de recursos para a sua aquisição, são similares aos apresentados em vários trabalhos(ABEBE et al., 2013;MARIANO, VILLANO & FLEMING, 2012). Entretanto, outros autores apontam para outras razões concorrentes para a não adopção deste tipo de sementes, nomeadamente, a necessidade de aquisição das sementes para cada campanha agrícola, e para o caso dos transgénicos, os potenciais riscos a biodiversidade, a saúde humana, e a incapacidade do agricultor produzir sua própria semente devendo depender do revendedor(FINCH et al., 2014;JHANSI, RANI & USHA, 2013).Olhando para as vantagens da adopção desta tecnologia, importa mencionar os altos rendimentos, maior tolerância a pragas e doenças, e aos fatores climáticos limitantes, menor ciclo das culturas e elevada qualidade dos produtos colhidos em comparação com as variedades tradicionais(DERWISCH et al., 2016;RICKER-GILBERT & JONES, 2015). ...
As projeções de crescimento populacional exigem resposta dinâmica na produção de alimentos. Deste modo, reformas devem ser feitas visando à transformação dos sistemas tradicionais para sistemas baseados em tecnologias mais produtivas, que incluem, dentre várias, o uso de sementes certificadas e mais produtivas que as tradicionais. O trabalho foi realizado no Distrito de Chibuto, e teve como objetivo obter informações sobre a dinâmica na adoção e uso de sementes melhoradas por parte dos agricultores locais. Para o efeito, foram realizadas entrevistas semiestruturadas envolvendo 35 agricultores. Constatou-se que mais de metade (62,9%) dos agricultores inqueridos utiliza sementes certificadas. Há necessidade de se acelerar o associativismo (11,43%) de forma que a assistência aos agricultores por parte de organizações públicas e privadas, possa abrangir mais famílias. 40% dos que tem acesso as sementes certificadas, mostram-se satisfeitos com os aumentos de produtividade.
... Grassland ecosystems serve important economic and ecological functions, such as material production, climate regulation, soil and water conservation, sand stabilization, soil improvement and biodiversity preservation [1][2][3]. However, grassland ecosystems are easily susceptible to disturbances and highly vulnerable to climate change and human activities, particularly in arid areas [4][5][6][7]. ...
Identifying the effects of grazing is critical for the conservation, protection and sustainable use of arid grassland ecosystems. However, research regarding the ecological effects of grazing along mountainous elevation gradients is limited in arid areas, particularly at the regional scale. Using the Biome-BGC grazing model, we explored the effects of grazing on grassland net primary productivity (NPP), evapotranspiration (ET) and water use efficiency (WUE) from 1979 to 2012 along an elevation gradient in the northern Tianshan Mountains. The NPP, ET and WUE values were generally lower under the grazing scenario than under the ungrazed scenario; the differences between the grazing and ungrazed scenarios showed increasing trends over time; and distinct spatial heterogeneity in these differences was observed. Distinct decreases in NPP and WUE under the grazing scenario mainly occurred in regions with high livestock consumption. The decrease in ET was greater in mountainous areas with high grazing intensity due to decreased transpiration and increased surface runoff. This study contributes to a better understanding of the ecological effects of grazing along an elevation gradient in the northern Tianshan Mountains and provides data to support the scientific management of grassland ecosystems.
... It is straightforward that the stages defined do not emulate exactly the burning processes of agricultural wastes in openair conditions, amidst other things, because they do not include the combustion of soil organic matter, which constitute an important carbon stock, with significant potential of CO 2 emissions for large periods (Abdalla et al. 2016). ...
Open-air burning of agricultural wastes from crops like corn, rice, sorghum, sugar cane, and wheat is common practice in Mexico, which in spite limiting regulations, is the method to eliminate such wastes, to clear the land for further harvesting, to control grasses, weeds, insects, and pests, and to facilitate nutrient absorption. However, this practice generates air pollution and contributes to the greenhouse effect. Burning of straws derived from the said crops was emulated in a controlled combustion chamber, hence determining emission factors for particles, black carbon, carbon dioxide, carbon monoxide, and nitric oxide throughout the process, which comprised three apparent stages: pre-ignition, flaming, and smoldering. In all cases, maximum particle concentrations were observed during the flaming stage, although the maximum final contributions to the particle emission factors corresponded to the smoldering stage. The comparison between particle size distributions (from laser spectrometer) and black carbon (from an aethalometer) confirmed that finest particles were emitted mainly during the flaming stage. Carbon dioxide emissions were also highest during the flaming stage whereas those of carbon monoxide were highest during the smoldering stage. Comparing the emission factors for each straw type with their chemical analyses (elemental, proximate, and biochemical), some correlations were found between lignin content and particle emissions and either particle emissions or duration of the pre-ignition stage. High ash or lignin containing-straw slowed down the pre-ignition and flaming stages, thus favoring CO oxidation to CO2.
... Chaplot et al. (2016) have found that grassland management practice based on high density and short duration of grazing to sequester atmospheric C into soils by traditional free grazing control system in South Africa. Abdalla et al. (2016) have also found that long-term (62 years old field trial) annual burning and mowing showed an increase in soil carbon in South Africa. The probable explanation could be that savanna grasslands are evolved with disturbances such as grazing and fire. ...
Controlled grazing management is considered as an effective strategy to enhance soil carbon sequestration, but empirical evidences are scarce. Particularly, the role of livestock exclusion related to soil carbon sequestration is not well understood in arid and semiarid savannas of Africa. We investigated the effectiveness of long-term (14–36 years old) exclosures in enhancing soil carbon in the semiarid savanna, southern Ethiopia. We tested for differences in soil carbon content between exclosures and adjacent open-grazed rangelands, while accounting for effects of age of exclosures and soil depths. We collected soil samples at two soil depths (0–20 cm and 20–50 cm depths) from 96 plots from 12 exclosure and adjacent open grazing sites. We found no significant differences (P > 0.05) between exclosures and adjacent open-grazed rangelands in soil carbon content in both soil depths. The age chronosequence further suggested a weak non-linear trend in increasing soil carbon content with increasing duration of exclosures. These results thus challenge the opinion that controlled grazing enhances soil carbon sequestration in semiarid savannas. However, we remain cautious in regard to the conclusiveness of these findings given the paucity of information regarding other confounding factors which may disentangle the effects of the exclosure, and most importantly in the absence of soil data prior to exclosures.
... Chaplot et al. (2016) have found that grassland management practice based on high density and short duration of grazing to sequester atmospheric C into soils by traditional free grazing control system in South Africa. Abdalla et al. (2016) have also found that long-term (62 years old field trial) annual burning and mowing showed an increase in soil carbon in South Africa. The probable explanation could be that savanna grasslands are evolved with disturbances such as grazing and fire. ...
Photovoltaic (PV) power generation is one of the world's most promising options for carbon emission reduction. However, whether the operation period of solar parks can increase greenhouse gas (GHG) emissions in hosting natural ecosystems has not been fully considered. Here, we conducted a field experiment to compensate for the lack of evaluation of the effects of PV array deployment on GHG emissions. Our results show that the PV arrays caused significant differences in air microclimate, soil properties, and vegetation characteristics. Simultaneously, PV arrays had more significant effects on CO2 and N2O emissions but a minor impact on CH4 uptake in the growing season. Of all the environmental variables included, soil temperature and moisture were the main drivers of GHG flux variation. The sustained flux global warming potential from the PV arrays significantly increased by 8.14% compared to the ambient grassland. Our evaluation models identified that the GHG footprint of PV arrays during the operation period on grasslands was 20.62 g CO2-eq kW h-1. Compared with our model estimates, GHG footprint estimates reported in previous studies were generally less by 25.46-50.76%. The contribution of PV power generation to GHG reduction may be overestimated without considering the impact of PV arrays on hosting ecosystems.
Soil carbon is vital for long-term ecosystem sustainability. Capturing of carbon in soil is cost- and time-effective strategies for reverting the process of soil degradation. Increasing carbon content in the soil, through good agricultural practices, results in enhancement of soil microbial biodiversity, soil quality, and soil water retention. Indian soils are universally deficient in soil organic carbon however has got good potential for soil carbon sequestration. Important strategies of soil C sequestration includes restoration of degraded soils and adoption of recommended management practices of agricultural and forestry soils. India should develop time-bound strategy for improving carbon storage in agricultural soils taking into account of antecedent/existing soil carbon content, soil texture, and climate (rainfall and temperature) of the region. Management interventions like balanced fertilization, INM, conservation agriculture, residue incorporation, crop rotations, and biochar application should be formulated to attain the desired goal under the given time frame. It is also imperative to formulate policy and procedure that should be auditable and verifiable with respect to baseline conditions and the additional benefits from adopting best management practices.KeywordsSoil carbonLand useConservation agricultureBiocharINMPolicy
Grasslands cover up to 40.5% of the world’s landmass and store 30% terrestrial carbon (C). Various practices, including mineral fertilization and liming, are used to manage these ecosystems with potential long-term effects on the size and distribution of soil aggregates and inevitably carbon dynamics. The objective of this study was to examine the long-term effects of nitrogen fertilization and liming on soil carbon storage and its dynamics in water-stable aggregates of a semi-arid grassland. Soil samples (0-10 cm) were collected from Ukulinga long-term grassland trial in Pietermaritzburg, South Africa where nitrogen fertilizers have been applied annually and lime every five years for 70 years. Ten treatments were studied: the control (0 kgN/ha and unlimed), lime at 2250 kg ha⁻¹ (L), ammonium sulphate at 70 kg ha⁻¹ (AS70) and 211 kg ha⁻¹ (AS211); ammonium nitrate at 70 kg ha⁻¹ (AN70) and 211 kg ha⁻¹ (AN211); AS70 + lime (AS70L); AS211 + lime (AS211L); AN70+ lime (AN70L) and AN211+lime (AN211L).
Nitrogen fertilizers significantly reduced soil pH and increased total soil N. Liming increased soil pH with no effect on total soil N. Lime and lime + N fertilizer treatments had no effect on mean weight diameter (MWD) while separate N application decreased MWD and large macro-aggregates (LMA). Lime only treatment had no effect on water stable aggregate (WSA) fractions. Nitrogen fertilization and liming (separately or in combination) did not affect total C concentration and stocks. Overall, soils had very high total soil organic carbon ranging from 49.7 – 57.6 g/kg across treatments. Nitrogen fertilization decreased organic carbon in LMA in AS70 (1.52%) and AN211 (1.67%) treatments compared to the control (3.40%) which was in concert with increases in C associated with small macro-aggregates (SMA) and micro-aggregates (MiA and SCA). Organic carbon in SMA was 2.67g/kg (AS70); AS211 (2.62 g/kg); AN70 (2.02g/kg); AN211 (2.49g/kg) compared to 1.26g/kg in the control. Lime + N fertilizer treatments increased C storage in all aggregate fractions compared to N fertilizer only treatments. The lack of response in total SOC to 70 years of N fertilization and liming suggests possible C saturation given the high soil C concentration and insignificant increase in total SOC. Changes in C associated with WSA fractions suggests their importance as diagnostic indicators of N fertilizer and liming induced changes in SOC. Findings also show that ammonium-based N fertilization is associated with soil acidification, dispersion of LMA resulting in an increase of microaggregates and C stored in them. Liming can counteracts acidifying and the dispersive effect on NH4⁺ associated with ammonium-based fertilizers thus restoring macro-aggregation in N fertilized grasslands. These findings suggests that long-term N addition may result in poor soil physical condition and possible stabilization of C in stable fractions.
Grasslands, including rangelands, shrublands, pastureland, and cropland sown with pasture and fodder crops, cover 35 million km² or 26% of the global ice-free land area. Grasslands support the livelihoods of 1 billion people with pastoralism (rising of livestock) being the most widespread human land-use system globally with 20 million km² of grassland used for livestock feed production. The global is under pasture has, particularly, strongly increased since prehistoric times. Many grasslands have suffered losses of soil organic carbon (SOC) because of soil disturbance, vegetation degradation, fire, erosion, nutrient shortage, and water deficit. The nature, frequency, and intensity of disturbance may play a key role in the SOC balance of grassland. Less well known are the effects of disturbance processes on the soil inorganic carbon (SIC) stock. However, bedrock, irrigation practices, soil acidification, liming, and grazing management potentially affect the SIC stock of grassland. In comparison, better studied are the SOC dynamics in grassland. Grasslands have a high inherent SOC stock with up to 343 Pg SOC stored to 1 m depth with a sequestration rate of 0.5 Pg C yr⁻¹. Grasslands sequester large amounts of SOC because of a high belowground C allocation, root turnover, and rhizodeposition. Grassland gross primary production (GPP) is the major natural soil C input and has been estimated at 31.3 Pg C yr⁻¹ for tropical savannas and grasslands, and to 8.5 Pg C yr⁻¹ for temperate grasslands and shrublands, respectively. The net primary production (NPP) of grassland denotes C assimilation by plants before losses caused by grazing, harvest, herbivory, mowing, and other processes. However, the numerous processes of NPP loss are among the reasons why direct measurements of NPP of grassland are challenging because not all of the biomass produced remains within the ecosystem. Further, all components of NPP of grassland must be measured in a single study. Additional research is also needed about the quantitative contribution of the major sources of SOC, and roots may play a critical role in maintaining SOC stocks in the future. Possible inputs of belowground C include: (i) incorporated surface plant residues, (ii) plant root litter and rhizodeposition, (iii) dung and urine of grazing animals, and (iv) black carbon (BC) in fire-affected grasslands. Grazing management must be targeted toward SOC sequestration due to the large global grazing land area and potential for considerable rates of increase in SOC stock.
Understanding spatio-temporal patterns of grassland evapotranspiration (ET) and water use efficiency (WUE) in arid areas is important for livestock production and ecological conservation. Xinjiang, China, was used as an example in the Biome-BGC model to explore spatio-temporal patterns of grassland ET and WUE from 1979 to 2012 in arid areas. The ET ranked from high to low as follows: among seasons, summer (142.4 mm), spring (49.7 mm), autumn (45.9 mm) and winter (7.7 mm); among regions, the Tianshan Mountains (357.9 mm), northern Xinjiang (221.3 mm) and southern Xinjiang (183.2 mm); among grassland types, mid-mountain meadow (387.7 mm), swamp meadow (358.3 mm), typical grassland (343.9 mm), desert grassland (236.2 mm), alpine meadow (229.7 mm), and saline meadow (154.7 mm). The WUE ranked from high to low as follows: among seasons, summer (0.60 g C kg H2O⁻¹), autumn (0.48 g C kg H2O⁻¹) and spring (0.43 g C kg H2O⁻¹); among regions, northern Xinjiang (0.73 g C kg H2O⁻¹), the Tianshan Mountains (0.69 g C kg H2O⁻¹) and southern Xinjiang (0.26 g C kg H2O⁻¹); among grassland types, mid-mountain meadow (0.86 g C kg H2O⁻¹), typical grassland (0.84 g C kg H2O⁻¹), swamp meadow (0.77 g C kg H2O⁻¹), saline meadow (0.52 g C kg H2O⁻¹), alpine grassland (0.37 g C kg H2O⁻¹) and desert grassland (0.34 g C kg H2O⁻¹). In Xinjiang grasslands, the spatio-temporal ET patterns were more strongly influenced by precipitation than by temperature, whereas most high WUE values occurred when precipitation and temperature were relatively conducive to grass growth.
Soil-surface CO2 flux (F(s)) is an important component in prairie C budgets. Although grazing is common in grasslands, its effects on F(s) have not been well documented. Three clipping treatments: (i) early-season clipping (EC); (ii) full-season clipping (FC); and (iii) no clipping (NC); which represented two grazing strategies and a control, were applied to plots in a tallgrass prairie in northeastern Kansas, USA. Measurements of F(s) were made with a portable gas-exchange system at weekly to monthly intervals for 1 yr. Concurrent measurements of soil temperature and volumetric soil water content at 0.1 m were obtained with dual-probe heat-capacity sensors. Measurements of F(s) also were obtained in grazed pastures. F(s) ranged annually from 8.8 x 10-3 mg m-2 s-1 during the winter to 0.51 mg m-2 s-1 during the summer, following the patterns of soil temperature and canopy growth and phenology. Clipping typically reduced F(s) 21 to 49% by the second day after clipping despite higher soil temperatures in clipped plots. Cumulative annual F(s) were 4.94, 4.04, and 4.11 kg m-1 yr-1 in NC, EC, and FC treatments, respectively; thus, clipping reduced annual F(s) by 17.5%. Differences in F(s) between EC and FC were minimal, suggesting that different grazing strategies had little additional impact on annual F(s). Daily F(s) in grazed pastures was 20 to 37% less than F(s) in ungrazed pastures. Results suggest that grazing moderates F(s) during the growing season by reducing canopy photosynthesis and slowing translocation of carbon to the rhizosphere.
The flat pampas in the state of Santa Fe in Argentina have soils with high silt content, variable carbon content, and diverse degrees of structural degradation. Aggregate stability has been used as an indicator of the structural condition of the soil. This study aimed to quantify the effect of the addition of crop residues and root activity on the agents of aggregation and mechanisms of aggregate breakdown in soils with different carbon contents and textures cultivated under no-till. An experimental trial was conducted on a loamy soil (Typic Hapludoll, Santa Isabel series) and a silty soil (Typic Argiudoll, Esperanza series) under controlled conditions for 112 days with the following treatments: (i) with and without wheat plant growth and (ii) with and without addition of wheat residues. Soil structural stability by a method allowing for differentiation of aggregate breakdown by slaking, mechanical effect and microcracking, total organic carbon content, particulate organic carbon, glomalin and carbohydrate fractions was assessed. In general, the addition of residues and the presence of plant with active roots increased the presence of all aggregation agents and decreased aggregate breakdown processes in both soils. Soluble carbohydrates and proteins related to glomalin were the most important aggregating agents and their function was to reduce the magnitude of breakdown mechanisms, slaking and microcracking, evidencing a greater impact on the silty soil.
The soil is important in sequestering atmospheric CO2 and in emitting trace gases (e.g. CO2, CH4 and N2O) that are radiatively active and enhance the ‘greenhouse’ effect. Land use changes and predicted global warming, through their effects on net primary productivity, the plant community and soil conditions, may have important effects on the size of the organic matter pool in the soil and directly affect the atmospheric concentration of these trace gases.
A discrepancy of approximately 350 × 1015 g (or Pg) of C in two recent estimates of soil carbon reserves worldwide is evaluated using the geo-referenced database developed for the World Inventory of Soil Emission Potentials (WISE) project. This database holds 4353 soil profiles distributed globally which are considered to represent the soil units shown on a 1/2° latitude by 1/2° longitude version of the corrected and digitized 1:5 M FAO–UNESCO Soil Map of the World.
Total soil carbon pools for the entire land area of the world, excluding carbon held in the litter layer and charcoal, amounts to 2157–2293 Pg of C in the upper 100 cm. Soil organic carbon is estimated to be 684–724 Pg of C in the upper 30 cm, 1462–1548 Pg of C in the upper 100 cm, and 2376–2456 Pg of C in the upper 200 cm. Although deforestation, changes in land use and predicted climate change can alter the amount of organic carbon held in the superficial soil layers rapidly, this is less so for the soil carbonate carbon. An estimated 695–748 Pg of carbonate-C is held in the upper 100 cm of the world's soils. Mean C: N ratios of soil organic matter range from 9.9 for arid Yermosols to 25.8 for Histosols. Global amounts of soil nitrogen are estimated to be 133–140 Pg of N for the upper 100 cm. Possible changes in soil organic carbon and nitrogen dynamics caused by increased concentrations of atmospheric CO2 and the predicted associated rise in temperature are discussed.
Fire and grazing have long been used as a grassland management tool in South Africa for livestock production. Despite the ecological importance of fire and grazing to the grassland ecosystem, the appropriate use of fire and grazing as a land use management tool has been questioned. The effects of different burning frequencies and stocking rates on species composition were studied between January and March 2008 using a Modified-Whittaker design in commercial farms, communal land and a nature reserve stocked with game herbivores in the highland grassland of Mpumalanga Province of South Africa. The results revealed that species assemblages of an annually burned site were completely dissimilar from a biennially burned site. The annually burned site was dominated by flora that is considered as fire-tolerant species. In contrast, the protection of some areas from burning in addition to regular burning of other areas ensured the presence of both fire-tolerant and fire-intolerant species and contributed to the high species composition of communal land. This study therefore suggests that biennial burning, or even longer intervals of burning of grazed land in addition to partial or mosaic burning should be employed to enhance the biodiversity conservation status of these montane grasslands.
Aims
Vegetation type is important in determining variations in soil carbon (C) efflux under grassland managements. This study was conducted to examine the effects of mowing and nitrogen (N) addition on soil respiration and their dependences upon vegetation types in an oldfield grassland of northern China.
Methods
Soil respiration, temperature, moisture and aboveground net primary productivity (ANPP) and belowground net primary productivity (BNPP) were examined in response to mowing and N addition among the three patches dominated by different species (named as grass, forb and mixed patches, respectively) in the growing seasons (May–October) from 2006 to 2008.
Important Findings
Across the 3 years, soil respiration in the grass patch was greater than those in the forb and mixed patches, which could have been ascribed to the higher soil moisture (SM) in the grass patch. Mowing had no impact on soil respiration due to unaltered SM and plant growth. Soil respiration was stimulated by 6.53% under N addition, and the enhancement was statistically significant in 2006 but not in 2007 or 2008 because of the limited water availability in the later 2 years. There were no interactive effects between mowing and N addition on soil respiration. Soil respiration showed positive dependence upon SM, ANPP and BNPP across plots. The results suggest that soil water availability and plant growth could be the primary factors in controlling the temporal and spatial variations in soil respiration and its response to different treatments. Our observations indicate that grassland managements (i.e. mowing for hay once a year) may have little influence on soil respiration of the oldfield grassland in northern China.
Soils are the largest terrestrial carbon store and soil respiration is the second-largest flux in ecosystem carbon cycling. Across China's temperate region, climatic changes and human activities have frequently caused the transformation of grasslands to woodlands. However, the effect of this transition on soil respiration and soil organic carbon (SOC) dynamics remains uncertain in this area. In this study, we measured in situ soil respiration and SOC storage over a two-year period (Jan. 2007-Dec. 2008) from five characteristic vegetation types in a forest-steppe ecotone of temperate China, including grassland (GR), shrubland (SH), as well as in evergreen coniferous (EC), deciduous coniferous (DC) and deciduous broadleaved forest (DB), to evaluate the changes of soil respiration and SOC storage with grassland conversions to diverse types of woodlands. Annual soil respiration increased by 3%, 6%, 14%, and 22% after the conversion from GR to EC, SH, DC, and DB, respectively. The variation in soil respiration among different vegetation types could be well explained by SOC and soil total nitrogen content. Despite higher soil respiration in woodlands, SOC storage and residence time increased in the upper 20 cm of soil. Our results suggest that the differences in soil environmental conditions, especially soil substrate availability, influenced the level of annual soil respiration produced by different vegetation types. Moreover, shifts from grassland to woody plant dominance resulted in increased SOC storage. Given the widespread increase in woody plant abundance caused by climate change and large-scale afforestation programs, the soils are expected to accumulate and store increased amounts of organic carbon in temperate areas of China.
The exchange of gases between soil and atmosphere is an important process that affects atmospheric chemistry and therefore climate. The static-chamber method is the most commonly used technique for estimating the rate of that exchange. We examined the method under hypothetical field conditions where diffusion was the only mechanism for gas transport and the atmosphere outside the chamber was maintained at a fixed concentration. Analytical and numerical solutions to the soil gas diffusion equation in one and there dimensions demonstrated that gas flux density to a static chamber deployed on the soil surface was less in magnitude than the ambient exchange rate in the absence of the chamber. This discrepancy, which increased with chamber deployment time and air-filled porosity of soil, is attributed to two physical factors: distortion of the soil gas concentration gradient (the magnitude was decreased in the vertical component and increased in the radial component) and the slow transport rate of diffusion relative to mixing within the chamber. Instantaneous flux density to a chamber decreased continuously with time; steepest decreases occurred so quickly following deployment and in response to such slight changes in mean chamber headspace concentration that they would likely go undetected by most field procedures. Adverse influences of these factors were reduced by mixing the chamber headspace, minimizing deployment time, maximizing the height and radius of the chamber, and pushing the rim of the chamber into the soil. 29 refs., 8 figs., 1 tab.
A mechanistic understanding of soil respiration is a major impediment to predicting terrestrial C fluxes spatially and temporally. Automated measurements of soil respiration offer the high-resolution information necessary to observe temporal variation in soil respiration, but spatially these measurements are under-represented in water-limited and non-forested ecosystems. We measured soil respiration with automated chambers over the growing season, at two sites with the same semi-arid climate, but with different dominant vegetation, perennial grasses and shrubs in the Owens Valley, CA, USA. An isotope mass balance technique was used to partition soil respiration into autotrophic and heterotrophic components at two time points, early and late growing season. Results showed large differences in the magnitude of growing season soil respiration between the two sites (910 versus 126 g C m-2 for grasses and shrubs respectively over 5 months). We attribute this to site differences in soil water availability and belowground allocation and productivity. Diel patterns of soil respiration between the two sites were similar. Temperature explained most of the diel variability in the early growing season, when soil moisture was greatest. As soil moisture declined over the growing season, diel patterns became increasingly decoupled temporally from temperature due to increased water-limitation on surface heterotrophic sources and hypothesized strong photosynthetic control over soil respiration rates. Partitioning of soil respiration into autotrophic and heterotrophic sources showed the dominance of autotrophic sources across seasons and ecosystems. However, heterotrophic respiration was more dynamic from early to late growing season, declining in the grass ecosystem; and a surprising increase in the shrub ecosystem, attributed to warming of the soil profile enhancing microbial decomposition at depth.
Prescribed fire is used as a management practice to maintain grassland dom- inance and reduce woody plant encroachment on grasslands and rangelands. Little is known regarding effects of these fires on CO 2 fluxes and their potential contribution to atmospheric CO2. The objectives of this study were (1) to quantify the effect of fire on net ecosystem CO2 flux above Prosopis glandulosa Torr. (honey mesquite) mixed-grass savannas using the Bowen ratio/energy balance (BREB) method, and (2) to compare these fluxes to fluxes determined by an empirical model that scaled measurements of leaf photosynthesis and leaf area of dominant species and soil CO2 fluxes to the ecosystem level. Measurements were made during a wet year (1995) and a dry year (1996) with different savanna areas burned in late winter (February-March) each year. In the wet year, BREB-estimated daily (24-h) CO2 flux averaged 20.1, 14.6, and 0.8 g/m2 on the unburned plot, and 15.7, 19.7, and 15.2 g/m2 on the burned plot during spring, summer, and fall periods, respectively, during the first growing season following the fire (positive values mean net CO 2 uptake). In the drought year, mean daily CO2 flux during spring, summer, and fall was 29.2, 4.1, and 4.8 g/m2 on the unburned plot, and 8.1, 20.9, and 4.6 g/m2 on the burned plot, re- spectively. The increased carbon uptake following a fire when compared to the unburned plot was estimated to offset the initial carbon loss from combustion within 28 growing- season days in the wet year, while it took 82 d in the dry year. Empirically determined daylight (12-h) CO2 fluxes, measured on two midsummer days each year, averaged 17.9 g/ m2 when determined by BREB, and 12.0 g/m2 when calculated from scaled-up leaf-level measurements. By the end of the first growing season following the burn, it is likely that the amount of carbon emitted during the burn had been taken up by the regrowing vegetation, in both a wet and a drought year.
The application of organic amendments in agroecosystems has been widely recommended, but the impact of their C/N ratio on the stabilization and sequestration of soil organic carbon (SOC) is often unaccounted for. The influence of the C/N ratio of amendments on soil physicochemical properties in a rice (Oryza sativa var. NDR97)-barley (Hordeum vulgare var. Lakhan) rotation tropical dryland agroecosystem was compared with an undisturbed grassland. Chemical fertilizer in the form of urea and three organic inputs (Sesbania aculeata shoot, low C/N ratio; air-dried straw of wheat (Triticum aestivum var. Malviya 533), high C/N ratio; and S. aculeata shoot+wheat straw, high and low C/N ratio combined) carrying an equivalent amount of N, were added to plots of the agroecosystem once during each annual cycle. Soil water-holding capacity (WHC), porosity, SOC, total N, and aggregate stability were improved in the wheat straw and S. aculeata shoot+wheat straw treatments, reaching levels comparable with the grassland. Soil WHC, porosity, and SOC influenced the productivity of the grassland and the agroecosystem. The grassland recorded highest SOC (53% higher relative to control) followed by the wheat straw (+47%), S. aculeata shoot+wheat straw (+37%) and soil total N was greatest in the S. aculeata shoot+wheat straw treatment (+37.5%). Aggregate stability and macroaggregate distribution were also higher in the wheat straw and S. aculeata shoot+wheat straw treatments, however, the microaggregate and silt + clay fractions showed a reverse trend. Management practices with a higher residue-C return in the agroecosystem resulted in increased aggregate stability and aggregate-associated SOC, with C storage attaining levels similar to the natural system.
Soil CO2 flux (J(CO2)) was measured at midday over a 2-yr period in undisturbed tallgrass prairie (Konza Prairie, Kansas, USA) to quantify seasonal and annual budgets, to evaluate temperature and moisture as determinants of soil CO2 flux, and to assess the effect of a common land management tool, spring fire, and fire history on soil respiration. We hypothesized that: (1) maximum rates and annual estimates of soil J(CO2) would be greater in more productive burned sites than in unburned sites, (2) soil J(CO2) would be greater in newly burned sites with a history of fire exclusion than in annually burned sites (consistent with differences in aboveground production), and (3) soil temperature and water availability would be primary abiotic determinants of soil J(CO2) in tallgrass prairie. A preliminary assessment of the effects of large herbivores on soil J(CO2) was included to evaluate the hypothesis that removal of aboveground biomass would reduce soil J(CO2). Results indicated that spring fire increased maximum monthly soil J(CO2) by 20-55% relative to unburned tallgrass prairie, with greatest monthly differences measured in April (fourfold higher in burned sites). In burned sites that differed in fire history, maximum monthly J(CO2) in annually burned prairie was 33% greater than in burned sites with a history of fire exclusion. Soil J(CO2) in these latter sites was still significantly higher than in unburned sites. Soil J(CO2) in sites grazed by bison was reduced by as much as 30% relative to adjacent ungrazed areas. Reduced root biomass and activity in grazed areas, unburned sites, and sites with a history of fire exclusion suggest that plants play a major role in determining soil J(CO2) in this grassland. Soil temperature at 5 cm was related strongly to midday J(CO2) in both annually burned sites (r2 = 0.58) and unburned sites (r2 = 0.71). In contrast, differences in soil moisture among sites, enhanced by comparing irrigated grassland to control areas, increased maximum monthly J(CO2) by only 8%. Thus, soil temperature was the primary abiotic determinant of soil J(CO2) during this study. Maximum monthly estimates of soil J(CO2) in tallgrass prairie ranged from 10.3 μmol CO2·m-2·s-1 in unburned sites to 15.1 μmol·m-2·s-1 in annually burned irrigated sites, whereas annual estimates varied from 4.7 to 7.8 kg CO2/m2. Over the 2-yr period, spring fire increased estimated annual soil J(CO2) by 38-51% relative to unburned sites, while irrigation increased annual soil J(CO2) by 13%. These estimates for tallgrass prairie are much higher than those reported for most temperate ecosystems but are similar to estimates for tropical forests. Characteristics of undisturbed tallgrass prairie that may lead to high levels of soil J(CO2) include: high above- and belowground productivity; a relatively high proportion of C stored belowground; levels of soil microbial biomass and activity that are among the highest in native ecosystems in the United States; and the lack of a single dominant factor such as temperature, moisture, or nutrient availability, that consistently limits biotic processes during the growing season. The sensitivity of soil J(CO2) in tallgrass prairie to different land use practices (fire and grazing) suggests that it is critical to include these factors in the development of grassland C budgets, as well as in regional models that estimate biogeochemical responses to land use change.
Soil CO2 efflux rates were measured in a eucalypt open
forest in a tropical savanna of northern Australia, with a portable closed
chamber and CO2 gas analyser. Both abiotic (soil
temperature and water content) and biotic (litterfall and fine-root growth)
factors that may influence soil CO2 efflux were
examined. Daytime rates of soil CO2 efflux rate were
consistently higher than nocturnal values. Maximal rates occurred during late
afternoons when soil temperatures were also maximal and minimum values were
recorded during the early morning (0400–0800 hours). Average soil
CO2 efflux was 5.37 mol m–2
s–1 (range 3.5–6.7 mol
m–2 s–1 during the wet
season and declined to 2.20 mol m–2
s–1 (range 1.2–3.6 mol
m–2 s–1) during the
dry season. The amount of carbon released from soil was 14.3 t
ha–1 year–1, with
approximately 70% released during the wet season and 30% during
the dry season. The rate of efflux was correlated with soil moisture content
and soil temperature only during the wet season, when root growth and
respiration were high. During the dry season there was no correlation with
soil temperature. These results are discussed in relation to the carbon
balance of tropical savannas.
Soil respiration (SR) is controlled by abiotic parameters (temperature, water availability) interacting with biotic characteristics of the vegetation (quantity and quality of litter inputs, root respiration) and the soil microbial community. Because SR is a major flux in the C cycle, it is important to understand how vegetation change may interact with predicted climate changes to alter SR and ecosystem C storage. We quantified the SR response to increased soil water availability in a subtropical savanna parkland in the Rio Grande Plains of southern Texas. Diel SR was measured monthly from July 1996 to August 1997 in control and irrigated plots located in grasslands and in three contrasting woody plant communities known to have developed on grassland during the past 100 yr. Irrigation increased SR in all plant community types. Soil respiration in woody communities was higher (12.7 g CO2 m(-2) d(-1) averaged across months and treatments) and more responsive (+103%) to increased water availability than grasslands (9-8 9 CO2 m(-2) d(-1) and +48%, respectively). This SR pattern is probably the result of woody communities having greater soil microbial biomass, soil C Pools, and root biomass than adjacent grasslands. Irrigation increased the sensitivity of SR to temperature (Q(10) = 1.6 and 2.6 for control and irrigated plots, respectively), but Q(10) values were similar in woody communities and grasslands. Results suggest SR is water limited, that sensitivity of SR to soil moisture availability increases with increasing woody plant abundance, and that shifts from grass to shrub dominance may have little impact on SR response to the changes in temperature projected to accompany global warming.
Fire is a disturbance in the Mediterranean region associated with frequent drought periods, and can affect
the soil microbial community, which plays a fundamental role in nutrient cycling. In the present study the effect of low- and high-severity experimental fires on the soil microbial communitywas evaluated in an Italian Mediterranean maquis. Burned and unburned soils were compared for functional diversity, specific activities, microbial biomass, fungal mycelia and fungal fraction of microbial carbon, during the first year after fire. In the first week after fire, changes in the functional diversity were observed in burned soils, differing also between low- and high-severity fires. Respiration responses to specific organic compounds were generally lower in burned soils during the whole study period, with a percentage of changed responses from 2 to 70%. The general reduction in burned soils of the fungal fraction of microbial carbon (19–61%) and active mycelia (16–55%), together with the increase in microbial biomass carbon (29–42%) during the first 3 months after fire, suggest a larger and longer effect of fire on fungi than on bacteria. The results indicate a rapid recovery of functional diversity in soil after burning despite the persistent reduction of microbial community activity and the change in its structure.
The present study investigates the impact of fire (low and high severity) on soil fungal abundance and
microbial efficiency in C assimilation and mineralisation in a Mediterranean maquis area of Southern Italy over 2 years after fire. In burned and control soils total and active fungal mycelium, microbial biomass C, percentage of microbial biomass C present as fungal C, metabolic quotient (qCO2) and coefficient of endogenous mineralisation (CEM) were assayed together with several chemical properties of soil
(i.e. pH and contents of organic C, total and mineral N, available K, Mg, Mn and water). Fire significantly decreased the fungal mycelium, whereas it stimulated microbial growth probably through the enhancement of bacterial growth because of the increase in organic C and nutrient contents in burned plots. This shift in microbial community composition might explain the observed reduction in soil microbial efficiency of C assimilation (high qCO2) and the increase in C mineralisation rate (CEM) in the first 84 days after fire. Therefore, fire might increase CO2 input to the atmosphere not only during combustion phase but also in the post-fire period.
Question: What is the long‐term compositional response of grass and forb species to various combinations of burning and mowing? Can these responses be predicted from simple plant traits?
Location: Ukulinga research and training farm (24°24′E, 30°24′S), Pietermaritzburg, KwaZulu‐Natal, South Africa.
Methods: Grass species relative abundance in 1996 in various burning and mowing treatments of a long‐term (> 50 a) experiment was calculated from data obtained using a point sampling method, whereas forb species abundance in 1999 was determined using the importance score method. The experiment consisted of different frequencies (annual, biennial and triennial) of burning and mowing in winter or spring in combination with different frequencies of summer mowing (none, early, late or both).
Results: Grasses responded to the type of disturbance (burn or mow) and frequency of burning, whereas forbs responded primarily to the presence or absence of any form of disturbance and secondarily to the timing of burning (spring versus winter). Summer mowing and annual or biennial dormant‐period burning maintained communities dominated by short grasses, whereas tall grasses dominated under annual dormant‐period mowing, triennial burning or protection from disturbance. Grass tillering strategy (below‐ or above‐ground) influenced response to burning frequency. Many erect herbaceous dicot species with aerial meristems were reduced in abundance by summer mowing whereas most small creeping herbaceous dicot species appeared to be dependent upon summer mowing.
Conclusions: This long‐term experiment demonstrated that: (1) grasses and forbs responded differently to burning and mowing; (2) simple plant traits, such as height, position of tiller initiation, and position of meristems have potential for predicting the response of species to the timing and frequency of burning and mowing.
[1] This paper aims at understanding the effect that shrub encroachment into mesic mountain grasslands has on soil organic carbon (SOC) stocks. Thus we compared organic C and N contents in contiguous soil profiles under a conifer shrub, a legume shrub, and grasses (mesic grasslands) on 21 sites. Soil C and N recalcitrance indexes (RIC and RIN) were estimated as the ratio of unhydrolyzable C and N to total C or N. Contrary to our hypothesis, shrub encroachment did not cause a well-defined change in soil C stocks. Only a slight increase in C was detected in the top 15 cm soil layer under both shrubs. The C accretion rate in this soil layer was estimated to be approximately 28–42 g m�2 per annum. Legume shrub encroachment also produced a slight decrease in the C/N ratio in the top 15 cm soil layer. No significant changes in the RIC were detected as a result of encroachment; however, slight decreases in the RIN were
found at medium depths. Both RIC and RIN showed a negative relationship with site temperature in the upper legume-shrub soil layers but not in conifer shrubs or under grasses, suggesting a priming effect on the recalcitrant soil stocks produced by the higher-quality inputs derived from legume encroachment.
In grasslands the proportionally largest emission of CO2 comes from the soil. This study aimed to assess how root respiration, a major flux component, is affected by land management and changes in land use. Respiration of roots, separated to classes of different diameter, was measured in 11 temperate mountain grasslands, including meadows, pastures and abandoned sites at three geographic locations. Specific root respiration was affected by nitrogen (N) concentration, root class and land use. The relationship between root N concentration and respiration differed between locations. With increasing root diameter there was a decrease in root respiration, N concentration, respiration per unit N and Q10. In grasslands abandoned for several years specific root respiration was lower than in meadows, pastures and a recently abandoned site. This was due to lower root N concentrations and/or lower respiration rates per unit N within each root class. Since root biomass was higher on abandoned grasslands, total ecosystem root respiration did not differ consistently between sites. Ecosystem root respiration showed distinct seasonal changes due to changes in root biomass, which were less pronounced on abandoned grasslands. Fine roots generally made up the largest portion of ecosystem root respiration, their contribution varying between 35% and 96%. On meadows, clipping increased soil and root respiration by increasing soil temperature. When corrected for temperature effects soil respiration was reduced by 20–50%, whilst root respiration was little affected, suggesting that carbohydrate reserves sustained root metabolism for several days and that microbial respiration strongly responded to short-term changes in assimilate supply.
The impact of fire on soil fluxes of CO 2 , CH 4 and N 2 O was investigated in a tropical grassland in Congo Braz-zaville during two field campaigns in 2007–2008. The first campaign was conducted in the middle of the dry season and the second at the end of the growing season, respectively one and eight months after burning. Gas fluxes and several soil parameters were measured in each campaign from burned plots and from a close-by control area preserved from fire. Rain events were simulated at each campaign to evaluate the magnitude and duration of the generated gas flux pulses. In laboratory experiments, soil samples from field plots were analysed for microbial biomass, net N mineralization, net nitrification, N 2 O, NO and CO 2 emissions under different water and temperature soil regimes. One month after burn-ing, field CO 2 emissions were significantly lower in burned plots than in the control plots, the average daily CH 4 flux shifted from net emission in the unburned area to net con-sumption in burned plots, no significant effect of fire was observed on soil N 2 O fluxes. Eight months after burning, the average daily fluxes of CO 2 , CH 4 and N 2 O measured in control and burned plots were not significantly different. In laboratory, N 2 O fluxes from soil of burned plots were sig-nificantly higher than fluxes from soil of unburned plots only above 70% of maximum soil water holding capacity; this was never attained in the field even after rain simulation. Higher NO emissions were measured in the lab in soil from burned plots at both 10% and 50% of maximum soil water holding capacity. Increasing the incubation temperature from 25 • C to 37 • C negatively affected microbial growth, mineraliza-tion and nitrification activities but enhanced N 2 O and CO 2 production. Results indicate that fire did not increase post-burning soil GHG emissions in this tropical grasslands char-acterized by acidic, well drained and nutrient-poor soil.
Fires in the tallgrass prairie are frequent and significantly alter nutrient cycling processes. We evaluated the short-term
changes in plant production and microbial activity due to fire and the long-term consequences of annual burning on soil organic
matter (SOM), plant production, and nutrient cycling using a combination of field, laboratory, and modeling studies. In the
short-term, fire in the tallgrass prairie enhances microbial activity, increases both above-and belowground plant production,
and increases nitrogen use efficiency (NUE). However, repeated annual burning results in greater inputs of lower quality plant
residues causing a significant reduction in soil organic N, lower microbial biomass, lower N availability, and higher C:N
ratios in SOM. Changes in amount and quality of below-ground inputs increased N immobilization and resulted in no net increases
in N availability with burning. This response occurred rapidly (e.g., within two years) and persisted during 50 years of annual
burning. Plant production at a long-term burned site was not adversely affected due to shifts in plant NUE and carbon allocation.
Modeling results indicate that the tallgrass ecosystem responds to the combined changes in plant resource allocation and NUE.
No single factor dominates the impact of fire on tallgrass plant production.
Nitrogen addition to soil can play a vital role in influencing the losses of soil carbon by respiration in N-deficient terrestrial ecosystems. The aim of this study was to clarify the effects of different levels of nitrogen fertilization (HN, 200 kg N ha−1 year−1; MN, 100 kg N ha−1 year−1; LN, 50 kg N ha−1 year−1) on soil respiration compared with non-fertilization (CK, 0 kg N ha−1 year−1), from July 2007 to September 2008, in temperate grassland in Inner Mongolia, China. Results showed that N fertilization did not change the seasonal patterns of soil respiration, which were mainly controlled by soil heat-water conditions. However, N fertilization could change the relationships between soil respiration and soil temperature, and water regimes. Soil respiration dependence on soil moisture was increased by N fertilization, and the soil temperature sensitivity was similar in the treatments of HN, LN, and CK treatments (Q
10 varied within 1.70–1.74) but was slightly reduced in MN treatment (Q
10 = 1.63). N fertilization increased soil CO2 emission in the order MN > HN > LN compared with the CK treatment. The positive effects reached a significant level for HN and MN (P < 0.05) and reached a marginally significant level for LN (P = 0.059 < 0.1) based on the cumulative soil respiration during the 2007 growing season after fertilization (July–September 2007). Furthermore, the differences between the three fertilization treatments and CK reached the very significant level of 0.01 on the basis of the data during the first entire year after fertilization (July 2007–June 2008). The annual total soil respiration was 53, 57, and 24% higher than in the CK plots (465 g m−2 year−1). However, the positive effects did not reach the significant level for any treatment in the 2008 growing season after the second year fertilization (July–September 2008, P > 0.05). The pairwise differences between the three N-level treatments were not significant in either year (P > 0.05).
Equilibrium carbon stock is the result of a balance between inputs and outflows to the pool. Changes in land-use are likely to alter such balance, resulting in different carbon stores under different land-use types in addition to the impacts of global climate change. In an agro-pastoral ecotone of Inner Mongolia, northern China, we investigated productivity and belowground carbon and nitrogen stores under six different types of land-uses, namely free grazing (FG), grazing exclusion (GE), mowing (MW), corn plantation (CP), fallow (FL), and alfalfa pasture (AP), and their impacts on litter and fine roots in semiarid grassland ecosystems. We found that there were great variations in aboveground net primary production (ANPP) across the six land-use types, with CP having markedly high ANPP; the FG had significantly reduced soil organic carbon (SOC) and nitrogen stores (SON) to 100cm depth compared with all other types of land uses, while very little litter accumulation was found on sites of the FG and CP. The top 20cm of soils accounted for about 80% of the root carbon and nitrogen, with very little roots being found below 50cm. About 60% of SOC and SON were stored in the top 30cm layer. Land-use change altered the inputs of organic matters, thus affecting SOC and SON stores accordingly; the MW and GE sites had 59 and 56% more SOC and 61% more SON than the FG. Our estimation suggested that restoring severely degraded and overgrazed grasslands could potentially increase SOC and SON stores by more than 55%; conversion from the native grasses to alfalfa could potentially double the aboveground biomass production, and further increase SOC and SON stores by more than 20%. Our study demonstrated significant carbon and nitrogen storage potential of the agro-pastoral ecotone of northern China through land-use changes and improved management in the context of mitigating global climate change.
The chamber-based method is currently the most popular approach used for measuring soil respiration of various ecosystems.
When this method is applied, aboveground plant tissues within the chamber need to be clipped some time (usually 24h) before
measuring soil respiration. However, plant clipping may change soil temperature and hence soil respiration because soil respiration
is highly temperature-dependent, particularly in cold regions. To determine to what extent soil respiration may be changed
by the clipping, we measured soil temperature and respiration of an alpine meadow of southwest China using a chamber-based
method over an annual cycle. Based on the measurements, an exponential equation was built to describe the relationship between
soil respiration and temperature. Concurrently we measured the soil temperature in clipped and unclipped plots on sunny days
of the study months in another independent experiment; subsequently soil respiration was estimated for these plots using the
exponential equation. Though daily mean soil temperature was insignificantly different between the clipped and unclipped plots,
the clipping increased soil temperature at 5cm depth by up to 4.3°C at daytime but decreased by up to 1.4°C at nighttime
during the growing season. The changes were 2.2 and 1.5°C at daytime and nighttime, respectively, in the non-growing season.
It was calculated that the clipping manipulation caused an overestimation of soil respiration by 28.6 and 21.2% for the growing
and non-growing seasons, respectively; nevertheless, this calculated overestimation should differ from the actual one because
the data were collected on sunny days only.
KeywordsSoil respiration–Chamber-based techniques–Soil temperature–Plant clipping–Grassland
The effects or burning and grazing on plant available nitrogen (NO3-N + NH4-N) and N-mineralization in a dry tropical savanna were examined. The plant available N ranged from 2.8 to 10.6 μg g−1 with maximum values in the dry period (summer season) and minimum values in the wet period (rainy season). The trend for N-mineralization was opposite to that of the size of the available N pool. N-mineralization rates ranged from 1.8 to 30.6 μg g−1 mo−1 within an annual cycle. On average the pool of available N was 54% higher in the burned treatment and 48% higher in the grazed treatment compared to the protected treatment, similarly the mean annual N-mineralization was 20% higher in the burned and 16% higher in the grazed savanna.
A thorough understanding of the role of microbes in C cycling in relation to fire is important for estimation of C emissions and for development of guidelines for sustainable management of dry ecosystems. We investigated the seasonal changes and spatial distribution of soil total, dissolved organic C (DOC) and microbial biomass C during 18 months, quantified the soil CO2 emission in the beginning of the rainy season, and related these variables to the fire frequency in important dry vegetation types grassland, woodland and dry forest in Ethiopia. The soil C isotope ratios (δ13C) reflected the 15-fold decrease in the grass biomass along the vegetation gradient and the 12-fold increase in woody biomass in the opposite direction. Changes in δ13C down the soil profiles also suggested that in two of the grass-dominated sites woody plants were more frequent in the past. The soil C stock ranged from being 2.5 (dry forest) to 48 times (grassland) higher than the C stock in the aboveground plant biomass. The influence of fire in frequently burnt wooded grassland was evident as an unchanged or increasing total C content down the soil profile. DOC and microbial biomass measured with the fumigation–extraction method (Cmic) reflected the vertical distribution of soil organic matter (SOM). However, although SOM was stable throughout the year, seasonal fluctuations in Cmic and substrate-induced respiration (SIR) were large. In woodland and woodland–wooded grassland Cmic and SIR increased in the dry season, and gradually decreased during the following rainy season, confirming previous suggestions that microbes may play an important role in nutrient retention in the dry season. However, in dry forest and two wooded grasslands Cmic and SIR was stable throughout the rainy season, or even increased in this period, which could lead to enhanced competition with plants for nutrients. Both the range and the seasonal changes in soil microbial biomass C in dry tropical ecosystems may be wider than previously assumed. Neither SIR nor Cmic were good predictors of in situ soil respiration. The soil respiration was relatively high in infrequently burnt forest and woodland, while frequently burnt grasslands had lower rates, presumably because most C is released through dry season burning and not through decomposition in fire-prone systems. Shifts in the relative importance of the two pathways for C release from organic matter may have strong implications for C and nutrient cycling in seasonally dry tropical ecosystems.
The facilitating effect of the exudation of carbon (C) compounds from roots on rhizospheric processes has been shown in controlled experiments; however, it still remains unclear how important this pathway of C from plants to the soil may be in energy and nutrient processes in grazed grasslands under natural conditions. Root exudation may be a particularly important C pathway in grazed grasslands and help promote positive feedbacks between large herbivores and plants. In this study we performed a 13C pulse-chase experiment on plots that were clipped or left unclipped in a mesic grassland in Yellowstone National Park. The dominant grass species in the plots was Poa pratensis and it was used to measure the effect of defoliation on root C exudation, the rhizospheric microbial community, and feedbacks on plant nutrient uptake over a time period of 24–72 h. Defoliation stimulated C exudation from roots by 1.5-fold, which concomitantly increased rhizospheric microbial biomass by the same factor. The facilitating effects of defoliation on rhizospheric processes resulted in positive feedback on soil inorganic N pools and leaf N content, which increased by 1.2- and 1.5-fold respectively. Changes in soil inorganic N pools during the experiment indicated that the effect of the C flush on the rhizospheric decomposer community of defoliated plants resulted in a 5-fold increase in rhizospheric daily net N mineralization rate. These findings demonstrate that in a natural grassland community defoliation-induced stimulation of C exudation stimulates rhizospheric N-mineralization which ultimately benefits defoliated plants. The results also indicate the important role that short-term root–rhizospheric microbe interactions play in the C and N processes in grazed grasslands.
To understand the roles of forest management practices in meeting the goals of forest sustainability and CO2 sequestration, we evaluated the effects of burning and thinning treatments on soil respiration and soil environments in an old-growth, mixed-conifer forest in California’s southern Sierra Nevada. Six experimental treatments with two levels of burning and three levels of thinning were implemented across three dominant patch types: closed canopy (CC), Ceanothus shrub (CECO), and open canopy (OC). We measured soil respiration rate (SRR), soil temperature (T10), moisture (Ms), and litter depth (LD), in the summers of 2000 and 2002. Soil total C and total N were measured in 2002. SRR was significantly different among the three patch types. In 2000, SRR was 0.75, 0.86, and 0.26 g CO2 m-2 hr-1 in CC, CECO, and OC, respectively. In 2002, SRR was 0.79, 0.97, and 0.44 g CO2 m-2 hr-1 in CC, CECO, and OC, respectively. The analysis of variance indicated that burning and thinning significantly affected soil respiration and soil environments. In particular, SRR significantly decreased in burned CECO patches but increased in unburned and thinned CECO. SRR in CC and OC did not significantly change. T10 and Ms increased, whereas LD and soil C decreased in treated patches. We also developed pre- and posttreatment exponential models to predict SRR using soil environmental variables. The effects of burning and thinning on soil CO2 efflux and soil environments imply that forest carbon pools would be reorganized with widespread application of these forest management practices. yes
Disturbance may be an important determinant of plant community composition and diversity owing to its effects on competitive interactions, resources, dominance and vigour. The effect of type, timing and frequency of disturbance on grass and forb species richness was examined using data from a long-term (> 50 yr) grassland burning and mowing experiment in KwaZulu-Natal, South Africa. Grass species richness declined considerably (> 50%) in the absence of disturbance, whereas forb species richness was unaffected. Annual burning in sites not mown in summer tended to increase grass species richness relative to triennial burning (22% increase) with the reverse being true in sites mown twice in summer (37% decline). Forb species richness declined by 25% in sites mown twice in summer relative to sites mown in early summer only. Disturbance was necessary to achieve maximum grass species richness presumably by removing litter and increasing the availability of light. The interaction of time of mowing in summer (early versus late) and time of burning during the dormant period (spring versus winter) had the most dramatic effect on species richness. Time of burning had no effect on richness in sites mown in early summer, but winter burning resulted in a dramatic decline (27-42%) in richness in sites mown in late summer. This effect may be related to possible greater soil desiccation with this combination of disturbances.
Soil respiration is an important part of the global carbon (C) cycle and the largest component of C flux from terrestrial ecosystems to the atmosphere. Global change and anthropogenic perturbations can profoundly impact soil respiration. A field experiment examined the seasonal variability of soil respiration in response to the addition of nitrogen (N), burning, clipping and their possible interactions throughout an entire growing season from April to October 2011, in semiarid grassland in northern China. Results showed that N addition and burning significantly increased mean soil respiration by 35.8% and 11.0%, respectively, and that burning and N addition synergistically enhanced soil respiration. However, the effects of N addition and burning on soil respiration were mediated by season. Clipping had no significant effect on soil respiration. Soil moisture was primarily responsible for the seasonal changes in soil respiration, whereas the positive responses of soil respiration to burning and N addition were attributable to elevated soil temperature, plant growth, root and microbial activity and respiration. In unfertilized plots, burning decreased temperature sensitivity (Q10) of soil respiration by 10.0%. In plots with N addition, burning and clipping decreased Q10 by 15.4% and 11.6%, respectively. We therefore conclude that burning can, and clipping may, decrease the dependence of soil respiration on temperature. We further observed that the magnitude of positive feedback in soil respiration to temperature increase weakened in the burned plots, and that the availability of N might regulate the degree of this weakening. The different mechanisms by which N addition, burning and clipping influence soil respiration and its sensitivity to temperature identified in this study may facilitate the simulation and prediction of C cycling in semiarid grassland under future scenarios of global change.
Moderate Resolution Imaging Spectroradiometer ( MODIS) on board the NASA Earth Observing System Terra and Aqua satellites provides global fire observations of unprecedented quality. This paper presents spatial and temporal distributions of active fires from 2001 and 2002, the first 2 years of the MODIS active fire data record. Monthly fire counts were analysed globally and within several regions of major fire activity and vegetation type. The global maximum of the annual cycle of fire activity for both years occurred in August; a combined result of burning during the dry season in the Southern Hemisphere tropics and the warm season over the Northern Hemisphere extratropics. The minimum of global fire activity occurred in March in both years. Burning in the tropics occurred mostly in savanna and shrubland areas with a high percentage of herbaceous vegetation. In the extratropics, fires were detected over croplands, grasslands and forests. The global total numbers of fire counts observed in 2001 and 2002 differed by less than 3%, but regionally significant differences were found between the two years in total and relative fire counts and in the timing of burning. Fire counts from daytime MODIS observations from Terra and Aqua also provided evidence of the diurnal cycle of fire activity. This analysis of 'fire/no fire' binary indicators is a first-order approximation of global spatio-temporal fire dynamics. For several applications, such as the estimation of pyrogenic emissions, further studies of burned area and fire characteristics are needed.
This work corroborates the hierarchical conceptual model for soil aggregate structure presented by Tisdall and Oades (1982), extends it to North American grassland soils, and elaborates on the aspects relating to the influence of cultivation upon losses of soil organic matter. Aggregate size distributions observed for our soils are very similar to those of Australian soils, indicating that the microaggregate‐macroaggregate model may hold for a wide array of grassland soils from around the world. The use of two wetting treatments prior to sieving demonstrated that the native sod soil had the same general structural characteristics as cultivated soil but the macroaggregates were more stable. When slaked, native and cultivated soil present in the microaggregate size classes had less organic C, N, and P than the soil remaining as macroaggregates, even when expressed on a sand‐free basis. Moreover, the C/N, C/P, and N/P ratios of microaggregates were narrower than those of macroaggregate size classes. Much more C and N was lost than P under the conditions of this study. Element‐specific differences in microbial catabolic processes vs. extracellular enzyme activity and its attendant feedback controls are postulated to account for this difference. When the macroaggregates were crushed to the size of microaggregates, mineralizable C as a percent of the total organic C was generally greater for macro‐ than microaggregates early in the incubation for the cultivated soil and throughout most of the incubation for the native sod soil. Mineralizable N as a percent of the total organic N was greatest in macroaggregates even when the macroaggregates were not crushed. The macroaggregate‐micraggregate conceptual model is applied to help explain accumulation of soil organic matter under native conditions and its loss upon cultivation.
Veld burning treatments applied annually, biennially or triennially during the first week of August or after the first substantial spring rains considerably reduced herbage yields during the season which followed the burn, but had no long term effect on the productivity of the veld. Long term effects did, however, result from differences in summer utilization. Where veld was not cut for hay in summer, it developed a potential to produce higher yields than veld which was cut during the summer season. This increased production potential is, however, accompanied by changes in the nature of the sward which in many respects are undesirable.
Land use is increasingly recognized as a major driver of biodiversity and ecosystem functioning in many current research projects. In grasslands, land use is often classified by categorical descriptors such as pastures versus meadows or fertilized versus unfertilized sites. However, to account for the quantitative variation of multiple land-use types in heterogeneous landscapes, a quantitative, continuous index of land-use intensity (LUI) is desirable. Here we define such a compound, additive LUI index for managed grasslands including meadows and pastures. The LUI index summarizes the standardized intensity of three components of land use, namely fertilization, mowing, and livestock grazing at each site. We examined the performance of the LUI index to predict selected response variables on up to 150 grassland sites in the Biodiversity Exploratories in three regions in Germany (Alb, Hainich, Schorfheide). We tested the average Ellenberg nitrogen indicator values of the plant community, nitrogen and phosphorus concentration in the aboveground plant biomass, plant-available phosphorus concentration in the top soil, and soil C/N ratio, and the first principle component of these five response variables.
Mediterranean soils under heathland are often shallow, with low capacity for water storage, and a high risk of erosion. In this context, recurrent wildfires can negatively affect their chemical and physical properties. Very little research has been carried out concerning the long-term variations on the ground surface after burning. The behaviour of plant communities and plant cover can regulate and control soil processes in the post-fire period, so that the evolution of vegetation communities must be taken into account when studying the evolution of soil processes after disturbance. In this study, the impact of fire on several physical and chemical soil properties have been investigated during 3 years after experimental burning in a Mediterranean heathland. On average, the soil organic matter content after the fire decreased strongly, and one year after the fire it did not vary substantially, although it increased slightly during the following two years until the end of experiments. Burning led to coarser
The extensive loss of species‐rich grasslands in Europe as a result of agricultural intensification has triggered a desire to recreate more diverse and natural grassland systems in set‐aside fields. Appropriate management and species introductions are necessary to overcome residual soil fertility, lack of suitable plant propagules and dominance of undesirable invasive species.
A field experiment was performed in a boreal former hayfield to test the effect of turf inoculation, mowing (twice annually) and spring burning. We surveyed changes in plant diversity, composition and productivity over a 3‐year period. Signature fatty acids and soil respiration measurements were employed to survey changes in the soil community.
Few changes in the vegetation and soil communities could be related to inoculation of turf monoliths. Most of the measured variables in mown plots differed from the set‐aside (control) plots, while burned plots displayed mainly similar responses. Mowing increased plant species richness and diversity, mainly by enhancing the number and frequency of forb species. Small‐statured forb species were promoted by mowing, whereas tall leafy grasses declined. Effects of mowing on soil communities comprised an increased soil respiration and stimulation of arbuscular mycorrhizal fungi.
Synthesis and applications . The results demonstrate the importance of reducing sward height in order to promote plant species coexistence in former boreal hayfields. In such systems, eliminating accumulated litter by spring burning has little influence on species composition when the sward is allowed to grow tall. Mowing is therefore the most efficient way of enhancing biodiversity. The results also show that mowing‐mediated changes in above‐ground plant communities may stimulate below‐ground symbiotic micro‐organisms, potentially resulting in a positive feedback on ecosystem development.
The merits of soil aggregate stability determination by rainfall simulator method were studied. This method is based on the supposition that in standard conditions aggregate breakdown is proportional to the kinetic energy of the rainfall applied. We compared three experiments using four different soils. Two of the experiments were in controlled conditions and the other at field conditions. In one of the laboratory experiments we applied sewage sludge to a degraded soil from a semiarid climate. In the other laboratory experiment a forest soil was heated to 200°C, 400°C and 600°C, and we studied the effect of heat and loss of organic matter in soil aggregation. In the third experiment, carried out in the field, we studied the response of two soils affected by forest fire in different intensities. Aggregate stability percentage and organic matter content of soils were determined to establish trends between these parameters. Aggregate stability in soils subjected to rainfall simulation was used as an indicator for potential degradation or restoration processes of the soils. In some burned soils positive and negative relationships were obtained between aggregate stability percentage and organic matter soil contents due to heat-aggregation processes. It showed that the aggregate stability percentage method based on disruptive energy of a rainfall simulator could not always be used as an index of degradation or restoration of soils or both.
This study compared annual and growing-season in situ soil respiration and soil C cycling in paired juniper woodland and C 4 -dominated grassland sites in eastern Kansas (USA) to determine if, under similar edaphic and regional climate conditions, vegetation change alters soil CO 2 dynamics. We found marked differences in soil respiration related to vegetation: Growing season mean woodland soil respiration rates (4.6 moles· m 2 ·s 1) averaged 38% less than paired grassland sites. Soil moisture did not explain the difference in soil respiration between woodlands and grasslands. Soil temperatures at the 10-cm depth were 5C cooler in woodlands during the growing season and significantly different between woodlands and grasslands throughout the year, explaining most of the low soil respiration in woodlands. However, there were subtle intrinsic differences in the response of soil respiration to temperature between woodlands and grasslands: Woodland and grassland respiration response was significantly different at the P 0.05 level, also indicated by a grassland Q 10 of 2.4 compared to 2.2 in woodlands. We found no significant differences between woodlands and grasslands in long-term (82-week) laboratory incu-bations of potentially mineralizable soil C and short-term incubations for microbial biomass C. Similarly, root biomass did not differ between woodlands and grasslands and could not explain the lower in situ woodland soil respiration. Thus, vegetation-mediated reduction in soil temperature under the canopy explained much of the lower in situ woodland soil respiration. Lower soil respiration in the woodland resulted in an annual flux of 533.6 (21.7) compared to 858.4 (14.5) g C·m 2 ·yr 1 in grasslands, nearly 38% lower in the woodland (means 1 SE). Assuming root respiration is 50% of soil respiration, we estimate that the turnover of woodland soil C stocks may be slowed by 15 years relative to grassland. This suggests that, if juniper expansion (now occurring across nearly 5 million hectares in the Great Plains) proceeds to canopy closure, annual soil C flux may be potentially reduced by as much as 19 10 6 Mg of C below C flux rates that occurred historically from tallgrass prairie soils.
Changes in soil respiration, one of the major fluxes of global carbon cycling, could significantly slow down or accelerate the increase in atmospheric CO2, with consequent feedbacks to climate change. It is critical to understand how substrate availability regulates soil respiration in projecting the response of carbon cycling to changed climate. We conducted a clipping and shading experiment for 1 year in a tallgrass prairie of the Great Plains, United States, to manipulate substrate supply to soil respiration. Our results showed that reduced substrate supply under clipping and/or shading significantly decreased soil respiration at all the timescales (diurnal, transient, and annual) irrespective of the minor concurrent changes in soil temperature and moisture. Annual mean soil respiration decreased significantly by 33, 23, and 43% for the clipping, shading, and clipping plus shading treatments, respectively. Temperature sensitivity of soil respiration decreased from 1.93 in the control plots to 1.88, 1.75, and 1.83 in the clipped, shaded, and clipped plus shaded plots, respectively. Rhizosphere respiration, respiration from decomposition of aboveground litter, and respiration from oxidation of soil organic matter and dead roots accounted for 30, 14, and 56% of annual mean soil respiration, respectively. Rhizosphere respiration was more sensitive to temperature than the other two components. Our results suggest a critical role of substrate supply in regulating soil respiration and its temperature sensitivity.
1] Open fire biomass burning and domestic biofuel burning (e.g., cooking, heating, and charcoal making) algorithms have been incorporated into a terrestrial ecosystem model to estimate CO 2 and key reactive GHGs (CO, NO x , and NMHCs) emissions for the year 2000. The emissions are calculated over the globe at a 0.5° Â 0.5° spatial resolution using tree density imagery, and two separate sets of data each for global area burned and land clearing for croplands, along with biofuel consumption rate data. The estimated global and annual total dry matter (DM) burned due to open fire biomass burning ranges between 5221 and 7346 Tg DM/yr, whereas the resultant emissions ranges are 6564– 9093 Tg CO 2 /yr, 438–568 Tg CO/yr, 11–16 Tg NO x /yr (as NO), and 29–40 Tg NMHCs/yr. The results indicate that land use changes for cropland is one of the major sources of biomass burning, which amounts to 25–27% (CO 2), 25 –28% (CO), 20–23% (NO), and 28–30% (NMHCs) of the total open fire biomass burning emissions of these gases. Estimated DM burned associated with domestic biofuel burning is 3,114 Tg DM/yr, and resultant emissions are 4825 Tg CO 2 /yr, 243 Tg CO/yr, 3 Tg NO x /yr, and 23 Tg NMHCs/yr. Total emissions from biomass burning are highest in tropical regions (Asia, America, and Africa), where we identify important contributions from primary forest cutting for croplands and domestic biofuel burning.
Disturbance may be an important determinant of plant community composition and diversity owing to its effects on competitive interactions, resources, dominance and vigour. The effect of type, timing and frequency of disturbance on grass and forb species richness was examined using data from a long-term (> 50 yr) grassland burning and mowing experiment in KwaZulu-Natal, South Africa.
Grass species richness declined considerably (> 50%) in the absence of disturbance, whereas forb species richness was unaffected. Annual burning in sites not mown in summer tended to increase grass species richness relative to triennial burning (22% increase) with the reverse being true in sites mown twice in summer (37% decline). Forb species richness declined by 25% in sites mown twice in summer relative to sites mown in early summer only. Disturbance was necessary to achieve maximum grass species richness presumably by removing litter and increasing the availability of light. The interaction of time of mowing in summer (early versus late) and time of burning during the dormant period (spring versus winter) had the most dramatic effect on species richness. Time of burning had no effect on richness in sites mown in early summer, but winter burning resulted in a dramatic decline (27–42%) in richness in sites mown in late summer. This effect may be related to possible greater soil desiccation with this combination of disturbances.
Using a 50-year-old field experiment, we investigated the effects of the long-term land management practices of repeated burning
and grazing on peatland vegetation and carbon dynamics (C). Plant community composition, C stocks in soils and vegetation,
and C fluxes of CO2, CH4 and DOC, were measured over an 18-month period. We found that both burning and grazing reduced aboveground C stocks, and
that burning reduced C stocks in the surface peat. Both burning and grazing strongly affected vegetation community composition,
causing an increase in graminoids and a decrease in ericoid subshrubs and bryophytes relative to unburned and ungrazed controls;
this effect was especially pronounced in burned treatments. Soil microbial properties were unaffected by grazing and showed
minor responses to burning, in that the C:N ratio of the microbial biomass increased in burned relative to unburned treatments.
Increases in the gross ecosystem CO2 fluxes of respiration and photosynthesis were observed in burned and grazed treatments relative to controls. Here, the greatest
effects were seen in the burning treatment, where the mean increase in gross fluxes over the experimental period was greater
than 40%. Increases in gross CO2 fluxes were greatest during the summer months, suggesting an interactive effect of land use and climate on ecosystem C cycling.
Collectively, our results indicate that long-term management of peatland has marked effects on ecosystem C dynamics and CO2 flux, which are primarily related to changes in vegetation community structure.
Soil respiration is one of the major carbon (C) fluxes between terrestrial ecosystems and the atmosphere and plays an important role in regulating the responses of ecosystem and global C cycling to natural and anthropogenic perturbations. A field experiment was conducted between April 2005 and October 2006 in a semiarid grassland in northern China to examine effects of topography, fire, nitrogen (N) fertilization, and their potential interactions on soil respiration. Mean soil respiration was 6.0% higher in the lower than upper slope over the 2 growing seasons. Annual burning in early spring caused constant increases in soil respiration (23.8%) over the two growing seasons. In addition, fire effects on soil respiration varied with both season and topographic position. Soil respiration in the fertilized plots was 11.4% greater than that in the unfertilized plots. Water- and plant-mediation could be primarily responsible for the changes in soil respiration with topography and after fire whereas the positive responses of soil respiration to N fertilization were attributable to stimulated plant growth, root activity and respiration. The different mechanisms by which topography, fire, and N fertilization influence soil respiration identified in this study will facilitate the simulation and projection of ecosystem C cycling in the semiarid grassland in northern China.
The savanna areas of South Africa can be divided into the moist and arid savanna types according to the availability of soil moisture. Bush encroachment is a serious veld management problem in all the savanna areas and veld burning is a potential eradication technique in situations with an adequate grass cover to support an intense fire. In the moist savannas fire per se can be used to control bush encroachment but in the arid savannas it has the role of maintaining trees and shrubs at an available height and in acceptable state for browsing animals. Intense head fires applied at the end of the dormant season are used for bush eradication. The frequency of burning is relatively high in the moist savannas but is very low in the arid savannas, being usually limited to years with above average rainfall when adequate grass fuel loads can be accumulated. Veld burning provides an attractive economic and energy saving technique of solving the problem of bush encroachment in the savanna areas of South Africa.