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Overgrazing decreases soil organic carbon stocks the most under dry climates and low soil pH: A meta-analysis shows

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Abstract

Grasslands occupy about 40% of the world’s land surface and store approximately 10% of the global soil organic carbon (SOC) stock. This SOC pool, in which a larger proportion is held in the topsoil (0–0.3 m), is strongly influenced by grassland management. Despite this, it is not yet fully understood how grassland SOC stocks respond to degradation, particularly for the different environmental conditions found globally. The objective of this review was to elucidate the impact of grassland degradation on changes in SOC stocks and the main environmental controls, worldwide, as a prerequisite for rehabilitation. A comprehensive meta-analysis was conducted using 55 studies with 628 soil profiles under temperate, humid, sub-humid, tropical and semi-arid conditions, to compare SOC stocks in the topsoil of non-degraded and degraded grassland soils. Grassland degradation significantly reduced SOC stocks by 16% in dry climates (<600 mm) compared to 8% in wet climates (>1000 mm) and Asia was the most affected continent (−23.7%). Moreover, the depletion of SOC stock induced by degradation was more pronounced in sandy (<20% clay) soils with a high SOC depletion of 10% compared to 1% in clayey (≥32% clay) soils. Furthermore, grassland degradation significantly reduced SOC by 14% in acidic soils (pH ≤ 5), while SOC changes were negligible for higher pH. Assuming that 30% of grasslands worldwide are degraded, the amount of SOC likely to be lost would be 4.05 Gt C, with a 95% confidence between 1.8 and 6.3 Gt C (i.e. from 1.2 to 4.2% of the whole grassland soil stock). These results by pointing to greater SOC losses from grasslands under dry climates and sandy acidic soils allow identification of grassland soils for which SOC stocks are the most vulnerable, while also informing on rehabilitation measures.

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... Moreover, the existing documents on the nongrowing season CO 2 emissions varied greatly across different meadows and showed site-and year-specific characteristics (Liptzin et al. 2009(Liptzin et al. , 2015Marcolla et al. 2011;Chang et al. 2013;Zhang et al. 2015) but rarely assessed grassland degradation effects. Overall, the effect of grassland degradation on CO 2 fluxes remains largely uncertain because of the extreme paucity of field observations and large spatial heterogeneity (Yang et al. 2008;Dlamini et al. 2016). Given the increasing conversion of the healthy vegetation cover to the degraded soil surfaces (Harris 2010;Li et al. 2013;Zhang et al. 2014), its non-growing season CO 2 emissions may be more sensitive to changes in climate. ...
... The difference in plant species between ZM1 and ZM2 was a result of succession of the plant community after the interference of the zokor. Following Daily (1995) and Dlamini et al. (2016), degraded grasslands exhibit a decline in grass productivity and/or vegetation cover, from moderate to substantial. In our study, these indicators decreased from HM to ZM1 (Tables 1 and 2). ...
... However, our results and those of others indicated that the non-growing season CO 2 emissions for alpine meadows were higher than those for steppe ecosystems including alpine and temperate steppes, but they were lower compared with alpine swamp meadows (see Supplementary Table S2; Fig. 4). This spatial trend might closely relate to climatic conditions (e.g., mean annual temperature and precipitation), grassland types (e.g., vegetation species and productivity) and soil physicochemical properties (e.g., soil pH, SOC, and soil texture) (Yang et al. 2008;Dlamini et al. 2016). For example, across all the summarized studies in Table S2, the non-growing season CO 2 emissions increased linearly with increasing mean annual precipitation as well as ANPP rather than mean annual temperature (Fig. 5). ...
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The alpine meadow ecosystem is one of the major vegetation biomes on the Qinghai-Tibetan Plateau, which hold substantial quantities of soil organic carbon. Pronounced grassland degradations (induced by overgrazing/climate change and further exacerbated by the subterranean rodent activities) that have widely occurred in this ecosystem may significantly alter the non-growing season carbon turnover processes such as carbon dioxide (CO 2) efflux, but little is known about how the non-growing season CO 2 emissions respond to the degradation (particularly the exacerbated degradations by plateau zokor), as most previous studies have focused primarily on the growing season. In this study, the effects of four degradation levels (i.e., the healthy meadow (HM), degraded patches (DP), 2-year-old zokor mounds (ZM2), and current-year zokor mounds (ZM1)) on CO 2 emissions and corresponding environmental and agronomic variables were investigated over the two non-growing seasons under contrasting climatic conditions (a normal season in 2013-2014 and a Bwarm and humid^season in 2014-2015). The temporal variation in the non-growing season CO 2 emissions was mainly regulated by soil temperature, while increasing degradation levels reduced the temperature sensitivity of CO 2 emissions due to a reduction in soil water content. The cumulative CO 2 emissions across the non-growing season were 587-1283 kg C ha −1 for all degradation levels, which varied significantly (p < 0.05) interannually. The degradation of alpine meadows significantly (p < 0.05) reduced the vegetation cover and aboveground net primary productivity as well as the belowground biomass, which are typically thought to decrease soil CO 2 emissions. However, the non-growing season CO 2 emissions for the degraded meadow, weighted by the areal extent of the DP, ZM2, and ZM1, were estimated to be 641-1280 kg C ha −1 , which was significantly higher (p < 0.05) as compared with the HM in the warm and humid season of 2014-2015 but not in the normal season of 2013-2014. Additionally, grassland degradation substantially increased the productivity-scaled non-growing season CO 2 emissions, which showed an exponential trend with increasing degradation levels. These results suggest that there is a strong connection between grassland degradation and soil carbon loss, e.g., in the form of CO 2 release, pointing to the urgent need to manage degraded grassland restoration that contributes to climate change mitigation.
... However, understandings of the controls on SOC distribution, and how they may vary with significant shifts in climate are pivotal to the success of these strategies. Within studies that have looked at large-scale distribution of SOC, the influence of specific variables varies depending on thresholds of temperature and precipitation (Bui et al., 2009;Chaplot et al., 2010;Dlamini et al., 2016;Hobley et al., 2015;Hoyle et al., 2016;Viscarra Rossel et al., 2014). In the Australian context, this regionalisation has been found to closely approximate the bioclimate regions (e.g. ...
... However, while a relationship was not found with MAP, aridification may further deplete SOC. Dlamini et al. (2016) demonstrated that drier climates lost more SOC than wetter environments (16% compared to 8%). While MAT accounts for 89% of the variation in SOC here, other factors, such as aridification and Table 7 Results of the partial correlation analyses, showing 0-order Pearson's r and then adjusted values when controlling for MAT, elevation and clay content.* ...
Article
The factors determining the spatial distribution of soil organic carbon (SOC) at large-scales closely align with bioclimate regions; reflecting climate, ecosystem and soil properties. Recent studies of the Köppen-Geiger climate zones of Australia have highlighted an extension of the hot, arid, steppe environment from central Australia into the southeast (SE) under future climate change scenarios (2071–2100 under RCP 8.5). As SOC concentrations are highest in Australia's SE, it is important the effect of this shift is quantified. This study assesses this and how changes in the factors that control SOC formation may alter SOC concentrations. Field measured SOC concentrations were compared to current climate, soil, topography, vegetation, and soil erosion variables for 12 grassland sites from SE to NW Australia. SOC concentrations ranged from 0.39% in northwest (NW) and Central Australia to as high as 6.88% in the SE. Using regression analyses; temperature, elevation and Normalised Difference Vegetation Index were found to be the only significant drivers (α = 0.95) of SOC across the sites. Partial correlation analyses then identified temperature, elevation and clay content as imparting a significant effect on the relationships between SOC and water availability variables. This indicates that an extension of the arid environment into SE Australia may lead to a decrease in SOC (up to 1.12%), as mean annual temperature exceeds threshold values that limit SOC concentration. This is significant as the majority of Australia's SOC is stored in this area and these environments exert a strong influence on global carbon cycling.
... Yet, limited work evaluates NDVI as a driver of soil health in agroecosystems. Meanwhile, in terms of soil edaphic properties, soil clay content and soil pH also critically affect soil health indicators (Chaplot et al., 2010;Dlamini et al., 2016). Clay content, a key soil edaphic property, provides surface area for organo-mineral complexes and micro pits for ions (Six et al., 2002). ...
... meaning the soil we studied was slightly acid. Under these slightly acidic conditions, the SOC and TSN pool were more degraded-a finding Dlamini et al. (2016) previously noted in their meta-analysis of SOC in semi-arid soils. Our results also support that soil pH increases SOC and TSN. ...
Article
Maintaining soil health is critical for sustainable field crop production. This on-farm study used participatory monitoring and employed a Bayesian linear regression model to investigate the impact of various drivers (i.e., climate, soil edaphic properties, management practices, cropping diversity, and tillage intensity) on soil health indicators. Over two years, we sampled 242 focal points in soybean fields on thirty-five farms across three regions in Michigan differing in climate, edaphic properties and management practices. Soils ranged from loam to sandy loam. Soil health indicators assessed included soil organic carbon (SOC), total soil nitrogen (TSN), permanganate oxidizable carbon (POXC), C mineralization (Cmin), potentially mineralizable nitrogen (PMN), phosphorus, calcium, soil surface and subsurface resistance, and wet aggregate stability (WAS). We observed location effects, with each of the three regions differing in their climate, soil edaphic properties, and management practices. We found that aridity and clay content are primary drivers of most soil health indicators. Specifically, crop diversity, irrespective of composition, was positively associated with Cmin and WAS. Tillage intensity was positively associated with PMN but negatively influenced POXC. Overall, we conclude that although climate and soil edaphic properties are the dominant drivers of soil health, management practices also play a critical role, especially when considering soil biological indicators.
... The higher clay content of Cambisols and Luvisols could contribute to increased soil organic C accumulation as clay improves soil organic matter accumulation by protecting the organic matter from decomposition (López-Ulloa et al., 2005;Dlamini et al., 2016). A meta-analysis conducted in Qinghai-Tibetan Plateau (Liu et al., 2020) indicated that grazing exclusion in major grassland types (e.g., Alpine meadow) significantly increased soil organic carbon. ...
... Both Cambisols and Luvisols are typically used intensively for agriculture and grazing in Ethiopia (Rabia et al., 2013); this can result in severe degradation of soil organic C and total soil N, requiring several years before the site is able to recover. A meta-analysis by Dlamini et al. (2016) carried out using 55 studies from across the globe indicated that degradation induced by livestock grazing considerably reduced soil organic C. Such global studies are key to providing a global perspective, but the changes observed are not specific to the situation in Ethiopia. This requires a focus on Ethiopian studies, as done in this study. ...
Article
Community-led watershed development activities, including the establishment of exclosures (areas where both livestock and farming activities are excluded) on degraded communal grazing land, have become a common practice in Ethiopia since the 1990s. However, it is not yet fully understood how these exclosures change soil organic carbon and total soil nitrogen in different soil types and under different agroecologies. A meta-analysis using data gathered from the most relevant peer reviewed articles from Ethiopian exclosure systems was conducted to assess the variation in the effects of exclosures on soil carbon and nitrogen and to investigate the factors controlling change. The results demonstrate that after 16 years, exclosures can increase soil organic carbon and total soil nitrogen up to an effect size greater than two. This is moderated by soil type, exclosure age, landscape position and agroecology. More effective restoration of soil carbon was observed in less developed Leptosols and Cambisols than in more developed Luvisols, and in drier than more humid agroecologies. The results suggest that soil type and agroecology should be taken into consideration when planning and implementing exclosures on degraded communal grazing land. The findings of this study provide base line information for the future expansion of exclosures, and guide where to focus implementation. They also provide criteria to be used when planning and establishing exclosures to restore soil carbon and nitrogen. In addition, the results generated through this meta-analysis provide better understanding of the spatial and temporal variation of the effectiveness of exclosures to restore soil carbon and nitrogen.
... Livestock grazing is the dominant land use in mountain grassland ecosystems (Alkemade et al., 2013), and has played a crucial role in people's livelihoods for millennia (Bengtsson et al., 2019), creating complex socio-ecological systems (Ingty, 2021). In general, the negative effects of overgrazing on the vegetation structure and ecosystem functioning of mountain grasslands worldwide are well documented (e.g., Hilker et al., 2014;Dlamini et al., 2016;Hao et al., 2018), even in productive ecosystems (Cingolani et al., 2014). However, traditional extensive livestock grazing in mountain regions, with low to moderate stocking densities and short seasonal use of grasslands, has been reported to support several ecosystem services, such as habitat biodiversity (Odriozola et al., 2017), primary production (Jarque- Bascuñana et al., 2022) and the conservation of cultural ecosystems associated with the traditions of local communities relying on pastoralism for their livelihood (Öllerer et al., 2019). ...
... The different patterns evidenced in the trends of the ecosystem functions considered (i.e., biodiversity, forage production, carbon sequestration and soil fertility) concerning grazing exclusion as a proxy of livestock abandonment conditions, suggest that grassland management policies may be biased when monitoring single ecosystem properties or functions exclusively (e.g., Schultz et al., 2011;Lu et al., 2015;Dlamini et al., 2016), instead of EMF (Ren et al., 2018). Overall, this study revealed a significant and gradual loss of ecosystem multifunctionality as time elapsed since livestock grazing exclusion. ...
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Understanding the effects of traditional livestock grazing abandonment on the ability of mountain grasslands to sustain multiple ecosystem functions (ecosystem multifunctionality; EMF) is crucial for implementing policies that promote grasslands conservation and the delivery of multiple ecosystem services. In this study, we evaluated the effect of short- and long-term transhumant sheep abandonment on EMF through a grazing exclusion experiment in a grassland of the Cantabrian Mountains range (NW Spain), where transhumant sheep flocks graze in summer. We considered four key ecosystem functions, derived from vegetation and soil functional indicators measured in the field: (A) biodiversity function, evaluated from total plant species evenness, diversity and richness indicators; (B) forage production function, evaluated from cover and richness of perennial and annual herbaceous species indicators; (C) carbon sequestration function, evaluated from woody species cover and soil organic carbon indicators; and (D) soil fertility function, evaluated from NH4+-N, NO3–-N, P and K content in the soil. The EMF index was calculated by integrating the four standardized ecosystem functions through an averaging approach. Based on linear mixed modeling we found that grazing exclusion induced significant shifts in the considered individual ecosystem functions and also on EMF. Long-term livestock exclusion significantly hindered biodiversity and forage production functions, but enhanced the carbon sequestration function. Conversely, the soil fertility function was negatively affected by both short- and long-term grazing exclusion. Altogether, grazing exclusion significantly decreased overall EMF, especially in long-term livestock exclusion areas, while the decline in EMF in short-term exclusions with respect to grazed areas was marginally significant. The results of this study support the sustainability of traditional transhumance livestock grazing for promoting the conservation of grasslands and their ecosystem function in mountain regions.
... Overgrazing is considered a serious threat to ecosystem health due to its negative impacts on land productivity and soil stability, particularly on slopes, causing severe erosion and reducing the soil water holding capacity (Czeglédi & Radácsi, 2005;Wang, 2014), as well as soil organic carbon (Dlamini et al., 2016). High livestock grazing intensities also reduce the regeneration of young woody plants (Kikoti et al., 2015;Lohbeck et al., 2020) and increase soil compaction as a result of trampling (Sharrow, 2007). ...
... We attribute the absence of a clear effect of trees on soil hydraulic properties in the presence of intensive grazing to the severe soil disturbance caused by livestock. Livestock trampling has been reported to cause soil compaction, decrease soil hydrological functioning (Donkor et al., 2002;Dreccer & Lavado, 1993;Dudley et al., 2002), and reduce soil organic carbon (Dlamini et al., 2016). Similarly, results from our study also indicate an increase in soil bulk density and decreasing soil organic carbon with increasing grazing intensity. ...
Article
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The increase in livestock grazing in African drylands such as Miombo woodlands threatens land productivity and ecosystem functioning. Trees have positive effects on soil hydraulic properties, but few studies have looked at grazing intensity and hydrological functioning in different land uses. Therefore, we conducted a biophysical survey in Morogoro Rural District, Tanzania, where we identified four main land uses and land cover types, i.e. Forest reserve, open-access forest, cropland under fallow, and active cropland. We assessed grazing intensity, measured infiltration capacity, and conducted dye tracer experiments to assess the degree of preferential flow in 64 plots. We also tested the effect of grazing exclusion on infiltration capacity in 12-year-old fenced plots. Our results show that irrespective of land use or cover type, soil bulk density increased by 10 % from low to high grazing intensity, whereas infiltration capacity and soil organic carbon decreased by 55 and 28 %, respectively. We found a positive relationship between infiltration capacity and tree basal area in plots with lowest grazing intensities. However, at higher grazing, the infiltration capacity remained low independently of basal area. Preferential flow in deeper soils was six times higher in areas with no grazing, indicating higher deep soil and groundwater recharge potential at low grazing intensities. We conclude that the negative impacts on soil hydrological functioning of excessive livestock grazing override the positive effect of trees, but restricting grazing can reverse the impact. This article is protected by copyright. All rights reserved.
... Grasslands, which account for about 70% of the global agricultural area (Abberton et al., 2010), have lost almost 300 GtC from the top one-metre depth of their soils (Lal, 2004a(Lal, , 2004b because of mainly land degradation caused by inappropriate management practices such as overgrazing, biomass burning and land use change Dlamini et al., 2016;Lal, 2004a;Lu et al., 2017). Grassland degradation increases C output from the soils leading to drastic SOCs depletion (Abdalla et al., 2018;Chaplot et al., 2016;Dlamini et al., 2014). ...
... However, SOCs depletion under degraded grassland soils is varied worldwide based on soil types and climatic conditions. In a global meta-analysis, Dlamini et al. (2016) reported average SOC losses of ~16% in arid environments compared with ~8% in wetter ones, with Asia being the most affected continent (−27%). The lost C from grassland soils could be restored and that grassland soils may constitute a net sink for atmospheric C if appropriate management practices are adopted (Conant et al., 2001(Conant et al., , 2017Tessema et al., 2020). ...
Article
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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.
... Some studies have reported that grazing had negative effects on soil carbon (C) and nitrogen (N) levels (Sun et al., 2011;Shi et al., 2013;Li H. Q. et al., 2016), while other studies found that grazing had no significant effect on either of these parameters . In addition, many previous studies have demonstrated that heavy grazing (HG) reduces plant diversity, plant biomass, and soil organic carbon (SOC) content in alpine grassland (Sun et al., 2011;Dlamini et al., 2016; and that moderate grazing (MG) might help to balance the competing factors of species diversity protection and biomass production (Li et al., 2011). However, the results of these studies are controversial and inconclusive due to differences in grazing intensity, grazing duration, grassland types, and environmental factors between individual studies (Li et al., 2017;He et al., 2020). ...
Article
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Grazing is one of the main human disturbance factors in alpine grassland on the Qinghai-Tibet Plateau (QTP), which can directly or indirectly influence the community structures and ecological functions of grassland ecosystems. However, despite extensive field grazing experiments, there is currently no consensus on how different grazing management approaches affect alpine grassland diversity, soil carbon (C), and nitrogen (N). Here, we conducted a meta-analysis of 70 peer-reviewed publications to evaluate the general response of 11 variables related to alpine grassland ecosystems plant diversity and ecological functions to grazing. Overall, the results showed that grazing significantly increased the species richness, Shannon–Wiener index, and Pielou evenness index values by 9.89% (95% CI: 2.75–17.09%), 7.28% (95% CI: 1.68–13.62%), and 3.74% (95% CI: 1.40–6.52%), respectively. Aboveground biomass (AGB) and belowground biomass (BGB) decreased, respectively, by 41.91% (95% CI: −50.91 to −32.88%) and 17.68% (95% CI: −26.94 to −8.52%). Soil organic carbon (SOC), soil total nitrogen (TN), soil C:N ratio, and soil moisture decreased by 13.06% (95% CI: −15.88 to −10.15%), 12.62% (95% CI: −13.35 to −8.61%), 3.27% (95% CI: −4.25 to −2.09%), and 20.75% (95% CI: −27.89 to −13.61%), respectively, whereas, soil bulk density and soil pH increased by 17.46% (95% CI: 11.88–24.53%) and 2.24% (95% CI: 1.01–3.64%), respectively. Specifically, moderate grazing, long-durations (>5 years), and winter grazing contributed to increases in the species richness, Shannon–Wiener index, and Pielou evenness index. However, AGB, BGB, SOC, TN, and soil C:N ratios showed a decrease with enhanced grazing intensity. The response ratio of SOC was positively associated with AGB and BGB but was negatively related to the Shannon–Wiener index and Pielou evenness index. Furthermore, the effects of grazing on plant diversity, AGB, BGB, SOC, and TN in alpine grassland varied with grazing duration, grazing season, livestock type, and grassland type. The findings suggest that grazing should synthesize other appropriate grazing patterns, such as seasonal and rotation grazing, and, furthermore, additional research on grazing management of alpine grassland on the QTP is needed in the future.
... Soil is the largest and most active carbon pool in terrestrial ecosystems, about twice as much as atmospheric carbon pool and 2-3 times as much as plant carbon pool [3]. Historically, terrestrial C pools, have been largely depleted by anthropogenic activities such as deforestation, tillage and overgrazing [4,5]. Nutrient deficiency and improper fertilization lead to decomposition of soil organic matter, increased greenhouse gas emissions and further soil degradation during forest or grassland extraction [6]. ...
Article
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Afforestation can improve soil nutrient content and microbial community structure, increase soil carbon sequestration, and reduce greenhouse gas emissions. However, at present, there is a lack of research on the low hills and mountainous areas in North China. In order to scientifically evaluate the effect of afforestation recovery with different forest types on the improvement of the soil ecological system, the Fanggan ecological restoration in North China was taken as the research sample, and the coniferous forests, mixed coniferous and broad-leaved forest quadrats and broad-leaved forests, as well as the contrast of barren hills bushes were set to achieve the research goals. Research results of different forest types on soil nutrient and bacterial community in the Fanggan ecological restoration area have shown that afforestation with broad-leaved forests most obviously improved the nutrition properties and bacterial community of soil. (1) Broad-leaved forest afforestation obviously improved water retention and ammonia nitrogen content but reduced the content of available phosphorus and nitrate nitrogen of surface soil. It also increased available phosphorus, ammonia nitrogen, and nitrate nitrogen content of lower soil. (2) Broad-leaved forest afforestation significantly increased α-diversity of the bacterial community in surface soil, but only enhanced the Chao1 and ACE indices of lower soil. In addition, afforestation has also significantly changed the structure of soil bacterial community and β-diversity index. (3) Proteobacteria, Acidobacteria, Actinobacteria, and Verrucomicrobia accounted for the highest proportion of soil bacterial community. Proteobacteria and Verrucomicrobia occupied higher proportion in broad-leaved forests than in other forest types, while the proportion of Acidobacteria and Actinobacteria was the opposite. (4) Afforestation decreased cooperation and increased competition among bacteria of surface soil as well as increased coexistence and rejection among subsoil bacteria. (5) pH, ammonia nitrogen, organic carbon, and available phosphorus have exhibited a significant impact on the structure of bacterial community in the surface soil, while the bacterial community structure of the lower soil was mainly affected by pH and available phosphorus. Results have fully demonstrated the positive effects of broad-leaved forest on the restoration of soil nutrients and microbial community structure. Meanwhile, the important combinations of soil physical and chemical factors affecting soil bacterial community structure were also explored. The results can provide scientific basis for revealing the mechanism of soil organic matter, nutrient and ecological function restoration by artificial afforestation, and also offer theoretical support and practical reference for the restoration of artificial afforestation in the hilly and mountainous areas of North China.
... Grasslands are not only vital components of global terrestrial ecosystems, but also main pastures. To obtain the effects of grazing on grassland ecosystems, more and more studies have examined the response of grassland plants and soils to grazing (Dlamini et al., 2016;Lu et al., 2017;Ren et al., 2016;Sun et al., 2019;Wang et al., 2017;Xiong et al., 2016). These previous grazing studies can provide some scientific guidelines for grasslands management and utilization. ...
Article
Plant diversity plays an important role in maintaining and upgrading ecosystem structure and functions, and there remain uncertainties on plant species and especially phylogenetic diversity to grazing in alpine grasslands. Therefore, this study compared the differences of plant species and phylogenetic α- and β-diversity between grazing and fencing conditions at three alpine grasslands (ASMWG: alpine steppe meadow for winter grazing; ASMSG: alpine steppe meadow for summer grazing; AMSG: alpine meadow for summer grazing), Northern Tibet. At the ASMSG site, grazing significantly decreased mean nearest taxon distance (MNTD) by 19.33%, and increased Pielou by 7.06%. Plant community compositions between fencing and grazing conditions were different (p=0.021) at the ASMSG site. However, the Pielou, MNTD and plant community composition were not significantly different between the fencing and grazing conditions at the ASMWG and AMSG site. Grazing significantly increased the niche overlap at the ASMWG (levins: 51.36%, schooner: 28.97%, pianka: 28.11%, Czech: 28.97%; morisita: 28.75%) and ASMSG site (schooner: 35.19%, petraitis: 4.63%, pianka: 26.45%, czech: 35.19%; morisita: 30.86%), indicating that grazing may increase plant species competition and competitive exclusion at the ASMWG and ASMSG site. In contrast, grazing did not significantly affect niche overlap at the AMSG site. Therefore, the response of plant diversity to grazing can be different between species and phylogenetic diversity, and among alpine grasslands.
... Grasslands, are one of the largest terrestrial ecosystems in the world and store about 10% of the global SOC (Dlamini, Chivenge, & Chaplot, 2016;Zhao et al., 2017). Grazing is the primary land-use strategy for livestock production in grasslands. ...
Article
Livestock grazing in grasslands regulates the multifunctionality of grassland ecosystems and has an adverse effect on soil carbon (C) dynamics and fractions. However, our understanding of grazing‐induced changes in soil microbial community and their links to soil organic C (SOC) fractions is limited. By using a long‐term grazing experiment in desert steppe, we examined impacts of different grazing intensity on the diversity and composition of soil microbial community and their potential contribution to SOC content and fractions. The results showed that 15‐year grazing reduced total SOC (TSOC), albeit not significant, but induced a notable decrease in both labile and recalcitrant SOC fractions, especially under high grazing intensity. Soil prokaryotic communities were not significantly impacted by grazing intensity. However, we observed that sensitive OTUs, identified by indicator taxa analysis, grouped in distinct modules that reflected the different grazing intensities, suggesting that groups of microbes may cluster together and respond to grazing intensity. Association networks of prokaryotic OTUs and organic C fractions showed that SOC fractions were significantly related to rare taxa, indicating that grazing practice may act as a kind of environmental filtering and strongly affected soil microbial rare taxa and thereafter SOC fractions. Together, our findings suggest that grazing intensity did not change total microbial community and TSOC but affected SOC fractions by altering rare taxa. Overall, our results indicated that soil C fractions and rare microbial taxa were more sensitive to grazing intensity, which could act as indicator of variations in ecosystem functions in the semi‐arid desert steppe.
... 41,42 Fire exclusion in some areas was driven by increases in sedentary domestic livestock outside the park, which alter the grazing impacts of migratory herbivores inside the park (e.g., wildebeest and zebra), reducing fuel loads and the ability of some areas to support fire. 42 Loss of fire as a result of fuel load decline and increasing amounts of bare earth have been linked to increased soil erosion, decreased soil carbon storage, and desertification, 43,44 as well as increases in human-wildlife conflict 45 that only exacerbates existing threats to species conservation. ...
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Carbon emissions from savanna burning contribute to global climate change. Improved fire management in Africa could dramatically reduce carbon emissions and build ecosystem resilience, reduce threats to biodiversity and provide much needed financial support to local economies. Potential carbon revenues could substantially reduce protected area funding gaps that are in crisis due to COVID-19 and diversify income to augment tourism. More funding to pilot projects is needed to realize this potential and accelerate the UN’s Decade of Ecological Restoration.
... Festuca gracillima) constitutes about one-third of forage intake during winter (Oliva et al. 2005). Livestock grazing reduces plant species diversity, productivity, and vegetation cover and induces changes in soil structure and nutrient contents (Jiang et al. 2011;Dlamini et al. 2016). Peri et al. (2016b) indicate a negative effect on plant biodiversity due to continuous overgrazing in heterogeneous large paddocks in Patagonia. ...
Article
Background: Biodiversity supports multiple ecosystem services, whereas species loss endangers the provision of many services and affects ecosystem resilience and resistance capacity. The increase of remote sensing techniques allows to estimate biodiversity and ecosystem services supply at the landscape level in areas with low available data (e.g. Southern Patagonia). This paper evaluates the potential biodiversity and how it links with ecosystem services, based on vascular plant species across eight ecological areas. We also evaluated the habitat plant requirements and their relation with natural gradients. A total of 977 plots were used to develop habitat suitability maps based on an environmental niche factor analysis of 15 more important indicator species for each ecological area (n = 53 species) using 40 explanatory variables. Finally, these maps were combined into a single potential biodiversity map, which was linked with environmental variables and ecosystem services supply. For comparisons, data were extracted and compared through analyses of variance. Results: The plant habitat requirements varied greatly among the different ecological areas, and it was possible to define groups according to its specialization and marginality indexes. The potential biodiversity map allowed us to detect coldspots in the western mountains and hotspots in southern and eastern areas. Higher biodiversity was associated to higher temperatures and normalized difference vegetation index, while lower biodiversity was related to elevation and rainfall. Potential biodiversity was closely associated with supporting and provisioning ecosystem services in shrublands and grasslands in the humid steppe, while the lowest values were related to cultural ecosystem services in Nothofagus forests.
... We considered studies included in four recent meta-analyses (Abdalla et al., 2018;Dlamini et al., 2016;McSherry & Ritchie, 2013;Wang et al., 2016 ...
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There is interest in reducing CO2 concentrations in the atmosphere by managing livestock grazing to increase carbon (C) storage in soil. However, our understanding of the value of this practice of “C ranching” is based on studies suffering substantial, overlooked methodological problems. We reviewed research into effects of grazing treatments on soil organic carbon (SOC) stocks (mass SOC × area‐1). We show the empirical basis for C ranching (C offset) projects relies mainly on studies with unrealistic and overly simplistic livestock grazing treatments (e.g. grazed vs. not grazed), suboptimal experimental designs (e.g. lack pretreatment data, low number of treatment replications), and problematic SOC stock metrics. Synthesis and applications. It’s not clear that grazing treatments differ enough in their effects on soil organic carbon (SOC) stocks to reliably offset CO2 generated by human activities and/or reduce CO2 concentrations in the atmosphere. Therefore, we caution against overselling the value of carbon (C) ranching. Knowledge of C ranching effects on SOC is inadequate to justify C offset projects that provide ranchers with payment for environmental services. To better quantify benefits of C ranching, we advise using current best practices and expanding C ranching research with more realistic treatments over either broader spatio‐temporal scales and/or climate change treatments (e.g. drought, warming, elevated CO2).
... Grassland ecosystems are an important part of global ecosystems, and they cover approximately 40% of the Earth's terrestrial surface (White et al., 2000;Dlamini et al., 2016). Grazing by livestock is one of the most important land uses of grasslands, and overgrazing has led to severely degraded grasslands (Xun et al., 2018). ...
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Background and aims In practice, a grazing exclusion (GE) is an effective management method that is used to restore degraded grasslands across the world. However, the effect of GEs on soil organic carbon (SOC) and soil microbial diversity is highly controversial and needs further research across different regions. Methods We investigated the impacts of short-term GEs (4-7 years) on SOC and soil bacterial diversity in sagebrush desert pastures on the northern slopes of Mt. Tianshan, Northwest China, with a paired experimental design. Five sagebrush desert sites were selected, namely, the Xinyuan plot, Bole plot, Manas plot, Hutubi plot, and Qitai plot. The SOC content was determined by using the Walkley-Black method, and soil bacterial diversity was analyzed by high-throughput gene detection. Results Compared with freely grazed plots, short-term GEs decreased the SOC content and SOC stock in the 0-10 cm layer. GEs significantly decreased the SOC in the 0-10 cm layer by 14.94% and 53.42% in the Xinyuan and Qitai plots, respectively, and significantly increased the SOC by 14.7% in the 0-5 cm layer of the Bole plot (P < 0.05). The dominant phyla of the soil bacterial community in the sagebrush desert were Actinobacteria, Proteobacteria, Acidobacteria, and Chloroflexi, and GEs altered their relative abundances. GEs increased the relative abundance of Acidobacteria by 1.18%-6.16% and decreased that of Bacteroidetes by 16.25%-31.51% (P > 0.05). The relative abundances of Acidobacteria and Firmicutes in the 0-5 cm layer increased by 7.40% and 10.37% in the GE plots, while those in the 5-10 cm layer decreased by 5.08% and 69.62%, respectively (P > 0.05). GEs reduced the Chao1 index, Shannon index and Pielou index of the soil bacterial communities (P > 0.05). GEs reduced the effect of soil bacterial diversity on SOC content. Conclusion The short-term GEs decreased the SOC content and SOC stock in the 0-10 cm layer in the sagebrush desert, and these values were even significantly reduced at some sites. Nevertheless, the short-term GEs had no significant effect on soil bacterial diversity or dominant bacteria such as Actinobacteria. Our results suggested that short-term GEs exhibited weak negative impacts on soil organic carbon and soil bacterial diversity in the sagebrush desert, and ecological restoration needs to be longer under grazing exclusions.
... Numerous studies have assessed the impact of grassland degradation on soil organic carbon (SOC) stocks. A meta-analysis by Dlamini et al. (2016) showed that, at the global scale, average SOC stock depletion in grassland ranged from 7% in lightly degraded grasslands to 13% in heavily degraded grasslands, and the SOC loss is much greater in the upper 10 cm . Compared with SOC, however, SIC was frequently disregarded because (1) it is partly a legacy of soil parent material, (2) it undergoes slow formation processes and (3) it exhibits slow exchange with atmospheric CO 2 (Mi et al., 2008;Monger, 2014;Yang et al., 2012a;Zamanian et al., 2016). ...
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Grassland is an important part of terrestrial ecosystems and contains substantial amounts of soil carbon. However, 90% of grasslands suffer from degradation in northern China, where soil inorganic carbon (SIC) is a major reservoir. Previous studies have focused primarily on soil organic carbon (SOC) stock, while the effects of grassland degradation in SIC stock remain largely unexplored. Therefore, accurate assessments of both SOC and SIC stocks and their profile distributions are necessary to fully understand the role of grassland degradation in China’s carbon budget. Here, we conducted an experiment to estimate the stocks, profile distributions, and environmental controls of both SOC and SIC in patchy saline-alkaline grasslands under three degraded degrees (non-degraded patches, ND; moderately degraded patches, MD, and heavily degraded patches, HD). Our results showed that grassland degradation destroys not only SOC but also SIC stocks in saline-alkaline grasslands. SIC is the main component of soil carbon in saline-alkaline grasslands, and their distributions changed dramatically. Compared with ND, SIC losses caused by degradation accounted for 84% and 86% of total carbon loss under MD and HD patches, respectively. SIC loss primarily occurred at the intermediate soil layers (30–70 cm), while the loss of SOC was mainly in the topsoil (0–40 cm). Moreover, the distributions of SIC from 20 to 60 cm were closely related to soil pH, while it is mainly regulated by EC from 60 to 100 cm. In addition, soil pH, EC, and aboveground biomass were important variables driving the profile distributions of SOC in the upper soil. Our work provides evidence that grassland degradation mainly damages the SIC stocks. Our findings, therefore, highlight the non-negligible role of SIC dynamics in the carbon budget of degraded grassland ecosystems and the need to consider these dynamics in terrestrial carbon cycle research.
... The Mediterranean climate is characterized by dry summers; therefore, the native vegetation must adapt to increasingly frequent and recurring conditions of water stress (Klausmeyer and Shaw 2009;Nardini et al. 2014). Some authors claimed that this situation will impact pasture (Dlamini et al. 2016;Abdalla et al. 2018), crop productivity (Rodrigo-Comino et al. 2021), and plant mortality (Peñuelas et al. 2001;Bréda et al. 2006), and, as a consequence, it will enhance the fuel for forest fires (Vidal et al. 1994;Alcasena-Urdíroz et al. 2019;Martínez-Torres et al. 2019;Fernandez-Anez et al. 2021). Thus, an increase in the intensity or frequency of droughts can limit productivity and the ecological and economic values of this fragile ecosystem (Guillot et al. 2019;Lobo Do Vale et al. 2019). ...
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Assessing soil hydrological conditions can provide essential information for understanding the environmental processes that affect ecosystem services and, particularly in the context of ongoing climate change. This is key in areas affected by water scarcity such as the Mediterranean belt. Therefore, the main goals of this research are (i) to assess the main rainfall dynamics and trends of some representative hotspots along with southern Spain and (ii) to determine the impact on the soil available water content (AWC) over the last two decades. An analysis of daily precipitation and soil hydrological conditions was combined with soil sampling (543) and laboratory analyses to evaluate the properties related to the soil infiltration and retention capacity. The results show that the organic factors control soil properties and their hydrodynamics in southern Spain. Furthermore, a general declining trend in soil water availability is observed over the last two decades. This is more extreme in arid and semi-arid areas, where there have been several years in the last decade with more than 200 days without the available water content. Moreover, in these areas, heavy rainfall during specific moments of the year is the key factor that manifests a greater incidence in areas with steeper slopes, which in turn, also conditions the biological factors and the hydrodynamics of the soil. In short, in the context of climate change, the analysis of soil hydrological dynamics could be used to identify biodiversity thresholds in the Mediterranean area and even to detect phenological changes in specific plant species.
... Livestock grazing, an ancient method of grassland utilisation worldwide, has long played a central role in maintaining ecosystem structures and functions as well as achieving land sustainability Wu et al. 2015). However, owing to widespread overgrazing over the past century, grasslands have undergone unprecedented degradation globally (Dlamini et al. 2016), especially in the eastern Eurasian temperate steppe , the world's largest remaining grassland. A large number of studies have revealed the mechanisms underlying the observed degradation distinctly from the perspective of plant responses (Diaz et al. 2007; Rotundo and Aguiar 2008). ...
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Aims Plants with a history of overgrazing show trait-mediated legacy effects. These legacy effects strongly influence the growth dynamics and stress tolerance of plants, thus affecting ecosystem functioning. Long-term overgrazing has dramatic effects on plant growth and carbon assimilation via asexual propagation. However, the link between nitrogen (N) absorbability and assimilation with grazing-induced plant legacy effects remains largely unknown. Methods We investigated the strength of legacy effects induced by long-term overgrazing on N uptake and metabolism in the clonal plant Leymus chinensis, and its associated changes at the physiological and molecular levels. These tests were conducted in both field and greenhouse experiments. Results The clonal offspring of overgrazed L. chinensis were significantly smaller than the control offspring, with lower individual N uptake and utilisation efficiency, indicating that the N dynamics were affected by plant legacy effects. The response ratios of root length and biomass to N patches in the clonal offspring of overgrazed L. chinensis were significantly higher than those of the control, indicating that root nutrient foraging plasticity increased in response to grazing-induced N heterogeneity. Moreover, the observed plant legacy effects decreased N acquirement but significantly increased N assimilation by increasing N resorption efficiency, with biotic stress memory activated at the enzymatic and transcriptional levels. Conclusions We propose that multigenerational exposure of perennial plants to herbivore foraging can produce a legacy effect on N uptake, which offers insights into the potential resilience of grasslands to overgrazing.
... The impact of grazing on soil properties has been studied and it is well known [8][9][10][11][12]. However, the interesting outcome of the present study was the absence of a significant difference between moderately grazed and no-grazing soils in BD, WHC and MWD. ...
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Understanding the importance of grassland management is crucial for predicting the effects on forage production, pasture and ecosystem stability. Studies about the impact of grassland management in temperate humid environments on soil, erosion and aboveground biomass properties are lacking. This study investigates the effect of different grassland managements—no grazing, moderate grazing and heavy grazing—on soil properties, hydrological responses and herbage quality in an organic farm located in Croatia. The results showed that heavy grazing significantly increased soil compaction, structural deterioration, erosion and nutrient transport compared with no grazing. Heavily grazed plots had significantly higher soil organic matter and nutrient concentrations compared with no-grazing plots. Moderately grazed plots had the highest biomass production and the herbage with higher quality compared with other treatments. Significantly higher ash contents on heavily and moderately grazed plots were due to cow trampling. Cow grazing behaviour was a more important factor for plant regrowth and herbage quality than soil properties. Moderate grazing did not induce serious soil erosion problems or reduce soil productivity. Soil conservation measures should focus only on the heavily grazed areas and include the introduction of rotational grazing in combination with various strategies: excluding grazing, reseeding and increasing the diversity of resting areas.
... Subtropical broadleaf forests of the western Himalayan Kashmir region are currently facing intense deforestation due to the increased influx of rapidly expanding human population in valley basins and foothills of the area (Ali et al., 2020). Socioeconomic transformations combined with land use changes, agricultural expansions, unsustainable utilization of the forest products like medicinal plants, fuelwood and timber etc. are continuously shrinking the forest cover and ultimately reducing the regional biomass carbon stocks (Aziz et al., 2019;Bisht et al., 2014;Dlamini et al., 2016;Johnson et al., 2010). ...
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Carbon stock quantification holds vital significance in evaluating the climate change mitigation potential and carbon management of forest ecosystems. The current study was designed to quantify the biomass carbon stocks in the lesser Himalayan subtropical broadleaf forests of the Kashmir region. Primary data about the structural attributes and species composition of the local forests was collected through quadrat-based sampling followed by the application of allometric equations for the estimation of forest biomass. The biomass carbon stocks were calculated as 135.2 Mg ha-1 ranging from a maximum of 226.64 Mg ha-1 to a minimum of 11.83 Mg ha-1. The tree layer contributed a biomass carbon content of 134.67 Mg ha-1 making up to 99% share in the total forest biomass as compared to the shrub and herb layers with a very low biomass carbon value of 0.37 Mg ha-1 and 0.17 Mg ha-1 respectively. Dalbergia sissoo was recorded as the most dominant tree species with a biomass carbon stock value of 40.70 Mg ha-1 followed by Mallotus philippensis (30.09 Mg ha-1) and Ficus palmata (20.11 Mg ha-1). Principal Component Analysis revealed that the variations in the local carbon stocks were significantly correlated with the distribution pattern of the dominant tree species. Generalized Linear models showed a strong affinity of biomass carbon reserves with the structural attributes of the forest stands. This study generated a standard scientific dataset of the local biomass carbon stocks in the subtropical broadleaf forests with dynamic implications in sustainable forestry and carbon pool management in the region.
... SOC stocks. Depletion of the SOC stock is aggravated by overgrazing (Dlamini et al. 2016) and tillage by ploughing (Lal 1976). Thus, the potential capacity of SOC sequestration is more for severely degraded and strongly depleted soils. ...
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An increase in atmospheric CO2 by ∼146% and global temperature by ∼1 °C since the year ca. 1750 has created an urgency to identify potential sinks for storage of excess CO2. The historic depletion of soil organic carbon (SOC) from agroecosystems is 135 petagrams of carbon (Pg C). Thus, soils of agroecosystems have a potential to sequester atmospheric CO2 and mitigate anthropogenic global warming. Of the total anthropogenic emissions of 11.3 Pg C in 2017, 4.1 Pg C (36.3%) was absorbed by land-based sinks. Hence, land-use and soil management systems that can create a positive soil/ecosystem carbon (C) budget have a potential to store C in soil. A positive soil C budget is created when input of biomass-C exceeds that of losses. Practices that can create a positive soil C budget in the surface layer (0–30 cm) are conservation agriculture, mulch farming, cover cropping, biochar and complex farming systems. Techniques to include SOC in the sub-soil (30–100 cm) are deep-rooted species and deep-burrowing earthworms. There exists a positive correlation between SOC concentration and aggregation, plant-available water capacity, nutrient retention, bulk density and porosity. Therefore, restoring the SOC stock of degraded soils is pertinent to advancing global food and climate security, allowing an agricultural solution to environmental issues.
... MAT was grouped as < 8, 8-15, and > 15 • C, and MAP was categorized as < 600, 600-1000, and > 1000 mm. We chose these thresholds for the level breakpoints based on the FAO guidelines for agro-climatic zoning (Fischer et al., 2001) and previous meta-analyses (e.g., Dlamini et al., 2016;Knorr et al., 2005; and the general level breakpoints of the compiled studies in our dataset (Table S1). Soil texture was grouped as sandy, loamy, and clayey (Liu et al., 2021). ...
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Determining the effect of crop rotation (CR) on soil organic carbon (SOC) and its controls is vital for improving the potential benefits of CR in agroecosystems to achieve carbon neutrality. However, there has been no comprehensive and systematic evaluation of the response of SOC content to CR and its underlying drivers on the global level. Using 513 pairwise data from 167 studies, we conducted a global-scale meta-analysis to illuminate the changes in SOC content induced by CR and to explore the roles of climatic, edaphic, and agronomic factors in driving such changes. Results revealed that CR overall enhanced SOC content by 6.6% relative to continuous crop monoculture. SOC content under CR increased more in regions with intermediate mean annual temperature (MAT, 8–15°C) and precipitation (MAP, 600–1000 mm) than in regions with other climate types. CR had greater SOC content benefits in neutral (pH = 6–8) soils with loamy texture and medium levels of initial SOC (15–20 g kg–1) and total nitrogen (1.00–1.50 g kg–1). Also, CR performed better in the soybean-based cropping systems with more rotation cycles, longer rotation length, medium nitrogen fertilization input rate (100–200 kg N ha–1 yr–1), and the applications of no-till, straw retention, and organic fertilizers. Furthermore, the variance partitioning analysis revealed that soil (31%) and climate variables (18%) accounted for the major variations in SOC content response. Moreover, the random forest model demonstrated that soil texture, climatic factors (i.e., MAT and MAP), and initial SOC content were the predominant drivers of the response of SOC content. Overall, our findings highlight that CR is a critical practice to increase SOC content in global croplands, whereas the variations in response are governed by specific climatic, edaphic, and agronomic factors. This study helps to establish and manage site-specific CR systems that could enhance SOC in agroecosystems, ultimately facilitating carbon neutrality.
... In addition, concentrations of Ca +2 , K + , and Mg +2 were much higher than the concentration of Na + which minimize the risk of soil sodification [42]. In addition, the estimated soil organic content (SOC) was 0.097 kg/m 2 and it is similar to the minimum value of 0.1 kg of C/m 2 in the 0.30 cm topsoil reported by [43] in a review of degraded and non-degraded grasslands worldwide. Probably, this low accumulation of SOC is due to the short time of vinasse discharge per year in this soil. ...
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Tequila vinasse is a liquid waste generated during the production of tequila, an emblem-atic alcoholic beverage in Mexico. The objective of this study was to carry out an investigation on the tequila factories located in the state of Jalisco in order to know the location of the factories in the state, the characterization of the vinasses including factories of different sizes, the current treatment methods, and disposal practices as well as the impacts of common practices of vinasse disposal. Part of the information was collected by applying a questionnaire to the tequila factories previously contacted (and physically located). For the vinasse characterization, 24 tequila factories provided a composite sample of vinasse. To assess the impact of common vinasse disposal practices, a stream running through tequila factories, soil that has been used for vinasse discharge for 14 years, and a well located near the soil were evaluated. In two main regions (Valle and Altos Sur), 110 tequila factories distributed in 10 municipalities, were identified. Vinasse disposal and treatment problems are mainly related to micro-factories that do not treat their vinasse at all. The most common method of disposal is discharging on soils. Only in the Valle region is disposal in surface waters a common practice, as well as discharges into sewage systems. The monitored stream is totally degraded with low pH, high concentrations of organic matter, suspended solids, etc. Soil fertility has not been affected due to a method of vinasse discharge-soil rest. The texture of the soils (high content of clay and silt) has been decisive in protecting groundwater from the infiltration of vinasse. The results obtained in this study could help the authorities to develop adequate strategies for the management of vinasses (treatment and disposal), mainly in micro and small tequila factories.
... Moreover, as the key regulator of carbon (C) cycling and greenhouse gas emissions, SOM accounts for 1500 Pg C to a depth 1 m of global soil cover, equivalent to almost twice the amount of C in atmosphere (Batjes, 1996). Even small changes in soil C stocks could result in a vast impact on the atmospheric CO 2 concentration (Dlamini et al., 2016;Muñoz-Rojas et al., 2013). The global atmospheric CO 2 concentration is expected to reach 500 μmol mol − 1 and the global average surface temperature to enhance by 2 • C during the middle of 21st century due to fossil fuel combustion and land use changes (IPCC, 2013;Solomon et al., 2009). ...
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To understand how climate change impacts soil fertility and ecosystem functioning, it is necessary to explore how different pools of soil organic matter (SOM) at aggregate scale are functionally affected in their molecular composition. Here, we collected rhizospheric soil at rice harvest from a paddy field in which a simulated climate change experiment was conducted for 6 years, including CO2 enrichment up to 500 μmol mol⁻¹ (CE), air warming by 2 °C (WA), combination of CO2 enrichment and air warming (CW), and the ambient environment as control. The soil samples were separated in three aggregate fractions (macroaggregates, 2000-250 μm; microaggregates, 250-53 μm; clay & silt, <53 μm) by wet sieving procedure, their molecular composition was detected by off-line pyrolysis gas chromatography mass spectrometry (GC/MS), and the analysis of microbial communities was conducted by phospholipid fatty acids (PLFAs). The mass proportion of macroaggregates increased by 32%, 55%, and 109%, while that of microaggregates decreased by 30%, 14% and 54%, compared to control under CE, WA, and CW treatments, respectively. The mass proportion of macroaggregates was significantly positively correlated with root biomass, while it was significantly negatively correlated in microaggregates, which suggested that the formation of macroaggregates was derived from microaggregates due to root entanglement, and/or mucilage. The molecular composition of SOM depleted in phenolic compounds (phenols and phenolic compounds) while accumulated in lipids (alcohols, alkanes/alkenes/alkynes and fatty acids) with decreasing aggregate size. The increased yields of lipids and phenolic compounds in macro-and microaggregates under CE treatment were likely related to the enhanced root litter, whereas they were reduced under WA treatment due to increase of fungal dominance. A lesser increment of those compounds was noticed under CW treatment and it was attributed to the antagonistic effect, in which the increment effect of CO2 elevation can be counteracted by warming. The molecular composition hardly changed in clay & silt fraction under all climatic treatments, thus suggesting that the effect of elevated CO2 and/or warming on SOM molecular composition faded with decreasing aggregate size. Shared by control and a climatic treatment, changes of common molecules in the whole soils depended on their distribution among aggregates. Moreover, the differences in common molecules distribution induced by climatic treatments were significantly correlated to those in mass proportion of aggregates. Considering that common molecules dominated the molecular abundance across all aggregate fractions, our findings indicate that the alteration of SOM molecular composition in the whole soils under climatic treatments appears to be modified by the variation in mass proportion of aggregates.
... Soil depth (0-100 cm) was classified into two subgroups using the same groupings as Shi et al. (2013): 0-20 cm, 20-40 cm, 40-60 cm, 60-80 cm and 80-100 cm. In accordance with Dlamini et al. (2016), soil texture (6-48% clay) was categorized into sandy soils (<20% clay), loamy soils (20-32% clay), clay soils (>32% clay). The initial SOC content (0.12-41.89 g kg − 1 ) was grouped as ≤6 g kg − 1 , 6-12 g kg − 1 , 12-20 g kg − 1 and >20 g kg − 1 ; the initial STN content (0.11-4.47 g kg − 1 ) was also grouped as ≤0.75 g kg − 1 , 0.75-1.5 g kg − 1 , 1.5-2 g kg − 1 and >2 g kg − 1 according to Du et al. (2020). ...
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Afforestation made great contributions to ecological benefits across China. Robinia pseudoacacia is widely used in the Grain-for-Green Program. The responses of soil organic carbon (SOC) and soil total nitrogen (STN) to afforestation with R. pseudoacacia on cropland depend on plantation attributes, climatic factors, topographic features, and edaphic variables, thus making a synthesis of these studies necessary for understanding the magnitude and direction of SOC and STN to afforestation and the associated regulating factors. A meta-analysis was employed by compiling data of 1202 paired observations from 94 peer-reviewed publications to depict potential mechanisms of change in SOC and STN stocks following afforestation with R. pseudoacacia on cropland. Afforestation with R. pseudoacacia on cropland, on average, significantly and positively increased SOC and STN stocks. The changes in SOC and STN stocks increased with plantation age and altitude, but decreased with mean annual temperature, slope gradients, soil depth, soil clay content, initial SOC content and initial STN content. Greater accumulation rates of SOC and STN stocks after afforestation were detected in middle canopy density (0.6–0.8) and middle mean annual precipitation (450–550 mm). Among four kinds of biotic and abiotic factors, plantation attributes made greatest contributes to the variance in the response size of SOC and STN stocks. In particular, plantation age was the most essential variable on the response size of SOC and STN stocks. These results indicated that SOC and STN stocks following afforestation with R. pseudoacacia on cropland could be enhanced through plantation management practices.
... The dominant grassland use was animal pasture. Over-grazing of pasture by cattle and other livestock may be partially responsible for enhanced SOM export (Dlamini et al., 2016). Protein-like fluorescence typically increases with increasing anthropogenic DOM inputs from households (i.e., sewage) and farm wastes (Baker et al., 2004). ...
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Land‐ocean dissolved organic matter (DOM) transport is a significant and changing term in global biogeochemical cycles which is increasing as a result of human perturbation, including land‐use change. Knowledge of the behavior and fate of transported DOM is lacking, particularly in the tropics and subtropics where land‐use change is occurring rapidly. We used Parallel Factor (PARAFAC) Analysis to investigate how land‐use influenced the composition of the DOM pool along a subtropical land‐use gradient (from near‐pristine broadleaf forest to agri‐urban settings) in Belize, Central America. Three humic‐like and two protein‐like components were identified, each of which was present across land uses and environments. Land‐use mapping identified a strong (R² = 0.81) negative correlation between broadleaf forest and agri‐urban land. All PARAFAC components were positively associated with agri‐urban land‐use classes (cropland, grassland, and/or urban land), indicating that land‐use change from forested to agri‐urban exerts influence on the composition of the DOM pool. Humic‐like DOM exhibited linear accumulation with distance downstream and behaved conservatively in the coastal zone whilst protein‐like DOM exhibited nonlinear accumulation within the main river and nonconservative mixing in coastal waters, indicative of differences in reactivity. We used a hydrodynamic model to explore the potential of conservative humics to reach the region's environmentally and economically valuable coral reefs. We find that offshore corals experience short exposures (10 ± 11 days yr⁻¹) to large (∼120%) terrigenous DOM increases, whilst nearshore corals experience prolonged exposure (113 ± 24 days yr⁻¹) to relatively small (∼30%) terrigenous DOM increases.
... If soils are managed inadequately, the carbon storage could significantly affect atmospheric greenhouse gas concentrations such as CO 2 (Batjes et al., 1998;Oertel et al., 2016). Given the capacity of soils to harbor greenhouse gasses, there is increasing interest in looking at soil carbon and ecosystem functions as an opportunity to mitigate and adapt to climate change (Donovan, 2013;Schlesinger et al., 2019) where the focus on arid and semi-arid rangelands as a potential carbon sink in increasing (Dlamini et al., 2016;Ahlstrom et al., 2015;Poulter et al., 2014;Wang et al., 2018). Modeling research suggests that the Mongolian plateau was a sink of at least 31 teragrams of carbon per year in the 1990s (Li et al., 2009), along with large annual and spatial variation in how much greenhouses these landscape bind per year (Lioubimtseva et al., 2004). ...
Thesis
Climate change is happening virtually everywhere and is one of the biggest threats facing humanity and life on Earth. As climate change continues across the world, global temperatures are expected to rise, weather events are predicted to become more severe and frequent, and the alteration of ecosystems and wildlife habitats is expected to accelerate. According to the IPCC Working Group Impact, adaptation, and vulnerability report (2007), desert and semi-desert ecosystems, are the most vulnerable ecosystems to climate change impacts due to precipitation fluctuation, future warming trends, and frequent disastrous events. However, there is little information about how climate change may affect the Gobi environment in Central Asia and people’s livelihoods at the regional and local scales. This research aims to understand how climate change will affect four different systems (atmosphere, biosphere, geosphere, anthroposphere) in Mongolia’s Gobi region. More specifically, the research aims to assess how climate change will affect 1. rangeland vegetation (biosphere) and 2. soil characteristics (geosphere) assess, 3. how herder livelihoods are affected by climate change impacts (anthroposphere) and assess 4. weather and climatic trends over the last 20 years at the local level in the South Gobi region (atmosphere). To do this, I used a multi-disciplinary approach, including empirical environmental research and both qualitative and quantitative social research. I examined vegetation responses to experimentally simulated climate change (warming, increased and decreased rainfall) and grazing (clipping vegetation) between 2016 and 2019 in Tost Bag in Gurvantes Soum of the South-Gobi, Mongolia. I also assessed how the soil physicochemical properties (soil pH, CaCO3, P2O5, SOC, EC, NO3, bulk density, and dry mass) responded to the experimental climate and grazing simulations. Soil physicochemical properties assessments were conducted at the Soil laboratory of the Institute of Geography and Geo-ecology, Mongolian Academy of Sciences. To assess how local herders were coping with climatic impacts, I conducted 42 semi-structured interviews in the Gurvantes Soum. I discussed with the herders how climatic factors such as dzud and drought could affect their livelihood decision-making, including engaging in informal or illegal mining, becoming a contracted herder, or opening a small business in nearby settlements. Climatic trends for the Gurvantes Soum were assessed by combining information from herder perceptions collected through 32 additional household surveys and meteorological data from a weather station in the Gurvantes Soum. I asked interviewees if they had perceived changes in eight meteorological variables, including winter temperature, summer temperature, summer precipitation, frequency in intense rain, frequency in drizzle rain, wind speed, number of windy days, and snow cover between 1995 and 2015. My experimental result revealed that grazing and climate change manipulations reduced vegetation cover by 35-37% (mean: 8.1 gm2) and biomass by 23% (mean: 1.67 gm2) but did not affect species richness (χ2=0.21, df= 3, p=0.98). All targeted plant species responded differently to increasing or decreasing trends to each climatic and grazing treatment and showed species-specific responses with some species increasing and some species decreasing. The climate warming chambers (n=10) showed an increased growth period by an average of 12 days (10-15 days). The soil physicochemical properties assessments showed that the mountain desert steppe landscape in the study area was characterized by sandy loam texture and was alkaline in nature (63.4% of sand content; 21.6% of silt content, and 5% of clay content). This result suggests that the soil was less capable of retaining organic carbon compared to clay-dominated soils. The climate change manipulations showed that an increase in both temperature and precipitation combined with grazing resulted in soil physicochemical properties. Temperature increases of 2 degrees Celsius led to a reduction in organic compounds of the soil and thereby and enrichment of sand in the soil sandy soil characteristics (Anova test: F1,9= 37.08, p>0.05) while a precipitation increase of 50% led to higher soil salinity (Anova test: F2,24= 10.47, p>0.05). In addition, grazing effects had a positive impact on soil organic carbon (Anova test: F1,16=23.69, p< 0.001). Our semi-structured interviews suggested that livelihood diversification strategies are linked to natural climatic hazards (n= 37, 89%), as well as to political and socio-economic factors (n= 5, 11%). Based on the number of livestock owned, different types of herding typologies were identified in the Gurvantes Soum, including ninja miners (livestock owned n=83.6, SD=58.9), contracted herders (livestock owned n=25, SD=18.7), shared herding (herders take turn to herd each others livestock) (livestock owned n=196, SD=61), herding for others (livestock owned n=321, SD=53.2), true herders herding only their own animals (100% sustain their livelihood by livestock income) (livestock owned n=391, SD=53.2) and rich herders (livestock owned n=784, SD=347). According to the additional household surveys, all herders perceived significant changes in the local weather patterns. Most (94% n= 31) herders reported seasonal shifts, with extreme variations between warm and cool seasons over the last 20 years. Based on focus group discussions, herders agreed that 6 of the 10 climate change scenarios presented would have strong negative impacts on their practices and livelihoods and that none of the scenarios would have positive effects. The meteorological data from the same time period showed an increase in windy days (tau = 0.434, p=0.008) and wind speed (tau = 0.354, p=0.027), a decrease in snow cover (tau = - 0.462, p=0.033), and trends for an increase in the frequency of intense rains (tau = 0.285, p=0.077) and a decreasing in the frequency of drizzle rains (tau = 0.328, p=0.090) although this was significant only at α = 0.10. My experimental results suggest that the mountain desert steppe zone is at risk of desertification from increasing temperatures and precipitation in the future. The temperature increase was found to decrease vegetation cover and biomass. The experiment also showed that increased precipitation, which was added to simulate intense rains where the total amount of rain increased but the frequency of rainy days decreased, also reduced vegetation cover and biomass. Furthermore, the experiment also showed that temperature increases reduced the organic carbon in the soils and that flush floods increased the salinity. The research also suggested that a range of livestock management strategies could mitigate climate change impacts. The climate change experiment results suggested that light grazing increased the soil’s carbon content, potentially offsetting carbon emissions in mountain desert steppe regions. I recommend further studies to assess vegetation and soil responses to different climate change and grazing strategies (heavy, medium, light). Another key finding from this study was that people’s livelihoods are impacted strongly by climate change. Rural herders reported a range of coping mechanisms for dealing with changes in the weather and the rangeland, including diversifying their livelihoods. Herders reported that they seek alternative sources of income from activities such as ninja mining when they lose livestock due to events such as natural hazards. The number of ninja miners could be used to indicate and measure climate change impacts on livelihoods in particular areas. Finally, my results suggest that herder perceptions of climate change appeared to be more focused on rangeland-related changes than the direct meteorological changes themselves. People’s perceptions of climate change are particularly important to provide insights on factors that put their livelihoods at risk directly. Based on my study, herders will be forced to move often with future changes in the climate, leading to rangeland competition among herders. Herder livelihood and herding decisions seemed to be highly responsive to climatic impacts, and their knowledge needs to be incorporated into rangeland and climate change management strategies. This research helps provide insights on understanding how climate change may impact the mountain desert steppe and the livelihoods of its inhabitants. It also provides recommendations on how to enhance future ecological and societal resilience to climate change. Traditional knowledge and working closely with herding communities by incorporating their perspectives and views will be essential to develop adapted pastoral management strategies. This work concludes that climate change impacts are influencing multiple aspects of the mountain desert steppe zone, including the climate, local vegetation, soil characteristics, herder livelihoods, and decision making. My research also shows that there is a need for continued research in understanding how climate change is influencing the Gobi environment and putting peoples’ livelihoods at risk. This research provides a foundation for future in-depth assessments.
... If soils are managed inadequately, the carbon storage could significantly affect atmospheric greenhouse gas concentrations such as CO 2 (Batjes et al., 1998;Oertel et al., 2016). Given the capacity of soils to harbor greenhouse gasses, there is increasing interest in looking at soil carbon and ecosystem functions as an opportunity to mitigate and adapt to climate change (Donovan, 2013;Schlesinger et al., 2019) where the focus on arid and semi-arid rangelands as a potential carbon sink in increasing (Dlamini et al., 2016;Ahlstrom et al., 2015;Poulter et al., 2014;Wang et al., 2018). Modeling research suggests that the Mongolian plateau was a sink of at least 31 teragrams of carbon per year in the 1990s (Li et al., 2009), along with large annual and spatial variation in how much greenhouses these landscape bind per year (Lioubimtseva et al., 2004). ...
Thesis
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Climate change is happening virtually everywhere and is one of the biggest threats facing humanity and life on Earth. As climate change continues across the world, global temperatures are expected to rise, weather events are predicted to become more severe and frequent, and the alteration of ecosystems and wildlife habitats is expected to accelerate. According to the IPCC Working Group Impact, adaptation, and vulnerability report (2007), desert and semi-desert ecosystems, are the most vulnerable ecosystems to climate change impacts due to precipitation fluctuation, future warming trends, and frequent disastrous events. However, there is little information about how climate change may affect the Gobi environment in Central Asia and people’s livelihoods at the regional and local scales. This research aims to understand how climate change will affect four different systems (atmosphere, biosphere, geosphere, anthroposphere) in Mongolia’s Gobi region. More specifically, the research aims to assess how climate change will affect 1. rangeland vegetation (biosphere) and 2. soil characteristics (geosphere) assess, 3. how herder livelihoods are affected by climate change impacts (anthroposphere), and assess 4. weather and climatic trends over the last 20 years at the local level in the South Gobi region (atmosphere). To do this, I used a multi-disciplinary approach, including empirical environmental research and both qualitative and quantitative social research. I examined vegetation responses to experimentally simulated climate change (warming, increased and decreased rainfall) and grazing (clipping vegetation) between 2016 and 2019 in Tost Bag in Gurvantes Soum of the South-Gobi, Mongolia. I also assessed how the soil physicochemical properties (soil pH, CaCO3, P2O5, SOC, EC, NO3, bulk density, and dry mass) responded to the experimental climate and grazing simulations. Soil physicochemical properties assessments were conducted at the Soil laboratory of the Institute of Geography and Geo-ecology, Mongolian Academy of Sciences. To assess how local herders were coping with climatic impacts, I conducted 42 semi-structured interviews in the Gurvantes Soum. I discussed with the herders how climatic factors such as dzud and drought could affect their livelihood decision-making, including engaging in informal or illegal mining, becoming a contracted herder, or opening a small business in nearby settlements. Climatic trends for the Gurvantes Soum were assessed by combining information from herder perceptions collected through 32 additional household surveys and meteorological data from a weather station in the Gurvantes Soum. I asked interviewees if they had perceived changes in eight meteorological variables, including winter temperature, summer temperature, summer precipitation, frequency in intense rain, frequency in drizzle rain, wind speed, number of windy days, and snow cover between 1995 and 2015. My experimental result revealed that grazing and climate change manipulations reduced vegetation cover by 35-37% (mean: 8.1 gm2) and biomass by 23% (mean: 1.67 gm2) but did not affect species richness (χ2=0.21, df= 3, p=0.98). All targeted plant species responded differently to increasing or decreasing trends to each climatic and grazing treatment and showed species-specific responses with some species increasing and some species decreasing. The climate warming chambers (n=10) showed an increased growth period by an average of 12 days (10-15 days). The soil physicochemical properties assessments showed that the mountain desert steppe landscape in the study area was characterized by sandy loam texture and was alkaline in nature (63.4% of sand content; 21.6% of silt content, and 5% of clay content). This result suggests that the soil was less capable of retaining organic carbon compared to clay-dominated soils. The climate change manipulations showed that an increase in both temperature and precipitation combined with grazing resulted in soil physicochemical properties. Temperature increases of 2 degrees Celsius led to a reduction in organic compounds of the soil and thereby and enrichment of sand in the soil sandy soil characteristics (Anova test: F1,9= 37.08, p>0.05) while a precipitation increase of 50% led to higher soil salinity (Anova test: F2,24= 10.47, p>0.05). In addition, grazing effects had a positive impact on soil organic carbon (Anova test: F1,16=23.69, p< 0.001). Our semi-structured interviews suggested that livelihood diversification strategies are linked to natural climatic hazards (n= 37, 89%), as well as to political and socio-economic factors (n= 5, 11%). Based on the number of livestock owned, different types of herding typologies were identified in the Gurvantes Soum, including ninja miners (livestock owned n=83.6, SD=58.9), contracted herders (livestock owned n=25, SD=18.7), shared herding (herders take turn to herd each others livestock) (livestock owned n=196, SD=61), herding for others (livestock owned n=321, SD=53.2), true herders herding only their own animals (100% sustain their livelihood by livestock income) (livestock owned n=391, SD=53.2) and rich herders (livestock owned n=784, SD=347). According to the additional household surveys, all herders perceived significant changes in the local weather patterns. Most (94% n= 31) herders reported seasonal shifts, with extreme variations between warm and cool seasons over the last 20 years. Based on focus group discussions, herders agreed that 6 of the 10 climate change scenarios presented would have strong negative impacts on their practices and livelihoods and that none of the scenarios would have positive effects. The meteorological data from the same time period showed an increase in windy days (tau = 0.434, p=0.008) and wind speed (tau = 0.354, p=0.027), a decrease in snow cover (tau = - 0.462, p=0.033), and trends for an increase in the frequency of intense rains (tau = 0.285, p=0.077) and a decreasing in the frequency of drizzle rains (tau = 0.328, p=0.090) although this was significant only at α = 0.10. My experimental results suggest that the mountain desert steppe zone is at risk of desertification from increasing temperatures and precipitation in the future. The temperature increase was found to decrease vegetation cover and biomass. The experiment also showed that increased precipitation, which was added to simulate intense rains where the total amount of rain increased but the frequency of rainy days decreased, also reduced vegetation cover and biomass. Furthermore, the experiment also showed that temperature increases reduced the organic carbon in the soils and that flush floods increased the salinity. The research also suggested that a range of livestock management strategies could mitigate climate change impacts. The climate change experiment results suggested that light grazing increased the soil’s carbon content, potentially offsetting carbon emissions in mountain desert steppe regions. I recommend further studies to assess vegetation and soil responses to different climate change and grazing strategies (heavy, medium, light). Another key finding from this study was that people’s livelihoods are impacted strongly by climate change. Rural herders reported a range of coping mechanisms for dealing with changes in the weather and the rangeland, including diversifying their livelihoods. Herders reported that they seek alternative sources of income from activities such as ninja mining when they lose livestock due to events such as natural hazards. The number of ninja miners could be used to indicate and measure climate change impacts on livelihoods in particular areas. Finally, my results suggest that herder perceptions of climate change appeared to be more focused on rangeland-related changes than the direct meteorological changes themselves. People’s perceptions of climate change are particularly important to provide insights on factors that put their livelihoods at risk directly. Based on my study, herders will be forced to move often with future changes in the climate, leading to rangeland competition among herders. Herder livelihood and herding decisions seemed to be highly responsive to climatic impacts, and their knowledge needs to be incorporated into rangeland and climate change management strategies. This research helps provide insights on understanding how climate change may impact the mountain desert steppe and the livelihoods of its inhabitants. It also provides recommendations on how to enhance future ecological and societal resilience to climate change. Traditional knowledge and working closely with herding communities by incorporating their perspectives and views will be essential to develop adapted pastoral management strategies. This work concludes that climate change impacts are influencing multiple aspects of the mountain desert steppe zone, including the climate, local vegetation, soil characteristics, herder livelihoods, and decision making. My research also shows that there is a need for continued research in understanding how climate change is influencing the Gobi environment and putting peoples’ livelihoods at risk. This research provides a foundation for future in-depth assessments.
... Numerous soil CH 4 flux measurements were performed during the last few decades to assess land-use change effects on grassland soil CH 4 flux (Liebig et al., 2010;Liu et al., 2017a;Mosier et al., 1991;Yang et al., 2019a), however large uncertainties still remain due to several key constraints. First, global overgrazing has caused serious environmental problems (Dlamini et al., 2016;Glindemann et al., 2009) and insufficient supply herbage mass for grazing livestock (Glindemann et al., 2009;Schönbach et al., 2012). Therefore, large areas of grazed grasslands have been converted to forage production systems to meet livestock requirements (Bai et al., 2008;Liebig et al., 2010). ...
... Numerous soil CH 4 flux measurements were performed during the last few decades to assess land-use change effects on grassland soil CH 4 flux (Liebig et al., 2010;Liu et al., 2017a;Mosier et al., 1991;Yang et al., 2019a), however large uncertainties still remain due to several key constraints. First, global overgrazing has caused serious environmental problems (Dlamini et al., 2016;Glindemann et al., 2009) and insufficient supply herbage mass for grazing livestock (Glindemann et al., 2009;Schönbach et al., 2012). Therefore, large areas of grazed grasslands have been converted to forage production systems to meet livestock requirements (Bai et al., 2008;Liebig et al., 2010). ...
... Numerous soil CH 4 flux measurements were performed during the last few decades to assess land-use change effects on grassland soil CH 4 flux (Liebig et al., 2010;Liu et al., 2017a;Mosier et al., 1991;Yang et al., 2019a), however large uncertainties still remain due to several key constraints. First, global overgrazing has caused serious environmental problems (Dlamini et al., 2016;Glindemann et al., 2009) and insufficient supply herbage mass for grazing livestock (Glindemann et al., 2009;Schönbach et al., 2012). Therefore, large areas of grazed grasslands have been converted to forage production systems to meet livestock requirements (Bai et al., 2008;Liebig et al., 2010). ...
... Numerous soil CH 4 flux measurements were performed during the last few decades to assess land-use change effects on grassland soil CH 4 flux (Liebig et al., 2010;Liu et al., 2017a;Mosier et al., 1991;Yang et al., 2019a), however large uncertainties still remain due to several key constraints. First, global overgrazing has caused serious environmental problems (Dlamini et al., 2016;Glindemann et al., 2009) and insufficient supply herbage mass for grazing livestock (Glindemann et al., 2009;Schönbach et al., 2012). Therefore, large areas of grazed grasslands have been converted to forage production systems to meet livestock requirements (Bai et al., 2008;Liebig et al., 2010). ...
... Numerous soil CH 4 flux measurements were performed during the last few decades to assess land-use change effects on grassland soil CH 4 flux (Liebig et al., 2010;Liu et al., 2017a;Mosier et al., 1991;Yang et al., 2019a), however large uncertainties still remain due to several key constraints. First, global overgrazing has caused serious environmental problems (Dlamini et al., 2016;Glindemann et al., 2009) and insufficient supply herbage mass for grazing livestock (Glindemann et al., 2009;Schönbach et al., 2012). Therefore, large areas of grazed grasslands have been converted to forage production systems to meet livestock requirements (Bai et al., 2008;Liebig et al., 2010). ...
... Numerous soil CH 4 flux measurements were performed during the last few decades to assess land-use change effects on grassland soil CH 4 flux (Liebig et al., 2010;Liu et al., 2017a;Mosier et al., 1991;Yang et al., 2019a), however large uncertainties still remain due to several key constraints. First, global overgrazing has caused serious environmental problems (Dlamini et al., 2016;Glindemann et al., 2009) and insufficient supply herbage mass for grazing livestock (Glindemann et al., 2009;Schönbach et al., 2012). Therefore, large areas of grazed grasslands have been converted to forage production systems to meet livestock requirements (Bai et al., 2008;Liebig et al., 2010). ...
... Numerous soil CH 4 flux measurements were performed during the last few decades to assess land-use change effects on grassland soil CH 4 flux (Liebig et al., 2010;Liu et al., 2017a;Mosier et al., 1991;Yang et al., 2019a), however large uncertainties still remain due to several key constraints. First, global overgrazing has caused serious environmental problems (Dlamini et al., 2016;Glindemann et al., 2009) and insufficient supply herbage mass for grazing livestock (Glindemann et al., 2009;Schönbach et al., 2012). Therefore, large areas of grazed grasslands have been converted to forage production systems to meet livestock requirements (Bai et al., 2008;Liebig et al., 2010). ...
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Methane (CH4) oxidation in the well-aerated soils of grassland is an important sink for atmospheric CH4, which could be largely modified by the land-use changes. However, the impacts of reclamation on grassland soil CH4 uptake remained uncertain currently in China. Therefore, a 2 year-round CH4 fluxes were measured from 3 land-use types (heavy grazing steppe (HG, control), artificial grassland (AG), and cropland (CL)) in the agro-pastoral ecotone of Northern China to evaluate this impact. Moreover, a meta-analysis was conducted to elucidate this effect across Chinese grasslands. Result showed that land-use types could not change the seasonal patterns but significantly (p < 0.05) influence the strength of soil CH4 uptake. Mean annual CH4 uptake followed the decreasing order of 14.7 ± 0.48 (mean ± 1 standard error) (CL), 3.28 ± 0.09 (AG), and 1.24 ± 0.07 kg CH4-C ha-1 yr-1 (HG) during 2012-2014. This spatial variation pattern was linear negatively (n = 6, "r" _"adj." ^"2" = 0.73, p < 0.05) associated to the annual mean soil water-filled pore space. Non-growing season CH4 uptake contributed 22-46% to the annual CH4 uptake across land-use types. Meta-analysis also confirmed that reclamation significantly (p < 0.05) promoted the annual soil CH4 uptake in the temperate grasslands of China. This is primarily related to significantly (p < 0.05) decreasing in soil water content and increasing in sand content by reclamation. Furthermore, nitrogen application ≤ 100 kg N ha-1 yr-1 into these N-limited ecosystems significantly (p < 0.05) promoted soil CH4 uptake. Collectively, our study demonstrated that reclamation combined with low N application promoted soil CH4 uptake in temperate grasslands of China. Comprehensive investigation of the reclamation impact on the budgets of greenhouse gas (carbon dioxide, nitrous oxide, and CH4) in grasslands is necessary for reliably evaluating the impact of land-use change on the climate change.
... SOC stocks depend generally on soil properties, forest type, stand age, litter productivity and decomposition rate [4]. Significant soil disturbances including erosion, overgrazing and deforestation have been reported from the study area posing a serious threat to the carbon stocks [49,50]. Biomass and soil carbon pools normally enjoy a linear relationship, as the soil carbon is augmented by the biomass inputs [51,52]. ...
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Tree regrowth plots are often utilised to reduce soil erosion and increase soil organic carbon (SOC) as well as providing shade for cattle. However, unfenced tree regrowth plots have been found to make limited improvements in soil health in grazing lands. To better inform land management decisions, the impact of an unfenced tree regrowth on soil erosion rates and soil properties was analysed for an improved (i.e., sown with introduced species) cattle pasture in Eastern Australia. Soil cores were collected to 20 cm depth for two paired transects: one with improved pasture and a tree plot, and one consisting only of improved pasture. Samples were analysed for soil organic carbon and soil properties and soil erosion rates were determined using the diffusion and migration model (DMM) and Revised Universal Soil Loss Equation (RUSLE). Maximum DMM erosion rates were similar for the two transects at 2.7 (tree plot) and 2.3 (pasture) t.ha⁻¹.yr⁻¹, with the tree plot not having a statistically significant effect. RUSLE erosion rates showed less similarity for the transects at 5.58 (pasture) and 3.08 (tree plot) t.ha⁻¹.yr⁻¹. SOC was lower within the tree plot compared to the rest of the transect, while it was significantly higher in the pasture than the tree plot transect (4.93% compared to 3.72%). To examine if the tree plot is buffering against higher erosion caused by this, the RUSLE cover factor was substituted for that of the pasture transect. However, no such effect was observed. Overall, the tree plot had no significant effect on SOC and erosion in this improved pasture grazing system. This has implications for the design of tree plots and their location, which is significant due to their perceived role in regenerative agriculture practices.
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The soil organic carbon (SOC) of grasslands is a vital component of the global carbon cycle. The SOC in grassland ecosystems in arid and semi-arid regions is sensitive to global climate change, but the dynamic drivers of the SOC content are still controversial. Grazing is the main factor affecting SOC contents in grasslands; however, the response of different types of grasslands to the grazing intensity remains unclear. Based on the Denitrification-Decomposition model and field investigations, in this study, the spatial and temporal dynamics of SOC and its drivers in the grasslands in Northern Xinjiang were investigated, and the response of the SOC in the different types of grasslands to various grazing intensities at the regional scale. The results reveal that the SOC content of the grasslands in Northern Xinjiang increased at a rate of 161.32 kg C ha⁻¹ yr⁻¹ from 2001 to 2020, and the spatial distribution of the SOC dynamics varied greatly. There was an increasing trend at higher elevations and a decreasing trend at lower elevations. Grazing contributed less to the SOC dynamics, and temperature and precipitation were the main drivers of the SOC dynamics. The overall effect of the grazing intensity on SOC content was negative. The responses of the different types of grassland to the grazing intensity varied greatly, with the least effect in alpine meadows and the greatest effect in lowland meadows and temperate desert grasslands.
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Terrestrial biomes in the U.S. can be managed for SOC sequestration. Sequestration for climate change adaptation and mitigation occurs when the soil C inputs are derived from atmospheric carbon dioxide (CO2) fixed by photosynthesis within a biome, and the synthesized SOC is protected and stabilized for long periods of time. Aside soil and land-use management practices, elevated CO2, nitrogen (N) additions, warming, irrigation and increases in biomass but also natural disturbances affect SOC stocks. The SOC sequestration in managed land of forest biomes in the U.S. can be managed by practices including: (i) harvesting, (ii) thinning, (iii) fertilization, (iv) liming, (v) drainage, (vi) irrigation, (vii) tree species selection and (viii) control of understory vegetation, and by managing natural disturbances. Management of stand-replacing disturbances (i.e., fire, insect outbreaks) is particularly promising to enhance SOC sequestration. However, forest management is focused on producing timber by silviculture and, until recently, not on soil management including SOC stocks resulting in limited understanding on how to enhance forest SOC sequestration. Fire strongly affects SOC sequestration in the boreal forest/taiga biome, but it is unclear how recent changes in fire size, severity and intensity together with changes in insect and pathogen outbreaks alter SOC stocks. Importantly, it is not possible to fully control and manage SOC sequestration in boreal U.S. forests because of its scale and remoteness. In contrast, forest management interventions in the temperate coniferous forest biome during harvesting, thinning, reforestation and prescribed burning can potentially enhance SOC sequestration. Reducing the extent of harvested area on a landscape level, N-fertilization, and introduction/favoring faster-growing trees species and those more tolerant of heat or drought are among the management options. The SOC sequestration in both temperate coniferous, and broadleaf and mixed U.S. forest biomes share the same key SOC vulnerabilities associated with harvest and fire. Specifically, recent changes in fire regimes in western U.S. forests are a major concern for the fate of SOC. In the tropical forest biome, hurricanes, typhoons and cyclones may increasingly affect SOC sequestration. Otherwise, SOC sequestration in tropical forests may be enhanced by: (i) fire management, (ii) prevention of grass invasions, (iii) selection of high-SOC species for plantations, (iv) mixed-species plantations, (v) reforestation of burned areas, (vi) grazer density control, (vii) reforestation, (viii) facilitation of N-fixer establishment, (ix) control of soil erosion, (x) selection of high-SOC species or genetic families on degraded soils and for plantations, and (xi) retaining logging residues. The SOC sequestration in the temperate grassland, savanna, and shrubland biome in the U.S. may be enhanced by: (i) improved grazing management, (ii) fertilization, (iii) irrigation, (iv) increasing species diversity, and (v) sowing legumes and improved grass species. In contrast, management activities to increase SOC sequestration in the tundra biome are limited. Terrestrial wetlands in the U.S. are not managed for SOC sequestration. However, restoration of drained peatlands to wetlands, wetland agriculture (‘paludiculture’) and reduction in peat mining may contribute to SOC sequestration. The potential for management of SOC sequestration in deserts and xeric shrublands is limited as plants are often near their physiological limits for temperature and water stress. Among the opportunities to enhance SOC sequestration are restoration of degraded lands and improved grazing management. Management practices to enhance cropland SOC sequestration in the U.S. include: (i) maintaining permanent cropland cover with vegetation (i.e., elimination of summer fallow, use of perennials and cover crops), (ii) protecting the soil from erosion (i.e., reduced tillage or no-till (NT), maintaining residue cover), and (iii) improved nutrient and water management. Irrigation, and applying organic fertilizers and biochar can also contribute to SOC sequestration in U.S. croplands. Human activities, i.e., land clearing, removal of vegetation, and disturbance of soils including adding impervious cover associated with construction activities affect SOC sequestration in settlements and urban areas. However, these soils are not managed for SOC sequestration, and any recommendations on SOC-enhancing soil and land use management practices are premature. This chapter will summarize potential alterations in SOC sequestration by soil and land-use management practices, and the effects of climate and global changes on sequestration processes. The chapter will also present approaches for carbon monitoring and accounting in terrestrial ecosystems in the U.S., and how SOC sequestration in terrestrial biomes is affected by natural disturbances and how sequestration can potentially be enhanced by management interventions.
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Soil carbon (C) is the largest C pool in the ter-restrial biosphere and includes both inorganic and organic components. Studying patterns and controls of soil C help us to understand and estimate potential responses of soil C to global change in the future. Here we analyzed topsoil data of 81 sites obtained from a regional survey across grasslands in the Inner Mongolia and on the Tibetan Plateau during 2006– 2007, attempting to find the patterns and controls of soil inor-ganic carbon (SIC) and soil organic carbon (SOC). The aver-ages of inorganic and organic carbon in the topsoil (0–20 cm) across the study region were 0.38 % and 3.63 %, ranging be-tween 0.00–2.92 % and 0.32–26.17 % respectively. Both SIC and SOC in the Tibetan grasslands (0.51 % and 5.24 % re-spectively) were higher than those in the Inner Mongolian grasslands (0.21 % and 1.61 %). Regression tree analyses showed that the spatial pattern of SIC and SOC were con-trolled by different factors. Chemical and physical processes of soil formation drive the spatial pattern of SIC, while bi-otic processes drive the spatial pattern of SOC. SIC was con-trolled by soil acidification and other processes depending on soil pH. Vegetation type is the most important variable driving the spatial pattern of SOC. According to our mod-els, given the acidification rate in Chinese grassland soils in the future is the same as that in Chinese cropland soils dur-ing the past two decades: 0.27 and 0.48 units per 20 yr in the Inner Mongolian grasslands and the Tibetan grasslands re-spectively, it will lead to a 30 % and 53 % decrease in SIC in the Inner Mongolian grasslands and the Tibetan grasslands respectively. However, negative relationship between soil pH and SOC suggests that acidification will inhibit decomposi-tion of SOC, thus will not lead to a significant general loss of carbon from soils in these regions.
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The distribution of vegetational organic matter above- and below-ground and its productivity was analyzed in an alpine area along a climosequence ranging from subalpine to alpine climates. Emphasis is placed on the quantification of carbon (C) and nitrogen (N) fixed in the above-ground and below-ground vegetation and its annual input. Annual C-input ranged from 17.9 to 60.2 g m—2 year—1 and the N-input from 0.74 to 2.48 g m—2 year—1. Above-ground phytomass and the annual production rate of organic matter showed a distinct correlation with the altitude and, thus, the climate. However, the measurement of the above-ground phytomass is bound to methodological problems: the commonly used harvesting method seems to underestimate the real situation. The harvesting method yielded in its average 100 to 300 g m—2 phytomass which was 35—83% of the values obtained by the soil core method. Thus, the calculation of turnover times of above-ground vegetation greatly depends on the method used. Calculated turnover times based on the harvesting method did not correlate with the climate while a clear tendency of lower turnover times with increasing altitude could be observed using the soil core method. The amount of below-ground phytomass was in the range of 1880 to 2469 g m—2 and the corresponding annual C-input (fixation in the roots) between 91.1 and 162 g m—2 year—1 and the N-input between 2.68 and 4.99 g m—2 year—1. The below-ground phytomass and its production rate in high alpine zones are of greater importance and exceed the above-ground ones. With increasing altitude, furthermore, the importance of the below-ground phytomass increases with respect to the biomass and to the C- and N-input. For high alpine areas, the phytomass is concentrated in the uppermost soil horizons. About 88.7 to 94.5% of the below-ground phytomass was found in the soil compartment 0-20 cm. The below-ground production rate of phytomass in alpine grassland is fundamental in order to calculate any C or N budgets and potential inputs to SOM: its neglection would introduce most significant errors in modeling any C or N cycles.
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The aim of this study was to determine the effect of land-use and forest cover depletion on the distribution of soil organic carbon (SOC) within particle-size fractions in a volcanic soil. Emphasis was given to the thermal properties of soils. Six representative sites in Mexico were selected in an area dominated by Andosols: a grassland site, four forested sites with different levels of degradation and an agricultural site. Soils were fractionated using ultrasonic energy until complete dispersion was achieved. The particle-size fractions were coarse sand, fine sand, silt, clay and particulate organic matter from the coarse sand sized fraction (POM-CS) and fine sand (POM-FS). Soil organic carbon decreased by 70% after forest conversion to cropland and long-term cultivation; forest cover loss resulted in a decrease in SOC of up to 60%. The grassland soil contained 45% more SOC than the cropland one. Soil organic carbon was mainly associated with the silt-size fraction; the most sensitive fractions to land-use change and forest cover depletion were POM followed by SOC associated with the silt and clay-sized fractions. Particulate organic matter can be used as an early indicator of SOC loss. The C lost from the clay and silt-sized fractions was thermally labile; therefore, the SOC stored in the more degraded forest soils was more recalcitrant (thermally resistant). Only the transformation of forest to agricultural land produced a similar loss of thermally stable C associated with the silt-sized fraction.
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