[Show abstract][Hide abstract] ABSTRACT: Ecosystem light use efficiency (LUE) is a key factor of production models for gross primary production (GPP) predictions. Previous studies revealed that ecosystem LUE could be significantly enhanced by an increase on diffuse radiation. Under large spatial heterogeneity and increasing annual diffuse radiation in China, eddy covariance flux data at 6 sites across different ecosystems from 2003 to 2007 were used to investigate the impacts of diffuse radiation indicated by the cloudiness index (CI) on ecosystem LUE in grassland and forest ecosystems. Our results showed that the ecosystem LUE at the six sites was significantly correlated with the cloudiness variation (0.24≤R2≤0.85), especially at the Changbaishan temperate forest ecosystem (R2 = 0.85). Meanwhile, the CI values appeared more frequently between 0.8 and 1.0 in two subtropical forest ecosystems (Qianyanzhou and Dinghushan) and were much larger than those in temperate ecosystems. Besides, cloudiness thresholds which were favorable for enhancing ecosystem carbon sequestration existed at the three forest sites, respectively. Our research confirmed that the ecosystem LUE at the six sites in China was positively responsive to the diffuse radiation, and the cloudiness index could be used as an environmental regulator for LUE modeling in regional GPP prediction.
PLoS ONE 11/2014; 9(11):e110988. · 3.53 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Aerobic methanotrophs present in wetlands can serve as a methane filter and thereby significantly reduce methane emissions. Sanjiang wetland is a major methane source and the second largest wetland in China, yet little is known about the characteristics of aerobic methanotrophs in this region. In the present study, we investigated the diversity and abundance of methanotrophs in marsh soils from Sanjiang wetland with three different types of vegetation by 16S ribosomal RNA (rRNA) and pmoA gene analysis. Quantitative polymerase chain reaction analysis revealed the highest number of pmoA gene copies in marsh soils vegetated with Carex lasiocarpa (10(9) g(-1) dry soil), followed by Carex meyeriana, and the least with Deyeuxia angustifolia (10(8) g(-1) dry soil). Consistent results were obtained using Sanger sequencing and pyrosequencing techniques, both indicating the codominance of Methylobacter and Methylocystis species in Sanjiang wetland. Other less abundant methanotrophy, including cultivated Methylomonas and Methylosinus genus, and uncultured clusters such as LP20 and JR-1, were also detected in the wetland. Methanotroph diversity was almost the same in three different vegetation covered soils, suggesting that vegetation types had very little influence on the methanotroph diversity. Our study gives an in-depth insight into the community composition of aerobic methanotrophs in the Sanjiang wetland.
[Show abstract][Hide abstract] ABSTRACT: Sinks of methane (CH4) become highly variable due to both human activity and climate change. An urgent need therefore exists to budget key sinks of CH4, such as forests and grasslands. In this study, CH4 uptake of forests and grasslands in China was first reviewed and then estimated based upon the review itself. Total uptake from the two CH4 sinks were 1.323 Tg CH4 yr−1 in China (ranging from 0.567 to 2.078 Tg CH4 yr−1), lower than a previous estimate in China (2.56 Tg CH4 yr−1). Among the uptake, 0.650 Tg CH4 yr−1 (ranging from 0.168 to 1.132 Tg CH4 yr−1) was consumed by grasslands and 0.675 Tg CH4 yr−1 (ranging from 0.399 to 0.946 Tg CH4 yr−1) by forests. The largest CH4 uptake of grasslands was found in the Qinghai-Tibetan Plateau High-Frigid Domain, which consumed 0.284 Tg CH4 yr−1, about 44% of the whole uptake of grasslands in China. The greatest CH4 uptake (0.553 Tg CH4 yr−1) of forests took place in Eastern Humid and Semi-humid Domain of the country, which was about 82% of the total annual CH4 uptake of forests in China. With forests and grasslands taken together, Eastern Humid and Semi-humid Domain was the largest CH4 consumer, taking up about 0.715 Tg CH4 yr−1, accounting for 82% of the whole forest uptake and 25% of the whole grassland uptake in China. On the ecoregion scale, due to extensive forest distribution and longer growing season, Southern Asia monsoon broadleaf forest ecoregion was the greatest CH4 uptake (0.320 Tg CH4 yr−1) of forests and grasslands in China, consuming more CH4 than the Northeastern Arid and Semi-arid Domain combined. Our results indicated that forests and grasslands are not constant sinks of CH4 but decreasing ones influenced by climate change and anthropogenic activity. More field data, mechanism understanding and process-based models could help better estimate and understand CH4 uptakes of forests and grasslands in China.
Soil Biology and Biochemistry 07/2014; 74:70–81. · 4.41 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Most studies about carbon dynamics of peatlands have been focused on boreal, subarctic and tropical peatlands. However, there is limited data about carbon dynamics of alpine peatlands, like Zoige peatlands on the Qinghai–Tibetan Plateau (QTP), which are sensitive to climate change and human disturbance. We studied the role of these peat deposits on the Zoige as a C reserve and sink by measuring peat depth, radiocarbon age and peat and C accumulation rates at 7 sites. The peat depths of the sample sites ranged from 0.20 to 6.0 m; the basal age on the plateau varied from 1635 to 14095 cal yr BP; the peat accumulation rates ranged from 0.12 to 0.85 mm yr−1, and the C accumulation rates from 5 to 48 g m−2 yr−1. Based on data of field studies and remote sensing, we regarded that with 3179 km2 of intact peatlands, about 1426 km2 of degraded peatlands, and the total area of Zoige peatlands was 4605 km2. The current peat C stock of Zoige peatlands was0.477 Pg (ranging from 0.206 to 0.672 Pg). We also estimated that peatlands covered an area of about 5091 km2on the QTP and sequestered 0.543 Pg C, 88% in Zoige and the rest in other parts of the plateau. Human activities, together with the ubiquitous warming on the plateau (temperature increased by 0.2 °C per decade over the past 50 years) not only shrank the area of intact peatlands, but also caused substantial carbon releasing from peatlands.
[Show abstract][Hide abstract] ABSTRACT: Accurate quantification of the spatio-temporal variation of gross primary production (GPP) for terrestrial ecosystems is significant for ecosystem management and the study of the global carbon cycle. In this study, we propose a MODIS-based Photosynthetic Capacity Model (PCM) to estimate GPP in Northern China and the Tibetan Plateau. The PCM follows the logic of the light use efficiency model and is only driven by the Enhanced Vegetation Index (EVI) and the Land Surface Water Index (LSWI). Multi-year eddy CO2 flux data from five vegetation types in North China (temperate mixed forest, temperate steppe) and the Tibetan Plateau (alpine shrubland, alpine marsh and alpine meadow-steppe) were used for model parameterization and validation. In most cases, the seasonal and interannual variation in the simulated GPP agreed well with the observed GPP. Model comparisons showed that the predictive accuracy of the PCM was higher than that of the MODIS GPP products and was comparable with that of the Vegetation Photosynthesis Model (VPM) and the potential PAR-based GPP models. The model parameter (PCmax) of the PCM represents the maximum photosynthetic capacity, which showed a good linear relationship with the mean annual nighttime Land Surface Temperature (LSTan). With this linear function, the PCM-simulated GPP can explain approximately 93% of the variation in the flux-observed GPP across all five vegetation types. These analyses demonstrated the potential of the PCM as an alternative tool for regional GPP estimation.
Remote Sensing of Environment 05/2014; 148:108–118. · 4.77 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We selected four sites of ChinaFLUX representing four major ecosystem types in China—Changbaishan temperate broad-leaved Korean pine mixed forest (CBS), Dinghushan subtropical evergreen broadleaved forest (DHS), Inner Mongolia temperate steppe (NM), and Haibei alpine shrub-meadow (HBGC)—to study the seasonal dynamics of ecosystem water use efficiency (WUE = GPP/ET, where GPP is gross primary productivity and ET is evapotranspiration) and factors affecting it. Our seasonal dynamics results indicated single-peak variation of WUE in CBS, NM, and HBGC, which were affected by air temperature (Ta) and leaf area index (LAI), through their effects on the partitioning of evapotranspiration (ET) into transpiration (T) (i.e., T/ET). In DHS, WUE was higher at the beginning and the end of the year, and minimum in summer. Ta and soil water content affected the seasonal dynamics of WUE through their effects on GPP/T. Our results indicate that seasonal dynamics of WUE were different because factors affecting the seasonal dynamics and their mechanism were different among the key ecosystems.
Journal of Forest Research 02/2014; · 1.01 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Climate change is likely to increase both intensity and frequency of drought stress. The responses of soil respiration (R s) and its components (root respiration, R r; mycorrhizal respiration, R m; and heterotrophic respiration, R h) to drought stress can be different. This work aims to review the recent and current literature about the variations in R s during the period of drought stress, to explore potential coupling processes and mechanisms between R s and driving factors in the context of global climate change.The sensitivity of soil respiration and its components to drought stress depended on the ecosystems and seasonality. Drought stress depressed R s in mesic and xeric ecosystems, while it stimulated R s in hydric ecosystems. The reductions in supply and availability of substrate decreased both auto- and heterotrophic respirations, leading to the temporal decoupling of root and mycorrhizal respiration from canopy photosynthesis as well as C allocation. Drought stress also reduced the diffusion of soluble C substrate, and activities of extracellular enzymes, consequently, limited microbial activity and reduced soil organic matter decomposition. Drought stress altered Q 10 values and broke the coupling between temperature and soil respiration. Under drought stress conditions, R m is generally less sensitive to temperature than R r and R h. Elevated CO2 concentration alleviated the negative effect of drought stress on soil respiration, principally due to the promotion of plant C assimilation subsequently, which increased substrate supply for respiration in both roots and soil microorganisms. Additionally, rewetting stimulated soil respiration dramatically in most cases, except for soil that experienced extreme drought stress periods. The legacy of drought stress can also regulate the response of soil respiration rate to rewetting events in terrestrial ecosystems through changing abiotic drivers and microbial community structure.There is increasing evidence that drought stress can result in the decoupling of the above- and belowground processes, which are associated with soil respiration. However, studies on the variation in rates of soil respiration and its components under different intensities and frequencies of drought stress over the ecosystems should be reinforced. Meanwhile, molecular phylogenetics and functional genomics should be applied to link microbial ecology to the process of R s. In addition, we should quantify the relationship between soil respiration and global change parameters (such as warming and elevated [CO2]) under drought stress. Models simulating the rates of soil respiration and its components under global climate change and drought stress should also be developed.
Journal of Soils and Sediments 01/2014; 14(1). · 2.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: To investigate the effect of sheep dung on soil carbon (C) sequestration, a 152 days incubation experiment was conducted with soils from two different Inner Mongolian grasslands, i.e. a Leymus chinensis dominated grassland representing the climax community (2.1% organic matter content) and a heavily degraded Artemisia frigida dominated community (1.3% organic matter content). Dung was collected from sheep either fed on L. chinensis (C3 plant with δ(13)C = -26.8‰; dung δ(13)C = -26.2‰) or Cleistogenes squarrosa (C4 plant with δ(13)C = -14.6‰; dung δ(13)C = -15.7‰). Fresh C3 and C4 sheep dung was mixed with the two grassland soils and incubated under controlled conditions for analysis of (13)C-CO2 emissions. Soil samples were taken at days 17, 43, 86, 127 and 152 after sheep dung addition to detect the δ(13)C signal in soil and dung components. Analysis revealed that 16.9% and 16.6% of the sheep dung C had decomposed, of which 3.5% and 2.8% was sequestrated in the soils of L. chinensis and A. frigida grasslands, respectively, while the remaining decomposed sheep dung was emitted as CO2. The cumulative amounts of C respired from dung treated soils during 152 days were 7-8 times higher than in the un-amended controls. In both grassland soils, ca. 60% of the evolved CO2 originated from the decomposing sheep dung and 40% from the native soil C. Priming effects of soil C decomposition were observed in both soils, i.e. 1.4 g and 1.6 g additional soil C kg(-1) dry soil had been emitted as CO2 for the L. chinensis and A. frigida soils, respectively. Hence, the net C losses from L. chinensis and A. frigida soils were 0.6 g and 0.9 g C kg(-1) soil, which was 2.6% and 7.0% of the total C in L. chinensis and A. frigida grasslands soils, respectively. Our results suggest that grazing of degraded Inner Mongolian pastures may cause a net soil C loss due to the positive priming effect, thereby accelerating soil deterioration.
PLoS ONE 11/2013; 8(11):e78578. · 3.53 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Purpose
The aim of this study was to investigate the effects of cattle grazing on the nitrous oxide (N2O) production potential from meadow-steppe grassland soil in northern China, and the relationship between cattle grazing and the abundance of different functional microbial genes for potential of N2O emissions.
Materials and methods
We collected soil samples at a depth of 0–20 cm over six times during two plant growing seasons in 2011 and 2012 on a native Leymus chinensis grassland. At each of the six sampling occasions, soil samples were taken from three pairs of the cattle grazed vs. ungrazed plots. We then determined (1) the soil moisture, pH, total carbon and nitrogen, and mineral N (NH4+ and NO3−) content, (2) the potential rates of N2O production from nitrification (NN2ONN2O) and from denitrification (DN2ODN2O and DN2DN2) using the acetylene inhibition method, and (3) the abundance of the amoA (ammonia monooxygenase) gene of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB), the narG (nitrate reductase) gene and nosZ (nitrous oxide reductase) gene using quantitative real-time PCR (qPCR). The relationship among the changes in the N2O production potential rates, the abundance of microbial functional groups and the soil environment was analyzed using mix effects modeling and structural equation modeling.
Results and discussion
The AOA, AOB, narG, nosZ genes and the potential N2O production rate all varied significantly with the season (P < 0.01). Grazing induced an overall reduction in soil moisture (P < 0.05) and soil total N in 2012 (P < 0.05), and a significant increase in the abundance of AOB genes (P < 0.05); but no significant difference between grazing treatments was found on the abundance of AOA, narG and nosZ genes, or on the NN2ONN2O and DN2ODN2O.
Approximately 80% of the variation in NN2ONN2O could be explained by the abundance of AOA and AOB genes (P < 0.0001), which in turn was explained by soil NH4+ content and soil moisture; The abundance of narG gene, along with total C, NO3− content and soil moisture, explained 87% of variation in the DN2DN2 (P < 0.0001). The abundance of narG gene was related to the production of N gases from denitrification (DN2ODN2O+N2), but not the DN2ODN2O. Soil moisture was the best predictor for DN2ODN2O.
The abundance of amoA and narG genes are good indicators for the potential nitrification and denitrification rates in the meadow steppe grassland. Soil moisture is the most important factor controlling the N2O emission potential in the meadow-steppe grassland. The grassland soils protected from animal grazing or that under a moderate grazing for five years did not show a significant difference in potential N2O emissions. Our results suggest that grazing induced grassland degradation may not necessarily be associated with a reduction in N2O emissions as reported in other semiarid grasslands in a more arid environment.
Soil Biology and Biochemistry 10/2013; · 4.41 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: With a pace of about twice the observed rate of global warming, the temperature on the Qinghai-Tibetan Plateau (Earth's "third pole") has increased by 0.2 °C per decade over the past 50 years, which results in significant permafrost thawing and glacier retreat. Our review suggested that warming enhanced net primary production (NPP) and soil respiration, decreased methane (CH4 ) emissions from wetlands and increased CH4 consumption of meadows, but might increase CH4 emissions from lakes. Warming induced permafrost thawing and glaciers melting would also result in substantial emission of old carbon dioxide (CO2 ) and CH4 . Nitrous oxide (N2 O) emission was not stimulated by warming itself, but might be slightly enhanced by wetting. However, there are many uncertainties in such biogeochemical cycles under climate change. Human activities (e.g., grazing, land cover changes) further modified the biogeochemical cycles and amplified such uncertainties on the plateau. If the projected warming and wetting continues, the future biogeochemical cycles will be more complicated. So facing research in this field is an ongoing challenge of integrating field observations with process-based ecosystem models to predict the impacts of future climate change and human activities at various temporal and spatial scales. To reduce the uncertainties and improve the precision of the predictions of the impacts of climate change and human activities on biogeochemical cycles, efforts should focus on conducting more field observation studies, integrating data within improved models, and developing new knowledge about coupling among carbon, nitrogen, and phosphorus biogeochemical cycles as well as about the role of microbes in these cycles. This article is protected by copyright. All rights reserved.
Global Change Biology 06/2013; · 8.22 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Purpose Carbon (C) dynamics in grassland ecosystemcontributes
to regional and global fluxes in carbon dioxide (CO2)
concentrations. Grazing is one of the main structuring factors
in grassland, but the impact of grazing on the C budget is still
under debate. In this study, in situ net ecosystem CO2 exchange
(NEE) observations by the eddy covariance technique were
integrated with a modified process-oriented biogeochemistry
model (denitrification–decomposition) to investigate the impacts
of grazing on the long-term C budget of semiarid
Materials and methods NEE measurements were conducted
in two adjacent grassland sites, non-grazing (NG) and moderate
grazing (MG), during 2006–2007. We then used daily
weather data for 1978–2007 in conjunction with soil properties
and grazing scenarios as model inputs to simulate
grassland productivity and C dynamics. The observed and
simulated CO2 fluxes under moderate grazing intensity were
compared with those without grazing.
Results and discussion NEE data from 2-year observations
showed that moderate grazing significantly decreased grassland
ecosystem CO2 release and shifted the ecosystem from
a negative CO2 balance (releasing 34.00 g Cm−2) at the NG
site to a positive CO2 balance (absorbing −43.02 g Cm−2) at
the MG site. Supporting our experimental findings, the 30-
year simulation also showed that moderate grazing significantly
enhances the CO2 uptake potential of the targeted
grassland, shifting the ecosystem from a negative CO2 balance
(57.08±16.45 g Cm−2year−1) without grazing to a
positive CO2 balance (−28.58±14.60 g Cm−2year−1)
under moderate grazing. The positive effects of grazing
on CO2 balance could primarily be attributed to an
increase in productivity combined with a significant
decrease of soil heterotrophic respiration and total ecosystem
Conclusions We conclude that moderate grazing prevails
over no-management practices in maintaining CO2 balance
in semiarid grasslands, moderating and mitigating the negative
effects of global climate change on the CO2 balance in
Journal of Soils and Sediments 06/2013; 13(6):1012-1023. · 1.97 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Climate change is causing measurable change in rainfall patterns with uncertain implications for key processes in ecosystem function and carbon cycling. We conducted a modeling analysis to identify how variation in amount and frequency of precipitation affected on CO2 fluxes and net primary productivity. The denitrification-decomposition model was used to quantify the effects of altered precipitation quantity and frequency under 12 climate scenarios over a period of 30-years on both a fenced and a moderately grazed temperate steppe in Inner Mongolia, China. The modeling results show the 12 climate scenarios had an obvious effect on gross primary productivity (GPP), ecosystem respiration (Re) and net primary productivity (NPP) in both a fenced and a grazed site. GPP, Re and NPP increased in both sites under increased precipitation scenarios called A3 (+20% precipitation) and A4 (+40%) when compared with baseline conditions, while GPP, Re and NPP declined under decreased precipitation scenarios A1 (−40% precipitation) and A2 (−20%) scenarios. The changed rainfall frequency resulted in a decline in GPP, Re and NPP compared with those parameters under the base conditions at both sites. The ecologically effective rainfall (ER), not total rainfall, controls the ecosystem CO2 sink/source function. When ER exceeded 318 mm yr−1 in the fenced site and 224 mm yr−1 in the grazed site, the steppe switched from CO2 emission to CO2 absorption. CO2 fluxes in the typical steppe which was fenced and moderately grazed are relatively responsive to changes in the amount of rainfall. However, in terms of the long-term modeling analysis, the modeled results suggest the effects of altered rainfall quantity, frequency and the interaction of rainfall quantity and frequency on CO2 fluxes and plant productivity had no significant difference because of the fluctuating interannual biotic and abiotic factors.
[Show abstract][Hide abstract] ABSTRACT: The study aimed to understand the inter-annual variations of methane (CH(4)) emissions from an open fen on the Qinghai-Tibetan Plateau (QTP) from 2005 to 2007. The weighted mean CH(4) emission rate was 8.37±11.32 mg CH(4) m(-2 )h(-1) during the summers from 2005 to 2007, falling in the range of CH(4) fluxes reported by other studies, with significant inter-annual and spatial variations. The CH(4) emissions of the year of 2006 (2.11±3.48 mg CH(4) m(-2 )h(-1)) were 82% lower than the mean value of the years 2005 and 2007 (13.91±17.80 mg CH(4) m(-2 )h(-1) and 9.44±14.32 mg CH(4) m(-2 )h(-1), respectively), responding to the inter-annual changes of standing water depths during the growing season of the three years. Significant drawdown of standing water depth is believed to cause such significant reduction in CH(4) emissions from wetlands in the year 2006, probably through changing the methanogen composition and decreasing its community size as well as activating methanotrophs to enhance CH(4) oxidation. Our results are helpful to understand the inter-annual variations of CH(4) emission and provide a more reasonable regional budget of CH(4) emission from wetlands on the QTP and even for world-wide natural wetlands under climate change.
PLoS ONE 01/2013; 8(1):e53878. · 3.53 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Few studies have conducted the responses of soil extracellular enzyme activities (EEA) to climate change, especially over the long term. In this study, we investigated the six-year responses of soil EEA to warming and increased precipitation in a temperate grassland of northern China at two depths of 0-10 and 10-20cm. These extracellular enzymes included carbon-acquisition enzymes (β-glucosidase, BG), nitrogen-acquisition enzymes (N-acetylglucosaminidase, NAG; Leucine aminopeptidase, LAP) and phosphorus-acquisition enzymes (acid and alkaline phosphatases). The results showed that warming significantly increased acid phosphatase at the 0-10cm depth and NAG at the 10-20cm depth, but dramatically decreased BG and acid phosphatase in the subsurface. In contrast, increased precipitation significantly increased NAG, LAP and alkaline phosphatase in the surface and NAG, LAP and acid phosphatase in the subsurface. There was a significant warming and increased precipitation interaction on BG in the subsurface. Redundancy analysis indicated that the patterns of EEA were mainly driven by soil pH and NH(4)(+)-N and NO(3)(-)-N in the surface, while by NH(4)(+)-N and microbial biomass in the subsurface. Our results suggested that soil EEA responded differentially to warming and increased precipitation at two depths in this region, which may have implications for carbon and nutrient cycling under climate change.
Science of The Total Environment 01/2013; 444C:552-558. · 3.16 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Sources of methane (CH4 ) become highly variable for countries undergoing a heightened period of development due to both human activity and climate change. An urgent need therefore exists to budget key sources of CH4 , such as wetlands (rice paddies and natural wetlands) and lakes (including reservoirs and ponds), which are sensitive to these changes. For this study, references in relation to CH4 emissions from rice paddies, natural wetlands, and lakes in China were first reviewed and then reestimated based on the review itself. Total emissions from the three CH4 sources were 11.25 Tg CH4 yr(-1) (ranging from 7.98 to 15.16 Tg CH4 yr(-1) ). Among the emissions, 8.11 Tg CH4 yr(-1) (ranging from 5.20 to 11.36 Tg CH4 yr(-1) ) derived from rice paddies, 2.69 Tg CH4 yr(-1) (ranging from 2.46 to 3.20 Tg CH4 yr(-1) ) from natural wetlands, and 0.46 Tg CH4 yr(-1) (ranging from 0.33 to 0.59 Tg CH4 yr(-1) ) from lakes (including reservoirs and ponds). Plentiful water and warm conditions, as well as its large rice paddy area make rice paddies in southeastern China the greatest overall source of CH4 , accounting for approximately 55% of total paddy emissions. Natural wetland estimates were slightly higher than the other estimates owing to the higher CH4 emissions recorded within Qinghai-Tibetan Plateau peatlands. Total CH4 emissions from lakes were estimated for the first time by this study, with three quarters from the littoral zone and one quarter from lake surfaces. Rice paddies, natural wetlands, and lakes are not constant sources of CH4 , but decreasing ones influenced by anthropogenic activity and climate change. A new progress-based model used in conjunction with more observations through model-data fusion approach could help obtain better estimates and insights with regard to CH4 emissions deriving from wetlands and lakes in China.
Global Change Biology 01/2013; 19(1):19-32. · 8.22 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Uncertainty about the effects of warming and grazing on soil nitrogen (N) availability, species composition, and aboveground net primary production (ANPP) limits our ability to predict how global carbon sequestration will vary under future warming with grazing in alpine regions. Through a controlled asymmetrical warming (1.2/1.7 degrees C during daytime/nighttime) with a grazing experiment from 2006 to 2010 in an alpine meadow, we found that warming alone and moderate grazing did not significantly affect soil net N mineralization. Although plant species richness significantly decreased by 10% due to warming after 2008, we caution that this may be due to the transient occurrence or disappearance of some rare plant species in all treatments. Warming significantly increased graminoid cover, except in 2009, and legume cover after 2008, but reduced non-legume forb cover in the community. Grazing significantly decreased cover of graminoids and legumes before 2009 but increased forb cover in 2010. Warming significantly increased ANPP regardless of grazing, whereas grazing reduced the response of ANPP to warming. N addition did not affect ANPP in both warming and grazing treatments. Our findings suggest that soil N availability does not determine ANPP under simulated warming and that heavy grazing rather than warming causes degradation of the alpine meadows.
[Show abstract][Hide abstract] ABSTRACT: Drought is likely to affect wetlands, including wetland soil microorganisms that drive soil biogeochemical cycling. Frequent drought could reduce the ability of wetlands to serve as sinks for global carbon or could eventually turn them into sources of atmospheric carbon in general and methane in particular. However, the response of microbial communities involved in methane production to drought remains unclear. The current study characterized archaeal communities of an alpine wetland in 2006, which was a drought year, and in 2007, which was not a drought year. A total of 12 soil samples (two years × two plant communities × three samples per plant community) were collected under two plant communities (dominated by Carex muliensis or Eleocharis valleculosa) at the Zoige wetlands on the Qinghai–Tibetan Plateau. Archaeal community size and structure were determined by qPCR and terminal restriction fragment length polymorphismanalysis of the 16S rRNA gene fragment, respectively. Methanosaeta, Methanomicrobiales, Methanobacteriales, uncultured Rice Cluster-II, and uncultured Crenarchaeota were detected. Ordination analysis indicated that archaeal community composition was strongly related to vegetation type and drought. The archaeal community was 10-times smaller in the drought year than in the non-drought year. The results indicated that drought may influence both archaeal community size and structure.
European Journal of Soil Biology 09/2012; 52:84–90. · 2.15 Impact Factor