Grassland Carbon Research Articles

A long-term high-resolution dataset of grasslands grazing intensity in China

Grazing is a significant anthropogenic disturbance to grasslands, impacting their function and composition, and affecting carbon budgets and greenhouse gas emissions. However, accurate evaluations of grazing impacts are limited by the absence of long-term high-resolution grazing intensity data (i.e., the number of livestock per unit area). This study utilized census livestock data and a satellite-based vegetation index to develop the first Long-term High-resolution Grazing Intensity (LHGI) dataset of grassland in seven pastoral provinces in western China from 1980 to 2022. The LHGI dataset effectively captured spatial variations in grazing intensity, with validation at 73 sites showing a correlation coefficient (R2) of 0.78. The county-level validation showed an averaged R2 values of 0.73 ± 0.03 from 1980 to 2022. This dataset serves as a vital resource for estimating grassland carbon cycling and livestock system CH4 emissions, as well as contributing to grassland management.

Estimation, Spatiotemporal Dynamics, and Driving Factors of Grassland Biomass Carbon Storage Based on Machine Learning Methods: A Case Study of the Hulunbuir Grassland

Precisely estimating the grassland biomass carbon storage is vital for evaluating grassland carbon sequestration potential and the monitoring and management of grassland resources. With the increasing intensity of climate change (CC) and human activities (HA), it is necessary to explore spatiotemporal variations in biomass carbon storage and its response to CC and HA. In this study, we focused on the Hulunbuir Grassland, utilizing sample plots data, MODIS data, environmental factors (terrain, soil, and climate), location factor, and texture characteristics to assess the performance of four machine learning algorithms: random forest, support vector machine, gradient boosting decision tree, and extreme gradient boosting in estimating grassland aboveground biomass (AGB). Based on the optimal model combined with root-shoot ratio data, grassland distribution data, and carbon content coefficients, the spatiotemporal characteristics and driving factors of biomass carbon storage from 2001–2022 were analyzed. The results showed that (1) the random forest achieved the highest prediction accuracy for grassland AGB, making it appropriate for AGB estimation in the Hulunbuir Grassland. (2) The spectral indices were the key variables of the grassland AGB, especially the enhanced vegetation index and difference vegetation index. (3) The 22-year average total biomass (TB) of the study area was 1037.10 gC/m2, of which the 22-year average AGB was 48.73 gC/m2 and 22-year average belowground biomass was 988.37 gC/m2, showing a spatial distribution feature of gradual increase from west to east. (4) From 2001–2022, TB carbon storage showed an insignificant growth trend (p > 0.05). The 22-year average carbon storage of TB was 72.34 ± 18.07 gC. (5) Climate factors were the main driving factors for the spatial pattern of grassland TB carbon density, while the combined effects of CC and HA were the main contributors to the interannual increase in grassland TB carbon density.

Contribution of soil microbial necromass carbon to soil organic carbon in grassland under precipitation change and its influencing factors in loess hilly region, Northwest China.

To investigate the contribution of microbial necromass carbon (MNC) to soil organic carbon (SOC) and its influencing factors under precipitation changes in grassland, we conducted a precipitation experiment with seven different precipitation levels in the Bothriochloa ischaemum restoration area in the loess hilly region. We analyzed the contents and characteristics of fungal necromass carbon (FNC), bacterial necromass carbon (BNC), and MNC in different fractions of SOC under different treatments, including natural precipitation (CK), and increased and decreased 20%, 40%, 60% of natural precipitation (I20, I40, I60, D20, D40, D60) . The results showed that 1) MNC content in mineral organic carbon (MAOC) ranged from 1.62 g·kg-1 to 2.17 g·kg-1, which was higher than that in particulate organic carbon (POC) ranging from 0.69 g·kg-1 to 1.31 g·kg-1. The former was approximately 1.4 to 2.8 times as that of the latter. 2) FNC and MNC exhibited similar changes in both MAOC and POC fractions. BNC content in MAOC was approximately 1-3.1 times as that of FNC. FNC content in POC was generally higher than BNC except for I40 and I60 where BNC exceeded FNC. 3) Overall, both increases and decreases in precipitation resulted in elevated MNC/MAOC and BNC/MAOC ratios, but decreased MNC/POC and FNC/POC ratios. The MNC/MAOC ratios in I60 and D60 were 33.2% and 18.1% higher than CK, respectively. The BNC/MAOC ratios in D60, I40 and I60 were 28.0%, 23.0% and 19.1% higher than those in CK, respectively. Except for D60, the FNC/POC and MNC/POC ratios were significantly lower than CK under other treatments. In terms of POC fractions, the MNC/POC ratios of D40, D20, I20, I40 and I60 were 28.4%, 23.3%, 28.8%, 23.3% and 32.2% lower than that of CK, respectively. The FNC/POC ratio of D40, D20, I20, I40 and I60 was found to be lower by 23.3%, 16.1%, 21.0%, 27.0% and 31.0% compared to that of CK, respectively. 4) NH4+-N and pH were the primary factors influencing the content of MNC in different carbon fractions under varying precipitation conditions. In summary, alterations in precipitation (either increase or decrease) enhanced the contribution of BNC-dominated MNC to MAOC, but reduced the contribution of FNC-dominated MNC to POC. This study was of significance for understanding the distribution of microbial necromass across different organic carbon fractions under precipitation alterations.

Responses of plant carbon, nitrogen, and phosphorus content in terrestrial ecosystems to warming: A Meta-analysis.

We conducted a Meta-analysis with 264 datasets from 55 publications to investigate the effects of warming duration and intensity on plant carbon, nitrogen and phosphorus contents. The results showed that warming significantly reduced shoot carbon (effect value of -1.7%), root carbon (-4.0%), litter carbon (-3.7%), shoot nitrogen (-7.0%) and litter nitrogen contents (-6.4%). For different ecosystem types, warming significantly decreased shoot carbon (-0.8%), shoot nitrogen (-5.9%), root carbon (-7.4%), litter carbon (-2.1%), and litter nitrogen content (-13.4%) in grasslands, while significantly increased shoot carbon (2.7%) in scrublands and litter phosphorus content (42.4%) in forests. Short-term warming (<5 years) decreased shoot carbon (-0.4%), shoot phosphorus (-0.4%) and litter nitrogen (-13.4%) contents, while medium- to long-term warming (5-10 years) increased shoot carbon (0.6%), shoot phosphorus (20.2%) and litter nitrogen (6.2%) contents. The 0-2 ℃ warming intensity increased shoot phosphorus (10.1%) and root phosphorus (27.4%) contents of plants, while the >2 ℃ warming intensity decreased shoot phosphorus (-3.7%) and root phosphorus (-6.5%) content. The effect values of plant shoot carbon and shoot nitrogen were significantly and positively correlated with humidity index. Warming showed negative effects on plant carbon, nitrogen and phosphorus contents in terrestrial ecosystems, and such effects were moderated by the duration and intensity of warming.

Warming decreased plant litter decomposition by modulating soil fauna interactions in a Tibetan alpine meadow

Litter decomposition is a vital process for maintaining ecosystem carbon cycling. It is affected by soil fauna which are predators and decomposers of litter. However, how the interactions of soil fauna communities affect litter decomposition remains unclear under warming. Here, we conducted a five-year in-situ manipulative warming experiment by Open-Top Chamber (OTC) in an alpine meadow on the Tibetan Plateau to reveal how warming affects litter decomposition. The results demonstrated that warming decreased the litter decomposition rate by 29 %, the soil collembola abundance by 25 %, and the nematode abundance by 27 %. Nematode ecological indices remain stable but a shift in the decomposition of litter to the fungivores pathway under warming. The piecewise structural equation modelling result revealed that the combined reduction in soil collembola and nematodes synergistically leads to a massive decline in litter decomposition rate under warming. Our results highlight that the interactions of soil fauna can regulate litter decomposition under warming, and collembola abundance as the “speed-limiter” of litter decomposition. Therefore, the response of changes in soil fauna relationships to warming should be completely considered in future climate change modelling of the grassland carbon cycle.

Forecasting Carbon Sequestration Potential in China’s Grasslands by a Grey Model with Fractional-Order Accumulation

This study aims to predict the carbon sequestration capacity of Chinese grasslands to address climate change and achieve carbon neutrality goals. Grassland carbon sequestration is a crucial part of the global carbon cycle. However, its capacity is significantly impacted by climate change and human activities, making its dynamic changes complex and challenging to predict. This study adopts a fractional-order accumulation grey model, using 11 provinces in China as samples, to analyze and forecast grassland carbon sequestration. The study finds significant differences in grassland carbon sequestration trends across the sample regions. The carbon sequestration capacity of the grasslands in Xizang (Tibet) and Heilongjiang province is increasing, while it is decreasing in other provinces. The varying prediction results are influenced not only by regional climatic and natural conditions, but also by human interventions such as overgrazing, irrational reclamation, excessive mineral resource exploitation, and increased tourism development. Therefore, more region-specific grassland management and protection strategies should be formulated to enhance the carbon sequestration capacity of grasslands and promote the sustainable development of ecosystems. The significance of this study lies not only in providing scientific guidance for the protection and sustainable management of Chinese grasslands, but also in contributing theoretical and practical insights into global carbon sequestration strategies.

Drought and warming interaction cause substantial economic losses in the carbon market potential of China's northern grasslands

Grasslands are being threatened by global drought and warming. Economic assessments of changing grassland carbon sequestration, a prerequisite for nature-based climate-change mitigation policies, are limited when researchers inadequate consider interactions between drought and warming. Here, we quantified the responses of 35 grass biomasses to combined drought and warming, based on manipulation experiments from 34 peer-reviewed papers; subsequently, we matched them with grasslands in northern China—the eastern range of the larger Eurasian Steppe—and further projected the economic implications for carbon market trading and carbon-sequestration costs. The results show that carbon sequestration in all grassland types, except for forbrich steppe, was significantly reduced by the synergistic interactions of drought and warming. Approximately 10 % of the grasslands in central Xinjiang, identified as forbrich steppe, showed resilience to these stressors. In contrast, the rest of northern China's grasslands suffered increased carbon losses due to drought and warming. The combined effects of drought and warming have caused a loss of 1.6 × 104 million Chinese yuan (CNY) in revenue and excess carbon-sequestration costs exceeding 1.1 × 105 million CNY. Overall, our study results indicate that the synergistic effects of drought and warming significantly undermine the economic viability of carbon sequestration in most of northern China's grasslands. As climate change intensifies, understanding and incorporating the complex interactions of drought and warming can aid in the sustainable management of grassland ecosystems and the development of effective climate-change mitigation policies in arenas, including carbon markets.

Evaluating MONICA's capability to simulate water, carbon and nitrogen fluxes in a wet grassland at contrasting water tables

Wet grasslands, which are vital for water and nutrient regulation, are characterised by distinct water, carbon (C) and nitrogen (N) dynamics, and their interactions. Due to their shallow groundwater table, wet grasslands promote a strong interconnection between diverse vegetation and soil water. Researchers have investigated how wet grasslands respond to environmental changes, using various simulation models to understand how these sites contribute to water, C and N dynamics. However, a comprehensive, simultaneous study of all three of these dynamics is still lacking. This study makes use of a grassland lysimeter study with differently managed groundwater levels and employs the process-based MOdel for NItrogen and Carbon dynamics in Agroecosystems (MONICA) to simulate these dynamics. By using SPOTPY (Statistical Parameter Optimization Tool) to optimise the relevant parameters, we find that MONICA performs well in simulating vegetation growth (aboveground biomass), and elements of the water (evapotranspiration), C (gross primary productivity, ecosystem respiration) and N (N in aboveground biomass, nitrate in soil solution, Nitrous oxide emissions) balance, with Willmott's Refined Index of Agreement always larger than 0.35. This level of accuracy demonstrates that MONICA is ready to be applied for scenario simulations of groundwater management and climate change to evaluate their impact on greenhouse gas emissions and long-term carbon storage, as well as water and nitrogen losses in wet grasslands.

Changes in productivity partitioning induced by precipitation extremes increase inaccuracy of grassland carbon estimation.

The fraction of net primary productivity (NPP) allocated to belowground organs (fBNPP) in grasslands is a critical parameter in global carbon cycle models; moreover, understanding the effect of precipitation changes on this parameter is vital to accurately estimating carbon sequestration in grassland ecosystems. However, how fBNPP responds to temporal precipitation changes along a gradient from extreme drought to extreme wetness, remains unclear, mainly due to the lack of long-term data of belowground net primary productivity (BNPP) and the fact that most precipitation experiments did not have a gradient from extreme drought to extreme wetness. Here, by conducting both a precipitation gradient experiment (100-500 mm) and a long-term observational study (34 years) in the Inner Mongolia grassland, we showed that fBNPP decreased linearly along the precipitation gradient from extreme drought to extreme wetness due to stronger responses in aboveground NPP to drought and wet conditions than those of BNPP. Our further meta-analysis in grasslands worldwide also indicated that fBNPP increased when precipitation decreased, and the vice versa. Such a consistent pattern of fBNPP response suggests that plants increase the belowground allocation with decreasing precipitation, while increase the aboveground allocation with increasing precipitation. Thus, the linearly decreasing response pattern in fBNPP should be incorporated into models that forecast carbon sequestration in grassland ecosystems; failure to do so will lead to underestimation of the carbon stock in drought years and overestimation of the carbon stock in wet years in grasslands.

Anthropogenic and climate impacts on carbon stocks of grassland ecosystems in Inner Mongolia and adjacent region

Up to date, most studies reported that degradation is worsened in the grassland ecosystems of Inner Mongolia and adjacent regions as a result of intensified grazing. This seems to be scientific when considering the total forage or total above-ground biomass as a degradation indicator, but it does not hold true in terms of soil organic carbon density (SOCD). In this study, we quantified the changes of grassland ecosystem carbon stock in Inner Mongolia and adjacent regions from the 1980s to 2000s and identified the major drivers influencing these variations, using the National Grassland Resource Inventory and Soil Survey Dataset in 1980s and the Inventory data during 2002 to 2009 covering 624 sampling plots concerned vegetal traits and edaphic properties across the study region. The result indicated that the above-, below-ground and total vegetation biomass declined from the 1980s to 2000s by ∼ 10 %. However, total forage production increased by 6.72 % when considering livestock intake. SOCD remained stable despite a 67 % increase in grazing intensity. A generalized linear model (GLIM) analysis suggested that an increase in grazing intensity from the 1980s to 2000s could only explain 1.04 % of the total biomass change, while changes in precipitation and temperature explained 17.7 % (p < 0.05) of total vegetation biomass (TVB) change. Meanwhile, SOCD change during 1980s - 2000s could be explained 10.08 % by the soil texture (p < 0.05) and <1.6 % by changes in climate and livestock. This implies that the impacts of climate change on grassland biomass are more significant than those of grazing utilization, and SOCD was resistant to both climate change and intensified grazing. Overall, intensified grazing did not result in significant negative impacts on the grassland carbon stocks in the study region during the 1980s and 2000s. The grassland ecosystems possess a mechanism to adjust their root-shoot ratio, enabling them to maintain resilience against grazing utilization.

Screening of environmental stimuli for the positive regulation of stomatal aperture in centipedegrass

Grasslands, the largest carbon pool in China, possess enormous potential for carbon sequestration. Increasing the stomatal aperture to increase the CO2 absorption capacity is a potential method to improve plant photosynthetic efficiency and ultimately enhance the carbon sequestration capacity of grass plants. Research on stomatal aperture regulation has focused mostly on Arabidopsis or crops, while research on grass plants in these areas is scarce, which seriously restricts the implementation of this grassland carbon sequestration strategy. Here, a widely used ecological grass, centipedegrass, was used as the experimental material. First, a convenient method for observing the stomatal aperture was developed. The leaves were floated in a potassium ion-containing open solution (67 mM KCl, pH 6.0) with the adaxial surface rather than the abaxial surface in contact with the solution and were cultivated under light for 1.5 h. Then, nail polish was applied on the adaxial surface, and a large number of open stomata were imprinted. Second, with the help of this improved method, the concentration‒response characteristics of the stomatal aperture to eleven environmental stimuli were tested. The stomatal aperture is dependent on these environmental stimuli in a concentration-dependent manner. The addition of 100 μM brassinolide led to the maximal stomatal aperture. This study provided a technical basis for manipulating stomatal opening to increase the carbon sequestration capacity of centipedegrass.

Changes in soil organic carbon, total nitrogen and total phosphorus in 2000–2020 and their driving mechanisms in Tibetan alpine grasslands

Soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP) and their ratios are important parts of global carbon, nitrogen and phosphorus cycle, but their responses to climate change and human activities remain controversial in alpine grasslands of the Tibetan Plateau. In this study, we quantified the influences of climate change and human activities on SOC, TN, TP and their ratios at three depths (0–10, 10–20 and 20–30 cm) during 2000–2020 across the Tibetan alpine grasslands. Under the combined influences of climate change and human activities, spatially average SOC, TN, TP, C:N, C:P and N:P at 0–10 cm, and C:N and C:P at 10–20 cm decreased by 3.42%, 1.35%, 0.99%, 0.39%, 1.75%, 0.51%, 0.03% and 0.88%, respectively, but the others increased by 0.01–3.26%. Under the single influence of climate change, spatially TP at 0–10 and 20–30 cm decreased by 0.30% and 1.05%, respectively, but the others increased by 0.14–4.35%. Under the single influence of human activities, spatially TN at 0–10 and 10–20 cm, C:P at 0–10 cm and N:P at 10–20 cm decreased by 15%, 1%, 7% and 4%, respectively, but the others increased by 1–157%. No matter under the double pressure of climate change and human activities or their individual pressure, the changes of SOC, TN, TP, C:N, C:P and N:P not always increased or decreased, but vary with longitude, latitude and elevation. The changes of SOC, TN, TP, C:N, C:P and N:P did not necessarily and linearly increase or decrease with their background values. Compared to precipitation change and warming, radiation change had a stronger influence on the change of SOC at 10–20 cm and TP at 20–30 cm under the double pressure of climate change and human activities, and the single pressure of human activities, respectively. Radiation change also had stronger influences on the change of SOC at 10–20 cm, TN at 0–10 cm, C:N at 20–30 cm, C:P at 0–10 and 10–20 cm, N:P at 0–10 and 10–20 cm under the single pressure of climate change. Therefore, in the past 20 years, the single effect of climate change or human activities on soil organic carbon, total nitrogen, total phosphorus and their ratios underestimated or overestimated their interactive effects in the Tibetan grasslands. Climate change and human activities reconstructed the spatial distribution patterns of soil organic carbon, total nitrogen, total phosphorus and their ratios. Radiation change should be given the same importance as warming and precipitation change, at least for the change of soil organic carbon, total nitrogen and total phosphorus of the Tibetan alpine grasslands.

Aridity-driven divergence in soil microbial necromass carbon in alpine grasslands of the Tibetan Plateau

Aridity-driven divergence in soil microbial necromass carbon in alpine grasslands of the Tibetan Plateau

Carbon Sink Effect of Plateau Grassland and Contribution of Carbon Cycle

This paper reviews the research progress of plateau grassland carbon sink effect and its contribution and role to global carbon cycle. The paper also evaluates the size and change of plateau grassland carbon sink effect, and reveals its spatiotemporal distribution and dynamic characteristics. The paper discusses the relationship between plateau grassland carbon sink effect and global carbon cycle, and elucidates its role and significance in contributing to global carbon balance, mitigating global climate change, and protecting global biodiversity. The paper analyzes the positive and negative effects and interactions of climate change, human activities, grassland type and management on plateau grassland carbon sink effect, and proposes the influencing mechanism and mode of plateau grassland carbon sink effect. The paper points out the difficulties and shortcomings of the research on plateau grassland carbon sink effect, and puts forward some suggestions and prospects for future research. The paper aims to provide reference and inspiration for deepening the understanding of the internal mechanism and external influence of plateau grassland carbon sink effect, and for formulating effective grassland protection and management measures.

Effect of foraging tunnels created by small subterranean mammals on soil microbial biomass carbon and organic carbon storage in alpine grasslands

Extensive foraging tunnel disturbances created by small subterranean mammals have important impacts on soil physical properties and nutrients in grasslands. This study took plateau zokor (Eospalax baileyi) as an example mammal to investigate the impacts of foraging tunnel disturbances by small subterranean mammals on soil microbial biomass carbon (SMBC) and soil organic carbon (SOC) storage. A paired design was used to locate 90 tunnel quadrats and 90 non-tunnel quadrats in alpine grasslands across three sites. This study showed that SMBC, SOC concentrations and SOC storage in tunnel quadrats were 47.4 %, 26.8 % and 22.0 % lower than those in non-tunnel quadrats, respectively. This study also showed that soil microbial biomass nitrogen was a major factor affecting SOC storage in non-tunnel quadrats, while it was not a major factor in tunnel quadrats. Soil pH and soil ammonium nitrogen were not major factors in non-tunnel quadrats, while they were the major factors influencing SOC storage in tunnel quadrats. In contrast to non-tunnel quadrats, foraging tunnel disturbances led to a new pathway in which soil pH positively affected SOC storage in tunnel quadrats. The findings of this study demonstrated that foraging tunnel disturbances had negative impacts on soil fertility due to lower SMBC concentrations and might cause soil carbon loss in alpine grasslands because of lower SOC storage. Given the effect of foraging tunnels on soil carbon cycling and climate regulation in the Qinghai-Tibet Plateau's alpine grasslands, it is crucial to take them into account when assessing grassland carbon storage and formulating strategies for effective grassland management and conservation.

Adaptive multi-paddock grazing increases mineral associated soil carbon in Northern grasslands

Grassland soils play an important role in sequestering carbon (C) and are primarily used for livestock grazing. Grazing management can increase the amount of C stored in soils and the distribution of C in different soil fractions by altering soil microbial community structure, thereby influencing the persistence of soil C over time. Adaptive multi-paddock grazing (AMP), grazing cattle at high stock densities with long periods between grazing events, is considered to enhance grassland sustainability, productivity, and soil C compared to more conventional grazing practices (continuous to slow rotational). However, whether and how AMP grazing might affect the amount of C stored in different soil fractions has received little attention. Soil samples (0–15 cm depth) were collected from 24 ranches in a paired design, where 12 ranches practiced AMP grazing and 12 neighboring ranches practiced conventional grazing. Soil organic C (SOC) and total nitrogen were measured in different soil particle size [fine (<53 µm), medium (53–250 µm) and coarse (>250 µm)], and density [light (>1.6 g cm−3), and heavy (<1.6 g cm−3)] fractions. Soil bacterial and fungal biomass and abundances were obtained from phospholipid fatty acid analysis. Mean weights of soil microaggregates and heavy fractions were higher in soil exposed to AMP grazing, whereas mean weights of macroaggregates and light fractions were higher in conventionally grazed soils. In warmer and drier climatic conditions, SOC in both bulk soils and within various size and density fractions tended to decrease. Soil organic C (both concentration and stock) were significantly higher in the fine soil fractions under AMP management than conventionally grazed grasslands. Given that SOC in fine fractions, is more mineral associated and recalcitrant, our results indicate that AMP grazing increased the size of the stable SOC pool. The increased carbon pool in the fine fraction was associated with greater fungal to bacterial ratios, suggesting a possible biological mechanism for the increase. Overall, the results indicate that AMP grazing may be beneficial for sequestering more stable carbon that helps mitigate the effects of climate change.

High stocking rates effects in continuous season long grazing reduces the contribution of microbial necromass to soil organic carbon in a semi-arid grassland in Inner Mongolia

Livestock grazing strongly influences the accumulation of soil organic carbon (SOC) in grasslands. However, whether the changes occurring in SOC content under different intensities of continuous summer long grazing are associated with the changes in microbially-derived necromass C remains unclear. Here, we established a sheep grazing experiment in northern China in 2004 with four different stocking rates. Soil samples were collected after 17 years of grazing and analyzed for physical, chemical, and microbial characteristics. Grazing decreased SOC and microbial necromass carbon (MNC). Notably, grazing also diminished contributions of MNC to SOC. MNC declined with decreasing plant carbon inputs with degradation of the soil environment. Direct reductions in microbial necromass C, which indirectly reduced SOC, resulted from reduced in plant C inputs and microbial abundance and diversity. Our study highlights the key role of stocking rate in governing microbial necromass C and SOC and the complex relationships these variables.

Soil amendment incorporation increases organic carbon by improving soil agglomerate and soil microbial biomass carbon in the alpine grassland

AbstractSoil amendments aiming to enhance soil quality and bolster carbon sequestration have been extensively investigated. However, the specific impacts of diverse soil amendment types on soil total organic carbon content (TOC), soil aggregate and the growth of ryegrass remain largely unexplored, particularly within the unique context of alpine grassland soils in northwest Sichuan. For this, four soil amendments (CK: no soil amendment, CM: cattle manure 2000 kg ha−1, CS: straw amendment 12,000 kg ha−1 and MS: mushroom substrate 18,000 kg ha−1) were applied to alpine grassland soils over a 2‐year duration, conducted in situ during 2017 and 2018, to investigate the influences of these soil amendments on 0–30 cm soil of TOC, total nitrogen (TN), microbial biomass carbon (MBC), soil aggregation, the above‐ground biomass (DMA) and root traits of ryegrass. Compared to CK, the above‐ground biomass exhibited an average of 348.78% in MS, 287.18% in CS and 115.54% in CM, all reaching statistical significance (p &lt; .05). In the topsoil (0–10 cm), the large soil aggregate rate (LSAR &gt; 0.25 mm) showed a significant increase in CM, CS and MS, particularly in 2018, compared to CK. Our findings further indicated that the improvement in alpine grassland LSAR &gt; 0.25 mm was correlated with a rise in TOC by over 69.89% and MBC by more than 27.14%. The MS treatment resulted in a significant increase in above‐ground biomass and TRL (total root length), while also increasing the levels of TN, MBC and soil aggregates (0.25 ~ 0.5 mm) within the 0–10 cm soil. A similar result of CS treatment was observed to increase the total chlorophyll content and RD (root diameter), as well as an increase in SWC and TOC levels. The TN, MBC, TOC and LSAR contributed 44.77%, 20.87%, 6.46% and 6.45% for ryegrass growth. The SEM indicated that soil amendments promote the growth of ryegrass by improving soil agglomerate and increasing MBC, TOC and TN. Our analysis revealed that ryegrass biomass production was limited by soil nutrients in the alpine grassland of northwest Sichuan. The study also highlights the potential impact of soil amendments on future management practices, contributing to a more comprehensive understanding of the subject.

Optimizing grazing exclusion duration for carbon sequestration in grasslands: Incorporating temporal heterogeneity of aboveground biomass and soil organic carbon

Grasslands account for approximately one-third of the global terrestrial carbon stocks. However, a limited understanding of the impact of grazing exclusion on carbon storage in grassland ecosystems hinders progress towards restoring overgrazed grasslands and promoting carbon sequestration. In this study, we conducted a comprehensive meta-analysis to investigate the effects of grazing exclusion on aboveground biomass (AGB) and soil organic carbon (SOC) in four grasslands: alpine grasslands (AP), tropical savannas (TS), temperate subhumid grasslands (TG), and a semi-desert steppe (SD). Our meta-analysis indicated that grazing exclusion significantly enhanced carbon sequestration in grassland ecosystems, and the benefits of carbon sequestration were most pronounced in the AP, followed by the TG, SD, and TS. Grazing exclusion duration (DUR) was a significant factor associated with the response of aboveground biomass (AGB) and soil organic carbon (SOC) to grazing exclusion. Moreover, the relationships between AGB and DUR were nonlinear, with existence thresholds of 18, 21, 12, 19, and 23 years in global grasslands (ALL), AP, TS, TG, and SD, respectively. However, the relationship between SOC and DUR was linear, with SOC continuing to increase as DUR increased (up to 40 years). The multi-objective optimization indicated that the optimal duration of grazing exclusion for grassland carbon sequestration was 18–20, 21–23, 12–14, 19–21, and 23–25 years for ALL, AP, TS, TG, and SD, respectively. Our study contributes to the enhancement of grazing management and offers better options for increasing carbon sequestration in grasslands.

Phenological characteristics of net ecosystem carbon exchange of Stipa krylovii steppe in Inner Mongolia, China and its remote sensing monitoring.

To accurately monitor the phenology of net ecosystem carbon exchange (NEE) in grasslands with remote sensing, we analyzed the variations in NEE and its phenology in the Stipa krylovii steppe and discussed the remote sensing vegetation index thresholds for NEE phenology, with the observational data from the Inner Mongolia Xilinhot National Climate Observatory's eddy covariance system and meteorological gradient observation system during 2018-2021, as well as Sentinel-2 satellite data from January 1, 2018 to December 31, 2021. Results showed that, from 2018 to 2021, NEE exhibited seasonal variations, with carbon sequestration occurring from April to October and carbon emission in other months, resulting in an overall carbon sink. The average Julian days for the start date (SCUP) and the end date (ECUP) of carbon uptake period were the 95th and 259th days, respectively, with an average carbon uptake period lasting 165 days. Photosynthetically active radiation showed a negative correlation with daily NEE, contributing to carbon absorption of grasslands. The optimal threshold for capturing SCUP was a 10% threshold of the red-edge chlorophyll index, while the normalized difference vegetation index effectively reflected ECUP with a threshold of 75%. These findings would provide a basis for remote sensing monitoring of grassland carbon source-sink dynamics.