Guocheng Wang

Accurate phenological model predictions are needed for assessing grassland ecosystem dynamics under climate change. However, most phenological models for arid and semi-arid grasslands remain temperature-based and have rarely been evaluated across the full growing season. Using long-term phenological and meteorological observations from 26 sites in the Inner Mongolian grassland, we compared five candidate model formulations for four dominant grassland species across five phenological stages: green-up, heading, flowering, fruiting, and brown-down. These formulations included the traditional thermal-time model ( M _t) and four temperature–precipitation models differing in precipitation metric (cumulative amount or frequency) and accumulation structure (parallel or sequential). Compared with M _t, precipitation-inclusive formulations had the lowest AICc in 15 of the 19 species–stage combinations; absolute RMSE reductions ranged from 0.18 to 7.39 d, with a median of 1.05 d, and 7 of the 15 reductions were M _t was top-ranked for flowering in three species and sequential formulations were top-ranked for all fruiting combinations. Seven of the 19 combinations retained competing alternatives (runner-up ΔAICc < 2), whereas all four brown-down combinations showed clear model separation (runner-up ΔAICc > 10). Precipitation-frequency formulations were supported in selected combinations, particularly for Stipa krylovii and Artemisia frigida , but did not consistently outperform cumulative precipitation amount. These results support a stage-specific modelling strategy for semi-arid grassland phenology, in which precipitation information should generally be considered, but precipitation metric and temperature–precipitation structure should be selected according to phenological stage and species rather than applied uniformly across the growing season.

Crop straw management presents a critical trade-off in climate mitigation: balancing straw return for carbon sequestration against conversion into carbon-neutral bioenergy. The potential for agricultural systems to synergistically achieve both ambitious soil carbon growth and substantial greenhouse gas (GHG) reductions remains not fully understood. The integration of the Rothamsted Carbon Model (RothC) and a Bioenergy-Emission-Economic Model (BEE) enabled a systematic evaluation of the carbon balance effects of straw management in China (2021–2100) under varying soil organic carbon (SOC) targets. The results demonstrate that even under an ambitious 4 per mille SOC target, allocating a substantial share of straw resources to bioenergy production still yields robust climate mitigation benefits for the agricultural system. Under this target, the agricultural system exhibits significant climate mitigation potential, capable of fully offsetting China’s total agricultural GHG emissions. Spatial analysis further identifies East and Central China as priority regions for implementing this synergistic pathway, due to their abundant straw resources and relatively high carbon sequestration efficiency. These findings indicate that enhancing soil carbon and deploying straw-based bioenergy are not mutually exclusive, but can act as synergistic pillars for achieving agricultural carbon neutrality through spatially optimized allocation. The agricultural sector has the potential to evolve into a reliable system for climate mitigation that supports carbon neutrality while safeguarding soil health.

The Inner Mongolia grassland has been facing critical degradation. To combat this issue, China has launched a series of ecological restoration programs since the early 2000s to promote the recovery of degraded grasslands (e.g., the Beijing–Tianjin Wind/Sand Source Control Program, the Grazing Withdrawal Project, and the Ecological Compensation Policy). However, the long-term effects of these measures on the recovery of the Inner Mongolia grassland still need further evaluation. To quantitatively assess the grassland degradation status and dynamics, we utilized long-term remote sensing datasets (GIMMS NDVI and MODIS NDVI) from 1982 to 2020 to calculate the fractional vegetation cover (FVC, the ratio of vegetation canopy's vertical projection area to the unit area) and grassland degradation index (GDI, the ratio of average FVC during peak growing season to historical optimum FVC). Results showed that across the study region, the average FVC was 42% over the past four decades, with degraded grassland (GDI < 0.9) accounting for 84.6% of the total area. Noteworthy spatial differences were observed. Specifically, study region to the west of 115°E had an average FVC of 20.7% with 98.2% areas exhibiting a degraded state. By contrast, study region to the east had an average FVC of 57.7% with 68.5% areas experiencing degradation. Over time, the proportion of degraded grassland generally decreased, particularly in the past two decades. However, approximately 3/4 of the grassland remained degraded in the last decade (2011–2020). Although degraded grassland is recovering, grassland degradation remains serious, especially in the west of 115°E, where 80.8% of the grassland was moderately and severely degraded (GDI < 0.6) in the last decade. Our findings suggest that while the implementation of ecological protection measures in Inner Mongolia has slowed down grassland degradation, the persisting degradation underscores the necessity of region-specific grassland protection and restoration.

Tailoring straw return strategies to specific regional conditions can optimize soil health, enhance crop yields, and contribute to climate change mitigation. By using the Rothamsted carbon model (RothC) and the bioenergy-emission-economic model (BEE), we assessed the spatially explicit, optimal straw harvest strategies to maintain soil organic carbon (SOC), and evaluated the climate benefits aquired from straw-based bioenergy. We found that the national average straw return rate needs to reach 43% to meet the 4 per mille SOC target. Most crop straws in Northeast China must be returned to cropland to maintain SOC level, while straws in East China and Central China could provide substantial quantities of biomass feedstock for energy production without SOC loss. Under future climate scenarios and designed straw harvest strategies, 0.3 to 0.7 Pg C of straw could become available annually for energy production, providing a greenhouse gas mitigation potential of 1.4 to 2.5 Pg CO2e using the combined heat and power (CHP) and integrated gasification combined cycle (IGCC) technologies (2020-2100). These region-specific straw management strategies offer insights into sustainable agricultural practices, soil carbon enhancement, and agricultural sector’s climate policies.

The joint effects of simultaneous warming and precipitation shifts on soil organic carbon (SOC)—the largest terrestrial carbon pool—remain poorly understood across large spatial extents. By evaluating a global dataset of SOC measurements in the top meter of soil through a space‐for‐change substitution approach, we show that, averaging across the globe, increased precipitation compensates for warming‐induced SOC reductions regardless of soil depth and vice versa. Although additive effects between these two factors are predominant, negative interactive effects, which exacerbate SOC losses, are also common, particularly in tropical and subtropical grasslands/savannas and Mediterranean/montane shrublands. SOC responses vary widely across the globe, primarily correlated to baseline SOC content and local climatic conditions. Notably, SOC responses in tundra systems are opposite the responses in other ecosystems, showing positive and negative responses to warming and precipitation increases, respectively. Under a scenario of 2°C air warming with projected precipitation changes, global SOC stocks in the 0–1 m depth are projected to decrease by 13.1% ± 6.6% (mean ± 95% confidence interval, or 351 ± 100 Pg C). These results demonstrate that accurately predicting SOC dynamics under climate change necessitates explicit consideration of local climatic conditions and existing SOC content in relation to concurrent precipitation shifts and warming.

Climate and land management changes are altering carbon inputs to soil. The consequence of such input changes on long‐term soil organic carbon (SOC) balance depends on the transit behavior of carbon inputs. Using observational carbon input and radiocarbon data in global soil profiles, we reveal that on average nearly 25% of new entering carbon leave soil in 1 year irrespective of entering depth, and the remained fraction after 30 years is only ∼13%. Nevertheless, the majority of SOC is older than 30 years in all soil depths. Together, these results demonstrate low transfer efficiency of carbon inputs to aged SOC which is the meaningful carbon component for long‐term SOC sequestration. Additionally, we reveal that SOC aging and carbon input transiting are two distinct processes, which should be simultaneously, but mechanistical‐separately, considered to predict and manage SOC dynamics in response to carbon input changes under climate and land management changes.