Spatial patterns of soil and ecosystem respiration regulated by biological and environmental variables along a precipitation gradient in semi-arid grasslands in China

Climatic warming enhances soil respiration resilience in an arid ecosystem

Precipitation plays a vital role in maintaining desert ecosystems in which rain events after drought cause soil respiration (R_s) pulses. However, this process and its underlying mechanism remain ambiguous, particularly under climatic warming conditions. This study aims to determine the magnitude and drivers of R_s resilience to rewetting. We conducted a warming experiment in situ in a desert steppe with three climatic warming scenarios-ambient temperature as the control, long-term and moderate warming treatment, and short-term and acute warming treatment. Our findings showed that the average R_s over the measurement period in the control, moderate and acute warming plots were 0.51, 0.30 and 0.30 μmol·CO₂·m^-2·s^-1, respectively, and significantly increased to 1.72, 1.41 and 1.72 μmol·CO₂·m^-2·s^-1, respectively, after rewetting. Both microbial and root respiration substantially increased by rewetting; microbial respiration contributed more than root respiration to total R_s. The R_s significantly increased with microbial biomass carbon and soil organic carbon (SOC) contents. The R_s increase by rewetting might be due to the greater microbial respiration relying heavily on microbial biomass and the larger amount of available SOC after rewetting. A trackable pattern of R_s resilience changes occurred during the daytime. The resilience of R_s in acute warming plots was significantly higher than those in both moderate warming and no warming plots, indicating that R_s resilience might be enhanced with drought severity induced by climatic warming. These results suggest that climatic warming treatment would enhance the drought resilience of soil carbon effluxes following rewatering in arid ecosystems, consequently accelerating the positive feedback of climate change. Therefore, this information should be included in carbon cycle models to accurately assess ecosystem carbon budgets with future climate change scenarios in terrestrial ecosystems, particularly in arid areas.

Effects of water and nitrogen addition on ecosystem respiration across three types of steppe: The role of plant and microbial biomass

Evaluating the regional variation of ecosystem respiration (R_eco) in its response to the changes of soil water and nitrogen (N) availability is crucial for fully understanding ecosystem carbon (C) exchange and its feedbacks to global changes. Here, we examined the responses of R_eco, plant community aboveground biomass (AB), microbial biomass carbon (MBC) and soil moisture (SM) to water and N addition, using intact soil monoliths from three different temperate steppes along a precipitation gradient, including meadow steppe, typical steppe, and desert steppe in northern China. We found that the meadow steppe held the highest value of R_eco. Water addition significantly enhanced R_eco while N addition had no effect on R_eco in all three ecosystems. The response of R_eco in the typical steppe was more sensitive than the other two ecosystems. The changes of plant community AB exhibited a much stronger explanatory power than that of MBC for R_eco in the typical steppe. In contrast, MBC was the dominant factor explaining the variation of R_eco in the desert steppe and the meadow steppe. These findings contribute to our understanding of regional patterns of ecosystem C exchange under scenarios of global changes and highlight the importance of water availability in regulating ecosystem processes in temperate steppe grasslands.

Regional variation in the temperature sensitivity of soil organic matter decomposition in China's forests and grasslands

How to assess the temperature sensitivity (Q₁₀ ) of soil organic matter (SOM) decomposition and its regional variation with high accuracy is one of the largest uncertainties in determining the intensity and direction of the global carbon (C) cycle in response to climate change. In this study, we collected a series of soils from 22 forest sites and 30 grassland sites across China to explore regional variation in Q₁₀ and its underlying mechanisms. We conducted a novel incubation experiment with periodically changing temperature (5-30 °C), while continuously measuring soil microbial respiration rates. The results showed that Q₁₀ varied significantly across different ecosystems, ranging from 1.16 to 3.19 (mean 1.63). Q₁₀ was ordered as follows: alpine grasslands (2.01) > temperate grasslands (1.81) > tropical forests (1.59) > temperate forests (1.55) > subtropical forests (1.52). The Q₁₀ of grasslands (1.90) was significantly higher than that of forests (1.54). Furthermore, Q₁₀ significantly increased with increasing altitude and decreased with increasing longitude. Environmental variables and substrate properties together explained 52% of total variation in Q₁₀ across all sites. Overall, pH and soil electrical conductivity primarily explained spatial variation in Q₁₀ . The general negative relationships between Q₁₀ and substrate quality among all ecosystem types supported the C quality temperature (CQT) hypothesis at a large scale, which indicated that soils with low quality should have higher temperature sensitivity. Furthermore, alpine grasslands, which had the highest Q₁₀ , were predicted to be more sensitive to climate change under the scenario of global warming.