Hydrologic gradient changes of soil respiration in typical steppes of Eurasia

Soil respiration (R-S) is affected by many factors and shows significant diurnal and seasonal changes at different spatial and temporal scales. However, in a semi-arid steppe, the mechanism of the dynamic influence of environmental factors on R-S is not clear, and the effect of subtle changes of soil water on R-S under drought stress is yet to be explored. Therefore, Xilin River Basin, was the study area and a hydrological gradient on the four ecosystems for R-S and hydrometeorological monitoring was selected. We proposed the use of dynamic sunrise and sunset time to distinguish day from night and determine related statistics. Additionally, we analyzed the temporal variation of R-S and its response process and mechanism for hydrometeorological factors during the growing season and at daily scales. Further, we quantitatively simulated the R-S of 594 scenarios in different growing season stages, ecosystems, and precipitation patterns. Results showed that: (1) in the hydrological gradient belt, different ecosystems exhibited the same trend but different characteristics of R-S regulation. From May to November 2020, R-S was 2.34-3.89, 1.89-5.97, 1.90-5.27 and 2.29-3.45 gC m(-2) day(-1) for the four ecosystems. (2) The use of dynamic sunrise and sunset time to distinguish day and night can more accurately describe the statistical value of each variable, which exhibits remarkable feasibility in daily scale research. (3) The changes in R-S were adequately explained by temperature at various time scales, and the photosynthetically active radiation was positively correlated with R-S at the daily scale. The special soil water content (M-S) condition in the study area was not sufficient to explain R-S. (4) Precipitation can affect R-S by changing soil and air; however, only when precipitation exceeds the effective precipitation threshold of 0.6 +/- 0.3 mm, it significantly affects R-S. (C) 2021 Published by Elsevier B.V.

Automated summary

The study examined the dynamic influence of environmental factors on soil respiration in a semi-arid steppe, revealing temperature and photosynthetically active radiation as key factors influencing R-S, while precipitation only significantly affects R-S when exceeding a certain threshold.