Contribution of biocrusts to soil respiration and its responses to soil temperature and rainfall in a typical steppe on the Loess Plateau, Northwest China.

Biological soil crusts (or biocrusts) exert a critical influence on carbon cycling in arid and semi-arid ecosystems. However, the contribution of biocrusts to soil respiration and the mechanisms underlying their environmental responses remain unresolved, hindering accurate quantification of soil carbon efflux in drylands. In this study, we conducted continuous in-situ monitoring of respiration rates, soil temperature, soil moisture, and rainfall of mixed biocrust communities (biocrust-covered soils versus biocrust-removed bare soils) on the Loess Plateau to investigate the contribution of biocrusts to soil respiration and their responses to those three factors. The results showed that the range of soil respiration rates was 0.07 to 1.66 μmol·m-2·s-1 in biocrust-covered soils and was -0.09 to 1.59 μmol·m-2·s-1 in biocrust-removed bare soils, with the former being significantly greater than the latter. The respiratory effect of the biocrust layer (calculated as the difference in respiration rate between biocrust-covered soils and biocrust-removed bare soils) ranged from -0.33 to 0.93 μmol·m-2·s-1, with its relative contribution to total soil respiration varying from -31% to 213%. Rainfall modulated both the respiratory effect of biocrust layer and its contribution to soil respiration. The average contribution of biocrust to soil respiration was -6% under rainfall-free conditions and was 27% during rainfall periods. The relative contribution of the biocrust layer to soil respiration was significantly positively correlated with soil moisture and rainfall amount, but negatively correlated with soil temperature. Rainfall explained the largest proportion of variance in biocrust contribution, indicating that rainfall was the primary driver of biocrust effects on soil respiration on the Loess Plateau. These findings could provide critical baseline data to support accurate assessments of biocrust effects on soil respiration in the context of climate change.