Extreme summer drought increased soil detachment capacity of biocrusts in subtropical China

Biological soil crusts (Biocrusts) are considered to have significant effects on soil detachment processes. Increasing extreme droughts are expected to affect the structure and functioning of biocrust ecosystems. However, understanding how biocrust ecosystems will respond to drought requires further investigation in the subtropical region. This study conducted continuously monitoring of understory biocrusts in subtropical China from May to November 2022, analyzed the monthly variation of near-surface characteristics of biocrusts and performed scouring experiments with six flow shear stresses (7.61-21.08 Pa) to assess the monthly variation of soil detachment capacity (Dc) of biocrusts. Finally, we elucidated the complex effects of summer drought (August-September) on Dc of biocrusts. Results showed that summer drought led to significant reductions in biocrust coverage (BC) and biocrust thickness (BT) (P<0.05), as well as notable declines in soil stability (including soil cohesion and Mean weight diameter) and soil nutrient content (including soil organic matter, total Nitrogen, total Phosphorus) (P<0.05), except for a non-significant increase in bulk density (P>0.05). Furthermore, Dc of biocrusts significantly increased by 172.2 % during the summer drought compared to the previous months (P<0.05). These changes of biocrusts are mainly affected by moisture stress more than heat stress. Partial least squares path modeling (PLS-PM) revealed that reduced rain and lower soil moisture increased Dc mainly by diminishing the BC and BT, followed by reducing soil cohesion and soil aggregate stability. The results provide empirical evidence for the cumulatively detrimental effects of future climate on biocrusts and contribute to more comprehensive understanding of biocrusts multifunctionality.