Ecohydrological influences of biocrusts and their pathways in a desert steppe ecosystem

Abstract

AbstractBiological soil crusts (biocrusts) are a prevalent form of organic cover in drylands across the world, and they play a crucial role in shaping the ecohydrological processes and functioning of dryland ecosystems. However, in desert steppe ecosystems, the ecohydrological influences of biocrusts and their pathways have not yet been thoroughly understood. Here, we examined the influences of three types of biocrusts (cyanobacterial, cyanobacterial‐moss mixed, and moss biocrusts) on soil water retention and infiltration in a typical desert steppe of northwestern China, and we also analysed the possible pathways through which biocrusts affect them. Accordingly, the field capacity (θf, indicating soil water‐holding capacity) and saturated hydraulic conductivity (Ks, indicating soil infiltrability) of each biocrust‐covered soil and bare soil were measured both at 0–5 and 5–10 cm depths, on Arenosols (loamy sand texture) and Calcisols (silty loamy texture), respectively. Our results showed that the presence of biocrusts increased surface soil (0–5 cm) water‐holding capacity while decreased soil infiltrability, creating a remarkable impact on soil water retention and infiltration. As compared to bare soil, the θf of cyanobacterial, cyanobacterial‐moss mixed, and moss biocrusts were increased by 16.5%, 21.4%, and 21.7% on Arenosols and by 9.6%, 18.9%, and 22.8% on Calcisols, while their Ks were reduced by 43.2%, 56.2%, and 38.2% on Arenosols, and by 49.0%, 68.7%, and 36.0% on Calcisols, respectively. The development of biocrusts on sandy textured soil had a more pronounced impact on both soil water retention and infiltration than loamy textured soil. We found that biocrusts mainly changed soil water retention and infiltration by increasing the contents of clay and organic matter. More specifically, the increase in clay content led to a more significant effect compared to the increase in organic matter content on Arenosols, while the opposite influence was observed on Calcisols. Among the three types of biocrusts, the soil infiltrability of the mixed biocrusts was the lowest, perhaps due to the interaction between the accumulation of clay particles by moss and the secretion of extracellular polymeric substances by cyanobacteria. Our study highlights the remarkable ecohydrological impacts of biocrusts on desert steppe ecosystems, and the results imply that it is of great necessary to integrate biocrusts and their influences into our understanding of ecohydrological processes in global drylands.