The role of biological soil crusts in soil moisture dynamics in two semiarid ecosystems with contrasting soil textures

Abstract

Summary The interplant soil surfaces in most arid and semiarid ecosystems are covered by biological soil crusts (BSCs). These crusts regulate water inputs and losses through soils and play major roles in local hydrological regimes. In recent years, the role of BSCs in infiltration and runoff has gained increasing importance and better knowledge of their effects on these processes has been acquired. However, the role of BSCs in other important components of the water balance, such as evaporation or soil moisture has hardly been studied, so their effects on these processes remain unknown. The aim of this study was to explore the influence of BSCs on soil moisture regimes in the top layer of the soil in two semiarid ecosystems in SE Spain with different particle-size distributions. At both study sites, soil moisture was monitored at 0.03 and 0.10 m under two types of BSCs, a cyanobacteria-dominated BSC and a lichen-dominated BSC, and in adjacent soils where they had been removed. Our results showed that during wet soil periods, removal of BSCs led to decreased soil moisture, especially in the upper layer (0.03 m), compared to soils covered by BSCs. Decrease in soil moisture was more noticeable after removal of lichens than cyanobacterial BSCs, and more so in fine than in coarse-textured soils. Soil water loss was also generally faster in soils with no BSCs than in soils covered by them. However, no difference was found in soil moisture under either crusted or scalped soils during soil drying periods. The type of BSC influenced soil moisture differently depending on soil water content. During wet soil periods, soil water loss was faster and soil moisture lower under cyanobacterial than under lichen BSCs. On the contrary, during soil drying periods, soils covered by lichens lost water faster and showed lower moisture than those covered by cyanobacteria. Our results show the major role of the presence of BSCs, as well as the types, in soil water content in semiarid ecosystems.