Biocrusts enhance non-rainfall water deposition and alter its distribution in dryland soils

Abstract Non-rainfall water deposition is an important water resource, critical for the survival of dryland vegetation and soil biota and maintaining dryland water balance. As a “living skin”, biocrusts are attracting increasing attention due to their potentially positive impacts on non-rainfall water deposition. However, the magnitude and underlying mechanisms of biocrust regulation of non-rainfall water are still unclear. In this study, we investigated the non-rainfall water deposition and distribution through continuous weighing micro-lysimeters (0–3, 3–6, and 6–10 cm depths) with bare soil and three types of biocrusts (cyanobacterial crusts, cyanobacterial-moss mixed crusts, and moss crusts) in a semiarid region of the Chinese Loess Plateau. Our results showed that the biocrusts were associated with significantly greater non-rainfall water deposition capacity (~13%–22%) in contrast to the bare soil, and biocrust type strongly influenced the daily non-rainfall water amount in the order: moss crusts > mixed crusts > cyanobacterial crusts > bare soil. Biocrusts were also associated with faster rates of non-rainfall water formation (42%; F ≥ 2.87, P ≤ 0.04), which may be linked to faster nighttime cooling in comparison to the bare soil. Atmospheric vapor condensation was the primary water source for non-rainfall water deposition at the 0–10 cm depth, as opposed to soil vapor condensation. Biocrusts had higher condensation from both sources, and had relatively more deposition from the atmosphere: atmospheric vapor condensation was greater by 114%-143% and soil vapor condensation was greater by 20%–30%. Moreover, >69% of the total non-rainfall water amount occurred in the top 3 cm of soil. The strong biocrust influence in the uppermost centimeters (F = 45.34, P