Moss-dominated biocrusts enhance water vapor sorption capacity of surface soil and increase non-rainfall water deposition in drylands

Abstract

Surface soil vapor sorption and non-rainfall water (NRW) deposition are important sources, and can be highly influential in soil water dynamics and biochemical processes in drylands. As an important living skin, biocrusts have great impacts on soil water balance and play a vital role in water transport at near surface soil, while it remains unclear how biocrusts affect soil water vapor sorption and NRW deposition. In this study, we analyzed and modeled the water vapor sorption isotherms (WSIs) of moss-dominated biocrusts and uncrusted surfaces on loess soil and aeolian sand in the Chinese Loess Plateau. Furthermore, the actual NRW deposition amount of the biocrusts and uncrused soil in field was continuously measured across ~4 months in summer. Our results showed that the vapor sorption amount of the biocrusts was increased by up to 130.5% on the loess and 157.1% on the aeolian sand, and soil vapor sorption capacity of the biocrusts was mostly attributed to their higher contents of fine particles (clay and silt) and organic matter, and the moss morphology in comparison to the uncrusted soil. The Guggenheim-Anderson-de Boer (GAB) model performed well (R2 > 0.97, RMSE < 0.0005 g g−1, E < 13.2%) in simulating WSIs of each treatment. Moreover, the biocrusts enlarged the hysteresis effects by > 23.1%-200.0% as compared with the uncrusted soil at 0–10 cm depth. Additionally, the daily NRW amount of the biocrusts was increased by 19.2% on loess soil and 22.0% on aeolian sand, respectively, which means that the biocrusts significantly increased the NRW deposition capacity at 0–10 cm depth (F ≥ 11.12, P < 0.001). Lastly, the surface soil temperature of the biocrust layer was averagely 1.0–2.3 °C higher than that of the uncrusted soil during daytime, indicating that the biocrust layer enlarged the daily soil temperature differences between the crusted and uncrusted soils, and consequently increased the hourly NRW amount. In conclusion, this study demonstrates the important effects of biocrusts in improving vapor sorption capacity and NRW deposition of surface soil, and these properties in return would further generate feedback impacts on surface soil water and heat balances, enhancing microbial activity within the soil profile and nutrient adsorption from NRW in drylands.