Freeze-Thaw Cycles Aggravated The Negative Effects Of Moss-Biocrusts On Hydraulic Conductivity In Sandy Land

Moss-biocrusts (BCs) play an essential role in soil stabilization, but it reduces soil hydraulic conductivity, hindering precipitation convert to soil water. Freeze-thaw cycles (FTCs) is a natural phenomenon, which can alter soil properties, causing widespread concern. However, few studies have focused on the effects of FTCs on hydraulic conductivity in BCs, which may alter the negative effects of BCs on hydraulic conductivity. We conducted an in-situ FTCs simulated experiment in BCs and bare sand (BS), to analyze the response of particle-size composition, water-stable aggregates and water repellency (WR) to FTCs, and their effects on saturated hydraulic conductivity (K-s). The results showed that the existence of BCs had affected water-stable aggregates, particle-size composition, WR and K-s. Compared with BS, the percentage of clay-size particle content increased by 44% and 60% in BCs layer and its underlying soil, respectively. The stability of water-stable aggregates was 19% higher in BCs than the measured stability in BS. K-s of BS was 2.4 times higher than that of BCs, and the increasing percentage of water-stable aggregates larger than 5 mm would reduce K-s in sandy land. FTCs had the significant effects on water-stable aggregates, WR and K-s. WR and K-s of BCs were decreased 57% and 25% after FTCs, respectively. Moreover, after FTCs, the percentage of soil water-stable aggregates > 5 mm reduced 19%, while 1-5 mm increased 18%. WR and sand content were significantly and negatively correlated with K-s, while clay content and the percentage of soil water-stable aggregates > 5 mm were significantly and positively correlated with K-s in BCs. Our results indicated that BCs and FTCs had a significant and negative effects on K-s. FTCs further decreased the hydraulic conductivity, which was not conductive to the supply of meltwater to soil water reservoir in the period of winter and early spring.