Biocrust functions in mitigating soil water and wind erosion after freezing-thawing
Description
Freezing-thawing regulates soil structural stability and erosion resistance in cold winters, and further governs soil responses to water and wind erosion during subsequent warm seasons. As multifunctional communities widespread across global terrestrial ecosystems, biocrusts are also ubiquitous in cold-winter drylands at middle to high latitudes. While biocrusts have been found to influence soil erosion, the specific mechanisms are yet to be fully elucidated. Particularly, previous studies have largely overlooked freezing-thawing, which is a critical prerequisite for water and wind erosion over the annual cycle in cold-winter drylands. To address this knowledge gap, we collected samples of biocrusts and bare soil and subjected them to 10–30 freezing-thawing cycles at varying antecedent water contents (0.15–0.35 cm3 cm–3). Subsequently, we assessed their resistance to single raindrop splash, rainfall splash, runoff scouring, and wind erosion, respectively. After the same freezing-thawing treatments, biocrusts exhibited 19.4%–61.9% higher raindrop penetration kinetic energy than bare soil, accompanied by a 16.2%–87.5% reduction in splash erosion amounts from both single raindrop and rainfall tests. The splash distance of soil particles was also diminished by 5.4%–13.9% due to biocrusts. Furthermore, after freezing-thawing, biocrusts increased the anti-scour coefficient of surface soil by 342%–1329% and decreased its detachment capacity by 77.0%–93.0%, thereby ultimately reducing the sediment yield. Although freezing-thawing cycles intensified water erosion compared to initial states, biocrusts partially buffered this negative effect and thus exhibited a lesser post-thaw increase in erosion compared to bare soil. Moreover, biocrusts reduced wind erosion by 99.1% compared to bare soil following freezing-thawing cycles, and their erosion amount was not affected by the number of freezing-thawing cycles or the antecedent moisture. The erosion resistance of biocrusts mainly originated from their high structural stability, as indicated by macroaggregate content. Following freezing-thawing, biocrusts had 8.6%–38.0% higher macroaggregate content than bare soil, and the relative decrease in macroaggregate content induced by freezing-thawing was reduced by 20.1%–40.1% compared to bare soil. Our study highlights the importance of biocrusts in soil protection against water and wind erosion after freezing-thawing. This biocrust effect could help sustain frozen soil structure, conserve aggregate-related carbon and nitrogen, and mitigate erosion-driven greenhouse gas emissions under warming climates, further supporting vegetation growth and ecosystem productivity in cold-winter drylands.