The role of root zone soil moisture return on vegetation green-up: A comparison of two degrading permafrost sites

The effects of permafrost degradation on ecological changes have attracted more and more attention, but the underlying interactive mechanisms are still not well understood. From a unique angle of view, this study focuses on the linkage between the freezing-induced root zone soil moisture return (SMR) and vegetation green-up along with climate warming and permafrost degradation. Using 7-year soil-weather monitoring data in the high altitude and high-latitude permafrost regions, we investigated the changes of root zone SMR in two degrading permafrost sites. Results demonstrate that, as one important water source for vegetation green-up, the ratio of root zone SMR to the soil moisture storage after final thawed, Rsmr, could reach 22.8 % and 10.5 % at the two sites, respectively. In contrast to the negligible change at the high-latitude permafrost site, a rapid increase rate of 7.7 % per decade in Rsmr was found at the high-altitude permafrost site over the monitoring period of 2012-2018. Generally, vegetation green-up definitely benefited from the enrichment of soil moisture storage, but their sensitivities to climate warming and permafrost degradation were different at the two sites. The increase of Rsmr effectively buffered the shrinking trend of soil water availability of the root zone both over the pre-freezing and the green-up period at the high-altitude permafrost site. The changing role of root zone SMR might be threatened during the vegetation green-up in the longer future. Whereas, there would be no water shortage risk for the foreseeable future at the high-latitude permafrost site. Overall, this study emphasized the importance ofSMR in enhancing soil water availability for vegetation green-up under the background of quick climate warming and permafrost degradation.

Automated summary

This study explores the interaction between permafrost degradation and climate warming on vegetation green-up, focusing on the role of freezing-induced root zone soil moisture return (SMR). Through analyzing soil-weather monitoring data in high altitude and high-latitude permafrost regions, the study finds that SMR is an important water source for vegetation green-up, with varying sensitivities to climate warming and permafrost degradation at different sites.