Effects of snow patch on the dynamics of potassium and sodium during litter decomposition in winter in a subalpine forest of western Sichuan

Aims Snow patches of varying thickness could play an important role in potassium (K) and sodium (Na) dynamics during litter decomposition in subalpine forests due to significant freeze-thaw events, but the detailed processes are unclear. Our objective was to understand how snow patches would affect the dynamics of K and Na during litter decomposition of six representative woody species in different snow cover periods.
Methods A field experiment was conducted to investigate litter decomposition in a subalpine forest of western Sichuan by using litterbag method. Air-dried litter of Salix paraplesia, Larix mastersiana, Abies faxoniana, Rhododendron lapponicum, Betula albosinensis, and Sabina saltuaria were placed in nylon litterbags, and placed on the forest floor along a snow thickness gradient from forest gap to under the canopy cover. The samples were retrieved at snow formation, during snow cover period, and at snow melt.
Important findings Net Na immobilization during litter decomposition was observed over the entire snow cover season regardless of species, with the highest net immobilization rate occurring during the snow cover stage. In contrast, K was mainly released from litter during the snow cover period, showing rapid K release at the snow melt stage. Compared with the treatments with thin and absence of snow patches, the treatments with thick and moderate snow patches had higher rates of K release during litter decomposition. Although showing less effect on the release of Na compared with K, the snow cover significantly enhanced Na release from decomposing litter of Salix paraplesia, L. mastersiana, A. faxoniana, and R. lapponicum. Statistical analysis indicates that the dynamics of K and Na during litter decomposition are significantly influenced by species and snow cover at different snow cover stages. The rate of K release was positively related to daily mean temperature regardless of species, while the rate of Na release was positively related to daily mean temperature in litter of all species but B. albosinensis and Sabina saltuaria. Results in this study suggest that a decrease in snow cover under the scenario of winter warming would inhibit K and Na release during litter decomposition in winter in the subalpine forests, with the degree of release being related to litter quality.