Effects of seasonal snow cover on decomposition and carbon, nitrogen and phosphorus release of Picea schrenkiana leaf litter in Mt. Tianshan, Northwest China

Abstract

Aims: The effects of freeze-thaw cycles on seasonal snow thickness may play a significant role in the decomposition process of forest litter in arid areas, whereas the understanding on this issue remains poor. Therefore, our objective was to understand the effects of snow cover on the decomposition and the carbon, nitrogen and phosphorus release of Picea schrenkiana leaf litter, the representative species in arid areas in northwest China. Methods: A field experiment was conducted in Mt. Tianshan of Xinjiang from October 2015 to October 2016 using litterbag method. Air-dried leaf litter of P. schrenkiana was put into nylon litterbags and the litterbags were placed on the forest floor along the gradient of snow cover depth from forest gap to full canopy. Mass loss rates and carbon, nitrogen and phosphorus release of P. schrenkiana leaf litter were measured at three critical stages (freeze-thaw period, deep-freeze period, thawing period) under snow cover and the growing seasons (early growing season and late growing season) during one year of decomposition. Important findings: The results showed that (1) after one year's decomposition, the decomposition rates of the P. schrenkiana leaf litter under different snow depths were 24.6%-29.2%, and there were significant difference (p < 0.05) between the decomposition rates under different snow depths. The decomposition constant (k) was highest under thick snow cover and lowest under no snow cover. (2) The decomposition during the winter snow cover period contributed 46.0%-48.5% of total decomposition of P. schrenkiana leaf litter in the whole year, and the litter decomposition was the fastest during the freeze-thaw cycles. (3) With the decomposition of leaf litter, the nitrogen content of P. schrenkiana leaf litter increased while the content of carbon and C:N decreased roughly. There was a significant difference (p < 0.05) in carbon content between different snow treatments in the deep freezing period and late growing season. The phosphorus content in leaf litter is irregular with the decomposition of leaf litter. Snow thickness significantly influenced the phosphorus content in leaf litter during freeze-thaw period and thawing period (p < 0.05). (4) Net N immobilization during leaf litter decomposition was observed in the whole snow cover season, C and P were mainly released. Among them, thin and medium snow patches showed higher carbon enrichment rates in the thawing period. Thin, medium and thick snow treatments in the freeze-thaw period, no and thick snow treatments in the thawing period and medium and thick snow patches in the late growing season showed higher nitrogen enrichment rates. In contrast, the effect of snow cover on the release of leaf litter phosphorus was not significant (p > 0.05).