The dynamics pattern of soil carbon and nutrients as soil thawing proceeded in the alpine/subalpine forest

Abstract

Little attention has been given to the dynamics of soil C and nutrients during the soil thawing period in subalpine/alpine forests. To understand the ecological linkages between the non-growing and growing seasons, soil C and nutrients were measured in the primary fir (Abies faxoniana) forest, fir and birch (Betula albosinensis) mixed forest and secondary fir forest in the subalpine/alpine regions of western China. Soils were sampled as soil thawing proceeded from 5 March, 15 March, 25 March, 5 April and 15 April to 25 April 2009, based on monitored soil temperatures. Frequencies of temperature fluctuations (below and above 0 °C) during the soil thawing period depended on the altitude. The soil organic layer showed higher contents and stocks of C, N and P compared with the mineral soil layer. Since the soil organic layer was more directly exposed to environmental changes, the variations of soil C and nutrients in the soil organic layer were more apparent than those in the mineral soil layer. The fluctuations of soil C and nutrients varied with the altitude during soil thawing period. Soil C and nutrient concentrations decreased sharply at the beginning of soil thawing, and thereafter increased in the mixed and secondary forest, which were different to the changes in the primary forest. Soil available nutrients, except for −N in the primary forest, showed an increasing tendency in the early stage of the thawing period, but soil available N and P decreased in the later stage of the thawing period. The increasing soil temperature had little effect on soil nutrient availability during the thawing period. The results indicated that soil carbon and nutrients were significantly affected by the length of freeze–thaw period, which is beneficial towards understanding the interactions between wintertime and the growing season.