Effects of snow removal on soil labile nitrogen in a subalpine spruce forest of western Sichuan,China

LI Zhi-jie;YANG Wan-qin;HE Ruo-yang;ZHUANG Li-yan;YANG Kai-jun;LIU Qun;LI Ting-ting;XU Zhen-feng;Sichuan Province Key Laboratory of Ecological Forestry Engineering,Institute of Ecology & Forestry,Sichuan Agricultural University;Collaborative Innovation Center of Ecological Security in the Upper Reaches of Yangtze River,Long-term Research Station of Alpine Forest Ecosystems,Sichuan Agricultural University;

snow removal;;freeze-thaw cycle;;ammonium;;nitrate;;nitrification rate;;mineralization rate

Warming-induced decrease in seasonal snow cover has a great potential to affect soil nitrogen cycle in alpine cold forest ecosystems. In this study,a wooden-shelter method was used to remove the snow accumulation. Soil nitrogen pools and mineralization rates in the snow removal and control plots were measured synchronously in three critical periods( early snow cover,deep snow cover and snow cover melting) in a subalpine spruce forest of western Sichuan,China. Seasonal snow cover kept soil from cold air temperature. Snow removal decreased average and minimum soil temperatures( 5 cm) by 0.33 and 1.17 ℃,respectively. In addition,snow removal caused a positive effect on soil frost depth and freeze-thaw cycle. There was a significant dynamic in soil labile nitrogen pool among different periods. Snow removal on average increased NH_4~+-N,NO_3~--N and dissolved organic nitrogen( DON) contents by 38.6%,23.5% and 57.3%,respectively,over the winter. Moreover,snow removal increased soil net nitrification and mineralization rates in the snow cover melting period. Overall,warming-induced decrease in snow cover could stimulate winter soil nitrogen cycle of subalpine forests.