关键词: 凋落物, 养分归还, 原始林芝云杉林, 西藏

Abstract:

Litters are the important component of forest ecosystem and play a key role in plant growth and ecosystem nutrient cycle. The Tibetan Plateau is a unique geographical cell on earth with an average elevation above 4000 m a.s.l., where forest has been known for exclusive tree species with special distribution law and rare highly productivities. Dark conifer forests make up 48% of forest areas and its stock volumes also make up 61% of total volumes in Tibet. Picea likiangensis var. linzhiensis which has been distributed in Linzhi and Shannan region of Tibet is one of the dominant tree species in these dark conifer forests. To understand the nutrient return through the litter in the primary Picea likiangensis var. linzhiensis forests which were located in Nanyigou area of the Tibet, ten 1 m×1 m litter traps made of nylon mesh (1 mm mesh size) were arranged randomly in the 50 m×50 m fixed sample plots which were located at the more than 20 m away from the forest edge area. The litter was collected at monthly intervals from January to December. Meanwhile six 1 m×1 m samples were arranged randomly in the 20 m×20 m sample plots which were located near the fixed sample, the whole litter was collected from the un-decomposed layer, semi-decomposed layer and decomposed layer, respectively. The results showed the annual litter in the Picea likiangensis forests were 3.40 t·hm^-2, the leaf litter and the branch litter constituted 24.29% and 26.07% of the total annual litter, respectively. During the whole observation year, the concentrations of N, P, K and Mg in the litter were lower than in the living organisms. The total annual nutrient returns of N, P, K, Ca and Mg were 82.14 kg·hm^-2. Among them Ca return was higher than those other four nutrient elements. The thickness of litter layer reached to 5.0 cm and the standing stock was 40.65 t·hm^-2. The average annual decomposition rate of litter layer was 0.08 t·hm^-2. The total amount of five nutrient elements was 937.65 kg·hm^-2, of which decomposed layer was 57.28%. In this study, we found the standing stock of Picea likiangensis var. linzhiensis forests in Tibet was far lower than those of the forests in Tianshan Mountains, but was higher than those of Abies forests in Ermeishan Mountain. However, the litter from Picea likiangensis var. linzhiensis was very difficult to be decomposed because the thickness of decomposed layer was only 24% of the whole litter layer. This study also proposed shrub played an important role in improving the fertility in primary forests.

Key words: litter, nutrient return, Picea likiangensis var. linzhiensis forest, Tibet