长白山白桦(Betula platyphlla)纯林和白桦山杨 (Populus davidiana)混交林凋落物的分解

采用交互分解实验，研究长白山白桦叶片和白桦、山杨与水曲柳混合叶片在白桦纯林和白桦山杨混交林内的分解过程。两年的分解实验结果表明，两种类型叶片均存在一个快速分解阶段和一个慢速分解阶段，森林类型和凋落物类型对凋落物分解率的影响在快速分解阶段不显著而在慢速分解阶段显著；混交林内的环境促进了凋落物分解和养分元素释放；在同一林型内，底物质量高的混合叶片其分解率和养分元素释放率均大于底物质量低的白桦叶片；凋落物的底物质量在一定程度上可以抵消森林类型对凋落物分解的影响；白桦山杨混交林混合叶片分解速率和养分元素释放率要显著大于白桦纯林内的白桦叶片，说明白桦山杨混交林的物质循环速度和养分元素供应能力要显著大于白桦纯林。

Litter decomposition processes in the pure birch (Betula platyphlla) forest and the birch and po;lar (Populus davidiana) mixed forest

Birch (Betula platyphlla) and poplar (Populus davidiana) are the typical heliophilous, fast growing species and frequently form the pure birch forest (BF) or birch and poplar mixed forest (BPF) in North China. A reciprocal litter bag experiment was carried out to investigate the leaf litter decomposition process in BF and BPF and the effect of forest types on litter decomposition using pure birch leaves litter and the mixed litter of birch, poplar and ash (Fraxinus mandshurica) leaves. The results of the two year decomposition showed that the effect of forest types and litter type on litter decomposition was not significant at the fast decomposing stage but at the slow decomposing stage. The environmental conditions of BPF contribute to the nutrient release and decay of the two litter types. Compared with birch leaves, mixed leaves had a significantly higher substrate quality and showed a substantially faster decomposing rate and nutrient release rate. Litter quality to some degree can mask the effect of forest type on litter decomposition. In conclusion, BPF exhibits a faster carbon and nutrient cycling rate than BF does.