3个温带阔叶树种根系长期分解速率研究

根系分解对土壤碳固持和养分长期有效性具有重要意义，但目前对根系的长期分解模式仍知之甚少。比较3个温带阔叶树种不同直径根系7 a分解动态，可为生态过程模型提供数据支撑。在帽儿山生态站采用分解袋法对白桦（Betula platyphylla）、春榆（Ulmus davidiana var.japonica）、水曲柳（Fraxinus mandshurica）的5个直径等级（< 1 mm）、（1-2 mm）、（2-5 mm）、（5-10 mm）、（10-20 mm）根系进行了7 a野外分解实验。重复测量方差分析表明：时间、树种、直径与树种交互作用、树种与时间交互作用显著影响根系质量保持率。根系质量保持率随时间呈指数下降趋势，7 a间根系经历早期快速分解和后期慢速分解两个阶段，实验结束时根系仍剩余相当部分的初始质量（24%-56%）。利用Olson指数衰减模型估计各树种根系分解系数发现：白桦根系分解系数与根直径间具有显著的线性正相关关系，水曲柳具有显著对数正相关关系，春榆的关系不显著。3个树种短期分解系数均高估根系分解速率，而且不能完全代表长期分解系数的种内、种间差异。研究结果对理解根系长期分解速率随直径变化模式提供了数据支撑。

Seven-year decomposition rates of roots with different diameters for three temperate broadleaf tree species

Root decomposition is of great significance for carbon sequestration and long-term soil nutrients availability, but the long-term decomposition patterns of different root diameters were poorly understood. In this paper, we compared the seven-year decomposition processes of different root diameters for three temperate broadleaf tree species to provide data supporting for ecological process model. We conducted a seven-year field decomposition experiment for five root diameter classes (< 1 mm, 1-2 mm, 2-5 mm, 5-10 mm, and 10-20 mm) of Betula platyphylla (BP), Ulmus davidiana var. japonica (UJ), and Fraxinus mandshurica (FM) with a litter-bag method at the Maoershan site. Repeated measures analysis of variance showed that time, tree species, the interaction of diameter and tree species, and the interaction of tree species and time significantly affected the root mass remaining. The root mass remaining exponentially declined with time; During the seven years, the roots experienced two periods, i.e., a rapid loss in the early stage and a slow loss in the later stage; At the end of the experiment, the roots remained a considerable proportion of its initial quality (24%-56%). The decomposition constant of roots with different diameters for each tree species was estimated with the Olson exponential decay model. There was a significant linear positive correlation between the decomposition constant and root diameter for BP, while a significant positive logarithmic correlation for FM, and no significant relationship for UJ. The short-term decomposition constants of the three tree species overestimated root decomposition rate, and they could not fully represent the intra-species and inter-species differences in the long-term decomposition constants. The results provide data support for understanding the varying pattern of long-term root decomposition rate with root diameter.