Decomposition of tree fine roots and nutrient dynamics in relation to symbiotic microbes

树木细根主要由菌根真菌定植。由于菌根根尖周转期短，每年从菌根向土壤的有机输入超过地上叶凋落物的量。但是，菌根的分解过程在很大程度上是未知的。在这项研究中，我们将含有菌根的网袋埋在森林地面下，并监测了两年多的分解过程。我们发现，菌根的分解远远慢于叶物质的分解。一个模型估计，菌根95%的分解需要近20年的时间。与分解过程中总干重和碳量的下降相反，即使在监测结束时，氮量也显著增加，这可能是由于富含氮的真菌和细菌的定居所致。我们还鉴定了导致菌根分解的细菌和真菌。

Fine roots of trees are mostly colonized by mycorrhizal fungi. Due to the short turnover periods of mycorrhizal root tips, annual organic input into soil from mycorrhizal roots exceeds the amount of above-ground leaf litter. But, the decomposition process of mycorrhizal roots is largely unknown. In this study, we buried mesh-bags containing mycorrhizal roots under forest floor and monitored decomposition processes over two years. We found that the decomposition of mycorrhizal roots was far slower than that of leaf materials. A model estimated that nearly 20 years would be required for 95% decomposition of mycorrhizal roots. In contrast to the decrease in total dry mass and C amount during decomposition, N amount significantly increased even at the end of the monitoring period, probably due to the colonization of nitrogen rich fungi and bacteria. We also identified bacteria and fungi that were responsible for the decomposition of mycorrhizal roots.