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

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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.