Key Laboratory of Forest Ecology and Management, Institute of Applied Ecology, Chinese Academy of Sciences, 110016 Shenyang, China;
Department of Ecology, Evolution and Behavior, University of Minnesota, St. Paul, MN 55108.
Proc Natl Acad Sci U S A. 2018 Oct 9;115(41):10392-10397. doi: 10.1073/pnas.1716595115. Epub 2018 Sep 25.
Decomposition is a key component of the global carbon (C) cycle, yet current ecosystem C models do not adequately represent the contributions of plant roots and their mycorrhizae to this process. The understanding of decomposition dynamics and their control by traits is particularly limited for the most distal first-order roots. Here we followed decomposition of first-order roots and leaf litter from 35 woody plant species differing in mycorrhizal type over 6 years in a Chinese temperate forest. First-order roots decomposed more slowly ( = 0.11 ± 0.01 years) than did leaf litter (0.35 ± 0.02 years), losing only 35% of initial mass on average after 6 years of exposure in the field. In contrast to leaf litter, nonlignin root C chemistry (nonstructural carbohydrates, polyphenols) accounted for 82% of the large interspecific variation in first-order root decomposition. Leaf litter from ectomycorrhizal (EM) species decomposed more slowly than that from arbuscular mycorrhizal (AM) species, whereas first-order roots of EM species switched, after 2 years, from having slower to faster decomposition compared with those from AM species. The fundamentally different dynamics and control mechanisms of first-order root decomposition compared with those of leaf litter challenge current ecosystem C models, the recently suggested dichotomy between EM and AM plants, and the idea that common traits can predict decomposition across roots and leaves. Aspects of C chemistry unrelated to lignin or nitrogen, and not presently considered in decomposition models, controlled first-order root decomposition; thus, current paradigms of ecosystem C dynamics and model parameterization require revision.
分解是全球碳 (C) 循环的关键组成部分，但当前的生态系统 C 模型不能充分代表植物根系及其菌根对这一过程的贡献。对于最远端的一级根，对分解动态及其受特性控制的理解尤其有限。在这里，我们在 6 年内跟踪了中国温带森林中 35 种不同菌根类型的木本植物的一级根和叶凋落物的分解情况。一级根的分解速度比叶凋落物慢（=0.11±0.01 年），在野外暴露 6 年后，平均只损失初始质量的 35%。与叶凋落物不同，非木质素根 C 化学物质（非结构性碳水化合物、多酚）解释了一级根分解的大种间变异的 82%。外生菌根（EM）物种的叶凋落物比丛枝菌根（AM）物种的分解速度慢，而 EM 物种的一级根在 2 年后，从分解速度较慢转变为比 AM 物种的分解速度更快。与叶凋落物相比，一级根分解的动态和控制机制有根本的不同，这挑战了当前的生态系统 C 模型、最近提出的 EM 和 AM 植物二分法，以及共同特性可以预测根系和叶片分解的观点。与木质素或氮无关、目前未被考虑在分解模型中的 C 化学方面，控制着一级根的分解；因此，当前的生态系统 C 动态和模型参数化范式需要修订。
