Root‐associated fungi not tree density influences stand nitrogen dynamics at the larch forest–tundra ecotone
Root‐associated fungi not tree density influences stand nitrogen dynamics at the larch forest–tundra ecotone
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DOI：
10.1111/1365-2745.13882
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发表时间：
2022-03
影响因子：
5.5
通讯作者：
R. Hewitt;H. Alexander;S. Miller;M. Mack
中科院分区：
文献类型：
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作者：
R. Hewitt;H. Alexander;S. Miller;M. Mack
随着气候变暖，冻土带-针叶林交错带(TTE)的树木密度和森林生产力预计会更高，并可能对气候系统产生反馈。然而，对氮(N)的竞争可能会影响TTE动态。更大的树木密度可能会增加氮素需求，同时通过土壤遮荫和较慢的分解速度减少氮素供应。我们探讨了对氮素吸收具有重要作用的根和根伴生真菌的特性是否响应了TTE密度的变化，并与地上部分的生产力和N的循环有关。测定了西伯利亚东北部单一优势落叶松天然密度梯度上的根系深度、各土层对N形态的吸收以及外生菌根(ECM)的定植和组成。我们测试了落叶松根系与真菌特性、地上生产力和林分水平氮素循环参数之间的关系。总体而言，与甘氨酸或硝酸盐相比，铵的吸收更优先。有机层浅层土壤吸氮量最大，与根系化学成分、根际伴生真菌和地上氮素循环参数有关，但这些关系的方向取决于氮素形态。不同氮素形态的吸收、根系深度、ECM定植和组成与树木密度无关，而真菌组成与根系氮素化学和地上氮素循环参数相关。除ECM外，暗隔内生真菌和其他子囊菌类群的丰度与氮素吸收和地上氮素循环参数呈正相关。综合。乔木密度对落叶松根系和真菌吸收N的相关参数影响不大，说明落叶松对N的竞争不会随着密度的增加而增强。然而，无论树木密度如何，根伴生真菌对N的吸收和林分N的动态都有很大的影响。总之，这表明根伴生真菌在TTE落叶松森林中N循环的大范围模式中发挥着重要作用，而不受气候变暖预期的树木密度变化的影响。
Greater tree density and forest productivity at the tundra–taiga ecotone (TTE) are expected with climate warming, with potential feedbacks to the climate system. Yet, competition for nitrogen (N) may impact TTE dynamics. Greater tree density will likely increase N demand, while reducing N supply through soil shading and slower decomposition rates. We explored whether characteristics of roots and root‐associated fungi important to N acquisition responded to changes in density at the TTE and were related to above‐ground stand productivity and N cycling. We measured rooting depth, uptake of N forms among soil layers and ectomycorrhizal (EcM) colonization and composition along a natural tree density gradient of monodominant larch Larix cajanderi in northeastern Siberia. We tested relationships between larch root and fungal characteristics, above‐ground productivity and stand‐level N cycling parameters. Overall, there was preferential uptake of ammonium compared to glycine or nitrate. Nitrogen uptake was greatest in shallow soils of the organic horizon and related to root chemistry, root‐associated fungi and above‐ground N cycling parameters, but the direction of these relationships depended on N form. Uptake of different N forms, rooting depth and EcM colonization and composition were not related to tree density, but fungal composition was correlated with root N chemistry and above‐ground N cycling parameters. In addition to EcM, the abundance of dark septate endophytes and other ascomycetous taxa was positively related to N uptake and above‐ground N cycling parameters. Synthesis. There was little impact of tree density on root and fungal parameters related to N acquisition suggesting intraspecific larch competition for N was not amplified with increased density. There was, however, a strong impact of root‐associated fungi on N uptake and stand N dynamics regardless of tree density. Together, this suggests an important role of root‐associated fungi on broadscale patterns of N cycling in TTE larch forests independent of changes in tree density expected with climate warming.