气候变暖下青藏高原东缘亚高山针叶林主要树种根序养分分配与化学计量比的模块化特征

Nutrient is the key factor to maintain growth of plants and its stoichiometry can reveal the regulation mechanism of the nutrients rations in ecosystems under climate warming. In the past, the research concerning on nutrient in root is mainly studied on the base of the “whole root” which was taken for homogeneous system. However, large woody root branch into smaller laterals which is heterogeneity and the lateral root branches are physiologically modules. And, there is no report concerning on macronutrients and micronutrients in root branches affected by global warming. Thus, this study aims to investigate the nutrients (C、N、P、K、Ca、Mg、Cu、Fe、Zn、Mn) accumulation and its stoichiometry in the coniferous tree roots based on the method of branch-order classification under warming using infrared heaters in the east Tibetan Plateau. And we also study the mechanisms of the warming effect on them through determing the root morphology, architecture, and the elements in the in-situ soil solution. Furthermore, we study the correlation of the nutrients in shoot with in root branches. This project can help us to deepen and enhance the theoretical study of root ecology, and there is great significance on comprehensive understanding the belowground process in terrestrial ecosystem in response to climate change. As well as it would provide scientific basis for speeding up the ecological recovery and sustainable management in forest.

养分是维持植物生长的关键因素，其化学计量比能更好地揭示气候变暖下生态系统养分比例的调控机制。过去对根系养分的研究主要是基于“整体法”将整个根系看成均值系统，然而树木根系呈现多级分枝，具有很强的异质性，并且这些分支根序呈现模块化特征。因此，本项目采用红外辐射加热模拟增温，基于“根序法”研究气候变暖下养分（C、N、P、K、Ca、Mg、Cu、Fe、Zn、Mn）在青藏高原东缘亚高山针叶林主要树种根序中的分布及其化学计量比的模块化特征，并通过根系形态、构型及原位土壤溶液理化性质的监测来揭示不同根序模块中元素含量及其化学计量比对气候变暖的响应机制；同时探讨这些元素在根序模块中的分配与其在地上部分布的关联性。本项目的实施可加深和提升根系生态学的理论研究，对于全面认识区域典型陆地生态系统地下过程对气候变化的响应机制具有重要理论意义，同时为加速生态恢复和科学化经营管理森林提供依据。

本项目依托课题组前期的野外生态站，选择青藏高原东缘亚高山针叶林主要建群种--粗枝云杉为实验对象，通过红外辐射加热器模拟气候变暖，基于根序分级法研究了云杉细根不同分级根序中养分元素的分配与化学计量比对气候变暖的响应，并探讨这些养分元素在根序模块中的分配与其在地上部的分布有何相关性。结果表明：1）在非增温条件下， C、P在不同根序中的积累分配没有显著差异，N、Mg、K、Fe、Zn、Cu、Mn含量均随着根序分级增加逐渐降低，且在前两级根的分配远高于后三级根，该结果表明这些养分分配具有独特的模块化特征，增温未改变这些元素在根序中的分配特征，但对不同元素的影响也不一致，且这些养分与根系形态具有很好的相关性；2）各元素之间化学计量比受增温影响趋势并不一致，且应对气候变暖植物体内的化学计量特征并不都是遵循内稳态机制以保持相对稳定的化学计量比；3）增温提高了N、K、Mg、Fe、Mn在叶片中的分配，降低了叶片中C和C/N比值，对P、Ca、Cu、Zn在叶片中分配的影响不显著；叶片中N、K、Mg、Mn、Fe与根系中该元素含量具有相关性，而叶片中Ca、P、Cu、Zn含量与根中该元素含量没有相关性，该结果表明植物地上部养分的积累与分配不仅仅与根系中养分含量相关，还可能受到其他生物因素的影响。