树种多样性对不同功能群细根生产力和周转的影响

Mixed tree plantations are important methods for construction and improvement of afforestation. Increasing species diversity by mixed tree plantations can promote productivity and stability of aboveground forest ecosystem. However, the effects of tree species richness on root growth remain to be studied. Roots with diameter less than 2mm are fine roots which contribute more than 33% of the NPP of global terrestrial ecosystem. Fine roots could be classified into absorptive roots and transport roots using the functional classification method. Because of the different turnover rates between them, fine-root productivity can only account for about 22% of the NPP of global terrestrial ecosystem. Therefore, studies about the productivity and turnover of different fine-root functional groups are helpful for accurately understanding the ecological functions and processes leading by fine roots. This project will be conducted in forest controlled experiment plots of Biodiversity-Ecosystem Functioning (BEF-China) project in Xingangshan town, Jiangxi province. Fine roots under different diversity levels will be harvested with sequential coring method in different seasons, and will be divided into live and dead roots of different functional root groups. Fine-root productivity and turnover rate will be calculated for both groups. Combining with biotic and abiotic factors, this project aims at analyzing the temporal and spatial dynamic patterns of different fine-root functional groups at community and species levels and key influential factors, and studying the effects and related mechanisms of tree species richness on the productivity and turnover of different fine-root groups. Our study will be helpful for expanding the theory system of biodiversity-ecosystem functioning, and providing scientific basis for using species diversity to raise forest quality.

混交林是营造和改良人工林的重要手段。通过树种混交增加物种多样性，能提升地上生态系统的生产力和稳定性，但物种多样性对地下根系生长的影响还有待研究。细根为直径小于2mm的根系，贡献了全球陆地生态系统NPP的33%。利用功能划分法又可分为吸收根和运输根，由于二者周转速率存在差异，划分功能群后细根对全球陆地生态系统NPP的贡献降为22%。因此基于功能划分法研究细根的生长和周转，有利于准确理解根系主导的生态学功能和过程。本项目拟在江西新岗山BEF-China森林控制实验样地实施，通过连续根钻法获取不同多样性水平的细根生物量和死亡量，并估算不同功能群细根生产力和周转速率，结合生物和非生物因子，阐明群落和物种水平上不同功能群细根的时空动态格局及影响因素，揭示物种丰富度对不同功能群细根生产力和周转的影响及相关机制，以期拓展生物多样性与生态系统功能研究的理论体系，为利用物种多样性提升森林质量提供科学依据。

在全球气候变化和物种丧失的背景下，生物多样性与生态系统功能的关系成为了生物多样性科学领域热点问题之一。但是相关研究大多集中在草地生态系统或森林地上生态系统，物种多样性怎样影响地下生态系统的功能及过程还不清楚。细根一般定义为直径小于2 mm的根系，由于较快的更新速率，对陆地生态系统的生物化学循环非常重要。因此，研究物种多样性对细根动态的影响有助于我们更全面地理解生物多样性与生态系统功能的关系。本研究利用土芯法和内生长芯法获取了根系生物量、再生长量并测量了相关根系性状。细根现存生物量和再生长量都随着物种丰富度的增加而增加。物种丰富度促使细根生物量在垂直方向上分布更加均匀，而这种根系分布模式提高了细根现存生物量。样方的每个个体都有明确的行列位置，我们根据根系取样周围的树木计算了香农多样性指数，并测量了样方土壤总碳、总氮含量和地形因子。利用结构方程模型和线性混合效应模型分别分析了生境因子之间的关系及细根生长对生境因子的响应。结构方程模型表明，样方物种丰富度显著降低了土壤总碳和总氮含量，增加了土壤碳氮比，从而增加了细根生长。线性混合效应模型表明，细根生长只与土壤碳氮比显著正相关。本研究表明森林生物多样性对细根生长具有积极作用，为全面理解物种多样性与生态系统功能关系提供了新的实验证据；而且，生物多样性对细根生长具有间接作用，补充了生物多样性效应的理论机制。