基于植物细根属性和养分吸收偏好性研究针叶林下补植阔叶树种的适应策略

我国南方人工林中针叶纯林超过60%，结构单一、生态功能较差且不稳定。林下补植阔叶苗木是目前最主要的人工林结构优化措施。浅层土壤中灌草细根生物量比重通常较高，且比乔木具有更大的形态可塑性和更强的养分竞争能力。因此，影响补植阔叶树苗生长的不仅仅是针叶林中的乔木，林下灌草也有重要作用。本项目将依托已有的人工针叶林补阔试验，基于植物种间细根的形态可塑性、生长物候多样性、空间分布差异性和养分吸收偏好，结合同位素示踪技术，研究不同林型（马尾松、湿地松）人工林中不同生境下（坡上、坡下）乔、灌、草和补植阔叶树的细根形态特征、生产力及养分偏好的时空变化格局，探讨补植阔叶树与乔、灌、草的养分竞争机制，揭示补植阔叶树苗在不同林型和生境中的适应策略，为亚热带人工针叶林结构优化提供科学支撑。

Coniferous monocultures comprise approximately 60% of all coniferous plantations in southern China. The planting monocultures are associated with low stability and vulnerable to disturbances. Replanting broadleaf seedlings under pure coniferous plantations is an important measure to optimize the structure of monospecific forests. In the shallow soil layer, fine root biomass of understory vegetation contributes a lot to the total fine root biomass. Moreover, the fine roots of understory vegetation have higher plasticity in terms of morphological traits and thus present higher nutrient absorption rates. Therefore, both the trees and understory vegetation would affect the performance of broadleaf seedlings. This project will investigate the interspecific differences in fine root morphological plasticity, phenology, vertical distribution and nutrient absorption preference based on a study site of supplanting coniferous plantations with polycultures. Combined with the stable isotope method, we will study the temporal and spatial variations in fine root morphological traits, production and nutrient absorption preference for the trees, shrubs, herbs, and broadleaf seedlings under different stand types (Pinus massoniana vs.Pinus elliottii) and habitats (uphill vs. downhill). This project will clarify the mechanisms of interspecific competition between broadleaf seedlings and different life forms (trees and understory vegetation) in coniferous monocultures and illustrate the adaption strategies of broadleaf seedlings under different stand types and habitats. The findings will have important implications in optimizing the stand structure of coniferous monocultures.