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

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.

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。

我国南方人工林中针叶纯林超过60%，结构单一、生态功能不稳定。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。本项目依托野外人工针叶林间伐补阔试验平台，结合温室盆栽实验，研究了乔木树种、林下灌草和补植阔叶树的细根形态特征、根际效应及养分偏好的时间变异规律；基于氮吸收速率与吸收根菌根侵染率及形态属性的关联性研究，探讨了不同肥力梯度下的植物种间作用。发现亚热带人工林乔、灌、草物种均偏好吸收铵态氮，氮素吸收速率与吸收根菌根侵染率和形态属性密切相关。湿地松（与含笑混交）和木荷（与马尾松混交）通过权衡吸收根生产量与无机氮吸收速率来响应种间竞争。在适应环境时，阔叶树苗吸收根会增大菌根侵染和比根长来提高氮素获取。与针叶树混交时，种间作用会抑制阔叶树的氮吸收速率。但施肥会导致针、阔叶树种间偏利关系发生变化，使原本中性或偏利阔叶树的种间关系改变为偏利针叶树。上述结果为亚热带人工针叶林结构优化、不同土壤肥力下的补植阔叶树优选及补植后期施肥管理提供重要的理论依据。

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