氮有效性增加对细根解剖、形态特征和菌根侵染的影响

氮(N)有效性增加对森林生态系统结构和功能有重要影响.细根作为树木地下最为活跃的组分,其对N有效性增加的响应已成为森林生态学研究的热点.本文对N有效性增加条件下细根解剖构造、形态和菌根侵染的响应趋势及潜在机制进行了综述.N有效性增加导致细根皮层厚度、皮层层数和皮层细胞直径下降,外皮层上通道细胞数量减少,而中柱和木质部横截面积,以及导管(或管胞)直径、数量和壁厚度均增加,根解剖构造的响应与植物激素浓度变化有关;N有效性增加后菌根侵染率下降,比根长(单位根干质量的长度)在外生菌根树种中普遍下降,而在内生菌根树种中增加;根直径和组织密度的变化趋势则表现出较大的种间差异.这些个体根和树种水平上的结果对于理解森林生态系统水平上的碳和养分循环具有重要意义.最后,根据目前研究中存在的不足提出了今后的研究方向与问题.

Effects of elevated N availability on anatomy,morphology and mycorrhizal colonization of fine roots: A review.

Increase of nitrogen (N) availability can greatly affect the structure and function of forest ecosystems. Fine root is critical to belowground ecological processes, thus its response to elevated N availability has become a focus of ecological researches. This article reviewed the trend and under-lying mechanism of fine root response to elevated N availability, including root anatomy, morphology and mycorrhizal colonization. We found that cross-sectional areas of root stele and xylem and the diameter, number and wall thickness of xylem vessel (tracheid) all increased, however, cortex thickness, the number of cortical cell layer, diameter of cortical cell and number of passage cell in exodermis decreased with higher N availability. The response of root anatomy was closely related to plant hormones. In addition, mycorrhiza colonization rate decreased after N fertilization, while specific root length (root length per unit root mass) generally decreased in arbuscular mycorrhizal species, while increased in ectomycorrhizal species. By contrast, the root diameter and tissue density varied widely among species under higher N status. These findings based on individual roots and species provided deeper understanding of carbon and nutrient cycles in terrestrial ecosystems. In addition, we discussed some knowledge gaps and proposed several research outlooks for guiding future researches.