季风常绿阔叶林演替系列菌根资源及其与群落多样性的关系

Mycorrhizae respond to plant diversity in monsoon evergreen broadleaved forest succession choronsequence

随着森林生态系统的正向演替,植物物种多样性、群落结构、生产力以及土壤条件均会发生显著的变化,这些变化对菌根类型和多样性会产生不同程度的影响。为了探讨群落结构和功能的变化对菌根资源可能产生的影响,选择季风常绿阔叶林及其演替系列上的代表性森林生态系统为对象,对菌根化根系、菌根类型和菌根真菌孢子密度进行调查,并结合已有的群落信息和土壤养分状况,分析在森林演替过程中菌根资源的变化情况和可能的影响因素。结果表明:季风常绿阔叶林各演替阶段的森林生态系统中菌根化比例接近70%,但不同演替阶段森林的优势菌根类型存在明显的差异。处于演替初期的马尾松(Pinus massoniana)林以丛枝菌根为主,占菌根总数的78%;演替中期的针阔叶混交林中的外生菌根占有绝对优势,占75%,是丛枝菌根的3倍;演替顶级的季风常绿阔叶林中的外生菌根和丛枝菌根的比例相当。马尾松林的菌根真菌孢子密度最高,每20 g风干土壤中的孢子数量高达2 925个,是针阔叶混交林的2.5倍,季风常绿阔叶林的2倍。演替系列上的森林生态系统的菌根类型的差异与植物物种多样性和群落结构,尤其是林下的灌木、草本层密度存在一定的相关性,同时也受土壤养分状况的影响。马尾松林具有较丰富的草本植物和较高的草本层密度,并且该森林的土壤相对贫瘠,这些条件都有利于丛枝菌根真菌侵染草本植物的根系形成丛枝菌根并产生大量孢子。针阔叶混交林中外生菌根的优势主要受该森林中外生菌根植物在群落组成上的绝对优势影响。季风常绿阔叶林的物种丰富,群落结构复杂,因此该森林呈现了两种类型菌根优势相当的现象。该文的结果表明,随着季风常绿阔叶林演替的进行,菌根资源在类型上会出现较大的分异,而这种变化受植物物种数量、群落结构的影响,与土壤养分状况存在一定的关系,并且不同演替阶段森林生态系统影响菌根组成的因素存在差异。

Plant species diversity, community structure, productivity and edaphic factors varied significantly with forest succession, these variations may influence the diversity of mycorrhizae. To understand how forest structure and fimction impact on mycorrhizae at ecosystem level, three subtropical forests were chosen along a forest succession series in South China to investigate mycorrhizae, ectomycorrhizae （ ECM ）, arbuscular mycorrhizae （ AM ）, and mycorrhizal fungal spores in the top soil （ 0-20 cm depth ）. Potential influences of forest structure on mycorrhizae were analyzed based on field census together with plant diversity and soil nutrients. The results showed that nearly 70% of fine roots less than 2 mm diameter in the top soil of each forest were colonized by mycorrhizal fungi, but dominate mycorrhizae types varied significantly in the three successional forests. AM accounted for 78% of total mycor- rhizae in the pine forest at early successional stage, ECM contributed to 75% of mycorrhizae in the mixed forest at middle succes- sional stage, and AM and ECM contributed equivalently to total mycorrhizae in the monsoon evergreen broadleaved forest at late succession stage. Mycorrhizal fungal spore density was highest in the pine forest （2 925 spores per 20 g dry soil）, which was 2.5 and 2 times of those in the mixed forest and monsoon evergreen broadleaved forest, respectively. We found that the difference of mycor- rhizae composition was associated with plant diversity, community structure and soil nutrient condition in successional forests. Spe- cies-rich and individual high density of grass plants and poor soil nutrient level in the pine forest may result in relatively high propor- tion of AM in the pine forest. Mycorrhizae were dominated by ECM resulting from the dominance of ECM plant in the mixed forest. Abundant plant species and complex community structure in the monsoon evergreen broadleaved forest contributed AM and ECM to equal distribution in the forest. These results suggest that mycorrhizae diversity changed with forest succession as a result of changes in plant diversity, community structure as well as soil nutrient condition, and the reasons varied at different successional stages.