Roles of pathogens on replacement of tree seedlings in heterogeneous light environments in a temperate forest: a reciprocal seed sowing experiment

1. In forest communities, the Janzen–Connell (J-C) hypothesis proposes that species diversity is maintained by non-competitive distance- and/or density-dependent seedling mortality caused by host-specific natural enemies. However, the effects of pathogen associations from nearby conspecifics vs. heterospecifics remain unknown in spatially heterogeneous light environments. 2. Seeds of hardwood species Cornus controversa (Cornus) and Prunus grayana (Prunus) were sown beneath 6–7 Cornus and Prunus adults in both the forest understory (FU) and in gaps (Gap) created by felling all woody vegetation near the focal adults. Seedling growth, mortality, killing agents (e.g. pathogens that cause damping-off and leaf diseases), and root infection by arbuscular mycorrhizal fungi (AMF) were investigated. 3. We found strong habitat effects on the expression of soil fungi beneath both tree species. Seedling mortality caused by soil-borne damping-off pathogens was greater in FU than in Gap, and AMF infec...1. 在森林群落中，詹森-康奈尔假说（Janzen–Connell hypothesis）提出，物种多样性由宿主特异性天敌引发的非竞争性距离依赖型和/或密度依赖型幼苗死亡率得以维持。然而，在空间异质性光照环境中，邻近同种与异种个体的病原菌关联所产生的生态效应仍未明确。 2. 本研究将硬阔树种灯台树（Cornus controversa，梾木属）与灰叶稠李（Prunus grayana，李属）的种子，分别播种于6至7株同种成年个体下方，实验设置了两种生境：森林下层（forest understory, FU），以及皆伐目标成年个体周边全部木本植被后形成的林隙（Gap）。后续对幼苗的生长状况、死亡率、致死因子（例如引发猝倒病与叶部病害的病原菌）以及丛枝菌根真菌（arbuscular mycorrhizal fungi, AMF）的根系侵染情况进行了调查。 3. 本研究发现，两种树木下方的土壤真菌群落特征均受到显著的生境调控。由土传猝倒病原菌引发的幼苗死亡率在森林下层显著高于林隙，且丛枝菌根真菌侵染……