Allelochemical and soil fungi co-determine conspecific density
dependence in a temperate forest
Abstract
Ecological theory predicts that high local diversity observed in plant
communities could be maintained by soilborne pathogens and allelopathic
autotoxicity that trigger negative conspecific density dependence (CDD),
but mutualistic fungi and allelopathic promotion could simultaneously
counteract these biotic processes. Here, we combined a phenolic-acid
addition experiment of tree seedlings associated with different
mycorrhizal fungi with an extensive field survey to test the
allelopathy-fungi mechanisms relate to CDD in a natural temperate
forest. Overall, allelopathic effects on seedling growth were generally
stronger than fungal effects, and allelochemicals altered how plants
interacted with soil fungi in a dose-dependent manner. Contrary to
expectation, ectomycorrhizal trees suffered stronger negative CDD than
arbuscular mycorrhizal trees driven largely by allelopathy, although
ectomycorrhizal fungi could offset some of this allelopathic
autotoxicity. Together, allelopathy may thus be an important driver of
CDD via affecting both plants and plant-microbe interactions, although
the precise effects should be species specific.