Researchers from the Institute of Applied Ecology of the Chinese Academy of Sciences have found that the composition of mycorrhizal fungi and the dominance of certain species jointly shape patterns of forest plant species richness and abundance.

Their study was published in Communications Earth & Environment.

Understanding how environmental conditions and biological interactions regulate plant diversity is fundamental to ecology. Climate and topography act as environmental filters that influence species distributions. Interactions among organisms, including fungal symbiosis and plant competition, further shape local communities.  

Many forest plants form symbiotic relationships with either arbuscular mycorrhizal (AM) or ectomycorrhizal (EcM) fungi. These two strategies differ in nutrient acquisition and may affect plant coexistence through resource use, plant-soil interactions, and competition. However, the joint regulation of different vegetation layers, including trees, shrubs, and herbs, by mycorrhizal composition and species dominance remains insufficiently understood.

To investigate these relationships, the researchers including LIU Bo, LIANG Yu, WANG Xugao, SUN Tao and YANG Jian, together with collaborators, conducted vegetation surveys from 1,917 plots across 38 nature reserves in northeastern China. They combined field observations of different vegetation layers with environmental information to identify the pathways linking climatic and topographic gradients, mycorrhizal strategies and plant community structure.

The researchers found that tree species richness peaked at intermediate levels of AM and ECM dominance. This finding supports the "mycorrhizal mixture hypothesis," which suggests that the coexistence of different mycorrhizal strategies promotes plant diversity. In contrast, higher species dominance generally reduced species richness across the tree, shrub, and herb layers while increasing community abundance.

The mycorrhizal composition of canopy trees can influence the plants growing beneath them. Forests with AM-dominated canopies were generally associated with higher species richness in the understory, but lower abundance, compared with forests with EcM-dominated canopies. These cross-layer effects were especially evident in shrub communities.

The researchers also found that climatic and geographical differences in northeastern China indirectly influenced forest communities by altering mycorrhizal composition and species dominance. Warmer, wetter temperate forests were more frequently associated with AM dominance and higher plant richness. In contrast, colder, drier boreal forests were more frequently associated with ECM dominance and lower species richness.