Effects of allelopathy and availability of nutrients and water resources on the survival and growth of plant species in a natural Dacrydium forest

A comprehensive understanding of mechanisms of allelopathy and resource availability is critical for protecting rare and endangered species, biodiversity, and ecosystems. We treated 20 major plant species with three concentrations of an aqueous extract of Dacrydium pierrei Hickel litter and different irrigation and nutrients to compare the relative importance of allelopathy and resource availability on roots, stem growth, and seed germination, using bioassays. The results showed that the height, ground diameter, and aboveground biomass of individuals increased more quickly in the early stage, and the rate of increase tended to slow down in the later stages. The allelopathy was species specific (inhibitory, neutral, or promotive), and the survival rate and growth rate of saplings changed significantly along a resource treatment gradient (P < 0.05), indicating that the native species diversity was reduced by lower or higher resource availability in natural forests. The effect of allelopathy on trees was relatively weak during the treatments, and that of resource availability was relatively strong. Resource availability is relatively more important than allelopathy in mediating the reduction in plant biodiversity. Therefore, water and nutrient availability and the species and number of allelochemicals released by plants have substantial influences on the survival and growth of plant species in a natural Dacrydium forest.