Litter nutrient release and allelopathy jointly contribute to the diversity–invasibility relationship

Elton's biotic resistance hypothesis suggests that diverse communities are more resistant to biological invasions. While below‐ground mechanisms play a crucial role in regulating the diversity–invasibility relationship, the role of litter as a key regulator of below‐ground processes remains underexplored. We used 15 common native plant species from temperate forests in China to create litter mixtures with five different levels of species richness (1, 3, 6, 9, 15), and the invasive plant Phytolacca americana as a model invader. We investigated how these litter mixtures affected the growth of the invader and explored the roles of nutrient release and allelopathy in this process. Our results demonstrate that increased litter species richness decreased the relative abundance of dominant saprotrophic fungi, resulting in reduced nutrient release and suppressed the growth of P. americana . Additionally, the allelopathic inhibitory effects of litter on the invader intensified as litter species richness increased. These findings elucidate the roles and mechanisms of litter species richness in resisting invasion, demonstrating that the combined effects of nutrient dynamics and allelopathy are major drivers of the diversity–invasibility relationship. We also highlight the potential of incorporating native plant litter into ecosystem management plans to enhance community resistance to invasions, as well as ecosystem stability and sustainability. Read the free Plain Language Summary for this article on the Journal blog.