Soil-borne pathogens have widely been recognized as an important agent for maintaining biodiversity (i.e., the Janzen-Connell effect). However, there is little understanding how climate change may affect the interaction between specialized pathogens and their hosts. We conducted field warming experiments using open-top chambers and collected soil-borne fungal DNA metabarcoding data to assess the effect of soil-borne pathogens on seedling recruitment of tree species in response to climate warming in a temperate forest and a subtropical forest. We specifically address (i) whether the strength of the Janzen-Connell effect is stronger in the subtropical forest than that in the temperate forest as assumed previously, (ii) how the Janzen-Connell effect responds to elevated temperature in these two forest ecosystems and (iii) how elevated temperature influences the soil-borne fungal composition and frequencies (especially for pathogenic fungi).
Results show that, although seedling mortality of study tree species induced by soil-borne pathogens was increased by warming treatment in both forests, increased mortality odds ratio of seedlings in the temperate forest was higher than that in the subtropical forest. Warming climate could intensify severity of plant diseases possibly because warming would increase host plant susceptibility and promote pathogen reproduction. Our results suggest that global warming would likely increase the effect of specialized pathogens on maintaining tree species diversity in temperate and the subtropical forests.