Factors affecting above- and belowground plant pathogens
Our results provide empirical support that both Evenness andProneness can shape community pathogen loads, highlighting the importance of including host community indices into disease ecology models (Liu et al., 2017; Halliday et al., 2019). Pronenessincreased with elevation, indicating that plant communities at higher elevations contained greater proportions of competent species (i.e. species with good growth but weak defensive abilities, thus harboring more pathogens; Liu et al., 2017), though this point was not fully supported by the study in the Swiss Alps (Halliday et al., 2021). We attribute the variation in the plant species level proneness index partly to the growth-defense trade-off, which suggests that the enhancement of defense systems comes at the cost of reduced growth, based on the assumption that plants share limited resources (Coley et al., 1985; Cappelli et al., 2020). The community proneness index was the best predictor of pathogen loads along the elevational gradient in the alpine meadow (explaining ~ 34.0% of variation), suggesting that plant communities dominated by host species with higher proneness (i.e. weak defense systems) might experience more serious disease. Thus, our study calls for the inclusion of host community composition into models that predict infectious disease (Halliday, Rohr, et al., 2020).
Our study provided empirical evidence for a negative biodiversity-disease relationship, which ecologists have long debated (Rottstock et al., 2014; Halliday et al., 2019; Halliday and Rohr, 2019; Liu, Chen, et al., 2020). Pielou’s evenness index was an effective predictor of pathogen load, even along such a sharp elevation gradient, consistent with the theoretical prediction that host community evenness should be a better predictor of disease than species richness (Chen and Zhou, 2015). The evenness index incorporates the distribution of relative abundances among host species, which can better describe the mechanism of encounter reduction between host biodiversity and plant diseases (Mitchell et al., 2002; Liu et al., 2016). Therefore, a higher community evenness index translates into a lower probability of focal individuals being infected through encounter reduction (Keesing et al., 2006).