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).