Effects of Different Livestock Grazing on Foliar Fungal Diseases in an Alpine Grassland on the Qinghai-Tibet Plateau

Abstract

In grassland ecosystems, the occurrence and transmission of foliar fungal diseases are largely dependent on grazing by large herbivores. However, whether herbivores that have different body sizes differentially impact foliar fungal diseases remains largely unexplored. Thus, we conducted an 8-year grazing experiment in an alpine grassland on the Qinghai-Tibet Plateau in China and tested how different types of livestock (sheep (Ovis aries), yak (Bos grunniens), or both)) affected foliar fungal diseases at the levels of both plant population and community. At the population level, grazing by a single species (yak or sheep) or mixed species (sheep and yak) significantly decreased the severity of eight leaf spot diseases. Similarly, at the community level, both single species (yak or sheep) and mixed grazing by both sheep and yak significantly decreased the community pathogen load. However, we did not find a significant difference in the community pathogen load among different types of livestock. These results suggest that grazing by large herbivores, independently of livestock type, consistently decreased the prevalence of foliar fungal diseases at both the plant population and community levels. We suggest that moderate grazing by sheep or yak is effective to control the occurrence of foliar fungal diseases in alpine grasslands. This study advances our knowledge of the interface between disease ecology, large herbivores, and grassland science.

Keywords: alpine grasslands; community pathogen load; fungal diseases; herbivores; species richness.

Figure 1

View of the study site (a); schematic diagram of the experimental design, including the number of yaks and sheep in each treatment and the area of the sample plots (b).

Figure 2

Effects of different livestock types on the community pathogen load (a) and community disease proneness (b). Different lowercase letters indicate significant differences between different livestock types at p < 0.05 (Tukey’s HSD). Error bars represent ±SE.

Figure 3

Effects of different livestock types on the pathogen load of different plant functional groups, i.e., Cyperaceae (a), forb (b), grass (c), and legume (d). Different lowercase letters indicate significant differences between different livestock types at p < 0.05 (Tukey’s HSD). Error bars represent ±SE.

Figure 4

Relative importance of plant species disease severity in predicting community pathogen load based on random forest analysis (the percentage of increase in the mean variance error (MSE)). Significance levels: * 0.01 < p < 0.05.

Figure 5

Effects of different livestock types on plant vegetation characteristics, i.e., species richness (a), Shannon–Weiner index (b), Pielou’s evenness index (c), plant total coverage (d), and plant aboveground biomass (e). ns indicates no significant difference; different lowercase letters indicate significant differences between different livestock types at p < 0.05 (Tukey’s HSD). Error bars represent ±SE.

Figure 6

Relationships between disease severity of individual species and plant community characteristics (PAB, plant aboveground biomass; PTC, plant total coverage; Je, Pielou’s evenness index; H′, Shannon–Weiner index; SR, species richness). Blue indicates a negative correlation, red indicates a positive correlation, and the depth of the color represents the magnitude of the correlation coefficient. Asterisks indicate statistical significance (* p < 0.05; ** p < 0.01).

Figure 7

Relationships between community pathogen load and species richness (a), Shannon–Weiner index (b), Pielou’s evenness index (c), plant total coverage (d), plant aboveground biomass (e), and community disease proneness (f). The black fitted regression lines indicate significant relationships at the level of p < 0.05, with 95% confidence intervals shown as shaded areas. The coefficient of determination (R²) and p values are shown.