DOI: 10.5061/dryad.dbrv15f60
title: Contrasting effects of sheep and cattle grazing on foliar fungal diseases by changing plant community characteristics

description: Pathogens are ubiquitous in ecosystems and play a key role in affecting
 host community structure. In grasslands large grazing animals such as
 cattle and sheep have been shown to affect foliar fungal pathogens.
 However, theory and empirical studies have come to conflicting conclusions
 because grazers can directly and indirectly impact pathogens through a
 wide variety of mechanisms and various grazers may impact pathogens in
 different ways. A better understanding of the mechanisms by which grazers
 impact pathogens is important for a fundamental understanding of herbivore
 pathogen interactions and also to optimize grazing managements to reduce
 pathogen outbreaks. Here, we investigate multiple mechanisms by which
 livestock grazing impacts foliar fungal pathogens in grasslands. We
 integrate a large-scale grazing experiment, with a removal experiment
 manipulating plant density and litter biomass, to identify direct and
 indirect effects of two herbivores on pathogens with different life
 histories (biotrophs and necrotrophs), in a temperate grassland in
 northeast China. We found that grazing by cattle and sheep had contrasting
 impacts: cattle grazing significantly reduced pathogen load, of both
 biotrophs and necrotrophs, whereas sheep grazing increased biotrophic
 pathogen load, but did not affect the necrotrophs. The grazing effects
 were mostly indirect and mediated by different impacts of the herbivores
 on plant community structure. Cattle grazing reduced pathogen load because
 it reduced the abundance of susceptible, fast-growing plants, and the
 overall density of plants, while sheep grazing increased pathogen
 infection because it reduced the abundance of resistant plant species.
 Plant diversity also reduced pathogen infection but these effects were
 independent of the herbivores. Our results show that different herbivores
 can have contrasting impacts on pathogen infection through contrasting
 impacts on host community competence. This suggests the importance of
 considering multiple mechanisms simultaneously to evaluate the impact of
 herbivores on host-pathogen interactions.
description: | VARIABLES USED IN ANALYIS OF CHINESE GRAZING EXPERIMENT | | |
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 | | | | | GRAZING EXPERIMENT | | | YEAR | YEAR OF DATA COLLECTION | |
 CATTLE | CATTLE GRAZING TREATMENT | | SHEEP | SHEEP GRAZING TREATMENT | |
 BLOCK | EXPERIMENTAL BLOCK | | PLOT | EXPERIMENTAL PLOT WITHIN WHICH
 GRAZING TREATMENTS WERE EMBEDDED | | QUADRAT | QUARAT FOR SAMPLING | |
 BIOTROPH | BIOTROPHIC PATHOGEN LOAD | | NECROTROPH | NECROTROPHIC PATHOGEN
 LOAD | | PL | COMMUNITY TOTAL PATHOGEN LOAD | | DENSITY | NUMBER OF
 INDIVIDUAL PLANTS (/M2) | | SLA\_CWM | COMMUNITY WEIGHTED MEAN SPECIFIC
 LEAF AREA (CM2/G) | | RICHNESS | SPECIES RICHNESS | | FORB\_COVER | FORB
 COVER (%) | | GRASS\_COVER | GRASS COVER (%) | | LITTER | LITTER BIOMASS |
 | L\_CHINENSIS | L. CHINENSIS ABOVEGROUND BIOMASS (G/M2) | | FORBS | OTHER
 GRASS ABOVEGROUND BIOMASS (G/M2) | | OTHER | FORB ABOVEGROUND BIOMASS
 (G/M2) | | LEGUME | LEGUME ABOVEGROUND BIOMASS (G/M2) | | TOTAL | PLANT
 COMMUNITY TOTAL ABOVEGROUND BIOMASS (G/M2) | | TEMPERATURE | AIR
 TEMPERATURE () | | HUMIDITY | AIR HUMIDITY (%) | | | | | REMOVAL
 EXPERIMENT | | | YEAR | YEAR OF DATA COLLECTION | | TREATMENT | DENSITY
 AND LITTER MANIPULATION TREATMENTS | | DR | DENSITY REDUCTION | | LR |
 LITTER REMOVAL | | DL | DENSITY REDUCTION AND LITTER REMOVAL
 SIMULTANEOUSLY | | CONTROL | NO DENSITY AND LITTER TREATMENT | | BLOCK |
 EXPERIMENTAL BLOCK | | PLOT | EXPERIMENTAL PLOT WITHIN WHICH DENSITY AND
 LITTER TREATMENTS WERE EMBEDDED | | QUADRAT | QUARAT FOR SAMPLING | |
 JUNE\_BIOTROPH | BIOTROPHIC PATHOGEN LOAD IN JUNE 2021 | |
 JUNE\_NECROTROPH | NECROTROPHIC PATHOGEN LOAD IN JUNE 2021 | | JUNE\_PL |
 COMMUNITY TOTAL PATHOGEN LOAD IN JUNE 2021 | | AUGUST\_BIOTROPH |
 BIOTROPHIC PATHOGEN LOAD IN AUGUST 2021 | | AUGUST\_NECROTROPH |
 NECROTROPHIC PATHOGEN LOAD IN AUGUST 2021 | | AUGUST\_PL | COMMUNITY TOTAL
 PATHOGEN LOAD IN AUGUST 2021 | | AUGUST\_DENSITY | NUMBER OF INDIVIDUAL
 PLANTS (/M2) IN AUGUST 2021 |