Contrasting effects of sheep and cattle grazing on foliar fungal diseases by changing plant community characteristics
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May 11, 2023 version files 51.07 KB
Feb 12, 2024 version files 51.07 KB
Abstract
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.
README
VARIABLES USED IN ANALYIS OF CHINESE GRAZING EXPERIMENT | |
---|---|
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 |