Contrasting effects of mammal grazing on foliar fungal diseases: patterns and potential mechanisms

Abstract

Summary Plant pathogens and their hosts often coexist with mammal grazers. However, the direction and strength of grazing effects on foliar fungal diseases can be idiosyncratic, varying among host plant species and pathogen types. We combined a 6 yr yak‐grazing experiment, a clipping experiment simulating different mammal consumption patterns (leaf damage vs whole‐leaf removal), and a meta‐analysis of 63 comparisons to evaluate how grazing impacts foliar fungal diseases across plant growth types (grass vs forb) and pathogen life histories (biotroph vs necrotroph). In the yak‐grazing experiment, grazing had no significant effect on disease severity, and grasses experienced a higher disease severity than forbs; there was a significant interaction between pathogen type and grazing. In both the yak‐grazing experiment and meta‐analysis, grazing decreased biotrophic pathogens (mainly rusts and powdery mildew), but did not affect necrotrophic pathogens (mainly leaf spots). The clipping experiment suggested that grazers might promote infection by necrotrophic pathogens by producing wounds on leaves, but inhibit biotrophic pathogens via leaf removal. In conclusion, our three‐part approach revealed that intrinsic properties of both plants and pathogens shape patterns of disease in natural ecosystems, greatly improving our ability to predict disease severity under mammal grazing.

Interactions between mammalian grazers and plant pathogens: an elephant in the room?

“…In this issue of New Phytologist, Liu et al . (2021; pp. 345–355) tested whether plant growth form, the consumption pattern of the herbivores and pathogen life history determined how grazing affected disease.…”

“…One such knowledge gap is revealed and explored in this issue of New Phytologist by Liu et al . (2021; pp. 345–355), who used a combination of experimental studies and a meta‐analysis to provide novel insights into effects of grazing mammals on fungal pathogens in grasslands.

‘The study by Liu et al.

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“…Although interactions between some primary consumers have been a subject of active research over the last few decades, surprisingly large knowledge gaps remain with regard to other players in these interactions. One such knowledge gap is revealed and explored in the recently published article in New Phytologist by Liu et al (2021;doi: 10.1111/nph.17324), who used a combination of experimental studies and a meta-analysis to provide novel insights into effects of grazing mammals on fungal pathogens in grasslands.…”

“…Fig.1Mechanisms by which mammal grazing can affect fungal pathogen infection, as discussed in the recent article published in New Phytologist byLiu et al (2021; doi: 10.1111/nph.17324). Mammals can remove mycelium and spores of pathogens together with the consumed plant material and thus reduce overall infection.…”

“…Fig.1Mechanisms by which mammal grazing can affect fungal pathogen infection, as discussed in this issue of New Phytologist byLiu et al (2021; pp. 345-355).…”