Higher plant diversity promotes higher diversity of fungal pathogens, while it decreases pathogen infection per plant

Abstract

Abstract. Fungal plant pathogens are common in natural communities where they affect plant physiology, plant survival, and biomass production. Conversely, pathogen transmission and infection may be regulated by plant community characteristics such as plant species diversity and functional composition that favor pathogen diversity through increases in host diversity while simultaneously reducing pathogen infection via increased variability in host density and spatial heterogeneity. Therefore, a comprehensive understanding of multi-hostmulti-pathogen interactions is of high significance in the context of biodiversity-ecosystem functioning. We investigated the relationship between plant diversity and aboveground obligate parasitic fungal pathogen (''pathogens'' hereafter) diversity and infection in grasslands of a long-term, large-scale, biodiversity experiment with varying plant species (1-60 species) and plant functional group diversity (1-4 groups). To estimate pathogen infection of the plant communities, we visually assessed pathogen-group presence (i.e., rusts, powdery mildews, downy mildews, smuts, and leaf-spot diseases) and overall infection levels (combining incidence and severity of each pathogen group) in 82 experimental plots on all aboveground organs of all plant species per plot during four surveys in 2006.Pathogen diversity, assessed as the cumulative number of pathogen groups on all plant species per plot, increased log-linearly with plant species diversity. However, pathogen incidence and severity, and hence overall infection, decreased with increasing plant species diversity. In addition, co-infection of plant individuals by two or more pathogen groups was less likely with increasing plant community diversity. We conclude that plant community diversity promotes pathogen-community diversity while at the same time reducing pathogen infection levels of plant individuals.

Herbivore and pathogen effects on tree growth are additive, but mediated by tree diversity and plant traits

“…Although we can only speculate on the underlying mechanism, previous studies have shown that while plant species richness reduced pathogen loads, it increased pathogen diversity (Hantsch et al., 2013; Rottstock et al., 2014). A higher pathogen diversity, with a higher probability of spillover of pathogen species from one tree species to another in mixtures with more tree species, could lead to a more diversified response (owing to a more diverse set of pathogens) and defense induction of plants (Spoel, Johnson, & Dong, 2007).…”

“…Findings from other forest ecosystems indicate that we can expect negative effects of tree species richness on pathogen damage (Hantsch, Braun, Scherer‐Lorenzen, & Bruelheide, 2013; Rottstock et al., 2014). In contrast, and opposing results from temperate forests (e.g., Guyot, Castagneyrol, Vialatte, Deconchat, & Jactel, 2016; Kambach et al., 2016), findings from natural forests in our study region revealed positive effects of tree species richness on herbivore damage (Schuldt et al., 2010).…”

Linking ecology and plant pathology to unravel the importance of soil-borne fungal pathogens in species-rich grasslands

“…Pinpointing the actual 'enemies' (and their interactions with other 'bad' and 'good guys'), such as herbivores (e.g. insects and nematodes (Bagchi et al 2014;de Deyn et al 2003;Knops et al 1999)) and pathogens (viruses, bacteria, and fungi (Maron et al 2011;Moore and Borer 2012;Packer and Clay 2000;Petermann et al 2008;Rottstock et al 2014)), has proven difficult, especially belowground (Alexander 2010). There is interest in the role of fungal pathogens to explain the maintenance of biodiversity (Bever et al 2015;Gilbert 2002), but in this review we focus on the other way around: the role of plant species diversity to reduce the build-up of soilborne fungal disease (Latz et al 2012;Mommer et al 2018;Yang et al 2015).…”

Positive effects of plant diversity on soil microbial biomass and activity are associated with more root biomass production

“…R 2 (regression coefficient) and P-values are shown next to significant fitted lines. Zhang et al 2010;Eisenhauer et al 2011;Rottstock et al 2014) may be due to root biomass production being mediated by other factors. Contrast to our question, facilitation among species did not lead to positive effects of plant diversity on the soil microbial functions.…”

“…However, actual observations showed positive (Stephan et al 2000;Zak et al 2003;Eisenhauer et al 2011;Lange et al 2015), negative or no response (Johnson et al 2008) of soil microbial biomass, activity and diversity to increasing plant diversity (Zhang et al 2010;Rottstock et al 2014). Soil micro-organisms are mostly heterotrophic; thus, they decompose plant material for food or use plant exudates (LorangerMerciris et al 2006).…”