Trophic control of grassland production and biomass by pathogens

Abstract

Current theories of trophic regulation of ecosystem net primary production and plant biomass incorporate herbivores, but not plant pathogens. Obstacles to the incorporation of pathogens include a lack of data on pathogen effects on primary production, especially outside agricultural and forest ecosystems, and an apparent inability to quantify pathogen biomass. Here, I report the results of an experiment factorially excluding foliar fungal pathogens and insect herbivores from an intact grassland ecosystem. At peak in control plots, 8.9% of community leaf area was infected by pathogens. Disease reduction treatment dramatically increased root production and biomass by increasing leaf longevity and photosynthetic capacity. In contrast, herbivory reduction had no detectable effects at the ecosystem or leaf scale. Additionally, biomass of foliar fungal pathogens in the ecosystem was comparable with that of insect herbivores. These results identify pathogens as potential regulators of ecosystem processes and promote the incorporation of pathogens into trophic theory.

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

“…While individual host species may vary in key traits directly affecting pathogen infection such as resistance or tolerance (Barrett et al 2009), overall community structure and architecture may additionally alter pathogen presence and transmission (Mitchell 2003). Complementary resource use with increased plant species and functional diversity influences community structure and three-dimensional space-filling capacity (Spehn et al 2000), and thus microclimatic conditions within the plant community.…”

“…Thus, plant communities may differentially affect the presence, infection, and diversity of plant pathogens (Keesing et al 2010, Scherber et al 2010a) via abundance and spatial distribution of susceptible and resistant genotypes, and of structural three-dimensional space-filling components (Garrett and Mundt 1999, Altizer et al 2003, Alexander 2010, King and Lively 2012. Plant community diversity can affect both pathogen communities and host-pathogen dynamics (Mitchell et al 2002, Ferrer and Gilbert 2003, Mitchell 2003, Keesing et al 2006, 2010. The increased number of potential host species may enable a diverse pathogen community of specialized pathogens (Hudson et al 2006) while also supporting the presence of generalists (Gilbert 2002, Keesing et al 2006.…”

Species richness and species identity effects on occurrence of foliar fungal pathogens in a tree diversity experiment

“…From the host species' perspective, lower levels of pathogen load would be considered positive, since an intact leaf area would provide a higher photosynthetic gain. As a fungal infection finally results in a higher mortality of single leaves or whole plants, and thus, presents a type of disturbance, a decreased pathogen load would finally be translated into a higher net primary production of the whole plant community (Mitchell 2003, Berger et al 2007). Thus, biodiversity ecosystem functioning would be negatively affected by leaf pathogens, because flux rates of matter and energy in the system would be reduced (Jiang et al 2008).…”

A model of co-occurrence: segregation and aggregation patterns in the mycoflora of the crayfish Procambarus clarkii in Lake Trasimeno (central Italy)

“…Until today, documentation of changes in fungal community represents a challenging research project little attempted (see Hu et al 2010). Even if fungal ectoparasite assemblage seems to receive little attention in scientific studies, these associations assume a great importance since they are fundamental components in shaping community, ecosystem structure and energy flow (Mitchell 2003;Kuris et al 2008). …”