Soil nutrients cause threefold increase in pathogen and herbivore impacts on grassland plant biomass

Abstract

Grasslands play a critical role in the global carbon (C) cycle, covering a quarter of the Earth's land surface and contributing up to 20% to the total terrestrial C sink (Xia et al., 2014). As with most ecosystems, C accumulation in grasslands reflects the balance and seasonal variation of C inputs via photosynthesis (gross primary production, GPP) and C emissions from respiration by microbes, plants and animals (ecosystem respiration, ER). Observational studies and field experiments manipulating food webs have shown that plant consumers

Plant growth–defense trade‐offs are general across interactions with fungal, insect, and mammalian consumers

“…2014; Dybzinski & Tilman, 2007;Eskelinen et al, 2022). Previous work in this experiment found that more biomass is allocated above than belowground following nutrient addition pointing to a potential shift in competition for light (Zaret et al, 2023). Overall forbs had the largest range of responses to consumer and nutrient manipulations and C4 grasses the least (Figure 4).…”

“…Under higher resource scenarios, consumers are predicted to have modified impacts on plant hosts due to a variety of mechanisms ranging from modified susceptibility or immunity in plants to herbivory or infection (Smith, 2007) as well as microbes and herbivores changing consumption strategies and preference among hosts under increased nutrients (Peters et al, 2006). Previous work in this system shows amplified foliar fungal and arthropod impacts on plant biomass in fertilized plots (Zaret et al, 2023), suggesting that a shift toward poorly defended species following nutrient addition (reflecting the growth-defense trade-off) has implications for ecosystem processes such as carbon cycling. Studies integrating defense trade-offs and ecosystem processes in the context of global changes such as increasing nutrient supplies would help clarify this knowledge gap.…”

“…Most plants in this system are perennial and changes in biomass are predominantly due to vegetative growth. The community is dominated by C4 and C3 grasses, forbs, and legumes with a mean aboveground biomass of approximately 200 g m −2 (Zaret et al, 2023). Plant communities at this site experience high levels of pathogen damage relative to other grasslands F I G U R E 1 Environmental manipulations reveal defense trade-offs among grassland plant species.…”

Grazing decreases net ecosystem carbon exchange by decreasing shrub and semi-shrub biomass in a desert steppe

“…Grazing by livestock influences the productivity and stability of grassland ecosystems, which in turn generates feedback mechanisms on the carbon cycle. However, the factors underlying the complex changes of vegetation and soil as a result of grazing and their impact on the processes underlying carbon cycling remain poorly understood (Yuanet al 2011;Hussain et al 2015;Oram et al 2023;Zaret et al 2023). Our results from a 16-year long grazing intensity manipulation study in a desert steppe grassland show that grazers alter patterns of net ecosystem exchange primarily via their negative influence on the biomass of shrub and semi-shrub, which play a prominent role in ecosystem functions.…”

Nitrogen Addition and Heterotroph Exclusion Affected Plant Species Diversity–Biomass Relationship by Affecting Plant Functional Traits

“…Heterotrophs include herbivores, predators, scavengers, and pathogens. Previous studies showed that the removal of arthropods and foliar fungi increased plant biomass [ 8 , 9 , 10 ], while the removal of soil fungi increased the forb biomass in grassland systems [ 11 ]. Removing foliar fungi also increased the biomass of trees in forest systems [ 12 ].…”