Root fungal symbionts interact with mammalian herbivory, soil nutrient availability and specific habitat conditions

Abstract

Herbivory, competition and soil fertility interactively shape plant communities and exhibit an important role in modifying conditions for host-dependent fungal symbionts. However, field studies on the combined impacts of natural herbivory, competition and soil fertility on root fungal symbionts are rare. We asked how mammalian herbivory, fertilization, liming and plant-plant competition affect the root colonization of arbuscular mycorrhizal fungi (AMF) and dark septate endophytic (DSE) fungi of the dicot herb, Solidago virgaurea. The 2-year full-factorial experiment was conducted in two contrasting habitats: non-acidic and acidic mountain tundra. We found that herbivory increased arbuscular colonization (i.e. the site of resource exchange) at fertile non-acidic sites, where vegetation was rich in species having AMF symbionts, whereas at infertile acidic sites, where plants having AMF symbiont are scarce, the response was the opposite. Herbivory of the host plant negatively affected DSE hyphal and sclerotial colonization in unfertilized plots, possibly due to reduced carbon flow from the host plant while there was no effect of herbivory in fertilized plots. DSE colonization was highest in unfertilized exclosures where soil nutrient concentrations were also lowest. Liming had a negative effect on DSE hyphal colonization, and its effect also interacted with herbivory and the habitat. Biomass removal of the neighboring plants did not affect the root colonization percent of either arbuscules or DSE. Our results show that the impacts of aboveground mammalian herbivory, soil nutrient availability and specific habitat conditions on belowground root fungal symbionts are highly dependent on each other. Arbuscule response to herbivory appeared to be regulated by specific habitat conditions possibly caused by differences in the AMF availability in the soil while DSE response was associated with availability of host-derived carbon. Our result of the relationship between herbivory and soil nutrients suggests an important role of DSE in ecosystem processes.

Fungal endophyte diversity in tundra grasses increases by grazing

“…Modification of the physiological environment is likely to affect the growth of fungal endophytes and possibly their hyphal structures. Colonization rate of arbuscular mycorrhizal fungi in common tundra plants is positively affected by grazing (Ruotsalainen & Eskelinen 2011). Likewise, damage to host plant tissue by herbivores could increase likelihood for new endophyte colonization (Clay et al 2005), increasing endophyte taxonomic unit richness in tundra grasslands.…”

Shading and litter mediate the effects of soil fertility on the performance of an understorey herb

“…Associations between fungal colonization and plant performance variables, when present, were somewhat negative (arbuscular mycorrhizae and abundance). These results could be due to the symbiotic nature of this biotic interaction -with plants allocating more carbon resources to fungi as plant nutrient or water stress increases (Ruotsalainen and Eskelinen, 2011), and reducing investment in symbiotic fungi under favourable abiotic conditions, leading to a weak relationship between colonization and abundance.…”

Hybridization inPopulusalters the species composition and interactions of root-colonizing fungi: consequences for host plant performance

“…Although not as well studied as AMF, DSE asymptomatically colonize plant roots, where they can function similarly to mycorrhizas (Newsham et al 2011; Porras-Alfaro and Bayman 2011). The two types of fungi often colonize roots simultaneously but can respond differently to environmental factors such as season of the year, herbivory, and soil nutrient availability (Mandyam and Jumpponen 2008;Ruotsalainen and Eskelinen 2011). Mandyam and Jumpponen (2008) observed substantial hyperparasitism of AM fungal structures by DSE, suggesting the potential for negative interactions between the two types of root symbionts.…”