Grman, E. and T. Robinson
Presented at the ASM at Estes Park (2006-09-01 to 2012-09-23 )
Arbuscular mycorrhizal fungi (AMF), ubiquitous plant symbionts, play a pivotal role in plant access to soil nutrients in grasslands. Plants limited by either N or P provide carbon to fungi in exchange for nutrients. However, when N and P are abundant and direct plant uptake can satisfy plant growth demands, reduced plant allocation to mycorrhizae should decrease fungal growth.Previous grassland LTER cross-site research suggests that the growth responses of AMF to long-term N additions may depend on underlying soil N:P. At a site where P was abundant relative to N (low soil N:P; Cedar Creek), N additions decreased fungal growth. At a site where P was more scarce (high soil N:P; Konza Prairie), N additions increased fungal growth. However, other characteristics also varied among sites. We propose to experimentally test the role of soil N:P in mycorrhizal growth at a site where soil N:P is intermediate (Kellogg Biological Station). In a successional grassland, we will cross P manipulations with long and short term N additions. Long term control and N fertilization plots contain divergent AMF communities and light levels; single-year N additions may avoid these confounding variables. We will manipulate P through separate additions of P and gypsum (to reduce P availability). We will measure soil N and P, light, colonization of the roots of several plant species, plant biomass, extraradical hyphal biomass, spore diversity, and fungal community composition.If N:P controls AMF biomass and root colonization, we should see an increase in fungal growth in plots with very high N:P (N fertilization and P reduction) or very low N:P (N control and P addition), relative to growth in intermediate N:P (N control and P control; N and P additions). This experiment will test whether soil N:P drives the correlative results of previous cross-site work. Understanding the role of site-specific characteristics, such as soil N:P, will help us predict the impacts of N enrichment on plant productivity and reliance on symbioses.KBS is a critical site for this experiment because of its intermediate N:P and inclusion in the previous study. However, we hope to collaborate with researchers at other LTER sites in the previous study. By conducting N and P manipulation experiments at sites with pre-existing extreme values of N:P, we will gain a more general understanding of resource flows between plants and fungi and their effects on plant and fungal growth.
Back to meeting | Show |