Arbuscular mycorrhizal fungi are an important part of freshwater wetlands of the tallgrass prairie

Background/Question/Methods

A mutualistic symbiosis with arbuscular mycorrhizal (AM) fungi has been shown to increase plant uptake of mineral nutrients, especially phosphorus. Evidence of these and other benefits to plant growth in terrestrial systems far exceed our understanding of the symbiosis in freshwater wetlands environments. Historically, aquatic macrophytes were assumed to be non- mycorrhizal, as AM fungi are aerobic. However, evidence of mycorrhizal presence in wetland soils and wetland plant roots is growing. Still, it is unknown whether AM fungi provide the same level of nutrient acquisition and growth benefits to species in inundated soils as those in dry soils. We hypothesized that AM fungal abundance in soils would be negatively affected by increasing soil moisture. Transects along natural soil moisture gradients were established at four wetlands at each of two native tallgrass prairie sites in Oklahoma and Kansas. Over two growing seasons we quantified fungal abundance using phospholipid fatty acid analysis and hyphal ingrowth bags. Plant community composition and annual production were measured each year as well as using PLFA analysis to assess the microbial community. Other environmental measurements included soil nutrient analysis, percent soil moisture, and pH.

Results/Conclusions

Preliminary data show that the abundance of AM fungal biomass, as measured by phospholipid profiles, was strongly positively correlated to percent soil moisture measured in the fall of 2012, accounting for nearly half of the variation in this measure (p=0.0107, r²=0.49). AM fungal biomass was also strongly negatively related to soil potassium content (p=0.0021, r²=0.63) but was unrelated to nitrogen, phosphorus, or pH. Hyphal production at the Oklahoma site in 2012 was unable to predict AM fungal abundance, suggesting that the two measures of fungal abundance may be measuring different tissue fractions in the soil.  Surprisingly, AM fungi appear to be most abundant in plots with the highest soil moisture, suggesting that increases in soil inundation may not limit fungal growth as originally hypothesized. Furthermore, soil nutrients may be contributing to variation in AM fungal growth. Additional environmental variables will be incorporated to improve our understanding of the abiotic factors at work. Further investigation of the relationship between the plant and microbial community may also expose biotic connections within wetland plant communities.