Understanding how desert ecosystems are responding to increasing atmospheric CO₂ concentrations is important because deserts are a strong carbon sink. The Nevada Desert FACE (Free Air CO2 Enrichment) Facility (NDFF), in the Mojave Desert, was designed to test the effects of long-term exposure to elevated CO₂ concentrations in desert ecosystems and simulate future atmospheric conditions. The goal of our study was to determine the effects of long-term CO₂ exposure on mycorrhizal fungi. Mycorrhizal fungi are obligate biotrophs, exchanging fixed carbon from plants for limiting soil resources like phosphorous and water. Mycorrhizal fungi likely play an important role in the cycling and uptake of carbon from the atmosphere and in the exchange of carbon between soils and the rhizosphere in deserts. We hypothesized that hyphal length would increase with CO₂ concentration, because increased carbon in the atmosphere should lead to increased nutrient exchange between plants and fungi as plants increase photosynthetic activity. We also hypothesized that fungal length would be greatest in under shrub sampling locations. To test this, we analyzed soil samples (0-10cm depth) taken from ambient, elevated and control CO₂ treatment plots in interspaces, under shrub, and under grass locations at the NDFF for hyphal length after ten years of treatments.
Results/Conclusions
Contrary to our hypothesis, analysis of hyphal length across CO₂ treatments (P=0.44) and sampling locations (P= 0.21) revealed no significant effects of CO₂ concentration sampling location on hyphal length. We offer two alternative hypotheses for these results. First, plants may not be increasing their photosynthesis rates with elevated CO2 because water is too limiting. In our next steps, we will compare the mycorrhizal hyphal lengths directly to the associated plant biomass. Second, biocrusts (a consortium of cyanobacteria, mosses and lichens) are prominent at this site and might be interacting with mycorrhizal fungi. Biocrusts fix ecosystem relevant levels of carbon and nitrogen. The fungal loop hypothesis suggests that nutrient exchange between the rhizosphere and biocrust may occur via mycorrhizal hyphae. If true, then mycorrhizal activity would be greatest in 0-1cm of soil underneath biocrusts. We will examine mycorrhizal hyphae from these depths next. Understanding how the components of desert ecosystems interact is important to understanding how they will react to climate change, which impacts carbon storage, and might offer insight into future conservation efforts.