Arbuscular mycorrhizal (AM) fungi are ubiquitous throughout the plant kingdom, and particularly important in grasslands. AM fungi deliver mineral nutrients such as nitrogen (N) and phosphorus (P) to plants in exchange for carbohydrates. Despite this important role in N and P cycling, their interactions with micronutrients, like calcium, are largely unexplored. Interactions with calcium (Ca) may be particularly important because of its role in the intracellular signaling system that helps hyphal tip growth. We determined how additions of Ca both alone and in conjunction with N and P affect the colonization rates of AM fungi in little blue stem (Schizachyrium scoparium). This perennial grass is a dominant graminoid in prairies across the US, including our study site, a coastal tallgrass prairie in Texas. Using a carbon steel soil auger (7.2cm diameter), we sampled S. scoparium roots in a large-scale (30m x 30m plots), factorial-designed fertilization experiment that manipulated Ca and N&P (n=8 replicate plots x 4 S. scoparium individuals x 4 treatments=128 total root samples). Each sample was washed to isolate root samples and stained with trypan blue, and we determined AM fungal colonization by quantifying the number of arbuscules, hyphae, and vesicles for each individual.
Results/Conclusions
We saw that Ca with N&P had significant effects on the overall rate of AM fungal colonization. We also saw independent effects of each nutrient on the degree of hyphal and vesicle colonization in the roots of S. scoparium. These results suggest that the micronutrient Ca is important for determining AM fungal colonization. We also observed at the field site that little blue stem found strictly in Ca plots were smaller in biomass in comparison to the plots that were treated with N&P; this includes the plots treated in conjunction with Ca. Taken together, these results suggest that AM fungi may benefit from Ca inputs, but this does not extend to an increased positive effect on the plant. Increased tropical storm intensity in this area may increase the amount of Ca deposited in these ecosystems, so better understanding its role in belowground and aboveground processes is crucial to maintaining ecosystem functioning. This work represents an important first step to understand more fully the effects of micronutrients on mycorrhizal fungi in terrestrial ecosystems.