The Effect of Nutrient Availability on the Ecological Role of Filamentous Microfungi: Lessons from Elemental Stoichiometry

Ecological stoichiometry theory helps us to better understand trophic interactions by analyzing the imbalances in the relative supplies of key elements (carbon, nitrogen, and phosphorus) between organisms and their resources. However, the mechanisms that control elemental stoichiometry in different taxonomic groups and the effects of nutrient supply imbalances are not yet clear. Aquatic microfungi are an ecological group of microorganisms ranging from those adapted to complete their life cycles in aquatic habitats to those that occurring in water fortuitously. Aquatic fungi are important regulators of plant productivity, community dynamics, and diversity in nutrient-poor and extreme ecosystems. Because aquatic fungi are heterotrophs, it has been assumed that they possess high degree of stoichiometric homeostasis. However, data concerning their elemental composition and their degree of homeostasis remain scarce. Herein, we analyzed the C:N:P stoichiometry of mycelia in ten aquatic microfungi isolated from three hydrological systems with different nutrient conditions within Cuatro Cienegas Basin (CCB). Our hypotheses were (a) variations in C:N:P ratios reflect divergent life history strategies between the three environments, independently of the fungal taxa involved, and (b) C:N:P ratios reflect physiological adjustments associated with specific taxa, independent of the environmental characteristics. Our results provide some support for the first hypothesis, as the apparent capacity for elemental stoichiometry regulation in the aquatic microfungi was not linked to phylogenetic relationships but appeared to be an adaptation to resource availabilities in the environment in which they grew. The microfungi isolated from the most oligotrophic site within the CCB (Pozas Rojas) most strongly regulated their elemental stoichiometry in comparison with fungal isolates from other sites within CCB.