Rising atmospheric carbon dioxide (CO2) concentrations can alter interactions between plants and other organisms, either by directly impacting plant mutualists or antagonists, or indirectly by modifying plant traits that mediate their interactions. Although increased CO2 concentrations have clear effects on leaf physiology, much less is known about how elevated CO2 affects the microorganisms that live inside of those leaves. Leaf microbiota, such as foliar endophytic fungi, can have important effects on plant physiology and ecology, so understanding their response to elevated CO2 concentrations may be important for predicting plant response to climate change. Using the Soybean Free Air gas Concentration Enrichment (SoyFACE) site at the University of Illinois, we tested the effects of elevated CO2 concentration on 1) plant traits, 2) endophytic fungal community composition, and 3) fungal traits. We collected leaves from field-grown soybean (Glycine max) individuals from three plots with elevated CO2, and three paired control plots with ambient CO2. We surface-sterilized plant tissue and used culture-dependent methods to describe the fungal endophyte communities.
Results/Conclusions
Soybean grown under elevated CO2 were taller and had increased leaf mass per area (LMA) compared to soybean grown under control conditions, and fungal community composition differed between the two environments. Surprisingly, fungal diversity was higher in the ambient plots, despite there being less habitable space for fungi per unit area of leaf (i.e., lower LMA) in these plants. In fact, while LMA was positively correlated with fungal diversity in ambient plots, as LMA increased under elevated CO2, fungal diversity decreased slightly, suggesting that under increasing atmospheric CO2 levels there may be selection for or against specific members of endophytic communities that reduces overall diversity, even as habitable leaf space increases. Finally, the most common endophyte under ambient conditions, Sporobolomyces sp., decreased in abundance under elevated CO2 conditions. Sporobolomyces is a yeast, and was found to inhibit growth of other fungi in culture. Thus, as CO2 concentrations increase, we may see changes in the defensive or antagonistic traits of plant-associated microbiota.