The importance of above-belowground interactions to the global change responses of two foundation species

Background/Question/Methods

Recent research demonstrates that aboveground and belowground communities have reciprocal influences on one another that can alter ecosystem function.  However, the extent to which these interactions are influenced by global change factors such as altered climate regimes and invasive species remains poorly understood.  We synthesize results of studies in two systems that illustrate the complexity and importance of linking the study of aboveground and belowground ecology to understand native plant responses to drought stress and to an invasive species that disrupts a key belowground mutualism. 

Results/Conclusions

Field, greenhouse and common garden studies of pinyon pine, Pinus edulis, a dominant tree of southwestern woodlands, demonstrate complex linkages between plant genetics, resistance to herbivory, mycorrhizal fungal community composition, plant neighbor interactions and drought tolerance.  Importantly, the fungal community linked to better growth and survival during drought is also associated with higher susceptibility to cone and seed herbivory, and reduced tree reproduction.  Above-belowground dynamics thus may have a strong influence on the population trajectories of this species as the southwest warms and dries.  In Fremont cottonwoods (Populus fremontii), an invasive plant competitor, tamarisk (Tamarix spp), alters the abundance and community composition of mycorrhizal fungi, while simultaneously increasing the abundance of non-mycorrhizal fungi, including plant pathogens. Reductions in mycorrhizal fungi have little impact on tamarisk, but strong negative effects on cottonwoods. A recently introduced biocontrol agent, the tamarisk leaf beetle (Diorhabda elongata), defoliates tamarisk, leading to altered litter dynamics and some tamarisk mortality.  Preliminary data suggest that, with time, feeding by the beetle alters the soil as well, including changes in root-associated fungi that could feedback to affect the likelihood of cottonwood re-establishment in tamarisk-dominated areas. These data suggest that aboveground herbivory alters the dynamics of plant-soil feedbacks. Taken together, these two studies argue that the responses of foundation plant species to global change may require better understanding of above-belowground interactions.