Microbes, herbivores, and grassland carbon cycling responses to biodiversity loss and nutrient pollution

Abstract

Plants are primary producers of organic carbon and energy that supports a diverse array of consumersranging from large mammalian herbivores to microscopic fungi in the soil. Ecologists have long recognized the importance of herbivores and microbes in regulating plant biomass production, however the potential for global change factors such as plant biodiversity loss or nutrient pollution to modify consumer impacts on plants and ecosystem carbon cycling remains understudied. I address this knowledge gap using two experiments that manipulate the abundance of soil fungi, foliar fungi, insects, and mammalian herbivores in combination with manipulations of either plant diversity or soil nutrients in grassland ecosystems. This work reveals that both biodiversity loss and nutrient pollution modify the impact of herbivores and fungi on plant biomass production. In addition, I find that plant species interactions with both herbivores and pathogens are constrained by a plant growth-defense trade-off, and that soil fungal community responses to nutrient addition have cascading impacts on ecosystem carbon fluxes. By integrating plant interactions with multiple members of the food web, my work demonstrates how human-driven global changes will alter species interactions and the implications of these changes to critical ecosystem processes.