GRASSLAND PLANT-SOIL-MICROBIAL RESPONSES TO CLIMATE EXTREMES AND LAND USE CHANGE

Abstract

Atmospheric warming is intensifying the global hydrological cycle, leading to increased occurrence of hydroclimatic extremes. Extreme droughts and deluges (persistent, torrential rain events) are already impacting ecosystems globally, with each leaving legacy effects of altered plant-soil interactions and ecosystem structure and function. The likelihood of co-occurring hydroclimatic extremes, such as droughts and deluges, increases with each degree of warming, yet little is known about how ecosystems will be affected when these events co-occur, particularly through altered interactions between plants and soil microbiomes. Similarly, climate solutions, such as renewable energy development, are altering abiotic determinants of ecosystem functionality (e.g., light and water availability). Solar photovoltaic energy (PV) is currently the cheapest, most scalable renewable energy option, though PV arrays occupy greater land area than alternative energy forms and may have unintended consequences for their host ecosystems. Thus, global change drivers are altering precipitation inputs and other abiotic factors in profound and unique ways, yet experimental assessments of their ecological impacts are limited and highly context dependent. Further, altered precipitation regimes and land use changes are likely to be especially consequential in grasslands, where water is the predominant limiting resource and PV deployment is most expansive. In this dissertation I investigated how these global change drivers impacted grassland ecosystems through altered plant function and soil microbial communities across the United States Great Plains. The first chapter examined the legacy effects of extreme drought on soil microbial communities across representative grassland types of the US Great Plains. The second chapter shifted focus to the shortgrass steppe of northeastern Colorado, where I investigated the ecosystem impacts of compounded extreme drought and deluge. The final chapter assessed plant-soil-microbial responses to a PV array in a C3 pasture in northeastern Colorado. Altogether, this work suggests that global change drivers will have immense contemporaneous and lasting impacts on grassland ecosystems, highlighting the pressing need to understand our ecosystems before they are irreversibly altered.