UC Riverside

Mutualistic species interactions are ubiquitous. Every species on Earth is involved, directly or indirectly, in a net beneficial partnership. Through shifts in partner phenology and distribution, climate change can disrupt mutualistic interactions, resulting in altered interactions and modified communities. However, research has focused on pairwise mutualisms, neglecting the fact that species interact with multiple mutualists simultaneously. In this dissertation, I explore the effects of climate change on nitrogen-fixing soil microbes, legume plants, and their pollinators. Climate change is predicted to affect the activity and ranges of belowground mutualists which will lead to changes in host plant germination timing and success, water use efficiency, floral traits, and, consequently, bee pollinator behavior. In the following chapters, I use a multi-year snowmelt timing manipulation, historical legume leaf tissue samples, and common garden techniques to assess the effects of belowground mutualism loss via climate stress on legume functional traits and legume-solitary bee interactions. I find evidence that climate warming, advanced snowmelt, and drought can lead to a short-term loss of interactions between soil microbes and leguminous plants, consequently leading to shifts in germination phenology, the quality floral rewards, plant nitrogen content, and consequently, pollinator floral preferences. Such costs could translate into reduced fitness and novel selection pressures for bees and flowering plants in the short term. My dissertation highlights the importance of studying multiple mutualisms in a climate change context and serves to identify the effects of soil microbial mutualism loss on legumes and on higher-order mutualists, such as bees.