Integration of plant responses to multiple stressors over time: interactions between winter and summer

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Response to multiple stresses has been a key topic in plant research, particularly in the context of global environmental change. While there has been a focus on plant responses to stresses that occur simultaneously, such as drought and heat stress, interactions between stresses also can occur sequentially in time. In some cases changes in the physiology of a plant in response to an initial stress can decrease vulnerability to future stress. However, in contrast to the potential benefits of this 'stress memory,' declines in plant condition in response to the initial stress can decrease the ability to tolerate future stress. Such interactions between multiple stresses have been studied extensively in the context of the growing season. In contrast, studies of carryover effects of winter stress on summer stress responses are lacking, despite the potential for variability in winter conditions to influence plant growing season performance substantially. Synergies between plant responses to variability in winter conditions and stress tolerance over summer are further complicated when examined in an ecosystem context. For example, frost not only has the potential to damage overwintering plants, but it also can affect soil microorganisms, nutrient availability, soil physical properties and moisture, and the interactions of these factors need to be accounted for when examining overall plant responses. ***The overarching question I will address with my research program is how variability in winter conditions alters the subsequent responses of herbaceous plants to stress over summer. I hypothesize that while frost damage over winter can reduce the performance of plants over summer, exposure to stress over winter nevertheless has the potential to reduce the vulnerability of plants to summer stresses. I will test this hypothesis and explore how soil processes can contribute to interactions between winter conditions and summer stress using a combination of controlled environment and field experiments. My short term objective is to examine how the timing and severity of frost exposure affect summer drought tolerance, the importance of direct effects versus the indirect effects in explaining interactions between frost and drought, and the performance tradeoffs that limit the abilities of plants with high stress memory to capitalize on extended growing season length. My long term objective is to examine the broader significance of plant winter/summer stress interactions in influencing plant community and ecosystem level processes, including plant species composition, soil nitrogen availability and retention, and plant litter decomposition. In terms of impact, my research will provide crucial information for predicting changes in species distributions and ecosystem function in response to extreme climate events, and transform how winter processes are integrated into plant and ecosystem ecology. *** **