Intraspecific variation in responses to extreme and moderate temperature stress in the wild species, Solanum carolinense (Solanaceae)

Adaptation or acclimation to local temperature regimes has often been used as a proxy for predicting how plant populations will respond to impending novel conditions driven by human-caused climate change. To understand how plants may successfully respond to increasing air temperatures (extreme and moderate) in the future, we explored how temperature tolerance traits differ in populations of Solanum carolinense from northern (MN) and southern (TX) regions of the continental USA in a two-experiment study. In the first experiment, we compared the heat and cold tolerance in vegetative (sporophyte) and reproductive (male gametophyte) traits. In the second experiment, we studied if long-term heat influences plant development by examining how development in moderate heat affected reproductive structures and reproductive success. We found that temperature sensitivity differed between southern populations, which regularly experience extreme heat, and northern populations which do not. In contrast to our expectations, northern populations appeared more heat-tolerant than southern populations for vegetative traits such as chlorophyll stability and reproductive traits such as pollen germination. Our results are consistent with a heat-avoidance, rather than tolerance mechanism to mitigate extreme heat during pollen germination. In the second experiment, plants developing under the moderate heat treatment had significantly smaller reproductive structures and reduced seed production (27% fewer seeds on average than in the control treatment). Reproductive structures that developed in moderate heat were also reduced in size, particularly in the northern populations relative to populations from the south. We conclude that rising temperatures have the potential to incur substantial negative consequences for the reproductive success of individuals in this species and that some populations already mitigate stressful temperature conditions through phenotypic plasticity. Climate change is rapidly altering local temperature regimes with important biological impacts. We can gain insight into how plants specifically might respond to change in the future by studying how they have responded in the past. We explored how a single plant species that has grown both in warmer and cooler climates in the past responds to extreme temperatures. Our approach was to grow horsenettle (Solanum carolinense ) plants from Texas (South) and Minnesota (North) side by side and test for their tolerance to extreme high and low temperatures. Overall, we found that heat has definite negative effects but, surprisingly, northern plants were more thermotolerant in extreme temperatures (including heat). Southern plants, in contrast, may use avoidancestrategies in extreme heat. We conclude that populations of horsenettle have adapted ways to mitigate temperature stress, which may allow them to persist in the face of unprecedented global change.