Evolutionary history underlies plant physiological responses to global change since the Last Glacial Maximum

Background/Question/Methods         

Assessing family and species-level variation in physiological responses to global change across geologic time is critical for understanding factors that underlie changes in species distributions and community composition. Ancient plant specimens preserved within packrat middens are invaluable in this context since they allow for comparisons between co-occurring plant lineages that exhibit different ecological, physiological, and life history traits. Here we used modern and ancient plants preserved within packrat middens from the Snake Range, NV to investigate the physiological responses of a mixed montane conifer community to changes in atmospheric [CO₂], climate, and nutrient availability since the last glacial maximum (LGM). In particular, we used a conceptual model to infer relative changes in stomatal conductance (g_s) and maximum photosynthetic capacity (A_max) from measures of leaf stable carbon isotope ratios, stomatal characteristics, and leaf %N. In doing so, this study provides new insights into fundamental mechanisms that underlie species, family, and community-level responses to long-term global change.

Results/Conclusions

Our results indicate that most of the sampled taxa decreased g_s and/or A_max in response to changing conditions since the LGM. However, plant families differed in the timing and magnitude of these physiological responses. Additionally, leaf-level responses were more similar within plant families than within co-occurring species assemblages. Our results also suggest that leaf-level physiology combined with unique life history traits influenced the distribution of Pinus longaeva, the dominant glacial species in the Snake Range. More broadly, however, it appears that changes in leaf-level physiology cannot fully explain shifts in community composition since the LGM. Instead, similar responses within plant families indicate that evolutionary history is an important determinant of physiological adaptation to global change.