Does the individual matter? Quantifying the role of intraspecific variation and phenotypic plasticity in plant responses to climate change

Abstract

Our ability to understand the underlying morphological and physiological responses of plants to changing temperature and precipitation regimes is crucial, as we seek to construct increasingly complex models to predict how ecosystems may respond to climate change. Here, I investigate trait variation and phenotypic plasticity at the species and population level using glasshouse experiments, field transplant manipulations, and large scale, multi-habitat, multi-species observational work.

Climate change models predict warming temperatures and increasingly variable precipitation and snow cover across the Australian Alps. Plasticity in water use traits and responsiveness to extremes in temperature may become important for the establishment and persistence of Australian alpine plants. Plants from relatively lower elevations inhabit a more heterogeneous environment with more frequent frosts, greater temperature extremes, and higher evapotranspiration. To test whether adaptive plasticity may be more common at lower elevations, I investigated the extent of plasticity and its adaptive value using a glasshouse and field experiment.

To test the responses of reduced water availability and determine if plasticity varies across elevation, seeds of three alpine species from low and high elevation sites were grown under ample and water-limited conditions in a glasshouse. Patterns of plasticity were highly variable among species and among traits within species, however, responses were independent of elevation. Furthermore, there were few instances of adaptive plastic responses. Given the lack elevational variation in plant responses, there is need to understand the extent to which microhabitat variation within a given elevation may be important in shaping the persistence of these alpine species.

Climatic changes leading to decreasing snowfall and earlier snowmelt in alpine areas may expose the underlying plants to frosts and wide range of thermal extremes. To test how populations from different elevations vary in their capacity to respond to such thermal extremes, I conducted a field manipulation using alpine seedlings in open-top chambers (OTCs). I proposed that seedlings from environments with greater thermal ranges would have a greater capacity to acclimate to warming temperatures and tolerate freezing events. The warmer conditions provided by the OTCs significantly increased seedling mortality, but seedlings that survived grew slightly taller. Warming did not affect freezing resistance, leaf production or photosynthetic efficiency. There was little evidence of intraspecific variation. A warming climate exposing plants to extreme events may lead to a reduction in seedling establishment and survival, although survivors may not exhibit any ongoing detrimental effects.

The links between ecology and evolution are driven by the variation in species traits, and these inform our capacity to predict species and community responses to changing conditions. In this final section, I sought to determine: 1) the extent of variation in trait values and plasticity at habitat to site scales, and among species and individuals; 2) whether patterns of variation were consistent across plant functional traits, and; 3) whether trait variation was associated with increased fitness consistent with adaptive plastic responses. I used field data from three habitats, six sites, 36 species, and repeated sampling of 30 individuals per species, resulting in over 200,000 leaf samples. Differences between species explained the largest component of variation in trait values and trait plasticity. A large proportion of variance in plasticity was explained by among individual variation, which, as the level at which selection acts, is important. That said, there were very few instances where indices of plasticity correlated with measures of fitness, providing little evidence of adaptive plasticity across the study.