Do plant physiological traits explain changes in plant abundance as a response to climate warming and competition?

Background/Question/Methods . Plant functional traits have been used to predict species coexistence, life history strategies and demographic changes. Despite the success of this approach in recent years, many of the previous studies have concentrated on morphological and structural traits, or used mean trait values per species. However, morphological traits do not always correlate well with physiological functions, and using average trait values ignores differences in phenotypic plasticity between species. Instead, direct measurements of plant physiology taking into account species’ ability to modify their traits in response to the environment should provide better predictions. To test this, we measured traits related to gas exchange and water and nutrient uptake of fourteen alpine plant species. The plants are part of a long-term field experiment in the Swiss Alps, in which turfs of alpine vegetation have been transplanted to lower elevation, mimicking climate warming. The changes in the community structure with warming and the introduction of novel low-elevation competitors were monitored for three years. We tested if the physiological traits significantly differed between species and if they responded to changes in temperature and competitive interactions.

Results/Conclusions . The fourteen species differed in their physiological traits, and none showed signs of photosynthetic or respiratory acclimatization to warmer temperature or physiological responses to the presence of novel competitors. Thus, plasticity in physiological traits does not seem to be important in explaining changes in plant community structure as a response to warming and to novel competitors. Next, we assessed if the physiological traits can predict changes in demographic rates and if they do, whether knowledge of these traits improves predictions compared to morphological traits alone. Uncovering the link between plant physiology and demographic changes could be invaluable in predicting how species distributions change in response to a warming climate. On the other hand, if detailed physiological measurements do not improve our predictions of demographic changes, future studies could concentrate on morphological traits which are easy to measure. Overall, our results provide novel insights into the mechanisms linking plant functional traits to performance.