Can Functional Traits Predict Plant Community Response to Global Change?

One primary goal at the intersection of community ecology and global change biology is to identify functional traits that are useful for predicting plant community response to global change. We used observations of community composition from a long-term field experiment in two adjacent plant communities (grassland and coastal sage shrub) to investigate how nine key plant functional traits were related to altered water and nitrogen availability following fire. We asked whether the functional responses of species found in more than one community type were context dependent and whether community-weighted mean and functional diversity were significantly altered by water and nitrogen input. Our results suggest varying degrees of context dependency. We found that plants with high leaf nitrogen concentration (specifically nitrogen fixers), shallow roots, and low leaf mass per unit area and plant-level transpiration were similarly negatively influenced by added nitrogen across community types. In contrast, responses to water manipulations exhibited greater context dependency; plants with high water-use efficiency, lower plant-level transpiration rates, and shallower roots were negatively impacted by simulated drought in the shrub-dominated community, but there was no significant relationship between these traits and changes in water inputs in the grassland community. Similarly, we found context dependency in community-wide trait responses to global change. Functional diversity tended to be higher in plots with reduced water as compared to those with added water in grassland, while the opposite trend was observed in coastal sage scrub. Our results indicate that some traits are strong predictors of species and community response to altered water and nitrogen availability, but the magnitude and direction of the response may be modulated by the abiotic and biotic context