Leaf-trait responses to environmental gradients in moorland communities: contribution of intraspecific variation, species replacement and functional group replacement

The values of many important traits of plants in a community change along environmental gradients. Such changes may involve intraspecific variation and replacement by species that have different trait values. We hypothesized that they also involve the variation within and among functional groups (FGs) to the environmental dependence of trait values at the community level. We studied environmental dependence of trait values in 27 moorlands at various scales and analyzed to what extent intraspecific variation, species replacement within FGs and FG replacement contribute to the gradient of community trait values. The community structure in moorlands was influenced mainly by two environmental factors: temperature and water condition. Plants inhabiting sites with low temperature and low-pH generally tended to have lower maximum leaf height, greater leaf mass per area, and smaller leaf size. At the community level, site-mean of maximum leaf height and leaf size generally increased with increasing temperature and water pH. Our analysis demonstrated that the relative contributions of intraspecific variation, species replacement within FGs and FG replacement differed depending on combinations of the traits and environments. The contribution of FG replacement varied considerably among cases (0.6-34.5 %). Species replacement within FGs, which has received little attention in previous studies, was most responsible for the community-level changes (31.6-65.3 %) and intraspecific variation also made a large contribution (22.9-57.9 %). Understanding such various mechanisms involving intraspecific variation and species replacement should help us better predict how the structure and functioning of moorland plant communities will respond to climate change.