Functional differences between herbs and woody species in a semiarid Mediterranean plant community: A whole‐plant perspective on growth, nutrient‐use and size

Abstract

Despite decades of research, a comprehensive understanding of trait coordination at the whole-plant level remains elusive. Furthermore, while the link between above-ground growth rates and leaf traits related to nutrient use is well established, much less is known about the below-ground compartment. Herbs and woody species exhibit distinct above-ground growth and nutrient-use strategies, but whether these differences extend to root traits below-ground remains unclear. We carried out a common garden experiment with 23 perennials (7 herbs and 16 woody species) coexisting in a Mediterranean shrubland and measured 17 above-ground and below-ground traits related to growth, nutrient use and size. We analysed the links between growth rate and nutrient use focusing especially on roots and considering potential differences between herbs and woody species. We also combined plant size data from experimental juveniles and field-sampled adults to determine the effects of life stage on whole-plant phenotypic integration. We found a significant relationship between growth rates (both above-ground and below-ground) and root nutrient-use strategies. Root diameter was negatively associated to growth rate only in herbs. Specific root area and root tissue density were positively and negatively correlated with growth rate, respectively, in both herbs and woody species. Moreover, we found significant differences in roots traits between herbs and woody species. Plant growth rate and root nutrient-use strategies were both positively associated to plant size (height and above-ground diameter) in juveniles, while a negative relationship was observed in adults. Our work provides insights on the links between whole-plant growth rate and nutrient-use strategies in species from a dry Mediterranan shrubland. Specifically, we show that whole-plant growth rate is strongly associated to root traits, with more acquisitive root nutrient-use strategies related to faster growth rates, which in turn translated to greater plant size in juveniles but smaller in adults. Our results also highlight root functional differences and contrasting patterns of whole-plant phenotypic integration between herbs and woody species, offering deeper insights into species coexistence in species-rich dry Mediterranean