Leaf economic strategies of a sclerophyllous plant (Eurya japonica): commonalities and particularities of trait correlation structures in low-moisture and low-phosphorus habitats

Sclerophylly proves an advantageous strategy in a variety of stressful environments. However, it is less clear how multiple phenotypic traits in sclerophyllous plants are integrated to accomplish proper functions under specific stressors. This study measured 10 leaf traits in a sclerophyllous species, Eurya japonica Thunb., in the Zhoushan Archipelago, eastern China, to examine how the structures of trait correlation (i.e. phenotypic integration) vary between two habitats with contrasting moisture and phosphorus (P) availability. Overall, the trait correlation matrices were similar between the two habitats under study (Mantel r > 0.5), reflecting a consistent trade-off between leaf outspreading (i.e. leaf area/mass ratio) and water-use efficiency (measured by δ13C). Stomatal conductance was correlated with leaf area, thickness and area/mass ratio only in the dry, P-rich habitat, whereas it was robustly correlated with leaf P per unit area in the wet, P-poor habitat. Moreover, leaf water-use efficiency was robustly correlated with leaf P and N per unit area in the dry habitat, but not so in the low-P one. These differences in trait correlation structures illustrate that the pathways of strategic compromise under contrasting stressors were locally specialised. This study highlights the importance of phenotypic integration as an emergent 'trait' in sustaining viable strategies.