Stem hydraulics mediates leaf water status, carbon gain, nutrient use efficiencies and plant growth rates across dipterocarp species

P>Stem vascular system strongly influences structure and functioning of leaves, life-history, and distribution of plants. Xylem structure and hydraulic conductivity of branches, leaf functional traits, and growth rates in 17 dipterocarp species in a mature plantation stand were examined to explore the functional relationships between these traits. Maximum hydraulic conductivity on the bases of both sapwood and leaf area (k(L)) were positively correlated with midday leaf water potential in the rainy season, stomatal conductance, area-based maximum photosynthetic rate, photosynthetic N (PNUE) and P use efficiencies (PPUE), and mean height and diameter growth rates. Moreover, k(L) was positively correlated with mesophyll thickness and mass-based maximum photosynthetic rate. These results revealed the mechanistic linkage between stem hydraulics and leaf photosynthesis through nutrient use efficiency and mesophyll development of leaves. A detrended correspondence analysis (DCA) using 37 traits showed that the traits related to stem hydraulics and leaf carbon gain were loaded on the first axis whereas traits related to light harvesting were loaded on the second axis, indicating that light harvesting is a distinct ecological axis for tropical canopy plants. The DCA also revealed a trade-off between photosynthetic water use efficiency and hydraulic conductivity along with PNUE and PPUE. The congeneric species were scattered fairly close together on the DCA diagram, indicating that the linkages between stem hydraulics, leaf functional traits, and plant growth rates are phylogenetically conserved. These results suggest that stem hydraulics mediates leaf water status, carbon gain, nutrient use efficiencies, and growth rates across the dipterocarp species. The wide variation in functional traits and growth rates among these dipterocarp species along with the trade-offs mentioned above provide a possible explanation for their co-existence in tropical forest communities.