Thursday, August 9, 2007 - 2:10 PMCOS 135-3: Diversification of hydraulic traits in nine Cordia species growing in tropical rainforests with contrasting precipitation
Brendan Choat, UC Davis, Lawren Sack, University of Hawaii, and N. Michele Holbrook, Harvard University.
Inter- and intra- specific variation in hydraulic traits was investigated in nine Cordia (Boraginaceae) species growing in three tropical rain forests with differing mean annual precipitation. Interspecific variation was examined for the different Cordia species found at each site, and populations of the widespread species Cordia alliodora were studied at each site to investigate intraspecific variation. We hypothesized that (a) there would be adaptive variation in hydraulic traits of Cordia species growing at sites differing in precipitation and that (b) C. alliodora would show greater plasticity in hydraulic traits than the other Cordia species with more limited distributions. Strong intra- and inter- specific variation were observed in vulnerability to drought-induced embolism. Species growing at drier sites were substantially more resistant to embolism than species growing at moister sites, and the same pattern was observed for populations of C. alliodora across the precipitation gradient. However, traits related to hydraulic capacity, including stem xylem vessel diameter, sapwood specific conductivity (Ks) and leaf specific conductivity (KL) all varied strongly but independently of precipitation. For C. alliodora, xylem anatomy, Ks, KL and Huber value varied little between populations growing at different sites, with Ks and KL being consistently high relative to other species at each site. Ks and KL were strongly related to theoretical conductivity, but independent of Huber value. Constitutively high hydraulic capacity coupled with plasticity or genotypic variation in vulnerability to embolism and leaf tissue water relations would contribute to the ability of C. alliodora to establish and compete across a wide precipitation gradient. The large variation across species at each site suggest functional diversification at a given precipitation regime which might contribute to co-existence.