Water relations of five tropical tree species on Barro Colorado Island, Panama.

Diurnal curves of xylem pressure potential (P) and leaf conductance (C) were measured for five tree species of the lowland tropical forest on Barro Colorado Island, Panama. Measurements were taken just before and just after the beginning of the rainy season. The species studied were: Cordia alliodora, Faramea occidentalis, Heisteria concinna, Macquira costaricana, and Trichilia cipo.For all species, predawn (base P) and daytime values of P increased markedly after the beginning of the rainy season. Diurnal patterns of C were quite diverse. C. alliodora showed a decline in C during the day whereas F. occidentaus, H. concinna, and M. costaricana showed little change. Conductance of the last three species was lower before the first rains. T. cipo exhibited more complicated behavior for P and C. Before the rainy season, low values of base P and midday P were observed (-26 bars and-39 bars, respectively). Conductance was also low. After the first rains, base P increased to-4 bars. At this time, midday P and C appeared to respond to vapor pressure deficit (VPD), being less on a day with high VPD than on a day with low VPD.