Abstract:
Summary . It is well known that whole-plant water-use efficiency (transpiration efficiency of carbon gain, TEC) varies among plant species with different photosynthetic pathways. However, less is known of such variation among tree species within the C3 group. Here we measured the TEC of seven C3 tropical tree species. Isotopic analyses (delta13C, delta18O, and delta15N) and elemental analyses (carbon and nitrogen) were undertaken to provide insight into sources of variation in TEC. . Plants were grown over several months in approx. 80% full sunlight in individual 38-l containers in the Republic of Panama. Soil moisture content was nonlimiting. . Significant variation was observed in TEC among the C3 tree species. Values ranged from 1.6 mmol C mol-1 H2O for teak (Tectona grandis) to 4.0 mmol C mol-1 H2O for a legume, Platymiscium pinnatum. . Variation in TEC was correlated with both leaf N concentration, a proxy for photosynthetic capacity, and oxygen-isotope enrichment, a proxy for stomatal conductance. The TEC varied with C-isotope discrimination within species, but the relationship broke down among species, reflecting the existence of species-specific offsets.
