资源环境科技发展态势分析平台

Tropical dry forests (TDFs) undergo a substantial dry season in which plant species must endure several months of drought. Although TDFs support a diverse array of plant growth forms, it is not clear how they vary in mechanisms for coping with seasonal drought. We measured organic tissue stable isotopic composition of carbon (delta C-13) and nitrogen (delta N-15) across six plant growth forms including epiphytes, terrestrial succulents, trees, shrubs, herbs, and vines, and oxygen (delta O-18) of four growth forms, to distinguish among patterns of resource acquisition and evaluate mechanisms for surviving annual drought in a lowland tropical dry forest in Yucatan, Mexico. Terrestrial succulent and epiphyte delta C-13 was around -14%, indicating photosynthesis through the Crassulacean acid metabolism pathway, and along with one C-4 herb were distinct from mean values of all other growth forms, which were between -26 and -29% indicating C-3 photosynthesis. Mean tissue delta N-15 across epiphytes was -4.95% and was significantly lower than all other growth forms, which had values around +3 parts per thousand. Tissue N concentration varied significantly among growth forms with epiphytes and terrestrial succulents having significantly lower values of about 1% compared to trees, shrubs, herbs and vines, which were around 3%. Tissue C concentration was highest in trees, shrubs and vines, intermediate in herbs and epiphytes and lowest in terrestrial succulents delta O-18 did not vary among growth forms. Overall, our results suggest several water-saving aspects of resource acquisition, including the absolute occurrence of CAM photosynthesis in terrestrial succulents and epiphytes, high concentrations of leaf N in some species, which may facilitate CO2 drawdown by photosynthetic enzymes for a given stomatal conductance, and potentially diverse N sources ranging from atmospheric N in epiphytes with extremely depleted delta N-15 values, and a large range of delta N-15 values among trees, many of which are legumes and dry season deciduous.