Reyes et al. 2008 (Article) Epiphyte

Water vapour isotopic exchange by epiphytic bromeliads in tropical dry forests reflects niche differentiation and climatic signals

Author(s):—C. Reyes G., M. Mejia C., G.D. Jones & H. Griffiths

Publication:—Plant, Cell & Environment 31(6): 828-841. (2008) — DOI

Abstract:—The 18O signals in leaf water (?18Olw) and organic material were dominated by atmospheric water vapour 18O signals (?18Ovap) in tank and atmospheric life forms of epiphytic bromeliads with crassulacean acid metabolism (CAM), from a seasonally dry forest in Mexico. Under field conditions, the mean ?18Olw for all species was constant during the course of the day and systematically increased from wet to dry seasons (from 0 to +6?), when relative water content (RWC) diminished from 70 to 30%. In the greenhouse, progressive enrichment from base to leaf tip was observed at low night-time humidity; under high humidity, the leaf tip equilibrated faster with ?18Ovap than the other leaf sections. Laboratory manipulations using an isotopically depleted water source showed that ?18Ovap was more rapidly incorporated than liquid water. Our data were consistent with a Craig?Gordon (C-G) model as modified by Helliker and Griffiths predicting that the influx and exchange of ?18Ovap control ?18Olw in certain epiphytic life forms, despite progressive tissue water loss. We use ?18Olw signals to define water-use strategies for the coexisting species which are consistent with habitat preference under natural conditions and life form. Bulk organic matter (?18Oorg) is used to predict the ?18Ovap signal at the time of leaf expansion.

Keywords:—Bromeliaceae, Craig?Gordon model, epiphytes, evaporative enrichment, 18O, water vapour exchange