Plasticity of source‐water acquisition in epiphytic, transitional and terrestrial growth phases of Ficus tinctoria

ABSTRACT Despite continued studies on the ecology and physiology of strangling hemiepiphytes, there is little quantitative information about the variations in source‐water uptake by these species under different growth phases. In this study, the water acquisition patterns of a hemiepiphyte, Ficus tinctoria , is investigated in relation to growth phase (epiphytic, transitional and terrestrial) and season (foggy, hot‐dry and rainy). Stable isotope compositions of water in xylem, soil, canopy humus, fog and rainfall were sampled on seasonally distinct dates, and soil water content and leaf carbon isotope composition were measured in order to determine the proportion of different water sources. Results indicated that F . tinctoria displayed a high degree of plasticity in source‐water acquisition associated with the growth‐phase transition from purely canopy‐rooted epiphyte to transitional plant to terrestrial tree. During the foggy season and the hot‐dry season, epiphytes utilized a combination of recently received rainwater (82–89%) and fog water (11–18%) present in canopy humus soil, whereas terrestrial trees exclusively depended on shallow and deep terrestrial soil water and exhibited marked flexibility in depth of soil water uptake. Transitional‐phase plants relied predominantly on shallow soil water (79–86%) and extracted only a small fraction of canopy humus water (14–21%). During the rainy season, epiphytes relied almost exclusively on recent rainwater (96%) and had a negligible water uptake from fog, whereas trees extracted their water primarily from the shallow soil and less from the deep soil. Plants in transitional‐phase drew a considerable fraction of water from canopy humus soil. This plasticity of source‐water uptake to cope with radical changes in rooting environment is likely the key feature enabling hemiepiphytic species to thrive and successfully establish in the tropical rainforests. Copyright © 2014 John Wiley & Sons, Ltd.