Physiological Ecology Group, Department of Plant Sciences, University of Cambridge, Cambridge, CB2 3EA, UK.
Physiological Ecology Group, Department of Plant Sciences, University of Cambridge, Cambridge, CB2 3EA, UK; and Unidad de Recursos Naturales, Centro de Investigación Científica de Yucatán, Calle 43 Num. 130 Churburná de Hidalgo, Mérida, 97200, México.
Funct Plant Biol. 2021 Jun;48(7):732-742. doi: 10.1071/FP21087.
The distributions of CAM and C3 epiphytic bromeliads across an altitudinal gradient in western Panama were identified from carbon isotope (δ13C) signals, and epiphyte water balance was investigated via oxygen isotopes (δ18O) across wet and dry seasons. There were significant seasonal differences in leaf water (δ18Olw), precipitation, stored 'tank' water and water vapour. Values of δ18Olw were evaporatively enriched at low altitude in the dry season for the C3 epiphytes, associated with low relative humidity (RH) during the day. Crassulacean acid metabolism (CAM) δ18Olw values were relatively depleted, consistent with water vapour uptake during gas exchange under high RH at night. At high altitude, cloudforest locations, C3 δ18Olw also reflected water vapour uptake by day. A mesocosm experiment with Tillandsia fasciculata (CAM) and Werauhia sanguinolenta (C3) was combined with simulations using a non-steady-state oxygen isotope leaf water model. For both C3 and CAM bromeliads, δ18Olw became progressively depleted under saturating water vapour by day and night, although evaporative enrichment was restored in the C3 W. sanguinolenta under low humidity by day. Source water in the overlapping leaf base 'tank' was also modified by evaporative δ18O exchanges. The results demonstrate how stable isotopes in leaf water provide insights for atmospheric water vapour exchanges for both C3 and CAM systems.
从碳同位素（δ13C）信号中确定了巴拿马西部沿海拔梯度分布的 CAM 和 C3 附生凤梨科植物，并通过氧同位素（δ18O）在干湿两季调查了附生植物的水分平衡。叶片水（δ18Olw）、降水、储存的“水箱”水和水蒸气在季节上有显著差异。在旱季，C3 附生植物的δ18Olw 在低海拔处被蒸发浓缩，这与白天相对湿度（RH）较低有关。CAM 的δ18Olw 值相对较低，这与夜间高 RH 下气体交换时水蒸气的吸收一致。在高海拔的云雾林地区，C3 的 δ18Olw 也反映了白天水蒸气的吸收。用非稳态氧同位素叶片水模型对 Tillandsia fasciculata（CAM）和 Werauhia sanguinolenta（C3）进行了微室实验和模拟。对于 C3 和 CAM 凤梨科植物，尽管在白天低湿度下 C3 的 Werauhia sanguinolenta 可以恢复蒸发浓缩，但在白天和夜间饱和水蒸气下，δ18Olw 逐渐变贫。重叠叶片基部“水箱”中的水源也受到蒸发δ18O 交换的影响。研究结果表明，叶片水中的稳定同位素如何为 C3 和 CAM 系统的大气水蒸气交换提供了见解。
