College of Science and Engineering, James Cook University, Cairns, Qld, 4878, Australia.
BEECA, Department of Evolutionary Biology, Ecology and Environmental Sciences, Universitat de Barcelona, Barcelona, Catalonia, 08028, Spain.
New Phytol. 2022 Jul;235(1):41-51. doi: 10.1111/nph.18113. Epub 2022 Apr 12.
We compiled hydrogen and oxygen stable isotope compositions (δ H and δ O) of leaf water from multiple biomes to examine variations with environmental drivers. Leaf water δ H was more closely correlated with δ H of xylem water or atmospheric vapour, whereas leaf water δ O was more closely correlated with air relative humidity. This resulted from the larger proportional range for δ H of meteoric waters relative to the extent of leaf water evaporative enrichment compared with δ O. We next expressed leaf water as isotopic enrichment above xylem water (Δ H and Δ O) to remove the impact of xylem water isotopic variation. For Δ H, leaf water still correlated with atmospheric vapour, whereas Δ O showed no such correlation. This was explained by covariance between air relative humidity and the Δ O of atmospheric vapour. This is consistent with a previously observed diurnal correlation between air relative humidity and the deuterium excess of atmospheric vapour across a range of ecosystems. We conclude that H and O in leaf water do indeed reflect the balance of environmental drivers differently; our results have implications for understanding isotopic effects associated with water cycling in terrestrial ecosystems and for inferring environmental change from isotopic biomarkers that act as proxies for leaf water.
我们编译了来自多个生物群落的叶片水的氢和氧稳定同位素组成（δH 和 δO），以研究其与环境驱动因素的变化。叶片水的 δH 与木质部水或大气蒸汽的 δH 更为密切相关，而叶片水的 δO 则与空气相对湿度更为密切相关。这是由于与 δO 相比，大气降水的 δH 比例范围更大，而叶片水的蒸发浓缩程度更大。接下来，我们将叶片水表示为相对于木质部水的同位素富集（ΔH 和 ΔO），以消除木质部水同位素变化的影响。对于 ΔH，叶片水仍然与大气蒸汽相关，而 ΔO 则没有这种相关性。这是由于空气相对湿度与大气蒸汽的 ΔO 之间存在协方差。这与之前在一系列生态系统中观察到的空气相对湿度与大气蒸汽的氘过剩之间的日变化相关性一致。我们得出的结论是，叶片水中的 H 和 O 确实反映了环境驱动因素的不同平衡；我们的研究结果对于理解与陆地生态系统水分循环相关的同位素效应以及从作为叶片水替代物的同位素生物标志物推断环境变化具有重要意义。
