Seasonal and diurnal trends in progressive isotope enrichment along needles in two pine species
Seasonal and diurnal trends in progressive isotope enrichment along needles in two pine species
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两种松树针叶上同位素渐进富集的季节和昼夜趋势
DOI：
10.1111/pce.13915
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发表时间：
2020
期刊：
影响因子：
--
通讯作者：
Ehleringer, James R.
中科院分区：
文献类型：
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作者：
Kannenberg, Steven A.;Fiorella, Richard P.;Anderegg, William R. L.;Monson, Russell K.;Ehleringer, James R.
克雷格-戈登型(C-G)叶水同位素富集模型假定富集水在叶表面均匀分布，尽管观察到Δ18O从叶基到叶尖可以变得越来越丰富。这种“渐进式同位素富集法”的数据集有限，无法全面了解(A)渐进式同位素富集法的大小和变异性，以及(B)渐进式富集法如何影响C-G叶水分模型预测的准确性。在这里，我们提出了两个针叶树种的渐进式丰富的观察，捕捉到了环境条件的季节和日变化。我们进一步研究了哪个叶水同位素模型最好地捕捉到了渐进富集对散装针叶水Δ18O的影响。在两个物种中观察到的渐进式富集量都很大，而且幅度相等。这种影响的大小随着水汽压差的季节性波动而变化，但在气象条件下面对日循环时是静止的。尽管进行了大量的渐进式浓缩，C-G模型的三个变种还是相当成功地预测了大块针Δ18O。因此，我们的结果表明，渐进富集的存在并不影响C-G模型的预测成功，而是对导致渐进同位素富集的生理和解剖学机制产生了新的见解。
The Craig–Gordon type (C–G) leaf water isotope enrichment models assume a homogeneous distribution of enriched water across the leaf surface, despite observations that Δ18O can become increasingly enriched from leaf base to tip. Datasets of this ‘progressive isotope enrichment’ are limited, precluding a comprehensive understanding of (a) the magnitude and variability of progressive isotope enrichment, and (b) how progressive enrichment impacts the accuracy of C–G leaf water model predictions. Here, we present observations of progressive enrichment in two conifer species that capture seasonal and diurnal variability in environmental conditions. We further examine which leaf water isotope models best capture the influence of progressive enrichment on bulk needle water Δ18O. Observed progressive enrichment was large and equal in magnitude across both species. The magnitude of this effect fluctuated seasonally in concert with vapour pressure deficit, but was static in the face of diurnal cycles in meteorological conditions. Despite large progressive enrichment, three variants of the C–G model reasonably successfully predicted bulk needle Δ18O. Our results thus suggest that the presence of progressive enrichment does not impact the predictive success of C–G models, and instead yields new insight regarding the physiological and anatomical mechanisms that cause progressive isotope enrichment.