Heavy water fractionation during transpiration
Heavy water fractionation during transpiration
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DOI：
10.1104/pp.106.093278
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发表时间：
2007-01-01
期刊：
影响因子：
7.4
通讯作者：
Barnes, Belinda
中科院分区：
文献类型：
--
作者：
Farquhar, Graham D.;Cernusak, Lucas A.;Barnes, Belinda
一小部分水分子含有氢和氧的较重同位素。这些较重的水分子在蒸腾过程中有在叶片中积累的趋势。这有几个有趣的影响，包括对有机物的同位素组成的影响，以及大气水蒸气，二氧化碳和氧气。反过来，这些影响又以各种方式帮助气候的时间重建和初级生产的空间和时间重建。最近，米勒等人的一项新报告。（2006年）表明，树木年轮18 O测量记录了飓风活动。我们实验室研究水同位素的动机是加强对蒸腾效率（TE;植物，作物或生态系统水平上叶片对水分利用效率的贡献）的研究。瞬时TE是A/[gwn]，其中A是CO2的光合吸收速率，gw是水蒸气从叶内蒸发部位扩散到大气的传导性（由气孔传导性gs和边界层传导性gb串联组成），n是叶与空气的水蒸气浓度差。通过测定叶片的碳同位素组成可以确定光合作用过程中的碳同位素区分度Δ 13 C。反过来，Δ 13 C与A/gt有关，A/gt是CO2同化速率与CO2从大气扩散到羧化位点的总传导率的比值。这两种测量明显相关，并且有人建议，叶材料的氧同位素组成（d18 O）可以用于拾取n的差异（Farquhar等人，1994年）。
A small proportion of water molecules contain the heavier isotopes of hydrogen and oxygen. There is a tendency for these heavier molecules of water to accumulate in leaves during transpiration. This has several interesting repercussions, including effects on the isotopic composition of organic matter, and of atmospheric water vapor, carbon dioxide, and oxygen. In turn, these effects aid temporal reconstruction of climate and spatial and temporal reconstruction of primary production in various ways. A recent, novel report by Miller et al.(2006) showed that tree-ring 18O measurements carried a record of hurricane activity. The motivation for our laboratory to study water isotopes was to enhance studies of transpiration efficiency (TE; the leaf contribution to water-use efficiency at the plant, crop, or ecosystem level). The instantaneous TE is A/[gwn], where A is the rate of photosynthetic uptake of CO2, gw is the conductance to diffusion of water vapor to the atmosphere from the sites of evaporation within the leaf (made up of the stomatal conductance, gs, and boundary layer conductance, gb, in series), and n is the leaf-to-air water vapor concentration difference. Carbon isotope composition of leaves can be measured to determine the carbon isotopic discrimination, Δ13C, during photosynthesis. In turn, Δ13C relates to A/gt, the ratio of CO2 assimilation rate to the total conductance to diffusion of CO2 from the atmosphere to the sites of carboxylation. The two measures are obviously related, and it was suggested that the oxygen isotope composition (d18O) of leaf material could be used to pick up differences in n (Farquhar et al., 1994).