A new measurement technique reveals temporal variation in δ18O of leaf-respired CO2
A new measurement technique reveals temporal variation in δ18O of leaf-respired CO2
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DOI：
10.1111/j.1365-3040.2007.01633.x
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发表时间：
2007-04-01
影响因子：
7.3
通讯作者：
McDowell, Nate G.
中科院分区：
文献类型：
--
作者：
Barbour, Margaret M.;Farquhar, Graham D.;McDowell, Nate G.
利用可调谐二极管激光（TDL）吸收光谱仪与便携式气体交换系统耦合，在非稳态条件下测量了蓖麻叶片呼吸CO2的氧同位素组成（δ O-18(R)），时间分辨率为3 min。TDL测量δ O-18的SD值为+/- 0.2 ppm，与传统质谱仪的SD值接近。此外，同位素稳定状态下的δ O-18(R)值与使用传统烧瓶采样和质谱技术获得的在相似环境条件下生长和测量的红豆的值相当。除了更高的时间分辨率外，这里描述的在线TDL方法与质谱技术相比具有许多优点。在强光下生长的植物同位素稳定状态下，需要“单向通量”模型来准确预测δ O-18(R)。对测量值和模型的比较表明，在弱光条件下生长的植物，要么叶绿体CO2的比例较低，与叶绿体水的同位素平衡，要么叶绿体中CO2的δ O-18更丰富，与当地水的不平衡。同位素测量的高时间分辨率允许在气孔导度快速变化时首次测量δ O-18(R)。在非稳态条件下，在不同光和水环境下生长的植物叶片的δ O-18(R)变化在50至220千分之一之间，单叶在10分钟内变化高达100千分之一。气孔导度范围为0.001 ~ 1.586 mol m(-2) s(-1)，对非稳态条件下δ O-18(R)有重要影响，不仅通过影响叶片水分(H2O)-O-18的富集，还通过影响CO2单向进出叶片的速率。
The oxygen isotope composition of CO2 respired by Ricinus communis leaves (delta O-18(R)) was measured under non-steady-state conditions with a temporal resolution of 3 min using a tunable diode laser (TDL) absorption spectrometer coupled to a portable gas exchange system. The SD of delta O-18 measurement by the TDL was +/- 0.2 parts per thousand and close to that of traditional mass spectrometers. Further, delta O-18(R) values at isotopic steady state were comparable to those obtained using traditional flask sampling and mass spectrometric techniques for R. communis grown and measured in similar environmental conditions. As well as higher temporal resolution, the online TDL method described here has a number of advantages over mass spectrometric techniques.At isotopic steady state among plants grown at high light, the 'one-way flux' model was required to accurately predict delta O-18(R). A comparison of measurements and the model suggests that plants grown under low-light conditions have either a lower proportion of chloroplast CO2 that isotopically equilibrates with chloroplast water, or more enriched delta O-18 of CO2 in the chloroplast that has not equilibrated with local water. The high temporal resolution of isotopic measurements allowed the first measurements of delta O-18(R) when stomatal conductance was rapidly changing. Under non-steady-state conditions, delta O-18(R) varied between 50 and 220 parts per thousand for leaves of plants grown under different light and water environments, and varied by as much as 100 parts per thousand within 10 min for a single leaf. Stomatal conductance ranged from 0.001 to 1.586 mol m(-2) s(-1), and had an important influence on delta O-18(R) under non-steady-state conditions not only via effects on leaf water (H2O)-O-18 enrichment, but also via effects on the rate of the one-way fluxes of CO2 into and out of the leaf.