Garten C T, Taylor G E
Environmental Sciences Division, Oak Ridge National Laboratory, P.O. Box 2008, 37830-6038, Oak Ridge, TN, USA.
Biological Sciences Center, Desert Research Institute, University of Nevada, P.O. Box 60220, 89506, Reno, NV, USA.
Oecologia. 1992 Apr;90(1):1-7. doi: 10.1007/BF00317801.
Foliar C-abundance (δC) was analyzed in the dominant trees of a temperate deciduous forest in east Tennessee (Walker Branch Watershed) to investigate the variation in foliar δC as a function of time (within-year and between years), space (canopy height, watershed topography and habitat) and species (deciduous and coniferous taxa). Various hypotheses were tested by analyzing (i) samples collected from the field during the growing season and (ii) foliar tissues maintained in an archived collection. The δC-value for leaves from the tops of trees was 2 to 3%. more positive than for leaves sampled at lower heights in the canopy. Quercus prinus leaves sampled just prior to autumn leaf fall had significantly more negative δC-values than those sampled during midsummer. On the more xeric ridges, needles of Pinus spp. had more positive δC-values than leaves from deciduous species. Foliar δC-values differed significantly as a function of topography. Deciduous leaves from xeric sites (ridges and slopes) had more positive δC-values than those from mesic (riparian and cove) environments. On the more xeric sites, foliar δC was significantly more positive in 1988 (a dry year) relative to that in 1989 (a year with above-normal precipitation). In contrast, leaf δC in trees from mesic valley bottoms did not differ significantly among years with disparate precipitation. Patterns in foliar δC indicated a higher ratio of net CO assimilation to transpiration (A/E) for trees in more xeric versus mesic habitats, and for trees in xeric habitats during years of drought versus years of normal precipitation. However, A/E (units of mmol CO fixed/mol HO transpired) calculated on the basis of δC-values for leaves from the more xeric sites was higher in a wet year (6.6±1.2) versus a dry year (3.4±0.4). This difference was attributed to higher transpiration (and therefore lower A/E) in the year with lower relative humidity and higher average daily temperature. The calculated A/E values for the forest in 1988-89, based on δC, were within ±55% of estimates made over a 17 day period at this site in 1984 using micrometeorological methods.
对田纳西州东部（沃克分支流域）温带落叶林中的优势树种进行了叶片碳同位素丰度（δC）分析，以研究叶片δC随时间（年内和年间）、空间（冠层高度、流域地形和生境）和物种（落叶和针叶类群）的变化。通过分析（i）生长季节从野外采集的样本和（ii）保存在存档收集中的叶片组织，对各种假设进行了检验。树冠顶部叶片的δC值比树冠较低高度处采集的叶片高2%至3%。秋季落叶前采集的栗栎叶片的δC值明显比仲夏时采集的叶片更负。在较干旱的山脊上，松树的针叶δC值比落叶树种的叶片更正。叶片δC值随地形变化显著。干旱地点（山脊和山坡）的落叶δC值比湿润地点（河岸和小海湾）的落叶更正。在较干旱的地点，1988年（干旱年份）的叶片δC值明显比1989年（降水高于正常水平的年份）更正。相比之下，湿润谷底树木的叶片δC在降水不同的年份之间没有显著差异。叶片δC的模式表明，与湿润生境相比，干旱生境中的树木以及干旱年份与正常降水年份相比，干旱生境中的树木净CO₂同化与蒸腾作用的比率（A/E）更高。然而，根据较干旱地点叶片的δC值计算的A/E（固定CO₂的mmol数/蒸腾H₂O的mol数）在湿润年份（6.6±1.2）比干旱年份（3.4±0.4）更高。这种差异归因于相对湿度较低和日平均温度较高的年份蒸腾作用较高（因此A/E较低）。基于δC计算的1988 - 1989年该森林的A/E值与1984年在该地点使用微气象方法在17天内进行的估计值相差±55%以内。
