Francey R J, Gifford R M, Sharkey T D, Weir B
CSIRO Division of Atmospheric Research, Private Bag No. 1, 3195, Mordialloc, Victoria, Australia.
CSIRO Division of Plant Industry, P.O. Box 1600, 2601, Canberra City, A.C.T., Australia.
Oecologia. 1985 May;66(2):211-218. doi: 10.1007/BF00379857.
Measurements of the light environment and stomatal and photosynthetic behaviour are reported for Huon Pine (Lagarostrobos franklinii, family Podocarpaceae) in western Tasmanian rainforest. For a variety of microenvironments, these are used in an analysis of stable carbon isotope measurements in the air, and in branch and leaf material, using a model for carbon isotope fractionation in leaves (Farquhar et al. 1982).The major features of δC variations with respect to branch position can be explained in terms of the direct influence of light level acting via the rate of CO assimilation. In addition a relatively constant δC gradient of about 2.6‰ between leaf tip and branch wood is observed.Alternative explanations are advanced for the tip-towood gradient in δC. If the δC of leaf tips is taken to represent the value for photosynthate, maintenance respiration is proposed as a mechanism for the further fractionation; a significant C depletion in respired CO is implied which is not supported by indirect measurements of atmospheric isotope ratio. Furthermore, an assumption of significant sampling errors (e.g. related to humidity effects on assimilation) is required to obtain good quantitative prediction of the light influence.If the branch wood δC is taken to represent that of the photosynthate, the tip-to-wood gradient may find an explanation, via the model, in terms of tip tissue comprising carbon from immature cells. Translocation of photosynthate from exposed to shaded branches is then proposed as a means of obtaining quantitative agreement with the predicted light influence.The support provided for the applicability of the Farqunar et al. (1982) model in the field is discussed in the context of the problem of obtaining past global atmospheric CO levels from δC in tree-rings.
本文报道了塔斯马尼亚西部雨林中泪柏（Lagarostrobos franklinii，罗汉松科）的光环境、气孔和光合行为的测量结果。针对多种微环境，利用叶片碳同位素分馏模型（Farquhar等人，1982年），对空气、树枝和叶片材料中的稳定碳同位素测量结果进行了分析。δC随树枝位置变化的主要特征可以通过光照水平对CO同化速率的直接影响来解释。此外，还观察到叶尖和树枝木质部之间存在约2.6‰的相对恒定的δC梯度。文中还提出了关于δC叶尖到木质部梯度的其他解释。如果将叶尖的δC视为光合产物的值，维持呼吸被认为是进一步分馏的机制；这意味着呼吸产生的CO中存在显著的碳消耗，但大气同位素比值的间接测量结果并不支持这一点。此外，为了获得光照影响的良好定量预测，需要假设存在显著的采样误差（例如与湿度对同化的影响有关）。如果将树枝木质部的δC视为光合产物的δC，那么叶尖到木质部的梯度可以通过该模型，解释为叶尖组织包含来自未成熟细胞的碳。然后提出光合产物从暴露树枝向遮荫树枝的转运，作为与预测的光照影响达成定量一致的一种方式。在从树木年轮的δC获取过去全球大气CO水平这一问题的背景下，讨论了Farqunar等人（1982年）模型在野外适用性所得到的支持。
