Short-term variation in the isotopic composition of organic matter allocated from the leaves to the stem of Pinus sylvestris:: effects of photosynthetic and postphotosynthetic carbon isotope fractionation
Short-term variation in the isotopic composition of organic matter allocated from the leaves to the stem of Pinus sylvestris:: effects of photosynthetic and postphotosynthetic carbon isotope fractionation
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DOI：
10.1111/j.1365-2486.2006.01205.x
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发表时间：
2006-10-01
影响因子：
11.6
通讯作者：
Gessler, Arthur
中科院分区：
文献类型：
--
作者：
Brandes, Elke;Kodama, Naomi;Gessler, Arthur
我们的目的是量化光合作用和光合作用后碳同位素识别对快速周转碳库的C-13增量(异养组织释放的水溶性有机碳和二氧化碳)的单独影响，包括它们在从树叶到树干底部的碳运输途径中的日变化。为此，我们在9天的时间里测定了总的C-13增量和树叶的水溶性有机质加上树枝韧皮部有机质中的C-13增量和O-18增量。这些数据与气象和光合作用参数以及树干排放的CO2的C-13增量有关。在冠层(树叶和树枝)中，可溶性有机质的C-13增量的变化幅度高达千分之1.9。在夜间/清晨记录到最大的C-13丰度，表明淀粉的储存和再动员对叶片输出的糖的碳同位素特征有很大的影响。C-13从叶片到枝条韧皮部再到茎韧皮部的可溶性有机质的富集，被认为是与源和库组织中的代谢过程有关的碳同位素分馏的结果。与韧皮部有机质相比，茎中释放的二氧化碳比韧皮部有机质富集率为2.3-5.2个百分点。在处理日变化时，叶片C-13和枝条韧皮部O-18分别受c(I)/c(A)和气孔导度(S)的强烈影响，这些结果表明，光合作用和光合作用后的碳同位素分馏都影响着有机质的C-13值随时间的变化，以及底瓣运输途径的长度。显然，在利用呼吸二氧化碳的C-13增量进行生态系统二氧化碳通量分配时，或在评估C(I)/c(A)中的C-13增量对环境影响时，必须考虑到这些对呼吸二氧化碳增量C-13的影响。
We aimed to quantify the separate effects of photosynthetic and postphotosynthetic carbon isotope discrimination on delta C-13 of the fast-turn-over carbon pool (water soluble organic carbon and CO2 emitted from heterotrophic tissues), including their diel variation, along the pathway of carbon transport from the foliage to the base of the stem.For that purpose, we determined delta C-13 in total and water-soluble organic matter of the foliage plus delta C-13 and delta O-18 in phloem organic matter of twigs and at three heights along the stem of Pinus sylvestris over a nine-day period, including four measurements per day. These data were related to meteorological and photosynthesis parameters and to the delta C-13 of stem-emitted CO2.In the canopy (foliage and twigs), the delta C-13 of soluble organic matter varied diurnally with amplitudes of up to 1.9 parts per thousand. The greatest C-13 enrichment was recorded during the night/early morning, indicating a strong influence of starch storage and remobilization on the carbon isotope signatures of sugars exported from the leaves. C-13 enrichment of soluble organic matter from the leaves to the twig phloem and further on to the phloem of the stem was supposed to be a result of carbon isotope fractionation associated with metabolic processes in the source and sink tissues. CO2 emitted from the stem was enriched by 2.3-5.2 parts per thousand compared with phloem organic matter. When day-to-day variation was addressed, water-soluble leaf delta C-13 and twig phloem delta O-18 were strongly influenced by c(i)/c(a) and stomatal conductance (G(s)), respectively.These results show that both photosynthetic and postphotosynthetic carbon isotope fractionation influence delta C-13 of organic matter over time, and over the length of the basipetal transport pathway. Clearly, these influences on the delta C-13 of respired CO2 must be considered when using the latter for partitioning of ecosystem CO2 fluxes or when the assessment of delta C-13 in organic matter is applied to estimate environmental effects in c(i)/c(a).