Mortazavi Behzad, Chanton Jeffrey P, Prater James L, Oishi A Christopher, Oren Ram, Katul Gabriel
Department of Oceanography, Florida State University, Tallahassee, FL 32306-4320, USA.
Oecologia. 2005 Jan;142(1):57-69. doi: 10.1007/s00442-004-1692-2. Epub 2004 Aug 31.
Temporal variability in the (13)C of foliage (delta(13)C(F)), soil (delta(13)C(S)) and ecosystem (delta(13)C(R)) respired CO(2) was contrasted between a 17.2-m tall evenly aged loblolly pine forest and a 35-m tall unevenly aged mature second growth mixed broadleaf deciduous forest in North Carolina, USA, over a 2-year period. The two forests are located at the Duke Forest within a kilometer of each other and are subject to identical climate and have similar soil types. The delta(13)C(F), collected just prior to dawn, was primarily controlled by the time-lagged vapor pressure deficit (VPD) in both stands; it was used for calculating the ratio of intercellular to ambient CO(2) ( Ci/ Ca). A remarkable similarity was observed in the relationship between Ci/ Ca and time-lagged VPD in these two forests despite large differences in hydraulic characteristics. This similarity emerged as a result of physiological adjustments that compensated for differences in plant hydraulic characteristics, as predicted by a recently proposed equilibrium hypothesis, and has implications to ecophysiological models. We found that in the broadleaf forest, the delta(13)C of forest floor CO(2) efflux dominated the delta(13)C(R), while in the younger pine forest, the delta(13)C of foliage respired CO(2) dominated delta(13)C(R). This dependence resulted in a more variable delta(13)C(R) in the pine forest when compared to the broadleaf forest due to the larger photosynthetic contribution. Given the sensitivity of the atmospheric inversion models to delta(13)C(R), the results demonstrate that these models could be improved by accounting for stand characteristics, in addition to previously recognized effects of moisture availability, when estimating delta(13)C(R).
在美国北卡罗来纳州，对一片17.2米高、树龄均匀的火炬松林和一片35米高、树龄不均匀的成熟次生阔叶落叶混交林，在两年时间里对比了叶片（δ¹³C(F)）、土壤（δ¹³C(S)）和生态系统（δ¹³C(R)）呼吸释放的CO₂的¹³C时间变异性。这两片森林位于杜克森林内，彼此相距一公里，气候相同，土壤类型相似。黎明前采集的δ¹³C(F)在两个林分中主要受滞后水汽压亏缺（VPD）控制；它用于计算细胞间CO₂与环境CO₂的比值（Ci/Ca）。尽管水力特征差异很大，但在这两片森林中，Ci/Ca与滞后VPD之间的关系存在显著相似性。正如最近提出的平衡假说所预测的，这种相似性是生理调节补偿植物水力特征差异的结果，对生态生理模型有影响。我们发现，在阔叶林里，森林地表CO₂通量的δ¹³C主导了δ¹³C(R)，而在较年轻的火炬松林中，叶片呼吸释放的CO₂的δ¹³C主导了δ¹³C(R)。由于光合贡献更大，这种依赖性导致松林的δ¹³C(R)比阔叶林更具变异性。鉴于大气反演模型对δ¹³C(R)的敏感性，结果表明，在估算δ¹³C(R)时，除了先前认识到的水分有效性影响外，考虑林分特征可以改进这些模型。
