Bowling David R, McDowell Nate G, Bond Barbara J, Law Beverly E, Ehleringer James R
Stable Isotope Ratio Facility for Environmental Research, Department of Biology, University of Utah, 257 South 1400 East, Salt Lake City, UT, 84112-0820, USA.
Department of Forest Science, Oregon State University, Corvallis, OR, 97331, USA.
Oecologia. 2002 Mar;131(1):113-124. doi: 10.1007/s00442-001-0851-y. Epub 2002 Mar 1.
Variation in the carbon isotopic composition of ecosystem respiration (δC) was studied for 3 years along a precipitation gradient in western Oregon, USA, using the Keeling plot approach. Study sites included six coniferous forests, dominated by Picea sitchensis, Tsuga heterophylla, Pseudotsuga menziesii, Pinus ponderosa, and Juniperus occidentalis, and ranged in location from the Pacific coast to the eastern side of the Cascade Mountains (a 250-km transect). Mean annual precipitation across these sites ranged from 227 to 2,760 mm. Overall δC varied from -23.1 to -33.1‰, and within a single forest, it varied in magnitude by 3.5-8.5‰. Mean annual δC differed significantly in the forests and was strongly correlated with mean annual precipitation. The carbon isotope ratio of carbon stocks (leaves, fine roots, litter, and soil organic matter) varied similarly with mean precipitation (more positive at the drier sites). There was a strong link between δC and the vapor saturation deficit of air (vpd) 5-10 days earlier, both across and within sites. This relationship is consistent with stomatal regulation of gas exchange and associated changes in photosynthetic carbon isotope discrimination. Recent freeze events caused significant deviation from the δC versus vpd relationship, resulting in higher than expected δC values.
在美国俄勒冈州西部，沿着降水梯度，使用基林曲线法对生态系统呼吸的碳同位素组成变化（δC）进行了为期3年的研究。研究地点包括6片针叶林，主要树种为西加云杉、异叶铁杉、花旗松、黄松和西方刺柏，分布范围从太平洋海岸到喀斯喀特山脉东侧（跨度250公里）。这些地点的年平均降水量在227至2760毫米之间。整体δC在-23.1至-33.1‰之间变化，在单一森林内，其变化幅度为3.5-8.5‰。森林中的年平均δC差异显著，且与年平均降水量密切相关。碳库（树叶、细根、凋落物和土壤有机质）的碳同位素比率随平均降水量的变化情况类似（在较干燥的地点更为正向）。在不同地点和同一地点内部，δC与5-10天前空气的水汽饱和亏缺（vpd）之间均存在紧密联系。这种关系与气孔对气体交换的调节以及光合碳同位素分馏的相关变化一致。近期的冰冻事件导致δC与vpd关系出现显著偏差，使得δC值高于预期。
