Associations between carbon isotope ratios of ecosystem respiration, water availability and canopy conductance
Associations between carbon isotope ratios of ecosystem respiration, water availability and canopy conductance
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DOI：
10.1111/j.1365-2486.2004.00837.x
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发表时间：
2004-10
影响因子：
11.6
通讯作者：
Nate G. McDowell;D. Bowling;A. J. Schauer;J. Irvine;B. Bond;Beverly E. Law;J. Ehleringer
中科院分区：
文献类型：
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作者：
Nate G. McDowell;D. Bowling;A. J. Schauer;J. Irvine;B. Bond;Beverly E. Law;J. Ehleringer
我们在美国俄勒冈州的半干旱老黄松（Pinus ponderosa）林中使用每周一次的Keeling样地（n=51）检验了生态系统呼吸的稳定碳同位素特征（δ 13 CR）受冠层电导（Gc）调节的假设。为了比较两种截然不同气候下的森林，我们还评估了位于太平洋附近的潮湿20年生道格拉斯冷杉（黄杉）种植园林δ 13 CR的趋势。δ 13 CR的年内变异在两个站点都大于8.0‰，在秋、冬、春三季降水丰沛时最高，夏旱时最低。干燥松林的δ 13 CR始终比湿润的道格拉斯-冷杉林更积极（平均年δ 13 CR：分别为−25.41‰和−26.23‰，P=0.07）。在道格拉斯冷杉林中，δ 13 CR-气候关系与基于气孔调节碳同位素区分（Δ）的预测一致。土壤含水量（SWC）和水汽压亏缺（vpd）是影响该林δ 13 CR的主要因子。相比之下，松树林的δ 13 CR对SWC或vpd相对不敏感，并且表现出比道格拉斯冷杉林干旱期间观察到的富集（105 ‰）更小的干旱相关富集（102 ‰）。松树林的地下水可缓冲干旱造成的冠层气体交换。尽管存在这种潜在的缓冲作用，但松树林的δ 13 CR与冠层电导（Gc）显著但微弱相关，表明尽管有地下水，δ 13 CR仍与冠层气体交换相关。在干旱期间，δ 13 CR与土壤温度在两个森林都有很强的相关性。支持冠层水平生理是δ 13 CR的关键调节器的假设;然而，地下呼吸在无雨期间可能变得更加重要。
We tested the hypothesis that the stable carbon isotope signature of ecosystem respiration (δ13CR) was regulated by canopy conductance (Gc) using weekly Keeling plots (n=51) from a semiarid old‐growth ponderosa pine (Pinus ponderosa) forest in Oregon, USA. For a comparison of forests in two contrasting climates we also evaluated trends in δ13CR from a wet 20‐year‐old Douglas‐fir (Pseudotsuga menziesii) plantation located near the Pacific Ocean. Intraannual variability in δ13CR was greater than 8.0‰ at both sites, was highest during autumn, winter, and spring when rainfall was abundant, and lowest during summer drought. The δ13CR of the dry pine forest was consistently more positive than the wetter Douglas‐fir forest (mean annual δ13CR: −25.41‰ vs. −26.23‰, respectively, P=0.07). At the Douglas‐fir forest, δ13CR–climate relationships were consistent with predictions based on stomatal regulation of carbon isotope discrimination (Δ). Soil water content (SWC) and vapor pressure deficit (vpd) were the most important factors governing δ13CR in this forest throughout the year. In contrast, δ13CR at the pine forest was relatively insensitive to SWC or vpd, and exhibited a smaller drought‐related enrichment (∼2‰) than the enrichment observed during drought at the Douglas‐fir forest (∼5‰). Groundwater access at the pine forest may buffer canopy–gas exchange from drought. Despite this potential buffering, δ13CR at the pine forest was significantly but weakly related to canopy conductance (Gc), suggesting that δ13CR remains coupled to canopy–gas exchange despite groundwater access. During drought, δ13CR was strongly correlated with soil temperature at both forests. The hypothesis that canopy‐level physiology is a critical regulator of δ13CR was supported; however, belowground respiration may become more important during rain‐free periods.