Response of the carbon isotopic content of ecosystem, leaf, and soil respiration to meteorological and physiological driving factors in a Pinus ponderosa ecosystem
Response of the carbon isotopic content of ecosystem, leaf, and soil respiration to meteorological and physiological driving factors in a Pinus ponderosa ecosystem
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DOI：
10.1029/2003gb002049
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发表时间：
2004-03
影响因子：
5.2
通讯作者：
Nate G. McDowell;D. Bowling;B. Bond;James R. Irvine;Beverly E. Law;P. Anthoni;J. Ehleringer
中科院分区：
文献类型：
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作者：
Nate G. McDowell;D. Bowling;B. Bond;James R. Irvine;Beverly E. Law;P. Anthoni;J. Ehleringer
了解生态系统呼吸的δ 13 C（δ 13 CR）的控制对于基于同位素的全球碳收支模型的应用以及理解同位素区分（Δ）的生态系统水平变化非常重要。区分可能强烈依赖于控制冠层尺度气孔导度（Gc）和光合作用的环境驱动因素的天气尺度变化，如大气蒸汽压差（vpd），光合有效辐射（PAR）和空气温度（Tair）。然而，这些潜在的关系是复杂的，这是由于碳同化和生态系统呼吸之间的时间滞后，这可能长达几天，并可能随组织而变化（即，叶与地下组织）。我们的目标是确定短期（2周）内气象和生理驱动因素与δ 13 CR及其组分，土壤呼吸δ 13 C（δ 13 CR-土壤）和树叶呼吸δ 13 C（δ 13 CR-树叶）之间是否存在关系。我们在美国俄勒冈州中部的一片250年的黄松林中测试了这些假设的关系。在我们第一个采样夜前3天，一个冷锋穿过该地区，导致降水（总降雨量14.6毫米），低vpd（最低日光平均值0.36 kPa）和接近冰点的温度（最低气温0.18°C ± 0.3°C），随后是相对较高vpd的变暖趋势（最大日光平均值3.19 kPa）。在这2周期间，Gc与vpd呈负相关（P < 0.01），而净生态系统CO2交换（NEE）与vpd呈正相关（P < 0.01），这与vpd对电导和净CO2吸收的限制一致。与气孔对Δ的影响一致，在δ 13 CR和2天前测量的Gc之间观察到负相关（即，2天的时间滞后，P = 0.04）;然而，δ 13 CR与其他测量变量无关。同样与气孔对辨别力的影响一致，δ 13 CR-土壤与Gc呈负相关（P < 0.01），与1至3天前测量的vpd和PAR呈正相关（P = 0.01和0.04）。与此相反，δ 13 CR-叶与vpd或Gc不相关，但与5天前测量的最低气温呈负相关（P < 0.01），支持冷空气温度导致呼吸CO2同位素富集的观点。δ 13 CR-树叶和δ 13 CR-土壤的显著驱动参数不同，可能是由于对组织特异性呼吸通量的同位素含量的不同控制，例如从同化部位到呼吸组织的碳运输时间不同，或者对最近与旧光合作用的依赖不同。与Gc对光合作用和Δ的控制一致，随着净CO2吸收的减少，δ 13 CR-土壤和δ 13 CR-叶片都变得富集（NEE更正，两者P < 0.01）。美国黄松叶片的δ 13 C值（−27.1‰，整个组织）比任何观察到的呼吸特征都要负0.5至3.0‰，支持叶片δ 13 C可能是呼吸通量同位素含量的不良代理的论点。对Gc和NEE的强气象控制与δ 13 CR-土壤的类似变化有关，但δ 13 CR的变化很小，这使我们得出结论，δ 13 CR不仅仅受冠层和地下过程的控制，而是受它们随时间变化的相互作用的控制。
Understanding the controls over ecosystem‐respired δ13C (δ13CR) is important for applications of isotope‐based models of the global carbon budget as well as for understanding ecosystem‐level variation in isotopic discrimination (Δ). Discrimination may be strongly dependent on synoptic‐scale variation in environmental drivers that control canopy‐scale stomatal conductance (Gc) and photosynthesis, such as atmospheric vapor pressure deficit (vpd) photosynthetically active radiation (PAR) and air temperature (Tair). These potential relationships are complicated, however, due to time lags between the period of carbon assimilation and ecosystem respiration, which may extend up to several days, and may vary with tissue (i.e., leaves versus belowground tissues). Our objective was to determine if relationships exist over a short‐term period (2 weeks) between meteorological and physiological driving factors and δ13CR and its components, soil‐respired δ13C (δ13CR‐soil) and foliage‐respired δ13C (δ13CR‐foliage). We tested for these hypothesized relationships in a 250‐year‐old ponderosa pine forest in central Oregon, United States. A cold front passed through the region 3 days prior to our first sample night, resulting in precipitation (total rainfall 14.6 mm), low vpd (minimum daylight average of 0.36 kPa) and near‐freeze temperature (minimum air temperature of 0.18°C ± 0.3°C), followed by a warming trend with relatively high vpd (maximum daylight average of 3.19 kPa). Over this 2‐week period Gc was negatively correlated with vpd (P < 0.01) while net ecosystem CO2 exchange (NEE) was positively correlated with vpd (P < 0.01), consistent with a vpd limitation to conductance and net CO2 uptake. Consistent with a stomatal influence over Δ, a negative correlation was observed between δ13CR and Gc measured 2 days prior (i.e., a 2‐day time lag, P = 0.04); however, δ13CR was not correlated with other measured variables. Also consistent with a stomatal influence over discrimination, δ13CR‐soil was negatively correlated with Gc (P < 0.01) and positively correlated with vpd and PAR measured one to 3 days prior (P = 0.01 and 0.04, respectively). In contrast, δ13CR‐foliage was not correlated with vpd or Gc, but was negatively correlated with minimum air temperature measured 5 days previously (P < 0.01) supporting the idea that cold air temperatures cause isotopic enrichment of respired CO2. The significant driving parameters differed for δ13CR‐foliage and δ13CR‐soil potentially due to different controls over the isotopic content of tissue‐specific respiratory fluxes, such as differing carbon transport times from the site of assimilation to the respiring tissue or different reliance on recent versus old photosynthate. Consistent with Gc control over photosynthesis and Δ, both δ13CR‐soil and δ13CR‐foliage became enriched as net CO2 uptake decreased (more positive NEE, P < 0.01 for both). The δ13C value of Pinus ponderosa foliage (−27.1‰, whole‐tissue) was 0.5 to 3.0‰ more negative than any observed respiratory signature, supporting the contention that foliage δ13C can be a poor proxy for the isotopic content of respiratory fluxes. The strong meteorological controls over Gc and NEE were associated with similar variation in δ13CR‐soil but only minor variation in δ13CR, leading us to conclude that δ13CR is not controlled solely by either canopy and belowground processes, but rather by their time‐dependent interaction.