Ellsworth David S, Oren Ram, Huang Ce, Phillips Nathan, Hendrey George R
Biosystems and Process Sciences Division, Department of Applied Science, Brookhaven National Laboratory, 11973, Upton, N.Y., USA.
School of the Environment, Duke University, 27708, Durham, N.C., USA.
Oecologia. 1995 Oct;104(2):139-146. doi: 10.1007/BF00328578.
Physiological responses to elevated CO at the leaf and canopy-level were studied in an intact pine (Pinus taeda) forest ecosystem exposed to elevated CO using a free-air CO enrichment (FACE) technique. Normalized canopy water-use of trees exposed to elevated CO over an 8-day exposure period was similar to that of trees exposed to current ambient CO under sunny conditions. During a portion of the exposure period when sky conditions were cloudy, CO-exposed trees showed minor (≤7%) but significant reductions in relative sap flux density compared to trees under ambient CO conditions. Short-term (minutes) direct stomatal responses to elevated CO were also relatively weak (≈5% reduction in stomatal aperture in response to high CO concentrations). We observed no evidence of adjustment in stomatal conductance in foliage grown under elevated CO for nearly 80 days compared to foliage grown under current ambient CO, so intrinsic leaf water-use efficiency at elevated CO was enhanced primarily by direct responses of photosynthesis to CO. We did not detect statistical differences in parameters from photosynthetic responses to intercellular CO (A -C curves) for Pinus taeda foliage grown under elevated CO (550 μmol mol) for 50-80 days compared to those for foliage grown under current ambient CO from similar-sized reference trees nearby. In both cases, leaf net photosynthetic rate at 550 μmol mol CO was enhanced by approximately 65% compared to the rate at ambient CO (350 μmol mol). A similar level of enhancement under elevated CO was observed for daily photosynthesis under field conditions on a sunny day. While enhancement of photosynthesis by elevated CO during the study period appears to be primarily attributable to direct photosynthetic responses to CO in the pine forest, longer-term CO responses and feedbacks remain to be evaluated.
利用自由空气CO₂富集（FACE）技术，在暴露于高浓度CO₂的完整松树（火炬松）森林生态系统中，研究了叶片和冠层水平对高浓度CO₂的生理响应。在8天的暴露期内，暴露于高浓度CO₂的树木的标准化冠层水分利用与晴天条件下暴露于当前环境CO₂浓度的树木相似。在暴露期的部分多云天气期间，与处于环境CO₂条件下的树木相比，暴露于高浓度CO₂的树木的相对液流通量密度略有降低（≤7%），但差异显著。短期（数分钟）内，气孔对高浓度CO₂的直接响应也相对较弱（高CO₂浓度下气孔孔径减少约5%）。与在当前环境CO₂浓度下生长的叶片相比，我们未观察到在高浓度CO₂下生长近80天的叶片气孔导度有调整迹象，因此高浓度CO₂下叶片的内在水分利用效率主要通过光合作用对CO₂的直接响应而提高。对于在高浓度CO₂（550 μmol/mol）下生长50 - 80天的火炬松叶片，与附近类似大小参考树在当前环境CO₂浓度下生长的叶片相比，我们未检测到光合作用对胞间CO₂响应参数（A - C曲线）的统计差异。在这两种情况下，550 μmol/mol CO₂浓度下的叶片净光合速率比环境CO₂浓度（350 μmol/mol）下的速率提高了约65%。在晴天的田间条件下，高浓度CO₂对每日光合作用的增强程度与之相似。虽然在研究期间高浓度CO₂对光合作用的增强似乎主要归因于松树林中光合作用对CO₂的直接响应，但长期的CO₂响应和反馈仍有待评估。
