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首页> 外文期刊>Global change biology >Three years of free-air CO2 enrichment (POPFACE) only slightly affect profiles of light and leaf characteristics in closed canopies of Populus
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Three years of free-air CO2 enrichment (POPFACE) only slightly affect profiles of light and leaf characteristics in closed canopies of Populus

机译：三年的自由空气CO2富集（POPFACE）仅对封闭的胡杨冠层的光和叶片特征轮廓产生轻微影响

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Modelling is used to predict long-term forest responses to increased atmospheric CO2 concentrations. Although productivity models are based on light intercepted by the canopy, very little experimental data are available for closed forest stands. Nevertheless, the relationships between light inside a canopy, leaf area, canopy structure, and individual leaf characteristics may be affected by elevated CO2, affecting in turn carbon gain. Using a free-air CO2 enrichment (FACE) design in a high-density plantation of Populus spp., we studied the effects of increased CO2 concentrations on transmittance (tau) of photosynthetic photon flux density (Q(p)), on ratios of red/far-red light (R/FR), on leaf area index (LAI), on leaf inclination, on leaf chlorophyll (chl) and nitrogen (N) concentrations, and on specific leaf area (SLA) in the 2nd and 3rd years of treatment. Continuous measurements of tau were made in addition to canopy height profiles of light and leaf characteristics. Two years of Q(p) measurements showed an average decrease of canopy transmittance in the FACE treatment, with very small differences at canopy closure. Results were explained by an unaffected LAI in closed canopies, without a FACE-induced stimulation of relative crown depth. In agreement, leaf inclination and extinction coefficients for light were similar in control and FACE conditions. Ratios of R/FR were not significantly affected by the FACE treatment, neither were leaf characteristics, with the exception of leaf N, which allows speculation about N limitation. In general, treatment differences in canopy profiles resulted from an initial stimulation of height growth in the FACE treatment. P. x euramericana differed from P. alba and P. nigra, but species did not differ significantly in their response to the FACE treatment. By the time fast-growing high-density forest plantations have passed the exponential growth phase and reached canopy closure, the likely effects of elevated atmospheric CO2 concentration on canopy architecture and absorption of Q(p) are minor. [References: 77]
机译：该模型用于预测森林对大气中CO2浓度升高的长期反应。尽管生产力模型基于树冠截获的光线，但封闭林分的实验数据却很少。但是，冠层内部的光，叶面积，冠层结构与单个叶片特征之间的关系可能会受到二氧化碳浓度升高的影响，进而影响碳的吸收。在高密度杨树人工林中使用自由空气CO2富集（FACE）设计，我们研究了CO2浓度增加对光合光子通量密度（Q（p））的透射率（tau）和比率的影响。红/远红光（R / FR），叶面积指数（LAI），叶倾角，叶绿素（chl）和氮（N）浓度以及第2和第3位的特定叶面积（SLA）多年的治疗。除了光和叶片特征的冠层高度轮廓外，还连续测量了tau。两年的Q（p）测量表明，在FACE处理中，冠层透射率平均下降，在冠层闭合时差异很小。结果由封闭冠层中未受影响的LAI解释，没有FACE引起的相对冠深度刺激。一致的是，在对照和FACE条件下，叶片的倾斜度和消光系数相似。 R / FR的比率不受FACE处理的影响不大，叶子的特性也没有受到影响，但叶子N除外，这可以推测N的限制。通常，冠层轮廓的处理差异是由FACE处理中高度生长的最初刺激引起的。 P. x euramericana与P. alba和P. nigra不同，但是物种对FACE处理的反应没有显着差异。当快速生长的高密度森林人工林通过指数生长期并达到树冠封闭时，大气CO2浓度升高对树冠结构和Q（p）吸收的影响很小。 [参考：77]

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