Davis J E, Arkebauer T J, Norman J M, Brandle J R
Department of Forestry, Fisheries and Wildlife, University of Nebraska-Lincoln, Lincoln, NE 68583-0814, USA.
Tree Physiol. 1987 Dec;3(4):387-92. doi: 10.1093/treephys/3.4.387.
Assimilation rate (A) versus intercellular CO(2) concentration (C(i)) relationships for leaflets of five-year-old green ash (Fraxinus pennsylvanica Marsh.) trees were computed from gas exchange measurements obtained in the field with a closed-circuit, portable photosynthesis measurement system comprising an LI-6200 gas analyzer and an LI-6000 computer, (Li-Cor, Inc., Lincoln, Nebraska, USA). Observations were made over a range of light intensities achieved by attenuating direct sunlight with neutral density filters, and over a range of ambient CO(2) concentrations achieved by breathing into the assimilation chamber and then lowering the CO(2) concentration to the desired level with the LI-6200's soda-lime scrubber. Boundary layer conductance was determined by use of a leaf replica made of moist filter paper. Typically, A-C(i) curves at four light intensities were obtained in three to four hours. The initial slope (when A = 0) of the A-C(i) curve obtained at a light intensity of 1750 micromol m(-2) s(-1) (full sunlight) was similar to that obtained at a light intensity of 840 micromol m(-2) s(-1). However, when light intensity was reduced further (to 370 and 160 micromol m(-2) s(-1)), the initial slope of the A-C(i) curve also decreased, indicating that at these light intensities, assimilation was limited by photochemical energy supply, as well as CO(2) concentration.
利用一套闭路便携式光合作用测量系统（该系统由一台LI - 6200气体分析仪和一台LI - 6000计算机组成，Li - Cor公司，美国内布拉斯加州林肯市）在野外获得的气体交换测量数据，计算了五年生美国绿梣（Fraxinus pennsylvanica Marsh.）树叶的同化速率（A）与细胞间二氧化碳浓度（C(i)）的关系。观测是在一系列光照强度下进行的，通过中性密度滤光片衰减直射阳光来实现不同光照强度；同时也在一系列环境二氧化碳浓度下进行观测，通过向同化室呼气，然后用LI - 6200的苏打石灰洗涤器将二氧化碳浓度降至所需水平来实现。边界层导度通过使用由湿滤纸制成的叶片复制品来测定。通常，在三到四个小时内获得了四个光照强度下的A - C(i)曲线。在1750 μmol m⁻² s⁻¹（全日照）光照强度下获得的A - C(i)曲线的初始斜率（当A = 0时）与在840 μmol m⁻² s⁻¹光照强度下获得的初始斜率相似。然而，当光照强度进一步降低（至370和160 μmol m⁻² s⁻¹）时，A - C(i)曲线的初始斜率也降低，这表明在这些光照强度下，同化作用受到光化学能量供应以及二氧化碳浓度的限制。
