Reekie E G, Bazzaz F A
Department of Organismic and Evolutionary Biology, Harvard University, 02138, Cambridge, MA, USA.
Oecologia. 1989 May;79(2):212-222. doi: 10.1007/BF00388481.
Seedlings of five tropical trees, Cecropia obtusifolia, Myriocarpa longipes, Piper auritum, Senna multijuga and Trichospermum mexicanum, were grown both as individuals, and in competition with each other at ambient (350) and two levels of elevated CO (525 and 700 μl l) for a period of 111 days. Growth, allocation, canopy architecture, mid-day leaf water potential and soil moisture content were assessed three times over this period for individually grown plants, and at the end of the experiment for competitively grown plants. In addition, leaf photosynthesis and conductance were assessed for the individually grown plants midway through the experiment, and light profile curves were determined for the competitive arrays at three stages of development. Elevated CO did not affect photosynthesis or overall growth of the individually-grown plants but did affect canopy architecture; mean canopy height increased with CO in Piper and Trichospermum and decreased in Senna. Stomatal conductance decreased slightly as CO increased from 350 to 525 μl l but this had no significant effect upon whole plant water use of leaf water potential. Soil moisture content for the individuals increased marginally as CO increased, but this did not occur in the competitive arrays. There was a marked effect of CO upon species composition of the competitive arrays; Senna decreased in importance as CO increased while Cecropia, Trichospermum and Piper increased in importance. Stepwise regression analysis using competitive performance as the independent variable, and the various morphological and physiological parameters measured on the individually grown plants as independent variables, suggested that canopy height was the single most important variable determining competitive ability. Also significant were photosynthetic rate (particularly at low light levels) and allocation to roots early in the experiment. Light profiles in the canopy revealed that less than 15% of incident light penetrated to the level of mean canopy height. Results suggest that competition for light was the major factor determining community composition, and that CO affected competitive outcome through its affect upon canopy architecture.
五种热带树木，钝叶蚁栖树、长柄多果乌桕、耳叶胡椒、多花番泻和墨西哥刺蒴麻的幼苗，分别单独种植，并在环境二氧化碳浓度（350 μl l）以及两个升高的二氧化碳水平（525和700 μl l）下相互竞争生长111天。在此期间，对单独种植的植株生长、分配、冠层结构、午间叶片水势和土壤水分含量进行了三次评估，并在实验结束时对竞争生长的植株进行了评估。此外，在实验中期对单独种植的植株的叶片光合作用和导度进行了评估，并在竞争组合的三个发育阶段测定了光强曲线。升高的二氧化碳对单独种植的植株的光合作用或整体生长没有影响，但对冠层结构有影响；在胡椒和墨西哥刺蒴麻中，平均冠层高度随二氧化碳浓度升高而增加，在番泻中则降低。随着二氧化碳浓度从350 μl l增加到525 μl l，气孔导度略有下降，但这对整株植物的水分利用或叶片水势没有显著影响。随着二氧化碳浓度增加，单独种植植株的土壤水分含量略有增加，但在竞争组合中未出现这种情况。二氧化碳对竞争组合的物种组成有显著影响；随着二氧化碳浓度增加，番泻的重要性降低，而蚁栖树、墨西哥刺蒴麻和胡椒的重要性增加。以竞争表现为自变量，以单独种植植株上测量的各种形态和生理参数为自变量进行逐步回归分析，结果表明冠层高度是决定竞争能力的唯一最重要变量。光合速率（特别是在低光照水平下）和实验早期对根系的分配也很重要。冠层中的光强曲线显示，不到15%的入射光穿透到平均冠层高度水平。结果表明，对光的竞争是决定群落组成的主要因素，二氧化碳通过影响冠层结构影响竞争结果。
