Arnone John A, Körner Christian
Department of Botany, University of Basel, Schönbeinstrasse 6, CH-4056, Basel, Switzerland.
Oecologia. 1993 Jul;94(4):510-515. doi: 10.1007/BF00566966.
Vertical structure of plant stands and canopies may change under conditions of elevated CO due to differential responses of overstory and understory plants or plant parts. In the long term, seedling recruitment, competition, and thus population or community structure may be affected. Aside from the possible differential direct effects of elevated CO on photosynthesis and growth, both the quantity and quality of the light below the overstory canopy could be indirectly affected by CO-induced changes in overstory leaf area index (LAI) and/or changes in overstory leaf quality. In order to explore such possible interactions, we compared canopy leaf area development, canopy light extinction and the quality of light beneath overstory leaves of two-storied monospecific stands ofRicinus communis exposed to ambient (340 μl l) and elevated (610 μl l) CO. Plants in each stand were grown in a common soil as closed "artificial ecosystems" with a ground area of 6.7 m. LAI of overstory plants in all ecosystems more than doubled during the experiment but was not different between CO treatments at the end. As a consequence, extinction of photosynthetically active radiation (PAR) was also not altered. However, under elevated CO the red to far-red ratio (R:FR) measured beneath overstory leaves was 10% lower than in ecosystems treated with ambient CO. This reduction was associated with increased thickness of palisade layers of overstory leaves and appears to be a plausible explanation for the specific enhancement of stem elongation of understory plants (without a corresponding biomass response) under elevated CO. CO enrichment led to increased biomass of overstory plants (mainly stem biomass) but had no effect on understory biomass. The results of this study raise the possibility of an important indirect effect of elevated CO at the stand-level. We suggest that, under elevated CO, reductions in the R:FR ratio beneath overstory canopies may affect understory plant development independently of the effects of PAR extinction.
由于上层和下层植物或植物部分的不同响应，在二氧化碳浓度升高的条件下，植物林分和冠层的垂直结构可能会发生变化。从长远来看，幼苗补充、竞争以及种群或群落结构可能会受到影响。除了二氧化碳浓度升高对光合作用和生长可能产生的不同直接影响外，上层冠层下方光照的数量和质量可能会因二氧化碳诱导的上层叶面积指数（LAI）变化和/或上层叶片质量变化而受到间接影响。为了探究这种可能的相互作用，我们比较了暴露于环境二氧化碳浓度（340 μl l）和升高的二氧化碳浓度（610 μl l）下的两层单种蓖麻林分的冠层叶面积发育、冠层光消光以及上层叶片下方的光质量。每个林分中的植物在共同的土壤中作为封闭的“人工生态系统”生长，占地面积为6.7平方米。在实验期间，所有生态系统中上层植物的叶面积指数增加了一倍多，但在实验结束时，不同二氧化碳处理之间没有差异。因此，光合有效辐射（PAR）的消光也没有改变。然而，在二氧化碳浓度升高的情况下，上层叶片下方测得的红/远红比（R:FR）比用环境二氧化碳处理的生态系统低10%。这种降低与上层叶片栅栏层厚度的增加有关，似乎是对二氧化碳浓度升高情况下下层植物茎伸长特异性增强（无相应生物量响应）的一个合理的解释。二氧化碳浓度升高导致上层植物生物量增加（主要是茎生物量），但对下层生物量没有影响。这项研究的结果提出了二氧化碳浓度升高在林分水平上产生重要间接影响的可能性。我们认为，在二氧化碳浓度升高的情况下，上层冠层下方R:FR比的降低可能会独立于PAR消光的影响而影响下层植物的发育。
