Hirose Tadaki, Ackerly David D, Traw M Brian, Bazzaz Fakhri A
Biological Institute, Graduate School of Science, Tohoku University, Aoba, 980-77, Sendai, Japan.
Department of Organismic and Evolutionary Biology, Harvard University, 16 Divinity Avenue, 02138, Cambridge, MA, USA.
Oecologia. 1996 Oct;108(2):215-223. doi: 10.1007/BF00334644.
Elevated CO may increase dry mass production of canopies directly through increasing net assimilation rate of leaves and also indirectly through increasing leaf area index (LAI). We studied the effects of CO elevation on canopy productivity and development in monospecific and mixed (1:1) stands of two co-occurring C annual species, Abutilon theophrasti, and Ambrosia artemisiifolia. The stands were established in the glasshouse with two CO levels (360 and 700 μl/l) under natural light conditions. The planting density was 100 per m and LAI increased up to 2.6 in 53 days of growth. Root competition was excluded by growing each plant in an individual pot. However, interference was apparent in the amount of photons absorbed by the plants and in photon absorption per unit leaf area. Greater photon absorption by Abutilon in the mixed stand was due to different canopy structures: Abutilon distributed leaves in the upper layers in the canopy while Ambrosia distributed leaves more to the lower layers. CO elevation did not affect the relative performance and light interception of the two species in mixed stands. Total aboveground dry mass was significantly increased with CO elevation, while no significant effects on leaf area development were observed. CO elevation increased dry mass production by 30-50%, which was mediated by 35-38% increase in the net assimilation rate (NAR) and 37-60% increase in the nitrogen use efficiency (NUE, net assimilation rate per unit leaf nitrogen). Since there was a strong overall correlation between LAI and aboveground nitrogen and no significant difference was found in the regression of LAI against aboveground nitrogen between the two CO levels, we hypothesized that leaf area development was controlled by the amount of nitrogen taken up from the soil. This hypothesis suggests that the increased LAI with CO elevation observed by several authors might be due to increased uptake of nitrogen with increased root growth.
高浓度二氧化碳（CO）可能直接通过提高叶片的净同化率，也可能间接通过增加叶面积指数（LAI）来提高冠层的干物质产量。我们研究了CO浓度升高对两种共生C一年生植物苘麻和豚草单种和混种（1:1）林分中冠层生产力和发育的影响。这些林分在温室中于自然光条件下设置了两种CO浓度水平（360和700 μl/l）。种植密度为每平方米100株，在生长53天内LAI增加到2.6。通过将每株植物种植在单独的花盆中来排除根系竞争。然而，在植物吸收的光量子数量和单位叶面积的光量子吸收方面，干扰是明显的。在混种林分中苘麻吸收更多光量子是由于不同的冠层结构：苘麻将叶片分布在冠层的上层，而豚草则将叶片更多地分布在下层。CO浓度升高并未影响混种林分中两种植物的相对表现和光截获。随着CO浓度升高，地上部总干质量显著增加，而未观察到对叶面积发育有显著影响。CO浓度升高使干物质产量增加了30 - 50%，这是由净同化率（NAR）提高35 - 38%和氮利用效率（NUE，单位叶氮的净同化率）提高37 - 60%介导的。由于LAI与地上部氮之间存在很强的总体相关性，并且在两种CO浓度水平下LAI与地上部氮的回归中未发现显著差异，我们推测叶面积发育受从土壤中吸收的氮量控制。这一假设表明，几位作者观察到的随着CO浓度升高LAI增加可能是由于根系生长增加导致氮吸收增加所致。
