亚热带不同林地植物光合作用对空气CO_2浓度增高的响应

PHOTOSYNTHETIC RESPONSES OF PLANTS IN DIFFERENT SUBTROPICAL FORESTS ON INCREMENT OF ATMOSPHERIC CO_2 CONCERTRATION

以桃金娘、荷木及九节和罗伞分别代表生长在密林、中等疏密林和疏林植物 .在较高空气CO2 浓度下 ,随着光强增加 ,疏林的桃金娘光合速率 (An/ μmolm-2 s-1)与光强关系曲线的最初直线部分斜率为 0 .0 5 1,而中等疏密林的荷木和九节则分别为 0 .0 39和 0 .0 34 ,密林的罗伞则较低 ,仅为 0 .0 2 2 .疏林桃金娘的不包括光呼吸的CO2 补偿点为Γ 38.1μLL-1,较荷木和九节分别约高 8.8%和 10 .7% ;较罗伞约高 14.7% .除罗伞有较低光呼吸速率外 ,疏林的桃金娘和中等疏密林荷木及九节的光呼吸速率 (Rd)相似 .光合作用的Rup2 饱和速率 (Vcmax)80 .2 μmolm-2 s-1,较荷木和九节分别高 2 4.8%和 2 2 .9% ,表明生长在疏林的桃金娘有较大羧化作用潜力 .实际电子传递速率与Rup2 再生有关 ,桃金娘的实际电子传递速率为 10 2 .7μmolm-2 s-1,明显较荷木和九节高 .罗伞有低的电子传导率 ,可能罗伞光合速率受Rup2 再生的明显限制 .桃金娘的光能转化效率δ为 0 .47electrons/quan tum .而中等疏密林的荷木和九节则为 0 .2 3和 0 .2 6electrons/quantum .疏林植物生长快 ,光合产物库不受限制时 ,空气CO2 浓度增高 ,有利于促进阳生阔叶树种的光合速率持续增高 ,促进其种群优势 .图 4表 1参

Rhodomyrtus tomentose , Schima superba , Psychotria rubra , and Ardisia quinquegone are the plants growing in the forests with opening, moderate and high densities, respectively. Photosynthetic rate in leaf of Rhodomyrtus tomentose growing in the open subtropical forest increased with an enhancement of irradiation under higher CO 2 concentration. The initial slope of the relationship between photosynthetic rate and irradiation density was 0.051, while it was 0.039 and 0.034 for Schima superba and Psychotria rubra growing in the forest with moderate density. Lower value of 0.022 was found in Ardisia quinquegone growing in the dense forest. The CO 2 compensation point in absence of respiration in light, Γ *, was 38.1 μ L L -1 for Rhodomyrtus . It was higher than those of Schima and Psychotria by 8.8% and 10.7%, and higher than that of Ardisia by 14.7%, respectively. Besides Ardisia quinquegone which had lower light respiration rate ( R d), R d in Rhodomyrtus was similar to those of the others. The Rup 2-saturated CO 2 assimilation rate ( V cmax ) was 80.2 μ mol m -2 s -1 for Rhodomyrtus , higher than those for Schima and Psychotria by 24.4% and 22.9%, respectively, suggesting that Rhodomyrtus have higher potential carboxylation. The actual electron transport rate ( J a) is related to Rup 2-regenerating rate. Ja was 10.27 μ mol m -2 s -1 in Rhodomyrtus , and significantly low J a was found in the plants growing in the moderate and dense forests. The light energy conversion efficiency ( δ ), was 0.47 electrons per quantum in Rhodomyrtus , and 0.23 and 0.26 electrons per quantum in plants grown on moderate sites. The results show that photosynthetic rate could be increased as air CO 2 concentration was increased in the plants growing in the open sites, in which photosynthetic sink is not limited. The enhancing CO 2 may take advantage of the development of species on the open sites of subtropic forests. Fig 4, Tab 1, Ref 12