外来入侵杂草薇甘菊及其伴生种基本光合特性的比较

COMPARISON OF BASIC PHOTOSYNTHETIC CHARACTERISTICS BETWEEN EXOTIC INVADER WEED MIKANIA MICRANTHA AND ITS COMPANION SPECIES

以ＬＣＡ４光合蒸腾测定系统测定了植物叶片的气体交换过程，比较分析了薇甘菊与周围其它藤本、草本和阔叶速生木本植物之间光合速率的差异。结果表明：（１）匍匐攀援草质藤本薇甘菊Ｍｉｋａｎｉａｍｉｃｒａｎｔｈａ具有较高的ＣＯ_2固定能力，净光合速率２１．５６μｍｏｌ ＣＯ_2 ｍ^-1S^-1，高于草质藤本野葛Ｐｕｅｒａｒｉａｌｏｂａｔａ（１６．９７），草质缠绕藤本五爪金龙 Ｉｐｏｍｏｅａ ｃａｉｒｉｃａ（１４．５５），与一年生鬼针草 Ｂｉｄｅｎｓ ｂｉｐｉｎｎａｔａ（２４．３２）接近，但低于多年生粗壮草本五节芒 Ｍｉｓｃａｎｔｈｕｓ ｆｌｏｒｉｄｕｌｕｓ（３３．７７）；（２）正午 １２：００后薇甘菊净光合速率和气孔导度出现一定程度的下降，降幅分别约为３０％和４７％，下降的起始时间滞后于林下灌木，光合作用光饱和点１００２ μｍｏｌ ｍ^-2s^-1，表明薇甘菊为喜阳植物；（３）当林内光强低至７０ μｍｏｌｍ^-2s^-1时，薇甘菊仍然维持 ２ μｍｏｌ ＣＯ_2 ｍ^-2s^-1左右的净光合速率，且其光合作用的光量子效率（ＱＵＥ）高于五节芒，光补偿点则相反，提示薇甘菊具有适应阴生环境的能力或特性。这些信息有助于解释薇甘菊生长迅速。

Gas exchange in leaves of selected plants was measured by using LCA-4 portable photosynthesis and transpiration system (ADC, England). Analysis of the difference in net photosynthetic rate (Pn) between Mikania micrantha and its companion species was also made. Results were as follows : (1) Mikania micrantha, a herbaceous vine, had a strong capacity for CO2 fixation, the Pn being 21 .56 μmol CO２ m-2S-1, which was higher than that in the accompanying somewhat woody twiner Pueraria lobata (16.97) and climbing herb Ipomoea cairica (14.55), and was close to that in annual herb Bidens bipinnata (24.32), with the exception of the grass Miscanthus floridulus (33.77). (2) Pn and leaf stomatal conductance (Gs) of Mikania micrantha increased before noon time and started to decrease after 12:00, the extent of decrement was little, and the time of revealable decrease was lagged more than those of understory shrubs, together with the high light compensation point of photosynthesis (1002 umol m-2s-1), it is suggested that Mikania micrantha is intrinsically a heliophylic species. (3) Compared to the sun grass Miscanthus floridulus, Mikania micrantha also showed its capability in acclimation to shade environment, which was observed by its higher quantum use efficiency and lower light compensation point, and by the evidence of maintaining the Pn at about 2 umol CO2 m-2s-1 when leaf incident light in the forest was lowered to 70 umol m-2s-1. The information presented in this paper would be helpful for understanding about Mikania micrantha in aspects of fast growing and spreading, large biomass and great production, and its distribution patterns in nature. It might also be useful to the advanced study on the control approaches of the growth and development of this exotic weed.