外来入侵植物北美车前繁殖及光合生理生态学研究

STUDIES ON THE REPRODUCTION AND PHOTOSYNTHETIC ECOPHYSIOLOGY OF THE EXOTIC INVASIVE PLANT, PLANTAGO VIRGINICA

北美车前 (Plantagovirginica)原产北美 ,2 0世纪 5 0年代进入我国华东地区 ,近年来其种群呈现爆发式增长态势 ,已分布到上海、浙江、江西、江苏等省区 ,是一种典型的生态入侵种。本文计测了该种在不同密度下的繁殖指标 ,统计了种群密度与繁殖指标间的关系 ;应用LAC_4 (ADC英国 )光合和蒸腾系统测定了该种及其伴生杂草一年蓬 (Erigeronannuus)、小飞蓬 (Conyzacanadensis)、野塘蒿 (Conyzabonarinsis)、马缨丹 (Lantanacamara)、空心莲子草 (Al ternatheraphiloxeroides)、菊芋 (Helianthustuberoses)、蓖麻 (Ricinuscommunis)、紫茉莉 (Mirabilisjalapa)、车前 (Plantagoasi atica)、苦苣菜 (Sonchusoleraceus)、羊蹄 (Rumexjaponicus)、藜 (Chenopediumalbum)和黄鹌菜 (Youngiajaponica)等杂草的光合作用指标 ,作出了它们的光合 光响应曲线。主要实验结果有 :1)北美车前个体花穗重 (Y1)、花数 /穗 (Y2 )与种群密度 (X)呈现倒数关系 (Y1=0 .1382 +15 .95 98/X ,Y2 =4 6 .30 6 9+6 914 .0 7/X) ;随着种群密度增加 ,北美车前的繁殖投资 (Y3 )、与繁殖投资关系密切的种子数 /营养器官重 (Y4)呈线性增加 (Y3 =0 .0 4 6 9+0 .0 0 0 2X ,Y4=130 .2 4 +0 .0 2 39X) ;2 )随着北美车前种群密度的增加 。

Plantago virginica, an annual weed species originating from North Ameri ca, was introduced into Eastern China during the 1950's. The populations of this invasive species have spread rapidly during recent years in Zhejiang, Jiangsu, Jiangxi, Guangdong and Hunan provinces. In the present paper, reproductive indic es of Plantago virginica, including spike weight per individual, flower numb er p er spike, reproductive biomass per vegetative biomass and Gini coefficient, whi ch indicates individual size inequality, were obtained from populations growing at different densities. The photosynthetic indices of Plantago virginica and its companion species were determined using a LCA-4 portable photosynthesis and transpiration system (ADC, England). The companion species included Erigeron annuus, Conyza canadensis, Conyza bonarinsis, Lantana camara, Mirabilis jalapa, Altern athera philoxeroides, Ricinus communis, Chenopodium album, Rumex japonicus, Plan tago asiatica, Sonchus oleraceus and Helianthus tuberoses. Their net photo synthe tic rates (Y) and leaf photosynthetic active radiation (X) were modeled using the equation Y=aX 2+bX+c. The main experimental results are summarized below. 1) During the reproductive phase, the relationships of the population density (X) with spike weight per individual (Y 1), flower number (Y 2), reproductive effort (Y 3) and seed numbers per vegetative biomass (Y 4) were as follows: Y 1 = 0.138 2+15.959 8/X, Y 2 = 46.306 9+6 914.07/X, Y 3 = 0.046 9 + 0.000 2X and Y 4 = 130.24 + 0.023 9X. 2) With an in crease in the population density of P. virginica, the individual size inequa lity (Gini coefficient, Y 5) declined by the following relationship: Y 5 = 0 .374 8 - 0.000 02X. 3) The individual size inequality (Y 5) was negatively re l ated to reproductive effort (X), following Y 5 = 0.379 3 - 0.106 6X, wh ich indicated that the population reproductive effort declined with an increase in individual size ine quality. 4) The photosynthesis (Y) - light (X) response curve followed: Y = -7E-06X 2+0.022 3X-0.831 2. The light compensation point, light satur ation point an d the maximum net photosynthetic rate of P. virginica were 37.32 μmol·m -2 ·s -1 , 1 593 μmol·m -2 ·s -1 and 16.93 μmol CO 2· m -2 ·s -1 , respectively, indicating that P. virginica is a typical heliophyte. The shade-tolerant ability of P . virgincia was lower than that of Plantago asiatica, Youngia japonica, Cony za canaden sis, Erigeron annuus, Conyza bonarinsis, Ricinus communis, Solidago canadensis, Sonchus oleraceus, Rumex japonicus and Lantana camara, its net photosynthe tic ra te was lower than that of Erigeron annuus, Conyza canadensis, Conyza bonarinsi s and Solidago canadensis, but higher than that of Chenopodium album, So nchus oleraceus, Ricinus communis and similar to that of Plantago asiatica. 5) During the last ten-day period of May, the photosynthetic “midday-depression” was not ap parent in the three typical weedy species (Erigeron annuus, Conyza canadensis and Alternathera philoxeroides) but obvious in P. virginica and the es caped species, Mirabilis jalapa. Plantago virginica is an early-spring weedy species, and th e high temperature and intensive light were not suitable for its growth during t he last ten-day period of May. We drew the following conclusions based on the experimental results. 1) The hig h population density of P. virginica resulted in self-thinning, which reduce d th e individual size inequality. Because of environmental stress resulting from hig h densities, the high-density population of P. virginica switched to an r-st rate gy to increase its reproductive output by producing more seeds in order to maint ain large numbers of offspring. Obviously, Plantago virgincia had the flexib ilit y to adapt its reproductive strategy to environmental conditions. 2) If there w as no human disturbance to the recipient environments, the populations of P. v irginica would rapidly decline in the community over five successive years due to