Chin J Plan Ecolo ›› 2004, Vol. 28 ›› Issue (6): 787-793.DOI: 10.17521/cjpe.2004.0103

• Research Articles • Previous Articles     Next Articles

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

GUO Shui-Liang1,2 FANG Fang1 HUANG Hua1 and QIANG Sheng3   

  1. (1 College of Chemistry and Life Sciences, Zhejiang Normal University, Jinhua, Zhejiang 321004, China)
  • Published:2004-11-10

Abstract: Plantago virginica, an annual weed species originating from North America, 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 indices of Plantago virginica, including spike weight per individual, flower number per spike, reproductive biomass per vegetative biomass and Gini coefficient, which 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, Alternathera philoxeroides, Ricinus communis, Chenopodium album, Rumex japonicus, Plantago asiatica, Sonchus oleraceus and Helianthus tuberoses. Their net photosynthetic rates (Y) and leaf photosynthetic active radiation (X) were modeled using the equation Y=aX2+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 (Y1), flower number (Y2), reproductive effort (Y3) and seed numbers per vegetative biomass (Y4) were as follows: Y1 = 0.138 2+15.959 8/X, Y2 = 46.306 9+6 914.07/X, Y3 = 0.046 9 + 0.000 2X and Y4 = 130.24 + 0.023 9X. 2) With an increase in the population density of P. virginica, the individual size inequality (Gini coefficient, Y5) declined by the following relationship: Y5 = 0.374 8 - 0.000 02X. 3) The individual size inequality (Y5) was negatively related to reproductive effort (X), following Y5 = 0.379 3 - 0.106 6X, which indicated that the population reproductive effort declined with an increase in individual size inequality. 4) The photosynthesis (Y) - light (X) response curve followed: Y = -7E-06X2+0.022 3X-0.831 2. The light compensation point, light saturation point and 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 CO2·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, Conyza canadensis, Erigeron annuus, Conyza bonarinsis, Ricinus communis, Solidago canadensis, Sonchus oleraceus, Rumex japonicus and Lantana camara, its net photosynthetic rate was lower than that of Erigeron annuus, Conyza canadensis, Conyza bonarinsis and Solidago canadensis, but higher than that of Chenopodium album, Sonchus 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 apparent in the three typical weedy species (Erigeron annuus, Conyza canadensis and Alternathera philoxeroides) but obvious in P. virginica and the escaped species, Mirabilis jalapa. Plantago virginica is an early-spring weedy species, and the high temperature and intensive light were not suitable for its growth during the last ten-day period of May. We drew the following conclusions based on the experimental results. 1) The high population density of P. virginica resulted in self-thinning, which reduced the individual size inequality. Because of environmental stress resulting from high densities, the high-density population of P. virginica switched to an r-strategy to increase its reproductive output by producing more seeds in order to maintain large numbers of offspring. Obviously, Plantago virgincia had the flexibility to adapt its reproductive strategy to environmental conditions. 2) If there was no human disturbance to the recipient environments, the populations of P. virginica would rapidly decline in the community over five successive years due to their higher light compensation point and their mucilage seeds. 3) Our suggestions for controlling Plantago virginica include protection of vegetation, planting horticultural plants with higher stalks and reducing disturbance to the recipient environments.