外来入侵植物加拿大一枝黄花繁殖生物学研究

Study on reproductive biology of the invasive plant Solidago canadensis

加拿大一枝黄花(Solidago canadensis)原产北美,自然条件下既能结实,同时又能以地下茎出芽的方式克隆繁殖,是目前我国东部地区危害严重的外来入侵杂草之一,对我国部分省市的农业生产和生态环境构成了严重威胁.连续3a定点观测其种群扩张规律,从生境因子、种子性状及萌发特性、残体无性克隆生长,地下部分形态特征和各器官热值能量的季节动态变化等方面对加拿大一枝黄花的繁殖生物学作了研究,同时比较了加拿大一枝黄花和其他4种菊科外来杂草的地下部分形态特征.研究结果表明:(1)自然条件下,加拿大一枝黄花种子在3～10月期间均可萌发,4～5月份气候适宜,雨水充沛,是种子萌发的高峰期.夏季的6～8月份是其营养生长和克隆增殖的旺盛期,9月份开始献蕾,花果期为10月至翌年1月份.加拿大一枝黄花的结实量高达20000粒/株,种子(瘦果)千粒重为0.045～0.050g,含水量在60%～80%之间;(2)加拿大一枝黄花自然条件下种子萌发率约为30%,在不同pH值、盐浓度和湿度环境条件下种子萌发的耐受性较强.不同环境胁迫下的种子萌发率和沪浙地区加拿大一枝黄花土壤生境因子的调查结果均表明,该种比较适应干燥、透气性良好的酸性低盐砂壤土,对Zn、Cu、Pb等重金属耐性较高;(3)加拿大一枝黄花地下茎和植株基部节处能萌生克隆分株.在机械除草等人为干扰条件下加拿大一枝黄花采用应激繁殖对策,容易产生更多的克隆分株.植株残体的无性繁殖能力为地下部分＞基部茎＞茎秆,20cm基部茎＞30cm基部茎＞45cm基部茎,从小到大的机械破坏程度使地下部分残体出芽数依次减少,但累计出芽数反而增加;(4)与其他菊科外来杂草相比,加拿大一枝黄花地下部分的长度、表面积、体积等指标最大,说明其在地下部分形态上具有广泛逸生的结构基础;(5)加拿大一枝黄花地上部分生长速率以及多数地下部分形态指标在9月份达到最大值.8月份过于高温干旱的气候使茎、叶中的部分能量转向地下部分,增加须根以吸收更多的水分.加拿大一枝黄花生长周期内地下部分形态指标和各器官热值能量的动态变化与其兼备有性繁殖和克隆生长的繁殖对策相适应.

Solidago canadensis, a perennial composite plant originating from North America, was introduced into China as a horticultural plant in 1935. Under natural conditions, S. canadensis allocates large amounts of energy to sexual reproduction and produces many seeds, which reflects an r-strategy with high seed number and small seed size. In addition, naturalized populations have a great capacity to grow clonally with underground stems. S. canadensis has become an invasive weed in eastern China, and caused serious damage to agricultural production and ecosystems in several provinces of China. In order to understand the reproductive characteristics of S. canadensis and effectively control its spread, we examined soil conditions, seed characteristics, seed germination and the capacity for asexual reproduction in different plant parts. We investigated the population dispersion of S. canadensis in fixed sites for three years, and analyzed the seasonal dynamics of morphological parameters of belowground plant parts and the caloric values of different organs of S. canadensis. We also compared differences in the root systems of S. canadensis and composite exotic weeds. The following results were obtained： （1） Under natural conditions, the germination season of S. canadensis lasts from March to October, with a germination peak in April and May. Vegetative growth and asexual reproduction were especially vigorous during the summer season. A suitable climate, promotes seed germination in the rainy season, while high temperatures and soil drought stress increase vegetative growth and asexual reproduction. Most S. canadensis flower between September and January, and fruit in late October. A mature plant can produce about 20000 seeds. The mean weight of 1000 seeds ranges from 0. 045g to 0. 050g, and mean seed moisture content ranges from 60% to 80%. The light-winged seeds disperse readily by air, water, vehicles, human activity or on livestock. （2） S. canadensis seeds have a wide tolerance for different values of pH, salinity and soil moisture. The mean percent germination of seeds is 30% under suitable conditions. The results of seed germination under various environmental stresses and the investigation of soil conditions indicate that well-aerated, slightly acid soils with low salinity are suitable for the growth of S. canadensis. Additionally, S. canadensis has a high tolerance for contamination by heavy metal elements including Zn, Cu and Pb, but has low accumulation coefficients for these elements. （3） S. canadensis reproduces asexually by underground rhizomes and nodes on the stem base to recruit new individuals, and uses this reproductive strategy to produce clonal shoots in plants that experience mechanical damage. The capacity for asexual reproduction among different plant parts ranked as belowground parts 〉 stem-base （20cm） 〉 stem-base （30cm） 〉 stem-base （45cm） 〉 stem. The quantity of shoots produced by the plant decreases with increasing mechanical damage. （4） The morphological parameters of the root system of S. canadensis including length, surface area, volume, and average diameter were greater than for composite exotic weeds. These parameters indicate that S. canadensis has the physiological potential to widely invade China. （5） The aboveground growth rate and most of the belowground morphological parameters varied remarkably among seasons, with a peak normally occurring in September. In August, a fraction of the energy in leaves and stems is allocated belowground to increase fine root growth and water uptake during hot weather. Additionally, the seasonal dynamics of the belowground morphological parameters and the caloric values of different organs of S. canadensis enhance its reproductive ability. Based on the results above, we conclude that S. canadensis has great invasive potential in China. We suggest that urgent measures should be taken to control its further spread, and to minimize its impact on local plant diversity.