论DNA C-值与植物入侵性的关系

Review on relationship between invasiveness of plants and their DNA C-value

外来植物的入侵已引起世界普遍关注,强调并迅速提高对外来植物的预警能力是目前首当其冲的任务,由此,如何预测植物的入侵能力,也就成为入侵生态学的一个核心问题。20世纪90年代以来,关于植物入侵争论的焦点集中于入侵植物本身的生物学特点或入侵生境特点,然而,争议多于结论,至今未能找出有效预测外来植物入侵性的答案。着重从DNAC-值与植物入侵性关系这一角度进行论述。自20世纪30年代以来,染色体数目、大小、倍性在细胞水平的变化被认为可能与植物入侵性相关,因为染色体数目、大小变化是物种在细胞水平上的一种表型变异形式,而细胞水平累积的效应有可能决定着植物整体水平上对环境的适应能力,从而决定植物的分布范围,最终与入侵性相关。但是,这些领域的研究也没有得到一致的结论。近年来,人们将注意力转移至被子植物DNAC-值变化在植物环境适应中的生物学意义。现有资料表明,DNAC-值与细胞大小、体积、重量、发育速率等细胞水平上的表型特征存在正相关关系,这些与核型相关的DNAC-值的影响效应,可扩展到多细胞植物有机体的发育速率,在植物生活史的各个阶段起作用,其中就影响到两个受时间因子限制同时又与植物分布相关联的特征——最短世代时间及生活周期类型,而许多入侵成功植物即表现为世代时间短等特点,对于入侵性植物,其不可避免会受生长时间及分布环境的限制,如能保证其在这两方面占有优势便能入侵成功。已有研究结果表明,某些外来入侵种比同属其它种类具有较低的核DNA含量,由此,提出通过研究植物DNAC值,就有可能预测植物入侵能力的强弱,低DNAC-值的植物具有更强的适应环境的能力,即与入侵性大小呈负相关,这为发现新的植物入侵性预测指标提供了思路。

More and more attention has been paid to invasive plants and their impact on native species, communities, and ecosystems. Prediction of the invasive potentials of alien species is an important subject in invasion ecology. Since the 1990s, most literature on predicting weediness or invasiveness of plants has focused on the characteristics of the plant, or on the invaded environment. Unfortunately, there has been no satisfactory answer about what attributes make some species more invasive. At the cellular level, the large variation in chromosome number and ploidy level may be an important form of phenotypic variation contributing to invasiveness. It has been questioned since the 1930s whether such variation is of adaptive significance and whether it is related to environmental factors ; however, no direct or causal links have yet been found. Because of the failure to demonstrate direct and causal relationships between chromosome number, ploidy level, and environmental factors, interest in gross genomic form has focused instead on the amount of DNA, especially after it was shown that the 1C amount is very variable among cohesive groups of species with similar organizational complexity. Variation in DNA C-value has far-reaching biological consequences and can be of considerable adaptive and hence ecological significance, especially in angiosperms. Considerable evidence has shown that striking positive relationships exist between DNA C-value and various phenotypic characters at the cellular level （i. e. cell size and mass, rate of cell development, etc. ）. DNA can affect the phenotype in two ways, firstly through expression of genetic information, and secondly, through the biophysical effects of its mass and volume, the latter defined as nucleotypic effects. Nucleotypic variation in DNA C-value sets absolute limits on both the minimum size and mass of the basic unit of plant anatomy （i. e. the cell） and the minimum time needed to produce a similar cell with newly synthesized organic molecules. Moreover, such effects are additive in complex multi-cellular vascular plants, and the potential effects of genome size （DNA C-value） can apply to every cell and tissue and act on many aspects of the life history of the plant, including growth rate, seed weight, minimum generation time and type of life cycle. Therefore, it profoundly affects where, when, and how plants grow. By reviewing current studies, we found that variation in DNA C-value has adaptive significance and is correlated with the environment and the geographical distribution of species. The success of different weed species was related many different traits, including the ability to： （1） establish quickly and display a short juvenile phase; （2） develop rapidly throughout the life cycle and have a short minimum generation time; and （3） rapidly produce many small seeds. All of these characters are known to correlate with low DNA C-value, especially in rapidly-changing environments. Thus, taking these various nucleotypic relationships together, it seems reasonable to predict that, as a class, successful weeds may tend to have smaller DNA C-values and a lower range of genome sizes than other species. In addition, plants of lower DNA C-value have more potential to acclimate to unstable environments, and become successful invaders, as evidenced by the negative relationship between nuclear DNA C-value and plant invasiveness. This review may provide a scientific basis for a predictive theory on plant invasiveness.