ABSTRACT Allelopathic suppression of the growth of co-occurring plant species in invaded ecosystems is an important factor in some plant invasions. This study uses leaf extracts of the invasive plant species Conyza canadensis to determine its allelopathic effects along a latitudinal gradient, and under different cover classes and degrees of invasion, on seed germination and growth of Lactuca sativa, a sensitive bioindicator of allelochemicals. The allelopathic effects of C. canadensis on seedling height, root length, seedling biomass, germination percentage, germination potential, germination index, germination rate index, and vigor index of L. sativa increased significantly with increasing latitude. A possible explanation is that the leaves of plants growing in high latitudes secrete a higher concentration of allelochemicals than do leaves of plants growing in low latitudes. The allelopathic effects of C. canadensis on seedling height, seedling biomass, germination potential, germination index, germination rate index, and vigor index of L. sativa decreased with increasing degree of invasion. The more intense allelopathic effects of C. canadensis at lower degrees of invasion may enable it to establish populations in ecosystems by inhibiting the seed germination and growth of co-occurring species.

ABSTRACT This study aims to determine the allelopathic potential of Amaranthus retroflexus (Ar) with different climatic zones on seed germination and growth of A. tricolor (At) treated with a gradient N addition. Ar leaf extracts only displayed significantly allelopathic potential on the underground growth of Ar but not the aboveground growth of At. The allelopathic potential of Ar leaf extracts on root length of At were enhanced under N addition and there may be a N-concentration-dependent relationship. The effects of the extracts of Ar leaves that collected from Zhenjiang on seed germination and growth of At may be higher than that collected from Jinan especially on root length of At under medium N addition. This reason may be the contained higher concentration of secondary metabolites for the leaves of plants that growths in high latitudes compare with that growth in low latitudes. This phenomenon may also partly be attributed to the fact that Ar originated in America and/or south-eastern Asia which have higher similarity climate conditions as Zhenjiang rather than Jinan. The allelopathic potential of Ar on seed germination and growth of acceptor species may play an important role in its successful invasion especially in the distribution region with low latitudes.

RESUMO Este estudo tem por objetivo determinar as características florísticas de espécies exóticas invasoras de plantas com sementes (EEIPS) na China. Há um total de quinhentas e treze EEIPS, pertencentes a duzentos e oitenta e três gêneros. Setenta famílias foram classificadas em nove tipos de distribuição ao nível de família. "Cosmopolita" e "Pantropical" são os tipos principais. Duzentos e oitenta e três gêneros foram classificados em doze tipos de distribuição ao nível de gênero. "Pantropical", "Asia Trop. & Amer. disjuntas" e "Cosmopolita" são os três tipos principais. Estes resultados revelam certo grau de diversidade entre EEIPS na China. As características florísticas ao nível de família exibem fortes características pantropicais. Duas possíveis razões para isso são as seguintes. Primeiramente, o sudeste da China é fortemente invadido por espécies alienígenas invasivas e esta região possui clima ameno. Em segundo lugar, o sudeste da China é mais perturbado por atividades humanas do que outras regiões da China. As características florísticas ao nível de gênero mostram forte distribuição pantrópica, mas com abundantes características temperadas. Isto pode ocorrer porque a China cruza cinco zonas climáticas e os ecossistemas nos quais a maioria das espécies invasoras ocorre tem o mesmo clima de seu habitat natural ou similar.

ABSTRACT This study aims to determine the floristic characteristics of alien invasive seed plant species (AISPS) in China. There are a total of five hundred and thirteen AISPS, belonging to seventy families and two hundred and eighty-three genera. Seventy families were classified into nine areal types at the family level, and "Cosmopolitan" and "Pantropic" are the two main types. Two hundred and eighty-three genera were classified into twelve areal types at the genus level, and "Pantropic", "Trop. Asia & Amer. disjuncted", and "Cosmopolitan" are the three main types. These results reveal a certain degree of diversity among AISPS in China. The floristic characteristics at the family level exhibit strong pantropic characteristics. Two possible reasons for this are as follows. Firstly, southeastern China is heavily invaded by alien invasive plant species and this region has a mild climate. Secondly, southeastern China is more disturbed by human activities than other regions in China. The floristic characteristics at the genus level display strong pantropic but with abundant temperate characteristics. This may be due to that China across five climatic zones and the ecosystems in which the most alien invasive plant species occur have the same or similar climate with their natural habitat.