南方菟丝子寄生对喜旱莲子草生长及群落多样性的影响

菟丝子属植物是一种有潜力的入侵植物的生物防治剂。以南方菟丝子(Cuscuta australis)天然寄生的喜旱莲子草(Alternanthera philoxeroides)群落为研究对象,对比分析了南方菟丝子寄生对入侵植物喜旱莲子草生长的影响,同时采用群落调查的方法分析南方菟丝子寄生对入侵群落多样性的影响,以判断南方菟丝子是否具有防治喜旱莲子草的能力。结果表明南方菟丝子寄生可以降低喜旱莲子草的根生物量、茎生物量、叶生物量和总生物量,但与对照之间均不存在显著性差异;南方菟丝子寄生可以显著降低茎生物量比,显著增加根生物量比和根冠比。在无南方菟丝子寄生的喜旱莲子草群落中,除南方菟丝子和喜旱莲子草外,共有10科14属14种植物;而在南方菟丝子寄生的喜旱莲子草群落中,除南方菟丝子和喜旱莲子草外,共有16科27属28种植物,南方菟丝子能以产生吸器而寄生生长的植物共有19种,占样地植物种数的67.86%。南方菟丝子寄生可使群落物种丰富度显著性增加,也可使群落Simpson指数、Shannon-Wiener指数、McIntosh指数和均匀度指数增加,但是与对照之间不存在显著性差异。南方菟丝子寄生使喜旱莲子草的多度显著性下降,使喜旱莲子草的盖度和高度下降,但与未寄生的喜旱莲子草群落相比不存在显著性差异。但是南方菟丝子寄生可使喜旱莲子草在群落上的相对盖度、相对高度和相对多度均显著性下降,从而导致群落中喜旱莲子草的重要值显著性下降。南方菟丝子寄生可以在一定程度上抑制入侵植物喜旱莲子草的生长,促使群落多样性增加,促进本地群落的恢复。

Effect of the parasitic Cuscuta australis on the community diversity and the growth of Alternanthera philoxeroides

Exotic plant invades threaten natural ecosystems and human economic interests. Biological control should be the preferred control strategy to eradicate invasive plants and restore the natural ecosystems. Cuscuta spp. are holoparasitic plants, which absorb nutrients and water from the host and inhibit host plant growth. Cuscuta spp. have been found to help restore native communities by inhibiting the growth of invasive plants, reducing the cover of invasive plants and increasing community diversity and have been demonstrated to be potential biological control agents for invasive plants. Alternanthera philoxeroides, native to South America, is a noxious invasive plant throughout the world and is widely distributed in China. Mechanical, chemical and biological methods have been used to control the weed but to limited success. In the field, we find that A. philoxeroides is naturally parasitized by C. australis. We investigate the possibility of using C. australis to control A. philoxeroides by comparing the growth of A. philoxeroides and native community diversity in field plots where C. australis was present compared to control plots where C. australis was absent. Parasitism by C. australis caused A. philoxeroides to reallocate resources to belowground structures, significantly decreasing the stem:mass ratio and significantly increasing root:mass and root:shoot ratios. Parasitism by C. australis also tended to reduce leaf biomass, stem biomass, root biomass and total biomass, height and percent cover of A. philoxeroides, although these effects were not statistically significant. C. australis also increased diversity. In the plots without C. austraslis, we found 14 plant species belonging to 14 genera in 10 families. In the community dominated by A. philoxeroides parasitized by C. australis, we observed 29 plant species belonging to 27 genera in 16 families, 68% of which can be parasitized by C. australis. Parasitism by C. australis significantly increased species richness and tended to increase the Simpson diversity index, Shannon-Wiener diversity index, McIntosh diversity index and uniformity of the community. Parasitism of C. australis significantly decreased the abundance of A. philoxeroides in the community and decreased the cover and height of A. philoxeroides although these effects were not statistically significant. Parasitism of C. australis significantly decreased the relative cover, relative height, relative abundance and thus the important value of A. philoxeroides in the community. The results indicated that parasitism of C. australis could inhibit the growth of A. philoxeroides and increase community diversity, facilitating the restoration of native communities and illustrating the potential for the parasitic C. australis as a biological control agent for A. philoxeroides.