入侵植物藿香蓟与常见伴生杂草的生态位特征

Niche characteristics of the invasive plant Ageratum conyzoides and its commonly associated weeds

基于传统生态位理论的生物入侵机制假说认为外来种和土著种生态位的差异是决定入侵成功与否和危害程度的关键。藿香蓟(Ageratum conyzoides L.)是一种在我国南方快速蔓延的恶性入侵种。为了了解藿香蓟与其他杂草在群落中的生态关系,探究造成藿香蓟成功入侵的可能机制及危害,在浙西南的丽水市开展了杂草群落调查,计算了藿香蓟和16种常见本地杂草的生态位宽度、生态位重叠和种间相关系数,并对主要物种进行典范对应分析(CCA)排序。结果表明(1)藿香蓟与常见本地杂草间的生态位重叠度显著高于本地杂草间的生态位重叠度,这与藿香蓟具有最大的生态位宽度有关;(2)藿香蓟与常见本地杂草的Pianka生态位重叠指数介于0.04—0.296之间,重叠度处于中下水平;(3)常见本地杂草对于藿香蓟的n-维超体积生态位重叠值显著高于藿香蓟对于常见本地杂草的n-维超体积生态位重叠值;(4)藿香蓟在CCA排序图上处于较中心的位置,说明其具有较高的中生性;不仅如此,外来杂草和本地杂草在排序图上充分混杂,说明外来种相对于本地种并无明显特化;(5)群落中大多数常见杂草间未出现显著种间负相关,仅7个种对显著正相关,大多数种对不相关。总的来说,丽水农村的杂草群落稳定较差,资源相对充足,种间生态位重叠较低,本地植物对于藿香蓟的竞争阻抗较小,加上藿香蓟本身较大的生态位宽度,导致了藿香蓟在本地区广泛而严重的入侵。

According to the hypothesized mechanism of biological invasion,which is based on traditional niche theory,niche differentiation between alien species and native species is the key to the success of invasion and the damage it causes.Ageratum conyzoides L.is a malignant invasive species that is spreading rapidly in southern China.In order to understand the ecological relationships between A.conyzoides and native weeds in the community and to explore the possible mechanism of A.conyzoides invasion and its harmfulness,an investigation of the weed community was carried out in southwestern Zhejiang Province(28°06′—28°44′N,119°32′—120°08′E)from 2014 to 2016.A total of 109 plots(1 m×1 m)and 286 plant species were investigated in the following habitats:roadside,abandoned farmland,streamside,and open forest.For each plot,all aboveground plant material was harvested,classified,and weighed according to species.In addition,slope,aspect,and altitude of the plot as well as the rate of sunshine arriving at the plot were measured.Moreover,pH value and the contents of total nitrogen,alkaline nitrogen,effective phosphorus,available potassium,and organic material in superficial soil(0—10 cm depth)of each plot were tested.Levin′s niche breadth,Pianka′s niche overlap,probability of n-dimensional niche overlap,and interspecific correlation coefficients of A.conyzoides and 16 common native weeds were calculated,and a canonical correspondence analysis(CCA)was conducted.The results showed that(1)the degree of niche overlap between A.conyzoides and common native weeds was significantly higher than that between any two native weeds,due to the largest niche breadth of A.conyzoides.(2)The Pianka niche overlap index between A.conyzoides and common native weeds was in the middle or lower level of 0.04—0.296.(3)The probabilities of n-dimensional niche overlap of common native weeds with A.conyzoides were significantly higher than those of A.conyzoides with common native weeds.(4)A.conyzoides was distributed in the central region of a CCA ordination chart,which indicated that A.conyzoides was a mesophilic species;moreover,exotic weeds(including A.conyzoides)and native weeds were fully mixed in the ordination chart,which indicated that there was no obvious specialization of exotic species relative to native species;and(5)there were no significantly interspecific negative correlations among the 17 common weed species;only 7 species pairs showed significantly positive correlation,and most species did not correlate with each other.In general,the weed community in the rural areas of southwestern Zhejiang Province is unstable,with relatively sufficient resources and low niche overlap among species.Low competition resistance from native plants and large niche width of A.conyzoides lead to extensive and serious invasion of A.conyzoides in the rural area of southwestern Zhejiang Province.