物种内的遗传和表型变异对进化过程的影响已众所周知,但人们对种内变异如何影响群落水平过程还知之甚少.在人类对自然系统造成影响的大背景下,由于人类活动可能会产生巨大的选择压力,因此具有生态意义的种内变异可能会特别重要.在一项温室实验中,我们研究了一种分布广泛的入侵物种和农业杂草石茅(Sorghum halepense)在受到种间竞争、种内竞争和土壤肥力的影响时,其在生物量和根茎方面发生的种内变异和生态型变异.与我们的预期和此前的研究结果不同的是,我们并没有在这一早期生命阶段中发现石茅各生态型生物量的改变.然而,我们确实发现石茅的生物量会随着竞争植株种类和土壤施肥方式的不同而发生很显著的变化,同时不同株之间也存在很大差异.农业生态型的根茎较其它生态型大了11％,经施肥处理后的增大幅度更高至3倍;虽然施肥后的根茎生物量增加了～50％,但生态型之间却并无差异.有趣的是,当受到种内竞争时,与玉米(Zea mays)发生种间竞争时的情况相比,石茅的生物量和根茎生物量产出分别减少了32％和20％.我们的研究结果表明,针对相邻植株的种类而发生的物种特异性竞争响应以及根茎分配的改变,石茅在受竞争时可能会产生适应性响应,从而使分配情况发生改变.“,”Aims Within-species genetic and phenotypic variation have well-known effects on evolutionary processes,but less is known about how within-species variation may influence community-level processes.Ecologically meaningful intraspecific variation might be particularly important in the context of anthropogenic impacts on natural systems,such as agriculture and species invasion,because human actions can cause strong selection pressures.Methods In a greenhouse study,we explored intraspecific(30 accessions)and ecotypic variation(representing agricultural and nonagricultural habitats)in biomass and rhizome production in response to inter-and intraspecific competition and soil fertility of Johnsongrass(Sorghum halepense),a widespread invasive species and agricultural weed.Important Findings Contrary to our expectations and previous results,we did not find variation in biomass production among Johnsongrass ecotypes at this early life stage.However,we did find that Johnsongrass biomass varied substantially depending on competitor identity,soil fertility treatments and among accessions.Rhizomes were 11％ larger in the agricultural ecotype and up to 3-fold larger in fertilized treatment;while rhizome biomass increased by～50％ when fertilized,but did not differ among ecotypes.Interestingly,in competition,Johnsongrass produced 32％ less biomass and 20％ less rhizome mass with a conspecific than when competing interspecifically with corn.Our results indicate species-specific competitive responses and changes in rhizome allocation in response to neighbor identity;suggesting the possibility of adaptation by Johnsongrass to shift allocation under competition.