Invasion by alligator weed,Alternanthera philoxeroides,is associated with decreased species diversity across the latitudinal gradient in China

Aims Invasive species occurrence and their effects on biodiversity may vary along latitudes.We examined the occurrence(species cover)and relative dominance(importance value)of invasive alligator weed,Alternanthera philoxeroides,in its terrestrial habitat in China through a large-scale latitudinal field investigation.Methods We established 59 plots along the latitudinal transect from 21°N to 37°N.We recorded species name,abundance,height and individual species coverage of plants in every quadrat.We then measuredα-species diversity variations associated with the A.philoxeroides community across the latitudinal range.We also analyzed the effect of latitude on plant species’distributions in this community by using canonical correspondence analysis(CCA).Important Findings We found that species cover and importance value of A.philoxe-roides increased in areas<35°N,but decreased at higher latitudes.Lower latitudes supported greater species diversity than higher latitudes.Small-scale invasion of A.philoxeroides was associated with higher species diversity,but community diversity was lower when A.philoxeroides species cover exceeded 36%.Community plant species changed from mesophyte to hygrophyte gradually from low to high latitude.Our research suggests that latitude had significant influences on community diversity which interacted with the biotic resistance of a community and impact of invasion.Consequently,A.philoxeroides may become more invasive and have greater negative impacts on community species diversity in higher latitudes as global climate changes.

Tallow tree allocates contrasting secondary chemicals in response to varying environments along elevational gradients

了解树木如何沿海拔梯度调节多种类型的次生代谢产物对于阐明植物如何采用生理和生态策略来应对各种生物及非生物环境变化至关重要。本研究旨在探索乌桕如何分配不同的次生代谢产物来响应海拔梯度上的环境变化。我们在中国沿海拔梯度对乌桕不同取食类型的植食性昆虫及其对乌桕叶片的危害率进行了野外实地调查,并对健康叶片和虫害叶片中的次生代谢产物(单宁和黄酮类)进行了测定分析。研究结果表明,乌桕叶片被危害(咀嚼或潜叶式危害)的可能性随海拔的升高而减小。遭受虫害叶片和未遭受虫害的健康叶片中黄酮类化合物的浓度随海拔梯度变化呈现相反的趋势,即随着海拔的升高,健康叶片和遭受虫害叶片受不同的生物和非生物因素驱动,健康叶片中黄酮类化合物浓度增加,而遭受虫害叶片中黄酮类化合物浓度下降,其中槲皮苷对黄酮类化合物随海拔梯度变化的贡献最大。单宁浓度随海拔梯度的变化未发生显著变化,高海拔地区乌桕健康叶片中单宁与黄酮类化合物的比例与低海拔相比相对较低。我们的研究揭示了沿海拔梯度昆虫植食性以及不同植物次生代谢产物的变化趋势,并强调了在理解植物的生理和生态策略中同时考虑多种次生代谢物质的重要性。