Comparative Study On Leaf Functional Traits Of Seven Invasive Plants And Their Co-occurring Congeners

Invasions of exotic plant species has caused tremendous impacts on society,economics and environments worldwide,and the number of invasive species is increasing with development of globalization.It is important to explore invasiveness of invasive plant species through comparing leaf functional traits between invasive and native plant species,especially the traits that are closely associated with growth of plants.In the past,many studies compared the differences of functional characters between invasive species and native species in different habitats in the field,due to the interference of environmental factors,the differences between characters could not explain the invasiveness well,and the influence of kinship was seldom considered.In this study we compared seven exotic invasive plant species with their co-occurring native congeners in a common garden.The following 20 leaf traits,were compared: specific leaf area,leaf nutrient(nitrogen,phosphorus,potassium and ash)and carbon concentration,leaf carbon to nitrogen,leaf nitrogen to phosphorus,leaf construction costs,ash-free heat of combustion,light-saturated photosynthetic rate,dark respiration rate,transpiration rate,leaf stomatal conductance,intercellular carbon dioxide concentration,photosynthetic resources-use(nitrogen,phosphorus,potassium and energy)efficiency,and leaf payback time of constrution costs.The main results are as follows:1)The seven invasive species were not significantly different in specific leaf area compared with their co-occurring natives in total,and the performance of interspecific differences among species pairs was inconsistent.For example,the invasive plant Chenopodium hybridum had significantly higher specific leaf area,the invasive plants Panicum dichotomiflorm,Bidens frondosa and Solanum rostratum had significantly lower specific leaf area than co-occurring native congeners,and there was no significant difference between the invasive species of Xanthium,luteolina and Gracilaria and the native species.2)Invasive species had no significant differences in leaf carbon,nitrogen,phosphorus,potassium and ash concentration,and element stoichiometric ratio with their co-occurring natives in total.The interspecific differences in each trait were different among species pairs.For example,invasive Melilotus albus and Chenopodium hybridum had significantly higher leaf nitrogen concentration than co-occurring native congeners,while invasive Bidens frondosa,Panicum dichotomiflorm and Xanthium strumarium had significantly lower leaf nitrogen concentration.The invasive M.albus had significantly higher leaf phosphorous concentration than co-occurring native,while invasive X.strumarium,B.frondosa and Chenopodium hybridum had significantly lower phosphorus than their co-occurring nativecongeners,respectively.3)The overall differences in leaf construction costs and ash-free heat of combustion were not significant for the seven invasives and their co-occurring natives.The interspecific differences in each trait were different among species pairs.For example,invasive Chenopodium hybridum had significantly higher leaf construction costs than co-occurring native C.strictum,while invasive Panicum dichotomiflorm had significantly lower leaf construction costs han their co-occurring native congener.Invasive Bidens frondosa had significantly lower ash-free heat of combustion than their co-occurring native B.biternata,but the interspecific differences in this trait were not significant in other species pairs.4)The overall differences in leaf photosynthetic characteristics were not significant for the seven invasives and their co-occurring natives.In leaf light-saturated photosynthetic rate and dark respiration rate were not consistent for all seven invasive and native species pairs.However,the interspecific differences in stomatal conductance,intercellular carbon dioxide concentration and transpiration rate were different among pecies pairs.For example,invasive Bidens frondosa had significantly higher intercellular carbon dioxide concentration than co-occurring native B.biternata,while invasive Xanthium strumarium had significantly lower intercellular carbon dioxide concentration than their co-occurring native congener.5)The overall differences in photosynthetic resources-use(nitrogen,phosphorus,potassium and energy)efficiency and payback time of leaf construction costs were not significant for the seven invasives and their co-occurring natives.The interspecific differences in each trait(except payback time)were different among species pairs.For example,invasive Panicum dichotomiflorm and Xanthium strumarium had significantly higher photosynthetic nitrogen-use efficiency than their co-occurring native congeners,while invasive Chenopodium hybridum had significantly lower photosynthetic nitrogen-use efficiency than their co-occurring native C.strictum.The invasive C.hybridum had significantly lower photosynthetic energy-use efficiency than the their co-occurring native congener,but the interspecific differences in this trait were not significant in other species pairs.6)In conclusion,in the seven pairs of species compared,the differences of characters of invasive plants and symbiotic native plants are not significant in general,and the differences of most characters among species are not consistent in the performance of each pair of species These results indicated that leaf trait differences between invasive and native plant species are context-dependent,i.e.,species-specific and trait-specific.When exploring traits associated with invasive species through invasive-native species comparisont,it is important to consider the effects of the identities of the invasive and native species compared,for example species abundances in communies,residence time of invasive species,and many others.