Differences In Leaf Functional Traits Between Exotic Invasive And Co-occurringnon-invasive Plants

With the increasing influence of humans,many exotic plants have invaded and continue to invade new range at an unprecedented rate,causing great threat to natural ecosystems and social economy.Leaf trait comparisons between invasive and their co-occurring native or non-invasive alien plants are effective methods to elucidate invasiveness of the invasive plants,and which is the foundation for managing and controlling the invasive plants in introduced ranges.The traits related with growth,defense and litter decomposition rates are closely associated with invasiveness of the invasive plants.However,the current results can not be refined a general conclusion due to most of these studies are limited to few species and common garden experiments.It urgently needs to perform a research with more species in a large scale range in the field to get a general conclusion.Using a meta-analytical approach,this study compared defense(52 pair of species),growth(173 pair of species)and leaf litter decomposition(147 pair of species)related traits between invasive and their co-occurring non-invasive(native and non-invasive alien)plants in 10 sites where range from southwest(Xishuangbanna)to northeast(Harbin)of China.The results are as follow:1.The results showed that invasive plants had significantly lower physical defensive compounds such as total cellulose,cellulose,hemicellulose,lignin,leaf tissue density,and leaf toughness than co-occurring native plants,but had no differences between invasive and non-invasive alien plants for these traits.There were no differences between invasive and native/non-invasive plants in chemical defensive compounds(phenols).The lower physical defensive compounds were related with low specialist enemy pressures(enemy release)which leads to increase the allocation of photosynthate to growth and reproduction,thus increasing the competitive abilities and contributing invasions.2.Invasive plants had significantly higher leaf nitrogen concentration(Nm),stomatal conductance(Gs),light-saturated photosynthetic rate(Pmax),photosynthetic energy-(PEUE),nitrogen-(PNUE),and phosphorus use efficiencies(PPUE),and had lower leaf carbon to nitrogen ratio(C:N)and payback time(PT)than co-occurring natives,but had no differences between invasive and non-invasive alien plants for these traits.There were no differences between invasive and native plants in leaf construction costs(CC),but the invasives had higher CC than the non-invasive aliens.Standardized major axis(SMA)regression analyses showed that Pmax and PEUE were positively correlated with Nm and Gs,respectively,and there were significant differences between invasive and non-invasive plants in shifts along the common slope with the invasives distributing toward the higher value of the end.These results suggested that the higher Nm and Gs contribute to the higher Pmax for the invasive plants.The higher Pmax results in the higher PEUE and the lower PT at similar CC,thus promoting invasions.Consistent with meta-analyses results,invasive plants had higher Pmax at a given Nm,which suggested that the invasives have significantly higher photosynthetic nitrogen-use efficiencies than the natives.3.Invasive plants had significantly higher leaf litter decomposition rate(Loss)than co-occurring natives,but had no differences between invasive and non-invasive alien plants.SMA analyses showed that the Loss was positively correlated with Nm and PEUE,respectively,and there were significant differences between invasive and non-invasive plants in shifts along the common slope with the invasives distributing toward the higher value of the end.These results suggested that the higher Nm not only contributes to the higher Pmax,but also contributes to the higher Loss for the invasive plants.The higher Loss may promote resource availability of habitat,increasing absorption and utilization of invasive plants to nutrients,thus increasing invasions.In conclusion,invasive plants with reduced physical defensive investments(lower lignin,cellulose and hemicellulose)may increase the allocation of photosynthate to growth and reproduction,increasing their competitive ability.Meanwhile,the reduced physical defensive investments could also increase the allocation of leaf nutrients(such as nitrogen)to physiological processes(photosynthesis),thus increasing the photosynthetic nutrient-use efficiencies(such as higher PNUE).Both the higher photosynthetic nutrient-use efficiencies and the higher nutrient absorptions(higher Nm)promote the higher photosynthetic rate for the invasive plants.The higher photosynthetic rate of the invasives contributes to the higher photosynthetic energy-use efficiency and the lower time of recover costs invested in constructing leaves(payback time)with the similar leaf construction costs relative to the natives,facilitating allocation of more photosynthate to growth and reproduction,thus contributing to invasions.In addition,both the lower physical defensive compounds and the higher leaf nitrogen concentration result in the higher leaf litter decomposition rate(Loss)for the invasive plants,which facilitates the absorption and utilization of invasive plants for the nutrients,thus increasing invasions.