外来入侵植物飞机草和本地植物异叶泽兰对大气CO_2浓度升高的响应

Responses of invasive Chromolaena odorata and native Eupatorium heterophyllum to atmospheric CO_2 enrichment

大气CO2浓度升高影响外来植物入侵,研究外来入侵植物和本地植物对大气CO2浓度升高响应的差异,有助于准确预测和管理外来植物入侵。基于封顶式CO2生长室,模拟大气CO2浓度变化(对照和700μmol/mol),比较研究了外来入侵植物飞机草(Chromolaena odorata)和本地植物异叶泽兰(Eupatorium heterophyllum)形态、生长、生物量分配和光合特性对大气CO2浓度升高响应的差异。结果表明:(1)在当前大气CO2浓度下,飞机草总生物量、株高、基径和总叶面积高于异叶泽兰,分枝数低于异叶泽兰;CO2浓度升高,飞机的总生物量、株高、基径、分枝数和总叶面积分别增加了92%、41%、60%、325%和148%,高于异叶泽兰的32%、14%、30%、64%和79%,飞机草生长优势进一步提高。(2)无论在高或低CO2浓度下,飞机草根生物量分数(RMF)都低于异叶泽兰,叶生物量分数(LMF)和茎生物量分数(SMF)都高于异叶泽兰;CO2倍增两种植物RMF均降低,LMF和SMF均升高,但这2个参数对CO2倍增响应的种间差异不显著。(3)无论在高或低CO2浓度下,飞机草和异叶泽兰的净光合速率差异均不显著,CO2倍增对两种植物的净光合速率的促进作用相似。上述结果表明,在未来大气CO2浓度升高的条件下,飞机草的入侵性可能提高,入侵危害将加剧。

Atmospheric CO2 concentration had increased from a pre-industrial level of 270 μmol /mol to 350 μmol /mol in2005 and continues to increase at 1. 9 μmol /mol per year on average. It is well known that atmospheric CO2 enrichment may influence the invasiveness of introduced plant species. Identifying the effects of elevated CO2 on invasiveness of exotic plants is very important for improving our ability to predict and control potentially invasive species. Four closed-top chambers were used to control CO2 concentration,ambient atmospheric CO2concentration（ control） and doubled atmospheric CO2concentration（ 700 μmol /mol）. To determine the effects of atmospheric CO2 enrichment on invasiveness of Chromolaena odorata,a noxious invasive perennial herb or subshrub in many countries of Asia,Oceania and Africa,we compared C.odorata and its phylogenetically related indigenous plant Eupatorium heterophyllum in terms of morphology,growth,biomass allocation,and photosynthesis at two CO2 concentrations. Fourteen traits related to morphology,growth,biomass allocation,and photosynthesis were measured when C. odorata and E. heterophyllum were treated for nearly three months.At ambient CO2 concentration,total biomass,height,stem diameter,and total leaf area were significantly higher and branch number were lower for invasive C. odorata than for native E. heterophyllum,which contribute to form dense monoculture for the invader,outshading native plant species. CO2 enrichment significantly increased total biomass,height,stem diameter,branch number,and total leaf area in both species. For C. odorata,total biomass,height,stem diameter,branch number and total leaf area were increased by 92%,41%,60%,325%,and 148%,respectively,much higher than 32%,14%,30%,64%,and 79% for E. heterophyllum. Consistently,growth advantage of the invader over the native became more evident at doubled atmospheric CO2 concentration.CO2enrichment decreased root mass fraction（ RMF） and increased stem mass fraction（ SMF） and leaf mass fraction（ LMF） for both the invasive and native species. However,the responses of these traits to CO2 enrichment were not significantly different between C. odorata and E. heterophyllum. C. odorata allocated more biomass to stems and leaves and less to roots than E. heterophyllum at either ambient CO2 concentration or doubled atmospheric CO2 concentration. Higher LMF and SMF may help C. odorata to increase carbon assimilation,and lower RMF may help C. odorata to reduce respiratory carbon loss,facilitating biomass accumulation. The more efficient strategy of biomass accumulation adopted by the invader might still provide stronger competitive ability against the native.In addition,atmospheric CO2 enrichment significantly increased net photosynthetic rate（ Pmax） for both species,and the increases were not significantly different between C. odorata and E. heterophyllum. At both low and high CO2 concentration,Pmaxwas not significantly different between two species. This indicates that higher biomass accumulation of C. odorata may not be associated with photosynthesis,and benefit from other aspects at doubled atmospheric CO2 concentration.In conclusion,our results indicate that CO2 enrichment stimulates growth more greatly for invasive C. odorata than for native E. heterophyllum,and that in the future with high atmospheric CO2 concentration invasions by C. odorata may become more serious.