Effects Of Elevated CO₂ And Different N Levels On Seedling Growth And Photosynthetic Characteristics Of Native And Exotic Mangrove Species

Mangroves are woody plant communities growing in the intertidal zones along the tropical and subtropical coasts.With the increase of global CO2 concentration and the eutrophication of coastal sea water,mangroves at the boundary between land and sea have attracted more and more attention.At present,there are few studies on the synergistic effects of elevated CO2(800 μmol·mol-1)and N eutrophication(1 mol·m-3,5 mol·m-3,10 mol·m-3)on mangrove seedlings.In this study,four mangrove species,Aegiceras corniculatum(Ac),Avicennia marina(Am),Laguncularia racemosa(Lr)and Sonneratia apetala(Sa)were cultivate in 120 days under controlled greenhouse conditions and the growth and photosynthetic characteristics were measured under the treaments of CO2 elevation and the increased N concentration.The conclusions are as follows:1.There was no significant difference in the growth indexes(stem high,branches,leaves,intermodal length)of Ac and Am seedlings under the condition of CO2 elevation,while the growth indexes(stem diameter,stem high,branches,leaves,intermodal length)of Lr were significantly increased,and those indexes of Sa were decreased under CO2 elevating condition.With the increase of N concentration under the same CO2 concentration,most of the growth indexes of the four mangrove plants showed a trend of increasing at first,and followed by decreasing.2.There was no significant effect of CO2 elevation on the biomass of Ac,Am and Sa,but the biomass of Lr increased significantly at medium and high N concentrations The biomass of Lr increased by 60.61%when N concentration was 5 mol·m3.The root to shoot ratio of Ac and Am increased significantly under no N concentration and high N concentration conditions,increased significantly under low N concentration conditions in Lr,but showed no significant effect on Sa.3.Under the CO2 elevated condition,the net photosynthetic rate of the four species of mangrove seedlings increased significantly under the low N concentration condition,and the percentage of increase was more than 10%.CO2 elevation had no significant effect on the leaf transpiration rate of Ac and Sa,but significantly increased the leaf transpiration rate of Am and Lr under the conditions of no and low N concentrations(245.2%and 51.84%increased).Under the conditions of no N and low N concentration,CO2 elevation had significant effect on the stomatal conductance of Am and Lr(increased by 405.82%and 88.15%),but had no significant effect on the stomatal conductance of Ac and Sa.Under the condition of no N and low N concentration,the WUE(Water Use Efficiency)of Ac and Sa was significantly increased,and under the condition of medium N and high N concentration,the WUE of Lr was significantly increased(56.34%and 109.68%),but the WUE of Am was not significantly affected.The CO2 effects on growth and photosynthetic characteristics of Lr and Sa were not significantly enhanced those in Sa.The response trend of the four mangrove speciese to N concentration was consistent.We can infer that,the communities of Ac and Am may remain stable,in the future CO2 elevated and N enrrophication.The growth and competing potenticals of Lr may increase,while may decrease in Sa.In the intersecting zone of Lr and native species,the possibility of successful invasion of Lr increased greatly,while in the intersecting zone of Sa and native species,the possibility of successful invasion of Sa decreased.