Effects Of Soil Saline-alkaline Stress On Water Use Efficiency And Functional Traits Of Phragmites Australis And Bolboschoenus Planiculmis

Salt marsh plants in the West Songnen Plain,northern China,are threatened by increasing soil salinity and alkalinity since the late 20^th century.To explore how these wetland ecosystems respond to environmental changes,we examined the effect of saline-alkaline stresses and water stress?flooding/drought?on water use efficiency?WUE,assessed with stable carbon isotopes?and functional traits of Phragmites australis and Bolboschoenus planiculmis under both greenhouse and field.Our study will contribute to a better understanding of the influence of climate change and increasingly serious human disturbances on the distribution and productivity of these two important wetland species.The main conclusions showed as follows:?1?Western Songnen plain wetlands are mainly suffering from slight saline-alkalization stress.HCO₃^-and Na⁺showed the highest ion contents,indicating that sodium bicarbonate?NaHCO₃?is the main component of salinization in the wetlands of Western Songnen Plain.?2?Higher soil ion content decreased standing biomass of P.australis and B.planiculmis in the field and greenhouse,and increased WUE in the greenhouse.With higher water level,standing biomass of P.australis increased,while that of B.planiculmis decreased in both the field and greenhouse.?3?Individual traits showed a strong response to saline-alkaline and water stress:the traits reached an explained variance of 74%.Traits that were best explained by saline-alkaline and water stress were traits that are part of the commonly accepted plant strategy schemes,which mainly reflect adaptations to light,nutrients and disturbance.P.australis and B.planiculmis adapted to soil saline-alkaline stress by regulating leaf shape traits and whole-plant traits.?4?Compared to water level and stress type,soil ion content,especially high alkaline ion content,exerted the stronger influence on growth of both species.However,low alkaline ion content promoted growth of B.planiculmis.Our findings suggest that under high ion contents,P.australis is more tolerant to flooding stress while B.planiculmis is more tolerant to drought stress.?5?In the field,plant abundance of the two species was indicated by plant height,leaf organic carbon content and specific leaf area?SLA?,while in the greenhouse,by plant dry weight,leaf shape traits and WUE.Plant abundance of P.australis was indicated by WUE and leaf shape traits and for B.planiculmis,by plant dry weight.?6?The traits indicating plant abundance of P.australis were different from those of B.planiculmis.WUE or leaf shape traits?such as leaf area,leaf length and SLA?indicated the change in abundance of specific leaf area,i.e.,small leaf and low SLA showed low abundance,while for B.planiculmis,whole plant traits?plant dry weight or height?indicated the change of community abundance,i.e.,slight plant dry weight and low plant height showed low abundance.?7?P.australis and B.planiculmis showed different adaptive strategies to saline-alkaline and water stresses.P.australis was more tolerant to high soil ion contents than B.planiculmis,particularly under alkaline conditions.On the other hand,B.planiculmis grew well under low water level conditions?<10 cm?,while P.australis preferred high water levels.Relative to other wetland plants,WUE of P.australis was the highest,indicating that P.australis had a high ability to modulate and increase WUE to resist its adverse environment.