Water Use Characteristics Of Six Plants In The Feldspathic Sandstone Area Of Ordos Plateau

It is imperative to restore and rebuild vegetation in the feldspathic sandstone area of Ordos Plateau due to less rainfall,severe erosion and deteriorating ecological environment.Water is the main limiting factor for local plant growth.Therefore,species selection is crucial to improve the stability and sustainability of vegetation restoration.Species with high water use efficiency and drought tolerance are necessary.This paper took six plants in the feldspathic sandstone area as research objects.They were Hippophae rhamnoides,Achnatherum splendens,Rheum palmatum,Amygdalus pedunculata,Pnnisetum amerieanum×P.pureum and Elaeagnus pungens.We hope to provide basic theoretical basis for vegetation restoration and reconstruction in the feldspathic sandstone area by comparing the water utilization characteristics,including diurnal photosynthesis,transpiration and water use efficiency,chlorophyll fluorescence parameters,tissue dehydration resistance indicated by PV curve parameters,and water use efficiency indicated by carbon isotope.The main results are as follows:?1?The diurnal variation of net photosynthetic rate showed different curve shapes due to different species.The diurnal variation of net photosynthetic rate of Hippophae rhamnoides and Achnatherum splendens showed a unimodal curve,while the others showed bimodal curves with the obvious midday depression phenomenon of photosynthesis.The peak of Hippophae rhamnoides was the highest,while Achnatherum splendens was the lowest among the six species.The daily variation curves of net photosynthetic rate and transpiration rate of 6 plants were integrated by finite calculus method.The daily CO2assimilation and water consumption per unit area of plant leaves,as well as the average daily water use efficiency?daily CO2 assimilation/daily transpiration water consumption?were obtained.The results showed that there were significant differences between species in daily CO2 assimilation,daily transpiration water consumption and average daily water use efficiency?P<0.05?.The daily CO2 assimilation and daily transpiration water consumption of H.rhamnoides were the highest,while the daily average water use efficiency was lower.Pnnisetum amerieanum×P.pureum leaves had higher daily CO2 assimilation and lower daily transpiration water consumption,which could obtain higher photosynthetic products with lower water consumption.Meanwhile,we also found that there were significant differences in?¹³C among species?P<0.05?.The order was E.pungens>R.officinale>A.pcdunculata>A.splendens>H.rhamnoides.Therefore,the water use efficiency of E.pungens was relatively high in the growing season,while that of H.rhamnoides was relatively low.?2?The initial fluorescence?Fo?of R.officinale was the highest,while that of H.rhamnoides was the lowest,indicating that the chlorophyll content of R.officinale was relatively high.The comparison of chlorophyll fluorescence quenching in high moisture period and low moisture period showed that the photochemical quenching was relatively high at high moisture period,the photosynthetic respiration activity was relatively high,while the non-photochemical quenching was relatively low.However,the non-photochemical quenching of Pnnisetum amerieanum×P.pureum in high moisture period was significantly higher than that in drought period,and the heat loss of light energy was more,while the photochemical quenching of Pnnisetum amerieanum×P.pureum in high water period was significantly lower than that in drought period.Combining with its higher maximum fluorescence,it was considered that Pnnisetum amerieanum×P.pureum could still maintain strong photosynthetic activity in drought period.?3?The water physiological parameters calculated by PV curve showed that A.splendens had the lowest saturated osmotic potential(?_s^sat)and osmotic potential at plasmolysis point(?_s^tlp)and the lagest maximum modulus of elasticity(?^max)among the six species,which indicated that the cell wall of A.splendens was better rigidity and weak in elasticity,and it maintained the swelling pressure mainly through osmotic adjustment,which was dehydration-tolerant type.The relative osmotic water content at plasmolysis point(ROWC^tlp)of E.pungens was the lowest,indicating that its anti-dehydration ability was the strongest and it was the dehydration-delayed type.The?^max of Pnnisetum amerieanum×P.pureum was smallest,indicating that it has soft cell wall,and strong water holding capacity.Thus the?_s^tlp of Pnnisetum amerieanum×P.pureum was high,while with poor resistance to dehydration of protoplasts,and high water use efficiency,indicating that Pnnisetum amerieanum×P.pureum is a high water potential delayed dehydration type.In summary,A.splendens showed strong ability in water use efficiency and dehydration tolerance;Hybrid Pennisetum can maintain high photosynthetic activity in drought period,and it had high water use efficiency and drought tolerance,which showed adaptability to arid environment in feldspathic sandstone area.