Leaf Gas Exchange and Water Potential Characteristics of Plants with Different Photosynthetic Pathways in Hunshandak Sandland
Field measurement on gas exchange,chlorophyll fluorescence and leaf water potential of three plant species with different photosynthetic pathways,Ulmus pumila (C3),Agriophyllum pungens (C4) and Orostachys malacophyllus (CAM) was carried out in their growth stage to understand their different strategies in both carbon gain and water losses in Hunshandak Sandland.It was found that U.pumila and A.pungens exhibited higher net photosynthetic rate (Pn) and stomatal conductance (Gs) than that of O.malacophyllus,especially under very high Tleaf(>40℃) and high PPFD(>2 100 μmol·m-2·s-1) in summer.The decrease of Pn with the daytime course was mainly due to stomatal closure.However,Pn of O.malacophyllus,the CAM species,was seriously depressed in daytime as shown by the negative Pn although its leaf water potential (Ψ) was the highest among the three species.Its maximal photochemical efficiency of PSⅡ (Fv/Fm) was the lowest at 14:00,indicating the injury of PSⅡ by heat happened at this stage.Carbon gain for CAM species happened only during night times.Both the C3 and C4 species undergo pronounced midday depress in Pn and Gs.Our results indicated that U.pumila and A.pungens were much more tolerant to heat and high radiations than that of O.malacophyllus,which fixed most of CO2 at the fast growing stages.Nevertheless,the CAM species in hot summer it had to survive the severe hot environment through strong respiration,and storage of CO2 only in the early morning and night.
high temperaturehigh radiationphotosynthetic ratestomatal conductanceFv/FmHunshandake Sandland
NETL
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万方数据
