Research On Physiological-ecological Characteristics Of3Psammophytes In Shapotou Area

In order to explore the differences of physiological-ecological characteristics andmoisture response mechanism of psammophytes in different configurations,3kindsof typical psammophyte in Tengger Desert in Shapotou area, Caragana korshinskii,Artemisia ordosica, atraphaxis bracteata, was chosen as research object, measuredtheir net photosynthetic rate (Pn), transpiration rate (E) and stomatal conductance (Gs)with Li-6400portable photosynthesis system, and then analyzed their water useefficiency (WUE) and light use efficiency (LUE). Draw the following conclusions:1. Net light curves of3species of diurnal variation of photosynthesis weretwo-peak patterns, with a midday depression of light intensity, sensitive reaction to light,could make full use of solar radiation. Atraphaxis bracteata’s photosynthetic rateremained at a high level, even in the middle of the day did not reduce too greatly;while Caragana korshinskii and Artemisia ordosica showed a drought adaptability,strong photosynthesis in the morning, but maintain a low level in the afternoon.2. The difference of photosynthetic rate of different configurations showed thatCaragana korshinskii could obtain more resource effectively allocation in punctateconfiguration than the strip configuration, so the photosynthetic rate was higher; thelarger atraphaxis bracteata population density was, the lower individualphotosynthetic rate would be; for Artemisia ordosica both in the reproductive period,different plant ages had certain effects on photosynthesis, photosynthetic capacitydecreased with age’s increasing.3. Stomatal conductance variation and transpiration rate of3species was notconsistent, which was a adaptability that species expressed to the environmentin aftera long-term environmental impaction. In order to reduce transpiration water losing toprotect plant from hydropenia, Caragana’s stomatal conductance was high in themorning and low in the afternoon.The10-year-old and15-year-old Artemisiaordosica’s transpiration didn’t decrease significantly with the decreasing of stomatalconductance at noon and in the afternoon, maybe their stomatal conductance levelwas still so high enough above stomatal threshold that it didn’t have much of an impact on transpiration so far, while the20-year-old’s transpiration decreasedsignificantly accordingly. Changes of stomatal conductance of atraphaxis bracteatashowed obvious consistency with photosynthesis’ and transpiration’s, more stomatalwas in an open state to photosynthesize, which precipitated different adaptivestrategies of different species.4. Population density had great effect on stomatal conductance and transpiration.The higher population density was,the smaller would the stomatal conductance tend tobe, maybe that’s a result of intraspecific water competition. Curves of daily variationof transpiration of Artemisia ordosica and atraphaxis bracteata were two-peak patterns,while Caragana korshinskii’s was one peak pattern, showed their different adaptationto the environment. Atraphaxis bracteata had a higher photosynthetic rate, rapidgrowth, but accompanied with greatly transpiration; while stomatal conductance ofCaragana korshinskii and Artemisia ordosica was greatly reduced at noon, so as toreduce water losing, but also causes the decreasing of photosynthetic rate.The WUE of different species in different configurations showed somedifference. Caragana’s curve of daily variation of water use efficiency was thetwo-peak patterns, the peaks occurs at the same time as photosynthetic peak point at9:00and17:00, which was corresponding with photosynthesis’s two peaks. Thecurves of daily variation of water use efficiency of atraphaxis bracteata and Artemisiaordosica were downward trend, because atraphaxis bracteata’s high levelphotosynthetic maintaining relied on lots of water consumption of transpiration, so thewater use efficiency was not different so significantly after9:00, and becauseArtemisia ordosica’s photosynthetic level was low in the afternoon,the water useefficiency also maintained at a low level. In different configurations, Caragana foresthad a higher water use efficiency than mixed forest, the density and age had a littleeffect on plant’s water use efficiency.Curve of daily variation of light utilization efficiency of Caragana korshinskii andArtemisia ordosica were inverted parabolic, while atraphaxis bracteata’s was smoothpattern. The main reason for this difference was that stomatal in Caragana korshinskiiand Artemisia ordosica’s leaves closure at noon would inhibit photosynthesis, which made the water use efficiency decreased,while atraphaxis bracteata hadphotosynthesis fastly all the day long.Therefore, atraphaxis bracteata grows fasterthan Caragana and Artemisia ordosica, accompanied with a increasing waterconsumption. This may be the physiological reason why atraphaxis bracteata have apoor adaptability and cannot distributes as widely as Caragana korshinskii Artemisiaordosica do in the natural vegetation in the arid flow and semi fixed dunes area. Lightutilization efficiency of different configurations, within the scope of the study,punctate configuration’s was higher than the strip configurations’s, small density’swas higher than high density’s, small plant age’s was higher than the big plant age’s.