Study On Transpiration Water Consumption Law And Scale Effect Of Shrub-Subshrub-Arbor In Horqin Sandy Land

Transpiration is one of the most basic physiological and ecological activities of plants,and it is also a key link for the movement of water in the soil plant atmospheric continuum(SPAC).90%of the water stored in the soil is lost to the atmosphere in the form of transpiration,so it is of great significance to study the process of vegetation transpiration and water consumption in arid and semi-arid areas.In this paper,three typical sand-fixing vegetations,Caragana microphylla,Artemisia halodendron,and Poplar,in Horqin Sandy Land are taken as research objects.Use Li-6400 photosynthesis instrument,FLOW32-1K wrapped,pin-type plant stem flow meter and Shuttle-Wallace(S-W)model combined with meteorological data of each test plot.The transpiration water consumption laws of different vegetation at the leaf scale,plant scale,and community scale were studied separately.The main results are as follows:(1)At the leaf scale,through the comparison of the photosynthesis processes of Caragana microphylla,Artemisia halodendron,and Poplar.It was found that the net photosynthetic rate Pn and transpiration water consumption of the three vegetations all increased to different degrees after precipitation,and the daily changes in net photosynthetic rate showed various degrees of"noon break" under drought stress.After the precipitation,the "lunch break"phenomenon of the three vegetations was weakened.By comparing the trend of stomatal limit Ls and intercellular CO2 concentration Ci during the "noon break".The analysis showed that the lunch break of Artemisia halodendron and Poplar was caused by stomatal limiting factors,while the lunch break of Caragana microphylla was caused by non-stomatal limiting factors.After further analysis and correlation analysis of meteorological factors and vegetation's own physiological and ecological indicators.The results show that PAR is the main environmental factor that promotes the photosynthesis of vegetation(average R2>0.9 during the dry period,R2>0.75 P<0.01 after the rain).Under the drought stress,the three vegetations performed different self-regulation methods to reduce their transpiration water consumption.After that,the Pn models of three vegetations under drought stress and after precipitation were established.The results revealed that Artemisia halodendron had the strongest adaptability to drought environment,followed by Caragana microphylla and poplar.(2)On the plant scale,the daily changes of stem and stem flow rates of Caragana microphylla and Poplar in the growing season showed a single peak curve.The monthly average stem flow rate shows a trend of July>June>September>August>April>May>October.The daily cumulative stem flow is distributed in an "S" curve,and the monthly cumulative trend of stem flow is consistent with the monthly sequence of stem flow rate.The daily fluctuation of the steam flow rate is controlled by the change of meteorological conditions,especially in rainy and rainy days,the stem flow starts time is delayed and the end time is advanced by about 30 minutes,and the steam flow rate is decreased significantly in each period.The water level in the shallow groundwater area is sensitive to poplar transpiration water consumption.After 14 days of rainfall,the groundwater level has dropped by 7.8 cm,and after 7 days,the groundwater level has only dropped by 1.7 cm.It shows that the more drought,the greater the consumption of poplar on groundwater,and the groundwater level in shallow groundwater area is very sensitive to poplar transpiration response.(3)On the stand scale,combined with different meteorological factors and poplar's own physiological and ecological indicators,a model with the best fitting R2 value at each period was established.Based on the stomatal conductance model established in each period,the S-W model was used to simulate the evapotranspiration of poplar community.Finally,the simulation results are verified by using the measured values of stem flow in the same period.The results show that the deviation between the simulated value and the measured value of the model as a whole is small,which can better simulate the evapotranspiration of the artificial poplar community in arid areas.However,the accuracy of S-W model simulation is not high for full-cloud or full-rain days with little solar radiation.