Study On Water Consumption Of Main Ecosystem Tree Species In High Cold Region On Loess Plateaus Of Qinghai

With the rapid economical development and enhanced Greenhouse Effect and collapsed ecosystem,all kind of resources and materials are deeply in shortage,especially short of water.Forestry plays a decisive role with respect to water-absorbing and water-purging.Thereby,how to guarantee and maintain basic water requirement for the normal growth and development of the forest is the core content of study.In view of the above situation,the paper studies the transpiration rates,water consumptive using,photosynthetic physiology features and the main factors of influence about Picea Crassifolia,Laric Principis-rupprechtii,Hippophae Rhamnoides Zinn,Shepherdia argentea Nutt from abroad,Betula platyphylla Sak which growth on high cold area at Qinghai province.Main research results:1.The evaporation of the forest stand in experimental zone in 2008 was calculated on the basis of Penman-Monteith model.The comparison between the values gained from calculation and measurement shows the equations is feasible.In growth season(from May to Aug.),simulated evaporation of the Picea Crassifolia is 267.78mm,actual evaporation which was tested by Stem Flow Gauge is 293.36mm The simulated evaporation of the Larix principis-rupprechtii is 277.60mm.The relative errors are under 10%.2.At growing season in 2008,the distribution coefficients of Picea Crassifolia are 1.97,1.49,1.67, 1.95.The potential evaporation is 988.25mm,soil evaporation is 143,90mm,and potential evapotranspiration is 471.7mm,during the whole growth season total rain fall is more than total evapotranspiration.Hence the rainfall can satisfy the demand of forest growth.3.At different weather conditions the stem flow rates have a great deal of difference.The stem flow rates graph change into broad peak in the sunny day.In the cloudy or rainy day the duration of transpiration peak persist short time and the graph become double or narrow peak.The Picea Crassifolia stem flow rate of large DBH are much higher and more stable than small DBH ones.The small DBH Picea Crassifolia is obviously influenced by environmental factors.The stem flow rate of mature Picea Crassifolia is bigger than Hippophae Rhamnoides Zinn.Larix principis-rupprechtii has the smallest stem flow rate.4.The transpiration rate of the leaves has closely relationships between stomatal resistance and meteorological factors.When there are enough water and mild stress,the relativity is above 0.9.But the relativity will sharply reduce to 0.65 and 0.48,when stresses become moderate and severe.Different nursery stock in different water conditions have diverse transpiration rate peak and curve shape.At the same time the points of the peak also have a lot of difference,the comparation of the unit area of transpiration rate is Hippophae Rhamnoides Zinn＞Shepherdia argentea Nutt＞Betula platyphylla Sak＞Picea Crassifolia.The whole variation tendency can predictable.5.The photosynthetic rates have strong ties with stomatal conductance,the CO₂ concentration of intercellular and soil moisture content.Results the difference values of moisture gradation were Betula platyphylla Sak,Shepherdia argentea Nutt and Hippophae Rhamnoides Zinn from small difference to large.When there are enough water and severe stress,the photosynthetic rate of Picea Crassifolia, Shepherdia argentea Nutt and Hippophae Rhamnoides Zinn are 5.0 umol·m^-2·s^-1,5.0 umol·m^-2·s^-1,20.0 umol·m^-2·s^-1;1.56 umol·m^-2·s^-1,2.0 umol·m^-2·s^-1,5.9 umol·m^-2·s^-1.The soil moisture content of the leaves of Picea Crassifolia,Shepherdia argentea Nutt and Hippophae Rhamnoides Zinn are 10.0%,11.0%and 9.5%,when the water utilization efficiency of leaves reach the highest.The critical values of maintain the highest net photosynthetic rates are 15.5%,16.1%and 15.8%.So the results shows that the optimum range of three tapes soil moisture content are 10.0%～15.5%,11.0%～16.1% and9.5%～15.8%.