| In the semi-arid area of Northwest of China,the water resources are scarce and surface water is scarce.It is significant that groundwater is used to maintain the ecosystem and promote economic development.The unreasonable exploitation of groundwater may cause water level constantly to decline,results damage to vegetation dependent on groundwater in semiarid area.By comprehensive uses of various technical methods such as in-situ monitoring,statistical analysis,predictive simulation,relies on Yulin groundwater field scientific observation base of Natural Resources Ministry,this paper selected typical groundwater dependent plants-saliz matsudana,populus microphylla of Mu Us sandy land as for study objects,the study was conduct on their water consumption,characteristics of water consumption and their responses to the changes of groundwater level,in order to provide scientific basis and guidance for the rational development and utilization of groundwater for semiarid area.In view of above problems,this paper will calculate the transpiration of saliz matsudana and populus microphylla,through the monitoring data sorting and analysis,further dynamic characteristics of transpiration by month,date,hour and its relationship with meteorological factors are analyzed.Under natural conditions,the relationship between water consumption of plants and groundwater depth was established,by potential evapotranspiration is used to eliminate the influence of meteorological factors;under the condition of exploitation,the prediction model of plant transpiration was established by uses of meteorological factors,quantitatively analyze the response of plants to the groundwater decline.By studying the interaction between groundwater and vegetation,the following main conclusions are obtained:(1)Determine the change rules of sap flow density of saliz matsudana and populus microphylla in different time,on the monthly scale,the total density of sap flow in saliz matsudana and populus microphylla gradually rising from May,and reached maximum in August,then decline;on the daily scale,the rising range of populus microphylla was larger than saliz matsudana,that lowest total density in rainy days;on the hour scale,the average highest sap flow density of saliz matsudana and populus microphylla appeared at 11:00am in May,and 3:00pm in August.(2)The effects of sap flow for saliz matsudana and populus microphylla with meteorological factors indicated:the correlation between net radiation factor and two vegetations was the best,and temperature factors was inferior to the former.At the same time,the time-lag effect of meteorological factors on the sap flow density of Salix psammophila and Populus simonii was also studied.The results showed that the average sap flow density of the two vegetations had a certain degree of time lag on the net radiation,and did not show VPD Obvious hysteresis,and relative to the net radiation,the lag time of trunk sap flow density change is about 1 h.(3)Under natural conditions,along with increases of groundwater depth,the water consumption of saliz matsudana and populus microphylla became linearly decreases.(4)Under the state of exploitation,along with increases of groundwater depth,that sap flow density of groundwater dependent plants decline.The average decline value of saliz matsudana in pumping period is 3.08 g·cm-2·h-1,and 9.63 g·cm-2·h-1for populus microphylla.The plants water consumption of populus microphylla decreased more,and affected more by pumping water.(5)During pumping water period,the lower the water level,the greater the impact on plant water consumption.And after rainfall,the sap flow of plant would be weakened or even not affected by pumping water. |
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