Research On The Discrepancy Of Sap Flow Of Salix Matsudana Uner Different Soil Condition In The Water-win Erosion Crisscross Region

The Loess Plateau is characterized by a harsh natural environment, such as a largenumber of deep gullies, undulating loessial slopes, severe soil erosion and low vegetationcoverage. This region is the most vulnerable ecological environment in China and even in theworld and water deficit is the greatest problem for vegetation growth in this region. In orderto improve the worsening ecological environment, the Grain-for-Green project wasimplemented. However, unscientific layout and water resources, soil and climate conditionswere not taken into accounted resulted in many trees became into “small aged tree”,especially in slope land. Therefore, it is important that making a deeper understanding oftranspiration characteristics of afforestation species combined with soil, climatic and waterconditions for solving contradiction between water shortage and vegetation construction, andachieved sustainable development of artificial vegetation.Sap flow of salix matsudana, which grow in sandy soil and loess soil, was measured bythe thermal dissipation probe (TDP) from May to October in2012and2013. Environmentalfactors were determined synchronously and the present study wants to clarify the reasons thataffect growth of Salix matsudana under same watershed. Aimed at clarifying salixmatsudana’s which grew in slope land and dam land, growth difference through analyzing thedifference in climate and soil water movement. The main conclusions are as follows:1．Diurnal and month variation of sap flow of salix matsudana in slope land wasconsistent with that in dam land, and it had a significant circadian rhythm. The sap flowstarted at about7:00in May, June and July, and reached the first peak at10:00, then began todecline, and reached the second peak at around15:00; yet sap flow began to rise at9:00, andthe peak of sap flow appeared between11:00to15:00in August, September and October. Thediurnal variation of sap flow in May, July and June could be exhibited a multiple-peaked,however, it was a broadly-peaked curve in August, September and October. At the scale ofmonth, the order of sap flow of salix matsudana in slope land and dam land in2012wasAug.>May>Jun.>Jul.>Sep., and in2013, the order was Aug.>May=Jun.>Jul.>Sep.>Oct. inslope land, May>Jun.>Jul.>Aug.>Sep.>Oct. in dam land. The sap flow in rainy days waslower than sap flow in sunny days, and sap flow showed significant fluctuations in rainy days. 2．The sap flow of salix matsudana in dam land was4.8times that in slope land in2012,and in2013it was4.5times. Annual rainfall in2013was1.4times the2012, correspondingly,the total sap flow in slope land in2013was1.6times as large as that in2012, and1.5times indam land. More water was lost to100cm soil layer after heavy rainfall events in slope land,but in dam land more water was kept in10cm-100cm soil layer. So less water could be usedby salix matsudana in slope land than in dam land.3．Sap flow of salix matsudana had a significant positive correlation with solarradiation, VPD, air temperature and speed, and a significant negative correlation with relativehumidity. The solar radiation and VPD were the main factors to sap flow. When the potentialatmospheric evaporation hosted by the meteorological factors risen to a certain extent, the sapflow did not continue to increase with the increase of the ET0, but kept a stable state. At thistime, the correlation between sap flow and meteorological factors had reduced.4．Fine root of slope land salix matsudana main distributed at the depth of0-100cm,accounted for66%; but88%of fine root of salix matsudana in dam land distributed at thedepth of0-80cm. At the same time, soil evaporation of slope land lower than that in dam land,but the seepage quantity of slope land was4.5times as higher as dam land. So there was lesswater could be used by salix matsudana in slope land than dam land.5．Meteorological factors of slope land and dam land were almost no difference, so themeteorological factor was not the main reason for the difference of sap flow of salixmatsudana in slope land and dam land. Due to the different soil texture, the soil water contentof slope land and dam land was different, and the different soil water content was the mainreason for the difference of sap flow of salix matsudana in slope land and dam land.There was no significant difference of meteorological factor in slope land and dam land, so itwas not the main reason for the discrepancy of sap flow of salix matsudana. The different soiltextures leads to the discrepancy of the available soil water, which is the real reason for thediscrepancy of sap flow of salix matsudana in slope land and dam land.