| Agricultural ecosystem is the main type among the arid area ecosystems,thus,to understand regional water balance,improve the management methods and the utilization rate of agricultural water resources,it is of great significance and practical value to reveal characteristics of evapotranspiration and crop water consumption,root distribution and water up take in such ecosystems in arid areas.Here,we analyzed the characteristics of the evapotranspiration,crop coefficients and its influencing factors of grapevines with different scales in the five growing seasons from 2014 to 2018.Finally,based on the analysis of root distribution,a preliminary study was conducted on the water up take of grapevines from June to August in 2017 and 2018 by using the hydrogen-oxygen stable isotope approach.The main conclusions are as follows:(1)Under different weather conditions,the diurnal variation of the flow rate of grapevines presents significant differences during the growth stages from 2014 to 2018: On sunny and cloudy days,the diurnal variation of the flow rate and environmental factors were revealed the single-peak curve,meanwhile,there is a small amount of flow at night due to the existence of root pressure;while on rainy days,the start-up time of the flow was not obvious,and it was obviously lower than the average daily flow rate on sunny and cloudy days.The average daily flow rate also showed an obvious seasonal variation during different months,the average daily flow rate was lower than others in May because of the weak solar radiation and the small transpiration tension;with the rapid increase of leaf area,the average daily flow rate of grape increased,reached the maximum value of the whole year from July to August;In September,the daily flow of the grapevines gradually decreased,and reached the minimum values during October due part to the fall off leaves and the lower solar radiation and canopy temperature.(2)On the half hour scale,the relationship between average instantaneous flow rate of grapevines and four environmental factors changed significantly with the change of months.There was a low correlation between sap flow rate of grapevines and four environmental factors during May.There was a hysteresis loop between sap flow to canopy temperature,relative humidity and water vapor pressure deficit,the characteristics of hysteresis loop became obvious at first and then basically disappeared,the loop direction between sap flow to canopy temperature and water vapor pressure deficit was clockwise,while that of relative humidity was counterclockwise From June to October.There was a positive linear correlation between photosynthetic active radiation and flow rate,and the correlation remained at the high level during the whole growth stages.The relationship between average instantaneous flow rate to leaf water potential and stomatal conductance of grapevines showed a linear correlation with the change of months,which first increased and then decreased,and the correlation reached a significant level(P<0.01).On the daily scale,there was a positive linear relationship between flow rate to canopy temperature,net radiation,relative humidity,vapor pressure deficit,photosynthetic effective radiation and reference crop evapotranspiration,the correlation reached a significant level(P<0.01),meanwhile,the strongest relationship was between flow rate and canopy temperature.(3)The average annual total canopy transpiration(T)and evapotranspiration(ET)of the vines in the study area was about 517.2 mm and 867.7 mm,the mean values of T and ET were 2.97 and 4.96 mm d-1 during the whole growing season,the range of the T/ET ratio was from 59.7 to 66.4%.The result shows that,compared with soil evaporation,crop transpiration(T)in the study area is the main water flux of total evapotranspiration(ET).By comparing the results of evapotranspiration partitioning in this study with those of different methods and ecosystems,the variation rules of evapotranspiration and its components in grapevines in the arid oasis can be further explained,which provides a data support for the study of T/ET in the global evapotranspiration research.(4)During the initial stage,the crop coefficient for soil evaporation(Ke)accounts for a large proportion of the crop coefficient for evapotranspiration(Kc),while the crop coefficient for transpiration(Kcb)was at a low value.During the middle stage,Kc and Kcb reached maximum values,respectively;while Ke gradually reached minimum values.As the growing season continued,the values of Kc and Kcb gradually declined and reached the minimum value at the end of the growing season..Both Kc and Kcb to Leaf Area Index(LAI)is a linear regression but to Canopy conductance(Gc)is an exponential one.LAI is a better indicator than Gc when it is used to predict Kc and Kcb.The effect of oasis advection effect on crop coefficient should not be ignored.(5)The concentration area of vertical root distribution appeared about 40-140 cm depth,the average root weight density of total roots and fine roots accounted for 91.4% and 86.1% of the total root(200cm)distribution,respectively.In the horizontal direction,the root of grapevines was mainly distributed within the range of 0-100 cm,and its root weight density and fine root weight density were 84.6% and 77.2% of the total root system,respectively.The difference of total root weight and the fine root weight was not significant with the increase of the radial distance after 80 cm from the trunk.Both the total root weight(length)density and fine root weight(length)density of grapevines seemed indicating the quadratic function with the increase of soil depth in the vertical direction.In the horizontal direction,the root systems on the left and right sides of the vines were asymmetrically distributed,on the right side,both the total root weight(length)density and the fine root weight(length)density showed an exponential distribution with the increase of radial distance,while on the left side,they showed a logarithmic distribution.The distribution of two-dimensional root of the grapevine can be described by quadratic function in the study area.There were significant differences in root water up take in different months of grapes.Therefore,in the arid oasis area,the distribution characteristics of plant roots were one of the main factors affecting the water up take strategies. |
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