| In this study,Robinia pseudoacacia and Euonymus bungeanus in the east sandy land of Yellow River were taken as research objects,the sap flow of Robinia pseudoacacia and Euonymus bungeanus was monitored continuously to clarify the characteristics of water consumption by transpiration which measured by Thermal Dissipation Probe(TDP)technique,as well as simultaneous records of micro-meteorological factors and volumetric soil water content to quantifying the transpiration response to environmental factor.The results showed that:(1)There were significant seasonal and tree species differences in the sap flow,which showed a trend of first increase and then decrease.From May to October,the sap flow of Robinia pseudoacacia were 1.496 g cm-2·h-1,1.595 g·cm-2·h-1,2.649 g·cm-2·h-1,1.560 g·cm-2·h-1,1.004 g·cm-2·h-1 and 0.436 g·cm-2·h-1,respectively.The sap flow of Euonymus bungeanus were 1.318 g·cm-2·h-1,1.477 g·cm-2·h-1,1.626 g·cm-2·h-1,1.283 g·cm-2·h-1,0.766 g·cm-2·h-1 and 0.434 g·cm-2·h-1,respectively.There were significant differences in tree species during the daily variation process.Different tree species showed different correlations with meteorological factors at different stages of the sap flow.At the stage of the sap flow rising,Robinia pseudoacacia was extremely significantly correlated with solar radiation(Rs),temperature(Ta),relative humidity(RH)and vapour pressure deficit(VPD),and at the stage of the sap flow falling,Robinia pseudoacacia was extremely significantly correlated with Rs and significantly correlated with Ta.There were significant correlations between sap flow of Euonymus bungeanus and Rs,Ta,RH and VPD during the rising and falling periods.(2)Under typical sunny days,the sap flow of Robinia pseudoacacia was earlier than that of Rs and VPD 105 and 330 min,respectively,and the sap flow of Euonymus bungeanus was earlier than that of Rs and VPD 45 and 270 min,respectively.The relationship between sap flow and meteorological factors(Rs,Ta,RH and VPD)showed a hysteresis loop in typical sunny days.It was indicated that there were time lag effects in the sap flow of two species response to transpiration driving factors.The time lag effects of Robinia pseudoacacia and Rs,Ta,RH and VPD were 30 min,120 min,105 min and 120 min,respectively.The time lag effects of Euonymus bungeanus and Rs,Ta,RH and VPD were 15 min,120 min,135 min and 135 min,respectively.(3)There were significant seasonal differences in transpiration consumption of Robinia pseudoacacia and Euonymus bungeanus.The monthly water consumption of Robinia pseudoacacia was July(53.23 ±2.01 kg)>August(31.34±1.69 kg)>June(31.01±1.49 kg)>May(29.08±1.22 kg)>September(19.52±1.42 kg)>October(8.75±1.66 kg),respectively.The monthly water consumption of Euonymus bungeanus was July(25.41±0.93 kg)>June(22.3±0.92 kg)>August(20.05±0.94 kg)>May(19.9 ± 0.85 kg)>September(11.59 ± 0.86 kg)>October(6.78 ± 1.20 kg),respectively.The average monthly water consumption of Robinia pseudoacacia(28.82±1.58 kg)was higher than that of Euonymus bungeanus(17.69±0.95 kg).The total water consumption of Robinia pseudoacacia at night accounted for 10.74%of the total water consumption,and that of Euonymus bungeanus at night accounted for 10.61%of the total water consumption.The ratio of water consumption at night to total water consumption of Robinia pseudoacacia was October(21.18%)>September(16.25%)>August(13.26%)>June(8.18%)>May(8.04%)>July(4.72%),and that of Euonymus bungeanus was October(24.10%)>May(12.40%)>September(10.92%)>August(9.47%)>July(9.15%)>June(7.48%),respectively.(4)In the early growing season,the main environmental factors affecting the daily water consumption of Robinia pseudoacacia and Euonymus bungeanus were VPD and Ta.In the middle growing season,the main environmental factors affecting the daily water consumption of specie was VPD.At the end of the growing season,VPD and SWC were the main environmental factors affecting the daily water consumption of two species. |
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