Water Consumption Of Eucalyptus Plantation And Its Response To Environmental Factors At Multi-time Scales

Eucalyptus is one of the three kinds of fast-growing tree species recommended by FAO,and it has become a strategic tree species in south China.The central and western of Hainan Island is an important area of Eucalyptus plantation,which belongs to semi-humid and semi-arid area.Eucalyptus plantation has good economic benefits,but it also causes a series of ecological problems,especially water ecological problems.In this study,we were chosen Eucalyptus trees as the research in Danzhou forest farm of Hainan,and used the tree stem flow measurement system to monitor the sap flow rate of 4-5a Eucalyptus for a long time and environmental factors,such as photosynthetically active radiation,air temperature,relative humidity,precipitation,soil moisture,etc.The flow rate of Eucalyptus plantation was analyzed at different time scales,such as hour,day and month.To explore its relationships with environmental factors,and investigate the main influencing factors of Eucalyptus sap flow at different time scales,by estimating the annual transpiration water consumption of 4-5a Eucalyptus plantations,it provides theoretical basis and practical guidance for water management and reasonable management of Eucalyptus plantation.The results show that:(1)At an hour,day and month scale,the effective solar radiation,the temperature and relative humidity changed significantly.The precipitation and soil moisture have changed significantly at the month scale.Soil moisture variation in different depth is different,but there was significant correlation and significant difference,and effective solar radiation is the main factor affecting soil moisture.(2)The results showed that the sap flow at different orientation: The sap flow rate in different orientation of Eucalyptus had similar diurnal variation pattern in sunny,cloudy and rainy days.A single peak curve in sunny days,cloudy and rainy days are multi-peak or non-peak curve.The time of starting and reaching the peak of Eucalyptus sap flow at the east and south was about 20 minutes earlier than that of the west and the north.Comparing the flow rate of different directions,the lower flow rate in the sunny day is 13.7% lower than that of the higher sap flow,34.4% in the cloudy day and 9.4% in the rainy day.The flow rate on the north side of the sunny day is closest to the mean.The sap flow on the north of the cloudy and rainy days can be corrected to reduce the error of the whole tree transpiration.(3)At the hourly scale,the sap flow rate of the Eucalyptus showed a change of daytime high and low night.The diurnal variation curve of Eucalyptus flow rate is different in different weather conditions,which flow curve of sunny day is mainly single peak,cloudy day is mainly single peak or multi-peak,rain is generally no change rule.The daily mean values of Eucalyptus flow in clear,cloudy and rainy days are 5.58 mL·cm-2·h-1,3.97 mL·cm-2·h-1 and 1.41 mL·cm-2·h-1.On the daily scale,the flow rate of Eucalyptus varied greatly,ranging from 4.86 to 145.12 mL·cm-2·d-1.Even the adjacent two days,the difference of flow rate is also great,because of the external environment factor that is the main reason for the difference.At monthly scale,the sap flow rate of Eucalyptus was followed by: July,June,September,August,May,October,April,November,December,March,February,January.The sap flow in rainy season(5~10 months)was significantly higher than that in dry season(1~4 months and 11~12 months),the former average was 2.82 L·cm-2·month-1,the latter was 1.47 L·cm-2 ·month-1.(4)On the hour scale,the photosynthetic active radiation of dry season had the greatest influence on the flow rate of Eucalyptus in sunny and cloudy days,followed by air relative humidity.However,the effect of photosynthetic radiation on the flow rate of Eucalyptus on sunny day was stronger than that of cloudy day.In rainy days,RH and PAR had a great influence on the flow rate of Eucalyptus,and RH had a greater effect on flow rate of rain day.Temperature and soil water has little effect on the flow rate of Eucalyptus in different weather conditions.In sunny,cloudy and rainy days of rainy season,the sap flow rate was affected by PAR,RH and AT,and the effect of solar radiation was the most significant.The temperature and soil moisture had little effect on the flow rate of Eucalyptus.On the daily scale,the PAR in the dry season is the main influencing factor of the flow rate of the Eucalyptus,the AT and PAR are the main influencing factors in the rainy season.At the monthly scale,PAR is the most important factor affecting the change of the sap flow rate in the whole year,and the 30-60 cm soil moisture is an important factor in the change of sap flow rate.(5)The daily cumulative amount of Eucalyptus sap flow is different due to the weather and DBH.The daily cumulative amount of liquid flow was the highest in sunny days and rainy days was the lowest,and the greater the DBH,the more the cumulative daily flow.There is a similar monthly variation in the water consumption of different diameter standard woods,but the larger the diameter of Eucalyptus,the greater the difference in monthly transpiration water consumption of single wood.In rainy season,7.51 cm,9.39 cm,12.45 cm diameter of Eucalyptus single tree transpiration water consumption was 223.86,766.31 and 2164.6L,respectively accounting for 61.72%,66.26% and 65.95% of the year.4-5a Eucalyptus plantation communities in water consumption reached 3137543.78L·hm-2 in 2016,accounting for about 26.15 to 39.2% of local annual precipitation for many years.Annual average daily transpiration water consumption reached 0.86mm;dry season daily transpiration water consumption reached 0.61mm;rainy season average daily water consumption up to 1.1 mm.