Transpiration characteristics of Eucalyptus pellita in Leizhou Peninsula and its relationship with soil water suction
[Objective]This study investigated the transpiration and water consumption of Eucalyptus in dry and rainy seasons and its relationship with soil moisture to provide guidance for Eucalyptus cultivation.[Method] In the Leizhou Peninsula area of Guangdong,an 11-year-old Eucalyptus forest was selected to set up a 20 m×20 m plot.According to sample-plot survey,3 sample trees with good growth were selected.From June to October 2017 (rainy season) and November 2017 to January 2018 (dry season) ,the transpiration rates were continuously monitored using a thermal diffusion shale flow meter (Germany,SF-G),and the meteorological factors,forest rainfall and soil water suction dynamics were simultaneously observed.The relationship between soil water suction in 0-100 cm soil layer and rainfall,the relationship between transpiration water consumption and daily evapotranspiration,and the relationship between transpiration water consumption and soil water suction were then studied.[Result]The soil water suction of each soil layer (every 20 cm as a soil layer in the depth of 0-100 cm) had significantly negative correlation with rainfall.Affected by rainfall,the average soil water suction in the rainy season (21.28 kPa) was significantly lower than that in the dry season (510.44 kPa).The changing trend was same for water suction in different soil layers during the observation period,but the variation ranges were quite different.The transpiration rates of E.pellita had seasonal variations.The rainy season was the main period of transpiration and water consumption of Eucalyptus with daily average transpiration rate of 1.8 times that of the dry season.The average individual transpiration water consumption was in the order of September>August>July>June>October> November>December>January and the values in rainy season were significantly greater than in the dry season.The daily potential evapotranspiration had significantly positive correlation with transpiration rate in both seasons.There was no significant correlation between transpiration rate of the rainy season and soil water suction in each layer,but there was very significant negative linear correlation between dry season transpiration rate and soil water suction.Soil moisture was the major limiting factor for transpiration and water consumption of the Eucalyptus in the dry season.The relationships between dry season transpiration rate and water suction of different soil layers were quite different.The correlation coefficient was in the order of 40-60cm>20-40cm>60-80cm>80-100cm>0-20cm.The soil layer of 20- 80 cm was the main water use layer of the 11-year-old E.[Conclusion]In the dry season of the Leizhou Peninsula,soil moisture was the main factor limiting the transpiration of the E.pellita,and it determined the transpiration together with potential evapotranspiration.With constant light and heat condition,proper water supplement measures in the dry season can effectively increase the transpiration and forest productivity of the Eucalyptus forest.
soil water suctionEucalyptus pellitaforest transpirationLeizhou Peninsula area of Guangdong