Abstract:

The use of Eucalyptus as plantation trees in the tropics has been criticized in the world wide on the grounds that they consume water in excessive amounts, but it is no general answer to the question of whether Eucalyptus consume water in excessive quantities because site conditions, climate and species all influence water use. In south China, however, there is little information on water use by Eucalyptus plantations. The purpose of this paper was to discuss effects of meteorological factors on dry seasonal dynamics of soil water content in Eucalyptus plantation on Leizhou peninsula of southern China. Based on the data obtained from locate oriented observation throughout the dry season from Oct. 1999 to Mar. 2000, the method, canonical correlation analysis, which could puts emphasis upon holistic meteorological factors and soil water content(SWC), was employed to analyze the relationship between them. The main results indicated as followings:(1)Soil water content varied markedly in different layers and mean water content of layers increased with the depth of soil(P=0.001);(2)The coefficient of weight for daily maximum temperature(T_max )and minimum temperature(T_min )was 1 260 and 0.840 ,respectively. And the main meteorological factors that changed soil water content of deeper layers(SM150, SM250, SM350)were vapour pressure deficit(VPD), daily minimum temperature(T_min ),solar radiation (R_s ), and maximum temperature (T_max ); SWC at SM350 had a significant relationship with precipitation (P_r)(P=0.001), while the main factors influencing SWC at SM50 were P _r and wind speed.(3)The canonical correlation coefficients between canopy meteorological factors and SWC were 0.841 and 0.548(P=0.001), respectively. And the multiple correlation coefficients between the two canonical variables was 70.7%;(4)The total variance in soil water content explained by first canonical covariates (U₁,W₁ ) was 40.4%. The two canonical variables, (U₁,W₁) and (U₂,W₂), explained total variation in soil water content was 43.0%. The first canonical variables U₁ can account for total variation in dependent variables of soil water content up to 57.2%; (5)The soil water content at SM350、SM250、SM150 were mainly affected by daily maximum temperature, minimum temperature, and solar radiation among the canopy meteorological factors.

Key words: Eucalyptus plantation, Dry seasons, Soil water content, Meteorological factors, Canonical correlation method