| By redistributing evapotranspiration of forest, soil infiltration and runoff, vegetation change impacts on hydrological processes ecologically, thus affecting the water balance of the forest. Evapotranspiration is the focus of ecohydrological research in forest ecosystems, but previous studies have not completely separated soil evaporation from evapotranspiration. Soil infiltration is an extremely important flux of rainfall redistribution, and directly affects the runoff process. It is the most important hydrological processes affecting the runoff. Studies of soil infiltration after conversion of relevant long rotation cycle forest to short period eucalyptus plantation has not been reported.Effect of sun illumination, wind speed, leaf age on eucalyptus saplings transpiration rate were studied by pot experiment, to investigate the process and characteristics of eucalyptus plantations effecting on the main eco-hydrological processes. Evaporation of the site under different soil moisture content and weeding was measured using small evaporators. Single rings were used to study the soil moisture infiltration characteristics of different stand ages (generations) of eucalyptus plantations and of afforestation front stand (Masson pine, Cunninghamia lanceolata (Lamb.) Hook, and conifer plantations). The main results are as follows:(1) Transpiration of eucalyptus increased when light intensity enhanced. When the light intensity increased over 720 mol·m-2·s-1 transpiration reduced in order to avoiding water loss. Light intensity decreased when sun went down at 17:00, then saturated vapor pressure and temperature compensated to transpiration of eucalyptus. The peak rate of transpiration of eucalyptus appeared at different times under different light intensity. The peak was between 0.018 g·cm-2·h-1 and 0.024g·cm-2·h-1 when light intensity was between 500μmol·m-2·s-1 and 720μmol·m-2·s-1.Transpiration rate of eucalyptus and leaf area were positively correlated, and 1-2 month-age leaves had better transpiration performance under low light intensity.(2) Wind effected on transpiration rate by acting on the air-temperature difference on leafs surface.(3) Eucalyptus transpiration rate was positively correlated with vapor pressure deficit, air temperature and light intensity, and negatively correlated with air humidity. On the condition of extreme light, transpiration rate was influenced more by other meteorological factors.(4) Soil evaporation of eucalyptus plantation increased with rainfall intensity enhanced. Average daily evaporation and rainfall increased in a significant exponential correlation, and inflected at 10mm rain intensity. Increasing of soil moisture enhanced the correlation of evaporation with radiation intensity and wind speed. But the correlation of soil evaporation with all of meteorological factors weakened when simulated rainfall reached 20mm.(5) Soil evaporation rate of eucalyptus plantation was accelerated by weeding significantly. Effect of weeding on soil evaporation regulated by rainfall and other seasonal conditions. Soil surface was bared rapidly after mechanical weeding. Soil evaporation rate speeded up in a short time. Weeding with herbicide promoted soil evaporation rate less than mechanical weeding within a month, but could maintain a longer period of time. The maximum of daily evaporation by herbicide weeding was 1.039±0.424mm·d-1, followed by mechanical weed control in 0.997±0.395 mm·d-1, followed by no-weeding control in 0.747 ± 0.260 mm·d-1.(6) Converted from mixed forest, Pinus massoniana and Cunninghamia lanceolata to eucalyptus, saturated hydraulic conductivity rate increased by 20%-467%, and soil infiltration capacity increased. Saturated hydraulic conductivity rate increased as the eucalyptus plantations generations increased, while it decreased as the age increased. It showed that mixed forest> Pinus massoniana>Cunninghamia lanceolata。... |
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