为了评估太湖流域土地利用类型之一--茶园的生态系统水量调节能力, 探究茶园修剪前后土壤 植被 大气连续体水分传输过程中的蒸散过程, 在太湖流域西部丘陵地区西渚镇盛道茶场, 选择3年和9年2种不同植茶年龄的茶园, 通过静态箱/红外气体分析仪监测茶园水汽浓度, 比较分析茶株修剪前、后茶园蒸散速率的变化。结果表明: 茶园修剪前后与未经修剪茶园蒸散速率日变化趋势一致, 蒸散速率呈以12:00为峰值的单峰曲线, 但茶株修剪后蒸散速率大幅下降, 3年茶园蒸散速率日均值下降幅度(36.73%)小于9年茶园(48.32%), 植茶年龄的增加会加大修剪后蒸散速率的下降幅度; 茶园修剪前后日均气温相近、土壤含水量较高, 两者均不是茶园修剪后蒸散速率大幅下降的限制因子, 而茶株被剪掉的枝、叶覆盖在茶株间, 增加了株间土壤的荫蔽, 降低了土壤的蒸发作用, 并且茶株高度的降低, 可能导致界面层导度减小, 减少了水分从茶株向大气的传输, 从而降低蒸散作用。
Using the Static Chamber/IRGA, water vapor concentrations in tea plantations with different growth durations (3, 9 and 12 years) were measured and compared for diurnal variations in evapotranspiration (ET) before and after pruning. The study aimed to evaluate the water regulating ability of tea trees which is the dominant land use type in Yixing City, west of Tai Lake watershed. The results showed that diurnal variations in ET rate of tea tree tracked uni-peak curve. ET rose from 6:00, reached peak value at 12:00 and dropped rapidly or slowly afterwards. After pruning, tea tree ET rate dropped considerably. Mean ET rates for the 3-year and 9-year tea trees were respectively measured at 6:00, 9:00, 12:00 and 15:00 on April 23 - the day before first pruning. These rates were higher than those measured on May 17 - the day after the first pruning. Daily mean ET rates for 3-year and 9-year tea trees before first pruning were 3.11 mmol·m-2·s-1 and 73.74% higher than that after first pruning (1.79 mmol·m-2·s-1). Also amplitude decline in ET for the 3-year tea trees was 36.73% and that in the 9-year tea trees was 48.32%. ET decline range increased with increasing growth duration of the tea trees. The influencing factors of ET were discussed as follows: (1) Although ET trend was similar to that of temperature and tea tree ET closely related with temperature (P＜0.01), air temperature was not obviously different between before and after pruning, 34.46 ℃ on April 23 (the day before first pruning) and 34.30 ℃ on June 14 (the day after pruning). This suggested that air temperature was not the main driving factor of ET in the study area. (2) The study area was in a humid region where soil water content was relatively high but changed with rainfall and tea tree cover. There was no close relationship between ET and soil moisture, a trend different from that noted in semiarid and arid regions. This also suggested that soil humidity was not a main driving factor of ET in the study area. (3) Tea tree height after pruning was almost half of that before pruning, which height change was similar to the change in ET. As a roughness factor of aerodynamics, air near leaf was much influenced by the ambient atmospheric conductance, inducing less boundary layer conductance at lower plant heights. Also as water transport in the soil-plant-atmosphere continuum (SPAC) was inefficient, the tea tree height dwarfing rapidly decreased ET rate. (4) Air temperature was similar and soil moistures relatively higher before than after pruning. As the 20-year tea crop coverage (without pruning) increased by 9.41%, shadow area widened and soil evaporation weakened. While vegetation coverage of the 3-year and 9-year tea trees (with pruning) decreased respectively by 15.85% and 24.93%, bare soil area didn't increase and soil evaporation became smaller. As pruned debris of tea trees covered soil surface, especially for the 9-year tea trees, soil water retention capacity increased, and at the same time ET rate range decreased.