梨树干木质部液流速度径向分布特征

采用热脉冲法对梨树树干液流速度径向变化规律进行了系统研究。结果表明：①梨树树干木质部不同深度液流速度在生长旺盛的晴天、阴天和小雨天呈单峰或双峰曲线；而在中到暴雨天、9月底小雨天和即将休眠的10月底晴天，各深度液流速度日变化不规则。②树干同一深度液流速度日峰值、日均值、日变幅在晴天、阴天、小雨和中到暴雨天的比例相同，约为5:4:3:2；不同方向液流速度径向变幅在以上天气的比例为6:4:3:2，而同一深度液流速度最小值在不同天气时差异不大。③梨树树干不同深度白天液流速度和液流速度径向变幅分别在5—7月、8—9月相近，8—9月、10月同一深度液流速度分别是5—7月的50%～60%和33%～50%；5—7月、8—9月和10月液流速度径向变幅比约为5:2:1。液流速度峰值主要出现在形成层至髓0.12～0.29的位置。④晚上液流速度径向季节变化趋势与相应的白天相似，整个生长季晚上液流速度和径向变幅分别为白天的43%±1%和29%±7%。

The Radial Distribution of Xylem Sap Flow Velocity in Trunks of Pear Trees

Daily and seasonal variability in the radial distribution of xylem sap flow velocity in trunks of pear trees were investigated by the heat pulse method. The results showed that sap flow velocity at different depths beneath the cambium exhibited one-, two-peak diurnal patterns in sunny, cloudy and light rainy days during the fully growing season, whereas diurnal sap flow velocity at different depths became irregular under different weather conditions at the end of growing season. The ratio of radial range of variation at different aspects, sap flow velocity in maximum, average and daily range of variation of the same depth in sunny, cloudy, light rain and moderate rain to storm days were 6:4:3:2 and 5:4:3:2, respectively, whereas minimum sap velocity was relatively similar under different weather conditions. The seasonal trends of daytime radial variation at the same aspect followed similar patterns, and showed three periods clearly- from May to July, August to September and October. Sap flow velocity at the same depth in August to September and October were about 50%–60%, 33%–50% of that from May to July. The ratio of radial range of variation from May to July and from August to September and October was 5:2:1. The seasonal patterns of nighttime radial variation were similar to the corresponding daytime where radial variation was lower compared with the daytime. The ratio of nighttime to daytime sap flow velocity became higher and higher with the extension of growing season. Throughout the season, nighttime sap flow velocity and radial range of variation were 43%±1% and 29%±7% of those of the daytime, respectively. Diurnal radial profile could be grouped into four types: high–low–low, low–high–low, high–low–high and low–high–low–high, which the maximum sap flow velocity mostly occurred in the position of 0.12–0.29 from the cambium.