生长季刺槐树干液流昼夜变化特征及其对气象因子的响应

  目的  研究刺槐Robinia pseudoacacia生长季树干液流昼夜变化规律，探究气象因子对刺槐蒸腾的影响，为估算林木耗水和林分水资源管理提供理论依据。  方法  在山西省吉县蔡家川流域刺槐样地选择8株样树，于2021年5—9月采用热扩散探针(TDP)对样树树干液流进行连续观测，并同步监测太阳辐射、气温、土壤温度、风速、相对湿度等气象因子，并采用随机森林与逐步线性回归法分析气象因子对树干液流的影响。  结果  ①生长季各月昼间树干液流速率从小到大依次为9月、5月、6月、8月、7月，昼间树干液流速率对整日树干液流速率的贡献率为88%~93%；夜间树干液流速率从小到大依为9月、5月、8月、7月、6月，夜间树干液流速率对整日液流速率的贡献率为7%~12%。②影响昼间树干液流速率的主导气象因子在各月基本一致，主要为太阳辐射和气温；影响夜间液流速率的主导气象因子在各月存在差异，5、6月主要为土壤温度、水汽压亏缺，7月主要为气温，8月主要为水汽压亏缺、相对湿度，9月主要为风速与水汽压亏缺。③采用随机森林回归法构建的各月昼夜树干液流速率模型拟合度优于逐步回归法。  结论  昼夜树干液流速率在各月存在明显差异，夜间树干液流对刺槐耗水的影响不可忽视，气象因子对昼夜树干液流速率的影响程度不同，在根据气象因子模拟树木蒸腾耗水时应该区分昼间和夜间。图3表6参24

Diurnal and nocturnal changes in stem sap flow of Robinia pseudoacacia during growing season and its response to meteorological factors

  Objective  The objective is to analyze the diurnal and nocturnal changes in stem sap flow of Robinia pseudoacacia in the growing season and explore the impact of meteorological factors on transpiration of R. pseudoacacia , so as to provide theoretical basis for estimating forest water consumption and forest water resource management.   Method  Eight sample trees were selected from R. pseudoacacia sample plots in Caijiachuan watershed, Ji County of Shanxi Province. From May to September 2021, thermal diffusion probe (TDP) was used to continuously observe stem sap flow of sample trees, and meteorological factors such as solar radiation, air temperature, soil temperature, wind speed and relative humidity were monitored simultaneously. Random forest and stepwise linear regression were used to analyze the influence of meteorological factors on stem sap flow.   Result  (1) The order of diurnal sap flow rate from small to large in the growing season was September, May, June, August and July, and the contribution rate of diurnal sap flow to full-day sap flow was 88%?93%. The nocturnal sap flow rate ranging from small to large was September, May, August, July and June, and the contribution rate of nocturnal sap flow to full-day sap flow was 7%?12%. (2) The main meteorological factors affecting the diurnal sap flow rate were basically the same, mainly solar radiation and air temperature. The dominant meteorological factors affecting nocturnal sap flow were different in each month. The main factors were soil temperature and water vapor pressure deficit in May and June, air temperature in July, water vapor pressure deficit and relative humidity in August, and wind speed and water vapor pressure deficit in September. (3) The fitting degree of the monthly day-night flow rate model constructed by random forest regression method was better than that by stepwise regression method.  Conclusion  There are obvious differences in diurnal and nocturnal sap flow rate in each month. The effect of nocturnal sap flow on water consumption of R. pseudoacacia should not be ignored, and the effect of meteorological factors on diurnal and nocturnal sap flow rate is different. Daytime and nighttime should be distinguished when simulating water consumption of tree transpiration according to meteorological factors. Ch, 3 fig. 6 tab. 24 ref.]