坝上地区人工林和草地生长季土壤水势动态

Dynamics of Soil Water Potential in Growing Season of Plantation and Grassland in Bashang Area

为研究坝上地区人工林土壤水势动态,以结缕草(Zoysia japonica)为对照,选取坝上地区典型人工林小叶杨(Populus simonii Carr.)和樟子松(Pinus sylvestris var.mongolica),研究其生长季不同时间、空间土壤水势和变异系数及晴天和降雨下土壤水势变化。结果表明:(1)人工林和草地土壤水势变化趋势相同,在生长季前期和后期土壤水势较高,中期土壤水势进入波动下降期,但不同植被进入波动期时间不同,樟子松晚于小叶杨和结缕草。小叶杨、樟子松、结缕草土壤水势最低值分别出现在70,10,30 cm处,最低值分别为-1257.24,-747.97,-830.11 kPa。小叶杨、樟子松和结缕草土壤水势变异系数最大值分别在9月10 cm、7月10 cm、7月30 cm处,其值分别为-155.9%,-208.0%,-183.6%。总体上,变异系数生长季中期大于前期和后期,表层大于深层。(2)晴天人工林和草地土壤水势差的最大值与日均温度之间存在显著的相关关系,随着日均温度升高,水势差最大值也增大。典型晴天大气温度在日内上下波动,土壤水势呈现滞后波动,在生长季浅层土壤最为明显。(3)不同降雨量与土壤水势差呈现相关关系,随着降雨量升高,土壤水势差也随之升高。典型降雨事件下,中雨和大雨剖面土壤水势迅速上升,小雨事件下主要呈现波动变化。从不同植被来看,草地土壤水势较人工林波动更为剧烈。综上,生长季樟子松土壤水势进入波动期最晚,波动幅度最大。而土壤水势对于大气温度和降雨的响应方面,结缕草最为敏感。研究结果对于指导当地人工林建设与水资源高效管理具有重要意义。

In order to study the dynamics of soil water potential of plantations in Bashang area,in this experiment,Zoysia japonica was taken as control,Populus simonii Carr.and Pinus sylvestris var.mongolica,which were typical plantations in Bashang area,were selected to study the soil water potential value and variation coefficient in different time and space in growing season,and the soil water potential variation under sunny days and rainfall in growing season.The results showed that:(1)The change trend of the soil water potential of plantation and grass was the same,the soil water potential was higher at the early and late stages of growing season,and the soil water potential entered the fluctuating and declining period at the middle stage,but different vegetation entered the fluctuating period at different time,and that of P.sylvestris var.mongolica was later than that of P.simonii Carr.and Z.japonica.In addition,the lowest soil water potential of P.simonii Carr.was -1257.24 kPa at 70 cm,that of P.sylvestris var.mongolica was -747.97 kPa at 10 cm,and that of Z.japonica was -830.11 kPa at 30 cm.The maximum variation coefficient of soil water potential of P.simonii Carr.,P.sylvestris var.mongolica and Z.japonica appeared at 10 cm in September,10 cm in July and 30 cm in July,with values of -155.9%,-208.0% and -183.6%,respectively.On the whole,the variation coefficient was greater in the middle of growing season than that at early and late stages,and that in surface layer was greater than that in deep layer.(2)In sunny days,there was a significant correlation between the maximum value of soil water potential difference of plantations and grasslands and the daily mean temperature.With the increasing of daily mean temperature,the maximum of soil water potential difference also increased.In typical sunny days,the atmospheric temperature fluctuated up and down in the day,and the soil water potential fluctuated with a lag,which was most obvious in the shallow soil during the growing season.(3)There was a correlation between different rainfall and soil water potential difference.With the increasing of rainfall,the soil water potential difference also increased.Under typical rainfall events,the soil water potential of moderate and heavy rainfall profiles rose rapidly,and fluctuated under light rainfall events.From the perspective of different vegetation,grass was more intense than artificial forest.To sum up,the soil water potential of P.sylvestris var.mongolica in the growing season entered into the fluctuating period at the latest,with the largest fluctuating range.The response of soil water potential of Z.japonica was the most sensitive to atmospheric temperature and rainfall.The results were of great significance for guiding the construction of local plantations and efficient management of water resources.