栓皮栎人工林树干液流对不同时间尺度气象因子及水面蒸发的响应

于2006-2008年主要生长季节,利用热扩散技术连续测算得到了华北土石山区30年生栓皮栎人工林液流量(SF),并结合同步测定的太阳辐射(Ra)、空气温度(Ta)、饱和水汽压亏缺(VPD)、风速(V)和降雨量(P)等气象因子、水面蒸发(EV0)及叶面积指数(LAI)等因子,分析了栓皮栎液流对不同时间尺度气象因子及水面蒸发的响应规律,探索建立长时间尺度水面蒸发与树干液流之间的关系模型。试验结果表明:(1)在主要生长季(4—9月份)期间,栓皮栎单株液流与同期测定的Ra、Ta、VPD和V等气象因子间均存在着较强的相关性。时间尺度为10min、1h、d、旬、月时,决定系数分别为0.388、0.482、0.539、0.654和0.812。说明随着时间尺度的增加,相关性越强;在不同时间尺度下,影响SF的最主要气象因子均为Ra。月SF与月Ra变化趋势的同步性尤为明显。(2)日尺度和月尺度上EV0与SF之间具有很好的线性关系,决定系数分别为0.578和0.876,比同时期、相等样本数条件下SF与Ra、Ta、VPD、V多元线性拟合的决定系数分别高3.6%和3.9%。(3)2006、2007、2008年生长季节降雨量分别为464.8、393.3mm和315.0mm,栓皮栎单株液流分别为2024.1L、1739.2L和1688.7L,年际间SF变化趋势与降雨量存在一定的一致性。

Responses of stem sap flow to meteorological factors and water evaporation at different time scales over Quercus variabilis plantation

Stem sap flow of 30-year-old Quercus variabilis individual trees in the rocky mountain areas of the North China was measured by thermal dissipation probe (TDP) during the growing seasons from 2006 to 2008. The responses of Quercus variabilis sap flow to meteorological factors and water evaporation at different time scales were analyzed. The purposes of the study were to establish model between sap flow and water evaporation at long-time scale and to provide theoretical basis for establishing water saving and drought resistance model. The results showed that: (1) During the growing seasons (from April to September), sap flow had positive correlation with solar radiation, air temperature, and vapor pressure deficit. However, the correlation between sap flow and wind speed was unremarkable. Determination coefficients at 10 min, 1 h, 1 day, 10-day, one month scales were 0.388, 0.482, 0.539, 0.654 and 0.812, respectively. It was proved that the longer time scale was, the more significant correlation was found between sap flow and meteorological factors. At short-time scales, such as 10 min and 1 h, the correlation between sap flow and meteorological factors was low due to the delay of the time and it was more obvious in early April. Solar radiation (Ra) was the dominant meteorological factor affecting on sap flow. The synchronism between Ra and sap flow was more evident at monthly scale. Solar radiation and sap flow in 2006, 2007 and 2008 peaked in June, May and May, repectively. Both monthly amount and the proportion to total sum of sap flow were consistent with solar radiation during experiment periods. (2) At daily and monthly scales, sap flow had good relations with water surface evaporation (EV0) and determination coefficients were 0.578 and 0.876, respectively, 3.6% and 3.9% higher than those obtained by the multiple linear equations between sap flow and meteorological factors. Longer time scale provided higher resolution for the simulation model. On the other hand, the model fitted by water surface evaporation was more precise than by meteorological factors. Moreover, water surface evaporation was easy to acquire. Hence, the model fitted by water surface evaporation had a wide application prospect. (3) During growing seasons, the precipitation from 2006 to 2008 was 464.8, 393.3 and 315.0 mm, respectively. Sap flow of Quercus individual trees at the same stages were 2024.1, 1739.2 and 1688.7 L, respectively. It showed that inter annual variation trend of sap flow was in agreement with that of rainfall. Annual sap flow increased with the rise of annual precipitation. However, sap flow was not consistent with rainfall at monthly scale. The reason was that water compensating for sap flow mainly came from the soil and soil water content was influenced by the factors such as precipitation intensity, soil percolating and canopy interception, and thus soil water content was not same even though the precipitation was same.