基于茎干直径微变化制定苹果灌溉制度

Assessment of trunk diameter fluctuation for irrigation schedule in apple trees

茎干直径的动态微变化是研究植物体水分和生长状况的重要指标。利用测树器监测西北旱区盛果期苹果树茎干直径微变化规律,根据监测记录获得茎干直径日最大值(MXTD)、茎干直径日最大收缩量(MDS)数据,并探讨茎干直径微变化规律及其对环境因素的响应,为茎干直径微变化用于指导精确灌溉提供科学依据。实验结果表明,晴天或多云天气下,苹果树茎干直径在每天的7:00或8:00时刻达到一天最大值,在16:00左右达到一天的最小值,茎干直径年增长量与果实产量成反比例关系。整个生育期MXTD呈先快速增加后平稳的变化特征。2010年MDS与茎干水势(φstem)呈显著负相关关系(r2=0.76***,n=14),这表明MDS可以反映苹果树的水势状况。生育后期的MDS对环境因素响应比生育前期敏感,全生育期MDS与气象因素的决定系数大小顺序为日最大水汽压差(VPDmax)>日最高温度(Tmax)>净辐射(Rn)。茎干直径微变化规律可以反映西北旱区盛果期果树的水分状况,可以为果园灌溉制度的确定提供科学依据。

Research on agricultural water consumption in northwest China is crucial to relieve problems associated with the water crisis. Apples are a typical crop in China that have been used in agriculture for centuries. As production increases for economic growth, it is essential to analyze water transport mechanisms and water accessibility to mature apple orchards in arid regions. Trunk diameter fluctuation is an effective indicator of the water condition of plants. Its role as an indicator of plant water conditions thus emphasizes that it is crucial to design an irrigation schedule. The changes in the trunk diameter of mature apple trees （Malus domestica Borkh. cv Golden Delicious） was monitored using dendrometers at the Shiyanghe Experimental Station for Water-saving in Agriculture and Ecology of China Agricultural University （37°52＇N, 102°51 ＇E, altitude 1581 m）. Stem water potential was measured using a pressure chamber. Wind speed, net radiation, relative humidity, and air temperature were monitored by an automatic meteorological station, and soil moisture was measured every 5 days using Time-Domain Reflectometry （TDR） methods based on the previously described data analysis. Change in the maximum daily trunk diameter （MXTD） and maximum daily diameter shrinkage （MDS）, as well as their response to environmental factors were also monitored. The results showed that MXTD occurred at 7：00 to 8：00 in the morning and minimum of daily trunk diameter （MNTD） occurred at approximately 16：00 during sunny or cloudy days in 2008 on a daily scale. The trunk diameter increased at night and decreased evapotranspiration. MXTD increased during bud development, during the day, which was meanly depended on reference flowering, and leaf expansion periods （ stage Ⅰ） and remained constant during the fruit expanding and maturing periods （ stage Ⅱ）, which was closely related to the MDS of the apple tree. Higher fruit yields were associated with smaller fruit stem diameter growth. MDS increased at the beginning and then gradually decreased during the entire growing stage. The relationship between MDS and stem water potential was linear and the determination coefficient was 0.76^＊＊＊. Consequently, MDS indicated the water status of the mature apple trees. However, MDS was more responsive to net radiation, reference evapotranspiration, vapor pressure deficit, and air temperature at stage Ⅱ than at stage Ⅰ because the canopy structure was not developed, and the water stored in the apple trees less frequently fluctuated during stage Ⅰ. The order of determination coefficient over the whole growing stage was as follows ： maximum vapor pressure deficit 〉 maximum air temperature 〉 net radiation. Multiple regression relationships among MDS and environmental factors can be used to calculate the MDS for well water supplied to apple trees, which could be considered as a reference value when the tree requires irrigation. Thus, the fluctuation regularities of tree trunk diameter could reflect the water status of the entire fruit period of fruit trees situated in arid areas of Northwest China and help improve orchard water management, as well as ensure the normal growth of fruit trees.