关键词: 蒸腾, 蒸散, 土壤蒸发, 毛白杨；人工林, 水分管理

Abstract:

Objective: This study aims to clarify the long-term water consumption pattern of short-rotation Populus tomentosa plantation during the rotation period and construct a (basic) crop coefficient curve, so as to provide a basis for water-saving irrigation and management of P. tomentosa plantation. Method: We continuously monitored the transpiration (Tr), soil evaporation (E_s), and stand evapotranspiration (ET) of 2–6-year-old P. tomentosa plantations under sufficient water supply. At the same time, we also collected data of meteorological factors, daily trunk growth (DGR), leaf area index (LAI), and groundwater level, and further calculated reference crop potential evapotranspiration (ET₀), basic crop coefficient (K_cb), and crop coefficient (K_c). Result: 1）The main growth stages of the stand were different each year, but the growth rate was the fastest from May to July, during which the diameter growth of trees in this period accounted for 69%~88% of the total growth in the whole growth season, and the cumulative ET accounted for 47%~61% of the total ET in the whole growth season. According to the average DGR and LAI seasonal dynamics of stand during the rotation period, the growth stages of P. tomentosa plantation were divided into the early growth stage, development stage, middle growth stage, and late growth stage, and the corresponding periods were from early April to mid-April, from mid-April to mid-June, from mid-June to mid-August, and from mid-August to the end of October, respectively. 2）The results showed that there were significant seasonal changes in Tr, E_s, and ET in the stand, but the change patterns were quite different in different stand ages. In addition, the seasonal variation of stand Tr was significantly positively correlated with ET₀ only in 3–6-year-old stands (P<0.05), and there was positive correlation betweenE_s and ET₀ (P<0.05) only in 2-year-old and 6-year-old stands, but there was a positive correlation between ET and ET₀ in all stand ages (P<0.05). The annual total ET and Tr increased exponentially (P<0.001) and linearly (P=0.004) with the increase of stand age, respectively, while the stand E_s gradually decreased with the plant age, but suddenly increased significantly in the 6-year-old stand. The proportions of Tr and E_s in ET increased and decreased yearly, respectively and tended to be stable in 5–6-year-old stands. 3）There were significant differences in seasonal variation characteristics of K_cb and K_c in different stand ages. The seasonal variation of K_cb and K_c was not affected by groundwater level, however, it was controlled by LAI in 3–6-year-old stands (P<0.05). Moreover, bothK_cb (R² = 0.44–0.87) and K_c (R² = 0.42–0.77) could establish an excellent quantitative relationship model with LAI. In addition, we constructed the (basic) crop coefficient curve and list of P. tomentosa plantations according to the change patterns of K_cb and K_c and the divided tree growth stages. Conclusion: The seasonal dynamic characteristics of evapotranspiration, transpiration, and evaporation of P. tomentosa stands have interannual changes. The fluctuation of ET₀ is an essential factor in controlling the seasonal dynamics of water consumption, but the control mode varies with water consumption components and stand ages. The growth stage of P. tomentosa can be divided into four periods, and the key period of water management in stands is from May to July every year. The established (basic) crop coefficient curve, list, and prediction model of P. tomentosa plantation can be used to estimate the stand water consumption and thereby formulate and optimize the irrigation schedule. In addition, the results can not only provide a reference for the efficient water management of other tree species, but also help deepen the understanding of the water relationship of the plantation.

Key words: transpiration, evapotranspiration, soil evaporation, Populus tomentosa; plantation, water management