Abstract: Vitex negundo is the native shrub species which was very popular in low mountain area of Taihang Mountains. It is widely used in such aspects as mountain greening, soil and water conservation, and ecological restoration due to its characteristics of strong resistance, and tolerance to barrenness. Studying on the water consumption of Vitex negundowas could not only reveal its water consumption dynamics and influencing mechanism, but also provide theoretical basis for local vegetation restoration and management. The water consumption of Vitex negundo and meteorological factors were measured with large weighing lysimeter and the automatic weather station, respectively. At the same time, reference evapotranspiration (ET0) was calculated by the Penman-Monteith equation recommended by FAO-56. The objective of the paper was to study the water consumption of Vitex negundo on different time scales, to find the adaption capacity to the arid environment, to reveal the relationship with ET0, and to provide empirical model for estimating the water consumption of Vitex negundo under the conditions of lacking measured data. The results showed that: (1) diurnal variation of water consumption of Vitex negundo showed single peak curve on typical days , which was consistent with solar radiation, air temperature, and vapor pressure deficit, but contrary to the relative humidity. Meanwhile, the peak time of water consumption of Vitex negundo. was 2 hours behind that of solar radiation, and time lag was found between them. Water consumption trendy of Vitex negundo on daily time scale showed low water consumption in the early and later growth period, and high in the middle growth period, and the value was 1.50mm, 2.00mm, and 4.00mm per day, respectively. Maximum and minimum of daily water consumption was found on 29th in August and 9th in October, with the value of 6.38mm and 0.20mm, respectively. The water consumption of Vitex negundo on monthly time scale showed the tendency of August >July > September > October> June > May. The total water consumption of Vitex negundo during the growth period was 513.5mm, and the rainfall was 526.6mm. The precipitation could meet the needs of water consumption Vitex negundo from the perspective of water balance. However, seasonal drought existed from May to June due to the less rainfall. (2) Vitex negundo has the feature of environmental adaptability and ecological plasticity. In rainy seasons, Vitex negundo was in prosperous growth period, the water transmission rate was high, and the water consumption was large. Adaptive mechanism started in arid season to reduce water consumption. (3) Good logarithmic relationship was found between daily water consumption of Vitex negundo and reference evapotranspiration in rainy seasons (July to October), while poor correlation was discovered between them in dry seasons ( May to June). The estimated value of water consumption was calculated with the fitting equation, and was compared with the measured valued by the lysimeter. The good consistency and small error were found between the estimated and measured values, which conformed the precision of the fitting equation. It was indicated the fitting equation was accurate to estimate water consumption of Vitex negundo in rainy seasons of the local area, but inaccurate in dry seasons.

Key words: Lysimeter, Vitex negundo, Time scale, Water consumption characteristics, Reference evapotranspiration, Estimation