| Urban green space system, as a main urban ecosystem component, plays a very important role in improving the urban environment, regulating urban climate, beautifying the urban landscape, increasing the urban space, taking precautions against earthquakes and reducing disaster. Conflicts between the consumption of water in green space and the comprehensive utilization of urban water resources are exacerbated due to the lack of the basic research in theory and key technology of water saving of urban green space, the low utilization rate of irrigation water, the serious and widespread waste of water, and the case is especially true in the arid and semi-arid regions of China where the water resources are generally scarce.Aimed at solving the water saving problem of urban green space, a comprehensive study on the evapotranspiration water consumption and soil moisture in the complex system of tree, shrub and grass in urban area was conducted, with four main plant configuration modes of trees+shrubs+grass, trees+grass, shrubs+grass and grass as the research objects according to their compound characteristics, using research methods (Continuous Dynamic Monitoring in Growing Season, Penman Formula, etc.) and instruments (Li-1600 Steady State Porometer, TDR (Time Domain Reflectometry), Soil Moisture Meter, Automatic Weather Stations) for water ecological characteristics of agroforestry systems. The water consumption characteristics and soil moisture dynamics for the four plant configuration modes were determined and urban green space irrigation model by simulation based on water consumption characteristics of the urban green space were established and optimized. It will provide a theoretical basis for the configuration mode, species selection and scientific irrigation for the urban green space complex system. The main conclusions are as follows:1, Investigation on types of urban green space showed that, the most common used plants were trees (117 species), bushes (77 species), herbaceous plants (315 species), vines (17 species). The major community-structures of plants were trees-bushes-herbs, trees-bushes, and trees only.2, Under single shrub configurations, diurnal changes for the transpiration rate of Yellow Clove showed an obvious single peak, while transpiration rate of Swida alba showed a less clear pattern of single peak and obvious pattern of double peaks, respectively in cloudy and sunny days in the growing season. The transpiration rate was significantly correlated with diffusion resistance and photon density. Under complex configurations, there is a slight variation in the curves for the transpiration rates of two species and the transpiration rates were significantly correlated with relative humidity and the diffusion resistance. Under the same conditions, the transpiration rates of the complex shrub configuration were lower 30% to 40% than those for the single configuration of shrub species. 3, Diurnal changes for the transpiration rates of Eucommia ulmoides and Prunus ceraifera cv. Pissardii showed a single peak, respectively in cloudy and sunny days in the growing season. The transpiration rates of Eucommia ulmoides were significantly correlated with the diffusion resistance, photon density and leaf temperature, and that of Prunus ceraifera cv. Pissardii with photon density and diffusion resistance.4, Sseasonal changes of the transpiration rate for the species tested showed that for Eucommia ulmoides a single-peak curve and Prunus ceraifera cv. Pissardii a bimodal curve. Under the single shrub configurations, Yellow Clove and Swida alba were basically consistent, showing a single-peak curve. Under the combined configurations, Yellow Clove and Swida alba showed a ladder-like decline, the transpiration rates for each month of the growing season decreased significantly, the transpiration rates for Yellow Clove under the complex shrub configurations dropped by an average of 31.7% compared with those under the single configurations, and 29.3% for Swida alba, showing there was a good water-saving potential for complex systems.5, The transpiration water consumptions per unit area of leaf for four species tested in sunny days were largest under different weather conditions of the growing season. Those were 3.00 kg.m-2.d-1,5.27 kg.m-2.d-1,1.86 kg.m-2.d-1 and 1.56 kg.m-2.d-1 for Eucommia ulmoides, Prunus ceraifera cv. Pissardii, Yellow Clove and Swida alba, respectively. Daily transpiration water consumptions for Yellow Clove and Swida alba under the complex configurations less about 50% compared with those under the single configurations.6, Under single grass configurations, cumulative evapotranspiration of a growing season being 499.6 mm, the average monthly evapotranspiration 71.4 mm, with evapotranspiration concentrated in May, July and August. Under complex configurations, the grass evapotranspiration for trees+shrubs+grass, trees+grass and shrubs+grass concentrated in June, July and October, and air relative humidity and solar radiation were the major factors influencing the grass evapotranspiration. The grass evapotranspirations under the single grass configurations in the whole growing season were much larger than those under the complex configurations by over 10 times. From the point of water-saving effectiveness, the descending order is as follows:trees+shrubs+grass, trees+grass, shrubs+grass and grass.7, Dynamic changes of soil moisture during the growing season under the different configurations indicated that:the active soil layers of water consumption were mainly the soil layers of 0-20cm below the soil surface, and might extend to the soil layers of 0-40cm below the soil surface varied with seasonal rainfall and growing season for grass. The active soil layers of water consumption were the soil layers 0-100cm below the soil surface for the shrubs+grass configuration, and 0-100cm below the soil surface for the trees+grass configurations but maximum amplitude of water consumption was in the soil layers of 0-40cm below the soil surface. Under the trees+shrubs+grass configurations, the active soil layers of water consumption tended to deepen gradually from 0-40cm to 100-120cm below the soil surface varied with the growing season. Overall, the active soil layers of water consumption were the soil layers of 0-120cm below the soil surface. 8, Average soil moisture at different depths for a variety of configuration mode showed that for the configuration modes of trees+shrubs+grass more water was consumed in the soil of 1 m below the soil surface and the major consumption areas were restricted to the soil of 40-100cm below the soil surface; The soil moisture of 0-100cm below the soil surface was mainly used for the trees+grass configurations and few deep soil moisture was used; The main soil layers of water consumption ranged in 0-100cm below the soil surface for the shrubs+grass configurations and deep layer water tended to be utilized better. The vertical dynamics of soil moisture 0-100cm below the soil surface for four configuration modes showed that the use of soil moisture for each configuration was similar and the soil moisture 0-120cm below the soil surface was mainly utilized. The soil moisture for the grass and shrubs+grass configurations was higher than that for the trees+shrubs+grass and trees+grass configurations and the trees+shrubs+grass configuration mode has the best stability of the soil moisture content.9, The seasonal changes of soil moisture for different configuration modes showed that:the amplitude of grass soil moisture during the growing season was the largest, followed by that for the trees+grass configuration mode, and the soil moisture for shrubs+grass and trees+shrubs+grass configuration modes were relatively stable. The soil moisture for the trees+grass was always better than that for shrubs+grass and trees+shrubs+grass configuration modes. The soil moisture under different type vegetation showed a similar seasonal dynamic change. Of the four vegetation types, the soil moisture content ofgrass was the highest and that for trees+shrubs+grass configuration the lowest. The soil moisture content for the shrubs+grass configuration was higher than that for the trees+shrubs+grass configuration and that for the trees+grass was only lower than that for the grass. The utilization of deep soil water 100 cm below the soil surface was in the order of trees+shrubs+grass> shrubs+grass> trees+grass. In the year with average precipitation, vegetation evapotranspiration was in sequence order:shrubs+grass> trees+grass> grass> trees+shrubs+grass.10, The monthly evapotranspirations of reference crops in the experimental area in 2004 were calculated, using the Penman integrated method with modified atmospheric pressure. The results showed that the evapotranspiration of reference crops changed dramatically from May to August within one year, increased first and then decreased, and reached to the maximum in July. The monthly irrigation management models for the different plant configurations were established based on the crop coefficient of different configurations calculated in combination with factors such as precipitation and irrigation efficiency. After validation and preliminary application, theoretical irrigation amount derived from the models could reflect the actual irrigation water and the monthly irrigation management models were operational and scientific. |
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