Time scale effect on main factors that influence jujube transpiration in hillside jujube orchard

Abstract: Jujube is widely cultivated in the Loess Plateau region with limited water resources because of its adaptation and high economic benefits. It is necessary to understand the jujube transpiration in order to provide a sustainable cultivation strategy with high water use efficiency. However, the results from the related studies vary partly because of the time-scale difference in different studies. This study aimed to investigate the influence of time scale effect on transpiration. Monthly and annual transpiration and its driving factors were monitored in the year of 2012-2013 in jujube plantations of the Loess Plateau. The relationship between transpiration and factors was analyzed. The results showed that: 1) With the ascension of time scale, the influence of meteorological factors on transpiration decreased, but the influence of crop growth status on transpiration increased, for both monthly transpiration and annual transpiration; however, the main impact factors of monthly transpiration were different from that of annual transpiration under the same time scale; 2) For monthly transpiration, the determination coefficient R2 of its main impact factors varied with the time: during the growth period (May to October), the R2 was higher than the dormant period, and the main impact factors at hourly, daily, and a period of ten days transpiration were photosynthetically active radiation (PAR), relative humidity (RH) and wind speed (WS), leaf area index (LAI) and leaf area (LA), respectively; 3) For annual transpiration, as the ascension of dimensions, the changing trends of R2 of its impact factors were classified into three types: increase first and then decrease (temperature TA), PAR, vapor pressure deficit VPD), increase (soil water content SW, LA, LAI), and decrease first and then increase (RH, WS). Transpiration on smaller time scales (hourly and daily) had significant (p<0.01) correlations with meteorological factors (except for wind speed that had a complicated influence), but with LAI, LA and SW only on larger time scales (ten daily and monthly). By the correlation analysis and comparison of transpiration and its impact factors under different time scales, we found that time scale was one of the important factors affecting their relationships. This conclusion is very important not only for revealing the impact mechanism of relevant factors on transpiration, but also for optimizing the management of jujube plantations in mountainous regions and guiding development of new type water-saving agricultural technology for dry land. Moreover, it has great value to improve the economic and ecological benefits of jujube plantations in mountainous regions, as well as to promote the sustainable development.