Abstract:The aim of this study was to obtain the diurnal and seasonal changes of trunk sap flow in desert-living Caragana korshinskii so as to understand its water requirement and ecological significance. The experiment was carried out with 15-year old Caragana korshinskii grown in north-west China under natural conditions. Heat pulse sensors based on the heat compensation theory were applied to measure the trunk sap flow, and soil moisture content at 0-300 cm layer, using tube-type time domain reflectometry (Tube-TDR). The solar radiation, the maximum and minimum air temperatures, relative humidity, wind speed, wind direction and precipitation were measured at a standard automatic weather station. The diurnal and seasonal variations of sap flow rate, the sap velocity at different positions in the trunk and the sap flow rate under different weather conditions were analysed. And the correlation between the sap flow rate and the meteorological factors was also analysed. Results showed that the trunk sap flow varied regularly in the diurnal term and the sap flow velocity decreased with the probe-inserted depth into the sapwood. Magnitude of sap flow changed considerably between sunny and rainy days. The order of the main meteorological factors affecting the sap flow rate of Caragana korshinskii shrubs were: vapour pressure deficit > solar radiation > air temperature > wind speed. The close correlation between daily sap flow rate and meteorological factors in the whole growing season can be used to estimate the transpiration of Caragana korshinskii.

Abstract:Global warming has resulted in increasingly frequent and severe drought and/or precipitation events. Severe drought limits crop water availability and impacts agricultural productivity and socioeconomic development. To quantify drought-induced yield loss during the main crop stages in Liaoning province, China, aspects of drought episodes (magnitude, duration, and frequency) were investigated during the period 1960-2015 using the Standardized Precipitation Index (SPI) and the Standardized Precipitation Evapotranspiration Index (SPEI), respectively. Then the relationship between the SPI/SPEI and the standardized yield residuals series (SYRS), and the drought-induced yield loss were analyzed for maize, rice, sorghum, soybean, and millet. Liaoning underwent a province-wide increase in temperature, reduced precipitation, and reduced reference crop evapotranspiration. As expected, Liaoning experienced province-wide meteorological drying trends during the main crop growth stages, while the drought frequency, duration, and magnitude were not as serious as revealed by using the SPI. As compared to the SPI, the SPEI considering potential evapotranspiration explained 39%-78% yield variability of SYRS and evaluated the drought-induced yield loss more accurately. The increased drought frequency mainly affected the rain-fed crops (maize, sorghum, soybean, and millet), while it did not reduce irrigated rice production. No major impact was exerted on the rain-fed crops caused by mild drought. However, severe drought (SPEI < −1.0) markedly reduced yield performance, in particular at the anthesis-silking stage for maize, the jointing-booting stage for sorghum, the flowering-podding stage for soybean, and the sowing-milking stage for millet. It is concluded that the SPEI is a more useful measure for the identification of drought episodes and the assessment of drought impact on agricultural production in Liaoning province.

Abstract:Tamarix elongata Ledeb is a desert shrub found in the desert region of Northwest China and is commonly cultivated as a sand-holding plant in this region. To understand its water requirement and the effects of climate conditions on its growth, trunk xylem sap flows of irrigated 8-year-old Tamarix elongata Ledeb plants were monitored continuously with heat-pulse sap flow meters for the entire season. Soil moisture contents at 0-300 cm layer depth were also measured with a tube type time domain reflectometry (Tube-TDR). Meteorological factors, i.e. solar radiation, air temperature, relative humidity and wind speed were simultaneously monitored by an automatic weather station at the site. Daily and seasonal variations of the trunk sap fluxes and their correlations with the meteorological factors, reference evapotranspiration and soil moisture contents in the root-zone were analysed. The results indicated that frost influenced the trunk sap flux greatly under irrigated conditions, although the flux generally fluctuated with the variation of environmental factors and showed a mean trunk sap flux of 4Ð18 l d1 . There was a significantly exponential relationship between sap flux and the reference value of crop evapotranspiration, with a correlation coefficient of R 2 D 0Ð7172. The sap flux also had a significant correlation with the soil water contents at a depth of 150-300 cm from soil surface (R 2 D 0Ð5014). The order of the main meteorological factors affecting the sap flux of Tamarix elongata Ledeb trees was solar radiation > air temperature > vapour pressure deficit > relative humidity > wind speed.

Phosphorus (P) deficiency often occurs in paddy fields due to its high fixation, and low solubility and mobility in soils, especially under water stress. Available soil P and plant P uptake could be improved through the application of zeolite. However, little is known about the impact of zeolite on P uptake in rice under water stress. A two-year lysimetric experiment using a split-split plot design investigated the effects of zeolite (0 or 15 t ha−1) and P (0 or 60 kg ha−1) applications on water use, P uptake, and grain yield in rice under two irrigation management systems (continuous flooding irrigation (CF) and improved alternate wetting and drying irrigation (IAWD)). Both irrigation systems produced equivalent effective panicles and grain yield. Compared with CF, IAWD reduced water use and aboveground P uptake and improved water-use efficiency (WUE) in rice. The applications of zeolite or P alone increased grain yield, WUE, soil available P, and stem, leaf, and panicle P concentration, and aboveground P uptake, but had no significant effect on water use. The enhanced grain yield induced by zeolite was related to the increase in aboveground P uptake. The zeolite application enhanced NH4+–N retention in the topsoil and prevented NO3−–N from leaching into deeper soil layers. Moreover, Zeolite made lower rates of P fertilizer possible in paddy fields, with benefits for remaining P supplies and mitigating pollution due to excessive P. These results suggest that the combined application of zeolite and P under improved AWD regime reduced water use, improved P uptake and grain yield in rice, and alleviated environment risk.