[Seasonal characteristics of δD and δ18O in precipitation and its water vapor sources in the Xiaolangdi Reservoir area of Yellow River, China].

The seasonal characteristics of δD and δ¹8O in precipitation and the influence factors were studied in the Xiaolangdi Reservoir area at the eastern monsoon region of China. The precipitation samples and the corresponding meteorological data were collected between April and October from the year 2011 to 2014. The local meteoric water lines (LMWL) of different seasons were established, and the water vapor sources in different seasons were investigated. The results showed that the δD and δ¹8O in precipitation exhibited an extremely wide range and a distinct seasonal variation, and they were enriched in the spring, and depleted in the fall. The δD and δ¹8O values showed negative correlations with the amount of precipitation from April to October and the fall, respectively. The δD values and the mean air temperature showed a negative correlation from April to October, but showed no correlation in seasonal precipitation. Both the slopes of LMWL and excess deuterium (d values) of precipitation were the smallest in the summer, and the largest in the fall. The results of air mass back trajectories of seasonal precipitation using the HYSPLIT model indicated a dominant effect of southeast and southwest maritime monsoon air masses in the summer and the co-influence of continental and oceanic monsoons air masses in the spring and fall in the study area.

[Effects of drought stress on growth and water use efficiency of two medicinal plants].

Growth characteristics, stable carbon isotope discrimination (Delta13C), water use efficiency (WUE), and their correlation of Cassia obtusifolia and Isatis indigotica were measured at three soil water levels, i. e., 30%, 50% and 75% of field water holding capacity (FWHC), and at three growth stages. The growth indices of the two medicinal plants at 75% of FWHC were higher than those at 30% and 50% of FWHC, suggesting that the two medicinal plants could obtain high production under sufficient moisture condition. The Delta13C(A) (aboveground biomass-based Delta13C) and Delta13C(T) (total biomass-based Delta13C) decreased, and the WUE(A) (aboveground biomass-based WUE) and WUE(T) (total biomass-based WUE) of C. obtusifolia and I. indigotica increased with the increasing degree of drought stress. The growth indices of the two medicinal plants had little difference in the different water treatments, which indicated that the two medicinal plants were insensitive to drought stress. Water use efficiency of I. indigotica had significant negative relationships with aboveground biomass and total biomass, while that of C. obtusifolia had a significant positive correlation with the root/shoot ratio.

[Diurnal variation of Quercus variabilis trunk diameter in response to environmental factors at south aspect of Taihang Mountains].

By using Circumference Dendrometer 2 (DC2), this paper studied the diurnal variation of trunk diameter in Quercus variabilis plantation at the south aspect of Taihang Mountains. During seasonal drought, the diurnal variation of Q. variabilis trunk diameter was quite evident. The time of the diameter shrinkage followed the start-up time of sap flow, but the appearance of the minimum trunk diameter lagged behind the maximum sap flow flux about 3-4 h. The maximum daily shrinkage (MDS) value of the trunk diameter presented a trend low-high-low, being significantly correlated with the diurnal differences of cumulative sap flow flux and leaf water potential and having a significant quadratic relationship with soil moisture content. The MDS value was affected by the variations of meteorological factors, being significantly correlated with the diurnal variations of air temperature, vapor pressure deficit, and relative humidity, but less correlated with the diurnal variation of solar radiation. After successive precipitation, soil moisture content was no longer the limiting factor of the diurnal variation of Q. variabilis trunk diameter. The MDS value had less correlations with the diurnal differences of cumulative sap flow flux, leaf water potential, soil moisture content, and other meteorological factors. Stepwise regression analysis indicated that the soil moisture content and air temperature in seasonal drought and rain seasons were the key factors affecting the diurnal variation of Q. variabilis trunk diameter.

[Measurement accuracy of granier calibration based on transpiration of Platycladus orientalis].

In order to understand the accuracy of Granier' s thermal dissipation method in measuring tree water consumption, a comparative study was made from May to June, 2010. The sap flow density of potted Platycladus orientalis was measured with thermal dissipation probe, which was compared with the whole-plant gravimetric measurement. There were significant linear relationships (R2 > 0.825) between the sap flow velocity in both north and south directions of P. orientalis measured by thermal dissipation probe and the transpiration rate measured by gravimetric method. The average daily sap flux in the north and south directions of P. orientalis were 10.6% and 15.1% lower than the daily average transpiration of P. orientalis, respectively, but the differences were not significant. Therefore, Granier's method had high reliability in the measurement of P. orientalis transpiration at daily scale, though the large temperature fluctuation between day and night could result in a lower daily sap flux than daily transpiration.