Vegetation restoration as an effective sand fixation measure has made great achievements in China. However, soil water conditions deteriorate with the development and maturity of sand-fixing vegetation. In this study, we investigated the relationship between soil water content (SWC) and vegetation coverage (VC) at different portion (top, middle and bottom) on ten sand dunes during the growing season (April to October) in Horqin Sandy Land, northern China. We analyzed the temporal and spatial variation characteristics of SWC under different VC. The results indicate that VC and soil water storage were negatively correlated. The effect of vegetation on soil water storage on the sand dunes was greater in the dry season than the wet season. The VC and coefficient of coefficient of SWC were positively correlated at the 20 to 140 cm soil depth. As VC increased, the effect of drought stress increased at the 20 to 200 cm soil depths. The VC and SWC were negatively correlated at all the three portions of the sand dunes. According to soil water conditions and the concept of wilting humidity at different VC, we found that the suitable VC values were less than 0.46, 0.52, and 0.71 at the top, middle and bottom of the sand dunes, respectively.

Satellite-based precipitation data have contributed greatly to quantitatively forecasting precipitation, and provides a potential alternative source for precipitation data allowing researchers to better understand patterns of precipitation over ungauged basins. However, the absence of calibration satellite data creates considerable uncertainties for The Tropical Rainfall Measuring Mission (TRMM) Multisatellite Precipitation Analysis (TMPA) 3B42 product over high latitude areas beyond the TRMM satellites latitude band (38°NS). This study attempts to statistically assess TMPA V7 data over the region beyond 40°NS using data obtained from numerous weather stations in 1998–2012. Comparative analysis at three timescales (daily, monthly and annual scale) indicates that adoption of a monthly adjustment significantly improved correlation at a larger timescale increasing from 0.63 to 0.95; TMPA data always exhibits a slight overestimation that is most serious at a daily scale (the absolute bias is 103.54%). Moreover, the performance of TMPA data varies across all seasons. Generally, TMPA data performs best in summer, but worst in winter, which is likely to be associated with the effects of snow/ice-covered surfaces and shortcomings of precipitation retrieval algorithms. Temporal and spatial analysis of accuracy indices suggest that the performance of TMPA data has gradually improved and has benefited from upgrades; the data are more reliable in humid areas than in arid regions. Special attention should be paid to its application in arid areas and in winter with poor scores of accuracy indices. Also, it is clear that the calibration can significantly improve precipitation estimates, the overestimation by TMPA in TRMM-covered area is about a third as much as that in no-TRMM area for monthly and annual precipitation. The systematic evaluation of TMPA over mid-high latitudes provides a broader understanding of satellite-based precipitation estimates, and these data are important for the rational application of TMPA methods in climatic and hydrological research.

Atmospheric nitrogen (N) deposition has been observed to impact plant structure and functional traits in terrestrial ecosystems. Although the effect of N deposition on plant water use has been well-evaluated in laboratories and in experimental forests, the linkages between water and carbon relations under N deposition are unclear. Here, we report on hydraulics, gas exchange and carbon reserves of two broad-leaved tree species (Quercus mongolica, and Fraxinus mandshurica) in a mature temperate forests after a seven-year experiment with different levels of N addition (control (CK), low (23 kg N ha⁻¹ yr⁻¹), medium (46 kg N ha⁻¹ yr⁻¹), and high (69 kg N ha⁻¹ yr⁻¹). We investigated variation in hydraulic traits (xylem-specific hydraulic conductivity (K_s), native percentage loss of conductivity (PLC) and leaf water potential), xylem anatomy (vessel diameter and density), gas exchange (maximum net photosynthesis rate and stomatal conductance) and carbon reserves (soluble sugars, starch and total non-structural carbohydrates (NSC)) with different N addition levels. We found that medium N addition significantly increased K_s and vessel diameter compared to control, but accompanied increasing PLC and decreasing leaf water potential, suggesting that N addition results in a greater hydraulic efficiency and higher risk of embolism. N addition promoted photosynthetic capacity via increasing foliar N concentration but did not change stomatal conductance. In addition, we found increase in foliar soluble sugar concentration and decrease in starch concentration with N addition, and positive correlations between hydraulic traits (vessel diameter and PLC) and soluble sugars. These coupled responses of tree hydraulics and carbon metabolism are consistent with a regulatory role of carbohydrates in maintaining hydraulic integrity. Our study provides an important insight into the relationship of plant water transport and carbon dynamics under increasing N deposition.