[Spatio-temporal variation of reference crop evapotranspiration and its climatic mechanism in Nenjiang River Basin, China]. / å«©æ±ŸæµåŸŸå‚è€ƒä½œç‰©è’¸æ•£é‡æ—¶ç©ºå˜åŒ–åŠå ¶æ°”å€™å½’å› .

To understand the temporal and spatial variations of reference crop evapotranspiration (ET0) in Nenjiang River Basin, and clarify the effects of climatic factors on ET0, we calculated the daily ET0 of each station in Nenjiang River Basin from 1970 to 2019 by Penman-Monteith formula, analyzed the temporal variation trend and spatial distribution pattern of ET0. We further quantitatively examined the sensitivity of ET0 to meteorological factors by sensitivity analysis, and explored the contribution of meteorological factors to ET0 changes. The results showed that ET0 generally showed an insignificant decreasing trend during the study period in the Nenjiang River Basin. ET0 decreased in spring, summer, and autumn, but increased in winter, and decreased from southeast to northwest. ET0 had the highest sensitivity to relative humidity at both temporal and spatial scales. The sensitivity coefficients of mean temperature, relative humidity and wind speed increased gradually, while that of sunshine hours decreased gradually. ET0 was sensitive to mean temperature in northern Greater Khingan Mountains and Lesser Khingan Mountains, while to wind speed in southern Greater Khingan Mountains and Songnen Plain. Wind speed was the main factor affecting the change of ET0 in the whole year, spring, autumn, and winter. Sunshine hours was the main affecting factor in summer. The mean temperature and relative humidity had the greatest contribution to ET0 in the north of Greater Khingan Mountains and Lesser Khingan Mountains, and it was the wind speed in Songnen Plain.

[Comparison of ecological characteristics of Carex tussock under natural and artificial reco-very.] / 人工恢复与自然恢复模式下苔草草丘生态特征比较.

We compared the ecological characteristics of tussock individuals and populations undergoing natural and artificial restoration in Carex tussock wetlands in the Sun Island in Harbin and identified the relationships between the growth of Carex tussock and environmental factors. Results showed that there were obvious seasonal dynamics in morphological characteristics of C. appendiculata. Tussocks grew rapidly from May to June, peaked in June, and then decreased steadily from July to August. There were significant differences in ecological characteristics of Carex tussocks between natural and artificial restorations. The morphological characteristics of individual tussock, including leaf area, leaf width, fresh weight per ramet, dry weight per ramet, and the hummock shape indicators (hummock height, diameter, volume and surface area) in natural restored area were significantly higher than those in artificial transplanting area. For the Carex tussock community, tussock density, coverage and biomass in natural restoration area were significantly lower than those in artificial transplanting area. Soil water content, water depth and hummock spacing in natural restoration area were significantly higher than those in artificial restoration area, which facilitated the formation and development of individual tussock. Higher transplanting density was the main factor leading to higher density, coverage, and biomass in artificial restoration area. Our results suggested that the distribution characteristics of tussocks in natural restoration area should be taken into account in future restoration and protection works. Appropriate adjustment of the distance between hummock (54.22-117.89 cm) and population density (1.9-3.1 ind·m-2), as well as proper water recharge measures in spring in arid areas to regulate soil water content and water depth, would be conducive to promoting the growth and rapid recovery of Carex tussock, which would maintain the long-term health and stability of tussock wetland.

[Response of meadow soil nitrogen to hydro-periods in Napahai plateau wetland].

A two-year field located monitoring was carried out to study the impacts of hydro-periods on the lakeshore meadow wetland soil total nitrogen (TN) and hydrolysable nitrogen (HN) in Napahai plateau wetland in northwestern Yunnan province. The results show that meadow soil alternate drying-wetting is the significant characteristic influenced by hydro-periods. Hydro-periods of meadow wetland control the physical environment of meadow soil, and the occurrence of TN in the upper layer (0-20 cm) was influenced more significantly than in the deeper layer (20-40 cm) by wetland hydro-periods. The dynamics of TN (0.96-1.30 g/kg) show a shape of anomalous "W" in the upper layer. And in the rainy season, the dynamics of TN was the same as the trend of water level fluctuation, while the HN was in the reverse trend. The enzyme activities were influenced by hydro-periods and then controlled the mineralization process of organic nitrogen. In August when wetland water fell, the highest amount of HN was 222.19 mg/kg (0-20 cm layer) and 47.41 mg/kg (20-40 cm layer) respectively. But when the wetland water level rose, the HN was moved to wetland water by the rising water level, and the decrease amplitude was 42% and 48% respectively. Therefore the deterioration of the environment of water was aggravated.