[Effects of multiple times of topdressing nitrogen application under equal level on utilization and distribution characteristics of 15N and 13C in winter jujube]. / 等量分次施氮对冬枣15N和13Cåˆ©ç”¨ä¸Žåˆ†é ç‰¹æ€§çš„å½±å“.

We explored the effects of multiple times of topdressing nitrogen application under equal level on the characteristics of absorption, utilization, accumulation, and distribution of 15N and 13C in four-year-old potted winter jujube during fruit developmental periods using the stable isotope tra-cer technology. The results showed that with the increases of nitrogen application times, the 15N derived from fertilizer (Ndff) in each organ significantly increased at the fruit maturity. The distribution rates of 15N in reproductive organ (fruit) and vegetative organs (leaf, deciduous spur, new branch, and fine root) were highest under four-time application, and lowest under one-time application. The opposite pattern was observed in storage organs (trunk, perennial branch, and coarse root). The 15N utilization rate under four-time application was 27.4% and 15.5% higher than one-time and two-time application, respectively. The more times N being applied, the more total N content and 15N absorption amount of plant. Soil 15N abundance and total N content continued to drop under one-time application and increased at the beginning and then declined with the time under two-time application. The relatively stable soil 15N abundance and total N content appeared in four-time application, which was significantly higher than those in the other treatments in later treatment stages. The chlorophyll content, leaf nitrogen content and photosynthetic rate displayed an order of four-time application > two-time application > one-time application during fruit white-mature period to fruit harvest period. The accumulation and distribution of 13C varied across different treatments. Increasing nitrogen application times would promote more 13C being transported to fruit and storage organs but decrease that in annual vegetative organs. Our findings indicated that four-time nitrogen application could enhance and optimize the accumulation and distribution of photosynthetic products by ensuring steady and adequate supply of nitrogen and improving the absorption and utilization of nitrogen during fruit development period, which facilitates the growth, yield and quality of winter jujube.

[Evolution pattern of impervious surface in the Yuqiao Reservoir Watershed, Tianjin, China during the process of urbanization.] / åŸŽé•‡åŒ–è¿‡ç¨‹ä¸­æµåŸŸä¸é€æ°´é¢æ¼”å˜æ ¼å±€­­ä»¥å¤©æ´¥äºŽæ¡¥æ°´åº“流域为例.

Imperviousness in watershed is a key index to measure urbanization status which exerts an important impact on both eco-hydrological process and spatio-temporal pattern. Taking Yuqiao Reservoir Watershed as a case study area, based on the ENVI 5.1 software, the basic impervious surface information was extracted from remote sensing images taken in 1984, 1994, 2004 and 2013. The linear spectral mixture analysis (LSMA) model was applied to extract the impervious surface area (ISA) in nine coverage classes of watershed in order to analyze its spatio-temporal varying trend in terms of the landscape pattern metrics. Results showed that the RMSE and IS pixel accuracy of all samples were 0.005 and 85.4% respectively, which indicated that the method of extracting impervious surface on a basin scale was feasible. The average of ISA showed a linear growth, from 0.16 to 0.23, the impervious surface area increased by 4.9% in the whole watershed, and the total impervious surface area increased by 1 time. In the sub-basin road network, the impervious surface area increased gradually with the density of the road network, and its expansion pattern was of infilling growth. The patch shape of the middle coverage degree was irregular, and its fragmentation degree was the highest. The fragmentation degree and diversity of the landscape in the whole river basin increased year by year due to increasing human disturbance.

[Dynamics of forest community structure and complexity in the process of secondary succession in bedrock area of west Shanxi Province].

In this paper, four plots representing the typical secondary succession stages of forest community were selected at the shady slope of bedrock area in Zhongyang County of West Shanxi, aimed to study the variation patterns of the structure and complexity of forest community in the process of secondary succession. The results showed that in the succession process of the community, there was an evident regularity in the variation of height and diameter class structure. The proportion of high and big individuals in the community increased gradually, while that of low and small ones increased first but decreased then. From the viewpoint of height class structure, the compositional complexity of tree species H (X), structural complexity of tree species H (Y/X), and complexity of whole community H (X,Y) all increased first, but decreased then with the succession. At the early, middle and arbor stages of succession, the H(X) value was 2.96, 3.85 and 3.75, while H (Y/X) value was 1.27, 1.66 and 1.37, respectively.