Variations of drought and its trend in the Loess Plateau from 1986 to 2019.

As one of the extreme climatic events, the frequency and intensity of drought have great impacts on regional water resource. Water is a main limiting factor for plant growth in arid and semi-arid regions. Therefore, it is of great scientific significance to explore the spatiotemporal variations and future tendency of drought for the ecological environment in the Loess Plateau. Based on grid data of monthly precipitation and temperature from 1986 to 2019, we calculated standardized precipitation evapotranspiration index (SPEI) and drought frequency. The spatiotemporal patterns and its variations were analyzed at the seasonal and annual scales in the Loess Plateau using the Mann-Kendall test and Sen's slope estimation method. Finally, the future trend of drought was analyzed in the Loess Plateau by the NAR neural network combined with Hurst index. Results showed that the trend of aridification became more significant in the Loess Plateau, and that the frequency of droughts events exhibited great spatial variations at the interannual and seasonal scales during the study period. Specifically, the highest frequency of drought in the interannual, spring and winter was found in the southeast and west of the Loess Plateau, whereas the frequency of drought in summer and autumn was higher in the northwest. The frequency of moderate drought was the highest in summer compared with other seasons while the frequency of slight drought was the highest in interannual and other seasons. The Loess Plateau showed a trend of aridification in spring and summer, but this trend in autumn and winter became weaker in most areas of the study area. The SPEI value in the interannual, spring, and summer exhibited a decline trend in a future period in the Loess Plateau. The aridification would be enhanced. The Hurst index value was the largest and the persis-tence of its change remained stronger in summer. The possibility of continuous drought in summer would be higher than that in other seasons in the future.

[Seasonal divergence in the responses of vegetation growth to PDO in Tibetan Plateau, China]. / 青藏高原植被生长对PDO响应的季节分异.

Regional-scale normalized difference vegetation index (NDVI) derived from satellite remote sensing observations and gridded climate data were used to study the seasonal responses and underlying mechanisms of vegetation growth over Tibetan Plateau to Pacific Decadal Oscillation (PDO) at period of 1982-2015, by performing Spearman correlation analysis and enhanced multivariate regression model: structural equation model (SEM). The results showed that there was significant negative correlation between PDO index and mean growing-season (April-October) NDVI over Tibetan Plateau; however, marked seasonal divergence in the relationship between PDO and vegetation growth existed among different seasons. It characterized with stronger negative correlation between PDO and NDVI in autumn than in summer, and winter PDO had significant effect on consequent summer vegetation growth. Additionally, it showed great divergence in control processes of PDO on vegetation growth among different seasons, with significant control of PDO on both temperature and precipitation in summer, and significant control of PDO on temperature only in autumn.

[Phosphorus Fractions and Release Risk in Surface Sediments of an Agricultural Headwater Stream System in Hefei Suburban, China].

A typical water system of agricultural headwater stream in Chaohu Lake basin was selected as the study area, and 17, 16, 14 and 13 surface sediments were collected from the four styles of stream, respectively, including ponds, branches, main channel and mainstream deep pools, in October 2014 (in autumn) and April 2015 (in spring). The forms and space-time variations of phosphorus in the sediments were analyzed. Clustering and variance analysis were conducted on the phosphorus forms data from the four styles of stream by means of multivariate statistical analyses. We quantified the phosphorus release risk (PSI) and identified the main impact factors of PSI via calculating the phosphorus sorption index (PSI) and the correlation analysis. The results showed that: (1) The contents of TP in the surface sediments ranged from 137.517 to 1709.229 mg x kg(-1) with an average value of 532. 245 mg x kg(-1), and the order of the average contents of phosphorus forms was IP (350.347 mg x kg(-1)) > OP (167.333 mg x kg(-1)) > Fe/Al-P ( 78. 869 mg x kg(-1)) > Ca-P (56.343 mg x kg(-1)) > Ex-P (6.609 mg x kg(-1)); (2) The contents of phosphorus forms had the same trend in all the four stream styles, which was deep pool > main channel > branch > pond; (3) In autumn, the deep pool and main channel were clustered into one class, while the pond and branch were clustered into the other class. In spring, branch, main channel and deep pool were clustered into the same class; (4) Variance analysis showed that the differences among the four stream styles were larger in autumn than in spring; (5) The PSI of the surface sediments ranged between 24.49 and 69.94 (mg x L(-1) x (100 g x micromol)(-1). The PSI in spring was lower than that in spring, indicating that phosphorus release risk of surface sediment was higher in spring than in autumn. (6) PSI had a significant negative correlation with Ex-P, IP and pH.

[Soil Phosphorus Forms and Leaching Risk in a Typically Agricultural Catchment of Hefei Suburban].

To investigate the soil phosphorus forms and leaching risk in a typically agricultural catchment of Ershibu River in Hefei Suburban, Chaohu Lake basin, 132 surface soil samples were collected from the catchment area. The spatial distribution of total phosphorus (TP) and bio-available phosphorus (Bio-P), and the spatial variability of soil available phosphorus (Olsen-P) and easy desorption phosphorus (CaCl2-P) were analyzed using the Kriging technology of AreGIS after speciation analysis of soil phosphorus. Moreover, the enrichment level of soil phosphorus was studied, and the phosphorus leaching risk was evaluated through determining the leaching threshold value of soil phosphorus. The results showed that the samples with high contents of TP and Bio-P mainly located in the upstream of the left tributary and on the right side of local area where two tributaries converged. The enrichment rates of soil phosphorus forms were arranged as follows: Ca-P (15.01) > OP (4.16) > TP (3. 42) > IP (2.94) > Ex-P (2.76) > Fe/Al-P (2.43) > Olsen-P (2.34). The critical value of Olsen-P leaching was 18.388 mg x kg(-1), and the leaching samples with values higher than the threshold value accounted for 16.6% of total samples. Generally, the high-risk areas mainly occurred in the upstream of the left tributary, the middle of the right tributary and the local area of the downstream of the area where two tributaries converged.

[Study on chemical constituents from petroleum ether-soluble parts of cones of Platycladus orientalis].

OBJECTIVE: To study chemical constituents from petroleum ether-soluble parts of cones of Platycladus orientalis. METHODS: The compound were isolaeed by repeated column chromatography of silica gel and Sephadex LH-20. The structures were elucidated by physicochemical properties and spectrum analysis. RESULTS: Seven constituents were isolated and identified as sandaracopimaric acid (1), 6alpha-hydroxy sandaracopimaric acid (2), ent-isopimara-8 (14), 15-dien-3beta, 19-diol (3), ent-isopimara-8 (9), 15-dien-3beta-ol (4), ent-isopimara-8 (14),15- dien-3beta-ol (5), isocupressic acid (6) and 15-acetylisocupressic acid (7). CONCLUSION: Compounds 2 and 7 are isolated from this genus for the first time.