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Qiao C.-K.,University of Sichuan | Liu X.-N.,University of Sichuan | Chen X.-W.,Fujian Normal University | Chen X.-W.,State Key Laboratory Breeding Base of Humid Subtropical Mountain Ecology | Cheng N.-S.,Nanyang Technological University
Sichuan Daxue Xuebao (Gongcheng Kexue Ban)/Journal of Sichuan University (Engineering Science Edition) | Year: 2013

Flow resistance in gravel-bed rivers is usually investigated by considering variation in relative roughness height, while relevant friction law for the porous permeable layers is not well understood. By applying Ergun equation, the friction law of seepage through packed beds composed of glass beads was investigated. Different flow regimes were observed with varying head loss measured. The results showed that the friction factor decreases with increasing Reynolds number and the data collected for different cases collapse almost into a single curve when the wall effects are considered. Finally an improved Ergun correlation was proposed to evaluate the flow resistance of packed permeable beds with small bed-to-particle ratios. Source


Chen X.,Fujian Normal University | Chen X.,State Key Laboratory Breeding Base of Humid Subtropical Mountain Ecology | Lin M.,Fujian Normal University | Cheng N.,Nanyang Technological University | Lin B.,Fujian Normal University
Shuikexue Jinzhan/Advances in Water Science | Year: 2013

The time-mean velocity profile of turbulent open-channel flows over rough and permeable beds is analyzed both experimentally and theoretically in this study. The velocity profile can be derived from a slip velocity at the bed surface and an origin displacement, a modified logarithmic law is thus obtained. The experiment is conducted in a glass-sided flume where the channel bed is prepared with uniform marbles 1 cm in diameter. The velocity is measured using a laser doppler velocimeter. The profile of the measured velocity is used to validate the theoretically derived profile. The result shows that the modified logarithmic law is able to well describe the measured velocity profile. Under the same flow condition, the shear velocity over the permeable bed would be greater than that over the impermeable bed. The value of the flow at the permeable interface is about 0.35 to 0.45 times that of the average stream flow. Source


Bingqiao G.,Fujian Normal University | Quanlin Z.,Fujian Normal University | Quanlin Z.,State Key Laboratory Breeding Base of Humid Subtropical Mountain Ecology | Yuzhu M.,Fujian Normal University | And 6 more authors.
Chinese Journal of Applied and Environmental Biology | Year: 2016

Forest ecosystems play an important role in global carbon cycle. Accurate understanding of below- and above-ground biomass allocation pattern (i.e. the root-shoot ratio, R/S) and its influencing factors would help to better characterize the regional and global carbon sink, stock and cycle of forest ecosystems. The purpose of this paper was to investigate the effects of climatic and stand factors on the root-shoot ratio of China's natural forests at a large scale. We classified all data of 1109 sample plots into 17 types of forest and calculated the R/S [root biomass / (stem + branch + leaf biomass)] of the forest communities. Because precipitation could not completely reflect the forest water conditions, the ratio of mean annual precipitation to potential evaporation was used to evaluate the impact of water availability on the R/S. Finally, latitude, longitude, temperature, water availability, stand density and stand age were selected to analyze their effects on the R/S using multiple linear regression. Our results showed the mean value of R/S in China's natural forests as 0.26. The R/S of deciduous forests was significantly higher than that of evergreen forests, and the R/S of broadleaved forests was higher than that of conifer forests. Furthermore, R/S of China's natural forests was significantly and negatively correlated with the stand age and water availability. The major influencing factors for the R/S of China's nature forests were latitude and stand density. The results suggested that we should include in consideration temperature and stand density in calculation of forest carbon stock and forest biomass allocation. Source


Chang Y.,Fujian Normal University | Zhong Q.,Fujian Normal University | Zhong Q.,State Key Laboratory Breeding Base of Humid Subtropical Mountain Ecology | Cheng D.,Fujian Normal University | And 4 more authors.
Journal of Plant Resources and Environment | Year: 2013

Taking twenty-six main dominant species in arbor, shrub and herb layers of Castanopsis carlesii (Hemsl.) Hayata natural forest in Youxi of Fujian Province as research objects, variation and correlation of C, N and P contents and their ratios in different organs of plants were analyzed, and distribution characteristics of their contents in different organs among different layers were also studied. The results show that in the same organ, C average content is the highest while P average content is the lowest. In which, contents of C, N and P in leaf are 344. 95-486. 15, 6. 26-19. 50 and 0. 18-0. 62 mg·g-1, and ratios of C/ N, C/ P and N/ P are 22. 52-61. 21, 696. 64-2 589. 72 and 11. 38-58. 94, respectively; contents of C, N and P in root are 277. 95-458. 30, 1. 41-12. 73 and 0. 13-0. 44 mg·g-1, and ratios of C/ N, C/ P and N/ P are 34. 63-296. 17, 731. 45-3 372. 69 and 8. 81-34. 41, respectively; contents of C, N and P in branch of plants in arbor and shrub layers are 407. 75-473. 75, 3. 10-7. 39 and 0. 09-0. 61 mg·g-1, and ratios of C/ N, C/ P and N/ P are 57. 43-148. 15, 776. 64-5 054. 44 and 7. 05-48. 11, respectively; and contents of C, N and P in trunk of plants in arbor layer are 432. 56-463. 32, 2. 67-6. 35 and 0. 16-0. 31 mg·g-1, and ratios of C/ N, C/ P and N/ P are 68. 12-167. 73, 1 494. 58-2 860. 63 and 11. 35-29. 06, respectively. In different organs of arbor layer plants, the order of C content from high to low is leaf, branch, trunk, root, while that of N and P contents is leaf, branch, root, trunk. In shrub layer plants, C content is the highest in branch and the lowest in root, while N and P contents are the highest in leaf and the lowest in branch. In herb layer plants, contents of C, N and P in above-ground part are higher than those in under-ground part. Except having extremely significantly positive correlation between contents of N and P in root, correlations among contents of C, N and P in the same organ are unsignificant, but most correlations between their contents and ratios of C/ N, C/ P and N/ P are extremely significant. Contents of C, N and P in different organs are varied with different layers of plants, in which, those in leaf of plant in arbor layer are the highest, while those in herb layer are the lowest. And C content is the highest and N content is the lowest in whole plant of arbor layer, and N content is the highest and C content is the lowest in whole plant of herb layer, while P content in whole plant of different layers is close. It is suggested that contents of C, N and P in leaf of plants of C. carlesii natural forest in Youxi are lower and P deficiency is likely to the most important element for limiting productivity of this forest. Source


Zhang L.-L.,Fujian Normal University | Zhang L.-L.,State Key Laboratory Breeding Base of Humid Subtropical Mountain Ecology | Zhong Q.-L.,Fujian Normal University | Zhong Q.-L.,State Key Laboratory Breeding Base of Humid Subtropical Mountain Ecology | And 10 more authors.
Chinese Journal of Applied Ecology | Year: 2015

To explore the effects of stand age on variation patterns of leaf C, N, P stoichiometric characteristics of Machilus pauhoi, two stands, i.e., 9 and 13 years old, were selected. The relationships between leaf nutrient contents (C, N and P) and diameters at breast height (DBH) of individual plants were analyzed. The data revealed that the individual variations of seedlings in M. pauhoi stands were strengthened with the stand development. The stand age had significant effects on leaf C, N, P contents and C:N ratio but not on C:P and N:P ratios. Specifically, the mean values of leaf C, N, P contents and N:P ratio in the 9-year-old stand were lower than those in the 13-year-old stand, whereas, inverse pattern of C:N and C:P ratios were found in the two stands. Furthermore, leaf N and P stoichiometry varied significantly within the stand. Specifically, leaf N and P contents, as well as their stoichiometric ratios, linearly correlated with DBH in the 9-year-old stand. On the contrary, leaf N and P stoichiometry showed quadratic correlation in 13-year-old stand (except leaf C:N which linearly correlated with DBH). Lastly, nutrient transfer rates of leaf N and P in the 9-year-old stand were higher than that in 13-year-old stand, and the discrepancies of leaf nutrient transfer strategy between growing and non-growing seasons were caused by the different growth phases and environmental conditions. ©, 2015, Editorial Board of Chinese Journal of Applied Ecology. All right reserved. Source

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