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361.
2015年3~10月,在崇明岛东滩湿地设置7块采样地,以不同水盐条件下生长的芦苇(Phragmites australis)为材料,应用便携式光合系统分析仪(Li-6400),对芦苇的光响应特征进行实地测定,探讨芦苇光合过程对干旱和盐胁迫的响应机理。结果表明:1各月采样日的水位与土壤电导率显著负相关(n=420,p0.01),适当增加土壤水位,有利于降低土壤电导率,从而缓解植物盐胁迫伤害;28月21日的芦苇叶片净光合速率、蒸腾速率和气孔导度与水位显著正相关(n=42,p0.01),而与土壤电导率显著负相关(n=42,p0.01);胞间CO2浓度与水位和土壤电导率不相关。当水位高于-50 cm,净光合速率随着水位下降而降低,非气孔因素可能是净光合速率下降的主要原因;当水位低于-50 cm时,土壤电导率高于10 m S/cm,叶片蒸腾速率快速降低,水分利用效率不断提高,芦苇叶片以较低的净光合速率来适应干旱胁迫和盐胁迫;芦苇叶片通过降低最大净光合速率、暗呼吸速率、光补偿点和光饱和点等光合生理特征来适应干旱胁迫和盐胁迫;芦苇叶片净光合速率和最大净光合速率对土壤水盐因子具有高度相关性,可以作为土壤水盐胁迫程度的反应指标。因此,在芦苇快速生长阶段,合理调控水位,对芦苇光合作用具有重要意义。 相似文献
362.
In this study, a coniferous tree species (Pinus tabuliformis Carr.) was investigated at a moderate-altitude mountainous terrain on the southern slope of the middle Qinling Mountains (QLM) to detect the trends in carbon isotope ratio (δ13C), leaf nitrogen content (LNC) and stomatal density (SD) with altitude variation in north-subtropical humid mountain climate zone of China. The results showed that LNC and SD both significantly increased linearly along the altitudinal gradient ranging from 1000 to 2200 m, whereas leaf δ13C exhibited a significantly negative correlation with the altitude. Such a correlation pattern differs obviously from that obtained in offshore low-altitude humid environment or inland high-altitude semi-arid environment, suggesting that the pattern of increasing δ13C with the altitude cannot be generalized. The negative correlation between δ13C and altitude might be attributed mainly to the strengthening of carbon isotope fractionation in plants caused by increasing precipitation with altitude. Furthermore, there was a remarkable negative correlation between leaf δ13C and LNC. One possible reason was that increasing precipitation that operates to increase isotopic discrimination with altitude overtook the LNC in determining the sign of leaf δ13C. The significant negative correlation between leaf δ13C and SD over altitudes was also found in the present study, indicating that increases in SD with altitude would reduce, rather than enhance plant δ13C values. 相似文献
363.
Currently, there is limited literature dealing with the length of stay of circular migrants in urban areas (LSCMU), although many studies have discussed the phenomenon of migration and the determinants of migration. This study attempts to fill that gap using survey data from the mountainous areas of Chongqing, Southwest China. From a comparative perspective, this study divided workers into two groups (a young group aged between 16 and 35 years and an old group aged between 36 and 65 years). The average LSCMU values for the young and old groups were 225 days and 174 days, respectively. Two multi-regression models were used to estimate the determinants of LSCMU in the two groups. The results showed that LSCMU was closely related to individual factors in both groups, including gender, age and job training. Family and community factors, including household size, arable land per capita and the distance from market, had much weaker effects on the dependent variable, especially in the older group. It was noticeable that job training had significant positive effects on LSCMU in both groups; these findings have special implications for the urbanization process in China. 相似文献
364.
Micro-communities are supposed to have more potential functions of biodegradation of polysaccharides than single strain; however, the intestinal micro-communities involved in the biodegradation of Enteromorpha polysaccharides (EP) were seldom reported. In order to obtain the EP-degrading micro-community, the intestines of Siganus oramin was obtained to isolate the micro-communities, which were enriched by 0.3% of EP as the sole carbon source. A stable micro-community with EP degradative capability was achieved after seven generations of subculture, named H1. Results showed that H1 was able to degrade 75% of EP within 24 hours, and the activity of EP lyases reached 500 U mL?1 in 32 hours. With denaturing gradient gel electrophoresis (DGGE) and 16S rRNA gene clone library analysis, ten bacteria closely related to Marinomonas pontica, Microbacterium sp., Leucobacter chironomi, Cyclobacterium sp., Algoriphagus winogradskyi, Pseudoalteromonas sp. and Vibrio sp. were determined. Furthermore, compared with the DGGE bands sequence and the clone library analysis, the dominant bacteria of the EP-biodegrading micro- community were Pseudoalteromonas sp. and Vibrio sp., with the respective proportion of 38% and 46%, and they should play an important role in EP degradation together with other degrading bacteria in the micro-community H1. 相似文献
365.
Zhongming Huo Xiaotong Li Qian Sun Yongren Li Xuekai Zhang Xiwu Yan Feng Yang 《中国海洋大学学报(英文版)》2016,15(6):1046-1050
In this study, the method of divergent selection was employed to test the larval and juvenile growth performance within a full-sib family of Manila clam Ruditapes philippinarum. The 10% largest and 10% smallest clam individuals (on the basis of shell length) of a full-sib family were selected as parents for the fast and slow growing lines, respectively. The difference in shell length was significant among the three lines (fast, control, and slow) tested. The sequence of shell length were fast line > control line > slow line. The responses to selection, realized heritability, and genetic gain were 0.06%–0.81%, 0.04%–0.47% and 0.58%–18.89% in the fast direction, respectively; and were 0.14%–1.27%, 0.08%–0.73%, and 0.31%–49.03% in the slow direction, respectively. The results suggested that there was a large portion of additive genetic variance affecting the growth in the full-sib family. Selection in the fast direction within the full-sib family would greatly improve the growth of R. philippinarum. 相似文献
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368.
库车坳陷的构造变形及演化与南天山造山带的发育密切相关。库车坳陷新近纪以来的喜马拉雅晚期构造运动最为强烈,形成了天山山前大型冲断带,并造就了现今的构造格局。通过对库车坳陷北部构造样式的识别及各种应力场指示标志的测量、统计和构造解析,对野外获得的应力场指示标志划分了期次,认为喜马拉雅晚期应力场标志为近南北向挤压。结合库车坳陷区域构造要素,如地质体几何形态、边界条件、岩石力学参数等,运用弹性力学有限元数值模拟的方法获得了喜马拉雅晚期库车坳陷的区域应力场。模拟结果表明,库车坳陷喜马拉雅晚期最大主压应力方向为近南北向,与古应力场标志拟合较高,可以为库车坳陷裂缝预测和评价提供依据,对勘探开发有应用价值。 相似文献
369.
J. Bai Z. Shen T. Yan 《International Journal of Environmental Science and Technology》2016,13(7):1723-1730
Pathogenic bacteria are a serious public health concern. Exposure to these microorganisms can result in illnesses or even death. Therefore, it is important to control pathogenic bacteria sources, transport mechanisms and fate. Best management practices proved to be very effective in the control of non-point source pollution. In this study, the soil and water assessment tool (SWAT) was modified and used to simulate the fecal coliform in Chao River of Miyun Reservoir watershed, China. The model was then used to explore the effectiveness of vegetative filter strips (VFS) in reducing fecal coliform abundance throughout the watershed. The water temperature equation within the SWAT was modified to align the model more closely with the characteristics of the study area and generate a more accurate simulation. The DAFSratio (20, 50, 80, 120 and 150) and DFcon (0.25, 0.4, 0.6 and 0.75) parameters were considered for VFS to see their effects on removal efficiency. The results show that calibration and validation results for fecal coliform and flow can be accepted. Different values for DAFSratio and DFcon have great influence on VFS. Increasing values resulted in a decrease in the removal efficiency of VFS. 相似文献
370.