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991.
根据2011-2013年每年8月昌黎生态监控区大型底栖动物监测数据,以Simpson优势度为指标分析了研究区大型底栖动物的物种组成及群落结构年际变化。运用物种多样性指数(H')、均匀度指数(J)、丰富度指数(dMa)深入探究了监控区底栖动物的多样性变化趋势。研究结果显示:1)多毛类、甲壳类、软体类动物是该海域大型底栖动物的主要类群;2)2011-08监控区平均密度为43个/m2,平均生物量为3.14g/m2;2012-08监控区平均密度为41个/m2,平均生物量为3.21g/m2;2013-08监控区平均密度为28.74个/m2,平均生物量为7.72g/m2;3)2013年监控区19个站位多样性指标均值远高于前两年;4)2011-08监控区第一优势种为绒毛细足蟹其Y值为0.029 4;2012-08监控区第一优势种为裸盲蟹其Y值为0.007 3;2013-08监控区第一优势种为长吻沙蚕其Y值为0.007 0。 相似文献
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993.
We measured the concentrations of dimethylsulfide (DMS), acrylic acid (AA), and dimethylsulfoniopropionate (DMSP) during growth of three microalgae: Prorocentrum micans, Gephyrocapsa oceanica, and Platymonas subcordiformis. The DMSP, AA, and DMS concentrations in culture media varied significantly among algal growth stages, with the highest concentrations in the late stationary growth stage or the senescent stage. In the stationary growth stage, the average DMSP concentration per cell in P. micans (0.066 5 pmol/cell) was 1.3 times that in G. oceanica (0.049 5 pmol/ cell) and 20.2 times that in P. subcordiformis (0.003 29 pmol/cell). The average concentrations of AA were 0.044 6, 0.026 9, and 0.003 05 pmol/cell in P. micans, G. oceanica, and P. subcordiformis, respectively, higher than the concentrations of DMS (0.272, 0.497, and 0.086 2 fmol/cell, respectively). There were significant positive correlations between cell density and AA, DMSP, and DMS concentrations. The ratios of DMS/AA and AA/(DMSP+AA) in the three algae differed significantly over the growth cycle. In all three microalgae, the DMS/AA ratios were less than 25% during the growth period, suggesting that the enzymatic cleavage pathway, which generates DMS, was not the main DMSP degradation pathway. The changes in the DMS/AA ratio indicated that there was a higher rate of enzymatic breakdown of DMSP in the early growth period and a lower rate during senescence. In all three microalgae, the AA/(DMSP+AA) ratio (degradation ratio of DMSP) decreased during the exponential growth phase, and then increased. The variations in these ratios can approximately indicate the cleavage mechanism of DMSP at different stages of algal growth. 相似文献
994.
Change of Soil Organic Carbon after Cropland Afforestation in ′Beijing-Tianjin Sandstorm Source Control′ Program Area in China 总被引:2,自引:1,他引:1
ZENG Xinhua ;ZHANG Wanjun ;LIU Xiuping ;CAO Jiansheng ;SHEN Huitao ;ZHAO Xin ;ZHANG Nan-nan ;BAI Yuru ;Yi Mei 《中国地理科学(英文版)》2014,24(4):461-470
Land use change is one of the major factors that affect soil organic carbon(SOC) variation and global carbon balance. However, the effects of land use change on SOC are always variable. In this study, using a series of paired-field experiments, we estimated the effects of revegetation types and environmental conditions on SOC stock and vertical distribution after replacement of cropland with poplar(Populus tomentosa) and korshinsk peashrub(Caragana korshinskii) in three climate regions(Chifeng City, Fengning City and Datong City of the ′Beijing-Tianjin Sandstorm Source Control′(BTSSC) program area. The results show that SOC sequestration rate ranges from 0.15 Mg/(ha·yr) to 3.76 Mg/(ha·yr) in the soil layer of 0–100 cm in early stage after cropland afforestation in the BTSSC program area. The SOC accumulation rates are the highest in Fengning for both the two vegetation types. Compared to C. korshinskii, P. tomentosa has greater effects on SOC accumulation in the three climate regions, but significantly greater effect only appears in Datong. The SOC density increases by 20%–111% and 15%–59% for P. tomentosa and 9%–63% and 0–73% for C. korshinskii in the 0–20 cm and 20–100 cm soil layers, respectively. Our results indicate that cropland afforestation not only affects SOC stock in the topsoil, but also has some effects on subsoil carbon. However, the effect of cropland afforestation on SOC accumulation varied with climate regions and revegetation types. Considering the large area of revegetation and relatively high SOC accumulation rate, SOC sequestration in the BTSSC program should contribute significantly to decrease the CO2 concentration in the atmosphere. 相似文献
995.
周其仁 《国土资源导刊(湖南)》2014,(8):16-16
正大家说思想性、学术性、针对性、贴近性城市密度的最高处,未来收益的预期最高,大家抢着要来,竞争也会把地价推到最高。这些年房价成为社会第一关注议题。依个人之见,决定性的因素还是既聚人气又聚财气的空间位置严重供不应求。1988年的宪法修正案,开启城市土地市场化的合法通道。当时宪法文本的表述是"土地的使用权可以依法流转",并没有限定唯城市土地才可流转,只不过要依法流转。而1990年颁布的是"城镇国有土地使用权流转"的规定,农村集体土地可不可以流转 相似文献
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997.
采用商河县2010年耕地地力评价有机质采样点的数据,运用GIS和地统计学相结合的方法,研究了商河县土壤有机质的密度及储量,并按照土类统计分析了不同土壤类型间的有机碳密度及储量差异。研究表明,商河县土壤有机碳密度范围为1.69~5.17kg/m2,平均3.44kg/m2;有机碳储量为0.26×1010kg。按乡镇统计,有机碳密度最大值为玉皇庙镇3.65kg/m2,最小值为郑陆镇3.15kg/m2,有机碳储量最大值玉皇庙镇3.47×108 kg,最小值张坊乡0.92×108 kg;按土壤类型统计,有机碳密度最大的为湿潮土3.46kg/m2,最小为风沙土3.29kg/m2,有机碳储量最大为潮土10.38×108 kg,最小为褐土化潮土1.34×108 kg。 相似文献
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