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目的：探讨巴戟天提取物对实验性骨质疏松症大鼠的影响。方法：健康雄性SD大鼠60只,随机分为假手术组、模型对照组、阳性对照组及巴戟天提取物高、中、低剂量组,每组各10只。对除假手术组外的其余组大鼠通过手术摘除大鼠双侧卵巢建立骨质疏松症模型,造模后分别给予阳性药物碳酸钙D3颗粒0.5mg/kg,巴戟天提取物高、中、低剂量（0.36g/kg、0.18g/kg、0.09g/kg）干预,假手术组与模型对照组给予等体积蒸馏水,每天1次,共90d,剥离右侧股骨测量股骨中心骨密度与远心端骨密度;称量股骨重量,采用原子吸收分光光度法测定骨钙含量。结果：与假手术组比较,模型对照组大鼠骨密度、骨钙含量、血清雌二醇含量均显著降低,血清碱性磷酸酶含量显著升高,差异均有统计学意义（P＜0.01）;与模型对照组比较,巴戟天高剂量组大鼠骨密度及高、中剂量组大鼠骨钙含量、血清雌二醇含量均显著升高,碱性磷酸酶含量显著降低,差异均有统计学意义（P＜0.05或P＜0.01）。结论：巴戟天提取物能够有效阻止骨丢失,促进钙沉积,从而改善骨质疏松症,其作用机制可能与调节雌性激素水平有关。 相似文献
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目的：研究金花茶、银杏叶单用及配伍对高脂饲料诱导的高脂模型大鼠体质量、脂肪指数、血脂水平以及肝脏的影响。方法：将40只雄性SD大鼠随机分为5组,即空白组、模型组、金花茶组（给药剂量为0.053 g/kg）、银杏叶组（给药剂量为0.013 g/kg）、银杏叶+金花茶组（给药剂量为0.066 g/kg）,空白组予以普通饲料喂养,其余各组均予以高脂饲料喂养40 d。饲养10 d后开始药物干预,灌胃体积均为1.0 ml /100 g,空白组与模型组给予同体积纯化水,给药时间为30 d。考察不同时期大鼠体质量与血脂水平的变化,检测大鼠脂肪指数、肝脏脂肪变性情况。结果：灌胃给予受试样品30 d,金花茶、银杏叶、金花茶+银杏叶均能控制高脂模型大鼠的体质量与脂肪指数,降低血清三酰甘油（TG）、总胆固醇（TC）、低密度脂蛋白胆固醇（LDL-C）水平,提高高密度脂蛋白胆固醇（HDL-C）水平,还可不同程度地改善大鼠肝脏的脂肪变性,其中以银杏叶+金花茶组效果最佳。结论：金花茶与银杏叶单用及合用均有降脂和改善、预防脂肪肝的作用,且综合各项指标的检测结果,二者配合使用的降脂功效最优。 相似文献
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目的：明确千杯少颗粒解酒作用机制。方法:取SPF级SD大鼠,按体质量分层随机分为空白组、模型组、阳性对照组（予海王金樽药液干预,给药剂量为0.81 g/kg）及千杯少颗粒低、中、高剂量组（予千杯少颗粒药液干预,给药剂量分别为8.1 g/kg、16.2 g/kg、32.4 g/kg）。除空白组外,各组均灌胃56°二锅头（10 ml/kg）制备醉酒模型,30 min后,给予相应药物干预,模型组及空白组灌胃等容积蒸馏水。给药1 h后将实验动物麻醉,腹主动脉采血,分离血清,测定乙醇含量及丙氨酸氨基转移酶（ALT）、门冬氨酸氨基转移酶（AST）水平。取肝组织,匀浆后,测定乙醇脱氢酶（ADH）与乙醛脱氢酶（ALDH）的活性。结果：与模型组比较,千杯少颗粒各剂量组均能不同程度地降低大鼠血清中乙醇含量及ALT、AST含量,提高大鼠肝组织中ADH、ALDH的活性,差异均有统计学意义（P＜0.05或P＜0.01）。结论：千杯少颗粒解酒作用机制可能与其增强肝组织中ADH、ALDH的活性及保护肝脏有关。 相似文献
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目的：观察黑蒜生姜大枣苹果醋口服液（GZ）对气虚血瘀证模型大鼠及微循环障碍模型大鼠的影响,研究其行气活血功效。方法：1）实验一。SD雄性大鼠60只,随机分成6组,分别为空白对照组、模型对照组,GZ口服液低（8.33 ml/kg）、中（16.6 ml/kg）、高（24.9 ml/kg）剂量组,芪参胶囊阳性药对照组（0.30 g/kg）;通过控制饮食及强迫大鼠在凉水（15℃）中游泳3周制备气虚血瘀证模型,按剂量给药 30 d。末次给药1 h后,检测大鼠耳郭微循环血流量,全血及血浆黏度,血内皮素（ET）、6-酮-前列腺素（6-keto-PGF1a）、一氧化氮（NO）含量。2）实验二。大鼠分组、给药方式和剂量均同“实验一”,各组按剂量给药30 d,末次给药1h后,舌下静脉给药10%高分子右旋糖酐制备大鼠微循环障碍模型,观察大鼠肠系膜微动脉口径、微静脉口径、红细胞流速变化、血小板聚集功能、血液黏度、红细胞变形指数及大鼠胃、肠、肝微循环血流量的变化。结果：GZ口服液可降低气虚血瘀证模型大鼠全血及血浆黏度,增加舒张血管因子NO、6-keto-PGF1a的含量,减少缩血管因子ET的含量,增加耳郭微循环血流量;亦可增加微循环障碍模型大鼠肠系膜微动脉、微静脉口径,加快红细胞流速,增加胃、肠、肝微循环血流量。结论：GZ口服液具有改善气虚血瘀模型大鼠的气虚血瘀症状及微循环障碍模型大鼠的微循环,表明其具有行气活血的功效。 相似文献
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目的：探讨鼻敏宁颗粒对变应性鼻炎（AR）大鼠行为以及鼻黏膜组织形态的影响。方法：将60只大鼠随机分成6组,即空白对照组,模型组,辛芩颗粒对照组（阳性对照组）,鼻敏宁颗粒高、中、低剂量组（简称为高、中、低剂量组）,每组各10只。造模成功后于局部激发第5次当日开始干预,高、中、低剂量组分别灌服2 、1、0.5 g/kg的鼻敏宁颗粒,阳性对照组给予5 g/kg的辛芩颗粒,空白对照组与模型组灌服同等容积的0.9%氯化钠注射液,连续干预7 d。观察大鼠行为以及鼻黏膜组织病理学变化。结果：干预后高、中、低剂量组与阳性对照组均能降低大鼠的分泌量、喷嚏及搔鼻评分,与干预前比较,差异均有统计学意义（P＜0.05）;干预后高剂量组与低、中剂量组及阳性对照组比较,差异均有统计学意义（P＜0.05）。组织病理学结果显示,鼻敏宁颗粒各剂量组黏膜炎症浸润明显比模型组轻。结论：鼻敏宁颗粒可改善AR大鼠模型的过敏性行为,降低AR大鼠模型鼻黏膜的炎性反应。 相似文献
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目的：证实麻杏石甘汤对脂多糖（LPS）诱导的发热模型大鼠的解热作用,探究其解热机制及其对大鼠脑组织硫化氢（H22S）/胱硫醚-β-合成酶（CBS）体系的影响。方法：将50只无特定病原体（SPF）SD大鼠随机分为空白组、对照组（蒸馏水）、阿司匹林组（0.125 g/kg阿司匹林肠溶片）、麻杏石甘汤低剂量组（3.125 g/kg麻杏石甘汤)、麻杏石甘汤高剂量组（6.250 g/kg麻杏石甘汤）,每组各10只。连续灌胃5 d,末次灌胃1 h后,各给药组予以腹腔注射20 μg/kg LPS溶液诱导大鼠出现发热模型,空白组予以等剂量0.9%氯化钠注射液。记录造模后5 h内大鼠肛温的变化情况。末次体温测量后,腹腔注射3%戊巴比妥钠麻醉大鼠,经腹主动脉收集血液,通过酶联免疫法（ELISA）检测血清白细胞介素-1β（IL-1β）、肿瘤坏死因子-α（TNF-α）、细胞干扰素-α（IFN-α）的水平;取大鼠脑组织,运用实时荧光定量聚合酶链式反应（RT-qPCR）测定脑组织中胱硫醚-β-合成酶（CBS）、硫化氢（H22S） mRNA的表达。结果：与对照组比较,麻杏石甘汤低、高剂量组具有良好的解热效果,且麻杏石甘汤低、高剂量组均能抑制发热大鼠血清中IL-1β、TNF-α的表达,麻杏石甘汤高剂量组能抑制发热大鼠血清IFN-α的表达,差异均有统计学意义（P<0.05）。麻杏石甘汤低、高剂量组CBS、H22S mRNA的含量较对照组显著降低,差异有统计学意义（P<0.01）。结论：麻杏石甘汤具有良好的解热作用,其机制可能与减少血清中炎症因子的释放有关;同时麻杏石甘汤能降低发热模型大鼠脑组织中CBS、H22S mRNA的表达,并可能发挥了其对脑组织的保护作用。 相似文献
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目的：研究3种不同配伍的复方猴头菇提取物对胃黏膜损伤动物模型的作用,并以此为依据筛选最佳的复方猴头菇提取物配方。方法：分别观察3种不同配伍复方猴头菇提取物（复方猴头菇提取物A：猴头菇提取物1g、蒲公英提取物0.8g;复方猴头菇提取物B：猴头菇提取物1g、蒲公英提取物0.8g、三七提取物0.2g、陈皮提取物0.4g;复方猴头菇提取物C：猴头菇提取物1g、蒲公英提取物0.8g、三七提取物0.2g、陈皮提取物0.4g、党参提取物0.46g、山药提取物0.5g）对急性酒精性胃溃疡大鼠的影响及对甲巯咪唑所致慢性浅表性胃炎小鼠的影响。结果：与模型对照组比较,复方猴头菇提取物A、B、C均能显著降低急性酒精性胃溃疡大鼠模型的损伤积分指数及慢性浅表性胃炎小鼠模型的病理学评分,差异有统计学意义（P<0.05,P<0.01）,而复方猴头菇提取物C在降低急性酒精性胃溃疡大鼠模型的损伤积分指数及降低慢性浅表性胃炎小鼠模型的病理学评分方面优于复方猴头菇提取物A、B,差异有统计学意义（P<0.05）。结论：复方猴头菇提取物C是3种复方猴头菇提取物的最佳组方。 相似文献
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目的：观察清瘟败毒饮对脓毒症大鼠炎症反应和脏器损伤的影响。方法：将80只大鼠随机分为模型组、西药组及中药高、低剂量组,每组各20只。采用盲肠结扎穿刺术进行造模。西药组灌胃盐酸小檗碱0.27 mg/kg,中药高剂量组灌胃清瘟败毒饮4.6 g生药/kg,中药低剂量组灌胃清瘟败毒饮2.3 g生药/kg,模型组灌胃等量0.9%氯化钠注射液。1次/d,连续3 d。观察比较各组大鼠进食、活动、皮毛色泽等一般情况,血清肿瘤坏死因子-α（TNF-α）、白细胞介素-1β（IL-1β）、白细胞介素-6（IL-6）、白细胞介素-10（IL-10）、白细胞介素-17A（IL-17A）水平以及大鼠肺脏、肝脏组织病理情况。结果：模型组出现寒战、呼吸加快、活动度降低、皮毛倒立、精神萎靡等情况,中药高、低剂量组大鼠的一般情况优于模型组;与模型组比较,中药高、低剂量组和西药组均可降低血清TNF-α、IL-1β、IL-6、IL-17A水平（P<0.05）,但中药高、低剂量组与西药组比较,指标差异无统计学意义（P＞0.05）。中药高、低剂量组肺脏、肝脏组织病理损伤程度较模型组改善。结论：清瘟败毒饮可以抑制脓毒症模型大鼠炎症反应,减轻脏器损伤。 相似文献
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目的：探讨芒果苷对高脂肪/高果糖饮食诱导大鼠代谢综合征（MS）的影响。方法：将60只大鼠随机分为正常组,模型组,阳性对照组,芒果苷高、中、低剂量组,每组各10只。每天饲喂17%脂肪/17%果糖饲料+20%果糖水,构建MS模型,造模8周。造模成功后阳性对照组灌胃二甲双胍50mg/kg,芒果苷高、中、低剂量组分别灌胃40、20、10mg/kg,正常组和模型组灌胃等体积0.5%羧甲基纤维素钠,连续给药8周。观察各组的体质量、内脏脂肪质量、脂体比及血清总胆固醇、三酰甘油、空腹血糖、胰岛素水平、胰岛素抵抗指数（IRI）、脂肪细胞因子（脂联素、抵抗素）水平。结果：与模型组比较,芒果苷高、中、低剂量组的体质量、内脏脂肪质量、脂体比、血清总胆固醇、三酰甘油、空腹血糖、胰岛素及抵抗素水平下降（P<0.01）,芒果苷高、中剂量组IRI降低（P<0.05）。结论：芒果苷通过调控糖脂代谢、脂肪细胞因子、脂肪堆积、胰岛素抵抗等途径干预大鼠MS的病理进程。 相似文献
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Abstract Phosphorus and nitrogen were measured in stream run‐off from the four catchments of the Taita Experimental Basin (41° 11′ S, 174° 58′ E). The land is used as exotic conifer forest, native forest, and hill pasture. Multiple regression analysis was used to estimate chemical losses per unit area in floods and at low flows. At low flows, the hill pasture (fertilised with lime at 630 kg·ba?1·y?1, and superphosphate at 380 kg·ha?1·y?1) tended to lose more phosphorus and nitrate than the forested land, but differences were small, and not always significant. During large floods, the hill pasture (No. 5 Catchment) lost about 3 times as much reactive phosphate and 2–5 times as much total phosphorus as the forested land, and 130–190 times as much nitrate as land in the Exotic Forest and Native Forest 2 Catchments. Nitrate losses from land in the No. 4 Catchment (mainly native forest) were as high as those from the hill pasture, so high nitrate loss is not associated solely with agriculture. Losses of total phosphorus via the catchment streams were estimated as: No. 5 Catchment (hill pasture), 293 g·ha?1·y?1; Native Forest 2 Catchment, 201 g·ha?1·y?1; No. 4 Catchment, 124 g·ha?1·y?1; Exotic Forest Catchment, 71 g·ha?1.y?1. Nitrate‐N losses were estimated to have been 1356 g·ha?1·y?1, 11.5 g·ha?1·y?1, 1436 g·ha?1·y?1, and 44 g·ha?1·y?1 respectively. Phosphorus and nitrate concentrations were similar in the Exotic Forest and Native Forest 2 streams, but the Exotic Forest tended to lose smaller amounts because it yielded about 50% less water per unit area. Over the 2‐y study, an estimated 47–70% of phosphorus losses and up to 83% nitrate losses occurred in large floods; 31% and 48% respectively were apparently lost from the hill pasture catchment in a single flood. Less than 20% of estimated phosphorus losses and as little as 1% of nitrate losses occurred at low flows. Run‐off of phosphorus and nitrate was spasmodic, and this should be considered in assessing the impact of surface run‐off on the biology and chemistry of receiving waters. 相似文献
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以江苏文蛤(Meretrix meretrix)为研究对象,采集红壳色文蛤原种、黄壳色文蛤原种、红壳色文蛤选育F1、红壳色文蛤选育F2 4个群体,检测其主要非挥发性鲜味物质成分单磷酸腺苷(AMP)、单磷酸鸟苷(GMP)、次黄嘌呤核苷酸(IMP)、琥珀酸、游离氨基酸、无机离子(Na~+、K~+、Cl~–、PO_4~(3–))的含量,并通过味道强度值(TAV)评价其呈味作用。鉴于核苷酸与氨基酸在呈味方面的协同效应,采用味精当量(EUC)评价不同文蛤群体的鲜味品质。结果表明,文蛤软体组织中AMP、琥珀酸、谷氨酸、精氨酸、丙氨酸、Na+、K~+、Cl~–的TAV值大于1,是文蛤鲜味的主要贡献者;红壳色文蛤原种的鲜味强度最大(4.92 g/100g),其子代红壳色文蛤F1(4.08 g/100g)、红壳色文蛤F2(4.09 g/100g)稍有降低,但仍显著高于黄壳色文蛤原种(3.34 g/100g)(P0.05),表明江苏红壳色文蛤在鲜味品质方面具有相对稳定的较高品质。 相似文献
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Blue mussels (Mytilus edulis L.) taken from 27 stations along the estuary and gulf of St. Lawrence were analyzed for their content in 3,4-benzopyrene. Most of the concentrations are below the detection limit for the analytical method, i.e. 0·15 μg kg?1 (dry weight) and probably reflect the natural baseline level. However, mussels from two stations located at the mouth of Saguenay Fjord exhibit very high contents: 24 and 28·5μg kg?1 (dry weight). A mussel transplantation experiment has shown that the entire Fjord is contaminated by anthropogenic 3,4-benzopyrene. 相似文献
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《Deep Sea Research Part II: Topical Studies in Oceanography》1999,46(3-4):745-765
Plankton community net and gross production and dark respiration were determined from in vitro changes in dissolved inorganic carbon and dissolved oxygen during September 1994 along a southeast offshore transect in the Arabian Sea. Surface rates of gross production decreased from 17±0.7 mmol C m-3 d-1 at a coastal upwelling station to 3±0.8 mmol C m-3 d-1 at the most offshore station. The euphotic zone at the time of sampling was predominantly heterotrophic, with integrated net community production values ranging from 15±7 mmol C m-2 d-1 inshore to −253±32 mmol C m-2 d-1 offshore. Calculations of the respiration attributable to the major plankton groups could account for 61–87% of the dark community respiration measured at the inshore stations, but only 15–26% of the community respiration determined offshore. Comparison of the fluxes of dissolved inorganic carbon and oxygen revealed a tendency for higher respiratory quotients than those calculated for organic metabolism prevailing at the offshore stations. 相似文献
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Alessandra Pugnetti Anna Maria Bazzoni Alfred Beran Fabrizio Bernardi Aubry Elisa Camatti Mauro Celussi Joan Coppola Erica Crevatin Paola Del Negro Alessandro Paoli 《Marine Ecology》2008,29(3):367-374
The changes in the plankton biomass structure in relation to nutrient inputs were studied in the Gulf of Venice (Northern Adriatic Sea), an area characterized by a very marked trophic state variability. The investigation was carried out at two stations, in March, May and July 2005 and 2006, considering the whole water column. The size structure (from picoplankton to mesozooplankton) of both autotrophs and heterotrophs was analysed. Signals of diluted waters and nutrient inputs were more marked in 2005 than in 2006. In 2005, the total plankton biomass was almost double (87 ± 37 μg·C·l?1) that in 2006 (44 ± 26 μg·C·l?1). The variations were determined mainly by phytoplankton, with a 70% decrease, and a shift from a community dominated by microphytoplankton (49 ± 12%) in 2005 to one dominated by bacteria (43 ± 11%) in 2006 was observed. The relationship between the heterotrophic (H) and autotrophic (A) biomass indicated a rapid decline of the H/A ratio with increasing phytoplankton biomass. This study, although temporally limited, is consistent with the results reported for other marine environments and it seems to confirm the importance of nutrient inputs in structuring the biomass of plankton community. 相似文献
17.
Kevin G. Sellner 《Estuarine, Coastal and Shelf Science》1983,17(2):197-206
Phytoplankton productivity, community composition and biomass were determined over a nine-month period in brackish waters of the lower Gunpowder River, a tributary of Chesapeake Bay. Primary productivity followed expected seasonal magnitudes for temperate estuaries with rates exceeding 142·4 mg C m?3 h?1 in July through September 1979 and minimum rates of 1·6 mg C m?3 h?1 in February 1980. Annual primary production was estimated at 45·5 gC m?2. Cell numbers were highest in August, September and November with cyanophytes dominating the planktonic algae. Primary productivity, chlorophyll concentrations and cell densities were dominated by nanoplanktonic forms (< 10 μm) through-out the study. Phytoplankton carbon calculated from cells volumes exceeded nutritional requirements of the pelagic herbivores in all months suggesting a mean daily export (to the bay or sediments) of 1607 mg C m?3 d?1. 相似文献
18.
Trophic Potential and Photoecology of Endolithic Algae Living within Coral Skeletons 总被引：3，自引：0，他引：3
Abstract. The biomass of the endolithic algae Ostreobium quekettii Phyllosiphoniaceae living within skeletons of the scleractinans Mycedium elephantotus and Leptoseris fragilis averages 300 μg protein. cm-2. This represents approximately 7% of the protein of the zooxanthekie-containing tissue of M. elephantotus and approximately 38% of that of L. fragilis. Oxygen production Pmaxnet of 0. querkettii in bare skeletons of M. elephantotus averaged 0.7 μg O2.cm-2· h-1 measured in large skeletal fragments. This amount is approximately 6% of the productivity of the zooxanthellae Symbiodinium microadriaticum living in the same scleractinian species at the same depth Pmaxnet 11 μg O2· Cm-2· h-1. Light compensation of O. quekettii - within skeletons - was reached at approximately 10 and saturation at 35 40 μE·m-2· s-1. Algae within the M. elephantotus skeletons receive a maximum of 4–6% of the ambient irradiance, which is approximately 0.9 μE · m-2· s-1 approximately 0.04% surface irradiance at a depth of 88 m. In L. fragilis at a depth of 145 m, the photon flux decreases to 0.3 μE·m-2· s-1, which is less than 0.004% of surface intensity. With increasing depth, the ratio of Chl b to Chl a increased in endolithic algae colonizing L. fragilis, indicating improvement of light harvesting under low light conditions. In free-living O. quekettii cultured at irradiance levels from 0.5–60 μE·m-2· s-1, the concentrations of chlorophylls increased and that of siphonein and β-carotene decreased with decreasing photon flux. 相似文献
19.
Nitrogen uptake in light versus darkness of the seagrass Zostera noltei: integration with carbon metabolism 
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下载免费PDF全文 We conducted a study that shows that light and dark conditions do not affect the uptake rates of ammonium and nitrate by the seagrass Zostera noltei. This is an important advantage over some seaweed species in which these rates are severely reduced at night. In the light, the ammonium uptake rates were initially higher (15 and 20 μmol·g?1·h?1) and stabilized at a rate of 5 μmol·g?1·h?1 after 1 h, whereas in the dark the rates remained constant at a rate of 10 μmol·g?1·h?1 over the first 180 min of incubation. The rates of nitrate uptake in the light were high within the first 120 min of incubation (7.2–11.1 μmol·g?1·h?1) and decreased afterwards to lower values (0.8–3.9 μmol·g?1·h?1), whereas in the dark the rates fluctuated around 0.0–11.1 μmol·g?1·h?1 throughout the whole incubation time (7 h). The soluble sugar content of Z. noltei leaves increased significantly with both ammonium and nitrate incubations in the light, indicating the metabolic outcome of photosynthesis. In the dark, there was no significant variation in either the soluble sugar or in the starch content of leaves, rhizomes or roots in either the ammonium or nitrate incubations. However, the total starch content of plants decreased at night whereas the total soluble sugars increased, suggesting a process of starch catabolism to generate energy with the consequent production of smaller monosaccharide products. The starch content of rhizomes decreased significantly during the light incubations with nitrate but not with ammonium. These results suggest that carbohydrate mobilization is necessary for Z. noltei to account for extra energetic costs needed for the uptake and assimilation of nitrate. Furthermore, our results suggest that nitrate uptake, at least during the day, requires the mobilization of starch whereas the uptake of ammonium does not. 相似文献
20.
《African Journal of Marine Science》2013,35(1):791-808
By simulating an upwelling event in a laboratory microcosm, it was possible to promote the development of a natural and diverse planktonic community. An initial bacterioplankton community which developed in response to phytoplankton growth was dominated by small coccoid forms (0,14–0,2 μm3) of the genera Vibrio and Pseudomonas. This group was heavily exploited by the heterotrophic microflagellate Pseudobodo sp. (30 μm3). Later, the bacterioplankton community was dominated by large rods (0,7 μm3) which the flagellates seemed unable to exploit. A Lotka-Volterra predator-prey model fitted to the observed data indicated that the flagellates consumed 2,4 times their carbon body mass per day or 19 bacteria·flagellate?1·h?1 when prey were not limiting. Clearance rates were inversely proportional to prey density and ingestion rate, ranging from 2 × 10?3 to 20 × 10?3) μ?·flagellate?1·h?1. At typical field densities of bacteria and heterotrophic flagellates in the southern Benguela region, between 5 and 30 percent of the water column could be cleared per day. Specific growth rates of the flagellates were positively related to prey density, the maximal rate being 0,84 · d?1. Their initially faster growth rates allowed bacteria to increase in numbers despite predation. The growth yield of the flagellates (34–36 per cent) was also positively related to food density. Such low values suggest inefficient transfer of carbon to higher trophic orders but considerable nitrogen regeneration. Nitrogen excretion rates were approximately 6–7 μg N·mg dry weight?1·h?1, comparable to other flagellates but faster than ciliates. These rates are comparable with in situ measurements of NH+4-N excretion in pycnoclinal regions based on 15N isotope studies but are only about 20 per cent of measured rates in surface waters. This is interpreted to mean that, in pycnoclinal regions where the relative input of "new" nitrogen is high, there are few regenerative steps and the model describes them satisfactorily. In surface waters, observed rates of excretion can only be accounted for by many regenerative steps in a highly complex food chain in which the cumulative total of nitrogen excretion at each step amounts to that based on 15N labelling studies. 相似文献