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1.
海水Ca2+浓度是计算碳酸钙饱和度的重要参数之一,通常由海水钙盐比值计算得出,但该方法在受多种因素影响的近海海域可能不适用。本研究开展了EGTA自动电位滴定法对不同盐度海水Ca2+浓度测定精度和准确度的研究,探究“盐效应”对Ca2+浓度测定可能存在的影响,并比较了近海养殖区海水实测Ca2+浓度与通过钙盐比估算值的差异。研究表明：①EGTA自动电位滴定法测定不同盐度海水Ca2+浓度精度较高,在各个盐度条件下,5次平行测定的标准偏差为0.001~0.006 mmol/kg,精度均优于0.1%;②在盐度20.00~34.62范围内,Ca2+的实测值与通过钙盐比值计算所得的相对误差为-0.043%~0.023%,准确度在± 0.05%内;③不同盐度海水样品Ca2+浓度的实测值与理论值基本吻合,电位滴定法测定Ca2+浓度不存在“盐效应”问题;④受陆源输入过程的影响,近海（烟台牟平养殖区）表层及底层海水Ca2+的实测值比按钙盐比值的计算值分别高出0.360 mmol/kg和0.333 mmol/kg,表明利用钙盐比值估算法不适用于近海海水中Ca2+浓度,通过实测Ca2+浓度计算近海海水碳酸钙饱和度可以更准确评估近海酸化的程度。  相似文献   

2.
南极大磷虾（Euphausia superba）为南大洋生态系统中的关键种，也是南极生态系统食物网中的重要枢纽。该种秋冬季转换期的营养信息对于理解其知之甚少的越冬机制非常重要。但关于此方面的少数研究在时空变化上仍存在着差异。为此，我们调查了南极半岛秋季（4-5月）和冬季（6月）磷虾成体δ13C和δ15N值的个体、月份及区域性差异。我们的目标旨在检验该期间磷虾的营养变化以及磷虾与其在南极海洋生态系统中的摄食环境之间的关系。结果如下：（1）磷虾δ13C值与体长之间无显著关系，但δ15N值与体长之间则存在显著相关性；（2）秋季磷虾δ13C值呈现增长趋势，但冬初季节并无显著变化，此期间δ15N值无显著不同；（3）布兰斯菲尔德与南设得兰群岛之间的δ15N平均值显著不同。我们的数据表明南极半岛秋至初冬转换期间磷虾成体营养呈现个体、季节性及区域性变化。  相似文献   

3.
在实验室内选用不进行营养盐加富的流水系统模拟研究了浒苔（Ulva prolifera）对海水营养盐的吸收，测定了浒苔体内不同形态的碳、氮、磷的含量变化，探讨了浒苔对海水中碳、氮、磷3种生源要素的转化作用。结果显示，流动海水的实验体系是一个能给藻体创造稳定环境的模拟装置，可以不断地给藻体更新海水和补充营养盐。浒苔对海水中溶解无机氮（DIN）、溶解有机氮（DON）、溶解无机磷（DIP）和溶解有机磷（DOP）都有吸收作用，其平均吸收速率分别为10.87 μmol·g-1·d-1、2.41 μmol·g-1·d-1、0.183 μmol·g-1·d-1和0.023 μmol·g-1·d-1。光照时段的DTN和DTP的平均吸收速率与无光照时段的平均吸收速率没有显著差异（P>0.05）。浒苔对海水中无机形态的营养盐的吸收量高于对该元素的有机形态的吸收量；而浒苔的体内有机形态的成分均远高于无机形态的成分。浒苔对无机形态的氮、磷和碳转化为自身有机形态的转化效率分别为：97.33%，99.99%和96.84%。以上结果表明，浒苔能快速吸收无机形态的生源要素并转化为有机形态，能够加快生源物质进入生态系统的物质循环。  相似文献   

4.
本研究利用三价钛还原法将标准样品、海水、湖水和雨水中硝酸根转化为N2O测试其氮氧同位素值,并优化实验条件（NO-3浓度、试剂量、反应时间和温度等）。结果表明：4 cm3硝酸根水样（浓度约为20 μmol/dm3）,加入100 mm3TiCl3溶液（浓度为150 g/dm3）,25 ℃反应24 h,NO-3还原为N2O的平均转化率为86.3%（n=5）。5种丰度硝酸根氮氧同位素标样校准曲线斜率分别为0.947和0.617,相关系数R2分别为0.999和0.994;方法检出限的NO-3浓度为2.5 μmol/dm3,其δ15N的标准偏差小于0.7‰(n=5),δ18OVSMOW值的标准偏差小于2.5‰(n=5);20 μmol/dm3硝酸根样品δ15N的标准偏差小于0.5‰（n=5),δ18OVSMOW值的标准偏差小于1.0‰（n=5）。该方法测定3种不同类型水样δ15N的标准偏差分别为0.3‰、0.6‰和0.5‰;δ18OVSMOW的标准偏差分别为2.1‰、2.0‰和1.6‰。三价钛还原法分析水体中硝酸根氮氧同位素操作步骤简单,测试效率高,但氧同位素结果需要系统校正。  相似文献   

5.
大型海藻组织碳、氮含量及δ15N值的变化对于指示营养盐来源及营养盐评价研究具有重要的意义。为探究大型海藻组织碳、氮含量及δ15N值的变化特征,于2020年7月至2021年6月逐月分析了小长山岛潮间带孔石莼（Ulva pertusa）、角叉菜（Chondrus ocellatus）、鼠尾藻（Sargassum thunbergii）3种大型海藻组织的碳、氮含量和δ15N值的变化,并对其生长环境中海水的理化因子进行了测定。结果发现：孔石莼组织的氮含量与海水中的NO3-N和DIN含量之间存在显著的相关性,角叉菜组织的氮含量与海水中的NH3-N含量之间也存在显著的相关性。然而,大型海藻组织的碳含量和C/N比值与海水中的碳、氮营养盐之间并无显著的相关性。孔石莼组织的δ15N值与海水中的NO3-N和DIN含量之间也存在显著的相关性。因此,孔石莼适于用作NO3-N和DIN来源的指示藻种。结果指示小长山岛潮间带海水中具有供大型海藻生长利用的充足的营养盐,其主要受到生活污水和养殖排放的影响。  相似文献   

6.
为明确哈维氏弧菌感染下,泥蚶（Tegillarca granosa）不同组织弧菌载量的变化规律,通过哈维氏弧菌浸泡感染泥蚶的方法,建立弧菌浓度计数标准曲线,记录攻毒水体和泥蚶组织中的哈维氏弧菌含量的动态变化及相关关系。结果显示,弧菌感染浓度为1×107CFU/mL,泥蚶血液中弧菌载量显著高于鳃、闭壳肌、外套膜和肝胰腺,各组织中的弧菌载量呈现先上升,后下降,最后维持较低水平的变化规律。持续感染6 d,泥蚶血液中弧菌载量降至102-104 CFU/mL,其他组织中弧菌载量降至100-102 CFU/mg。检测不同浓度弧菌（1×105,1×106,1×107,5×107 CFU/mL）浸泡感染后泥蚶肝胰腺的弧菌载量变化,结果显示,1 d时各感染组肝胰腺弧菌载量均较对照组显著增加（81.0-667.8倍）,且与浸泡水体中弧菌浓度呈显著正相关（Spearman''s ρ=0.762,P<0.001）,5 d时各侵染组肝胰腺弧菌载量均较1 d明显降低,但仍然高于对照组。研究结果为泥蚶感染弧菌发病过程中,免疫识别及免疫响应机制的研究提供了参考。  相似文献   

7.
2012年南海西北陆架冬季水文特征的观测分析   总被引：1，自引：0，他引：1  
本文基于2012年12月南海西北部陆架海区的温盐和流速实测资料，分析了粤西和琼东陆架海区冬季三维温、盐结构和流场特征，给出沿陆架和跨陆架方向的水体和热盐通量。结果表明：（1）在50m以浅，粤西和琼东海区温度均由近岸向外海递增，深层则相反；冬季近岸海区混合层较深，外海密度跃层位于60—120m深度且层结较强，浮力频率大于10–2/s；（2）海流大致沿等深线向西南流动，30m以深流速大小在0.03—0.40m/s之间，且随着深度增加而略有减小；琼东海区100m等深线附近在60m以浅水层观测到水体辐聚并有明显温度锋面存在；（3）沿陆架方向的水体和热盐输送均大于跨陆架方向，其中粤西单位面积沿/跨陆架水体通量平均值为0.13×10–6/0.03×10–6Sv/m2，低于琼东海区的0.91×10–6/0.56×10–6Sv/m2。  相似文献   

8.
本文报道2015年9月和2016年5月期间天然放射性核素224Ra和223Ra在吕宋海峡及周边海域表层和垂向水体的分布特征。为理解日本福岛核事故的影响，本文亦分析研究区域内人工放射性核素137Cs的分布特征。结果表明，224，223Ra和137Cs比活度水平均处于我国南海海洋天然放射性本底变化范围之内。224Ra在吕宋海峡以西南海北部海域比活度较高，在吕宋海峡以东菲律宾海域比活度较低。137Cs没有明显的分布趋势。基于三站位（LS3，LS5和LS8）224Ra、137Cs以及温盐的垂向分布特征，本文揭示224Ra和137Cs在热带表层水、次表层水和中-深层水中比活度水平和梯度变化的差异特征。彩虹台风事件扭转了整个吕宋海峡及周边海域的海流循环过程。大量以低水平224Ra为特征的西太平洋海水涌入南海，降低水体224Ra比活度水平。但是，西太平洋和南海北部海域水体137Cs比活度水平没有明显差异，台风导致的海流变化对水体137Cs比活度没有明显影响。  相似文献   

9.
透明胞外聚合颗粒物（Transparent exopolymer particles，TEPs）在海洋中分布广泛，其沉降被认为是海洋中生物碳沉降的途径之一。本研究于2011年春季和夏季调查了长江口邻近海域TEPs的浓度和沉降速率，并且估算了其碳沉降通量。研究发现，TEPs浓度春季介于40.00~1040.00 μg Xeq L-1，平均值为209.70±240.93 μg Xeq L-1；夏季介于56.67~1423.33 μg Xeq L-1，平均值为433.33±393.02 μg Xeq L-1。两个季节，TEPs在水华站位的浓度明显高于非水华站位。相关性分析表明，TEPs与水体叶绿素a浓度呈显著正相关性，表明在调查区浮游植物是TEPs的主要生产者。TEPs沉降速率在春季介于0.08~0.57 m d-1，平均值为0.28±0.14 m d-1；夏季介于0.10~1.08 m d-1，平均值为0.34±0.31 m d-1。经估算，TEPs碳沉降通量春季介于4.95~29.40 mg C m-2 d-1，平均值为14.66±8.83 mg C m-2 d-1；夏季介于6.80~30.45 mg C m-2 d-1，平均值为15.71±8.73 mg C m-2 d-1。TEPs的碳沉降通量可以占到浮游植物碳沉降通量的17.81%~138.27%。水华站位TEPs的碳沉降通量明显高于非水华站位，这是由于水华站位较高的TEPs浓度及沉降速率所致。本研究表明，TEPs的沉降在长江口邻近海域是碳沉降的有效途径，在相应的碳沉降相关研究中应该被考虑进来。  相似文献   

10.
南极磷虾是南大洋生态系统的关键物种, 种群聚集在南大洋的大西洋扇区。海冰在南极磷虾生活史中起着重要作用, 海冰及其冰下环境为磷虾越冬提供了避难场所, 但海冰是否为磷虾越冬提供了重要的饵料存在一定的争议, 对此问题的解决需要量化源于海冰的冰藻对南极磷虾越冬期间饵料及碳源的贡献。基于2020年冬季(3~8月)于南大洋大西洋扇区48.1亚区(布兰斯菲尔德海峡周边区域)和48.3亚区(南乔治亚岛周边海域)采集的磷虾样品, 通过两种高支链类异戊二烯化合物(IPSO25和HBI III)分别作为源于海冰的冰藻和源于水体浮游植物的生物标志物, 对两个区域冬季磷虾对冰藻和浮游植物的依赖进行研究。结果显示, 处于较高纬度、海冰密集度较高的48.1亚区的南极磷虾体内含有更高的IPSO25, 而处于开阔水域48.3亚区的磷虾体内有更高比例的HBI III, 另外48.3亚区磷虾的δ13C和δ15N稳定同位素显著高于48.1亚区的磷虾。48.1亚区南极磷虾越冬期间对浮游植物和冰藻的依赖与体长相关, 其中体长相对较短的早期成体呈现更高的依赖性, 同时该区域磷虾对冰藻的摄食提高了其营养级地位。48.3区南极磷虾越冬期间两种类异戊二烯含量与δ15N稳定同位素数值呈负相关关系, 表明该区域南极磷虾在初级生产匮乏时会摄食动物性饵料。若未来南大洋大西洋扇区海冰持续减少, 这将对整个磷虾种群、磷虾渔业的可持续发展和区域生态系统的稳定性产生威胁。  相似文献   

11.
Uptake rates of ammonium, nitrate, urea and nitrite were measured for 1 year (1988) at a coastal station in the well-mixed waters of the western English Channel. Ammonium was the major form of nitrogen (N) utilized (48%) by phytoplankton, followed by nitrate (32%), urea (13%) and nitrite (7%). Seasonal changes of uptake of ammonium, nitrate and urea showed a broad, intense summer maximum. Nitrite uptake was low throughout the year except for a peak value in June. Uptake rates of ammonium and nitrate were independent of substrate concentrations, whereas those of urea and nitrite were not. The summer maxima of ammonium, nitrate and total N uptake, and the significant relationships of N-uptake index to ambient light, and of chlorophyll-a-specific N uptake to surface-incident light, indicate that light is the major factor controlling N uptake in these waters. This is due to the permanent vertical mixing which reduces the mean light available for N uptake to <15% of the incident light. Mixing also injects regenerated N continuously into the euphotic zone, thus alleviating nitrogen limitation and accounting for the larger proportion of regenerated N uptake in total N uptake.  相似文献   

12.
Oceanographic samples were collected across the Antarctic Polar Front (APF) region in the vicinity of 60°S, 170°W during the US JGOFS program from December 1997 to March 1998. This paper reports the uptake rates of new (nitrate) and regenerated (ammonium and urea) nitrogen measured by 15N tracer techniques together with the levels of ammonium, urea-N and dissolved free amino acids (DFAAs) during December and mid-February–March. The APF was an important biological boundary, and in December rates of new (nitrate) uptake were greatest south of the APF, exceeding 10 mmol m−2 d−1 near the retreating ice edge. In February, nitrate uptake rates were an order of magnitude lower. Rates of ammonium uptake in both periods were greater in the warmer water north of the front. Nitrogen f-ratios varied from 0.50 to less than 0.05, with larger values associated with the >5 μm size fraction at the ice edge and generally lower values north of the APF. Urea was an important nitrogen source north of the APF, and lowered f-ratios there by 22% on average when included as part of total nitrogen uptake. Urea uptake was less important south of the APF. Ammonium concentrations increased dramatically south of the APF later in the season, suggesting a system dominated by regeneration. Seasonal changes in the concentrations of regenerated organic compounds such as urea and DFAAs were less obvious, although DFAAs exhibited consistent maxima in the high flow regions of the APF. A mass balance based of ammonium fluxes suggests that nitrification was significant at locations south of the APF in February. In these nitrate-replete waters, light/mixing conditions in the surface water (the Sverdrup criterion) accounted for over 50% of the variance in nitrate uptake rates. The stability responsible for higher new production south of the APF is due both to the separation of this region from the maximum zonal wind field to the north as well as to melt-water contribution from the retreating ice field. Estimated new production and exportable carbon production exceeded 500 mmol nitrate m−2 yr−1 and 40 g C m−2 yr−1, respectively, south of the APF. Thus, new production in the marginal ice zone of the Southern Ocean rivals that in coastal systems and indicates that this is an important region for export production.  相似文献   

13.
The purpose of this research was to investigate the potential causes of low oxygen levels in the bottom water of the Oyster Grounds region of the shallow southern North Sea, an area which provides suitable conditions for low oxygen levels to develop. At the end of the summer stratified period, relevant biogeochemical processes were investigated using a combination of sedimentary and water column rate measurements. Phytoplankton nitrate and ammonium uptake was measured throughout the water column using (15)N labelled isotopes and showed ammonium uptake dominated in the upper and bottom mixed layer with a maximum 294.4 micromol N m(-3)h(-1). In the deep chlorophyll maximum at the thermocline, primary production was dominated by nitrate uptake, with an average of 35.0 micromol N m(-3)h(-1), relative to ammonium uptake, with an average of 24.6 micromol N m(-3)h(-1). This high relative nitrate uptake will in part result in exportable new production to the isolated bottom mixed layer and sediments, as opposed to regenerated ammonium driven uptake. This biomass export was indicated by significant benthic oxygen consumption rates in the stratified region (782-1275 micromol O(2)m(-2)h(-1)micromol N m(-3)h(-1)) long after the end of the spring bloom. The sediments were also an active net source of nitrate, ammonium, phosphate and silicate into the bottom mixed layer of 4.4, 8.4, 2.3 and 68.8 micromol m(-2)h(-1), respectively. The export of new production within the thermocline to the bottom mixed layer and the consequent sediment oxygen consumption in the isolated bottom mixed layer in the Oyster Grounds are expected to have contributed to the low bottom water oxygen concentrations of 2.07 mg l(-1) (64.7 micromol l(-1)) measured. The long stratified period associated with this low oxygen is predicted to occur more regularly in the future and continued monitoring of this ecologically important region is therefore essential if the causes of these potentially damaging low oxygen levels are to be fully understood.  相似文献   

14.
Polar regions are poorly understood components of global biogeochemical cycles. This paper discusses the influences of nitrate and ammonium concentrations on nitrate uptake (and hence new production), particularly with regard to data collected within marginal ice zones in the Arctic and Antarctic. Subsurface ammonium maxima in waters over 150 m are frequently encountered in the Arctic and occasionally in the Antarctic. Such maxima result from the heterotrophic remineralization of organic matter, and because stratified environments occur more frequently in the Arctic, significant concentrations of ammonium accumulate as a result of lower diffusive losses. Causal agents (bacteria vs. Zooplankton) may also be different in the Arctic from those in the Antarctic. Elevated ammonium concentrations significantly reduce nitrate uptake, and it is suggested that this nutrient interaction may play a significant role in controlling new production, particularly in open water regions. The new production of the Southern Ocean is estimated, and it is suggested that the production and flux from the surface layer is significant relative to the world's oceans.  相似文献   

15.
Nitrate and ammonium uptake rates were measured during a series of cruises in the well-mixed region of the southern North Sea from February to September. Water column-integrated uptake rates ranged between 0.01 and 8.7 mmol N m−2 d−1 and 0.01 and 12.2 mmol N m−2 d−1 for nitrate and ammonium, respectively, with ammonium uptake dominating after the phytoplankton spring bloom in May. A moored buoy continuously measuring nitrate and chlorophyll a and seabed current meters were also deployed in the central southern North Sea in the region of the East Anglian plume—a permanent physical feature which transports nutrients towards continental Europe. This enabled the flux of water and hence of nutrients across the southern North Sea to be determined and an assessment of the contribution of freshwater nutrients to the flux to be made. A simple box model is developed to relate the phytoplankton uptake of nitrate and ammonium to the transport of nitrate, ammonium and particulate organic matter (POM) across the southern North Sea. This showed the importance of the plume region of the North Sea in the processing of nitrogen, with nitrate dominating total nitrogen transport prior to the spring bloom (10 340×103 kg N inflow to the plume in March) and transport of nitrogen as ammonium, nitrate and POM in approximately equivalent amounts during summer (2560, 2960 and 2151×103 kg N inflow to the plume, respectively, in July). The box model also demonstrates more generally the need to assess nitrogen transport as nitrate, ammonium and POM if an improved understanding of the impact of nutrient input in shelf seas is to be achieved.  相似文献   

16.
Recent changes in climate and environmental conditions have had great negative effects such as decreasing sea ice thickness and the extent of Arctic sea ice floes that support ice-related organisms. However, limited field observations hinder the understanding of the impacts of the current changes in the previously ice-covered regions on sea ice algae and other ice-related ecosystems. Our main objective in this study was to measure recent primary production of ice algae and their relative contribution to total primary production (ice plus pelagic primary production). In-situ primary productivity experiments with a new incubation system for ice algae were conducted in 3 sea ice cores at 2 different ice camps in the northern Chukchi Sea, 2014, using a 13C and 15N isotope tracer technique. A new incubation system was tested for conducting primary productivity experiments on ice algae that has several advantages over previous incubation methods, enabling stable carbon and nitrogen uptake experiments on ice algae under more natural environmental conditions. The vertical C-shaped distributions of the ice algal chl-a, with elevated concentrations at the top and bottom of the sea ice were observed in all cores, which is unusual for Arctic sea ice. The mean chl-a concentration (0.05 ± 0.03 mg chl-a m?3) and the daily carbon uptake rates (ranging from 0.55 to 2.23 mg C m?2 d?1) for the ice algae were much lower in this study than in previous studies in the Arctic Ocean. This is likely because of the late sampling periods and thus the substantial melting occurring. Ice algae contributed 1.5–5.7% of the total particulate organic carbon (POC) contents of the combined euphotic water columns and sea ice floes. In comparison, ice algae contributed 4.8–8.6% to the total primary production which is greater than previously reported in the Arctic Ocean. If all of the ice-associated productions were included, the contributions of the sea ice floes to the total primary production would be greater in the Arctic Ocean and their importance would be greater in the arctic marine ecosystems.  相似文献   

17.
海洋浮游生物氮吸收动力学及其粒级特征   总被引：7，自引：3，他引：7  
焦念志 《海洋与湖沼》1995,26(2):191-198
于１９９１年秋－１９９２年夏在中国科学院生态网络站之一的胶州湾进行了４个季节的现场实验，运用＾１５Ｎ同位素示踪方法研究胶州湾浮游生物群落对两种主要源铵态氮和硝态氮的吸收动力学及其粒级特征。研究初步阐明自然浮游生物落在不同季节，对不同氮源的吸收特性和受控机制，首次在群落水平上给出不同粒级浮游生物氮吸收特征的定量描述，从而为新生产力研究，生态系能流分配和生源要素生物地化循环研究提供重要参数。  相似文献   

18.
基于气温的浮冰侧向融化速率参数化方案实验研究   总被引：3，自引：3，他引：0  
艾润冰  谢涛  刘彬贤  赵立  方贺 《海洋学报》2020,42(5):150-158
为定量探究影响冰层侧向融化的主导因素，并简化冰层侧向融化速率参数化方案，在实验室模拟了无风、静水、无辐射、纯热力学条件下纯水冰的融化过程，测量了冰层的侧向融化量，并记录了融化期间实验室气温、冰面皮温、水温及冰温等要素。观测结果表明，无辐射纯热力学条件下冰层侧向融化整体较均匀，侧向上层和下层融化速率相对中间层较快；相关性分析结果表明，气温与水温、冰温、冰面皮温之间都有很好的线性相关；信息流结果表明，气温是影响冰层侧向融化的最主要因素；最后通过拟合建立了用气温表征冰层侧向融化速率的参数化方案，并与前人的方案进行了比较，结果显示本文参数化方案模拟效果较好，所得标准偏差最小，为0.08 mm/h，达到了简化参数的目的。  相似文献   

19.
The tropical seagrass Halophila stipulacea is dominant in most regions of the Indo‐Pacific and the Red Sea and was introduced into the Mediterranean Sea after the opening of the Suez canal. The species is considered invasive in the Mediterranean Sea and has been progressively colonizing new areas westward. Growth and photosynthetic responses of H. stipulacea have been described but no information is yet available on the nitrogen nutrition of the species. Here we simultaneously investigated the uptake kinetics of ammonium and nitrate and the internal translocation of incorporated nitrogen in H. stipulacea using 15N‐labelled substrates across a range of Ni levels (5, 25, 50 and 100 μm ). The ammonium uptake rates exceeded the nitrate uptake rates 100‐fold, revealing a limited capacity of H. stipulacea to use nitrate as an alternative nitrogen source. The uptake rates of ammonium by leaves and roots were comparable up to 100 μm 15NH4Cl. At this concentration, the leaf uptake rate was 1.4‐fold higher (6.22 ± 0.70 μmol·g?1 DW h?1) than the root uptake rate (4.54 ± 0.28 μmol·g?1 DW h?1). The uptake of ammonium followed Michaelis–Menten kinetics, whereas nitrate uptake rates were relatively constant at all nutrient concentrations. The maximum ammonium uptake rate (Vmax) and the half‐saturation constant (Km) of leaves (9.79 μmol·g?1 DW h?1 and 57.95 μm , respectively) were slightly higher than that of roots (6.09 μmol·g?1DW h?1 and 30.85 μm , respectively), whereas the affinity coefficients (α = Vmax/Km) for ammonium of leaves (0.17) and roots (0.20) were comparable, a characteristic that is unique among seagrass species. No substantial translocation (<2.5%) of 15N incorporated as ammonium was detected between plant parts, whereas the translocation of 15N incorporated as nitrate was higher (40–100%). We conclude that the Ni acquisition strategy of H. stipulacea, characterized by a similar uptake capacity and efficiency of leaves and roots, favors the geographical expansion potential of the species into areas with variable water‐sediment N levels throughout the Mediterranean.  相似文献   

20.
Short-lived halocarbons were measured in Arctic sea–ice brine, seawater and air above the Greenland and Norwegian seas (~81°N, 2–5°E) in mid-summer, from a melting ice floe at the edge of the ice pack. In the ice floe, concentrations of C2H5I, 2-C3H7I and CH2Br2 showed significant enhancement in the sea ice brine, of average factors of 1.7, 1.4 and 2.5 times respectively, compared to the water underneath and after normalising to brine volume. Concentrations of mono-iodocarbons in air are the highest ever reported, and our calculations suggest increased fluxes of halocarbons to the atmosphere may result from their sea–ice enhancement. Some halocarbons were also measured in ice of the sub-Arctic in Hudson Bay (~55°N, 77°W) in early spring, ice that was thicker, colder and less porous than the Arctic ice in summer, and in which the halocarbons were concentrated to values over 10 times larger than in the Arctic ice when normalised to brine volume. Concentrations in the Arctic ice were similar to those in Antarctic sea ice that was similarly warm and porous. As climate warms and Arctic sea ice becomes more like that of the Antarctic, our results lead us to expect the production of iodocarbons and so of reactive iodine gases to increase.  相似文献   

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