The impact of surface-adsorbed phosphorus on phytoplankton Redfield stoichiometry

The Redfield ratio of 106 carbon:16 nitrogen:1 phosphorus in marine phytoplankton is one of the foundations of ocean biogeochemistry, with applications in algal physiology, palaeoclimatology and global climate change. However, this ratio varies substantially in response to changes in algal nutrient status and taxonomic affiliation. Here we report that Redfield ratios are also strongly affected by partitioning into surface-adsorbed and intracellular phosphorus pools. The C:N:surface-adsorbed P (80-105 C:15-18 N:1 P) and total (71-80 C:13-14 N:1 P) ratios in natural populations and cultures of Trichodesmium were close to Redfield values and not significantly different from each other. In contrast, intracellular ratios consistently exceeded the Redfield ratio (316-434 C:59-83 N:1 intracellular P). These high intracellular ratios were associated with reduced N2 fixation rates, suggestive of phosphorus deficiency. Other algal species also have substantial surface-adsorbed phosphorus pools, suggesting that our Trichodesmium results are generally applicable to all phytoplankton. Measurements of the distinct phytoplankton phosphorus pools may be required to assess nutrient limitation accurately from elemental composition. Deviations from Redfield stoichiometry may be attributable to surface adsorption of phosphorus rather than to biological processes, and this scavenging could affect the interpretation of marine nutrient inventories and ecosystem models.     

Variable ageing and storage of dissolved organic components in the open ocean

Seawater dissolved organic matter (DOM) is the largest reservoir of exchangeable organic carbon in the ocean, comparable in quantity to atmospheric carbon dioxide. The composition, turnover times and fate of all but a few planktonic constituents of this material are, however, largely unknown. Models of ocean carbon cycling are thus limited by the need for information on temporal scales of carbon storage in DOM subcomponents, produced via the 'biological pump', relative to their recycling by bacteria. Here we show that carbohydrate- and protein-like substances in the open Atlantic and Pacific oceans, though often significantly aged, comprise younger fractions of the DOM, whereas dissolved lipophilic material exhibits up to approximately 90 per cent fossil character. In contrast to the millennial mean ages of DOM observed throughout the water column, weighted mean turnover times of DOM in the surface ocean are only decadal in magnitude. An observed size-age continuum further demonstrates that small dissolved molecules are the most highly aged forms of organic matter, cycling much more slowly than larger, younger dissolved and particulate precursors, and directly links oceanic organic matter age and size with reactivity.     

Fate of secondary effluent dissolved organic matter during soil-aquifer treatment

The reduction of mass and trihalomethane formation potential (THMFP) of dissolved organic matter (DOM) and its fractions from secondary effluent during laboratory-scale soil-aquifer treatment (SAT) soil columns were studied. Reduction in dissolved organic carbon (DOC), absorbance of ultraviolet light at 254 nm (UV-254), biodegradable dissolved organic carbon (BDOC) and nonbiodegradable dis- solved organic carbon (NBDOC) for the bulk DOM averaged 72.35%, 53.98%, 97.49% and 35.33% across the soil columns, respectively. Using XAD-8 and XAD-4 resins, DOM was fractionated into 3 fractions: hydrophobic acid (HPO-A), transphilic acid (TPI-A) and hydrophilic fraction (HPI). HPO-A was removed by 61.06%, TPI-A by 54.86% and HPI by 74.95% as DOC as a consequence of the laboratory-scale SAT, respectively. The reduction of THMFP from HPO-A, TPI-A and HPI was 27.24%, 26.24% and 36.08%, respectively. Proton nuclear magnetic resonance (1H-NMR) spectra revealed that the HPO-A isolated from the secondary effluent contained more aromatic functional groups than the corresponding TPI-A. Fourier-transform infrared (FT-IR) spectrum analysis illustrated that TPI-A had decreased hydrocarbon and increased aromatics content in the SAT columns. Specific ultraviolet light absorbance (SUVA) and specific THMFP for each DOM fraction increased across the soil columns and HPI exhibited greater increase in both than HPO-A and TPI-A. The most problematic THM precursor was found to be HPO-A with its high quantity present in recharged water and high chlorine reactivity.     

Optimal nitrogen-to-phosphorus stoichiometry of phytoplankton

Redfield noted the similarity between the average nitrogen-to-phosphorus ratio in plankton (N:P = 16 by atoms) and in deep oceanic waters (N:P = 15; refs 1, 2). He argued that this was neither a coincidence, nor the result of the plankton adapting to the oceanic stoichiometry, but rather that phytoplankton adjust the N:P stoichiometry of the ocean to meet their requirements through nitrogen fixation, an idea supported by recent modelling studies. But what determines the N:P requirements of phytoplankton? Here we use a stoichiometrically explicit model of phytoplankton physiology and resource competition to derive from first principles the optimal phytoplankton stoichiometry under diverse ecological scenarios. Competitive equilibrium favours greater allocation to P-poor resource-acquisition machinery and therefore a higher N:P ratio; exponential growth favours greater allocation to P-rich assembly machinery and therefore a lower N:P ratio. P-limited environments favour slightly less allocation to assembly than N-limited or light-limited environments. The model predicts that optimal N:P ratios will vary from 8.2 to 45.0, depending on the ecological conditions. Our results show that the canonical Redfield N:P ratio of 16 is not a universal biochemical optimum, but instead represents an average of species-specific N:P ratios.     

不同分子量DOM对垃圾渗滤液生物处理组合工艺中DBP和DEHP去除率的影响

采用小型生物处理组合工艺(上流式厌氧污泥床+曝气生物滤池+缺氧反应器+膜生物反应器, UASB+ BAF+ANO+MBR)处理老龄垃圾渗滤液, 考察了邻苯二甲酸二丁酯(DBP)和邻苯二甲酸二(2-乙基己基)酯(DEHP)两种内分泌干扰物在组合工艺中的去除, 以及与渗滤液中溶解性有机质(DOM)去除的关系。结果表明, 组合工艺对DBP和DEHP的去除率可分别达到92.9%和95.2%, 且与DOM腐殖化作用(即腐殖质的芳香性和分子量)密切相关。溶解性有机碳(DOC)主要分布在分子量为1~100 kDa的有机组分中, 此时腐殖质的芳香性较强, DBP和DEHP的浓度也较高。经过工艺处理后, 该组分的DOC和芳香性有效降低, 相应两种污染物的去除效果也更为明显。渗滤液原水及各工艺段中DOC与DBP及DEHP浓度的正相关性, 表明二者之间相互作用更有利于污染物的有效去除。     

Enhanced biological carbon consumption in a high CO2 ocean

The oceans have absorbed nearly half of the fossil-fuel carbon dioxide (CO2) emitted into the atmosphere since pre-industrial times, causing a measurable reduction in seawater pH and carbonate saturation. If CO2 emissions continue to rise at current rates, upper-ocean pH will decrease to levels lower than have existed for tens of millions of years and, critically, at a rate of change 100 times greater than at any time over this period. Recent studies have shown effects of ocean acidification on a variety of marine life forms, in particular calcifying organisms. Consequences at the community to ecosystem level, in contrast, are largely unknown. Here we show that dissolved inorganic carbon consumption of a natural plankton community maintained in mesocosm enclosures at initial CO2 partial pressures of 350, 700 and 1,050 microatm increases with rising CO2. The community consumed up to 39% more dissolved inorganic carbon at increased CO2 partial pressures compared to present levels, whereas nutrient uptake remained the same. The stoichiometry of carbon to nitrogen drawdown increased from 6.0 at low CO2 to 8.0 at high CO2, thus exceeding the Redfield carbon:nitrogen ratio of 6.6 in today's ocean. This excess carbon consumption was associated with higher loss of organic carbon from the upper layer of the stratified mesocosms. If applicable to the natural environment, the observed responses have implications for a variety of marine biological and biogeochemical processes, and underscore the importance of biologically driven feedbacks in the ocean to global change.     

Ocean nutrient ratios governed by plankton biogeography

The major nutrients nitrate and phosphate have one of the strongest correlations in the sea, with a slope similar to the average nitrogen (N) to phosphorus (P) content of plankton biomass (N/P = 16:1). The processes through which this global relationship emerges despite the wide range of N/P ratios at the organism level are not known. Here we use an ocean circulation model and observed nutrient distributions to show that the N/P ratio of biological nutrient removal varies across latitude in Southern Ocean surface waters, from 12:1 in the polar ocean to 20:1 in the sub-Antarctic zone. These variations are governed by regional differences in the species composition of the plankton community. The covariation of dissolved nitrate and phosphate is maintained by ocean circulation, which mixes the shallow subsurface nutrients between distinct biogeographic provinces. Climate-driven shifts in these marine biomes may alter the mean N/P ratio and the associated carbon export by Southern Ocean ecosystems.     

南黄海及长江口邻近海域夏季溶解有机碳的分布特征及其影响因素

【目的】海水中溶解有机碳(DOC)的研究对于碳的生物地球化学循环具有重要意义。通过对南黄海及长江口邻近海域夏季溶解有机碳的分布特征及其影响因素的研究,为进一步丰富我国陆架边缘海碳循环的研究提供数据支持和参考依据。【方法】利用高温燃烧氧化法对2013年夏季南黄海及长江口邻近海域水体中的DOC进行测定,初步分析夏季南黄海DOC的分布特征,并结合水文、化学、生物同步观测参数,探讨影响DOC分布的主要因素。【结果】2013年夏季南黄海及长江口邻近海域DOC的含量为0.24~2.37mg/L,平均值为(1.34±0.42)mg/L。整体而言,调查海区平面分布呈现北部浓度高,向南部逐渐降低,近岸浓度高远岸浓度低的分布趋势。DOC的垂直分布呈现表层高,逐渐向底层减小,在底层又有所增加的趋势。【结论】研究海区DOC的分布受水团物理混合控制作用十分明显,近岸DOC高值区的分布主要受鲁北沿岸流和陆源输入影响,南部的低值区主要受黑潮表层水及台湾暖流的稀释作用影响,而生物作用对DOC的分布影响较弱。     

Self-organization of dissolved organic matter to micelle-like microparticles in river water

In aquatic systems, the concept of the 'microbial loop' is invoked to describe the conversion of dissolved organic matter to particulate organic matter by bacteria. This process mediates the transfer of energy and matter from dissolved organic matter to higher trophic levels, and therefore controls (together with primary production) the productivity of aquatic systems. Here we report experiments on laboratory incubations of sterile filtered river water in which we find that up to 25% of the dissolved organic carbon (DOC) aggregates abiotically to particles of diameter 0.4-0.8 micrometres, at rates similar to bacterial growth. Diffusion drives aggregation of low- to high-molecular-mass DOC and further to larger micelle-like microparticles. The chemical composition of these microparticles suggests their potential use as food by planktonic bacterivores. This pathway is apparent from differences in the stable carbon isotope compositions of picoplankton and the microparticles. A large fraction of dissolved organic matter might therefore be channelled through microparticles directly to higher trophic levels--bypassing the microbial loop--suggesting that current concepts of carbon conversion in aquatic systems require revision.     

垃圾渗滤液厌氧降解中溶解性有机物的光谱特性

为探讨渗滤液厌氧降解出水中有机物的构成特点和变化规律,采用XAD-8和XAD-4树脂将溶解性有机物(DOM)依亲疏水性和酸碱性特征分为5种组分,对不同水力停留时间(HRT)下厌氧序批式反应器(ASBR)出水中各组分的含量和特性进行了比较研究.结果表明:ASBR处理渗滤液中溶解性有机碳(DOC)去除率可达53.0%～94.7%;芳香类物质多存在于疏水性组分中,厌氧处理后各组分UV254明显下降,芳香类、羧酸和氨基化合物去除明显;随着HRT的延长,富里酸类荧光物质易在出水中累积而造成累计荧光强度Фi,n增大,而芳香性蛋白及溶解性微生物副产物较之更易降解.可见ASBR能有效降解渗滤液DOM各组分物质.     

生物炭在矿区农田土壤中与镉的纵向共迁移行为

以广东韶关大宝山矿山废水污染的农田为研究对象,利用超纯水和甲苯/甲醇提取的溶解性有机质(DOM)的三维荧光光谱平行因子分析(EEM-PARAFAC)技术,追踪荔枝树枝生物炭1年内在土壤层0~100 cm深度范围的迁移行为及其协同重金属镉(Cd)的纵向迁移性质. 结果表明:生物炭增加了0~60 cm深土壤层溶解性有机碳(DOC)的质量分数,增加了表层土壤的pH,对深层土壤pH无明显影响;EEM-PARAFAC解析得到3个DOM组分(1个类蛋白和2个类腐殖质组分),生物炭的添加增大了0~60 cm深土壤层类腐殖质的质量分数;并且甲苯/甲醇提取的DOM在0~60 cm深土壤层中均检测出生物炭特有的多环芳烃结构,说明生物炭在1年内发生了明显的纵向迁移;生物炭能够有效降低0~20 cm深土壤中有效态Cd的质量分数,但20~60 cm深土层中有效态Cd与对照组的相比最高增加了148%左右. 研究表明:需要特别关注生物炭协同重金属在土壤中纵向迁移行为所带来的环境影响.     

Uptake of dissolved organic carbon and trace elements by zebra mussels

Zebra mussels (Dreissena polymorpha) are widespread and abundant in major freshwater ecosystems in North America, even though the phytoplankton food resources in some of these systems seem to be too low to sustain them. Because phytoplankton biomass is greatly depleted in ecosystems with large D. polymorpha populations and bacteria do not seem to be an important food source for this species, exploitation of alternative carbon sources may explain the unexpected success of D. polymorpha in such environments. Here we examine the possibility that absorption of dissolved organic carbon (DOC) from water could provide a nutritional supplement to zebra mussels. We find that mussels absorb 14C-labelled DOC produced by cultured diatoms with an efficiency of 0.23%; this indicates that DOC in natural waters could contribute up to 50% of the carbon demand of zebra mussels. We also find that zebra mussels absorb some dissolved metals that have been complexed by the DOM; although absorption of dissolved selenium was unaffected by DOC, absorption of dissolved cadmium, silver and mercury by the mussels increased 32-, 8.7- and 3.6-fold, respectively, in the presence of high-molecular-weight DOC.     

聚硅酸铁对溶解性有机物与浊度的去除

采用透射电镜法及光子相关光谱法对自制的氧化性聚硅酸铁(PSF)与聚合硫酸铁(PFS)进行微观表征,同时以254 nm的吸光度A(UV_(254))溶解性有机碳质量浓度c(DOC)、色度及比紫外吸光值A(SUV_(254))作为溶解性有机物(DOM)的检测指标,对PSF降低以上各指标与浊度去除效果及相关性进行研究.结果表明:PSF由很短的链节样物种及枝状结构组成,形态尺寸及分维数较大,并且较稳定;PSF具有良好的混凝效果,对浊度及色度的去除率超过95%,对A(UV_(254)),A(SUV_(254)),c(DOE)的去除率分别达到85%,80%,60%;用于评价PSF去除DOM性能的各指标间及其与余浊之间均具有良好的相关性.     

草地造林40年后土壤可溶性有机碳下降

为了解天然草地造林后土壤可溶性有机碳的变化,以河北塞罕坝的羊草草甸草原以及在草甸草原上营造的樟子松人工林和落叶松人工林为研究对象,比较了3种植被类型土壤表层0-30cm的土壤可溶性有机碳、土壤总有机碳和土壤全氮等指标。结果表明,人工针叶林的土壤可溶性有机碳、土壤有机碳和土壤全氮含量均低于草甸草原,天然草地营造人工针叶林40年后土壤可溶性有机碳、土壤有机碳和土壤全氮都有所下降,人工林生态系统的土壤异质性低于草甸草原。     

原始红松林皆伐后穿透雨对凋落物淋溶过程的影响

【目的】揭示原始红松林皆伐恢复演替为60年生的次生阔叶林后,凋落物对淋溶过程土壤养分归还及酸沉降的缓冲作用的影响,为评价森林生态功能的变化提供参考。【方法】以小兴安岭地区典型的原始红松林和皆伐后恢复演替60 a的次生阔叶林为研究对象,在两个样地内选择非林隙且林木通直分布均匀处放置30个体积为1 L的冠层穿透雨收集器,在每个穿透雨收集器附近设置1个凋落物淋溶液收集器。于2017年4—11月期间每隔45 d野外原位收集林下穿透雨和凋落物的淋溶液,以穿透雨为对照,对两者凋落物淋溶液中养分元素、可溶性有机物 (DOM) 的含量及pH的变化规律进行比较。【结果】与原始红松林相比,次生阔叶林凋落物中养分元素溶出总量显著偏低 (P<0.05),但不同元素的溶出规律并不一致,两个林型凋落物养分元素的释放高峰多集中于6月和7月;两者相比,原始红松林凋落物中DOM的溶出总量、可溶性有机碳 (DOC) 和可溶性有机磷 (DOP) 都极显著偏高,而可溶性有机氮 (DON) 的溶出量则极显著偏低 (P<0.01)。两个林型穿透雨中养分元素与DOM的变化规律与淋溶液基本一致。整个实验期间,两种林型的林下穿透雨pH变动范围为5.34~7.21,而凋落物淋溶液pH变动范围为6.37~7.65,凋落物层能对穿透雨的pH进行有效调节。两者相比,原始红松林凋落物层对林内穿透雨的调节作用更大。【结论】原始红松林皆伐恢复演替为60年生的次生阔叶林后,凋落物层在淋溶过程对土壤养分及DOM归还的能力减弱;凋落物层可以对穿透雨的pH进行有效调节,两者相比,原始红松林凋落物层对林内穿透雨的酸缓冲作用更强。     

Dissolved organic carbon trends resulting from changes in atmospheric deposition chemistry

Several hypotheses have been proposed to explain recent, widespread increases in concentrations of dissolved organic carbon (DOC) in the surface waters of glaciated landscapes across eastern North America and northern and central Europe. Some invoke anthropogenic forcing through mechanisms related to climate change, nitrogen deposition or changes in land use, and by implication suggest that current concentrations and fluxes are without precedent. All of these hypotheses imply that DOC levels will continue to rise, with unpredictable consequences for the global carbon cycle. Alternatively, it has been proposed that DOC concentrations are returning toward pre-industrial levels as a result of a gradual decline in the sulphate content of atmospheric deposition. Here we show, through the assessment of time series data from 522 remote lakes and streams in North America and northern Europe, that rising trends in DOC between 1990 and 2004 can be concisely explained by a simple model based solely on changes in deposition chemistry and catchment acid-sensitivity. We demonstrate that DOC concentrations have increased in proportion to the rates at which atmospherically deposited anthropogenic sulphur and sea salt have declined. We conclude that acid deposition to these ecosystems has been partially buffered by changes in organic acidity and that the rise in DOC is integral to recovery from acidification. Over recent decades, deposition-driven increases in organic matter solubility may have increased the export of DOC to the oceans, a potentially important component of regional carbon balances. The increase in DOC concentrations in these regions appears unrelated to other climatic factors.     

Effects of dissolved organic matter on the growth and pigments synthesis of Spirulina platensis (Arthrospira)

Excessive accumulation of dissolved organic matter (DOM) in the culture ponds of Spirulina platensis is usually considered to be one of the potential factors affecting the production of S. platensis, however, we are not quite aware of effects of DOM on the growth and pigments synthesis of S. platensis. In the present study, S. platensis was grown in batch or semi?continuous cultures using the filtrate in the culture ponds that had not been renewed for years. It was found that disssolved organic carbon up to 60 mg/L did not bring about an inhibitory effect on the growth of S. platensis, but increased the contents of chlorophyll a and phycocyanin instead. However, further accumulation of dissolved organic matter could decrease the content of chlorophyll a.     

Riverine export of aged terrestrial organic matter to the North Atlantic Ocean

Global riverine discharge of organic matter represents a substantial source of terrestrial dissolved and particulate organic carbon to the oceans. This input from rivers is, by itself, more than large enough to account for the apparent steady-state replacement times of 4,00-6,000 yr for oceanic dissolved organic carbon. But paradoxically, terrestrial organic matter, derived from land plants, is not detected in seawater and sediments in quantities that correspond to its inputs. Here we present natural 14C and 13C data from four rivers that discharge to the western North Atlantic Ocean and find that these rivers are sources of old (14C-depleted) and young (14C-enriched) terrestrial dissolved organic carbon, and of predominantly old terrestrial particulate organic carbon. These findings contrast with limited earlier data that suggested terrestrial organic matter transported by rivers might be generally enriched in 14C from nuclear testing, and hence newly produced. We also find that much of the young dissolved organic carbon can be selectively degraded over the residence times of river and coastal waters, leaving an even older and more refractory component for oceanic export. Thus, pre-ageing and degradation may alter significantly the structure, distributions and quantities of terrestrial organic matter before its delivery to the oceans.     

Flushing submarine canyons

The continental slope is a steep, narrow fringe separating the coastal zone from the deep ocean. During low sea-level stands, slides and dense, sediment-laden flows erode the outer continental shelf and the continental slope, leading to the formation of submarine canyons that funnel large volumes of sediment and organic matter from shallow regions to the deep ocean(1). During high sea-level stands, such as at present, these canyons still experience occasional sediment gravity flows(2-5), which are usually thought to be triggered by sediment failure or river flooding. Here we present observations from a submarine canyon on the Gulf of Lions margin, in the northwest Mediterranean Sea, that demonstrate that these flows can also be triggered by dense shelf water cascading (DSWC)-a type of current that is driven solely by seawater density contrast. Our results show that DSWC can transport large amounts of water and sediment, reshape submarine canyon floors and rapidly affect the deep-sea environment. This cascading is seasonal, resulting from the formation of dense water by cooling and/or evaporation, and occurs on both high- and low-latitude continental margins(6-8). DSWC may therefore transport large amounts of sediment and organic matter to the deep ocean. Furthermore, changes in the frequency and intensity of DSWC driven by future climate change may have a significant impact on the supply of organic matter to deep-sea ecosystems and on the amount of carbon stored on continental margins and in ocean basins.     

Bacterial carbon processing by generalist species in the coastal ocean

The assimilation and mineralization of dissolved organic carbon (DOC) by marine bacterioplankton is a major process in the ocean carbon cycle. However, little information exists on the specific metabolic functions of participating bacteria and on whether individual taxa specialize on particular components of the marine DOC pool. Here we use experimental metagenomics to show that coastal communities are populated by taxa capable of metabolizing a wide variety of organic carbon compounds. Genomic DNA captured from bacterial community subsets metabolizing a single model component of the DOC pool (either dimethylsulphoniopropionate or vanillate) showed substantial overlap in gene composition as well as a diversity of carbon-processing capabilities beyond the selected phenotypes. Our direct measure of niche breadth for bacterial functional assemblages indicates that, in accordance with ecological theory, heterogeneity in the composition and supply of organic carbon to coastal oceans may favour generalist bacteria. In the important interplay between microbial community structure and biogeochemical cycling, coastal heterotrophic communities may be controlled less by transient changes in the carbon reservoir that they process and more by factors such as trophic interactions and physical conditions.