Long-term nutrient trends and harmful cyanobacterial bloom potential in hypertrophic Lake Taihu,China

Rapid economic development in China’s Lake Taihu basin during the past four decades has accelerated nitrogen (N) and phosphorus (P) loadings to the lake. This has caused a shift from mesotrophic to hypertrophic conditions, symptomized by harmful cyanobacterial blooms (CyanoHABs). The relationships between phytoplankton biomass as chlorophyll a (Chla) and nutrients as total nitrogen (TN) and total phosphorus (TP) were analyzed using historical data from 1992 to 2012 to link the response of CyanoHAB potential to long-term nutrient changes. Over the twenty year study period, annual mean Chla showed significantly positive correlations with both annual mean TN and TP (P < 0.001), reflecting a strong phytoplankton biomass response to changes in nutrient inputs to the lake. However, phytoplankton biomass responded slowly to annual changes in TN after 2002. There was not a well-defined or significant relationship between spring TN and summertime Chla. The loss of a significant fraction of spring N loading due to denitrification likely weakened this relationship. Bioavailability of both N and P during the summer plays a key role in sustaining cyanobacterial blooms. The frequency of occurrence of bloom level Chla (>20 μg L^?1) was compared to TN and TP to determine nutrient-bloom thresholds. A decline in bloom risk is expected if TN remains below 1.0 mg L^?1 and TP below 0.08 mg L^?1.     

Effects of nutrient loading,temperature regime and grazing pressure on nutrient limitation of periphyton in experimental ponds

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Salinity tolerance of four freshwater microalgal species and the effects of salinity and nutrient limitation on biochemical profiles

Microalgae are ideal candidates for bioremediation and biotechnological applications. However, salinity and nutrient resource availability vary seasonally and between cultivation sites, potentially impacting on biomass productivity. The aim of this study was to screen pollutant-tolerant freshwater microalgae (Desmodesmus armatus, Mesotaenium sp., Scenedesmus quadricauda and Tetraedron sp.), isolated from Tarong power station ash-dam water, for their tolerance to cultivation at a range of salinities. To determine if biochemical composition could be manipulated, the effects of 4-day nutrient limitation were also determined. Microalgae were cultured at 2, 8, 11 and 18 ppt salinity, and nutrient uptake was monitored daily. Growth, total lipid, fatty acid (FA), and amino acid contents were quantified in biomass harvested while nutrient-replete and, after 4 days, nutrient-deplete. D. armatus showed the highest salinity tolerance actively growing in up to 18 ppt while Mesotaenium sp. was the least halotolerant with decreasing growth rates from 11 ppt. However, Mesotaenium sp. at 2 and 8 ppt had the highest biomass productivity and nutrient requirements of the four species, making it ideal for nutrient remediation of eutrophic freshwater effluents. Salinity and nutrient status had minimal influence on total lipid and FA contents in D. armatus and Mesotaenium sp., while nutrient depletion induced an increase of total lipid and FAs in S. quadricauda and Tetraedron sp., which was further increased with increasing salinity. As none of the growth conditions affected amino acid profiles of the species, these findings provide a basis for species selection based on site-specific salinity conditions and nutrient resource availability.     

<Emphasis Type="Italic">Daphnia</Emphasis> versus copepod impact on summer phytoplankton: functional compensation at both trophic levels

Here we report on a mesocom study performed to compare the top-down impact of microphagous and macrophagous zooplankton on phytoplankton. We exposed a species-rich, summer phytoplankton assemblage from the mesotrophic Lake Schöhsee (Germany) to logarithmically scaled abundance gradients of the microphagous cladoceran Daphnia hyalina×galeata and of a macrophagous copepod assemblage. Total phytoplankton biomass, chlorophyll a and primary production showed only a weak or even insignificant response to zooplankton density in both gradients. In contrast to the weak responses of bulk parameters, both zooplankton groups exerted a strong and contrasting influence on the phytoplankton species composition. The copepods suppressed large phytoplankton, while nanoplanktonic algae increased with increasing copepod density. Daphnia suppressed small algae, while larger species compensated in terms of biomass for the losses. Autotrophic picoplankton declined with zooplankton density in both gradients. Gelatinous, colonial algae were fostered by both zooplankton functional groups, while medium-sized (ca. 3,000 µm³), non-gelatinous algae were suppressed by both. The impact of a functionally mixed zooplankton assemblage became evident when Daphnia began to invade and grow in copepod mesocosms after ca. 10 days. Contrary to the impact of a single functional group, the combined impact of both zooplankton groups led to a substantial decline in total phytoplankton biomass.     

Food web modelling on the structure and functioning of a Mediterranean lentic system

A number of modelling results suggested thermocline shifts as a consequence of global climate change in stratifying lakes. Abundance and composition of the phytoplankton assemblage is strongly affected by the stratification patterns, and therefore, change in the thermocline position might have a substantial effect on this community or even on the whole lake ecosystem. In this study, thermocline depths in large mesocosms installed in Lake Stechlin (Germany) were deepened by 2 meters and phytoplankton changes were analysed by comparing changes to untreated mesocosms. Higher amounts of SRP were registered in the hypolimnion of treatment mesocosms than in the controls, and there were no differences in the epilimnion. Small but significant changes were observed on the phytoplankton community composition related to the effect of deepening the thermocline; however, it was weaker than the yearly successional changes. The most remarkable differences were caused by Planktothrix rubescens and by chlorophytes. P. rubescens became strongly dominant at the end of the experiment in the mesocosms, and in the open lake as well. The results of the experiment cannot clearly support the proliferation of cyanobacteria in general; however, the deepened thermocline can modify the behaviour of some species, as was observed in case of P. rubescens.     

Effects of phosphorus addition with and without nitrogen addition on biological nitrogen fixation in tropical legume and non-legume tree plantations

It is well documented that phosphorus (P) input stimulates biological nitrogen (N) fixation (BNF) in tropical forests with non-legume trees. However, in tropical legume forests with soil N enrichment and P deficiency, the effects of P availability and its combination with N on BNF remain poorly understood. In this study, we measured BNF rate in different compartments, i.e., bulk soil, forest floor, rhizosphere, and nodules, in two tropical plantations with legume trees Acacia auriculiformis (AA) versus non-legume trees Eucalyptus urophylla, (EU) in southern China after 4 years of P addition and combined N and P additions. The objective was to investigate how P addition and its combination with N addition regulate BNF in a tropical legume plantation, and to compare the effects with those in a non-legume plantation. Our results showed that total BNF rates were significantly higher in the P-addition plots than in the control plots by 27.4 ± 4.3 and 23.3 ± 1.7 % in the EU and AA plantations, respectively. Total BNF rates were significantly higher in the NP-addition plots than in the control plots by 27.7  ± 5.0 and 8.5 ± 1.4 % in the EU and AA plantations, respectively, which contrasted to our previous result that total BNF rates were significantly lower in N-addition plots than in the control plots in the AA plantation. These findings suggest that P input can stimulate BNF in tropical forest biome dominated by legume trees, even in consideration of elevated atmospheric N deposition. Thus, our study revealed the important role of P in regulating biological N input, which should be taken into account in the modeling of biogeochemical cycles in the future.     

Kin recognition in plants with distinct lifestyles: implications of biomass and nutrient niches

Kin recognition has been demonstrated by plant biomass allocation and morphology traits as well as by nitrogen (N) uptake, but has not been examined from a nutrient-niche view yet. In this study, four species with distinct lifestyles, including Glycine max (L.) Merr. (herbaceous legume), Belamcanda chinensis (L.) DC. (herbaceous non-legume), Caesalpinia pulcherrima (L.) Sw. (woody legume), and Populus tomentosa (L.) Carr. (woody non-legume) were used to demonstrate kin recognition by estimating their biomass and allocation, as well as nutrient niches based on their uptake efficiency for N, phosphorus (P), sulfur (S), potassium (K), calcium (Ca), magnesium (Mg), and iron (Fe). For G. max, kin recognition was achieved by increased biomass, and by reduced nutrient-uptake efficiency of N, P, S, K, Ca, Mg, and Fe (decreased nutrient niches) to decrease nutrient competition among kin plants compared to the strangers. Although B. chinensis and C. pulcherrima had no biomass response, kin plants of B. chinensis increased, whereas C. pulcherrima decreased their S-uptake efficiency compare to strangers. Therefore, kin competition occurred in B. chinensis through increased nutrient niche whereas kin recognition occurred in C. pulcherrima through decreased nutrient niche. By comparison, P. tomentosa showed the co-occurrence of kin recognition and competition by increased root allocation and decreased P-uptake efficiency. These findings suggest that the biomass allocation and plant nutrient niches based on their nutrient-uptake efficiency can be used as potential parameters to identify kin recognition.     

Nutrient allocation and photochemical responses of <Emphasis Type="Italic">Populus</Emphasis> × <Emphasis Type="Italic">canadensis</Emphasis> ‘Neva’ to nitrogen fertilization and exogenous <Emphasis Type="Italic">Rhizophagus irregularis</Emphasis> inoculation

Arbuscular mycorrhizal fungi (AMF) can promote plant growth performance, but their effectiveness varies depending on soil nitrogen (N) availability. To clarify the effectiveness of exogenous AMF along an N-fertilization gradient (0, 2, 10, 20, and 30 mM), the impacts of exogenous Rhizophagus irregularis and N on the growth, photochemical activity, and nutritional status of Populus?×?canadensis ‘Neva’ in natural soil were evaluated in a pot experiment. The results showed that the 10 mM N level was the optimal fertilization regime with the highest promotion effect on plant growth and the maximum quantum yield of photosystem II (PSII) (F_v/F_m). Excess N (20 and 30 mM) fertilization reduced the actual quantum yield of PSII (ФPSII) and the F_v/F_m of the plants. Regardless of the N availability, inoculated plants exhibited greater F_v/F_m values than did non-inoculated plants. The biomass of inoculated plants was significantly higher compared with the control under low N levels (0 and 2 mM). Under high N levels, inoculated plants showed significant increases in ФPSII. Moreover, the nutrient imbalance of plants inoculated with exogenous R. irregularis was eased by increasing P, Fe, Mn and Cu uptake in roots and higher P, Ca, Mg, Fe, Mn and Zn concentrations in leaves. Moreover, the F_v/F_m and ФPSII exhibited positive correlations with P, Ca, Mg and Zn concentrations in leaves. In conclusion, inoculation with exogenous R. irregularis can benefit plant fitness by improving the photochemical capacity and nutrient composition of poplar under different N levels.     

The contrasting effects of nutrient enrichment on growth,biomass allocation and decomposition of plant tissue in coastal wetlands

Background

Most studies focus on macronutrient of C, N and P and ignore other elements, which restrict our understanding on the strategy of plant nutrient adaption and nutrient cycling.

Methods

We investigated 14 element (C, N, P, S, K, Ca, Mg, Fe, Mn, Zn, Cu, Na, Al, and Ba) concentrations of green and senesced leaves in Quercus variabilis along the altitude in the Baotianman Mountains, China, and assessed their relationships with climate, soil, and plant functional traits.

Results

Leaf N,S and K increased with, C, Ca, Na, Fe, Mn, Cu and Ba decreased with, and P, Mg, Al, Zn and N:P did not change significantly with altitude. NRE and SRE increased with, and CRE decreased with altitude (p < 0.05). Among the 14 elements, nucleic acid-protein elements (N, K, S and P) were resorbed preferentially, compare to structural (Ca, Mn, and B) and enzymatic (C, Cu, Mg and Zn) that were discriminated against, and toxic (Al and Fe) elements that were totally excluded.

Conclusions

Q. variabilis can synergetically regulate green leaf multielement stoichiometry and nutrient resorption in responses to environment change. Deciduous plants may have a trade-off mechanism at the end of growing season to rebalance somatic nutrients.

     

Impact of DOC trends resulting from changing climatic extremes and atmospheric deposition chemistry on periphyton community of a freshwater tropical lake of India

Recent measurements have demonstrated unprecedented increase in atmospheric deposition of nutrients in many parts of India. To determine whether atmospheric nutrient inputs would increase phytoplankton growth and catchment dissolved organic carbon (DOC) flushing to constrain benthic algae, we analyzed NO₃ ^? and PO ₄ ^?3 in atmospheric deposits; nutrients and DOC in runoff and lake water and standing crop biomass of phytoplankton and periphyton at Jaisamand Lake of Rajasthan, India. Atmospheric deposition of NO₃ ^? (7.18–29.95 kg ha^?1 year^?1) and PO ₄ ^?3 (0.56–2.15 kg ha^?1 year^?1) showed a consistently rising trend across the year. Microbial biomass and activity in catchment increased in response to atmospheric deposition. Lake DOC and nutrients showed strong coherence with their terrestrial and atmospheric fluxes. Phytoplankton development showed significant linearity with atmospheric input of nutrients. Air-driven input appeared to have compensated the nutrient constraints to phytoplankton during drought. The N:P stoichiometry of deposition and that of lake water indicated that, although there was a seasonal switchover to N- or P-limitation, phytoplankton were mainly co-limited by N and P due probably to the synergistic effects of combined N + P enrichment in the pelagic zone of the lake. Periphyton standing crop showed inverse relationship with phytoplankton and lake DOC. The study indicated that enhanced phytoplankton development and terrestrial DOC flushing in response to atmospheric nutrient input attenuated light penetration to constrain algal periphyton. We suggests that data on these issues may be considered in developing aquatic ecosystem models to establish future links between changing air–water–land interactions and associated shifts in lake ecosystem functioning for more accurately predicting climate change drivers and designing integrated lake basin management strategies.     

Global dataset for carbon and nitrogen stable isotope ratios of lotic periphyton

Carbon and nitrogen stable isotope ratios (δ¹³C and δ¹⁵N) have been widely employed in food web analysis. In lotic environments, periphyton is a major primary producer that makes a large contribution to food web production as well as carbon and nitrogen cycling. While the δ¹³C and δ¹⁵N values have many advantages as a natural tracer, the controls over their high spatial and temporal variability in stream periphyton are not well known. Here, we present the global dataset of δ¹³C and δ¹⁵N values of lotic periphyton from 54 published and two unpublished sources, including 978 observations from 148 streams/rivers in 38 regions around the world, from arctic to tropical sites. The 54 published sources were articles recorded during the period of 1994–2016 in 25 academic journals. The two unpublished sources were from the authors’ own data. The dataset showed that δ¹³C and δ¹⁵N values of periphyton ranged from ?47.3 to ?9.3‰ and from ?5.6 to + 22.6‰, respectively. The dataset also includes physicochemical factors (altitude, coordinates, catchment area, width, depth, geology, vegetation, canopy coverage, biome, season, presence of anadromous salmon, temperature, pH, current velocity, and discharge), nutrient data (nitrate and ammonium concentrations), and algal attributes (chlorophyll a concentration, algal species compositions, and carbonates removal) in streams/rivers studied, all of which may help interpret the δ¹³C and δ¹⁵N values of periphyton. The metadata file outlines structure of all the data and with references for data sources, providing a resource for future food web studies in stream and river ecosystems.     

Influence of short periods of increased water temperature on species composition and photosynthetic activity in the Baltic periphyton communities

Periphyton plays a vital ecological role in shallow, well-lit ecosystems which are vulnerable to rapidly changing environmental conditions, including raising temperature due to global warming. Nevertheless, little is known on the effect of increased temperatures on the taxonomic structure and functioning of periphytic communities. In this study, the influence of short-term temperature increase on the species composition and photosynthetic activity of the Baltic periphytic communities was investigated. The collected communities were exposed to increased temperature of 23 °C (ca. 4 °C above the summer average) for 72 h. After this time, species composition of the communities was studied under light microscope and their photosynthetic performance was evaluated using PAM fluorometry. Results showed that the biomass of cyanobacteria slightly increased. There were significant changes in the abundance of diatom species, among which Fragilaria fasciculata and Navicula ramosissima, were negatively affected by the elevated temperature and their cell number significantly decreased, whereas, Diatoma moniliformis and N. perminuta were stimulated by the increased temperature. Additionally, a shift towards higher abundance of smaller taxa was also observed. The higher quantum yield of photosystem II (PSII) (higher ΦPSII) accompanied by the lower value of non-photochemical quenching (NPQ) observed in communities kept at 23 °C showed more efficient photosynthesis. This was further confirmed by the changes in rapid light curves (higher photosynthetic capacity, rETR_max, and photoacclimation index, E_k). The obtained data constitute evidence that short periods of increased temperature significantly affect the structure and functioning of the Baltic periphyton.     

Competition between native Antarctic vascular plants and invasive <Emphasis Type="Italic">Poa annua</Emphasis> changes with temperature and soil nitrogen availability

Over the last decades human have introduced non-native organisms to Antarctica, including the grass species Poa annua. This non-native grass under constant growth temperatures has been shown negatively affect the growth of the only two native Antarctic vascular plants, Deschampsia antarctica and Colobanthus quitensis, under constant growth temperatures. However, whether there are changes in the interaction between these species under warmer conditions is an important question. In cold ecosystems, soil nutrient status directly affects plant responses to increases in temperature and Antarctic soils are highly variable in nutrient supply. Thus, in this study we experimentally assessed the interaction between the non-native Poa with the two native Antarctic vascular plant species at two different temperatures and levels of nutrient availability. Individual mats of the study species were collected in King George Island, and then transported to Concepcion where we conducted competition experiments. In the first experiment we used soil similar to that of Antarctica and plants in competition were grown at two temperatures: 5°/2° and 11°/5 °C (day/night temperature). In a second experiment plants were grown in these two temperature regimes, but we varied nitrogen (N) availability by irrigating plants with Hoagland solutions that contained 8000 or 300 µM of N. Overall, Poa exerted a competitive effect on Deschampsia but only at the higher temperature and higher N availability. At 5°/11 °C the competitive response of Deschampsia to Poa was of similar magnitude to the competitive effect of P. Deschampsia, and the competitive effect was greater with at low N. The competitive effect of Poa was similar to the competitive response of Colobanthus to Poa at both temperatures and N levels. Thus, at low temperatures and N soil content the native Antarctic species might withstand Poa invasion, but this might change with climate warming.     

Effects of sediment-borne nutrient and litter quality on macrophyte decomposition and nutrient release

Macrophyte decomposition is a critical process that affects carbon and nutrient cycling, and energy flow, although the majority of the details involved in the process remain unclear. For the present study, a litter bag experiment was conducted to investigate the effects of sediment-borne nutrient and litter quality on the decomposition rates and nutrient release of four macrophyte life forms (emergent macrophyte: Phragmites australis, free-floating macrophyte: Hydrocharis dubia, floating-leaved macrophyte: Nymphoides peltata, submerged macrophyte: Ceratophyllum demersum), and a species mixture. Our results indicated that litter quality significantly influenced macrophyte decomposition and nutrient release. High-quality litter species (high initial nitrogen and phosphorus contents, as well as low C:N, C:P, and N:P ratios) decomposed more rapidly than low-quality litter species, and the initial C:N and C:P ratios, rather than the initial N and P contents, were effective indicators of the decomposition rate of macrophytes. Sediment-borne nutrients had little effect on the decomposition rate, yet a strong effect on the release of N and P, although the interactions between litter quality and sediment-borne nutrients significantly affected the decomposition rate. Three-way ANOVA analysis revealed that the litter quality imparted a more potent effect on the macrophyte decomposition rate and release of N and P than sediment-borne nutrients. These results implied that litter quality interacts with sediment-borne nutrients and may control macrophyte decomposition in shallow lakes.     

Decomposition rate and nutrient release from plant litter of Norway spruce forest in the Bohemian Forest

The role of litter composition and quality on the nutrient release was studied in three month laboratory experiment. Spruce needles and leaves of four species dominant in understorey vegetation of the Norway spruce forest were collected in early autumn and incubated at 5°C, 10°C and 15°C. C mineralization was measured every two weeks, concentration of NH₄, NO₃, dissolved organic N, dissolved organic C and oxalate extractable P at the beginning and end of incubation and decay rate and nutrient release was calculated. Freshly senescent leaves contained less N and P indicating nutrient reallocation. Effect of temperature on a decay rate and nutrient transformation was not significant while the effect of litter quality expressed by C/N ratio at the end of incubation was. The decay rate was the fastest for the fern (Athyrium alpestre) and decreased in order: Callamagrostis villosa > Vaccinium myrtillus > Avenella flexuosa > spruce needles. The critical C/N ratio bellow which mineral N was released in high amount was around a value of 32. The results indicte that an increase of coverage of understorey vegetation can increase a risk of nutrient release.     

Comparative analyses of physiological assays and chlorophyll <Emphasis Type="Italic">a</Emphasis> variable fluorescence parameters: investigating the importance of phosphorus availability in oligotrophic and eutrophic freshwater systems

Diverse measurements of nutrient status indicators were used to test the severity of physiological phosphorus (P) limitation of phytoplankton among lake systems ranging from oligotrophic to eutrophic, based on P and chlorophyll a (Chl a) concentrations. Metabolic assays and particulate nutrient ratios were used to estimate nutrient status at sites located in Lake Erie, Lake Ontario and Lake Huron. Variable fluorescence ratios (F _v/F _m), relative electron transport rates and their response to irradiance were measured by the pulse-amplitude-modulated fluorometer. Under summer stratified conditions, P deficiency was strongest in the oligotrophic sites and nitrogen (N) status indicators and Chl a variable parameters revealed no severe N deficiency. Nutrient amendment assays showed positive associations with P additions and Chl a fluorescence parameters at P-deficient sites. In the most oligotrophic sites, N additions revealed a modest increase only detected by the Chl a fluorescence parameters. Phytoplankton communities were also associated with nutrient status, where chrysophytes and cryptophytes were important in P-deficient sites and cyanobacteria, phyrrophyta, and diatoms were prevalent in nutrient-rich sites. The results confirmed that Chl a fluorescence parameters can reveal P deficiency and indicate its severity among the range of trophic status in aquatic systems.     

Effects of both substrate and nitrogen and phosphorus fertilizer on <Emphasis Type="Italic">Sphagnum palustre</Emphasis> growth in subtropical high-mountain regions and implications for peatland recovery

Human activities have recently caused severe destruction of Sphagnum wetlands in subtropical high-mountain regions, calling for urgent efforts to restore Sphagnum wetlands. Through a greenhouse experiment in western Hubei, China, we studied the effects of different substrate types (peat and mountain soil) and different levels of nitrogen (N) (0, 2, 4, 6, 10 g m^?2 year^?1) and phosphorus (P) (0, 0.2, 0.5, 1, 2 g m^?2 year^?1) on the growth of Sphagnum palustre, which was evaluated by four growth indicators: length growth, number of capitula, coverage change and biomass. We aimed to determine the optimal nutrient conditions for S. palustre growth, which would contribute to the rapid colonization and restoration of Sphagnum wetlands. The results showed that the different substrates significantly influenced S. palustre growth. Compared with those of peat, the acidic properties of the local yellow brown soil in the subtropical high-mountain regions were more favorable for S. palustre growth. As N addition increased, the four growth indicators responded inconsistently to the different substrates. While the number of capitula markedly increased, the other three indicators significantly decreased in the mountain soil or exhibited no definitive changes in the peat. The addition of P markedly promoted S. palustre growth in both substrates. However, a threshold for P fertilization existed; the highest productivity occurred at P additions of 0.2 and 0.5 g m^?2 year^?1 in the peat and mountain soil, respectively. The N and P contents in the capitula increased in parallel as the N and P fertilization rates increased, suggesting that these nutrients were absorbed proportionately and were used during the growth of S. palustre.     

Changes in growth and composition of the marine microalgae <Emphasis Type="Italic">Phaeodactylum tricornutum</Emphasis> and <Emphasis Type="Italic">Nannochloropsis salina</Emphasis> in response to changing sodium bicarbonate concentrations

Oils, carbohydrates, and fats generated by microalgae are being refined in an effort to produce biofuels. The research presented here examines two marine microalgae, Nannochloropsis salina (green alga) and Phaeodactylum tricornutum (diatom), when grown with 0 (no addition), 0.5, 1.0, 2.0, and 5.0 g L^?1 NaHCO₃ added to an f/2 medium during the growth phase (GP) and a nutrient induced (nitrate limitation) lipid formation phase (LP). We hypothesize that the addition of NaHCO₃ is a sustainable and practical strategy to increase cellular density and concentrations of lipids in microalgae as well as the rate of lipid accumulation. In N. salina, final cell densities were significantly (p?<?0.05) higher in the NaHCO₃-treated cells than the control while in P. tricornutum the cell densities were higher with >[NaHCO₃] during the GP. During the LP, cell densities were generally higher in the NaHCO₃-treated cells compared with controls. F _V/F _M (efficiency of photosystem II) patterns paralleled those for cell density with generally higher values with higher concentrations of NaHCO₃ and significantly different values between controls and 5.0 g L^?1 NaHCO₃ at the end of the GP (p?<?0.05). F _V/F _M was variable between treatments in P. tricornutum (0.3–0.65) but less so in N. salina for (0.5–0.7) regardless of [NaHCO₃]. The lipid index (measured with Nile red), used as a proxy for triacylglycerides (TAGs), was 10.2?±?6.5 and 4.4?±?2.9 (fluorescence units/OD cells ×1000) for N. salina and P. tricornutum, respectively, at the end of the GP. At the end of the LP, the lipid index was eight and four times higher than during the GP in the corresponding 5.0 g L^?1 NaHCO₃ treatments, revealing that N. salina was accumulating more lipid than P. tricornutum. Dry weights essentially doubled during LP compared with GP for N. salina; this was not the case for P. tricornutum. In general, the percentage of ash in dry weights was significantly higher in the LP relative to the corresponding GP treatments for P. tricornutum; this was not the case for N. salina. During the LP, there was also less soluble protein in N. salina compared to GP; differences were not significant in cells growing with 2.0 or 5.0 g L^?1 NaHCO₃. In P. tricornutum, faster growing cells had more soluble protein during the GP and LP; differences between treatments were significant. P. tricornutum generally accumulated significantly more crude protein than N. salina at higher [NaHCO₃]; there was three times more crude protein in the highest NaHCO₃ (5.0 g L^?1) treatment compared with the controls. C:N ratios (mol:mol) were similar across treatments during GP: 7.03?±?0.12 and 10.16?±?0.41 for N. salina and P. tricornutum, respectively. Further, C:N ratios increased with increasing [NaHCO₃] during LP. Species-specific fatty acid methyl ester (FAMEs) profiles were observed. While C16:0 was lower in P. tricornutum compared to N. salina, the diatom produced more C16:1 and C14 but not C18:3. Monounsaturated fatty acids (MUFA) significantly increased in N. salina in the LP compared to GP and in response to increasing [NaHCO₃] (t tests; p?<?0.05). Saturated fatty acids (SFA) responded similarly but to a lesser degree. There were more polyunsaturated fatty acids (PUFA) in N. salina than MUFAs or SFAs. In P. tricornutum, there were generally more SFAs, MUFAs and PUFAs in P. tricornutum during LP than GP in the corresponding NaHCO₃ treatments. These findings reveal the importance of considering NaHCO₃ as a supplemental carbon source in the culturing marine phytoplankton in large-scale production for biofuels.     

Influence of suspended particulate matter on nutrient biogeochemistry of a tropical shallow lagoon,Chilika, India

The behaviour of suspended particulate matter (SPM), salinity profile, dissolved nutrients, total (T.Chl-a) and size fractionated chlorophyll-a (F.Chl-a) were studied seasonally at Chilika Lagoon, east coast of India, during 2008–2009. The study showed large spatio-temporal variations among these parameters. The concentration of dissolved inorganic nitrogen and inorganic phosphate were found to be maximum during the monsoon, followed by post- and pre-monsoon, although the mean N:P ratios, which indicate the relative availability of N with respect to P, were 9.13 ± 3.09, 16.57 ± 11.53 and 5.47 ± 3.13, respectively. It was evident from the results that during pre-monsoon and postmonsoon, the lagoon exhibits nitrogen limitation. Mean T.Chl-a biomass in the lagoon showed distinct seasonality with maximum values during the pre-monsoon (23.12 ± 9.75 mg m^?3) followed by monsoon and post-monsoon. Irrespective of seasons, maximum T.Chl-a was found in the northern part of the lagoon. SPM concentrations during the monsoon were relatively higher in the freshwater dominated zones compared to seawater dominated areas, indicating its riverine sources. The correlation between SPM and various dissolved nutrients (p < 0.05) suggests its influence on the physico-chemical conditions at varying levels. It is summarized that seasonal variation of SPM and nutrients contributed by rivers, wind induced re-suspension events and in situ  regeneration processes play a crucial role in the lagoon biogeochemical cycle.     

Adaptations in phytoplankton life strategies to imposed change in a shallow urban tropical eutrophic reservoir,Garças Reservoir,over 8 years

This study aimed at evaluating the phytoplankton adaptive strategies of phytoplankton in a shallow urban eutrophic tropical reservoir, Garças Reservoir, over temporal and vertical scales. Samples were taken monthly for eight consecutive years (1997–2004) at a fixed set of depths in the water column. At the beginning, the reservoir was eutrophic with 20% of its surface covered by water hyacinth Eichhornia crassipes (phase I). Then, in phase II, water hyacinth grew to cover up to 40–70% of the surface. In phase III it was mechanically removed. After macrophyte removal the limnology changed, drastically. This removal modified nutrient dynamics, drastically reduced water transparency, and increased both primary production and phytoplankton biomass, the latter impeding light penetration. Phytoplankton life strategies during water hyacinth dominance (phase II) responded promptly to this environmental disturbance in conditions of low dissolved oxygen (DO) and soluble reactive phosphorus (SRP) and high free CO₂ values. After macrophyte removal, a permanent cyanobacterial monoculture was established. Phase I was dominated basically by Sphaerocavum brasiliense, mainly during the stratified months, represented by non-flagellate colonies, the M functional group, S-strategists, and greater biomass of species with high maximal axial linear dimension (MLD) and cell volumes. Phase II was dominated by Cryptomonas curvata, C. erosa, C. marssonii, Trachelomonas sculpta, T. volvocinopsis, T. kelloggii, T. hispida, Peridinium spp., Aphanocapsa spp., and Aphanothece spp., and was represented by unicellular flagellate species, Y, W2, K, L_O functional groups, and C-strategists, greater biomass of species with intermediate MLD and cell volumes. Phase III was dominated by Microcystis aeruginosa, M. panniformis, Cylindrospermopsis raciborskii, Planktothrix agardhii, and Aphanizomenon gracile, represented by non-flagellate colonies, M, S, H1, S functional groups, and S and R-strategists, greater biomass of species with high MLD and cell volumes (>50 μm and >10⁴ μm³, respectively).