Reduce Nutrient Concentrations Research Articles

Long-term declines in chlorophyll a and variable phenology revealed by a 60-year estuarine plankton time series

Long-term ecological time series provide a unique perspective on the emergent properties of ecosystems. In aquatic systems, phytoplankton form the base of the food web and their biomass, measured as the concentration of the photosynthetic pigment chlorophyll a (chl a), is an indicator of ecosystem quality. We analyzed temporal trends in chl a from the Long-Term Plankton Time Series in Narragansett Bay, Rhode Island, USA, a temperate estuary experiencing long-term warming and changing anthropogenic nutrient inputs. Dynamic linear models were used to impute and model environmental variables (1959 to 2019) and chl a concentrations (1968 to 2019). A long-term chl a decrease was observed with an average decline in the cumulative annual chl a concentration of 49% and a marked decline of 57% in winter-spring bloom magnitude. The long-term decline in chl a concentration was directly and indirectly associated with multiple environmental factors that are impacted by climate change (e.g., warming temperatures, water column stratification, reduced nutrient concentrations) indicating the importance of accounting for regional climate change effects in ecosystem-based management. Analysis of seasonal phenology revealed that the winter-spring bloom occurred earlier, at a rate of 4.9 ± 2.8 d decade-1. Finally, the high degree of temporal variation in phytoplankton biomass observed in Narragansett Bay appears common among estuaries, coasts, and open oceans. The commonality among these marine ecosystems highlights the need to maintain a robust set of phytoplankton time series in the coming decades to improve signal-to-noise ratios and identify trends in these highly variable environments.

Enhancing Leaf Nutrient Levels in Polyembryonic Mango (Mangifera indica L.) Seedlings: The Impact of Saline Water Irrigation and 28-Homobrassinolide Spray

The leaf nutrients play a key role in the growth of a plant. Therefore, a study was undertaken to evaluate the effect of saline water and spray of 28-homobrassinolide on leaf nutrient status of polyembryonic mango (Mangifera indica L.) seedling during the years 2021-22 and 2022-23 at Agriculture Experimental Station, Navsari Agricultural University, Paria, (Gujarat). The experiment was laid out in Completely Randomized Design with factorial concept comprising of four salinity levels [S1: Best available water (control), S2: 2 dS m-1, S3: 4 dS m-1, S4: 6 dS m-1] and three spray concentration of 28-homobrassinolide [H1: No spray, (control), H2 : 0.5 ppm and H3 : 1 ppm]. Saline water application and 28-homobrassinolide spray was started at 80 days after sowing up to 240 days. The treatment containing application of water having lowest salinity (best available water) resulted in significantly higher leaf nutrient contents except Na up to 9 months after sowing during both years and in pooled analysis. Application of saline water having EC 6 dS m-1 adversely affected the growth of polyembryonic mango seedlings, reduced nutrient contents after 6 months of sowing. After 6 month of sowing, highest nutrient contents except Na was noted in mango seedlings treated with spray of 1 ppm 28-homobrassinolide during both years and in pooled analysis. The interactions of salinity levels and 28-homobrassinolide spray significantly affect leaf nutrient content of mango seedlings. Leaf nutrient contents except Na up to 9 months after sowing during both the years and in pooled analysis were recorded in treatment combination of best available water along with 1 ppm spray of 28-homobrassinolide. Maximum content of Na was observed in plants irrigated with 6 dS m-1 salinity level without spray of 28-homobrassinolide. Hence, it can be concluded that polyembryonic mango seedlings can be grown with saline irrigation having salinity up to 4 dS m-1 along with 1 ppm 28-homobrassinolide spray for better growth, biomass, nutrient contents and higher survival up to 9 months after sowing.

Water quality trends of streams in Puerto Rico: Evaluating 50 years of the Clean Water Act.

Water quality regulations entail a substantial commitment of resources from governments and private entities. It is important to continually evaluate the effectiveness of these regulations to ensure they are having the intended impact. In this paper, we evaluated nutrient data as indicators of primary productivity and dissolved oxygen (DO) concentrations and pH as response variables to assess historical water quality trends from 55 stations of Puerto Rico. The stations were divided into impaired versus non-impaired categories based on their historical total phosphorus (TP) mean concentration. Mean TP and total nitrogen (TN) concentrations were significantly higher in the impaired stations relative to the non-impaired stations. In contrast, DO mean concentrations and mean pH values were significantly lower in the impaired stations. A generalized additive mixed model was used to demonstrate temporal trends. A significant decrease in TP and TN concentrations was observed with time at the impaired stations. This was accompanied by significant increases in DO concentrations and pH. The non-impaired stations showed a marginal (statistically nonsignificant) decreasing trend with time. The large reductions in nutrient concentrations observed at the impaired stations seem to be related to the closure of several primary wastewater treatment plants (WWTPs) across the island. The conversion of abandoned crop agricultural lands into secondary forest in recent decades has resulted in small but significant decreases in TN (not TP) in receiving streams. We conclude that the Clean Water Act has promoted improvements in water quality in Puerto Rico by advancing upgrades in sanitary infrastructure and the regulation of point sources of pollution.

Prioritizing river basins for nutrient studies

Increases in fluxes of nitrogen (N) and phosphorus (P) in the environment have led to negative impacts affecting drinking water, eutrophication, harmful algal blooms, climate change, and biodiversity loss. Because of the importance, scale, and complexity of these issues, it may be useful to consider methods for prioritizing nutrient research in representative drainage basins within a regional or national context. Two systematic, quantitative approaches were developed to (1) identify basins that geospatial data suggest are most impacted by nutrients and (2) identify basins that have the most variability in factors affecting nutrient sources and transport in order to prioritize basins for studies that seek to understand the key drivers of nutrient impacts. The “impact” approach relied on geospatial variables representing surface-water and groundwater nutrient concentrations, sources of N and P, and potential impacts on receptors (i.e., ecosystems and human health). The “variability” approach relied on geospatial variables representing surface-water nutrient concentrations, factors affecting sources and transport of nutrients, model accuracy, and potential receptor impacts. One hundred and sixty-three drainage basins throughout the contiguous United States were ranked nationally and within 18 hydrologic regions. Nationally, the top-ranked basins from the impact approach were concentrated in the Midwest, while those from the variability approach were dispersed across the nation. Regionally, the top-ranked basin selected by the two approaches differed in 15 of the 18 regions, with top-ranked basins selected by the variability approach having lower minimum concentrations and larger ranges in concentrations than top-ranked basins selected by the impact approach. The highest ranked basins identified using the variability approach may have advantages for exploring how landscape factors affect surface-water quality and how surface-water quality may affect ecosystems. In contrast, the impact approach prioritized basins in terms of human development and nutrient concentrations in both surface water and groundwater, thereby targeting areas where actions to reduce nutrient concentrations could have the largest effect on improving water availability and reducing ecosystem impacts.

Microalgae-Based Remediation of Real Textile Wastewater: Assessing Pollutant Removal and Biomass Valorisation.

The textile industry generates highly contaminated wastewater. It severely threatens local ecosystems without proper treatment, significantly diminishing biodiversity near the discharge point. With rapid growth rates, microalgae offer an effective solution to mitigate the environmental impact of textile wastewater, and the generated biomass can be valorised. This study sets out to achieve two primary objectives: (i) to assess the removal of pollutants by Chlorella vulgaris from two distinct real textile wastewaters (without dilution) and (ii) to evaluate microalgal biomass composition for further valorisation (in a circular economy approach). Microalgae grew successfully with growth rates ranging from 0.234 ± 0.005 to 0.290 ± 0.003 d-1 and average productivities ranging from 78 ± 3 to 112.39 ± 0.07 mgDW L-1 d-1. All cultures demonstrated a significant reduction in nutrient concentrations for values below the legal limits for discharge, except for COD in effluent 2. Furthermore, the pigment concentration in the culture increased during textile effluent treatment, presenting a distinct advantage over conventional ones due to the economic value of produced biomass and pigments. This study underscores the promise of microalgae in textile wastewater treatment and provides valuable insights into their role in addressing the environmental challenges the textile industry poses.

Model of nitrogen-phosphorus ratio and phytoplankton relationship in lake Laut Tawar, Indonesia

Phytoplankton blooms in the lake cause ecological, economic, health, energy, and aesthetic losses. It reduces water quality and biota diversity, creates toxins in the waters, and changes the structures and functions of the ecosystem. The essential nutrients for the growth of phytoplankton are nitrogen and phosphorus. Controlling phytoplankton growth can be managed by controlling the limiting nutrient input. This study aims to identify the limiting nutrient, analyze variations in TN:TP ratio spatially and temporally, and model TN:TP ratio and chlorophyll-a relationship. This study used secondary data from previous studies, namely TN, TP, and chlorophyll-a observed monthly in seven stations purposively during a year. Rainfall data was also obtained from the previous study. Limiting nutrients were determined by Redfield theory, and data were analyzed by Spearman correlation, One-way ANOVA, Kruskal-Wallis, and regression analysis. The results showed phosphorus was a limiting nutrient for phytoplankton growth in Lake Laut Tawar. TN:TP ratio and chlorophyll-a did not vary spatially, indicating the lake surface waters were evenly mixed. The parameters varied temporally, expressing the influence of hydroclimatological factors, especially rainfall. Rainfall increases nutrient input to the lake, but only rain below 200 mm/month causes an increase in the concentration of nutrients in the lake. The rainfall above 200 mm/month increases lake water volume significantly, thereby reducing nutrient concentrations. TN:TP ratio and chlorophyll-a related negatively and formed a non-linear relationship with an empirical model Chlorophyll-a = 2770.285 (TN/TP)-1.871. Eutrophication of Lake Laut Tawar should be anticipated by controlling the anthropogenic phosphorus input.Keywords:AnthropogenicChlorophyll-aEutrophication,Limiting nutrientRainfall

Integrating transcriptome and metabolome to explore the growth-promoting mechanisms of GABA in blueberry plantlets.

Tissue culture technology is the main method for the commercial propagation of blueberry plants, but blueberry plantlets grow slowly and have long growth cycles under in vitro propagation, resulting in low propagation efficiency. In addition, the long culturing time can also result in reduced nutrient content in the culture medium, and the accumulation of toxic and harmful substances that can lead to weak growth for the plantlets or browning and vitrification, which ultimately can seriously reduce the quality of the plantlets. Gamma-aminobutyric acid (GABA) is a four-carbon non-protein amino acid that can improve plant resistance to various stresses and promote plant growth, but the effects of its application and mechanism in tissue culture are still unclear. In this study, the effects of GABA on the growth of in vitro blueberry plantlets were analyzed following the treatment of the plantlets with GABA. In addition, the GABA-treated plantlets were also subjected to a comparative transcriptomic and metabolomic analysis. The exogenous application of GABA significantly promoted growth and improved the quality of the blueberry plantlets. In total, 2,626 differentially expressed genes (DEGs) and 377 differentially accumulated metabolites (DAMs) were detected by comparison of the control and GABA-treated plantlets. Most of the DEGs and DAMs were involved in carbohydrate metabolism and biosynthesis of secondary metabolites. The comprehensive analysis results indicated that GABA may promote the growth of blueberry plantlets by promoting carbon metabolism and nitrogen assimilation, as well as increasing the accumulation of secondary metabolites such as flavonoids, steroids and terpenes.

95 Culture medium with reduced nutrient concentrations alters the mTORC1 and AMPK pathway activities in bovine blastocysts

95 Culture medium with reduced nutrient concentrations alters the mTORC1 and AMPK pathway activities in bovine blastocysts

Topsoil removal for Sphagnum establishment on rewetted agricultural bogs

Rewetting drained agricultural peatlands aids in restoring their original ecosystem functions, including carbon storage and sustaining unique biodiversity. 30–60 cm of topsoil removal (TSR) before rewetting for Sphagnum establishment is a common practice to reduce nutrient concentrations and greenhouse gas emissions, and increase water conductivity. However, the topsoil is carbon-dense and preservation in situ would be favorable from a climate-mitigation perspective. The effect of reduced TSR on Sphagnum establishment and nutrient dynamics on degraded and rewetted raised bogs remains to be elucidated. We conducted a two-year field experiment under Sphagnum paludiculture management with three TSR depths: no-removal (TSR0), 5–10 cm (TSR5), and 30 cm (TSR30) removal. We tested the effects of TSR on Sphagnum establishment and performance, nutrient dynamics, and hotspot methane emissions. After two years, TSR5 produced similar Sphagnum biomass as TSR30, while vascular plant biomass was highest in TSR0. All capitula nitrogen (N > 12 mg/g) indicated N-saturation. Phosphorus (P) was not limiting (N/P < 30), but a potential potassium (K) limitation was observed in year one (N/K > 3). In TSR0, ammonium concentrations were > 150 µmol/l in year one, but decreased by 80% in year two. P-concentrations remained high (c. 100 µmol/l) at TSR0 and TSR5, and remained low at TSR30. TSR30 and TSR5 reduced hotspot methane emissions relative to TSR0. We conclude that all TSR practices have their own advantages and disadvantages with respect to Sphagnum growth, nutrient availability and vegetation development. While TSR5 may be the most suitable for paludiculture, its applicability for restoration purposes remains to be elucidated. Setting prioritized targets when selecting the optimal TSR with peatland rewetting is pivotal.

Assessment of oceanographic conditions during the North Atlantic EXport processes in the ocean from RemoTe sensing (EXPORTS) field campaign

This manuscript presents an overview of NASA’s EXport Processes in the Ocean from Remote Sensing 2021 Field Campaign in the North Atlantic (EXPORTS NA) and provides quantitative and dynamical descriptions of the physical processes modulating water transformations during the study. A major programmatic goal was to conduct the sampling in a Lagrangian mode so that ocean ecological and biogeochemical changes can be observed independent from physical advective processes. To accomplish this goal, EXPORTS NA conducted a multi-ship, multi-asset field sampling program within a retentive, anticyclonic mode water eddy. Beneath depths of ∼ 100 m, Lagrangian sampling assets remained within the eddy core waters (ECWs) throughout the experiment, demonstrating that the ECWs within the mode water eddy were retentive. However, strong westerly winds from four storm events deepened the mixed layer (ML) of the surface core waters (SCWs) above the eddy’s mode water core by 25–40 m and exchanged some of the SCWs with surface waters outside of the eddy via Ekman transport. Estimates of flushing times ranged from 5 to 8 days, with surface exchange fractions ranging from 20 to 75 % and were consistent with particle tracking advected by combined geostrophic and Ekman velocities. The relative contributions of horizontal and vertical advection on changes in ECW tracers depended on the horizontal and vertical gradients of that tracer. For example, horizontal advection played a large role in ECW salinity fluxes, while vertical entrainment played a larger role in the fluxes of nutrients into SCW ML. Each storm injected nutrients and low oxygen waters into the ML, after which the surface ocean ecosystem responded by reducing nutrient concentrations and increasing %O2 saturation levels. Overall, ECW values of chlorophyll and POC were the largest at the onset of the field program and decreased throughout the campaign. The analysis presented provides a physical oceanographic context for the many measurements made during the EXPORTS NA field campaign while illustrating the many challenges of conducting a production-flux experiment, even in a Lagrangian frame, and the inherent uncertainties of interpreting biological carbon pump observations that were collected in a Eulerian frame of reference.

Impact of artificial mixing and oxygenation on bacteria in a water transfer reservoir: Community succession and the role in water quality improvement

Artificial mixing and oxygenation induced by water-lifting aerations (WLAs) have the potential to improve water quality in reservoirs. However, there is a limited understanding of the bacterial community composition, assembly, and mechanisms behind water quality improvement under the influence of WLAs, especially in a water transfer reservoir. Here, the dynamics and relationship between water quality, bacterial diversity, and composition during the pre-operation, in-operation, and post-operation stages of WLAs were analyzed using high-throughput sequencing technology to explore the effects of artificially regulated bacteria on water quality improvement. WLAs operation led to the elimination of water stratification, significant bottom oxygenation, and reduction in nutrient concentrations. In addition, the operation of WLAs significantly changed the bacterial community composition, with an increase in richness, negligible difference in diversity, and a significant increase in the abundance of species with pollutant degradation functions, resulting in a shift from stochastic to deterministic processes of the bacterial community assembly. As a result, enhancement of the dominant bacteria responsible for organic matter degradation and denitrification and suppression of the emergence of algae-related bacteria were observed during the WLAs operation, and the ecosystem stability improved. Multiple analyses indicated a direct correlation between artificial mixing and oxygenation; changes in the bacterial community; and the reduction of nitrogen, phosphorus, and permanganate index in the water column. This study provides novel insights into in situ water quality enhancement and a valuable reference for understanding bacterial change patterns under artificially intervened conditions in water transfer reservoirs.

Performance on nutritive solution utilization by Tarragon (Artemisia dracunculus L.) cultivated in hydroponic

The interest in species with multiple benefits and many molecules with potential uses in different areas of knowledge has recently grown. The demand generates the search for production to meet the needs in quantity and quality. The advantages of the hydroponic system in the cultivation of leafy and aromatic herbs are known. However, the efficiency information of what would be the most responsive nutrition for aromatic species deserves attention and further studies. Thus, the objective was to evaluate the response of tarragon plants submitted to different rates of nutrient solution. The following proportions of the nutritive solution for leaves were evaluated: I - 50%, II - 75%, III - 100%, and IV 125%. Such a solution was chosen as a standard due to the balance between nutrients and the wide use by hydroponic producers. Hydroponic cultivation is a good alternative to grown Tarragon. The 100% nutrient solution shows good performance for most of the characteristics evaluated. The 15% reduction provides maximum production of the fresh mass of shoots, however, it causes a reduction of 11.3% in the production of dry mass, 6% in the number of stems, and 3.4% in height, which would not be interesting to meet dry mass demand. For fresh consumption, a 25% reduction in nutrient concentration generates a drop of only 1.3% in the maximum fresh mass of tarragon in hydroponic cultivation.

Urbanization shifts long-term phenology and severity of phytoplankton blooms in an urban lake through different pathways.

Climate change can induce phytoplankton blooms (PBs) in eutrophic lakes worldwide, and these blooms severely threaten lake ecosystems and human health. However, it is unclear how urbanization and its interaction with climate impact PBs, which has implications for the management of lakes. Here, we used multi-source remote sensing data and integrated the Virtual-Baseline Floating macroAlgae Height (VB-FAH) index and OTSU threshold automatic segmentation algorithm to extract the area of PBs in Lake Dianchi, China, which has been subjected to frequent PBs and rapid urbanization in its vicinity. We further explored long-term (2000-2021) trends in the phenological and severity metrics of PBs and quantified the contributions from urbanization, climate change, and also nutrient levels to these trends. When comparing data from 2011-2021 to 2000-2010, we found significantly advanced initiation of PBs (28.6 days) and noticeably longer duration (51.9 days) but an insignificant trend in time of disappearance. The enhancement of algal nutrient use efficiency, likely induced by increased water temperature and reduced nutrient concentrations, presumably contributed to an earlier initiation and longer duration of PBs, while there was a negative correlation between spring wind speed and the initiation of PBs. Fortunately, we found that both the area of the PBs and the frequency of severe blooms (covering more than 19.8 km2 ) demonstrated downward trends, which could be attributed to increased wind speed and/or reduced nutrient levels. Moreover, the enhanced land surface temperature caused by urbanization altered the thermodynamic characteristics between the land and the lake, which, in turn, possibly caused an increase in local wind speed and water temperature, suggesting that urbanization can differently regulate the phenology and severity of PBs. Our findings have significant implications for the understanding of the impacts of urbanization on PB dynamics and for improving lake management practices to promote sustainable urban development under global change.

Rock phosphate improves nutrient uptake and oil accumulation in olive fruit

Phosphorus deficiency is one of the main constraints to olive production in alkaline soils. The high cost of phosphorus fertilizers may represent an insurmountable obstacle in many countries, leaving the exploitation of their own rock phosphate (RP) as the only low-cost and long-term alternative. The aim of this work was to study the long-term effect of agronomic application of RP (amounts applied: 150 kg ha−1) in a field of olive trees on specific microbial groups in the rhizosphere, nutrient uptake and oil accumulation in the fruit. The results revealed that agronomic application of RP increased the rhizosphere fatty acid methyl ester (FAME) biomarkers indicative of Gram-negative bacteria, fungi and actinobacteria. The level of FAME 16:1ω5 in rhizosphere decreased significantly after agronomic application of RP, indicating that the functioning of arbuscular mycorrhizas was altered. Decreased FAME 16:1ω5 due to RP amendment was not associated with a significant reduction of nutrient concentrations in the olive root; while a significant increase in root P and K contents was observed. However, the level of N did not appear to be significantly influenced. The experimental results also showed that RP-fertilized plants had significantly greater fruit weight and pulp/stone ratio. Fruits of RP-fertilized plants also had significantly higher oil content (+8.67% on average). Our results support the hypothesis that, following agronomic application of RP, the complex interactions of root and microbial community in the olive rhizosphere is a potential factor influencing oil accumulation in the olive fruit.

Woodland Establishment Reduces Nutrient Losses to Waterbodies in Urban Catchments: A Review of the Evidence

AbstractSystematic review of peer‐reviewed literature was undertaken to establish benefits of urban forests on reducing nutrient concentrations in adjacent or downstream waterbodies. Following screening, a small number of articles (40) were found relevant, representing studies quantifying non‐point source nutrient losses from urban and peri‐urban environments. Evidence was split between plot‐ and catchment‐scale. Plot‐scale studies often included evaluations of engineered nature‐based solutions. At catchment‐scale, studies of streamwater quality typically investigated influence of contributory catchment nutrient sources. Wide ranges of beneficial reductions were apparent, and at both scales not all studies identified significant benefits. Summarizing against this backdrop, at plot (micro‐) scale woodland reduces mean concentrations in runoff, soil or groundwater by an average of 44.2% for total nitrogen (TN) and 47.0% for total phosphorus (TP). At catchment (meso‐) scale, evidence suggests a 20% areal addition of forest at the expense of mixed urban fabric can reduce mean concentrations by 15.7% and 12.6% for TN and TP respectively. Additionally, some articles reveal potential drawbacks reducing benefits provided specifically by street trees and riparian woodland. Leaf litter falling on impervious surfaces can heighten risk of TP leaching to streams, but has little impact on TN. Riparian woodland was found to have complex water quality impacts. Canopy cover suppresses stream channel biological nitrogen uptake, which based on all evidence appears considerable. However, unshaded headwaters can foster accelerated primary productivity with undesirable downstream consequences. Overall, gathering further evidence is encouraged, given current uncertainties, especially to address differences between impervious, permeable and riparian urban woodland settings.

Effects of rainfall and land use on nutrient responses in rivers in the Brazilian semiarid region.

This paper investigated whether rainfall promotes dilution or increase in nutrient concentrations and which land use indicators are the main predictors of nutrients in intermittent rivers in a large Brazilian semiarid region. The total phosphorus (TP) and total inorganic nitrogen (TIN) were monitored between 2013 and 2018 at 92 river water quality monitoring sites. The monthly rainfall (Rn) was obtained from 575 rain gauges. Pearson's correlation (R) between Rn and nutrient concentration was performed. The correlation patterns were also analysed based on land use data: urban area (%), agricultural field area (%), demographic density (inhabitants/km2), sewer system coverage (%), and reservoir density (reservoir/km2). Backward stepwise regression was performed to identify predictors of nutrient concentrations. The results revealed a marginal effect of rainfall on nutrients when the effects of urbanisation outweigh all other aspects. However, in regions with greater accumulated rainfall and lower reservoir density, the rainfall was related to a linear increase in nutrient concentrations (R > 0.8). Contrastingly, in the basins with less accumulated rainfall and greater inter-basin hydrological disconnection, there was a linear reduction in nutrient concentration (R < - 0.5). In the backward stepwise regression, sewer system coverage and Rn had the greatest influence for TP, and the urban area was the strongest predictor for TIN. Importantly, our results demonstrated that in semiarid rivers in densely populated regions, there is no single pattern of variability in nutrient concentration, on a wide scale of assessment. Therefore, adaptative and decentralised management can be more effective in improving water quality in these regions.

Large root cortical cells and reduced cortical cell files improve growth under suboptimal nitrogen in silico.

Suboptimal nitrogen availability is a primary constraint to plant growth. We used OpenSimRoot, a functional-structural plant/soil model, to test the hypothesis that larger root cortical cell size (CCS), reduced cortical cell file number (CCFN), and their interactions with root cortical aerenchyma (RCA) and lateral root branching density (LRBD) are useful adaptations to suboptimal soil nitrogen availability in maize (Zea mays). Reduced CCFN increased shoot dry weight over 80%. Reduced respiration, reduced nitrogen content, and reduced root diameter accounted for 23%, 20%, and 33% of increased shoot biomass, respectively. Large CCS increased shoot biomass by 24% compared with small CCS. When simulated independently, reduced respiration and reduced nutrient content increased the shoot biomass by 14% and 3%, respectively. However, increased root diameter resulting from large CCS decreased shoot biomass by 4% due to an increase in root metabolic cost. Under moderate N stress, integrated phenotypes with reduced CCFN, large CCS, and high RCA improved shoot biomass in silt loam and loamy sand soils. In contrast, integrated phenotypes composed of reduced CCFN, large CCS, and reduced LRBD had the greatest growth in silt loam, while phenotypes with reduced CCFN, large CCS, and high LRBD were the best performers in loamy sands. Our results support the hypothesis that larger CCS, reduced CCFN, and their interactions with RCA and LRBD could increase nitrogen acquisition by reducing root respiration and root nutrient demand. Phene synergisms may exist between CCS, CCFN, and LRBD. CCS and CCFN merit consideration for breeding cereal crops with improved nitrogen acquisition, which is critical for global food security.

Understanding the relationship between nutrient availability and freshwater cyanobacterial growth and abundance

ABSTRACT Anthropogenic eutrophication is a well-established cause of cyanobacterial blooms in freshwaters. Early studies proposed eutrophication control focused on phosphorus (P) as the key limiting nutrient. The rationale was that nitrogen (N) limitation is alleviated by diazotrophic cyanobacteria that fix atmospheric N. However, more recently, studies suggest that the importance of N fixation may have been overstated, and some call for anthropogenic N control as well as P. Reducing nutrient concentrations below critical levels clearly reduces phytoplankton biomass, but increasing evidence shows that cyanobacterial species can adapt to low and variable nutrient conditions, outcompeting eukaryotic phytoplankton. Strategies supporting cyanobacterial dominance include (1) high affinity P uptake, (2) preferencing cellular storage of P over immediate metabolic utilization for growth, (3) alternation between N fixation and inorganic N utilization as needed, and (4) use of organic nutrients when inorganic nutrient supplies are limited. Predicting the ecological responses of cyanobacteria to nutrients therefore requires more complex models than the simple resource models using inorganic nutrients widely used for contemporary studies. Additionally, many ecological studies are not conducted on timescales relevant to understanding how nutrient fluxes drive physiological responses. We advocate for greater use of high-frequency automated measurements of nutrients and cyanobacteria to address the timescale issue. Additionally, field-based experimental studies focused on nutrient cycling, fluxes, and pools are needed to validate laboratory findings and extrapolate them to in situ conditions. The challenge is to undertake these studies at sufficient spatial and temporal scales to predict large-scale responses of cyanobacteria to nutrients.

Phenotypic Switch and Growth of Melanoma Spheroids in the Presence of Mast Cells: Potential Impact of Nutrient-starvation Effects.

Mast cells are abundant in melanoma tumors, and studies suggest that they can be either detrimental or protective for melanoma growth. However, the underlying mechanisms are not fully understood. Here, we adopted an established hanging-drop spheroid system to investigate how mast cells influence melanoma growth and phenotype in a 3-D context. To address the underlying mechanism, we conducted transcriptomic and pathway analyses. In the presence of mast cells or mast cell-conditioned medium, growth of melanoma spheroids was profoundly reduced. Transcriptomic analysis revealed that mast cell-conditioned medium had extensive effects on the gene-expression patterns of melanoma. Pathway analyses revealed profound effects on the expression of genes related to amino acid and protein metabolism. The conditioned medium also induced up-regulation of cancer-related genes, including adhesion molecules implicated in metastatic spreading. In line with this, after transfer to a Matrigel extracellular matrix milieu, spheroids that had been developed in the presence of mast cell-conditioned medium displayed enhanced growth and adhesive properties. However, when assessing the possible impact of nutrient starvation, i.e., reduced nutrient content in mast cell-conditioned medium, we found that the observed effects on growth of melanoma spheroids could potentially be explained by such a scenario. Our findings suggest that the phenotypic alterations of melanoma spheroids grown in the presence of mast cells or mast cell-conditioned media are, at least partly, due to nutrient starvation rather than to the action of factors secreted by mast cells. Our findings may provide insight into the effects on gene-expression events that occur in melanoma tumors under nutrient stress.

Nutrients and Saltwater Exchange as Drivers of Environmental Change in a Danish Brackish Coastal Lake over the Past 100 Years

Many northwest European lake systems are suffering from the effects of eutrophication due to continued loading and/or poor, ineffective management strategies. Coastal brackish lakes are particularly difficult to manage due to complex nitrogen, phosphorus, and salinity dynamics that may exert varying influence on lake biological communities, but long-term data on how these important and often biodiverse systems respond to change are rare. In this study, palaeolimnological data (including sedimentary parameters, diatoms, and plant macrofossils) and environmental monitoring data (for the last ~40 years) have been used to assess environmental change over the last 100 years in Kilen, a brackish lake in northwest Jutland, Denmark. Kilen has been regularly monitored for salinity (since 1972), TP (from 1975), TN (from 1976), and since 1989 for biological data (phytoplankton, zooplankton, and macrophytes), which allows a robust comparison of contemporary and paleolimnological data at high temporal resolution. The palaeolimnological data indicate that the lake has been nutrient rich for the last 100 years, with eutrophication peaking from the mid-1980s to the late 1990s. Reduced nutrient concentrations have occurred since the late 1990s, though this is not reflected in the sediment core diatom assemblage, highlighting that caution must be taken when using quantitative data from biological transfer functions in paleolimnology. Lake recovery over the last 20 years has been driven by a reduction in TN and TP loading from the catchment and shows improvements in the lake water clarity and, recently, in macrophyte cover. Reduced salinity after 2004 has also changed the composition of the dominant macrophyte community within the lake. The low N:P ratio indicates that in summer, the lake is predominately N-limited, likely explaining why previous management, mainly focusing on TP reduction measures, had a modest effect on the water quality of the lake. Despite a slight recovery, the lake is still nutrient-rich, and future management of this system must continue to reduce the nutrient loads of both TN and TP to ensure sustained recovery. This study provides an exceptional opportunity to validate the palaeolimnological record with monitoring data and demonstrates the power of using this combined approach in understanding environmental change in these key aquatic ecosystems.