Effects Of Limitation Research Articles

Large-Scale Simulation of a Shipping Speed Limitation Measure in the Western Mediterranean Sea: Effects on Underwater Noise

Underwater noise from shipping activity can impact marine ecosystems in the long term and at large scale. Speed limitation has been considered to reduce noise emission levels. In this article, the effects of speed limitation on shipping noise levels are investigated at high spatial resolution (5 arc-min) in the Western Mediterranean Sea. Scenarios of maximum speed limits of 10 kt and 15 kn are computed. The impact of a speed reduction is time-dependent and tends to redistribute sources of noise temporally, smoothing the contrasts existing in marine traffic at the daily scale. The effectiveness of the measure is evaluated over short successive time windows (6 h), allowing for capture of the dynamic of the effect of speed reduction. Several metrics are proposed to evaluate the effectiveness of speed reduction as a mitigation measure according to its temporal stability. This study illustrates complex phenomena related to (1) the increased vessel density in the speed limitation area due to longer navigation time and (2) deep-water and shallow-water propagations. The bathymetry and the local distribution of traffic are two elements of importance with respect to the effectiveness and the stability of the measure, whereas the traffic properties seem to impact the stability of the effect in particular, and deep waters seem to increase the effectiveness. This research shows the areas in which the proposed measure would be the most effective.

Nitrogen limitation and hydrogen peroxide act synergistically to enhance lipids accumulation via ROS/Ca2+ dependent mechanism in Chlorella sorokiniana

The main aim of the present study is to assess the effects of combined nitrogen limitation and hydrogen peroxide (H2O2) treatment on lipid accumulation in Chlorella sorokiniana. Furthermore, to study the regulative networks involved in the lipid accumulation of microalgae, the relationships between reactive oxygen species (ROS), Ca2+ and four lipogenic genes (mitogen-activated protein kinase: MAPK; heteromeric acetyl-CoA carboxylase beta subunit: accD; b-ketoacyl-ACP synthase III: KASIII; diacylglycerol acyltransferase: DGAT) were also analyzed. The results indicated that the contents of chlorophyll a, carbohydrate and protein were decreased, while the lipid content and levels of endogenous ROS, Ca2+ were increased under nitrogen limitation groups with H2O2 added. Further research indicated that the increased ROS level could affect lipid accumulation through lipogenic genes expression. In addition, the interplays of ROS and Ca2+ may be found. This study provides an effective strategy to improve the lipid accumulation in C. sorokiniana, and offers evidence of ROS, Ca2+ and lipogenic genes in the accommodation of lipid biosynthesis in microalgae under combined treatment of nitrogen limitation and H2O2.

Effects of sulfur and phosphorus concentration on the lipid accumulation and fatty acid profile in Chlorella vulgaris (Chlorophyta).

Nutrient deficiency induces a variety of cellular responses, including an increase in lipid accumulation in microalgae. Nitrogen starvation is the most studied deprivation. Here, we determine the effects of phosphorus and sulfur limitation on lipid accumulation in Chlorella vulgaris. A set of 9 experiments were performed, varying the initial concentration of these nutrients (set to 0, 50, and 100% of their original composition in Bold's basal medium). According to our results, the variation of P and S modified the specific growth rate, lag phase, and cell generation time. The ratio of 50%P and 0%S significantly increased the total lipid concentration. The fatty acid profile was dominated by C16:0, C18:0, and C18:1; a considerable increase in C20:5 was observed with 0%P and 50%S and 0%P and 100%S. Regarding neutral lipids, the response surface methodology (RSM) indicates that the maximum was observed when S was between 40 and 60% and P was between 95 and 100%. Therefore, the enhanced production of lipids caused by P and S limitation may contribute to the efficient oil production useful for algal biofuels.

Sublethal behavioral impacts of resource limitation and insecticide exposure reinforce negative fitness outcomes for a solitary bee

Contemporary landscapes present numerous challenges for bees and other beneficial insects that play critical functional roles in natural ecosystems and agriculture. Pesticides and the loss of food resources from flowering plants are two stressors known to act together to impair bee fitness. The impact of these stressors on key behaviors like foraging and nesting can limit pollination services and population persistence, making it critical to understand these sublethal effects. We investigated the effects of insecticide exposure and floral resource limitation on the foraging and nesting behavior of the solitary blue orchard bee, Osmia lignaria. Bees in field cages foraged on wildflowers at high or low densities, some treated with the common insecticide, imidacloprid, in a fully crossed design. Both stressors influenced behavior, but they had differential impacts. Bees with limited food resources made fewer, but longer foraging trips and misidentified their nests more often. Insecticide exposure reduced bee foraging activity. Additionally, insecticides interacted with bee age to influence antagonistic behavior among neighboring females, such that insecticide-exposed bees were less antagonistic with age. Our findings point towards mechanisms underlying effects on populations and ecosystem function and reinforce the importance of studying multiple drivers to understand the consequences of anthropogenic change.

环境筛选和扩散限制对长江流域湖北段湿地植物群落构建的共同影响

PDF HTML阅读 XML下载 导出引用 引用提醒 环境筛选和扩散限制对长江流域湖北段湿地植物群落构建的共同影响 DOI: 10.5846/stxb202201110110 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 湖北省教育厅项目（T201701）；湖北省科技厅项目（2020CFA005）；国家自然科学基金项目（31570366） Environmental filtering and dispersal limitation jointly affect wetland plant community assembly in Hubei section of the Yangtze River Basin Author: Affiliation: Fund Project: Project of Department of Education of Hubei Province(T201701); Project of Department of Science and Technology of Hubei Province(2020CFA005);Project of National Natural Science Foundation of China(31570366) 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:湿地植物群落构建机制的研究可为湿地生态系统管理和受损湿地生态恢复与重建提供重要理论依据。地处长江流域的湖北省是我国湿地资源最为丰富的地区之一，通过野外调查研究了长江流域湖北段内不同类型湿地中的主要湿地植物群落类型，分析了研究区内湿地植物群落物种β多样性格局；利用相关性检验（Mantel test）方法和基于相似或相异度矩阵的多元回归模型（MRM）分析了环境差异和地理距离与湿地植物群落的物种相异性的相关性，及其对该区域湿地植物群落构建的相对贡献率。结果表明长江流域湖北段8个不同类型湿地内的湿地植物群落物种相异性指数差异显著，群落间物种相异性指数与地理距离和环境距离均呈显著正相关关系；MRM分析表明环境筛选和扩散限制共同解释了研究区内群落物种变异指数的54.72%；其中，环境距离独立解释率为22.03%，地理距离独立解释率为9.98%，二者联合解释率为22.71%。结果表明环境筛选和扩散限制共同影响了长江流域湖北段湿地植物群落构建过程，且环境筛选贡献更大。建议除了考虑空间尺度、环境因子、植被类型外，未来需进一步研究时间尺度及人类干扰等因子对该区域湿地植物群落构建的影响。 Abstract:Studies on the mechanism of wetland plant community assembly can provide an important theoretical basis for wetland ecosystem management and ecological restoration and reconstruction of the damaged wetlands. There are very abundant wetland resources in Hubei Province located in the Yangtze River Basin. In this study, we investigated main wetland plant communities by conducting the field survey and analyzed the β-diversity of wetland plant community in Hubei section of the Yangtze River Basin. The correlation between species dissimilarity of wetland plant communities and environmental distance and geographic distance, and relative contribution of environmental differences and geographic distance for accounting for community assembly were tested, using the Mantel test method and a multiple regression model based on similarity or dissimilarity matrices. The results showed that the species dissimilarity index of wetland plant communities in eight different types of wetlands in Hubei section of the Yangtze River Basin were significantly differed. The species dissimilarity indexes among wetland communities significantly were positively correlated with geographical distance and environmental differences. MRM analysis showed that environmental filtering and diffusion limitation together explained 54.72% of the community species variability index in the study area. The independent effects of the two tested hypotheses above mentioned were 22.03% and 9.98%, respectively. Our findings implied that the combined effects of environmental filtering and diffusion limitation decided wetland plant community assembly in Hubei section of the Yangtze River Basin, and in comparison to diffusion limitation, the environmental filtering had stronger effects. We argue that other factors, such as time scale and interference, should be considered in a study of wetland plant community assembly, beside spatial scale, environmental factors, and vegetation types. 参考文献 相似文献 引证文献

Is there a species swarm paradox? Spatial segregation of related species in the understorey of a tropical plant community

AbstractQuestionIndividual plants of some highly diverse angiosperm families occur in aggregated spatial patterns in tropical plant communities, which have been defined as species swarms. Although this spatial aggregation seems paradoxical, because related species should segregate in space owing to expected ecological similarities, it has yet to be tested. We assessed whether species of the family Rubiaceae segregate in space in the understorey of a tropical plant community.LocationAn Atlantic Forest fragment in southeast Brazil.MethodsWe surveyed all local aggregates of Rubiaceae species within an 18.75‐ha plot across a topographic gradient. Based on the species abundance distribution, we used the 10 most abundant species to model their spatial patterns using univariate and bivariate spline spatial correlations. Bubble graphs were used to show how these species were distributed across the gradient.ResultsA total of 12,258 individuals of 47 species were found distributed in 543 local aggregates. The 10 studied species corresponded to 86% of the total abundance and were aggregated in space, at distances from 0 to 10–300 m. Pairwise comparisons revealed a segregation pattern at scales ranging from 0 to 10–230 m. Local aggregates were strongly dominated by a single species, whereas many other species occurred at very low abundances.ConclusionThe studied species of Rubiaceae shared the understorey environment by occupying different portions of available space. Habitat preferences, negative interactions, dispersal limitation and priority effects may explain the observed spatial patterns. Swarms are not paradoxical because species of Rubiaceae use different microhabitats within the forest understorey.

ПЕРЕШКОДИ У ДОСЯГНЕННІ КОНТРОЛЮ БРОНХІАЛЬНОЇ АСТМИ В КЛІНІЧНІЙ ПРАКТИЦІ В УМОВАХ ПАНДЕМІЇ COVID-19)

The main goals of bronchial asthma (BA) treatment are to achieve good symptoms control and to minimize future risk of asthma-related mortality, exacerbations, persistent airflow limitation and adverse effects of therapy. Despite the availability of effective treatments for asthma the real life asthma control is lower than expected. The aim of this study was to evaluate the barriers in achieving asthma control in clinical practice during the COVID-19 pandemic according to the literature data. There are both general and COVID-19-related barriers in achieving the goals of asthma treatment. In most patients, the causes for the lack of asthma control are incorrect inhaler technique, poor adherence to treatment, overuse of short-acting bronchodilators, comorbidities, the influence of adverse environmental conditions and psychosocial factors. The COVID-19 pandemic has affected the asthma control through quarantine restrictions and the influence of post-acute COVID-19 disorders. On the one hand, quarantine restrictions had a positive effect on the asthma course: there was a decrease in the seasonal respiratory viral infections and the asthma exacerbations frequency. On the other hand, asthma patients were significantly affected by the pandemic due to a high level of anxiety, stress and limited access to routine medical care. Health disorders in post-COVID-19 period negatively affect the control of BA. After recovery from acute COVID-19 a proportion of asthma patients experienced poorer control and required increased asthma maintenance therapy. Approaches to improving asthma control include adherence to established asthma management guidelines, patient and healthcare professional education, regular asthma monitoring and assessment, review of inhaler technique, provision of a written asthma action plan, use of digital technologies. Key words: bronchial asthma, asthma control, COVID-19.

Integrative analysis of transcriptome and metabolism reveals potential roles of carbon fixation and photorespiratory metabolism in response to drought in Shanlan upland rice

Shanlan upland rice is an important landrace rice resource and is characterized with high drought stress (DS) tolerance relative to cultivated rice. However, the molecular mechanism of DS response in Shanlan upland rice remains unclear. In this study, we performed an integrated analysis of transcriptome and targeted metabolism to decipher the key biological pathways that responded to drought tolerance using two Shanlan upland rice lines. Results show that SL10 possesses 64% higher photosynthetic efficiency (Pn) and 2-fold higher water use efficiency (WUE) than that in SL1 exposed to DS. The decrease in Pn by DS is not due to stomatal limitation effects for SL1. Transcriptome analysis suggests photosynthesis relevant pathways (photosynthesis-antenna proteins and carbon fixation) and photorespiration relevant pathway (glycine, serine and threonine metabolism) in SL1 under DS were significantly enriched in the down-regulated and up-regulated DEGs list, respectively. There are 412 up-regulated and 233 down-regulated drought responsive genes (DRGs) in SL10 relative to SL1 induced by DS. Targeted metabolism results suggest that the contents across five metabolites related to carbon fixation pathway were declined by 36 and 8% in SL1 and SL10 caused by DS, respectively. We finally summarized the both gene expression and metabolites involved in photorespiration and carbon fixation pathways in response to DS in both rice lines. This study provides valuable information for better understanding the molecular mechanism underlying drought tolerance in Shanlan rice.

Influence of Substrate on the Fermentation Characteristics and Culture-Dependent Microbial Composition of Water Kefir

Water kefir is a sparkling fermented beverage produced by fermenting water kefir grains in a sucrose solution containing dried fruits or fruit extracts. The objective of this study was to investigate the influence of substrate composition on the fermentation kinetics and culture-dependent microbial composition of water kefir. First, the impact of different fruit substrates and nitrogen limitation was examined. Fermentation of different fruit-based media with a single water kefir culture demonstrated that the substrate mainly influenced the type and ratio of the organic acids produced. These organic acid profiles could be linked to the culture-dependent microbial composition. In addition, the microbial composition and the associated dominant microorganisms observed were influenced by the water kefir fermentation conditions. Investigation of the effect of nitrogen limitation on the fermentation kinetics of several water kefir cultures showed that under such conditions, the fermentative capacity of the cultures declined. However, this decline was not immediate, and specific water kefir microorganisms may have enabled some cultures to maintain a higher fermentative capacity for longer. Thus, the water kefir fermentation kinetics and characteristics could be linked to the substrate composition, microorganisms present, and the process conditions under which the fermentations were performed.

Dietary sterol availability modulates heat tolerance of Daphnia

Abstract The increasing frequency and intensity of summer heatwaves are pushing freshwater zooplankton towards their upper thermal tolerance limits. At the same time, higher temperatures and prolonged water column stratification can favour the dominance of cyanobacteria in phytoplankton. Even when not toxic or grazing resistant, these prokaryotes lack phytosterols as essential precursors for cholesterol, the main sterol in animal tissues. Cholesterol plays a crucial role in the physiological adaptation of ectotherms to high temperature. Therefore, the shift to cyanobacteria‐dominated systems may increase the vulnerability of zooplankton to heatwaves by intensifying cholesterol limitation. Here, we used death time curves that take into consideration the intensity and duration of a thermal challenge and a dynamic model to study the effects of cholesterol limitation on the heat tolerance of the keystone species Daphnia magna and to simulate the cumulative mortality that could occur in a fluctuating environment over several days of heatwave. We show that increasing cholesterol limitation does not affect the slope between time‐to‐immobilisation and temperature, but does decrease the maximal temperature that Daphnia can withstand by up to 0.74°C. This seemingly small difference is sufficient to halve the time individuals can survive heat stress. Our simulations predicted that, when facing heatwaves over several days, the differences in survival caused by cholesterol limitation build up rapidly. Considering the anticipated intensity and duration of future (2070–2099) heatwaves, cholesterol limitation could increase mortality by up to 45% and 72% under low and medium greenhouse gas emission scenarios, respectively. These results suggest that the increasing risk of cholesterol limitation due to more frequent cyanobacterial blooms could compromise the resistance of zooplankton populations to future heatwaves. More generally, this study shows the importance of considering the nutritional context in any attempt to predict ectotherm mortality with increasing temperatures in the field.

Polymer Composites with Self-Regulating Temperature Behavior: Properties and Characterization.

A novel conductive composite material with homogeneous binary polymer matrix of HDPE (HD) and LLDPE (LLD), mixed with conductive filler consisting of carbon black (CB) and graphite (Gr), was tested against a HDPE composite with a similar conductive filler. Even the concentration of the conductive filler was deliberately lower for (CB + Gr)/(LLD + HD), and the properties of this composite are comparable or better to those of (CB + Gr)/HD. The kinetic parameters of the ρ-T curves and from the DSC curves indicate that the resistivity peak is obtained when the polymer matrix is fully melted. When subjected to repeated thermal cycles, the composite (CB + Gr)/(LLD + HD) presented a better electrical behavior than composite CB + Gr)/HD, with an increase in resistivity (ρmax) values with the number of cycles, as well as less intense NTC (Negative Temperature Coefficient) effects, both for the crosslinked and thermoplastic samples. Radiation crosslinking led to increased ρmax values, as well as to inhibition of NTC effects in both cases, thus having a clear beneficial effect. Limitation effects of surface temperature and current intensity through the sample were observed at different voltages, enabling the use of these materials as self-regulating heating elements at various temperatures below the melting temperature. The procedure based on physical mixing of the components appears more efficient in imparting lower resistivity in solid state and high PTC (Positive Temperature Coefficient) effects to the composites. This effect is probably due to the concentration of the conductive particles at the surface of the polymer domains, which would facilitate the formation of the conductive paths. Further work is still necessary to optimize both the procedure of composite preparation and the properties of such materials.

Physiological conditions favorable to domoic acid production by three Pseudo-nitzschia species

Twenty-six species of the cosmopolitan genus Pseudo-nitzschia can produce domoic acid (DA), a neurotoxin responsible for amnesic shellfish poisoning (ASP). To improve knowledge on this issue, we studied the physiological conditions favorable to DA production and accumulation by three Pseudo-nitzschia species from French coastal waters: P. australis, P. pungens, and P. fraudulenta. They were grown in batch cultures under silicate limitation to characterize their physiological traits and calculate their DA production rates. Three strains were studied per species to consider intraspecific diversity and better characterize interspecific differences. DA production was not influenced by growth or silicate limitation in any of the three species. In contrast, silicate limitation in the stationary phase led to DA accumulation by inhibiting cell division, while DA production was still active. The maximum cellular DA (cDA) production rate was 2.95 pg cell−1 d−1 for P. australis, 0.07 pg cell−1 d−1 for P. pungens, and 0.03 pg cell−1 d−1 for P. fraudulenta. The physiological conditions favorable to cDA production and accumulation by P. australis and P. pungens differed. The three species presented similar growth rates, but P. australis had higher photosynthetic capacities that could partly explain its higher DA production potential. The cDA production and the net dissolved DA (dDA) production in the culture medium were favored by different growth conditions. The cDA production to net dDA production ratio was species specific, with P. pungens excreting proportionally more of its produced DA. These laboratory results on cultures imply that cDA production and net dDA production can occur during all phases of P. australis, P. pungens, and P. fraudulenta blooms. The interactions between the species composition of the bloom, the species-specific capacity for DA production, and the effect of silicate limitation – among other factors – on DA cell quotas drive the toxigenicity of Pseudo-nitzschia blooms.

Sulfate supplementation affects nutrient and photosynthetic status of Arabidopsis thaliana and Nicotiana tabacum differently under prolonged exposure to cadmium

Hydroponic experiments were performed to examine the effect of prolonged sulfate limitation combined with cadmium (Cd) exposure in Arabidopsis thaliana and a potential Cd hyperaccumulator, Nicotiana tabacum. Low sulfate treatments (20 and 40 µM MgSO4) and Cd stress (4 µM CdCl2) showed adverse effects on morphology, photosynthetic and biochemical parameters and the nutritional status of both species. For example, Cd stress decreased NO3- root content under 20 µM MgSO4 to approximately 50% compared with respective controls. Interestingly, changes in many measured parameters, such as chlorophyll and carotenoid contents, the concentrations of anions, nutrients and Cd, induced by low sulfate supply, Cd exposure or a combination of both factors, were species-specific. Our data showed opposing effects of Cd exposure on Ca, Fe, Mn, Cu and Zn levels in roots of the studied plants. In A. thaliana, levels of glutathione, phytochelatins and glucosinolates demonstrated their distinct involvement in response to sub-optimal growth conditions and Cd stress. In shoot, the levels of phytochelatins and glucosinolates in the organic sulfur fraction were not dependent on sulfate supply under Cd stress. Altogether, our data showed both common and species-specific features of the complex plant response to prolonged sulfate deprivation and/or Cd exposure.

Effects of nitrogen limitation on Leymus Chinensis clonal growth form and bud bank

Nitrogen is an important element which affects the growth and clonal growth of plant species in grassland. Leymus chinensis (Trin.) Tzvel is a dominant species in grasslands with a high nutritional quality; however, data on the effects of low nitrogen concentration on L. chinensis clonal growth strategy are limited. The aim of this study is to evaluate the response of clonal growth of L. chinensis to low nitrogen concentrations. The growth form and biomass allocation ratios of L. chinensis under different low nitrogen concentrations were evaluated, and the quantitative characteristics of three bud types were analyzed. The proportion of spreading ramets was favored by low nitrogen supply, indicating that L. chinensis under low nitrogen conditions primarily exhibits a guerrilla growth form, meaning a long mean spacer length and production of spreading ramets. Under limited nitrogen conditions, biomass distribution was mainly concentrated in underground organs (including the roots and rhizomes), while the high proportion of axillary rhizome buds suggested that L. chinensis grows primarily by occupying effective living spaces under low nitrogen conditions. The balance between two clonal growth form and the change in the proportion of different types of buds is an important strategy for L. chinensis to cope with nutrient limitations.

Feedback control of actuation‐constrained moving structure carrying Timoshenko beam

AbstractThis article deals with tracking control and active vibration suppression of a hybrid rigid‐elastic vibrational mobile system with a nonlinear elastic foundation in the presence of actuator bandwidth limitation and control input saturation. The system consists of a rigid rectilinearly mobile frame on an elastic foundation, and a flexible Timoshenko beam clamped to it with a heavy attached concentrated mass. The hybrid partial differential equation (PDE)‐ordinary differential equation (ODE) system of the plant is obtained using Hamilton's principle and then is converted to a system of ODEs using the assumed mode method (AMM). Next, the model will be discretized in the time domain using the two‐step Adams‐Bashforth technique. Considering the first‐order dynamics to cover the bandwidth limitation of the actuator, a discrete‐time sliding mode controller (DSMC) is designed based on a positive definite Lyapunov functional. Following that, an innovative optimal predictive algorithm is proposed to compensate for the effects of input saturation. The proposed algorithm is based on a positive definite cost function and using an intelligent regime of optimizations and decisions, minimizes the cost function in a predefined prediction horizon. The vibratory behavior of the system also is included in the mentioned cost function. Consequently, the overall control scheme called optimal rigid‐elastic interaction control (OREIC) will be able to follow the desired tracking trajectory, suppress the beam vibrations, and compensate for the effect of bandwidth limitation as well as the effect of input saturation. The performance of the OREIC algorithm is compared with a saturated DSMC controller and the simulation results demonstrate the efficiency of the method in vibration control of mobile rigid‐elastic systems subjected to actuator bandwidth frequency and saturation limitations.

Polyhydroxybutyrate production in one-stage by purple phototrophic bacteria: Influence of alkaline pH, ethanol, and C/N ratios

This work aimed to evaluate the effect of alkaline pH, nutrient limitation, nitrogen source, C/N ratio, and ethanol addition on polyhydroxybutyrate (PHB) production by a photoheterotrophic mixed culture enriched in Rhodopseudomonas palustris. The results demonstrated the natural alkalinization of the culture medium was enough to induce PHB accumulation in the mixed culture. The combination of alkaline pH, nitrogen, sulfur, or phosphate deficiency negatively affected polymer production. The incorporation of glutamate for biomass synthesis was better than that of ammonium, which had a positive effect on PHB production. Interestingly, ethanol addition improved the PHB accumulation by 25 %, but without consumption. PHB production improved at low C/N ratios, where 27 ± 0.9% of the carbon source was transformed into biopolymers. The evaluated factors allowed the biomass PHB content to increase by 60%, reaching PHB production of 219 ± 5 mg/L. The PHB production by the photoheterotrophic mixed culture is associated with growth, allowing the PHB production in one stage. That has significant advantages in technical-practical terms, such as reducing the time of the process, dispensing with the separation of biomass from the feast phase to the famine phase, and requiring a single reactor.

Effects of nutrient limitation on cell growth, exopolysaccharide secretion and TEP production of Phaeocystis globosa

Phaeocystis globosa (P. globosa) often colonizes and produces mucus, which may cause massive blooms in coastal areas. To understand mechanism of the growth and the impact factors for better control of the bloom, we conducted a laboratory experiment on the effect of nitrogen (N) or phosphorus (P) limitation on the cell growth, production of exopolysaccharide (EPS), and transparent exopolymeric particles (TEP) of P. globosa. Results show no obvious differences in the N- and/or P-limitation in TEP production, polysaccharide secretion, and colony growth of P. globosa. Particularly in the death phase of the algae growth, the TEP production level in the experiment differed significantly, and was higher in the P-limitation group than that in the N-limitation group; additionally, the P-limitation group produced a relatively higher amount of EPS than N-limitation group, with greater cellular chlorophyll-a content, and in greater photosynthetic reaction rate of P. globosa cells, than those of the N-limitation group. However, under N-limited conditions, the algae colony survived longer. Under P-limited condition, P. globosa cells spend the photosynthesis-produced substances and energy for the secretion of extracellular substances but for cell reproduction, which was indicated by P. globosa cell growth and carbon content ratio between TEP and biomass.

Effect of phosphorus limitation on Se uptake efficiency in the microalga Nannochloropsis oceanica

Microalgae are considered an efficient accumulator and promising source of Se for feed additive purposes. This study aimed at investigating, for the first time, the effect of phosphorus limitation on Se accumulation and uptake efficiency in N.oceanica. A range of phosphorus concentrations (0–2470 µM) were tested in either the presence or absence of sodium selenite (0, 5, 30 µM). Se accumulation was increased up to 16-fold and Se uptake efficiency was increased up to 3.6-fold under phosphorus growth-limiting concentrations. N.oceanica was then cultivated in a 1.8L flat-panel photobioreactor in batch operation under two phosphorus growth-limiting concentrations (250 and 750 µM) where the accumulation of Se in the microalgal biomass, as well as its presence in the spent medium were analysed. This study is the first to investigate the effect of phosphorus limitation for increasing Se accumulation in microalgae, and to prevent the release of Se in wastewater.

Phosphorus limitation determines the quality of dissolved organic matter released by marine heterotrophic prokaryotes

AbstractWe determined phosphorus (P) limitation effect on the quantity and quality of dissolved organic matter (DOM) released by heterotrophic prokaryotes (HP). We grew two single‐bacterial strains from different lifestyles, the copiotrophic Photobacterium angustum and the oligotrophic Sphingopyxis alaskensis, and natural HP communities collected in fall and spring from the Mediterranean Sea, on glucose under two treatments: P‐replete versus P‐limiting. DOM release by HP comprised up to 30% of the initial carbon provided for growth. P‐availability influenced carbon allocation to different cellular processes (respiration vs. growth), but did not significantly affect the net quantity of DOM released by HP. However, using fluorescence spectroscopy, we demonstrated an effect of P‐limitation on DOM quality, with a predominance of humic‐like compounds under P‐limitation but protein‐like compounds under P‐repletion. Our results suggest that P‐limitation could determine the fate of HP‐derived DOM in the ocean, thus affecting the microbial carbon pump.

Climate and forest loss interactively restructure trait composition across a human-modified landscape.

Traits determine species response to climate conditions and the match between phenotypes and climate mediates spatial variation in species composition.These trait-climate linkages can be disrupted in human-modified landscapes. Human land use creates forest fragments where dispersal limitation or edge effects exclude species that may otherwise suit a given macroclimate. Furthermore, stressful macroclimate can limit viable trait combinations such that only a subset of values of any given trait occurs with respect to another trait, resulting in stronger trait covariance. Because forest loss can compound climatic stress, trait covariance from benign to harsher climates is expected to be stronger in fragments compared to contiguous forests. In a wet tropical forest landscape in the Western Ghats Biodiversity Hotspot of peninsular India, I compared fragments with adjacent contiguous forests for signatures of trait-mediated assembly of tree communities. Using four key plant traits-seed size, specific leaf area (SLA), wood density, and maximum height-I evaluated trait-abundance associations and trait covariance across climate, soil, and elevation gradients. In the contiguous forest, smaller-seeded, shorter, thinner-leaved species became more abundant from low to high elevations. In fragments, species with higher SLA were more abundant at sites with more seasonal climates and lower precipitation, and larger seeded species were less abundant at warmer sites. However, traits only weakly predicted abundances in both habitats. Moreover, only contiguous forests exhibited significant compositional change via traits, driven by trait syndromes varying along a composite gradient defined by elevation, water deficit, and soil C:N ratio. Site-level trait covariance revealed that warmer, wetter conditions in fragments favored taller species for given seed size, as compared to similar conditions in contiguous forests. Overall, trait syndromes and trait covariance, rather than single traits, determined the phenotypes best suited to macroclimate conditions and should inform management or restoration goals in fragments.