Decrease In Nutrient Availability Research Articles

Nutrient limitation shortly before harvest promotes high accumulation of antioxidants in lettuce

AbstractPlants exposed to drought not only have to cope with a shortage of water, but also with a simultaneous decrease in nutrient availability. In this greenhouse experiment, the responses of antioxidants and key metabolites to 2 or 4 days of water limitation immediately prior to harvest were compared to the effect of nutrient limitation with continued water supply in lettuce leaves. Water limitation led to a faster increase in stress intensity than nutrient limitation. While moderate drought stress led to a slight increase in the antioxidant compounds studied, there was a concomitant sharp decrease in starch content. Under nutrient limitation, an increase in the content of ascorbic acid, the proportion of reduced ascorbic acid and the content of phenolic compounds, flavonoids, soluble sugars and starch was observed in the mild phase of stress. These results suggest that reducing nutrient availability shortly before harvest could be a suitable means of improving the nutritional value of crops through cultivation practices as opposed to breeding.

Influence of Vinasse and Mechanized Harvesting on the Physical and Chemical Aspects of Soil in Paudalho Municipality - PE

Sugarcane cultivation methods and processes usually have negative impacts on the environment. However, this industry has been seeking more sustainable technologies, ranging from the adequate disposal of the organic residues produced to the elimination of pre-harvest burning and introduction of mechanized harvest. The objective of this work was to verify the influence of vinasse application and mechanized harvesting on the physical and chemical aspects of a dystrophic Red Yellow Argisol of medium texture, cultivated with sugarcane. For this, a field experiment in a Completely Randomized Design, with a factorial scheme was conducted. Four management treatments, with three replications, were evaluated: T1 - Without application of vinasse, burned cane followed by manual harvest, without irrigation; T2 - With application of vinasse, mechanized harvest, without irrigation; T3 - With application of vinasse, mechanized harvest, with irrigation; T4 - With application of vinasse, burned cane followed by manual harvest, without irrigation. Soil samples were collected in three depths (0 – 20 cm, 20 – 40 cm and 40 – 60 cm) and soil physical and chemical characteristics were determined. The data obtained were submitted to ANOVA and compared by the Tukey test (p≤0.05) of probability, using the statistical program ASSISTAT 7.7 beta. The results showed that fertigation with vinasse did not influence soil density, particle density, and total porosity. However, mechanized harvesting increased soil density and total porosity. The soil in the experimental unit without vinasse application presented a more acidic pH and high levels of aluminum saturation, causing a decrease in the availability of nutrients, and the soils treated with vinasse had an increase in nutrient availability. Therefore, the addition of vinasse can be an important strategy in maintaining and increasing long-term soil fertility in sugarcane cropping systems.

Carbon content and other soil properties of near-surface peats before and after peatland restoration.

Peatland restoration usually aims at restarting the peatlands' function to store carbon within peat. The soil properties of the near-surface peat can give a first understanding of this process. Therefore, we sampled pH value, total organic carbon content (TOC), total nitrogen content (TN), C/N ratio as well as dry bulk density (BD), and describe the structure of near-surface peats in six restored fens in North-East Germany before (2002-2004) and after (2019-2021) restoration. Before restoration, the study sites showed peat degradation to various extents in their near-surface peats. pH values remained relatively stable over time. Comparing the degraded peat horizons, TOC increased significantly in four study sites, ranging from 35.7% to 47.8% in 2002-2004 and from 42.5% to 54.0% in 2019-2021. TN varied from 1.5% to 3.5% in 2002-2004 and from 1.8% to 3.2% in 2019-2021, but changes were only significant in one site, showing a slight decrease. In three sites, the increase in C/N ratio was significant, indicating lower nutrient availability. BD ranged from 0.08 to 0.48 g/cm3 in 2002-2004 and from 0.10 to 0.16 g/cm3 in 2019-2021, decreasing significantly in four sites. The structure of the degraded peat horizons changed after restoration to a more homogenous, sludge mass with larger re-aggregates. In three sites, new peat moss peat layers above the degraded soil horizon were present in 2019-2021, with a mean thickness of 6.8 to 36.1 cm. The structure was comparable to typical, slightly decomposed peat moss peat. Our findings suggest that within about 17 years after fen restoration, and thereby a water table rise close to surface, TOC of the near-surface peats increased to values that are typical for undisturbed peatlands. This indicates that restoration can lead to the re-establishment of peatlands as potential carbon sinks, with TOC within the near-surface peat as one key factor in this process. Further, we assume that the decrease in nutrient availability, decrease of BD, and new, undisturbed peat layers can favor the establishment of mire-specific biodiversity and support ecosystem services similar to near-natural mires.

Effect of temperature and Q10 values of acid phosphatase activity in alfisols and vertisols of Andhra Pradesh

The enzyme phosphatase plays an important role in the mineralization of organically bound P that leads to absorption of P by the plants. Phosphatases are inducible enzymes that are produced predominantly under conditions of low phosphorus availability. The abiotic enzymes present in the soil play an important role in catalyzing several important reactions necessary for the life processes of microorganisms in soils and thereby stabilizing the soil structure, the decomposition of organic wastes, organic matter formation, and nutrient cycling. When the temperatures are increased due to various changes caused by global warming it has a profound influence on soil enzymes. Every enzyme has its optimum temperature below which the enzyme activity is less due to inactivation. Further, with an increase in temperature the enzymes get denatured and result in a decrease in nutrient availability and indirectly affecting productivity. To study the effect of temperature on soil enzyme activity, four alfisols and four vertisols were collected and labortory incubation studies were carried out at different temperatures ranging from 20oC to 90oC. The acid phosphatase activity (µg of 4-nitrophenol g-1 soil h-1) ranged from 62.3 to 516.4 in alfisols while in vertisols the activity varied from 35.1 to 486.0. Temperature coefficient values (Q10) were calculated in the temperature range of 20 to 90oC. These values depending on the type of soil varied from 0.42 to 1.91 in alfisols and 0.36 to 1.95 in vertisols.

Effects of ammonia nitrogen and organic carbon availability on microbial community structure and ecological interactions in a full-scale partial nitritation and anammox (PN/A) system

Nutrient availability significantly impacts microbial biosynthesis, cell growth, and cell cycle progression. In this study, a full-scale plug-flow partial nitritation/anammox (PN/A) system was used to investigate variations in the microbial community structure in both immobilized carriers and flocs, as well as a gradual decrease in nutrient availability from upstream to downstream. We found that reduced ammonia nitrogen (from 150.4 to 30.6 mg/L) and organic carbon (from 415.7 to 342.8 mg/L) availability significantly lowered microbial diversity and altered microbial communities in biofilms other than flocs from upstream to downstream. The abundance of all anammox bacteria increased by 1.97 times, from 3.25×1010 to 6.40×1010 copies per gram of wet sludge, in the biofilm core microbiome. Furthermore, from upstream to downstream, taxa with lower ribosomal RNA operon copy numbers were consistently enriched in both biofilm and floc communities, indicating that slow-growing microorganisms are more likely to be enriched in low-nutrient environments. Rare taxa with a relative abundance of less than 0.1% exhibited unique metabolic functions, including amino acid, carbohydrate, cofactor, and vitamin metabolisms, which was inferred by PICRUST2 and persisted across the nutrient gradient in both the biofilm and floc communities. Despite their low abundance, they may play important roles in mediating the stability and function of the PN/A system. Overall, the results demonstrate the impact of a naturally formed ammonia nitrogen and organic carbon gradient in a full-scale plug-flow PN/A installation on nutrient availability and its effects on microbial diversity, community composition, and microbial interactions, which expands our fundamental understanding of this energy-efficient and promising biotechnology for treating high-strength ammonium wastewater.

Effect of Temperature on Alkaline Phosphatase Activity in Alfisols and Vertisols of Andhra Pradesh

Soil enzymes play an important role in catalyzing several important reactions necessary for the life processes of microorganisms in soils thereby stabilizing the soil structure, the decomposition of organic wastes, organic matter formation, and nutrient cycling. Alkaline phosphatase belongs to the group of Phosphomoesterases and helps in the mineralization of phosphorus from organic form. The activity of enzymes in soils is influenced by the temperature, moisture and pH of soil. The temperature increase caused by global warming have a profound influence on soil enzymes. Every enzyme has its optimum temperature below which the enzyme activity is less due to inactivation. Further, with an increase in temperature, the enzymes get denatured resulting in a decrease in nutrient availability and indirectly affecting productivity. To study the effect of temperature on soil enzyme activity, four alfisols and four vertisols were collected and laboratory incubation studies were carried out at different temperatures ranging from 20oC to 90oC. The alkaline phosphatase activity (µg of 4-nitrophenol g-1 soil h-1) ranged from 23.08 to 120.55 in alfisols while in vertisols the activity varied from 66.58 to 536.88. Temperature coefficient values (Q10) were calculated in the temperature range of 20 to 90oC. These values depend on the type of soil which varied from 0.31 to 1.88 in alfisols and 0.38 to 1.92 in vertisols

Impact of Aluminium on Nutrient Profile of Soil under Various Genotypes of Garden Pea

The aim of this study was to examine the influence of Al on nutrient profile of soil grown with various pea genotypes. The study involved growing two tolerant pea (Kashi Samrath and Kashi Samridhi) and two susceptible (Matar Ageta-7 and AP-3) genotypes with increasing added rate of Al (0, 12 ppm and 24 ppm) in soil. Al application in soil resulted in significant decrease in nutrient availability of soil mainly nitrogen, phosphorus and potassium. The addition of Al caused decrease in soil pH causing a negative effect on the yield of susceptible pea genotypes. However, in tolerant genotypes, there was no significant effect on yield, despite a decrease in soil pH and an imbalance of nutrients.

Escherichia coli Lrp Regulates One-Third of the Genome via Direct, Cooperative, and Indirect Routes.

The global regulator Lrp plays a crucial role in regulating metabolism, virulence, and motility in response to environmental conditions. Lrp has previously been shown to activate or repress approximately 10% of the genes in Escherichia coli However, the full spectrum of targets, and how Lrp acts to regulate them, have stymied earlier study. We have combined matched chromatin-immunoprecipitation sequencing (ChIP-seq) and RNA sequencing (RNA-seq) under nine physiological conditions to comprehensively map the binding and regulatory activity of Lrp as it directs responses to nutrient abundance. In addition to identifying hundreds of novel Lrp targets, we observe two new global trends, as follows: first, that Lrp will often bind to promoters in a poised position under conditions when it has no regulatory activity to enable combinatorial interactions with other regulators, and second, that nutrient levels induce a global shift in the equilibrium between less-sequence-specific and more-sequence-specific DNA binding. The overall regulatory behavior of Lrp, which as we now show extends to 38% of E. coli genes directly or indirectly under at least one condition, thus arises from the interaction between changes in Lrp binding specificity and cooperative action with other regulators.IMPORTANCE To survive, bacteria such as E. coli must rapidly respond to changing environmental conditions, including nutrient levels. A decrease in nutrient availability causes bacteria to stop rapid replication and enter stationary phase, where they perform limited to no cell division. The E. coli global regulatory protein Lrp has been previously implicated in modulating the expression of genes particularly important at this transition from rapid to slowed growth. Here, we monitor Lrp's DNA binding locations and effect on gene expression under three different nutrient conditions across three growth stages. We find that Lrp's role is even broader than previously suspected and that it appears to interact with many other bacterial regulators to perform its function in a condition-specific manner.

Seasonal flux patterns of planktonic foraminifera in a deep, oligotrophic, marginal sea: Sediment trap time series from the Gulf of Aqaba, northern Red Sea

Annual and interannual planktonic foraminifera (PF) fluxes, species assemblage composition, vertical distribution (0–600 m) and shell-size-distribution (63–125, 125–500, 500–1000 µm) were characterized in the marginal oligotrophic Gulf of Aqaba (GOA), northern Red Sea, between January 2014 and February 2016 using a monthly resolved sediment trap time series.PF fluxes in the GOA demonstrate strong seasonality, with low values observed during summer months, gradually increasing during the autumn-winter. This increase is coeval with decreasing sea-surface temperatures and deepening of the mixed layer depth in the GOA that drives the admixing of nutrient-replete subsurface waters into the mixed layer. This in turn, triggers an increase in primary productivity, expressed by enhanced chlorophyll-a concentrations.Spinose species constitute the majority of the PF assemblage. The dominant shell size-fraction is between 63 and 125 µm (~86% of the total flux), which has generally been overlooked in previous studies, resulting in a significant knowledge gap related to the neanic stages and the small-adult-size PF. Indeed, the 63–125 µm size-fraction is dominated by the smallest species Turborotalita clarkei (36–92% of this size fraction). The 125–500 µm size-fraction (~13%) is dominated by the species Globigerinoides ruber, while less than 1% of the shells are in the range of 500–1000 µm, dominated by Orbulina universa.Over the last few decades, the already low number of PF species decreased in the GOA from 13 to 10, including the disappearance of Trilobatus sacculifer, the most common species in the GOA during the 1970s. This finding could reflect the sensitivity of the geographic location of the GOA, at the edge of a > 2000 km transect that begins in the productive Arabian Sea, and spans across the Red Sea, where a gradual decrease in nutrient availability and increase in surface salinity imposes a corresponding decrease in PF species richness, abundances and diversity. Thus, the northern GOA is an extreme case of an oligotrophic system whose ecosystem is already pre-screened by the Red Sea transect. Combined with previous episodes of Trilobatus sacculifer disappearance identified in downcore records in the Red Sea, we conclude that the change in the PF community over recent decades is probably not the result of local eutrophication processes, as has been suggested in recent studies, but rather, more likely reflects environmental changes on a larger regional to global scale.

Coral bleaching is linked to the capacity of the animal host to supply essential metals to the symbionts

Massive coral bleaching events result in extensive coral loss throughout the world. These events are mainly caused by seawater warming, but are exacerbated by the subsequent decrease in nutrient availability in surface waters. It has therefore been shown that nitrogen, phosphorus or iron limitation contribute to the underlying conditions by which thermal stress induces coral bleaching. Generally, information on the trophic ecology of trace elements (micronutrients) in corals, and on how they modulate the coral response to thermal stress is lacking. Here, we demonstrate for the first time that heterotrophic feeding (i.e. the capture of zooplankton prey by the coral host) and thermal stress induce significant changes in micro element concentrations and isotopic signatures of the scleractinian coral Stylophora pistillata. The results obtained first reveal that coral symbionts are the major sink for the heterotrophically acquired micronutrients and accumulate manganese, magnesium and iron from the food. These metals are involved in photosynthesis and antioxidant protection. In addition, we show that fed corals can maintain high micronutrient concentrations in the host tissue during thermal stress and do not bleach, whereas unfed corals experience a significant decrease in copper, zinc, boron, calcium and magnesium in the host tissue and bleach. In addition, the significant increase in δ65 Cu and δ66 Zn signature of symbionts and host tissue at high temperature suggests that these isotopic compositions are good proxy for stress in corals. Overall, present findings highlight a new way in which coral heterotrophy and micronutrient availability contribute to coral resistance to global warming and bleaching.

Phosphorus limitation and heat stress decrease calcification in <i>Emiliania huxleyi</i>

Abstract. Calcifying haptophytes (coccolithophores) sequester carbon in the form of organic and inorganic cellular components (coccoliths). We examined the effect of phosphorus (P) limitation and heat stress on particulate organic and inorganic carbon (calcite) production in the coccolithophore Emiliania huxleyi. Both environmental stressors are related to rising CO2 levels and affect carbon production in marine microalgae, which in turn impacts biogeochemical cycling. Using semi-continuous cultures, we show that P limitation and heat stress decrease the calcification rate in E. huxleyi. However, using batch cultures, we show that different culturing approaches (batch versus semi-continuous) induce different physiologies. This affects the ratio of particulate inorganic (PIC) to organic carbon (POC) and complicates general predictions on the effect of P limitation on the PIC ∕ POC ratio. We found heat stress to increase P requirements in E. huxleyi, possibly leading to lower standing stocks in a warmer ocean, especially if this is linked to lower nutrient input. In summary, the predicted rise in global temperature and resulting decrease in nutrient availability may decrease CO2 sequestration by E. huxleyi through lower overall carbon production. Additionally, the export of carbon may be diminished by a decrease in calcification and a weaker coccolith ballasting effect.

Estimating the production and mortality of fine roots using minirhizotrons in a Pinus densiflora forest in Gwangneung, Korea

The aim of this study was to estimate fine root production (FP) and fine root mortality (FM) at 0–10, 10–20, and 20–30 cm soil depths using minirhizotrons in a 75-year-old Pinus densiflora Sieb. et Zucc. forest located in Gwangneung, Korea. We developed the conversion factors (frame cm−2) of three soil depths (0.158 for 0–10 cm, 0.120 for 10–20 cm, and 0.131 for 20–30 cm) based on soil coring and minirhizotron data. FP and FM were estimated using conversion factors from March 26, 2013 to March 2, 2014. The annual FP and FM values at the 0–30 cm soil depth were 3200.2 and 2271.5 kg ha−1 yr −1, respectively. The FP estimate accounted for approximately 17 % of the total net primary production at the study site. FP was highest in summer (July 31–September 26), and FM was highest in autumn (September 27–November 29). FP was positively correlated with seasonal change in soil temperature, while FM was not related to that change. The seasonality of FP and FM might be linked to above-ground photosynthetic activity. Both FP and FM at the 0–10 cm depth were significantly higher than at 10–20 and 20–30 cm depths, and this resulted from the decrease in nutrient availability with increasing soil depth. The minirhizotron approach and conversion factors developed in this study will enable fast and accurate estimation of the fine root dynamics in P. densiflora forest ecosystems.

Effect of organic carbon and metal accumulation on the bacterial communities in sulphidogenic sediments.

A unique geochemical setting in Lake Cadagno, Switzerland, has led to the accumulation of insoluble metal sulphides in the sedimentary record as the result of past airborne pollution. This offers an exceptional opportunity to study the effect of these metals on the bacterial communities in sediments, and in particular to investigate further the link between metal contamination and an increase in the populations of endospore-forming bacteria observed previously in other metal-contaminated sediments. A decrease in organic carbon and total bacterial counts was correlated with an increase in the numbers of endospores in the oldest sediment samples, showing the first environmental evidence of a decrease in nutrient availability as a trigger of sporulation. Proteobacteria and Firmicutes were the two dominant bacterial phyla throughout the sediment, the former in an area with high sulphidogenic activity, and the latter in the oldest samples. Even though the dominant Firmicutes taxa were stable along the sediment core and did not vary with changes in metal contamination, the prevalence of some molecular species like Clostridium sp. was positively correlated with metal sulphide concentration. However, this cannot be generalized to all endospore-forming species. Overall, the community composition supports the hypothesis of sporulation as the main mechanism explaining the dominance of endospore formers in the deepest part of the sediment core, while metal contamination in the form of insoluble metal sulphide deposits appears not to be linked with sporulation as a mechanism of metal tolerance in this sulphidogenic ecosystem.

Further Understanding of the Impacts of Rainfall and Agricultural Management Practices on Nutrient Loss from Rice Paddies in a Monsoon Area

As rice paddies are widespread sources of water pollution in the agricultural regions of the Asian monsoon area, a mechanistic understanding of nutrient loss from paddies is critical for water quality management. A 2-year experiment was conducted in a typical monsoon-affected rice field to improve our understanding of the impacts of rainfall and agricultural management practice on nitrogen (N) and phosphorus (P) loss. Samples of paddy drainage water were collected during rainfall events (n = 25) and analyzed for total N (T-N) and total P (T-P) concentrations. The impacts of rainfall (amount, duration, and intensity) and agricultural management practice (transplanting and fertilization) on the event mean concentration (EMC) and loss of nutrient were assessed using regression analyses. The results showed that T-N and T-P concentrations were affected by agricultural practice; meanwhile, loss of T-N and T-P was correlated with rainfall characteristics. Specifically, the EMC of T-N but T-P was negatively (p < 0.001) correlated with the number of days after agricultural practice in both years, which likely represents a decrease in nutrient availability in paddy water over time. Loss of T-N and T-P was positively (p < 0.01) correlated with rainfall amount, and this suggests that the rainfall-runoff process is a key driver of nutrient loss in the study area. Our results suggest that rainfall amount and days after transplanting need to be taken into account when estimating nutrient loss from rice paddies in monsoon regions.

Long-term changes in belowground and aboveground resource allocation of boreal forest stands

Age-related decline of forest stand growth is a common phenomenon, but the associated physiological causes remain uncertain. This study investigated a possible mechanism that could explain stand growth decline observed after canopy closure. We hypothesised that the proportion of resource allocation to roots increases with stand age as a response to a decrease in nutrient availability, which is related to the long-term accumulation of organic matter in boreal forests. Proxies based on soil respiration measurements and stem biomass production were used to describe temporal changes in the proportion of carbon allocated to belowground and aboveground stand components along a 1067-year post-fire chronosequence. The proportion of resources that were allocated belowground increased in the first 200years following fire and declined thereafter. The inverse pattern was observed for the organic matter decomposition rate. Stand-level decline in wood productivity that was observed during the first 60-year period after fire can be attributed to a greater proportion of carbohydrates being allocated to roots in response to a decrease in nutrient availability. However, the relatively low productivity of old-growth stands was not associated with high belowground allocation, suggesting that other mechanisms operating at the tree- or stand-level may be involved.

The effect of long term under- and over-feeding on the expression of genes related to lipid metabolism in the mammary tissue of goats

Fat synthesis is under the control of a large number of genes whose nutritional regulation is still poorly documented. In this study, we examined the effect of long term under- and over-feeding on the expression of genes (acetyl-CoA carboxylase: ACACA, fatty acid synthetase: FASN, lipoprotein lipase: LPL, stearoyl-Co A desaturase 1: SCD1, peroxisome proliferator activated receptor G2: PPARG2, sterol regulatory element binding protein-1c: SREBP-1c and hormone sensitive lipase HSL) related to FA metabolism in goat mammary tissue (MT). Twenty four lactating goats were divided into three homogenous sub-groups and fed the same ratio in quantities covering 70% (underfeeding), 100% (control) and 130% (overfeeding) of their energy and crude protein requirements. The results showed a significant reduction on mRNA of ACACA, FASN, LPL, SCD1 and HSL in the MT of underfed goats, compared with the respective overfed. A numerical decrease on the mRNA level of PPARG2 and SREBP-1c in the MT of the underfed goats, compared with the respective controls and the overfed was also observed. In conclusion, the negative, compared to positive, energy balance in goats down regulates the ACACA, FASN, LPL, SCD1 and HSL expressions in their MT which indicates that the decrease in nutrient availability may lead to lower rates of lipid synthesis.

The effect of long term under- and over-feeding on the expression of genes related to lipid metabolism in mammary tissue of sheep.

Milk fatty acid (FA) synthesis by the mammary gland involves expression of a large number of genes whose nutritional regulation remains poorly defined. In this study, we examined the effect of long-term under- and over-feeding on the expression of genes (acetyl Co A carboxylase, ACC; fatty acid synthetase, FAS; lipoprotein lipase, LPL; stearoyl Co A desaturase, SCD; peroxisome proliferator activated receptor γ2, PPARγ2; sterol regulatory element binding protein-1, SREBP-1c; and hormone sensitive lipase, HSL) related to FA metabolism in sheep mammary tissue (MT). Twenty-four lactating sheep were divided into three homogenous sub-groups and fed the same ration in quantities covering 70% (underfeeding), 100% (control) and 130% (overfeeding) of their energy and crude protein requirements. The results showed a significant reduction of mRNA of ACC, FAS, LPL and SCD in the MT of underfed sheep, and a significant increase on the mRNA of LPL and SREBP-1c in the MT of overfed compared with the control respectively. In conclusion, the negative, compared to positive, energy balance in sheep down-regulates ACC, FAS, LPL, SCD, SREBP-1c and PPARγ2 expression in their MT which indicates that the decrease in nutrient availability may lead to lower rates of lipid synthesis.

Numerical exploration of the combined effect of nutrient supply, tissue condition and deformation in the intervertebral disc

Novel strategies to heal discogenic low back pain could highly benefit from comprehensive biophysical studies that consider both mechanical and biological factors involved in intervertebral disc degeneration. A decrease in nutrient availability at the bone–disc interface has been indicated as a relevant risk factor and as a possible initiator of cell death processes. Mechanical behaviour of both healthy and degenerated discs could highly interact with cell death in these compromised situations. In the present study, a mechano-transport finite element model was used to investigate the nature of mechanical effects on cell death processes via load-induced metabolic transport variations. Cycles of static sustained compression were chosen to simulate daily human activity. Healthy and degenerated cases were simulated as well as a reduced supply of solutes and an increase in solute exchange area at the bone–disc interface. Results showed that a reduction in metabolite concentrations at the bone–disc boundaries induced cell death, even when the increased exchange area was simulated. Slight local mechanical enhancements of glucose in the disc centre were capable of decelerating cell death but occurred only with healthy mechanical properties. However, mechanical deformations were responsible for a worsening in terms of cell death in the inner annulus, a disadvantaged zone far from the boundary supply with both an increased cell demand and a strain-dependent decrease of diffusivity. Such adverse mechanical effects were more accentuated when degenerative properties were simulated. Overall, this study paves the way for the use of biophysical models for a more integrated understanding of intervertebral disc pathophysiology.

Low nutrient availability reduces high‐irradiance‐induced viability loss in oceanic phytoplankton

In situ viability of oceanic phytoplankton may be relatively low in open oceans. This is assumed to be related to the high‐irradiance and low‐nutrient conditions typical for oligotrophic regions. However, experimental evidence for this phenomenon was not yet available. In the present study, the importance of nutrient availability in high‐irradiance‐induced viability loss was therefore studied for three key oceanic phytoplankton species. Prochlorococcus marinus, Ostreococcus sp., and Thalassiosira oceanica were acclimated to two different N : P ratios. Growth, viability, and photophysiology were assessed under nutrient‐replete and N‐ and P‐starved conditions. Simultaneously, high‐irradiance‐induced photoinhibition and viability loss were measured and three inhibitors were used to investigate the underlying physiological mechanisms contributing to viability loss. High‐irradiance exposure caused viability loss in P. marinus and Ostreococcus sp., but not in T. oceanica. Low‐nutrient availability enhanced survival during high‐irradiance exposure, although species‐specific differences were observed. The lower sensitivity to high‐irradiance intensities at low‐nutrient availability was related to conformational changes in photosystem II in P. marinus, to enhanced photoprotection by the xanthophyll pigment cycle and alternative electron transport in Ostreococcus sp., and to enhanced photoprotection by the xanthophyll pigment cycle in T. oceanica. Climate change may lead to enhanced stratification in the open ocean. The resulting increase in the average irradiance intensity phytoplankton experience may promote viability loss in the smallest phytoplankton size fraction. However, this effect may partially be counteracted by the simultaneously expected decrease in nutrient availability.

Description of the long-term (1991–2005) temporal and spatial distribution of phytoplankton carbon biomass in the Dutch North Sea

Since the beginning of the 1990s phytoplankton species composition and abundance have been monitored at a high frequency (bi-weekly in the growing season and monthly in winter) at a number of fixed stations on the Dutch Continental Shelf, of which 18 are used in this study. Phytoplankton carbon biomass has been calculated from species-specific biovolume/cell data and summed over all species per functional group enumerated in the samples. The species are divided into four functional groups i. e. diatoms, flagellates, autotrophic and mixotrophic dinoflagellates and Phaeocystis spp. The total number of phytoplankton samples analysed up to and including 2005 is almost 4000. The annual mean phytoplankton biomass over all stations remained stable at around 145 mg C m − 3 . However, the phytoplankton composition has changed significantly, with increases in diatoms and dinoflagellates and compensating decreases in flagellates and Phaeocystis. With increasing distance from the shore, coinciding with a decrease in nutrient availability and increasing water depth, total phytoplankton biomass as well as the biomass of diatoms, flagellates and Phaeocystis spp. decreased. This pattern was not true for the dinoflagellates, which occurred at more or less the same biomass throughout the region. Stations near river mouths and in the Wadden Sea outlets had much higher phytoplankton biomass than stations further from freshwater discharges. The data, split in two periods (1991–1998) and (1999–2005) and averaged over the whole Dutch Continental Shelf, had been aggregated into seasonal biomass distributions. The seasonal phytoplankton biomass distribution was unimodal in both periods, with similar spring maxima of around 300 mg C m − 3 . The spring maximum occurred one month earlier, in April, in the second period. Phaeocystis over the whole study period remained the dominant near-shore species as it has been since the first phytoplankton observations at the end of the 19th century.