Low Nutrient Levels Research Articles

PENGARUH PEMBERIAN DOLOMIT DAN PEMUPUKAN NPK TERHADAP PERTUMBUHAN DAN HASIL OKRA (Abelmoschus esculentus L.) PADA TANAH HISTOSOL

Abstract Histosol is an organic soil with a high acidity value (pH 4.5) and low levels of nutrients N, P, and K that is effects to plant growth and yield. This study aims to examine the effect of dolomite and NPK fertilization on the growth and yield of Okra (Abelmoschus esculentus L.) on Histosol soil. This research was conducted in the Experimental Garden of the Faculty of Agriculture, Teuku Umar University, West Aceh. This study used a factorial 4 x 4 randomized block design (RBD) with 3 replications. The factors studied include: 1) Dolomite factor (D) consists of 4 levels, namely: D0= without liming, D1= 22.5 grams/polybag, D2= 45 grams/polybag, D3= 67.5 grams / polybag; 2) NPK fertilizer factor (N) consists of 4 levels, namely: N0= zero NPK fertilizer application, N1= 11.25 gram/polybag, N2 = 18.75 grams/polybag, N3= 26.25 grams/polybag. The results showed that dolomite dose had a very significant effect on plant height, stem diameter and number of leaves of okra plants aged 15, 30, 45 and 60 HST. Very significant effect on the length of the okra fruit aged 73 HST and significant effect on the weight of the fruit age 73 HST, but no significant effect on fruit diameter, number of fruit age and production per hectare (tons) 73 HST. NPK fertilizer has a very significant effect on plant height and stem diameter aged 15, 30, 45 and 60 HST. Very significant effect on fruit length and diameter okra fruit aged 73 HST. Not significant effect on the number of fruits, fruit weight and per hectare production (tons) of okra aged 73 HST. There was no interaction between dolomite and NPK fertilizer from all treatments.Keywords : Histosol, acidity, liming and fertilizing, growth and yield of okra plants

Mechanisms of acid-resistant Rhodopseudomonas palustris strains to ameliorate acidic stress and promote plant growth

Abstract The low level of nutrients in acid sulfate soils (ASS) presents a serious obstacle to plant growth. This study aimed to investigate the mechanisms that acid-resistant purple nonsulfur bacteria (PNSB) use to resist acidic stress; Rhodopseudomonas palustris strains TLS06, VNW02, VNW64 and VNS89 released plant growth promoting substances (PGPS) including the plant nutrients NH4+ and PO43−. All tested PNSB strains produced siderophores to solubilize PO43− from Al–P and Fe–P, either as individual or combined P sources. Siderophores were produced under both aerobic dark and microaerobic light incubating conditions. A strong positive relationship was indicated between released siderophores and released P with correlation indices (r) of 0.6362–0.6567 and 0.7415 to 0.8656 in light and dark conditions, respectively. In addition, the release of PGPS by PNSB coincided with an increase in pH from an initial 4.5 to 6.5–7.90. A positive high correlation between released PGPS and pH existed: for NH4+, siderophores, indole-3-acetic acid (IAA) and 5-aminolevulinic acid (ALA), respective r values were 0.8155–0.9980, 0.7576–0.8294, 0.8869–0.9980 and 0.5185–0.9919. It can be concluded that the mechanisms by which PNSB release PGPS and plant nutrients significantly increased pH. By overcoming acidic stress in this way, PNSB show great potential for use as plant growth promoters in paddy fields on ASS.

Responses of Marine Diatom Skeletonema marinoi to Nutrient Deficiency: Programmed Cell Death.

Diatoms are important phytoplankton and contribute greatly to the primary productivity of marine ecosystems. Despite the ecological significance of diatoms and the importance of programmed cell death (PCD) in the fluctuation of diatom populations, little is known about the molecular mechanisms of PCD triggered by different nutrient stresses. Here we describe the physiological, morphological, biochemical, and molecular changes in response to low levels of nutrients in the ubiquitous diatom Skeletonema marinoi The levels of gene expression involved in oxidation resistance and PCD strongly increased upon nitrogen (N) or phosphorus (P) starvation. The enzymatic activity of caspase 3-like protein also increased. Differences in mRNA levels and protein activities were observed between the low-N and low-P treatments, suggesting that PCD could have a differential response to different nutrient stresses. When cultures were replete with N or P, the growth inhibition stopped. Meanwhile, the enzymatic activity of caspase 3-like protein and the number of cells with damaged membranes decreased. These results suggest that PCD is an important cell fate decision mechanism in the marine diatom S. marinoi Our results provide important insight into how diatoms adjust phenotypic and genotypic features of their cell-regulated death programs when stressed by nutrient limitations. Overall, this study could allow us to better understand the molecular mechanism behind the formation and termination of diatom blooms in the marine environment.IMPORTANCE Our study showed how the ubiquitous diatom S. marinoi responded to different nutrient limitations with PCD in terms of physiological, morphological, biochemical, and molecular characteristics. Some PCD-related genes (PDCD4, GOX, and HSP90) induced by N deficiency were relatively upregulated compared to those induced by P deficiency. In contrast, the expression of the TSG101 gene in S. marinoi showed a clear and constant increase during P limitation compared to N limitation. These findings suggest that PCD is a complex mechanism involving several different proteins. The systematic mRNA level investigations provide new insight into understanding the oxidative stress- and cell death-related functional genes of diatoms involved in the response to nutrient fluctuations (N or P stress) in the marine environment.

Postintroduction evolution contributes to the successful invasion of Chromolaena odorata.

The evolution of increased competitive ability (EICA) hypothesis states that, when introduced in a novel habitat, invasive species may reallocate resources from costly quantitative defense mechanisms against enemies to dispersal and reproduction; meanwhile, the refinement of EICA suggests that concentrations of toxins used for qualitative defense against generalist herbivores may increase. Previous studies considered that only few genotypes were introduced to the new range, whereas most studies to test the EICA (or the refinement of EICA) hypotheses did not consider founder effects.In this study, genetic and phenotypic data of Chromolaena odorata populations sampled across native and introduced ranges were combined to investigate the role of postintroduction evolution in the successful invasion of C. odorata.Compared with native populations, the introduced populations exhibited lower levels of genetic diversity. Moreover, different founder effects events were interpreted as the main cause of the genetic structure observed in introduced ranges. Three Florida, two Trinidad, and two Puerto Rico populations may have been the sources of the invasive C. odorata in Asia.When in free of competition conditions, C. odorata plants from introduced ranges perform better than those from native ranges at high nutrient supply but not at low nutrient level. The differences in performance due to competition were significantly greater for C. odorata plants from the native range than those from the introduced range at both nutrient levels. Moreover, the differences in performance by competition were significantly greater for putative source populations than for invasive populations.Quantities of three types of secondary compounds in leaves of invasive C. odorata populations were significantly higher than those in putative source populations. These results provide more accurate evidence that the competitive ability of the introduced C. odorata is increased with postintroduction evolution.

Nutritivni aspekti poremećaja kognitivnih funkcija

Many scientific arguments in this area, implicate low level of important nutrients in cognitive decline, simultaneously suggesting better nutritional status as an important goal in the management of cognitive aging. Key nutrients for the protection of cognitive function are B-group vitamins, polyphenols, vitamin D, and omega-3 polyunsaturated fatty acids (PUFAs). The body of scientific evidence widely supports the roles of folic acid and metabolically related B6 and B12 vitamins in protecting cognitive function in old age. High concentrations of polyphenols in dementia therapy showed a significant increase in cerebral blood volume. Although low vitamin D blood levels were associated with a higher risk of developing dementia, vitamin D supplementation alone was not sufficient to improve cognitive outcomes. In relation to the role of omega-3 PUFAs, research findings indicate protective effects in individuals with cognitive decline. The importance of diets and a healthy lifestyle in the prevention of cognitive impairment are extensively accepted. The Mediterranean diet is the most investigated dietary pattern in observational studies. MIND diet (Mediterranean-DASH Intervention for Neurodegenerative Delay) is updated dietary approach of the Mediterranean-DASH diets. Its components are linked to dementia prevention and overall neuroprotection. It is also reported that regular physical activity maintains the brain function improving blood flow and oxygen supply.

Anaerobic Co-Digestion of Wastewater Sludge: A Review of Potential Co-Substrates and Operating Factors for Improved Methane Yield

Anaerobic digestion has been widely employed in waste treatment for its ability to capture methane gas released as a product during the digestion. Certain wastes, however, cannot be easily digested due to their low nutrient level insufficient for anaerobic digestion, thus co-digestion is a viable option. Numerous studies have shown that using co-substrates in anaerobic digestion systems improve methane yields as positive synergisms are established in the digestion medium, and the supply of missing nutrients are introduced by the co-substrates. Nevertheless, large-scale implementation of co-digestion technology is limited by inherent process limitations and operational concerns. This review summarizes the results from numerous laboratory, pilot, and full-scale anaerobic co-digestion (ACD) studies of wastewater sludge with the co-substrates of organic fraction of municipal solid waste, food waste, crude glycerol, agricultural waste, and fat, oil and grease. The critical factors that influence the ACD operation are also discussed. The ultimate aim of this review is to identify the best potential co-substrate for wastewater sludge anaerobic co-digestion and provide a recommendation for future reference. By adding co-substrates, a gain ranging from 13 to 176% in the methane yield was accomplished compared to the mono-digestions.

Physical space interacts with clonal fragmentation and nutrient availability to affect the growth of Salvinia natans.

Physical space, clonal fragmentation and nutrient availability can each affect the growth of clonal plants, but their interactive effect has been little studied. We grew un-fragmented (connected) and fragmented (disconnected) ramet pairs of the floating, clonal plant Salvinia natans in cylindrical containers with different diameters and heights (volumes) filled with solutions of two nutrient levels (high vs. low). To simulate competition environments that are commonly confronted by S. natans, we also added two ramets of another floating plants Spirodela polyrrhiza in each container. Biomass (total biomass, floating biomass and submerged biomass) and number of ramets of S. salvinia were higher in the containers with a larger diameter. Compared to the low nutrient level, the high nutrient level increased number of ramets, and altered submerged to floating mass ratio of S. salvinia. The impacts of physical space on floating mass and number of ramets were stronger under the high than under the low nutrient level. Clonal fragmentation positively affected biomass in the containers with a smaller volume (a smaller height and diameter), but had little impact in the containers with a larger volume (a larger height or diameter). Our results suggest that physical space can interact with nutrients and clonal fragmentation to affect the performance of S. salvinia under competition.

The effects of turbulence on phytoplankton and implications for energy transfer with an integrated water quality-ecosystem model in a shallow lake

Turbulence has significant influences on the growth rate and community structure of phytoplankton in large shallow lakes. Phytoplankton in moving water may be influenced by turbulence and nutrient concentration gradients on a short time scale. To assess this issue, our research used an ensemble water quality and ecological model by internally coupling the three-dimensional hydrodynamic model, the Environmental Fluid Dynamics Code (EFDC), and the one-dimensional ecosystem model, PCLake. The results showed that turbulence dramatically inhibited phytoplankton growth, while nutrients had the opposite effect. In addition, turbulence was the key factor contributing to phytoplankton growth. However, the effects of turbulence on phytoplankton correlated with nutrient concentrations. For lower nutrient concentrations, phytoplankton growth was controlled by nutrients. Logistic regression models were established with the modeled chlorophyll a, total nitrogen (TN), total phosphorus (TP) and turbulent kinetic energy (Ke). The results also showed that turbulence could improve nutrient uptake by phytoplankton, especially at low nutrient levels. The effects of turbulence on phytoplankton may imply that energy transfer occurs between water turbulence and phytoplankton. Our study will provide insight into management and remediation strategies of ecosystems based on energy processes in the future.

Type‐Maastrichtian gastropod faunas show rapid ecosystem recovery following the Cretaceous–Palaeogene boundary catastrophe

AbstractThe study of the global mass extinction event at the Cretaceous–Palaeogene (K/Pg) boundary can aid in understanding patterns of selective extinction, and survival and dynamics of ecosystem recovery. Outcrops in the Maastrichtian type area (south‐east Netherlands, north‐east Belgium) comprise a stratigraphically expanded K/Pg boundary succession that offers a unique opportunity to study marine ecosystem recovery within the first few thousand years following the mass extinction event. A quantitative analysis was performed on systematically sampled macrofossils of the topmost Maastrichtian and lowermost Danian strata at the former Ankerpoort‐Curfs quarry (Geulhem), which represent ‘snapshots’ of the latest Cretaceous and earliest Palaeogene marine ecosystems, respectively. Molluscs in particular are diverse and abundant in the studied succession. Regional ecosystem changes across the K/Pg boundary are relatively minor, showing a decline in suspension feeders, accompanied by an ecological shift to endobenthic molluscs. The earliest Paleocene gastropod assemblage retains many ‘Maastrichtian’ features and documents a fauna that temporarily survived into the Danian. The shallow, oligotrophic carbonate platform in this area was inhabited by taxa that were adapted to low nutrient levels and resistant to starvation. As a result, the local taxa were less affected by the short‐lived detrimental conditions related to K/Pg boundary perturbations, such as darkness, cooling, starvation and ocean acidification. This resulted in relatively high survival rates, which enabled rapid recolonization and recovery of marine faunas in the Maastrichtian type area.

Effects of nutrient level and planting density on population relationship in soybean and wheat intercropping populations.

A positive interaction between plant populations is a type of population relationship formed during long-term evolution. This interaction can alleviate population competition, improve resource utilization in populations, and promote population harmony and community stability. However, cultivated plant populations may have insufficient time to establish a positive interaction, thereby hindering the formation of the positive interaction. As current studies have not fully addressed these issues, our study established soybean/wheat intercropping populations beneficial for growth and explored the effects of nutrient level and planting density on the positive interaction between the two crops. Changes across population modules in both sole cropping and intercropping populations of soybean and wheat were analyzed. Results using nutrient levels of ½- or ¼-strength Hoagland solution indicated that soybean/wheat intercropping population modules significantly increased at low planting densities (D20 and D26) and significantly decreased at high planting densities (D32 and D60). Therefore, as planting density increased, the modules of both intercropping populations initially increased before decreasing. Similarly, positive interaction initially strengthened before weakening. Moreover, at an intermediate planting density, the population modules reached their maxima, and the positive interaction was the strongest. Under the same planting density, ¼-strength Hoagland solution recorded better growth for the soybean/wheat intercropping population modules compared to results using the ½-strength Hoagland solution. These findings indicated that low nutrient level can increase the positive interaction of intercropping populations at a given planting density, and that environmental nutrient level and population planting densities constrain the positive interaction between soybean and wheat populations in the intercropping system. This study highlights issues that need to be addressed when constructing intercropping populations.

Xylanase, Glucanase, and Phytase in the Diet of Light Laying Hens

SUMMARY The aim of this study was to evaluate the effect of enzymes (endo-1,4-β-xylanase [EC 3.2.1.8], endo-1,3(4)-β-glucanase [EC 3.2.1.6], and 6-phytase [EC 3.1.3.26]) in light layer hen diets during the second production cycle (75–95 wk old). Five treatments were used: positive control (PC); negative control 1 (NC1): reduction of dietary nutritional load, as of 100% of the nutritional matrix that the enzymes provide; negative control 2 (NC2): reduction of dietary nutritional load, as of 125% of the nutritional matrix that the enzymes provide; NC1+100% enzymes (NC1–100%): 100% of the matrix, enzymes provide, reformulated and, NC1+125% enzymes (NC2–125%): 125% of the matrix, enzymes provide, reformulated, with 8 replicates and 8 hens for each. Feed intake (P = 0.0059), egg production (P = 0.0096), egg mass (P = 0.0280), feed conversion per egg mass (P = 0.007), and feed conversion per dozen of eggs (P = 0.003) were significantly different with enzyme supplementation. The eggshell weight (P = 0.975), shell thickness (P = 0.920), specific gravity (P = 0.198), and yolk color (P = 0.639) were not affected; however, the relative weights of albumen (P = 0.075) and yolk (P = 0.021) were affected. In conclusion, the use of a multi-carbohydrase complex containing phytase is able to compensate the negative impact of lower nutrient levels, improving the productive performance of layer hens in the second production cycle.

Response of Cladocera fauna to environmental change based on sediments from Shengjin Lake, a Yangtze River-connected lake in China

Shengjin Lake is a typical Yangtze River-connected lake, that is also a national nature reserve and a Wetland of International Importance. In order to evaluate the eco-environmental evolution of Shengjin Lake, a210Pb- and 137Cs-dated sediment core collected from the upper part of the lake was analyzed. Based on a biological indicator (subfossil cladoceran) and geochemical indicators (loss on ignition (LOI), total organic carbon (TOC), δ13C of bulk sediments (δ13Corg), total phosphorous (TP) and total nitrogen (TN)), we revealed the changes in the cladoceran assemblages and eco-environmental processes of Shengjin Lake. The results showed that there was a healthy ecological environment with low nutrient levels in Shengjin Lake before the 1980s. However, the increasing levels of the eutrophic species B. longirostris, nutrients (TN and TP) and organic matters (LOI and TOC), and the decreasing δ13Corg in recent decades indicated that the trophic state of Shengjin Lake has increased since the 1980s. This corresponded with increasing anthropogenic effects, including land reclamation, chemical fertilizer application, and sluice construction. In addition, the droppings of water birds also promoted increases in nutrient and organic matters levels in Shengjin Lake.

Trait-based community assembly of submersed macrophytes subjected to nutrient enrichment in freshwater lakes: Do traits at the individual level matter?

Abstract Understanding how functional traits distributed across ecological scales as well as environmental gradients are central issues of trait-based assembly processes. However, whether environmental filters act on individuals or species mean traits remains poorly tested. Here, we measured four functional traits – shoot height, specific leaf area, lamina thickness, and leaf dry mass content – of 4432 individuals from 30 submersed macrophyte species across 26 lakes in south China, covering a broad nutrient gradient. We partitioned trait variances into four nested ecological scales (i.e., region, community, species, individual) and assessed how the internal and external filters structured the submersed macrophyte community, either through acting on individual or on species mean traits, and how these processes related to nutrient enrichment. For the four tested traits, 13–60% of trait variability occurred within species (individual level), while 35–86% occurred among species (species level), followed by community and regional level. Species turnover contributed most to the community-wide variance along the nutrient gradient caused considerable intraspecific variations of shoot height. We found significant strong internal filtering effects on the submersed macrophyte community, which increased towards higher nutrient levels. The external filtering effects were only observed at individual level, with lower shoot height, specific leaf area, and leaf dry mass content than expected at low nutrient levels, and lower lamina thickness than expected at high nutrient levels. Our study provides new insight into the assembly processes by showing that niche overlap (i.e., intraspecific interaction) and niche differentiation (i.e., interspecific interaction) can simultaneously occur in different functional traits, both potentially promoting local species diversity. We conclude that an individual trait-based approach can help to detect assembly processes within and among lakes.

Soil nitrogen assimilation of 1-year oak seedlings: Implication for forest fertilization and management

Reserves in cotyledons and nutrients in soil are essential for the early development of seedlings of oaks. However, much less is known to what extent the reserves in seeds and/or soil nutrients contribute to seedling development and growth at early stages, especially at multi-species level. We carried out an indoor experiment in which the soil was enriched in 15N to quantify N uptake and its distribution in the seedlings of five red and white oak species. Dry masses of seedlings did not vary significantly with N fertilization rates, reflecting the low morphological and physiological plasticity of oak seedlings to soil fertility. However, dry masses of roots of white oak species were much higher than those of red oak species. Soil-derived N incorporated into the seedlings of the five oak species increased with seedling growth and enhanced 15N fertilization rates. Soil-derived N in the seedlings of white oak species was much higher than those of red oak species. Acorn-derived N in seedlings decreased with N fertilization rates, implying that acorn N mobilization can be accelerated under low soil nutrient level. We found higher soil N/acorn N ratio in the seedlings of white oak species than those of red oak species, indicating the rapid uptake of soil N in the seedlings of white oak species. Acorn N rather than soil N played a crucial role in supporting oak seedling development and growth at the early stage. Our results provide insight into the role of acorn N and soil fertility to 1-year oak seedlings and have great implication for forest fertilization and management.

Complex responses of phototrophic communities to climate warming during the Holocene of northeastern Ontario, Canada

Historical changes in Holocene climate in northeastern Ontario were quantified using analyses of sedimentary pollen, diatoms, and pigments in a small boreal lake. Modern analog reconstructions of average temperature from Holocene pollen assemblages of Charland Lake showed temperature was ~2°C warmer than present conditions ~7800–4500 cal. yr BP, a time period consistent with the Holocene thermal maximum (HTM). Pollen data suggest a two-phase HTM: warm and dry conditions based on the presence of primarily Pinus spp., followed by warm and wet conditions based on increases in cedar. Overall, algal production was low during the HTM, as reflected by low concentrations of pigments and diatoms. In the late HTM, increases in cedar pollen and planktonic diatoms suggest sustained increases in water levels for the remainder of the Holocene. During the Post-HTM Period (~4500–2000 cal. yr BP), a period that was warmer than today but cooler than the HTM, overall pigment production was significantly higher than all other periods. However, changes in diatom species composition suggest this period was not uniform, with variation occurring between diatoms indicative of higher and lower nutrient levels. The last ~2000 cal. yr BP was less productive than the Post-HTM Period but more productive than the HTM with higher production from diatoms and cyanobacteria. This study suggests that the relationship between climate and lake water production can be quite complex, and that changes in temperature, precipitation, light, lake levels, and mixing patterns are among factors that are related to changes in subfossil phototroph assemblages.

Nutrient-demanding species face less negative competition and plant-soil feedback effects in a nutrient-rich environment.

Plant-soil feedbacks (PSFs) and plant-plant competition influence performance and abundance of plants. To what extent the two biotic interactions are interrelated and thus affect plant performance in combination rather than in isolation remains poorly explored. It is also unclear how the abiotic context, such as resource availability, modifies individual and joint effects of PSFs and of plant-plant competition. Using a garden experiment, we assessed the strengths of PSFs, competition, and their combined effects explored under low and high nutrient levels, and related them to abundance of 46 plant species and their ecological optima with respect to soil nutrients. We found that PSFs reduced but did not eliminate differences in competitive ability of plant species. Isolated and combined effects of the biotic interactions poorly predicted local or regional abundance of species. They were rather related to species' ecological optima, as nutrient-demanding plants experienced less negative biotic effects but only in a nutrient-rich environment. Our study demonstrates that soil biota can mitigate differences in competitive ability among species. It remains to be tested whether such an equalizing effect can maintain coexistence under high nutrient availability, in which nutrient-demanding species may disproportionately benefit from less negative competition and PSF effects.

Soil microbial community characteristics under different vegetation types at the national nature reserve of Xiaolongshan Mountains, Northwest China

Microorganisms provide ecosystem services, such as decomposition and mineralization processes in forest soils. Quercus aliena var. acuteserrata and Larix kaempferi are the main natural forest and planted forest, respectively, in the national nature reserve of the Xiaolongshan Mountains of China. Understanding the composition and structure of soil microbial communities under these two typical vegetation types is critical for achieving effective management and sustainable utilization of the forest vegetation in the Xiaolongshan Mountain region. In this study, we analysed and compared the soil microbial communities of the Q. acuteserrata natural forest and L. kaempferi planted forest using high-throughput sequencing technology, and cultivated land soil samples were selected as controls. The results indicated that soil nutrient contents and stoichiometric ratios (organic carbon to total nitrogen ratio (C:N), organic carbon to total phosphorus ratio (C:P) and nitrogen to phosphorus ratio (N:P)) were higher in the natural forest than in the planted forest and were lowest in the cultivated land. The soil bacterial community in the Q. acuteserrata natural forest had lower diversity indices than that in the L. kaempferi planted forest and cultivated land, and the soil fungal community in the Q. acuteserrata natural forest had higher diversity indices than that in the cultivated land. Proteobacteria was more abundant in the natural forest soil with higher nutrient levels, and Acidobacteria was more abundant in the plantation forest soil with lower nutrient levels. Ascomycota abundance was lowest in the natural forest, and Basidiomycota abundance was lowest in the plantation forest. Microbial composition was sensitive to soil nutrients and the stoichiometric ratio, which explained 82.67% and 70.72% of the total variations in the soil bacterial and fungal community composition, respectively. There were significant differences in soil microbial community composition and structure between the natural forest and planted forest, and these changes were influenced by soil nutrient conditions. Total phosphorus (TP) may be an important factor regulating microbial community structure in different vegetation soil types.

Effects of exogenous lanthanum(III) exposure on the positive interaction between mutually beneficial populations.

Rare earth elements (REEs) are widely used in various fields, and their accumulation has been reported to pose environmental risks. Most studies confirmed the damage of excessive REE exposure to individual plants; however, little attention has been given to their effects on plant populations. A positive interaction indicates a mutually beneficial relationship between two populations, which is beneficial to the survival and growth of the populations. However, it remains unknown whether exogenous REEs affect the positive interactions between populations. This study investigated the effects of exogenous lanthanum(III) [La(III)] exposure on the positive interaction between soybean (Glycine max L.) and wheat (Triticum aestivum L.) populations by their modules. At normal nutrient level (½-strength Hoagland), the inhibition of excessive La(III) on population modules decreased with increasing population density. Decreases of 39.26 to 1.05% for soybean and 41.45 to 2.41% for wheat indicated the inhibition of La(III) on the positive interaction of both populations weakened with increasing population density. At low nutrient level (¼-strength Hoagland), the inhibition of excessive La(III) on population modules increased with increasing population density. Decreases of 5.82-57.14% for soybean and 4.22-59.04% for wheat indicated the inhibition of La(III) on the positive interaction of both population was strengthened with increasing population density. In summary, the inhibitory effects of exogenous La(III) exposure on the positive interaction between populations vary with both nutrient level and population density. This is a new factor that needs to be considered when evaluating the safety risks of REEs in the environment.

Combined effects of CO2 level, light intensity, and nutrient availability on the coccolithophore Emiliania huxleyi

Continuous accumulation of fossil CO2 in the atmosphere and increasingly dissolved CO2 in seawater leads to ocean acidification (OA), which is known to affect phytoplankton physiology directly and/or indirectly. Since increasing attention has been paid to the effects of OA under the influences of multiple drivers, in this study, we investigated effects of elevated CO2 concentration under different levels of light and nutrients on growth rate, particulate organic (POC) and inorganic (PIC) carbon quotas of the coccolithophorid Emiliania huxleyi. We found that OA treatment (pH 7.84, CO2 = 920 μatm) reduced the maximum growth rate at all levels of the nutrients tested, and exacerbated photo-inhibition of growth rate under reduced availability of phosphate (from 10.5 to 0.4 μmol l−1). Low nutrient levels, especially lower nitrate concentration (8.8 μmol l−1 compared with 101 μmol l−1), decreased maximum growth rates. Nevertheless, the reduced levels of nutrients increased the maximum PIC production rate. Decreased availability of nutrients influenced growth, POC and PIC quotas more than changes in CO2 concentrations. Our results suggest that reduced nutrient availability due to reduced upward advective supply because of ocean warming may partially counteract the negative effects of OA on calcification of the coccolithophorid.

AMPK and AKT protein kinases hierarchically phosphorylate the N-terminus of the FOXO1 transcription factor, modulating interactions with 14-3-3 proteins

Forkhead box protein O1 (FOXO1) is a transcription factor involved in various cellular processes such as glucose metabolism, development, stress resistance, and tumor suppression. FOXO1's transcriptional activity is controlled by different environmental cues through a myriad of posttranslational modifications. In response to growth factors, the serine/threonine kinase AKT phosphorylates Thr24 and Ser256 in FOXO1 to stimulate binding of 14-3-3 proteins, causing FOXO1 inactivation. In contrast, low nutrient and energy levels induce FOXO1 activity. AMP-activated protein kinase (AMPK), a master regulator of cellular energy homeostasis, partly mediates this effect through phosphorylation of Ser383 and Thr649 in FOXO1. In this study, we identified Ser22 as an additional AMPK phosphorylation site in FOXO1's N terminus, with Ser22 phosphorylation preventing binding of 14-3-3 proteins. The crystal structure of a FOXO1 peptide in complex with 14-3-3 σ at 2.3 Å resolution revealed that this is a consequence of both steric hindrance and electrostatic repulsion. Furthermore, we found that AMPK-mediated Ser22 phosphorylation impairs Thr24 phosphorylation by AKT in a hierarchical manner. Thus, numerous mechanisms maintain FOXO1 activity via AMPK signaling. AMPK-mediated Ser22 phosphorylation directly and indirectly averts binding of 14-3-3 proteins, whereas phosphorylation of Ser383 and Thr649 complementarily stimulates FOXO1 activity. Our results shed light on a mechanism that integrates inputs from both AMPK and AKT signaling pathways in a small motif to fine-tune FOXO1 transcriptional activity.