LN Conditions Research Articles

Proteomic Profiling for Metabolic Pathways Involved in Interactive Effects of Elevated Carbon Dioxide and Nitrogen on Leaf Growth in a Perennial Grass Species

Elevated atmospheric CO2 and nitrogen are major environmental factors affecting shoot growth. The objectives of this study are to determine the interactive effects of elevated CO2 and nitrogen on leaf growth in tall fescue ( Festuca arundinacea) and to identify major proteins and associated metabolic pathways underlying CO2-regulation of leaf growth under insufficient and sufficient nitrate conditions using proteomic analysis. Plants of tall fescue treated with low nitrate level (0.25 mM, LN), moderate nitrate level (4 mM, MN) and high nitrate level (32 mM, HN) were exposed to ambient (400 μmol mol-1) and elevated (800 μmol mol-1) CO2 concentrations in environment-controlled growth chambers. Increased atmospheric CO2 concentration increased leaf length and shoot biomass, which corresponded to increased content of indo-acetic acid, gibberellic acid, cytokinins and reduced content of abscisic acid under sufficient nitrate conditions (MN and HN conditions). Low nitrate supply limited shoot growth and hormonal responses to elevated CO2. Proteomic analysis of plants exposed to elevated CO2 under LN and MN conditions demonstrated the increases in the abundance of many proteins due to elevated CO2 under MN condition involved with cell cycle and proliferation, transcription and translation, photosynthesis (ribosomal and chlorophyll a/b-binding proteins), amino acids synthesis, sucrose and starch metabolism, as well as ABA signaling pathways (ABA-induced proteins). Our results revealed major proteins and associated metabolic pathways associated with the interactive effects of elevated CO2 and nitrate regulating leaf growth in a perennial grass species.

Nitrogen physiology of contrasting genotypes of Chenopodium quinoa Willd. (Amaranthaceae)

Quinoa has been highlighted as a promising crop to sustain food security. The selection of physiological traits that allow identification genotypes with high Nitrogen use efficiency (NUE) is a key factor to increase Quinoa cultivation. In order to unveil the underpinning mechanisms for N-stress tolerance in Quinoa, three genotypes with similar phenology, but different NUE were developed under high (HN) or low (LN) nitrogen conditions. N metabolism processes and photosynthetic performance were studied after anthesis and in correlation with productivity to identify principal traits related to NUE. We found that protein content, net photosynthesis and leaf dry-mass were determinant attributes for yield at both HN and LN conditions. Contrastingly, the enhancement of N related metabolites ({{rm{NH}}}_{4}^{+}, proline, betacyanins) and processes related with re-assimilation of {{rm{NH}}}_{4}^{+}, including an increment of glutamine synthetase activity and up-regulation of CqAMT1,1 transporter expression in leaves, were negatively correlated with grain yield at both N conditions. Biochemical aspects of photosynthesis and root biomass were traits exclusively associated with grain yield at LN. The impact of N supply on seed quality is discussed. These results provide new insights towards the understanding the N metabolism of Quinoa.

Nitrogen Can Alleviate the Inhibition of Photosynthesis Caused by High Temperature Stress under Both Steady-State and Flecked Irradiance.

Nitrogen is one of the most important elements for plants and is closely related to photosynthesis. High temperature stress significantly inhibits photosynthesis under both steady-state and flecked irradiance. However, it is not known whether nitrogen can affect the decrease in photosynthesis caused by high temperature, especially under flecked irradiance. In the present study, a pot experiment was conducted under two nitrogen (N) supplies with rice plants, and the steady-state and dynamic photosynthesis rates were measured under 28 and 40°C. High temperature significantly increased leaf hydraulic conductance (Kleaf) under high N supply (HN) but not under low N supply (LN). The increased Kleaf maintained a constant leaf water potential (Ψleaf) and steady-state stomatal conductance (gs,sat) under HN, while the Ψleaf and gs,sat significantly decreased under high temperature in LN conditions. This resulted in a more severe decrease in steady-state photosynthesis (Asat) under high temperature in the LN conditions. After shifting from low to high light, high temperature significantly delayed the recovery of photosynthesis, which resulted in more carbon loss under flecked irradiance. These effects were obtained under HN to a lesser extent than under LN supply. Therefore, it is concluded that nitrogen can alleviate the inhibition of photosynthesis caused by high temperature stress under both steady-state and flecked irradiance.

Interrelations among Early Vigor, Flowering Time, Physiological Maturity, and Grain Yield in Tropical Maize (Zea mays L.) under Multiple Abiotic Stresses

We studied the interrelation among time to anthesis, physiological maturity, and grain yield in tropical maize (Zea mays L.) facing terminal drought and nitrogen deficiency. Sixty‐one hybrids were grown under optimum, nitrogen‐deficient (LN), and drought‐stressed (DS) conditions. Grain yield was negatively correlated with time to anthesis under DS (r = −0.4*) and positively correlated with the grain‐filling period (optimum: r = 0.54**; LN: r = 0.61***; DS: r = 0.69***) across treatments. These results suggest that coselecting for grain yield, early anthesis, and a long grain‐filling period within a maturity group could help increase grain yield. A second experiment involving eight hybrids contrasting for grain yield and time to anthesis was conducted under similar stresses to identify secondary traits associated with grain yield and time to physiological maturity: early vigor (measured as normalized differential vegetation index) correlated with grain yield under optimum (r = 0.77*) and LN conditions (r = 0.72*). Time to physiological maturity was associated with senescence across treatments (optimum: r = −0.97***; LN: r = −0.82*; DS: r = −0.81*), making senescence suitable to approximate physiological maturity. Repeatability for secondary traits (r2 = 0.79 on average) was higher than for grain yield (r2 = 0.68) across treatments. In light of the association of these traits with grain yield and their high repeatability, grain yield could be increased within a maturity group by simultaneously selecting for high normalized differential vegetation index during vegetative growth and early anthesis and low senescence during grain filling, in addition to grain yield.

Leaf photosynthesis and associations with grain yield, biomass and nitrogen-use efficiency in landraces, synthetic-derived lines and cultivars in wheat

Future genetic progress in wheat grain yield will depend on increasing above-ground biomass and this must be achieved without commensurate increases in N fertilizer inputs to minimise environmental impacts. Our objective was to quantify variation in grain yield, above-ground biomass and N-use efficiency (NUE) and associated traits in a panel of diverse hexaploid wheat germplasm comprising: (i) landraces from the AE Watkins collection, (ii) synthetic-derived hexaploid lines in a cv. Paragon spring wheat background and (iii) UK modern cultivars including cv. Paragon under low N and high N conditions. A field experiment was carried out in two seasons examining 15 genotypes (five landraces, five synthetic-derived (SD) hexaploid lines and five UK modern cultivars) under low N and high N conditions at Nottingham University farm, UK. Machine-harvested grain yield, above-ground biomass and NUE were measured. Physiological traits were assessed including flag-leaf light-saturated photosynthetic rate (Amax) and relative chlorophyll content (SPAD) under HN conditions; and flag-leaf senescence duration and rate and Normalized Difference Vegetative Index (NDVI) under LN and HN conditions. Under HN conditions, the modern cultivars overall produced higher grain yield than the SD lines (+9.7%) and the landraces (+60.4%); and the modern cultivars and SD lines also produced higher biomass than the landraces (30.3% and 28.4%, respectively). Under LN conditions, reduction in grain yield and biomass compared to HN conditions was least for the landraces (−1% and −8.6%, respectively), intermediate for the SD lines (−7.4 and −10.2%, respectively) and highest for the modern cultivars (−9.3 and −24.6%, respectively). As a result, the SD lines had higher biomass (+17%) than the modern cultivars under LN conditions. Under HN conditions the synthetic derivatives (23.8μmolm−2s−1) and modern cultivars (241.1μmolm−2s−1) had higher pre-anthesis Amax than the landraces (19.7μmolm−2s−1) (P<0.001). Pre-anthesis Amax was strongly positively linearly associated with above-ground biomass (R2=0.63, P<0.001) and grain yield (R2=0.75, P<0.001) amongst the 15 genotypes. Flag-leaf Amax was also positively linearly associated with flag-leaf relative chlorophyll content at anthesis (R2=0.74; P<0.001). Comparing the SD lines to the recurrent parent Paragon, under HN conditions one line (SD 22) had higher pre-anthesis flag-leaf Amax than Paragon (P<0.05). Under LN conditions one line (SD 24, +27%) had higher yield than Paragon (P<0.05) and two lines (SD 24 and SD 38, +32% and +31%, respectively) had more biomass than Paragon (P<0.05). Our results indicated that introgressing traits from synthetic-derived wheat and landraces into UK modern wheat germplasm offers scope to raise above-ground biomass and grain yield in moderate-to-low N availability environments.

Combined Effects of Ocean Acidification and Light or Nitrogen Availabilities on 13C Fractionation in Marine Dinoflagellates.

Along with increasing oceanic CO2 concentrations, enhanced stratification constrains phytoplankton to shallower upper mixed layers with altered light regimes and nutrient concentrations. Here, we investigate the effects of elevated pCO2 in combination with light or nitrogen-limitation on 13C fractionation (εp) in four dinoflagellate species. We cultured Gonyaulax spinifera and Protoceratium reticulatum in dilute batches under low-light (‘LL’) and high-light (‘HL’) conditions, and grew Alexandrium fundyense and Scrippsiella trochoidea in nitrogen-limited continuous cultures (‘LN’) and nitrogen-replete batches (‘HN’). The observed CO2-dependency of εp remained unaffected by the availability of light for both G. spinifera and P. reticulatum, though at HL εp was consistently lower by about 2.7‰ over the tested CO2 range for P. reticulatum. This may reflect increased uptake of (13C-enriched) bicarbonate fueled by increased ATP production under HL conditions. The observed CO2-dependency of εp disappeared under LN conditions in both A. fundyense and S. trochoidea. The generally higher εp under LN may be associated with lower organic carbon production rates and/or higher ATP:NADPH ratios. CO2-dependent εp under non-limiting conditions has been observed in several dinoflagellate species, showing potential for a new CO2-proxy. Our results however demonstrate that light- and nitrogen-limitation also affect εp, thereby illustrating the need to carefully consider prevailing environmental conditions.

Strigolactones are required for nitric oxide to induce root elongation in response to nitrogen and phosphate deficiencies in rice.

The response of the root system architecture to nutrient deficiencies is critical for sustainable agriculture. Nitric oxide (NO) is considered a key regulator of root growth, although the mechanisms remain unknown. Phenotypic, cellular and genetic analyses were undertaken in rice to explore the role of NO in regulating root growth and strigolactone (SL) signalling under nitrogen-deficient and phosphate-deficient conditions (LN and LP). LN-induced and LP-induced seminal root elongation paralleled NO production in root tips. NO played an important role in a shared pathway of LN-induced and LP-induced root elongation via increased meristem activity. Interestingly, no responses of root elongation were observed in SL d mutants compared with wild-type plants, although similar NO accumulation was induced by sodium nitroprusside (SNP) application. Application of abamine (the SL inhibitor) reduced seminal root length and pCYCB1;1::GUS expression induced by SNP application in wild type; furthermore, comparison with wild type showed lower SL-signalling genes in nia2 mutants under control and LN treatments and similar under SNP application. Western blot analysis revealed that NO, similar to SL, triggered proteasome-mediated degradation of D53 protein levels. Therefore, we presented a novel signalling pathway in which NO-activated seminal root elongation under LN and LP conditions, with the involvement of SLs.

Effect of Elevated CO2 Concentration, Elevated Temperature and No Nitrogen Fertilization on Methanogenic Archaeal and Methane-Oxidizing Bacterial Community Structures in Paddy Soil.

Elevated concentrations of atmospheric CO2 ([CO2]) enhance the production and emission of methane in paddy fields. In the present study, the effects of elevated [CO2], elevated temperature (ET), and no nitrogen fertilization (LN) on methanogenic archaeal and methane-oxidizing bacterial community structures in a free-air CO2 enrichment (FACE) experimental paddy field were investigated by PCR-DGGE and real-time quantitative PCR. Soil samples were collected from the upper and lower soil layers at the rice panicle initiation (PI) and mid-ripening (MR) stages. The composition of the methanogenic archaeal community in the upper and lower soil layers was not markedly affected by the elevated [CO2], ET, or LN condition. The abundance of the methanogenic archaeal community in the upper and lower soil layers was also not affected by elevated [CO2] or ET, but was significantly increased at the rice PI stage and significantly decreased by LN in the lower soil layer. In contrast, the composition of the methane-oxidizing bacterial community was affected by rice-growing stages in the upper soil layer. The abundance of methane-oxidizing bacteria was significantly decreased by elevated [CO2] and LN in both soil layers at the rice MR stage and by ET in the upper soil layer. The ratio of mcrA/pmoA genes correlated with methane emission from ambient and FACE paddy plots at the PI stage. These results indicate that the decrease observed in the abundance of methane-oxidizing bacteria was related to increased methane emission from the paddy field under the elevated [CO2], ET, and LN conditions.

Effects of planting density and nitrogen fertilization level on grain yield and harvest index in seven modern tropical maize hybrids (Zea maysL.)

SUMMARYTo support tropical maize (Zea maysL.) breeding efforts, the current work aimed to assess harvest index (HI) in modern hybrids and determine the effect of different planting densities on grain yield and HI under well-fertilized (HN) and nitrogen (N) deficient conditions. Harvest index and grain yield of 34 hybrids on average reached 0·42 and 7·06 t/ha (five environments), indicating a large potential for improvement in HI relative to temperate hybrids. Ear weight (r= 0·88), HI (r= 0·78) and shoot dry weight (r= 0·68) were strongly associated with grain yield. In the second experiment, seven hybrids were evaluated at planting densities of 5, 7, 9 and 11 plants/m2under HN (six environments) and N deficient (LN) conditions (four environments) to assess the effect of planting density on grain yield and HI. Grain yield increased by 40·4 and 21·8% under HN and LN conditions when planting density was increased relative to the lowest planting density. Harvest index increased from 0·42 at 5 plants/m2to 0·45 at 11 plants/m2under HN conditions and decreased from 0·44 at 5 plants/m2to 0·42 at 9 plants/m2under LN conditions. Harvest index was maximized at planting densities of 8·33 plants/m2and 5·30 plants/m2under HN and LN conditions, respectively, while grain yield was maximized at 9·93 plants/m2and 7·89/m2. Optimal planting density maximizing both HI and grain yield were higher than planting densities currently used in tropical germplasm. It can be concluded that productivity in tropical maize could be increased both under intensive (+40·4%) and lower-input management (+21·8%) by increasing planting densities above those currently used in smallholder agriculture in Latin America and Sub-Saharan Africa, in environments targeted by the International Maize and Wheat Improvement Center.

Nitrate limitation and ocean acidification interact with UV-B to reduce photosynthetic performance in the diatom &amp;lt;i&amp;gt;Phaeodactylum tricornutum&amp;lt;/i&amp;gt;

Abstract. It has been proposed that ocean acidification (OA) will interact with other environmental factors to influence the overall impact of global change on biological systems. Accordingly we investigated the influence of nitrogen limitation and OA on the physiology of diatoms by growing the diatom Phaeodactylum tricornutum Bohlin under elevated (1000 μatm; high CO2 – HC) or ambient (390 μatm; low CO2 – LC) levels of CO2 with replete (110 μmol L−1; high nitrate – HN) or reduced (10 μmol L−1; low nitrate – LN) levels of NO3- and subjecting the cells to solar radiation with or without UV irradiance to determine their susceptibility to UV radiation (UVR, 280–400 nm). Our results indicate that OA and UVB induced significantly higher inhibition of both the photosynthetic rate and quantum yield under LN than under HN conditions. UVA or/and UVB increased the cells' non-photochemical quenching (NPQ) regardless of the CO2 levels. Under LN and OA conditions, activity of superoxide dismutase and catalase activities were enhanced, along with the highest sensitivity to UVB and the lowest ratio of repair to damage of PSII. HC-grown cells showed a faster recovery rate of yield under HN but not under LN conditions. We conclude therefore that nutrient limitation makes cells more prone to the deleterious effects of UV radiation and that HC conditions (ocean acidification) exacerbate this effect. The finding that nitrate limitation and ocean acidification interact with UV-B to reduce photosynthetic performance of the diatom P. tricornutum implies that ocean primary production and the marine biological C pump will be affected by OA under multiple stressors.

Response of Roots of Maize Varieties Released in Different Years to Low Nitrogen and Drought Stresses

The changes in root characteristics were studied under low nitrogen stress(LN) and combined stress of low nitrogen and drought(LD) using six maize varieties released from 1973 to 2009, including Zhongdan 2, Danyu 13, Yedan 13, Nongda 108, Zhengdan 958, and a new variety Yudan 606. The result showed that root dry weight, root length and root surface area of the varieties increased at first and then decreased, finally increased again in the process of time. The increase of the three parameters in earlier released varieties could get more water and nutrition from soil, the decrease of these in later released varieties was available to reduce the redundant organ's dry matter consumption, and the increase again of these in the new variety would meet water and nutrition requirements for yield increase continuously. Compared with the old varieties, root dry weight of the modern varieties changed smaller, root length and surface areas increased more, root average diameter became thinner, root bleeding sap decreased non-significantly under the LN and LD conditions. These results suggested that root characteristics of the varieties have been optimized gradually, the adjustment ability of root morphology, and the LN and LD stress tolerance in modern varieties have been increased.

Effect of ultraviolet radiation on photosynthesis, biomass, and fatty acid content and profile of a Scenedesmus rubescens-like microalga

The effects of ultraviolet radiation (UVR) and nitrogen (NaNO3) concentration on photosynthesis, biomass, and fatty acid content and profile of a Scenedesmus rubescens-like microalga were measured in an outdoor 8-day culture study. UV-induced photoinhibition decreased from 42.6% to 3.5%, in the presence of 75mg/L NaNO3 (HN) and from 52.9% to 22.6% in the presence of 7.5mg/L NaNO3 (LN) nitrogen concentration, respectively. The concentrations of UV-absorbing compounds increased 4.3 and 4.9 times under HN and LN, respectively. Biomass accumulation was suppressed (10.7%) by UVR under HN, but not under LN conditions. Carotenoid content decreased from 1.05±0.06 to 0.96±0.15 (with UV radiation) and to 0.91±0.07 (without UV radiation), respectively, under HN, while it decreased to 0.05±0.04 (with UV radiation) and to 0.11±0.08 (without UV radiation), respectively, under LN. The content of C18:1n9 fatty acids increased by about 430%, whereas that of C18:3n3 decreased by about 65% in both radiation treatments during nitrogen starvation. The results showed that the absence of UVR screening does not change the fatty acid content and profile of S. rubescens-like algae cultivated outdoors under HN and LN conditions.

Root growth in response to nitrogen supply in Chinese maize hybrids released between 1973 and 2009

Root growth has a fundamental role in nitrogen (N) use efficiency. Nevertheless, little is known about how modern breeding progress has affected root growth and its responses to N supply. The root and shoot growth of a core set of 11 representative Chinese maize (Zea mays L.) hybrids released between 1973 and 2009 were investigated under high N (4 mmol L(-1), HN) and low N (0.04 mmol L(-1), LN) levels in a solution culture system. Compared with LN, HN treatment decreased root dry weight (RDW), the root: shoot ratio (R/S), and the relative growth rate for root dry weight (RGR(root)), but increased the total root length (TRL) and the total lateral root length (LRL). The total axial root length (ARL) per plant was reduced under HN, mostly in hybrids released before the 1990s. The number of seminal roots (SRN) was largely unaffected by different N levels. More recently released hybrids showed higher relative growth rates in the shoot under both HN and LN. However, the roots only showed increased RGR under HN treatment. Correspondingly, there was a positive linear relationship with the year of hybrid release for TRL, LRL and ARL under HN treatment. Together, these results suggest that while shoot growth of maize has improved, its root growth has only improved under high N conditions over the last 36 years of selective breeding in China. Improving root growth under LN conditions may be necessary to increase the N use efficiency of maize.

Recurrent, thermally-induced shifts in species distribution range in the Humboldt current upwelling system

El Niño-Southern Oscillation (ENSO) is a global climate variablility, which fundamentally influences environmental patterns of the Humboldt Current System (HCS) off Chile and Peru. The surf clams Donax obesulus and Mesodesma donacium are dominant and highly productive bivalves of exposed sandy beaches of the HCS. Existing knowledge indicates that El Niño (EN, warm phase of ENSO) and La Niña (LN, cold phase of ENSO) affect populations of both species in a different way, although understanding of the mechanisms underlying these effects is still lacking. The aim of this study was to test hypotheses attempting to explain field observations on the effect of strong EN or LN events by using controlled experimental conditions. Growth and mortality rates of both species were registered during a four-week experiment under EN temperature conditions, normal temperature conditions and LN temperature conditions. While D. obesulus exhibited reduced growth and higher mortality under LN conditions, M. donacium showed reduced growth and higher mortality under EN conditions. The results clearly indicate different temperature tolerance windows for each species, possibly reflecting the evolutionary origins of the Donacidae and Mesodesmatidae in regions with contrasting temperature regimes. These results provide experimental support for previous hypotheses suggesting that thermal tolerance is the driving factor behind observed changes in the species distributions of D. obesulus and M. donacium during the extreme phases of ENSO.

Root and nitrate distribution as related to the critical plant N status of a fertigated tomato crop

SummaryLow fertiliser-use efficiency and high N losses from leaching are still reported in drip-irrigated tomatoes. One reason for this is the lack of reference data for soil N status, to allow proper N nutrition under conditions of high nitrate gradients in the soil profile. In this study, root colonisation, nitrate concentration, and plant N uptake were monitored dynamically on a tomato crop at two levels of N nutrition: sufficient (445 kg N ha–1; HN), or limiting (256 kg ha–1; LN). N stress in the LN treatment resulted in a 180% increase in root length and a 200% increase in the total soil volume occupied by the roots, along with reduced aerial growth. Root spatial development tended to decrease at the end of the season in the HN treatment, while root expansion was continuous in the LN conditions. Differences in soil N concentrations between treatments were found only in wetted soil zones with low or no root growth, while soil N in well-rooted zones was uniformly low in both treatments. As a result, the best linear relationship between soil nitrate concentration and plant N status (assessed by the nitrogen nutrition index; NNI) was found when the mean soil nitrate concentration was calculated for a large soil volume; in this case, a hemisphere approx. 65 cm in radius. In this volume, the critical nitrate concentration required to obtain a NNI of 1.0 was 102 mg l–1. Nitrate accumulation at the periphery of the wetted soil volume should be checked regularly to improve fertiliser-use efficiency.

Improving Nitrogen‐Use Efficiency in European Maize

Maize (Zea mays L.) cultivars with improved N‐use efficiency would be beneficial for low‐input production systems. Our objective was to estimate quantitative genetic parameters to optimize breeding programs for improving productivity under low N levels. Results of 21 field experiments with European breeding materials belonging to the flint and dent gene pool are presented. The study was performed during 1989 and 1999 at several locations in typical maize growing regions of Germany and France. All experiments were conducted at high (HN) and low (LN, no N fertilizer applied) N levels. Average grain yield was reduced by 37% at LN compared with HN. Coefficients of genotypic correlation between HN and LN were variable with an average of rG = 0.74 for grain yield and generally high for grain dry matter content. For grain yield, analyses of variance were computed from relative data, where plot values were expressed as percentage of the trial mean. Variances caused by genotype (G), G × location (L) interaction, and error effects were higher at LN compared with HN, with similar heritabilities at both N levels. For the untransformed data, components of variance were higher at HN than at LN. Genotype × N as well as G × L × N level interaction variances were significant in most experiments. Efficiency of improvement of grain yield at LN through indirect selection at HN was 70% compared with direct selection at LN. A trend toward increased efficiency of direct selection under LN conditions was evident with decreasing grain yield at LN.