Effects Of Nitrogen Limitation Research Articles

Nitrogen deprivation strongly affects Photosystem II but not phycoerythrin level in the divinyl-chlorophyll b-containing cyanobacterium Prochlorococcus marinus

Effects of nitrogen limitation on Photosystem II (PSII) activities and on phycoerythrin were studied in batch cultures of the marine oxyphotobacterium Prochlorococcus marinus. Dramatic decreases in photochemical quantum yields (FV/FM), the amplitude of thermoluminescence (TL) B-band, and the rate of QA reoxidation were observed within 12 h of growth in nitrogen-limited conditions. The decline in FV/FM paralleled changes in the TL B-band amplitude, indicative of losses in PSII activities and formation of non-functional PSII centers. These changes were accompanied by a continuous reduction in D1 protein content. In contrast, nitrogen deprivation did not cause any significant reduction in phycoerythrin content. Our results refute phycoerythrin as a nitrogen storage complex in Prochlorococcus. Regulation of phycoerythrin gene expression in Prochlorococcus is different from that in typical phycobilisome-containing cyanobacteria and eukaryotic algae investigated so far.

Redox modulation of chloroplast DNA replication in Chlamydomonas reinhardtii.

We constructed a plasmid probe containing DNA sequences unique for chloroplast (Cp) genome and nuclear genome of Chlamydomonas reinhardtii. Using this probe and quantitative Southern blot analyses, we determined the content ratio of Cp DNA/nuclear DNA in total DNA isolated from cells grown in different conditions. Algal cells grown photoheterotrophically with acetate as an added carbon source contain the highest amount of Cp DNA compared with cells grown in other conditions tested. We investigated the effect of nitrogen limitation, 5-fluorodeoxyuridine treatment, cadmium exposure, photoautotrophic growth, and heterotrophic growth in darkness. The change in the Cp/nuclear DNA ratio in cells shifted from one growth condition to another depended on cell division; Cp DNA content in undivided cells remained constant. Therefore, the reduction of Cp DNA content was attributed by under replication rather than selective degradation of Cp DNA. Cells with low Cp DNA content often contained less reduced glutathione, suggesting the possible effect of redox status. Low Cp DNA content was detected in cells treated with inhibitors that block electron flow of photosystems and in mutants with PS I defective phenotype. On the basis of these data, we propose that in C. reinhardtii, Cp DNA replication be modulated by redox status.

Effect of nitrogen limitation on foliar antioxidants in relationship to other metabolic characteristics.

The long-term effect of limiting soil nitrogen (N) availability on foliar antioxidants, thermal energy dissipation, photosynthetic and respiratory electron transport, and carbohydrates was investigated in Spinacia oleracea L. Starch, sucrose, and glucose accumulated in leaves of N-limited spinach at predawn, consistent with a downregulation of chloroplast processes by whole-plant sink limitation in response to a limited supply of N-based macromolecules throughout the plant. On a leaf-area or dry-weight basis, levels of chlorophyll, carotenoid pools, photosynthetic electron transport capacity, as well as activities for the predominantly chloroplast-localized antioxidant enzymes ascorbate peroxidase (EC 1.11.1.11) and glutathione reductase (EC 1.6.4.2) were much lower in N-limited versus N-replete plants. When expressed on a chlorophyll basis, foliar levels of all of these parameters were similar in N-replete versus N-limited plants. However, on a total-protein basis, antioxidant enzyme activities were higher in N-limited plants. Nitrogen-limited spinach showed higher levels of thermal energy dissipation and of zeaxanthin and antheraxanthin at midday, as well as slightly higher ascorbate contents relative to chlorophyll. These results indicate that strong, long-term N limitation led not only to alterations in the balance between different processes but also to an overall downregulation of light collection, photosynthetic electron transport capacity, and chloroplast-based antioxidant enzymes. This is further supported by the finding that glucose-feeding of excised leaves led to strong concomitant decreases in photosynthetic electron transport capacity and ascorbate peroxidase activity. On a leaf-area basis, neither superoxide dismutase (EC 1.15.1.1) activity nor dark repiration rates showed a treatment effect. This indicates that overall mitochondrial electron transport activity does not decrease under long-term N limitation and is consistent with localization of an important fraction of foliar superoxide dismutase in mitochondria.

Effects of nitrogen limitation on biofilm formation in a hydrocarbon-degrading trickle-bed filter.

The effect of nitrogen limitation on young and mature steady-state biofilm in a trickle-bed filter was studied. Toluene and n-heptane were the sole carbon source. Biomass concentration, respiration, substrate-induced respiration, metabolic quotient, and total hydrocarbon degradation efficiency were measured. The aim of the experiment was to control excess biomass production in the trickle-bed filter by limiting the mineral nutrients and to achieve increased mineralization of the carbon source. Biofilm growth responded strongly to the amount of available nitrogen, whereas hydrocarbon degradation efficiency reached a maximum of 60% and could not be increased even by further addition of nitrogen. The experiments showed that 95% of the adsorbed carbon was mineralized completely and only 5% was used for biofilm formation. This complete mineralization can also be concluded from the metabolic quotient. The value of the latter was about 6-10 mg CO2-C g-1 Cmic h-1, indicating an expanded energy demand due to stress effects in the presence of nutrient deficiency. It was postulated that determination of the metabolic quotient could be an simple instrument to measure the rate of mineralization of carbon sources and also the rate of biomass formation in trickle-bed filters or biofilters.

The adverse effect of nitrogen limitation and excess-cellobiose on Fibrobacter succinogenes S85

Fibrobacter succinogenes S85 cultures that were cellobiose-limited converted cellobiose to succinate and acetate, produced little glucose or cellotriose, maintained an intracellular ATP concentration of 4.1 mM and a membrane potential of 140 mV for 24 h, did not lyse at a rapid rate once they had reached sta- tionary phase, and had a most probable number of viable cells that was greater than 10 6 /ml. When the cel- lobiose concentration was increased 6-fold (5 mM to 30 mM), ammonia was depleted and the cultures left 10 mM cellobiose. Cultures provided with excess cello- biose produced succinate and acetate while they were growing, but there was little increase in fermentation acids after the ammonia was depleted and growth ceased. The stationary-phase, cellobiose-excess cultures had a lysis rate that was 7-fold faster than that of the cellobiose-limited cultures, and the most probable number was only 3.3 · 10 3 cells/ml. The stationary- phase, cellobiose-excess cultures had 2.5 times as much cellular polysaccharide as the cellobiose-limited cultures, but the intracellular ATP and membrane potential were very low (0.1 mM and 40 mV respectively). Met- hylglyoxal, a potentially toxic end-product of carbohy- drate fermentation, could not be detected, and fresh inocula grew rapidly in spent medium that was supple- mented with additional ammonia. Stationary-phase, cellobiose-excess cultures converted cellobiose to glucose and cellotriose, but the apparent Km of cellotriose for- mation was 15-fold lower than the Km of glucose pro- duction (0.7 mM compared to 10 mM).

Degradation of chlorophenoxyacetic acids by the lignin-degrading fungus Dichomitus squalens.

We have examined the degradation of 14C ring- and side-chain-labelled 2,4,5-trichlorophenoxyacetic acid by Dichomitus squalens and Phanerochaete chrysosporium. The effects of Mn2+ on the degradation of these radiolabeled substrates by D. squalens and the effect of nitrogen limitation on their degradation by D. chrysosporium suggested that in both fungi, side-chain cleavage was catalysed by a mechanism independent of the lignin degradation system, whereas the degradation of the aromatic ring was dependent on the lignin degradative system. Using unlabelled substrates, a pathway for the degradation of chlorophenoxyacetic acids was elucidated in D. squalens. Time courses for the degradation of unlabelled chlorophenoxyacetic acids by D. squalens demonstrated that the corresponding chlorophenol was the initial product formed. The chlorophenol intermediate was xylosylated to form the chlorophenolxyloside. In turn, the chlorophenolxyloside could be hydrolysed by an intracellular -xylosidase to regenerate the chlorophenol. The chlorophenol product of the xylosidase reaction was oxidatively dechlorinated to form 2-chloro-p-benzoquinone which could undergo subsequent further dechlorination and ring-opening reactions, as has been reported previously for P. chrysosporium.

Nitrogen starvation of the rice blast fungusMagnaporthe griseamay act as an environmental cue for disease symptom expression

The effect of nitrogen limitation on the rice blast fungusMagnaporthe griseawas examined. Nitrogen starvation-stress induced expression of a large number of genes expressed during growth of the fungus in plant tissue, particularly during disease symptom outbreak. Nitrogen starvation-stress elicited production of secreted products which were isolated from culture filtrates ofM. grisea, and caused senescence of rice leaves within 48 h of application. Leaf senescence was associated with uptake of the secreted product(s) and rapid leaf water loss. The senescence-promoting activity was restricted to a high molecular weight culture filtrate fraction and was eliminated by boiling or prolonged treatment with proteinase K. The production of the activity was conserved in different host-limited forms of the fungus and was not associated with melanin or MPG1 hydrophobin production. Strains carrying mutations at the NUT1 locus controlling nitrogen source utilization, or the NPR1 and NPR2 loci which regulate nitrogen metabolism and pathogenicity, produced only residual senescent activity. We conclude that nitrogen starvation-stress may act as one of the inductive cues for disease symptom expression during rice blast infections.

Differential Effects of Nitrogen Limitation on Photosynthetic Efficiency of Photosystems I and II in Microalgae.

The effects of nitrogen starvation on photosynthetic efficiency were examined in three unicellular algae by measuring changes in the quantum yield of fluorescence with a pump-and-probe method and thermal efficiency (i.e. the percentage of trapped energy stored photochemically) with a pulsed photoacoustic method together with the inhibitor 3-(3,4-dichlorophenyl)-1,1-dimethylurea to distinguish photosystems I and II (PSI and PSII). Measured at 620 nm, maximum thermal efficiency for both photosystems was 32% for the diatom Thalassiosira weissflogii (PSII:PSI ratio of 2:1), 39% for the green alga Dunaliella tertiolecta (PSII:PSI ratio of 1:1), and 29% for the cyanobacterium Synechococcus sp. PCC 7002 (PSII:PSI ratio of 1:2). Nitrogen starvation decreased total thermal efficiency by 56% for T. weissflogii and by 26% for D. tertiolecta but caused no change in Synechococcus. Decreases in the number of active PSII reaction centers (inferred from changes in variable fluorescence) were larger: 86% (T. weissflogii), 65% (D. tertiolecta), and 65% (Synechococcus). The selective inactivation of PSII under nitrogen starvation was confirmed by independent measurements of active PSII using oxygen flash yields and active PSI using P700 reduction. Relatively high thermal efficiencies were measured in all three species in the presence of the PSII inhibitor 3-(3,4-dichlorophenyl)-1,1-dimethylurea, suggesting the potential for significant cyclic electron flow around PSI. Fluorescence or photoacoustic data agreed well; in T. weissflogii, the functional cross-sectional area of PSII at 620 nm was estimated to be the same using both methods (approximately 1.8 x 102 A2). The effects of nitrogen starvation occur mainly in PSII and are well represented by variable fluorescence measurements.

Use of dyes in solid medium for screening ligninolytic activity of selective actinomycetes

Lignin, a three-dimensional biopolymer, not only encrusts the cellulose microfibrils in a sheath-like manner, but is also bonded physically and chemically to the plant polysaccharides. Unless the lignin is depolymerized, solubilized, or removed, the cellulose and hemicelluloses cannot be easily hydrolyzed by respective enzymes for their bioconversion into biofuels and chemicals. By now it has been established that lignin peroxidase (LiP) of white-rot fungus Phanerochaete chrysosporium is responsible for degradation of lignin. It has been reported that LiP is produced during secondary metabolism under carbon or nitrogen limitation by this organism. In literature, usually low yields (per unit volume) of LiP with P. chrysosporium have been reported. The reasons for low yields may be attributed to insufficient nitrogen in production media, which ultimately affects the synthesis of LiP protein. Therefore, it necessitated a search for an organism that can produce a ligninolytic enzyme system during its primary metabolism, without any effect of nitrogen limitation in the fermentation medium and without supply of extra oxygen to the cultures. Glenn and Gold were the first to report that decolorization of polymeric dyes in liquid cultures is related to the lignin degradation system. They demonstrated that like lignin degradation, the decolorization of polymericmore » dyes by the white-rot basidiomycete P. chrysosporium occurred during secondary metabolism, was suppressed in cultures grown in the presence of high levels of nitrogen, and was strongly dependent on the oxygen concentration in the cultures. The present study was undertaken to establish if certain dyes in solid media could be used to screen ligninolytic activity of selective actinomycetes during their primary metabolism without the limitation of nitrogen in the medium.« less

Effects of nitrogen limitation on water relations of jack pine (Pinus banksiana Lamb.) seedlings

ABSTRACTThe water relations of shoots of young jack pine (Pinus banksiana Lamb.) seedlings were examined 6 and 15 weeks after the initiation of four different dynamic nitrogen (N) treatments using a pressure‐volume analysis. The N treatments produced a wide range of needle N concentrations from 12 to 32 mg g−1 dry mass and a 10‐fold difference in total dry mass at 15 weeks. Osmotic potential at full turgor did not change over the range of needle N concentrations observed. Osmotic potential at turgor‐loss point, however, declined as N concentrations decreased, indicating an increased ability of N‐deficient jack pine plants to maintain turgor. The increase could be attributed largely to an increase in cell wall elasticity, suggesting that elasticity changes may be a common, significant adaptation of plants to environmental stresses. Dry mass per unit saturated water almost doubled as needle N level dropped from 32 to 12 mg g−1 and was inversely correlated to the bulk modulus of elasticity. This suggests that cell wall elasticity is determined more by the nature of its cross‐linking matrix than by the total amount of cell wall material present. Developmental change was evident in the response of some water relation variables to N limitation.

Effects of nitrogen limitation on growth and nitrite excretion rates of the dinoflagellate Prorocentrum minimum

Continuous nitrate-limited cultures of the dinoflagellate Prorocentrum minimum were grown under saturating photon flux densities to study the effects of nitrate pulses on the time variations of nitrate uptake, nitrite excretion, and cell division rate. In the first experiment, 5 chemostats were stabilized at the same dilution rate and, after stopping of the renewal supplies, received successively 1 pulse of nitrate at 24 h intervals. In the second, nitrate pulses were added about every 12 h in 1 chemostat. In the third experiment, 4 chemostats stabilized at different growth rates received 1 pulse of nitrate. Nitrate uptake process showed decreasing initial rates and lower maximum rates in cultures subjected to longer starvation times. In all cases, the amount of nitrite excreted before reabsorption represented an important proportion of the initially supplied nitrate (up to 45 %). This suggested that for nitrogen-deprived cells of L? minimum reduction of nitrite by the nitrite reductase is the more limiting step in the nitrateassimilatory pathway. The proportion of pulsed nitrate which is excreted as nitrite increased for decreasing growth rates. For 1 and 2 d of nitrate deprivation, the ratio nitrite excretion ratehitrate uptake rate integrated during each perturbation experiment increased, but decreased after longer times of starvation. This suggests that the processes of nitrate uptake and nitrite reduction are affected at different rates during nitrogen deprivation. The implications of nitrite excretion in N-limited cells on the determination of new production are discussed.

Regulation of the amino acid permeases in nitrogen-limited continuous cultures of the yeast Saccharomyces cerevisiae.

In the yeast Saccharomyces cerevisiae, there is a general amino acid permease, regulated by nitrogen catabolite repression, and several specific permeases whose nitrogen regulation is not well understood. In this study, we used continuous cultures to analyse the effect of nitrogen limitation and pH on the activity of general and several specific amino acid permeases. General permease activity was maximal in severe nitrogen limitation and diminished 400-fold in cells grown under nitrogen excess. For the specific permeases, the maximal uptake activity was found between mild limitation and nitrogen excess, while very small activity was detected under strict limitation. These results indicate that the nitrogen regulation of the general and the specific amino acid carriers is coordinated in such a way that no redundancy exists in amino acid transport. The regulation of the specific permeases was similar to that found for a system with anabolic function in nitrogen metabolism. All of these permeases are supposed to work through a proton symport mechanism, and thus rely on pH gradients to carry out their function. We studied the effect of pH on the kinetic constants of the general permease. Our results show that the effect of pH on the Km was different for acidic, neutral and basic amino acids, while the effect on Vmax was independent of the electrical charge of the amino acids.

Effect of nitrogen limitation on the biodegradability and toxicity of nitro- and aminophenol isomers to methanogenesis

Monosubstituted nitro- and aminophenol isomers exhibited limited biodegradability under methanogenic conditions when supplied as the sole source of carbon and energy. This was examined by supplying to the same sediment samples, each isomer of nitro- and aminophenol as a sole source of added carbon under either N-supplemented or N-deprived methanogenic conditions. The results demonstrated that under N-supplemented conditions, only 2-NP (NP = nitrophenol), 4-NP and 4-AP (AP = aminophenol) were stoichiometrically mineralized, 2-AP, 3-AP, and the 3-AP metabolite formed from 3-NP reduction were persistent over the 51-week incubation period. In addition, NP isomers inhibited initial rates of methanogenesis, while all AP amended cultures exhibited no significant inhibition in the rate of methanogenesis. Under N-deprived conditions, 2-NP, 2-AP and 4-AP were mineralized, while 3-NP, 4-NP and 3-AP were persistent over the 51-week incubation period. Although all NP isomers were still metabolized through the corresponding AP isomer, the deprivation of nitrogen significantly depressed both the rate and extent of methanogenesis. In general, nitrogen supplemented cultures produced 25% more methane than the nitrogen limited cultures, and the initial rates of methanogenesis were four times greater. While these data showed that under N-deprived conditions methanogenesis was inhibited to a greater extent by these compounds, it also suggests that N-deprived conditions may have facilitated the establishment of a 2-AP metabolizing consortium.

Effects of nitrogen limitation on species replacement dynamics during early secondary succession on a semiarid sagebrush site.

A soil nitrogen (N) availability gradient was induced on a disturbed sagebrush site in northwestern Colorado by fertilizing with nitrogen (high available N), applying sucrose (low available N), and applying neither nitrogen nor sucrose (control). Species composition was studied for 3 years. At the end of the study, N concentration of aboveground tissue of 3 major species was determined. The rate of species replacement was most rapid on plots receiving the sucrose treatment and was slowest on plots receiving the N treatment. Early-seral dominats had greater tissue N concentrations when availability of the resource was high but lower tissue N concentrations when available soil N became limited. Midseral dominants displayed the opposite pattern. These results suggest that the supply of available soil N, and therefore the dynamics of N incorporation in perennial plant tissue, is a primary mechanism in controlling the rate of secondary succession within this semiarid ecosystem.

Temporal Variation in Enrichment Effects during Periphyton Succession in a Nitrogen-Limited Desert Stream Ecosystem

Periphyton succession was studied over 89 d in longitudinally adjacent reaches (a riffle and run) in Sycamore Creek, a spatially intermittent desert stream. Effects of nitrogen limitation were assessed by comparing algal development on clay saucers containing either nitrate-enriched or unenriched agar. We evaluated effects of grazing on periphyton accrual by amending agar in half the substrata from each enrichment condition with an insecticide (Malathion). Early successional (25-d) communities on unenriched substrata were dominated by Epithemia sorex, a diatom capable of N2 fixation; non-fixing diatoms dominated enriched communities. NO3-N enrichment increased algal diversity (H') and delayed late-successional dominance by Calothrix, a heterocystous cyano- bacterium. Replacement of diatoms by cyanobacteria was likely facilitated by autogenic changes in nutrient and light conditions within the periphyton and temporal increases in water temperature. Three measures of algal biomass exhibited nearly linear increases in all treatments over the 3-mo study. Enrichment enhanced standing crops of chlorophyll a and ash-free dry mass (AFDM) in both reaches, an effect most pronounced within the first 3-4 wk. Algal populations unable to fix N2 were stimulated by enrichment but remained in low abundance on unenriched substrata whereas biov- olume of N2-fixing populations was lower on enriched substrata relative to controls. Malathion reduced the density of only one common grazer, the moth larva Petrophila jaliscalis, which was abundant only in the riffle. Addition of Malathion to enriched substrata in this habitat had no significant effect on net primary productivity or total algal biovolume but resulted in increased chlorophyll a and AFDM, suggesting that Petrophila did influence algal communities, but by a mechanism that remains unclear. Spatial heterogeneity of nutrient supply in this system contributes to maintenance of algal di- versity; but over long successional seres diversity declines regardless of enrichment owing to autogenic changes that occur during succession. Our results confirm earlier observations that low nitrogen availability limits accrual of algal biomass following spates and constrains algal community structure in Sycamore Creek. However, highly significant early successional differences in algal standing crop and community structure among enrichment treatments were eliminated or much reduced in mid to late stages of succession. We propose that this temporal change in enrichment response was caused by development of a thick periphyton mat that reduced availability of both water-column or substratum-derived nutrients to algae, and increased reliance on internal nutrient recycling.

Effect of nitrogen limitation on long-side-chain poly-beta-hydroxyalkanoate synthesis by Pseudomonas resinovorans.

Pseudomonas resinovorans produced poly-beta-hydroxyalkanoates (PHAs) when grown on hydrocarbons but not on glucose. In a chemostat culture, the PHA composition was beta-hydroxybutyrate (C4)-beta-hydroxyhexanoate (C6)-beta-hydroxyoctanoate (C8)-beta-hydroxydecanoate (C10) (1:15:75:9) on octanoate and C4-C6-C8-C10 (8:62:23:7) on hexanoic acid. Contrary to the reported behavior of Pseudomonas oleovorans, the PHA accumulation rate increased under ammonium limitation on octanoate.

Effects of nitrogen limitation on uptake of inorganic carbon and specific activity of ribulose-1,5-bisphosphate carboxylase/oxygenase in green microalgae

The effects of nitrogen limitation on the characteristics of inorganic carbon-dependent O2 evolution have been examined in the green microalgae Chlorella emersonii and Gloeomonas sp. When cells were grown under 5% CO2 or air, decreasing the growth rate (increasing nitrogen limitation) caused a decrease in maximum rates of photosynthetic O2 evolution, although when expressed on a per cell basis such changes were only evident at growth rates below 0.16 day−1. Severe nitrogen limitation also caused a marked decrease in k1/2 (CO2) in light- and CO2-dependent O2 evolution. Although values for this parameter were not as low as for low CO2 grown cells with a fully induced CO2-concentrating mechanism, they were less than one-half the corresponding values from cells with the mechanism fully repressed. Nitrogen-limitation also resulted in decreases in the activity and cellular content of ribulose-1,5-bisphosphate carboxylase/oxygenase. The changes to activity and levels of this enzyme were not equivalent so the specific activity decreased dramatically between growth rates of 0.57 and 0.25 day−1. Similar effects were noted in Gloeomonas and in air-grown Chlorella. The results are discussed in relation to regulation of CO2 uptake and assimilation in microalgae. Key words: microalgae, CO2 assimilation, nitrogen limitation, Rubisco, Chlorella.

Alleviation of the effects of nitrogen limitation in high gravity worts through increased inoculation rates

There are few inexpensive, practical methods to increase the usable nitrogen level in a substrate to be fermented to a potable alcohol product, but the provision of adequate assimilable nitrogen to a fermentation medium is critical for rapid and full “wort” attenuation. One practical solution to circumvent the problem may be to increase the inoculation rate to much higher than recommended levels. In this work, an increase in the pitching rate from 1.6×107 cfu/ml to 8×107 cfu/ml was shown to alleviate fermentation problems caused by nitrogen limitation. Attenuation and ethanol production rates became independent of the initial wort-free amino nitrogen (FAN) concentration, as did yeast viability and maximal yeast cell number. However, the final total cell mass was lower if the wort was nitrogen-deficient, regardless of the pitching rate. These cells were smaller and/or lighter and contained less protein at the end of fermentation. Such yeast could cause problems in subsequent fermentations if reuse of yeast (common in brewing) was considered.

DEVELOPMENT OF PHOTOSYNTHETIC ACTIVITY IN PORPHYRIDIUM PURPUREUM (RHODOPHYTA) FOLLOWING NITROGEN STARVATION1,2

ABSTRACTThe effects of nitrogen limitation on laboratory cultures of Porphyridium purpureum Bory, Drew and Ross were studied under continuous white light illumination (35 μE · m−2· s−1). Growth ceased, respiration exceeded photosynthesis, chlorophyll content was reduced by 80%, and phycoerythrin content was reduced by 99% over a period of 14 days under nitrogen limitation. Recovery upon addition of nitrogen resulted in increased phycobiliprotein content, appearance of phycobilisomes attached to the thylakoids, increased oxygen evolution, and increased fluorescence emission from photosystem 1 (720 nm) and photosystem 2 (685 nm) upon excitation by green light. Growth resumed after 72 h and was concomitant with an increase of chlorophyll, phycoerythrin and phycobilisomes per thylakoid area. The results suggest that photosystem 1 was less affected by nitrogen starvation than photosystem 2 and that the recovery was largely dependent on the restoration of phycobilisomes and other photosystem components.

Optimal Fertilizer Nitrogen and Residual Nitrate-Nitrogen Levels for Irrigated Corn and Effects of Nitrogen Limitations: An Economic Analysis

Fertilizer N and residual NO3-N in the soil profile interact in their effects on crop yield. Fertilizer expenditures present a tempting point for reducing production costs. This study was conducted to (i) examine the effects of residual soil NO3-N levels on the optimal use of applied fertilizer N for irrigated corn (Zea mays L.) and (ii) examine the effects of fertilizer N limitations on producer returns for soils in which N accumulation has been shown to occur. Data for the economic analyses were obtained from 4 yr of N fertilizer research with irrigated corn grown on a Pullman clay loam (fine, mixed, thermic Torrertic Paleustolls). Soil samples were taken prior to fertilizer application and analyzed for NO3-N. Fertilizer N was applied at 0, 40, 80, 120, 160, and 200 lb/acre. Over the course of the study, NO3-N levels varied from 12 to 70 lb/acre in the 0 to 6 in. increment and average grain yields varied from 52 to 183 bu/acre. Estimates of the response function of grain yield as affected by residual soil NO3-N and applied fertilizer N were obtained by regression analyses. A statistical model was evaluated with an iterative, non-linear constrained optimization routine for determining optimal long-term levels of applied fertilizer for maximization of net returns. For soils that accumulate unused NO3-N, amounts of fertilizer N necessary to optimize net returns for investment in fertilizer for long term production were found to be relatively independent of crop prices, fertilizer costs, and interest rates. Nitrogen fertilizer rates necessary to maximize profits for long term production were 12–14 lb/acre more than the rate for maximizing profit for a single year. Even small reductions in applied fertilizer N below that required for optimum long-term profit resulted in much greater reductions in revenue than savings in fertilizer cost, and the effects carried over to subsequent years. These analyses indicate that a producer could afford to borrow money at high rates of interest in order to apply the optimum rate of fertilizer N such that long term net returns would be maximized.