Nitrogen-stressed Plants Research Articles

Ectomycorrhiza and ethylenediurea reduced the impact of high nitrogen and ozone stresses and increased the growth of Cedrus deodara

Cedrus deodara is the central conifer plant affected by ozone and nitrogen pollutants among forest species worldwide. The growth of C. deodara depends upon the ectomycorrhizal (ECM) association, which is usually disturbed by these factors. This study aims to understand how these factors affect plants at physiological and biochemical levels. Three fungal strain consortiums were inoculated with two-year-old C. deodara seedlings. The stresses of 100 kg N h−1and 100 ppb O3 were applied for six months to study their impact on chlorophyll and antioxidant enzymes (SOD, CAT, and APX). The results showed that C2 (Consortium of Cedrus deodara) positively impacted the growth of selected plant species. The high photosynthesis rate was determined by enhanced chlorophyll content, and C2-treated plants showed high chlorophyll content. Relatively, chlorophyll a and b contents increased significantly in the seedlings treated with Ethylenediurea (EDU) alone and with ozone stress. In addition, a significant difference was observed between EDU and O3-treated plants (14% EDU400-O3 and 23% EDU600-O3) and the control. Overall, antioxidant activities were higher in the treated samples than in the control. The order of SOD activity was C2 (448 U/gFW) and lowest (354.7 U/gFW) in control. APX also showed higher activity in treated plants in C1 ≥ C2 ≥ C3+O3, whereas CAT activity was the highest in C2 treatments. Ozone and nitrogen-stressed plants showed higher activities than EDU-treated plants compared to non-treated ones. Our findings highlight the importance of understanding the signaling effects of numerous precursors. Moreover, an extended investigation of seedlings developing into trees must be conducted to verify the potential of ectomycorrhizal strains associated with C. deodara and comprehend EDU's role as a direct molecular scavenger of reactive toxicants.

Raman spectroscopy for nutritional stress detection in plant vascular tissue

Next-generation agriculture must address its high energy-intensive resource utilization footprint such as excessive use of fertilizer and water. Plants are also sources of natural polymers (cellulose, lignin, and pectin) that have important implications in sustainable materials design. Hence healthy plant growth with optimum utilization and production is essential for future growth, which demands new technologies and sensors for on-field precision agriculture. Here we used Raman spectroscopy (RS) to non-invasively monitor soybean development, a plant of immense economic importance for fuel, feed, and food. We focus on its compositional changes at multiple time points as it transitions from the vegetative (or rapid growth) to the reproductive (or flowering) stage subjected to nitrogen and nutrient stress to identify several indicators of health. The longitudinal growth was severely limited under total nutritional stress. Simultaneously, the cell wall showed early lignification to control growth and allow for efficient transport of limited resources. Healthier plants showed activation of early defense mechanisms via tetraterpenes, greater protein production capacity via glutamic acid, and late lignification by week 12. Nitrogen stressed plants also showed stunted growth though they showed a similar defense mechanism and later lignification as the healthy condition. These differences in the concentrations of structural polymers, stress signaling molecules, and structural growth inhibitors at different time points and variable stress demonstrated the suitability of Raman spectroscopy for precision plant health monitoring. Development such as the current study is a step towards creating tools, devices, and computational models for next-generation farming.

The Role of Engineering Thermodynamics in Explaining the Inverse Correlation between Surface Temperature and Supplied Nitrogen Rate in Corn Plants: A Greenhouse Case Study

Nitrogen stress plays a critical role in corn yield reduction. Thermal remote sensing has many applications: as an assessment tool for urban heat island, as an ecological indicator of ecosystem development, and as a water-stress-detection tool. In this study, it was hypothesized that corn crops supplied with optimum or high rates of nitrogen would have lower surface temperatures compared to corn grown under nitrogen-stressed conditions. Two experiments were conducted in the greenhouse at the University of Guelph, Canada, from the period between 2015 and 2016, involving three rates of nitrogen (high, medium, and low rates) supplied to corn plants after seed emergence. Leaf and whorl temperatures were collected by using a high-resolution thermal camera, an infrared handheld point measurements gun, and a type T thermocouple, respectively. An approximate difference of 2 °C was observed in temperatures between plants receiving high and low rates of nitrogen. These results supported the hypothesis that nitrogen-stressed plants have higher temperatures compared to less stressed plants, at a 0.05 significance level. This study investigated the application of the exergy destruction principle through thermal remote sensing, to detect crop stress at early growth stages under greenhouse conditions, to increase the production and reduce the harmful environmental impact.

An Inverse Correlation between Corn Temperature and Nitrogen Stress: A Field Case Study

Nitrogen is one of the most important yield‐limiting nutrients for corn (Zea mays). The ability of thermal remote sensing to detect nitrogen deficiency in corn may enable precision agriculture to modify nitrogen rates according to field conditions. This study applies the exergy destruction principle as a theory to explain the inverse relationship between surface temperature and nitrogen rate. Two hypotheses were developed. First, it was hypothesized that agricultural crops experiencing greater growth and providing greater yield will have lower surface temperature. The second hypothesis was that corn grown under optimum levels of nitrogen will have lower surface temperatures compared to corn grown under nitrogen stressed conditions. Field studies were conducted during two summer seasons (2016 and 2017) on an established long‐term field trial of corn yield response to varying rates of nitrogen. It was found that corn surface temperature decreased as the rate of nitrogen increased. A shallow but statistically significant (P < 0.05) negative slope was observed consistently with increasing rates of nitrogen. Surface temperature measurements, however, were variable. This variability was the result of external and weather dependent variables that influenced leaf surface temperature. Despite this variability, the exergy destruction principle provides a theory from which thermal remote sensing can be applied through the use of surface temperature measurements to detect physiological stress in crop plants.Core Ideas Thermal remote sensing was proposed to detect nitrogen stress in corn plants. Nitrogen stressed plants had higher surface temperatures than less stressed plants. Temperature trends were consistent with the exergy destruction principle. Nitrogen‐temperature correlations were statistically significant at the 0.05 significance level. Corn yield increases with nitrogen rate increase and surface temperature decrease.

Secondary Metabolism-Inducing Treatments During in vitro Development of Turmeric (Curcuma longa L.) Rhizomes

Turmeric (Curcuma longa L.) plants that were grown in vitro for 17 or 22 weeks as a fed-batch culture in 2.5 L vessels yielded 39 to 43 g and 62 to 70 g of fresh rhizomes per vessel, respectively (95 % confidence interval). The MS liquid medium was maintained at 6 % sucrose through media addition twice during the experiment. Various methods were employed in attempts to increase secondary metabolism. Antioxidant and total phenolics assays were employed to characterize phytochemical activity. A first experiment exposed four clones to phenylalanine and/or methyl jasmonate (MeJa) from week 12 to 17 in culture. In a second experiment, a clone was given short-term exposure (1.5 weeks) to either proline, a natural proline-rich fish extract, MeJa, or chitosan beginning during the twentieth week of culture. This experiment also included a nitrogen stress treatment (weeks 16–22). The 5-week phenylalanine and MeJa treatments lowered biomass accumulation and antioxidant capacity of the tissue. The magnitude of antioxidant depression was dependent on genotype and, within each genotype, the degree of depression was similar for phenylalanine and MeJa, alone and in combination. In the second experiment, only the low-nitrogen treatment yielded an increase in phenolic content to 4.7 % of dry weight compared to untreated microrhizomes (4.1 % of dry weight). Nitrogen-stressed plants also had less leaf growth, but rhizome mass was unaffected and averaged 63 g FW per vessel. None of the short-term treatments had a significant effect on biomass, antioxidant capacity, or phenolic content. None of the treatments significantly affected radical scavenging, although the low-nitrogen treatment might have improved this activity (p = .1207). Results indicated that plants grown in a high-nitrogen MS media were not responsive to elicitation.

Changes of Root Hydraulic Conductivity and Root/Shoot Ratio of Durum Wheat and Barley in Relation to Nitrogen Availability and Mercury Exposure

The aim of this research was to verify, on whole plant level and during all the plant cycle, the hypothesis that nitrogen deficiency reduces root hydraulic conductivity through the water channels (aquaporins) activity, and that the plant reacts by changing root/shoot ratio. Root hydraulic conductivity, plant growth, root/shoot ratio and plant water status were assessed for durum wheat (Triticum durum Desf.) and barley (Hordeum vulgare L.), as influenced by nitrogen availability and HgCl2 treatment. On both species during the plant cycle, nitrogen deficiency induced lower root hydraulic conductivity (-49 and -66% respectively for barley and wheat) and lower plant growth. On wheat was also observed cycle delay, lower plant nitrogen content, but not lower leaf turgor pressure and epidermic cell dimension. The lower plant growth was due to lower plant dimension and lower tillering. Root /shoot ratio was always higher for nitrogen stressed plants, whether on dry matter or on surface basis. This was due to lower effect of nitrogen stress on root growth than on shoot growth. On wheat HgCl2 treatment determined lower plant growth, and more than nitrogen stress, cycle delay and higher root/shoot ratio. The mercury, also, induced leaf rolling, lower turgor pressure, lower NAR, higher root cell wall lignification and lower epidermic cell number per surface unity. In nitrogen fertilized plants root hydraulic conductivity was always reduced by HgCl2 treatment (-61 and 38%, respectively for wheat and barley), but in nitrogen unfertilized plants this effect was observed only during the first plant stages. This effect was higher during shooting and caryopsis formation, lower during tillering. It is concluded that barley and durum wheat react to nitrogen deficiency and HgCl2 treatment by increasing the root/shoot ratio, to compensate water stress due to lower water root conductivity probably induced by lower aquaporin synthesis or inactivation. However, this compensation is not enough to keep a normal water status and this leads to lower plant growth. At the same time some doubts persist about mercury toxicity on other plant functions besides the aquaporin blockage.

The effect of fungal infection and nitrogen fertilization on the carbohydrate composition of Rumex obtusifolius leaves

The effect of infection by the rust fungus Uromyces rumicisand fertilization by different concentrations of nitrate or ammonium solutions on the concentrations of alcohol-soluble carbohydrates, fructans and starch in Rumex obtusifolius leaves was investigated. In leaves from healthy plants there was an increase in concentration of alcoholsoluble carbohydrates and fructans as the concentration of nitrate given was decreased, with the exception of nitrogen-stressed plants (those fed less than 10 mM l 1 nitrate) which had a lower concentration of alcohol-soluble carbohydrates than plants fed 10 mM l 1 nitrate. There was an increase in fructan and starch concentration in leaves as the concentration of ammonium solution given was decreased. The concentration of alcohol-soluble carbohydrates was reduced in infected leaves and increased in healthy leaves on infected plants, while the fructan concentration increased in infected leaves, compared to healthy leaves. The effects of infection were consistent over the range of nitrogen concentrations used, and thus were additive to the effects of fertilization. These results confirm the known effects of fertilization or fungal infection, singly, and indicate that, when combined, nitrogen deficiency and fungal infection may produce an additive stress on the plant.

The effect of nitrogen deficiency on leaf gas exchange and chlorophyll fluorescence parameters in sunflower

Fully expanded leaves of sunflower ( Helianthus annuus L.) growing with either complete or nitrogen-deficient nutrition solution were analysed for gas exchange and chlorophyll fluoresence after 24 days from the transplanting. Under N-stress the decline in photosynthesis and the rise in stomatal conductance determined at light saturation level were accompanied by an increase of the intercellular CO 2 concentration (about +60%). This indicates that the decline in A max (photosynthetic activity at light saturation level) was due to limitation related to a reduced mesophyllic activity, rather than to stomatal limitation. At low light intensity photosynthetic efficiency of PSII was not affected. In N-stressed plants starch content decreased significantly in leaves. The sucrose/starch ratio rose in N-stressed plants, indicating that the carbon partitioning trend had shifted towards sucrose. This result is in accordance with the lower shoot/root ratio observed in nitrogen-stressed plants.

Soluble carbohydrate allocation to roots, photosynthetic rate of leaves, and nitrate assimilation as affected by nitrogen stress and irradiance.

Upon resupply of exogenous nitrogen to nitrogen-stressed plants, uptake rate of nitrogen is enhanced relative to nonstressed plants. Absorption of nitrogen presumably is dependent on availability of carbohydrates in the roots. A buildup in soluble carbohydrates thus should occur in roots of nitrogen-stressed plants, and upon resupply of exogenous nitrogen the increased uptake rate should be accompanied by a rapid decline in carbohydrates to prestress levels. To evaluate this relationship, three sets of tobacco plants growing in a complete hydroponic solution containing 1.0 mM NO3- were either continued in the complete solution for 21 d, transferred to a minus-nitrogen solution for 21 d, or transferred to a minus-nitrogen solution for 8-9 d and then returned to the 1.0 mM NO3- solution. These nitrogen treatments were imposed upon plants growing at photosynthetic photon flux densities of 700 and 350 micromoles m-2 s-1. Soluble carbohydrate levels in roots increased during onset of nitrogen stress to levels that were fourfold greater than in roots of non-stressed plants. Following resupply of external nitrogen, a rapid resumption of nitrogen uptake was accompanied by a decline in soluble carbohydrates in roots to levels characteristic of nonstressed plants. This pattern of soluble carbohydrate levels in roots during onset of and recovery from nitrogen stress occurred at both irradiance levels. The response of net photosynthetic rate to nitrogen stress could be expressed as a nonlinear function of concentration of reduced nitrogen in leaves. The net photosynthetic rate at a given concentration of reduced nitrogen, however, averaged 10% less at the lower than at the higher irradiance. The decline in net photosynthetic rate per unit of reduced nitrogen in leaves at the lower irradiance was accompanied by an increase in the nitrate fraction of total nitrogen in leaves from 20% at the higher irradiance to 38% at the lower irradiance.

Alterations in nitrogen assimilation and partitioning in nitrogen stressed plants

Alterations in nitrogen assimilation and partitioning in nitrogen stressed plants

Alterations in nitrogen assimilation and partitioning in nitrogen stressed plants

Although nutrient stress is known to alter partitioning between shoots and roots, the physiological basis for the phenomenon is unresolved. Experiments were conducted to examine assimilation of 15NO3 by N‐stressed plants and to determine whether apparent changes in assimilation in the root contributed to alterations in whole‐plant partitioning of reduced‐N. Tobacco plants (Nicotiana tabacum L. cv. NC 2326) were exposed to a low concentration of NO3− in solution (80 μM) for 9 days to effect a N‐stress response. Exposure of plants to 1000 μM15NO3− for 12 h on selected days revealed that roots of N‐stressed plants developed an increased capacity to absorb NO3−, and accumulation of reduced‐15N in the root increased to an even greater extent. When plants were exposed to 80 or 1000 μM15NO3− in steady‐state, 15NO3− uptake over a 12 h period was noticeably restricted at the lower concentration, but a larger proportion of the absorbed 15N still accumulated as reduced‐15N in the root. The alteration in reduced‐15N partitioning was maintained in N‐stressed plants during the subsequent 3‐day “chase” period when formation of insoluble reduced‐15N in the root was quantitatively related to the disappearance of 15NO3− and soluble reduced‐15N. The results indicate that increased assimilation of absorbed NO3−, in the root may contribute significantly to the altered reduced‐N partitioning which occurs in N‐stressed plants.

Alterations in Leaf Carbohydrate Metabolism in Response to Nitrogen Stress

A series of experiments was conducted to characterize alterations in carbohydrate utilization in leaves of nitrogen stressed plants. Two-week-old, nonnodulated soybean plants (Glycine max [L.] Merrill, ;Ransom'), grown previously on complete nutrient solutions with 1.0 millimolar NO(3) (-), were transferred to solutions without a nitrogen source at the beginning of a dark period. Daily changes in starch and sucrose levels of leaves were monitored over the following 5 to 8 days in three experiments. Starch accumulation increased relative to controls throughout the leaf canopy during the initial two light periods after plant exposure to N-free solutions, but not after that time as photosynthesis declined. The additional increments of carbon incorporated into starch appeared to be quantitatively similar to the amounts of carbon diverted from amino acid synthesis in the same tissues. Since additional accumulated starch was not degraded in darkness, starch levels at the beginning of light periods also were elevated. In contrast to the starch effects, leaf sucrose concentration was markedly higher than controls at the beginning of the first light period after the N-limitation was imposed. In the days which followed, diurnal turnover patterns were similar to controls. In source leaves, the activity of sucrose-P synthase did not decrease until after day 3 of the N-limitation treatment, whereas the concentration of fructose-2,6-bisphosphate was decreased on day 2. Restricted growth of sink leaves was evident with N-limited plants within 2 days, having been preceeded by a sharp decline in levels of fructose-2,6 bisphosphate on the first day of treatment. The results suggest that changes in photosynthate partitioning in source leaves of N-stressed plants resulted largely from a stable but limited capacity for sucrose formation, and that decreased sucrose utilization in sink leaves contributed to the whole-plant diversion of carbohydrate from the shoot to the root.

Nitrogen and dry-matter partitioning in soybean plants during onset of and recovery from nitrogen stress.

The study tested the hypothesis that resupplying nitrogen after a period of nitrogen stress leads to restoration of the balance between root and shoot growth and normal functional activity. Nonnodulated soybean plants were grown hydroponically for 14 days with 1.0 mM NO3- in a complete nutrient solution. One set of plants was continued on the complete nutrient solution for 25 days; a second set was given 0.0 mM NO3- for 25 days; and the third set was given 0.0 mM NO3- for 10 days followed by transfer to the complete solution with 1.0 mM NO3- for 15 days. In continuously nitrogen-stressed plants, emergence and expansion of main-stem and branch leaves were severely inhibited as low nitrogen content limited further growth. This was followed by a shift in partitioning of dry matter from the leaves to the roots, resulting in an initial stimulation of root growth and a decreased shoot:root ratio. Reduced nitrogen also was redistributed from the leaves into the stem and roots. When nitrogen stress was relieved, leaf initiation and expansion were renewed. With the restoration of the balance between root and shoot function, the shoot:root ratio and distribution of reduced nitrogen within the plant organs returned to levels similar to those of nonstressed plants.

Expansion and photosynthetic rate of leaves of soybean plants during onset of and recovery from nitrogen stress.

This study reports on the effects of nitrogen stress and restoration of nitrogen availability after a period of stress on expansion and photosynthetic rate of soybean leaves of differing maturity. We hypothesized that nitrogen resupply would lead to additional accumulation of reduced nitrogen in the leaves and, ultimately, resumption of leaf initiation and expansion and photosynthetic activity. In continuously nitrogen-stressed plants, expansion of middle trifoliolates of main-stem trifoliates and leaf area at full expansion were severely restricted. Leaves showing the greatest effects were initiated after removal of nitrogen. When the reduced nitrogen concentration in mature leaves of continuously stressed plants fell below 9 mg dm-2, the photosynthetic rate per unit leaf decreased rapidly, reaching a minimum of ca. 6-8 mg dm-2 h-1. The older mature leaves tended to abscise at this point, while the youngest leaves remained on the plant and continued to photosynthesize slowly. When nitrogen was resupplied, leaf expansion and final leaf area increased. Leaf initiation was also stimulated as reduced nitrogen levels rose in the leaves. Photosynthetic rates of the oldest and youngest pair of mature leaves returned to values comparable to those of similar-aged leaves of nonstressed soybean plants.

Plant-herbivore interactions: Examination of potential effects of bison saliva on regrowth of Bouteloua gracilis (H.B.K.) lag.

Laboratory experiments were performed to determine whether regrowth of blue grama was affected by potential growth-promoting substances in saliva of North American bison. We observed no statistically significant effects of foliar application of whole bison saliva on net photosynthesis (PN), root respiration (RR), allocation patterns of photosynthetically fixed 14C, or regrowth rates over a 10-day period following clipping to various heights. In a 10-week experiment, there were no significant effects of saliva on leaf, crown or root growth or tiller production in plants clipped to heights of 6, 4 or 2 cm above crowns. Similarly, nitrogen-stressed plants failed to show significant changes in growth rates or tillering in response to saliva over a 3-week period. Clipped blue grama plants did exhibit significant compensatory growth responses, including higher PN rates from 3-10 days following clipping and allocation of a higher proportion of current photosynthate to synthesis of new leaf tissue with increasing severity of defoliation. Nevertheless, unclipped plants invariably outproduced clipped plants following defoliation.