N-uptake Rate Research Articles

Shift of root nitrogen-acquisition strategy with tree age is mediated by root functional traits along the collaboration gradient of the root economics space.

Root nitrogen (N)-uptake rate and uptake preference, and their association with root morphological and chemical traits are important to characterize root N-acquisition strategies of trees. However, how the root N-acquisition strategy varies with tree age, especially for those species that coexist at a common site, remains unknown. In this study, a field isotopic hydroponic method was used to determine the uptake rate and contribution of NH4+, NO3- and glycine, for three coexisting ectomycorrhizal coniferous species [Pinus koraiensis (Korean pine), Picea koraiensis (Korean spruce) and Abies nephrolepis (smelly fir)] at three age classes (young, middle-aged and mature) in a temperate forest. Concurrently, root morphological and chemical traits, as well as mycorrhizal colonization rate were determined. Our results show that the root uptake rate of total N and NH4+ gradually decreased across all three species with increasing tree age. The three species at all age classes preferred NH4+, except for middle-aged Korean spruce and mature smelly fir, which preferred glycine. In contrast, all three species showed the lowest acquisition of NO3-. According to the conceptual framework of 'root economics space', only a 'collaboration' gradient (i.e. dimension of root diameter vs specific root length or area) was identified for each species, in which root N-uptake rate loaded heavily on the side of 'do-it-yourself' (i.e. foraging N more by roots). Young trees of all species tended to exhibit the 'do-it-yourself' strategy for N uptake, and mature trees had an 'outsourcing' strategy (i.e. foraging N by a mycorrhizal partner), whereas middle-aged trees showed a balanced strategy. These findings suggest that shifts of root N-acquisition strategy with tree age in these species are mainly mediated by root traits along the 'collaboration' gradient, which advances our understanding of belowground competition, species coexistence and N cycling in temperate forests.

Mycorrhizal suppression decouples the coordination of plant functional traits that mediate nitrogen acquisition under different soil water contents in a subtropical wetland ecosystem

In subtropical wetland ecosystems, climate change can alter both the composition of nitrogen (N) deposition and the levels of soil water, affecting nutrient acquisition. Arbuscular mycorrhizal fungi (AMF) can regulate the effects of soil water availability and the NH4+: NO3− ratio on plant N acquisition. However, exactly how N acquisition is affected by soil water content and AMF symbiosis remains unclear. We transplanted the dominant wetland species, Carex thunbergii, collected in freshwater wetlands in our study area in southern China, into microcosms in a greenhouse experiment. In this context, we were able to manipulate both the amount of water supply and the NH4+: NO3− ratio in the soil, combined with and without AMF symbiosis. Three months after our treatments were imposed, we examined N-uptake rate, along with plant growth and functional traits, in response to these experimental manipulations. Soil water content dominated the level of plant growth, whereas variations in plant functional traits (e.g., specific root length, SRL, and specific leaf area, SLA) could largely be ascribed to soil NH4+: NO3− ratio. Collectively, plant-AMF symbiosis enhanced plant N acquisition under conditions of variable water availability, for instance promoting plant N-uptake rate more at lower level of soil water (30%) compared to higher level of soil water(70%), and also when N was applied at a 3:1 of NH4+: NO3− ratio compared to other ratios. SLA was significantly negatively correlated with SRL, and thus indirectly contributed to N acquisition. However, mycorrhizal suppression decoupled the coordination between leaf and root traits, mainly affecting SRL, rather than SLA, which remained rather stable. The correlations between root and leaf traits, adjusted by AMF symbiosis, were crucial for plant N use strategies.

Diurnal regulation of rice N uptake ability under interrupted N supply.

Plants take up nitrogen (N) both day and night. The diurnal variation in N uptake results from interactions between aboveground and belowground tissues. We examined the long-term effects of interrupted N supply (day only or night only) under hydroponic conditions to test whether plant acclimatisation response to the interrupted N supply differs by day or night. Seedlings experienced 32 days under daytime-fed (DF), night-time-fed (NF), or continuous (CT) N supply. The root N uptake rate (NUR) differed between DF and NF from day 3 of treatment, after which NUR was significantly increased (by up to 82%) in DF and NF plants. The increased NUR during each half-day did not fully compensate for lost access to N during the other half-day, resulting in lower N accumulation by the end of the treatment. The reduction was smaller in DF plants than NF plants. The underlying mechanism of diurnal variation of N uptake is discussed in terms of transpiration demand and gene expression in roots.

A meta-analysis of the combined effects of elevated carbon dioxide and chronic warming on plant %N, protein content and N-uptake rate.

Elevated CO2 (eCO2) and high temperatures are known to affect plant nitrogen (N) metabolism. Though the combined effects of eCO2 and chronic warming on plant N relations have been studied in some detail, a comprehensive statistical review on this topic is lacking. This meta-analysis examined the effects of eCO2 plus warming on shoot and root %N, tissue protein concentration (root, shoot and grain) and N-uptake rate. In the analyses, the eCO2 treatment was categorized into two classes (<300 or ≥300 ppm above ambient or control), the temperature treatment was categorized into three classes (<1.5, 1.5–5 and >5 °C above ambient or control), plant species were categorized based on growth form and functional group and CO2 treatment technique was also investigated. Elevated CO2 alone or in combination with warming reduced shoot %N (more so at ≥300 vs. <300 ppm above ambient CO2), while root %N was significantly reduced only by eCO2; warming alone often increased shoot %N, but mostly did not affect root %N. Decreased shoot %N with eCO2 alone or eCO2 plus warming was greater for woody and non-woody dicots than for grasses, and for legumes than non-legumes. Though root N-uptake rate was unaffected by eCO2, eCO2 plus warming decreased N-uptake rate, while warming alone increased it. Similar to %N, protein concentration decreased with eCO2 in shoots and grain (but not roots), increased with warming in grain and decreased with eCO2 and warming in grain. In summary, any benefits of warming to plant N status and root N-uptake rate will generally be offset by negative effects of eCO2. Hence, concomitant increases in CO2 and temperature are likely to negate or decrease the nutritional quality of plant tissue consumed as food by decreasing shoot %N and shoot and/or grain protein concentration, caused, at least in part, by decreased root N-uptake rate.

Elevated Carbon Dioxide and Chronic Warming Together Decrease Nitrogen Uptake Rate, Net Translocation, and Assimilation in Tomato.

The response of plant N relations to the combination of elevated CO2 (eCO2) and warming are poorly understood. To study this, tomato (Solanum lycopersicum) plants were grown at 400 or 700 ppm CO2 and 33/28 or 38/33 °C (day/night), and their soil was labeled with 15NO3− or 15NH4+. Plant dry mass, root N-uptake rate, root-to-shoot net N translocation, whole-plant N assimilation, and root resource availability (%C, %N, total nonstructural carbohydrates) were measured. Relative to eCO2 or warming alone, eCO2 + warming decreased growth, NO3− and NH4+-uptake rates, root-to-shoot net N translocation, and whole-plant N assimilation. Decreased N assimilation with eCO2 + warming was driven mostly by inhibition of NO3− assimilation, and was not associated with root resource limitations or damage to N-assimilatory proteins. Previously, we showed in tomato that eCO2 + warming decreases the concentration of N-uptake and -assimilatory proteins in roots, and dramatically increases leaf angle, which decreases whole-plant light capture and, hence, photosynthesis and growth. Thus, decreases in N uptake and assimilation with eCO2 + warming in tomato are likely due to reduced plant N demand.

Effects of Elevated Carbon Dioxide and Chronic Warming on Nitrogen (N)-Uptake Rate, -Assimilation, and -Concentration of Wheat.

The concentration of nitrogen (N) in vegetative tissues is largely dependent on the balance among growth, root N uptake, and N assimilation. Elevated CO2 (eCO2) plus warming is likely to affect the vegetative-tissue N and protein concentration of wheat by altering N metabolism, but this is poorly understood. To investigate this, spring wheat (Triticum aestivum) was grown for three weeks at two levels of CO2 (400 or 700 ppm) and two temperature regimes (26/21 or 31/26 °C, day/night). Plant dry mass, plant %N, protein concentrations, NO3− and NH4+ root uptake rates (using 15NO3 or 15NH4), and whole-plant N- and NO3--assimilation were measured. Plant growth, %N, protein concentration, and root N-uptake rate were each significantly affected only by CO2, while N- and NO3−-assimilation were significantly affected only by temperature. However, plants grown at eCO2 plus warming had the lowest concentrations of N and protein. These results suggest that one strategy breeding programs can implement to minimize the negative effects of eCO2 and warming on wheat tissue N would be to target the maintenance of root N uptake rate at eCO2 and N assimilation at higher growth temperatures.

Elevated CO2 plus chronic warming reduce nitrogen uptake and levels or activities of nitrogen-uptake and -assimilatory proteins in tomato roots.

Atmospheric CO2 enrichment is expected to often benefit plant growth, despite causing global warming and nitrogen (N) dilution in plants. Most plants primarily procure N as inorganic nitrate (NO3- ) or ammonium (NH4+ ), using membrane-localized transport proteins in roots, which are key targets for improving N use. Although interactive effects of elevated CO2 , chronic warming and N form on N relations are expected, these have not been studied. In this study, tomato (Solanum lycopersicum) plants were grown at two levels of CO2 (400 or 700 ppm) and two temperature regimes (30 or 37°C), with NO3- or NH4+ as the N source. Elevated CO2 plus chronic warming severely inhibited plant growth, regardless of N form, while individually they had smaller effects on growth. Although %N in roots was similar among all treatments, elevated CO2 plus warming decreased (1) N-uptake rate by roots, (2) total protein concentration in roots, indicating an inhibition of N assimilation and (3) shoot %N, indicating a potential inhibition of N translocation from roots to shoots. Under elevated CO2 plus warming, reduced NO3- -uptake rate per g root was correlated with a decrease in the concentration of NO3- -uptake proteins per g root, reduced NH4+ uptake was correlated with decreased activity of NH4+ -uptake proteins and reduced N assimilation was correlated with decreased concentration of N-assimilatory proteins. These results indicate that elevated CO2 and chronic warming can act synergistically to decrease plant N uptake and assimilation; hence, future global warming may decrease both plant growth and food quality (%N).

Kinetics of nitrogen incorporation at the SiO2/4H-SiC interface during an NO passivation

Nitridation of the SiO2-4H-SiC interface using post-oxidation annealing in nitric oxide (NO) is the most established process for obtaining high quality 4H-SiC MOS interfaces. In this paper, a detailed study of the interfacial nitrogen uptake kinetics is reported for the (0001) Si-terminated and (000-1) C-terminated crystal faces of 4H-SiC. The results indicate a significantly faster kinetics for the C-face compared to the Si-face. For the first time, the correlation between N-uptake and the interface trap density reduction was observed on the C-face. First-order kinetics models are used to fit the nitrogen up-take. Empirical equations predicting N coverage at the SiO2-4H-SiC interface via NO annealing have been established. The result also shows that the N-uptake rate is associated with the oxidation rate.

Effects of inorganic nitrogen forms on growth, morphology, nitrogen uptake capacity and nutrient allocation of four tropical aquatic macrophytes ( Salvinia cucullata, Ipomoea aquatica, Cyperus involucratus and Vetiveria zizanioides)

This study assesses the growth and morphological responses, nitrogen uptake and nutrient allocation in four aquatic macrophytes when supplied with different inorganic nitrogen treatments (1) NH 4 +, (2) NO 3 −, or (3) both NH 4 + and NO 3 −. Two free-floating species ( Salvinia cucullata Roxb. ex Bory and Ipomoea aquatica Forssk.) and two emergent species ( Cyperus involucratus Rottb. and Vetiveria zizanioides (L.) Nash ex Small) were grown with these N treatments at equimolar concentrations (500 μM). Overall, the plants responded well to NH 4 +. Growth as RGR was highest in S. cucullata (0.12 ± 0.003 d −1) followed by I. aquatica (0.035 ± 0.002 d −1), C. involucratus (0.03 ± 0.002 d −1) and V. zizanioides (0.02 ± 0.003 d −1). The NH 4 + uptake rate was significantly higher than the NO 3 − uptake rate. The free-floating species had higher nitrogen uptake rates than the emergent species. The N-uptake rate differed between plant species and seemed to be correlated to growth rate. All species had a high NO 3 − uptake rate when supplied with only NO 3 −. It seems that the NO 3 − transporters in the plasma membrane of the root cells and nitrate reductase activity were induced by external NO 3 −. Tissue mineral contents varied with species and tissue, but differences between treatments were generally small. We conclude, that the free-floating S. cucullata and I. aquatica are good candidate species for use in constructed wetland systems to remove N from polluted water. The rooted emergent plants can be used in subsurface flow constructed wetland systems as they grow well on any form of nitrogen and as they can develop a deep and dense root system.

Effect of nutrient inputs on growth, chlorophyll, and tissue nutrient concentration of Ulva reticulata from a tropical habitat

Green tides caused by overgrowth of Ulva species are an increasing problem in tropical areas. The effect of dissolved nutrients on uptake rates, growth, chlorophyll, and tissue nutrient concentration of Ulva reticulata was examined in laboratory experiments lasting up to 7 d. Sterile seawater was enriched with nitrate, ammonium, phosphate, ammonium + phosphate and nitrate + phosphate. U. reticulata expressed luxury uptake of both nitrogen (N) and phosphorus (P). The maximum N-uptake rate was found when ammonium was added alone. The maximum relative growth rate was about 15.1% per day but this was in the nitrate-fed algae not the ammonia-fed algae. N-enrichment resulted in an increase in chlorophyll concentration on day 4 and a decrease on day 7, probably as a result of cell division. P-enrichment had no significant effect on chlorophyll concentration. Treatments with added N, P or N+P showed significant increase in tissue N and P content on day 4. On day 7, N content in macroalgal tissue decreased while P content continued to increase. U. reticulata responded most strongly to added N; responses to P were much lower than for added N and there was little or no evidence for an additive effect of N+P. The N:P ratio of U. reticulata of control material suggested that N was the most limiting nutrient at the collection site (Paklok, Phuket, Thailand).

A trade‐off between nitrogen uptake and use increases responsiveness to elevated CO2 in infrequently cut mixed C3 grasses

The aim of this study was to evaluate whether the responsiveness of mixed C3 grass species to elevated CO2 is related more to nitrogen uptake or to N-use efficiency. Nitrogen uptake and whole-plant N-use efficiency were investigated with two binary mixtures: Lolium perenne was mixed either with Festuca arundinacea or with Holcus lanatus. The swards were grown on sand with or without CO2 doubling, and subjected to two cutting frequencies. A C20 alcohol was used as a marker to determine species proportion in the total root mass of the mixtures. The mean residence time of N was calculated from that of 15N-labelled fertilizer. Lolium perenne took up significantly more N per unit root mass than its grass competitors, but its N-use efficiency was lower. Elevated CO2 significantly reduced the N uptake of the three grass species. A trade-off between N capture and use was found, as N-use efficiency and N-uptake rate were negatively correlated. A high N-use efficiency, and conversely low N uptake appeared to favour the responsiveness to elevated CO2 of the infrequently cut grasses.

Carbon allocation and nitrogen acquisition in a developing Populus deltoides plantation.

We established Populus deltoides Bartr. stands differing in nitrogen (N) availability and tested if: (1) N-induced carbon (C) allocation could be explained by developmental allocation controls; and (2) N uptake per unit root mass, i.e., specific N-uptake rate, increased with N availability. Closely spaced (1 x 1 m) stands were treated with 50, 100 and 200 kg N ha(-1) year(-1) of time-release balanced fertilizer (50N, 100N and 200N) and compared with unfertilized controls (0N). Measurements were made during two complete growing seasons from May 1998 through October 1999. Repeated nondestructive measurements were carried out to determine stem height and diameter, leaf area and fine-root dynamics. In October of both years, above- and belowground biomass was harvested, including soil cores for fine-root biomass. Leaves were harvested in July 1999. Harvested tissues were analyzed for C and N content. Nondestructive stem diameter and and fine-root dynamic measurements were combined with destructive harvest data to estimate whole-tree biomass and N content at the end of the year, and to estimate specific N-uptake rates during the 1999 growing season. Shoot growth response was greater in fertilized trees than in control trees; however, the 100N and 200N treatments did not enhance growth more than the 50N treatment. Root biomass proportions decreased over time and with increasing fertilizer treatment. Fertilizer-induced changes in allocation were explained by accelerated development. Specific N-uptake rates increased during the growing season and were higher for fertilized trees than for control trees.

The influence of temperature and nitrogen source on growth and nitrogen uptake of two polar-desert species, Saxifraga caespitosa and Cerastium alpinum.

Polar-desert plants experience low average air temperatures during their short growing season (4–8 °C mean July temperature). In addition, low availability of inorganic nitrogen in the soil may also limit plant growth. Our goals were to elucidate which N sources can be acquired by polar-desert plants, and how growth and N-uptake are affected by low growth temperatures. We compared rates of N-uptake and increases in mass and leaf area of two polar-desert species (Cerastium alpinum L. and Saxifraga caespitosa L.) over a period of 3 weeks when grown at two temperatures (6 °C vs. 15 °C) and supplied with either glycine, NH4+ or NO3−. At 15 °C, plants at least doubled their leaf area, whereas there was no change in leaf area at 6 °C. Measured mean N-uptake rates varied between 0.5 nmol g−1 root DM s−1 on glycine at 15 °C and 7.5 nmol g−1 root DM s−1 on NH4+ at 15 °C. Uptake rates based upon increases in mass and tissue N concentrations showed that plants had a lower N-uptake rate at 6 °C, regardless of N source or species. We conclude that these polar-desert plants can use all three N sources to increase their leaf area and support flowering when grown at 15 °C. Based upon short-term (8 h) uptake experiments, we also conclude that the short-term capacity to take up inorganic or organic N is not reduced by low temperature (6 °C). However, net N-uptake integrated over a three-week period is severely reduced at 6 °C.

Organic Farming Challenge of Timing Nitrogen Availability to Crop Nitrogen Requirements

Groundwater has become increasingly degraded by NO3, and this degradation has been partially attributed to the use of commercial inorganic N fertilizers. Conversion from conventional fertilizer management to organic farming has been proposed as a means to reduce groundwater degradation. Matching soil inorganic N supply with crop N requirement on a temporal basis is important to achieve high yield and low water degradation. Dynamics of N mineralization from two manures and N‐uptake dynamics for two crops were derived from published data, and multi year simulations were done using the ENVIRON‐GRO computer model, which accounts for N and irrigation management effects on crop yield and N leaching. The temporal N‐mineralization and N‐uptake curves did not match well. The potential N uptake for corn (Zea mays L.) exceeded the cumulative mineralized N during a significant period that would cause reduced yield. Wheat (Triticum aestivum L.) has a low and flat N‐uptake peak, so that the cumulative mineralized N met N demand by wheat during the growing season. A crop with a very high maximum N‐uptake rate, such as corn, would be difficult to fertilize with only organic N to meet peak demands without excessive N in the soil before and after crop growth. In order to satisfy crop N demand, a large amount of manure, which would leave much N or subsequent leaching, must be applied. It took two or more years after conversion to organic sources of N to reach maximum yield because of carryover of unmineralized manure and accumulation of mineralized N after crop uptake which was not completely leached during the winter. High initial applications to build up the organic pool followed by reduced inputs in subsequent years would be appropriate.

Growth analysis of dry matter accumulation and N uptake of forage maize cultivars affected by N supply

The productivity of eight forage maize cultivars (Zea mays L.) in response to N was investigated in a 3-year field experiment located in Northern Germany. Nitrogen fertilizer applications were zero, 50 and 150 kg N/ha given each year shortly after sowing. Each cultivar was grown on the same plot, beginning in 1993, following the ploughing up of a 2-year old grass sward, to which slurry had been added. Plants were sampled regularly for dry matter (DM) production and N uptake. A non-linear regression equation was used to compare the data. Growth analysis and N uptake characteristics (maximum crop growth rate, duration of maximum crop growth rate, period until maximum crop growth rate, maximum N uptake rate, duration of maximum N uptake rate, period until maximum N uptake rate) which derived from the function were used to compare the cultivars.The cultivars DM yield and N uptake were highest in 1993 and declined in the next two years partly due to a decrease in soil N mineralization following the ploughing of the grass sward and partly due to the drier weather conditions during the summers of 1994 and 1995. Duration of the maximum crop growth rate was greater during the cool year of 1993. In contrast, maximum crop growth rate was at its highest in the dry vegetation period of 1995. A significant N×cultivar interaction for growth analysis characteristics (P&lt;0·05) was found in 1995. Cultivars with a high maximum crop growth rate (above the average value of the eight cultivars tested) and a short duration of maximum crop growth rate (below the average) accumulated more DM than those genotypes which showed an inverse relationship.Increasing N yield was determined by increased maximum N uptake rather than by a greater duration of maximum N uptake. A significant N×genotype interaction for N uptake parameters (P&lt;0·05) was found in 1994 and 1995. With some exceptions, cultivars with a high maximum N uptake rate (above average) accumulated more N per unit area compared to those genotypes which had low uptake rates. The exceptions had a longer duration of uptake, which could not, however, compensate for the lower rate. Maximum N uptake rate occurred earlier and duration of maximum N uptake rate increased compared to the start and duration of maximum crop growth rate. Especially in 1995, the amount of N taken up before the day of maximum crop growth rate accounted for 71% of total N uptake. The N uptake rate and the amount of accumulated N until the day of maximum crop growth rate were highly correlated with DM yield.This result indicates the availability of genotypic variability in crop growth and N uptake rate to assist the improvement of DM yield by selection.

Variation in nitrogen response among spring rape ( Brassica napus) cultivars and its relationship to nitrogen uptake and utilization

Growth, development and yield of 40 diverse spring rape ( Brassica napus) cultivars were measured at three different levels of applied nitrogen in the field. There were significant cultivar differences in yield under a limiting N supply and in yield response to higher N application rates. Cultivars with the lowest yields at the lowest N level generally responded more markedly to increase in N application rates than cultivars with higher yields in this treatment. A greater yield response was associated with relatively greater rates of growth and development at higher N levels. Measurements of dry weights and N contents of above-ground plant parts over a period between 42 and 66 days after sowing of the field experiment were used to calculate N-uptake rates and N-utilization (change in dry weight/unit change in N content) indices. Significant cultivar differences were observed only at the lowest N level for N-utilization index and only at the intermediate level for N-uptake rate. If cultivars were grouped on the basis of their geographic origin—Japanese, Canadian, European—those of Japanese origin generally had the highest uptake rates and utilization indices in the respective treatments in which significant differences were detected. Two solution-culture experiments were also conducted in a daylight phytotron at 20/15°C with the same cultivars. Significant cultivar differences in N-uptake rate and N-utilization index were detected with an initial concentration of 1m M N, but not with an initial concentration of 8 m M N. Cultivar differences in root growth and N uptake per unit root dry weight were significant at both concentrations. Again, most of the cultivars with the highest uptake rates or utilization indices were of Japanese origin. Uptake rate was correlated with uptake rate per unit dry weight, but not with initial root dry weight or increase in root weight over the course of the experiment. The significance of geographic variation in N-uptake rate in both field and controlled experiments is discussed with particular reference to the use of this character as a selection criterion in breeding programs utilizing recently developed another culture techniques.

Foliar N-uptake by Eight Turfgrasses Grown in Controlled Environment

Abstract Urea frequently is applied to turfs in liquid formulation at low water application rates which enhance potential foliar N uptake. This study was conducted to evaluate foliar N uptake by several cool-season turfgrasses treated with urea applied at low water volume (35 ml · m−2). Urea was applied foliarly to 8 turfgrasses at 2.5 g N m−2 in 35 ml m−2 of water. Verdure was harvested prior to treatment and after treatment at 24, 48, and 72 hr. Total N-uptake increases were primarily a response to increased the percentage of N, since dry matter production was stable for each turfgrass throughout the 72 hr. Maximum N-uptake occurred 24 hr after treatment. Any significant decrease in N-uptake over time suggested N-movement out of the sampling zone. Turfgrass species and cultivars showed differences in total N-uptake which resulted from initial variations in dry matter, percentage of tissue N, and variations in N-uptake rate. The percentage of N recoveries ranged from 31% to 61% for ‘Park’ Kentucky bluegrass and ‘Highlight’ chewings fescue, respectively. Cultivar differences indicated that ‘Baron’ Kentucky bluegrass was more efficient in relation to foliar N-uptake than ‘Park’ Kentucky bluegrass.