High Nitrogen Supply Research Articles

盐氮处理下盐地碱蓬种子成熟过程中的离子积累和种子萌发特性

PDF HTML阅读 XML下载 导出引用 引用提醒 盐氮处理下盐地碱蓬种子成熟过程中的离子积累和种子萌发特性 DOI: 10.5846/stxb201306081433 作者: 作者单位: 山东师范大学生命科学学院,山东师范大学生命科学学院,山东师范大学生命科学学院,山东师范大学生命科学学院,山东师范大学生命科学学院,山东师范大学生命科学学院 作者简介: 通讯作者: 中图分类号: 基金项目: 山东省自然科学基金资助项目(ZR2010CM005);国家支撑计划资助项目(2009BADA7B05) Characteristics of ion accumulation and seed germination for seeds from plants cultured at different concentrations of nitrate nitrogen and salinity Author: Affiliation: Shangdong Normal University,,,,,College of Life Science, Shandong Normal University Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:研究了盐氮处理条件下盐地碱蓬种子成熟过程中的离子积累以及种子萌发特性,以理解盐地碱蓬在种子发育及萌发过程中对高盐低氮生境的适应性。结果表明,种子成熟过程中,不同浓度盐氮处理下(0.5和5 mmol/L NO3--N;1和500 mmol/L NaCl),与果皮和果枝相比, 胚中Na+、K+、Cl- 和NO3-离子含量几乎没有变化。所有盐氮处理下Na+ 和Cl-都是果皮和果枝中高于胚中,尤其是在高盐处理下。高盐处理下,K+ 和NO3-含量呈现相反的趋势。高氮时无论高盐还是低盐,果皮中NO3-离子含量高于胚中,而果枝中NO3-离子含量低于胚中。而低氮时果皮及果枝中NO3-离子含量均显著低于胚中。与高氮环境下收获的种子相比,低氮环境下收获的种子萌发率,萌发指数,活力指数都要明显高。上述结果说明,盐地碱蓬种子成熟过程中存在完善的离子调控机制,保护胚免受Na+ 和Cl-等有害离子的伤害并且促进K+ 和NO3-等营养离子的积累。低NO3--N下收获的种子对外界的NO3-含量比较敏感,施以较高浓度的NO3-能够促进种子萌发,提高萌发指数和活力指数,可能与盐地碱蓬长期适应高盐低氮生境有关。 Abstract:Suaeda salsa is an annual euhalophyte. Fresh branches of S. salsa are valued as a vegetable, and the seeds contain edible oil. Seeds of S. salsa have a high germination rate under high salinity, but the soil NO3--N is very low in the habitat where the species occurs naturally. However, it is unknown how combined salinity and nitrate nitrogen during seed maturation affects the salt tolerance of seeds for this species. In the present study, we investigated the characteristics of ion accumulation and germination of seeds from plants cultured in different concentrations of nitrate nitrogen and salinity, in an attempt to understand the adaptation of S. salsa to high salinity and low nitrogen during seed maturation and germination. The results showed that S. salsa had a higher ability to maintain ion homeostasis (e.g., Na+, K+, Cl- and NO3-) in embryos compared to pericarp or fruiting branches when plants were cultured at different concentrations of nitrogen and salinity (i.e., 0.5 and 5 mmol/L NO3--N combined with 1 and 500 mmol/L NaCl). Na+ and Cl- concentration in the pericarp and fruiting branches were higher than those in embryos, especially at high NaCl (500 mmol/L) regardless of NO3--N concentration. At 500 mmol/L NaCl, the opposite trend was shown for K+ and NO3-. At 5 mmol/L NO3--N, the NO3-was higher in the pericarp, but lower in the fruiting branches than that in the embryos when plants was cultured in either 1 or 500 mmol/L NaCl, while the NO3-was lower in the pericarp and fruiting branches than that in the embryos at 0.5 mmol/L NO3--N supply. At 0.5 mmol/L NO3--N, the concentrations of Na+, K+ and Cl- in embryos and pericarp were higher than those at 5 mmol/L NO3--N. The seed germination, germination index and vigor index were higher for seeds from plants cultured at lower nitrogen supply than seeds from plants cultured at higher nitrogen supply. In conclusion, the species may have a perfect ion regulation mechanism to maintain ion homeostasis during seed maturation. Compared to seeds from plants cultured in higher nitrogen supply, seeds from plants cultured in lower nitrogen supply had higher seed germination, germination index and vigor index, which may be related with higher concentrations of Na+, K+ and Cl- in embryos and pericarp of seeds from plants cultured in lower nitrogen supply. The trait may be related to the adaptation of S. salsa to low soil NO3--N content in the habitat where the species occurs. 参考文献 相似文献 引证文献

The effect of nitrogen excess in the feeding of cucumber plants (Cucumis sativus L. ) growing in conditions of various medium humiditv

Reaction of 21 days old cucumber plants on high nitrogen supply during the growth in the conditions of 70% and 30% fwc sand humidity was studied in the phytotron. Obtained results showed that nitrogen in concentration 24 mmol·dm<sup>-3</sup> (9 mmol higher than in Hoagland's medium) increased WSD, g<sub>s</sub>, E, P<sub>n</sub>, as well as content of some monosaccharides (ribose, glucose, fructose), disaccharides (saccharose, trehalase), proline and trigoneline but fresh mass of plants, leaf area and c, value in cucumber plants decreased„ However the effect of higher N dose on chlorophyll content in leaves and its fluorescence parameters (F<sub>v</sub>/F<sub>m</sub>, F<sub>v</sub>'/F<sub>m</sub>', ΦPSII, Q<sub>p</sub> i Q<sub>n</sub>) have not been noticed. Moreover, it has been shown that influence of supraoptimal N dose on the value of determined plant physiological activity index was considerably bigger in 30% than 70% sand humidity. The authors suggest that high concentration of nitrogen in medium evokes changes in metabolity of carbohydrates and nitrogen substances which lead to an osmoprotectans increase in plant cells. In this way plants are more resistant to an environmental stress effect.

Nitrate reduces the negative effect of UV radiation on photosynthesis and pigmentation in Gracilaria tenuistipitata (Rhodophyta): the photoprotection role of mycosporine-like amino acids

Barufi J.B., Mata M.T., Oliveira M.C. and Figueroa F.L. 2012. Nitrate reduces the negative effect of UV radiation on photosynthesis and pigmentation in Gracilaria tenuistipitata (Rhodophyta): the photoprotection role of mycosporine-like amino acids. Phycologia 51: 636–648. DOI: 10.2216/10.77.1Photoprotection of the agarophyte red alga Gracilaria tenuistipitata against ultraviolet radiation (UVR) was investigated in algae submitted for 1 week to photosynthetically active radiation (PAR, 260 μmol photons m−2 s−1) or PAR + UVR (UV-A, 8.13 W m−2 and UV-B, 0.42 W m−2) under different nitrogen concentrations: 0, 0.1, and 0.5 mM of NO3−. Photosynthetic pigments decreased during the time of the experiment mainly under low nitrogen supply and UVR. Incubation under high nitrogen supply (0.5 mM) sustained the photosynthetic levels over time. In contrast, mycosporine-like amino acids (MAAs) increased up to eightfold in the presence of UVR and 0.5 mM NO3−. Under PAR + UVR, maximal quantum yield was positively correlated to MAA abundance, whereas under PAR no correlation was found. The photosynthetic yield of algae cultivated during seven days under PAR + UVR was less affected by a 30-min exposure of high UVR (16 W m−2) and fully recovered after transferring to low PAR irradiances, whereas algae kept under PAR were more affected by UV exposure and no full recovery was observed. Growth rates decreased after three days in the presence of UVR and under low nitrate supply. However, these rates were similar when compared with treatments of PAR and PAR + UVR after seven days, with the exception of samples in 0 mM NO3−, indicating that the acclimation after one week's exposure is related to nitrate supply. In conclusion, the lowest negative effect of UVR on photosynthesis and growth rate in high N-supply-grown algae could be explained by the stimulation of photoprotection mechanisms, such as accumulation of MAAs. Photostimulation of MAA accumulation by UVR under high N supply was observed in G. tenuistipitata even after 20 years in culture without the induction of this photomorphogenic light signal.

Trait Values, Not Trait Plasticity, Best Explain Invasive Species' Performance in a Changing Environment

The question of why some introduced species become invasive and others do not is the central puzzle of invasion biology. Two of the principal explanations for this phenomenon concern functional traits: invasive species may have higher values of competitively advantageous traits than non-invasive species, or they may have greater phenotypic plasticity in traits that permits them to survive the colonization period and spread to a broad range of environments. Although there is a large body of evidence for superiority in particular traits among invasive plants, when compared to phylogenetically related non-invasive plants, it is less clear if invasive plants are more phenotypically plastic, and whether this plasticity confers a fitness advantage. In this study, I used a model group of 10 closely related Pinus species whose invader or non-invader status has been reliably characterized to test the relative contribution of high trait values and high trait plasticity to relative growth rate, a performance measure standing in as a proxy for fitness. When grown at higher nitrogen supply, invaders had a plastic RGR response, increasing their RGR to a much greater extent than non-invaders. However, invasive species did not exhibit significantly more phenotypic plasticity than non-invasive species for any of 17 functional traits, and trait plasticity indices were generally weakly correlated with RGR. Conversely, invasive species had higher values than non-invaders for 13 of the 17 traits, including higher leaf area ratio, photosynthetic capacity, photosynthetic nutrient-use efficiency, and nutrient uptake rates, and these traits were also strongly correlated with performance. I conclude that, in responding to higher N supply, superior trait values coupled with a moderate degree of trait variation explain invasive species' superior performance better than plasticity per se.

Virtual Special Issue (VSI) on mechanisms of plant response to global atmospheric change

Virtual Special Issue (VSI) on mechanisms of plant response to global atmospheric change

Identification of Differentially Senescing Mutants of Wheat and Impacts on Yield, Biomass and Nitrogen PartitioningF

Increasing photosynthetic capacity by extending canopy longevity during grain filling using slow senescing stay-green genotypes is a possible means to improve yield in wheat. Ethyl methanesulfonate (EMS) mutated wheat lines (Triticum aestivum L. cv. Paragon) were screened for fast and slow canopy senescence to investigate the impact on yield and nitrogen partitioning. Stay-green and fast-senescing lines with similar anthesis dates were characterised in detail. Delayed senescence was only apparent at higher nitrogen supply with low nitrogen supply enhancing the rate of senescence in all lines. In the stay-green line 3 (SG3), on a whole plant basis, tiller and seed number increased whilst thousand grain weight (TGW) decreased; although a greater N uptake was observed in the main tiller, yield was not affected. In fast-senescing line 2 (FS2), yield decreased, principally as a result of decreased TGW. Analysis of N-partitioning in the main stem indicated that although the slow-senescing line had lower biomass and consequently less nitrogen in all plant parts, the proportion of biomass and nitrogen in the flag leaf was greater at anthesis compared to the other lines; this contributed to the grain N and yield of the slow-senescing line at maturity in both the main tiller and in the whole plant. A field trial confirmed senescence patterns of the two lines, and the negative impact on yield for FS2 and a positive impact for SG3 at low N only. The lack of increased yield in the slow-senescing line was likely due to decreased biomass and additionally a possible sink limitation.

Differential response of wheat genotypes to applied nitrogen: biochemical and molecular analysis

Nitrogen-efficient and nitrogen-inefficient wheat genotypes were identified on the basis of the differential response of 16 wheat genotypes with low (1 mM) and high (25 mM) nitrogen (N) supply. Growth performance, measured in terms of fresh weight, dry weight and length of root and shoot, was higher in N-efficient than N-inefficient wheat genotypes at low N levels. Interestingly, although the growth of N-efficient genotypes did not show any change with increasing level of N supply, there was a marked increase in the growth of N-inefficient genotypes with the increase in N level. To work out the basis of this differential response of wheat genotypes to low N levels, we investigated the nitrate uptake rate of root and activities of nitrate assimilatory enzymes in the leaves of N-efficient and N-inefficient wheat genotypes. Nitrate uptake kinetics of these genotypes revealed that the uptake of nitrate in N-efficient genotypes was mediated by high-affinity nitrate transporter systems, whereas those of N-inefficient genotypes was mediated by low-affinity nitrate transporter systems. Study of the activities and expression levels of nitrate assimilatory enzymes in N-efficient and N-inefficient wheat genotypes showed that nitrate reductase (NR) and glutamine synthetase (GS) play important roles in N assimilation under low-nitrogen conditions.

Influence of nitrogen rate on the efficacy of herbicides with different modes of action

Sønderskov M, Swanton CJ & Kudsk P (2012). Influence of nitrogen rate on the efficacy of herbicides with different modes of action. Weed Research 52, 169–177.SummaryOutdoor pot experiments and field experiments were conducted to examine the influence of nitrogen rate on herbicide efficacy. Growth of unsprayed Tripleurospermum inodorum increased with increasing nitrogen rate in pot experiments; increasing nitrogen also increased the susceptibility to tribenuron‐methyl. An increased susceptibility at high nitrogen rate was also observed for Anagallis arvensis, but in contrast to T. inodorum, growth of unsprayed A. arvensis was unaffected by nitrogen rate. Growth of unsprayed Chenopodium album was also promoted by nitrogen supply. However, no influence of nitrogen rate on herbicide efficacy was evident for C. album with tribenuron‐methyl or ioxynil+bromoxynil in pot experiments. Field experiments with tribenuron‐methyl were conducted on natural populations of C. album in spring barley grown at different nitrogen rates showed similar results. In conclusion, nitrogen rate affected herbicide efficacy for some but not all combinations of weed species and herbicide. Decreased herbicide efficacy was only observed at very low nitrogen rates. The results suggest that the effect of nitrogen rates on herbicide efficacy will be marginal in intensive farming systems with high nitrogen supply, but in low intensity systems, weed patchiness might increase.

Organ‐specific responses of tomato growth and phenolic metabolism to nitrate limitation

Phenolic compounds are secondary metabolites involved in plant innate chemical defence against pests and diseases. Their concentration varies depending on plant tissue and also on genetic and environmental factors, e.g. availability of nutrient resources. This study examines specific effects of low (LN) and high (HN) nitrogen supply on organ (root, stem and leaf) growth and accumulation of major phenolics [chlorogenic acid (CGA); rutin; kaempferol rutinoside (KR)] in nine hydroponically grown tomato cultivars. LN limited shoot growth but did not affect root growth, and increased concentrations of each individual phenolic in all organs. The strength of the response was organ-dependent, roots being more responsive than leaves and stems. Significant differences were observed between genotypes. Nitrogen limitation did not change the phenolic content in shoots, whereas it stimulated accumulation in roots. The results show that this trade-off between growth and defence in a LN environment can be discussed within the framework of the growth-differentiation balance hypothesis (i.e. GDBH), but highlight the need to integrate all plant organs in future modelling approaches regarding the impact of nitrogen limitation on primary and secondary metabolism.

增强UV-B辐射和氮对谷子叶光合色素及非酶促保护物质的影响

以谷子(<em>Setaria italica </em>(L.) Beauv.)为对象,从拔节期开始持续给予低氮(1.875 mmol/L)和高氮(15 mmol/L)两种氮供应条件并从抽穗期开始进行26 d两种强度(4.29、7.12 kJ·m^-2·d^-1)的增强UV-B辐射处理,研究了谷子叶中光合色素含量、类黄酮含量和苯丙氨酸解氨酶(PAL)活性的变化。结果表明:与高氮供应条件相比,低氮供应条件明显降低了谷子叶中光合色素含量但提高了类胡萝卜素/叶绿素含量比值;在开花期中段和灌浆期中段,高氮供应条件下谷子叶中光合色素含量对增强UV-B辐射比低氮供应条件下的谷子更敏感。从灌浆期开始到处理结束,两种影响因子对谷子叶中类黄酮含量均有显著影响,增强UV-B辐射导致谷子叶中类黄酮含量逐渐升高,且相同增强UV-B辐射强度下低氮供应条件下的谷子叶中类黄酮含量明显高于高氮供应条件下的谷子。谷子叶中PAL活性对两种影响因子的响应较类黄酮含量更加敏感,低氮供应条件使谷子叶中PAL活性明显提高。结合上述指标的相关性分析结果可知,低氮供应条件加强了处于繁殖期主要阶段的谷子叶中类黄酮的积累,并使谷子叶中的类胡萝卜素/叶绿素含量比值明显提高,进而有助于维持谷子叶中光合色素含量在增强UV-B辐射条件下的相对稳定性,对植株抵抗UV-B辐射伤害有利。;Enhanced UV-B radiation resulting from ozone depletion in stratosphere with the increase of human activities can harm plants greatly, whereas the change of nitrogen supply can affect the sensitivity and resistance to UV-B radiation in plants. Foxtail millet (<em>Setaria italica </em>(L.) Beauv.), a typical C₄ crop plant, was chosen as experimental model to investigate the effects of enhanced UV-B radiation and nitrogen supply on photosynthetic pigments and non-enzymatic protection system in leaves. The plants of foxtail millet were fertilized under two different nitrate-nitrogen conditions (1.875, 15 mmol/L) from the jointing stage to the grouting stage, and were stressed by two different intensities of enhanced UV-B radiation (4.29, 7.12 kJ·m^-2·d^-1) from the heading stage to the grouting stage (26 days). During this period, the photosynthetic pigments and flavonoids content and the phenylalanine ammonia-lyase (PAL) activity in leaves of foxtail millet were measured. The nitrogen supply showed significant effect on the photosynthetic pigments contents in leaves of both UV-B treated and non-treated foxtail millet. The leaves in low nitrogen supply group showed significantly lower photosynthetic pigments content but higher carotenoid/chlorophyll ratio when compared to those of high nitrogen supply group according to most of statistical test results (<em>P</em><0.05, least-significant difference, LSD). However, enhanced UV-B radiation treatment showed significant effects on the photosynthetic pigments contents in leaves of foxtail millet in only the 11th day and the 21st day, and the photosynthetic pigments were more sensitive to enhanced UV-B radiation treatment at the high nitrogen group compared to the low nitrogen group. The nitrogen supply showed significant effect on PAL activity in leaves of foxtail millet during the whole period of this experiment, whereas enhanced UV-B radiation showed significant effect on the PAL activity only after the 11th day. Meanwhile, most LSD results showed that the PAL activity in leaves of foxtail millet increased in the low nitrogen supply group compared to the high nitrogen group, whether treated by enhanced UV-B radiation or not. Furthermore, both the nitrogen supply and enhanced UV-B radiation affected the flavonoids content in leaves of foxtail millet significantly after the 16th day, and the flavonoids content in leaves increased significantly in the low nitrogen supply in the 26th day independent of enhanced UV-B radiation. There was a significant positive correlation between the flavonoids content and the PAL activity, but both the flavonoids content and the PAL activity had a significantly negative correlation with the chlorophyll content. Moreover, there was a significant correlation between the chlorophyll content and the carotenoid content. This study indicated that in leaves of foxtail millet, low nitrogen supply treatment could enhanced accumulation of flavonoids and the carotenoid/chlorophyll ratio, thus caused more stability of photosynthetic pigments contents when foxtail millet was stressed by enhanced UV-B radiation compared to the high nitrogen supply during the breeding period. Therefore, low nitrogen supply treatment may improve the resistance to UV-B radiation in plants.

Nitrogen efficiency of Brussels sprouts under different organic N fertilization rates

The identification of nitrogen efficient varieties is important to improve yielding abilities in organic farming systems which are usually N-limited. This holds true particularly for crops with a long growing period and high nitrogen demand such as Brussels sprouts. Two field experiments with two different fertilizer levels were conducted on a hapludalf soil under the conditions of organic farming. Ten Brussels sprouts varieties with different growing periods were evaluated. For N accumulation efficiency differences between cultivars were not consistent over both experimental years, but similar under different levels of nitrogen supply. An allometric relationship between bud dry matter and total plant nitrogen accumulation comprising all varieties in both years and both fertilizer levels explained 56% of the total variation. Additionally, nitrogen utilization efficiency (NUE) was influenced by bud nitrogen content and harvest index. We found different relationships between bud dry matter and bud nitrogen with contrasting bud nitrogen percentage between years. However, relating bud nitrogen to total aboveground N again gave a linear relationship unifying all factors. Harvest index was linearly related to NUE indicating that dry matter partitioning is a major determinant of NUE. Varietal differences in NUE differed between years. Within years, yields of individual cultivars grown under different nitrogen levels were linearly related. We conclude that nitrogen accumulation in buds is environmentally stable, whereas dry matter partitioning into the same organs is more variable. Apparently, varieties performing well under high nitrogen supply yield also high under limited nitrogen. Further investigations are needed since the large genotypic variation between years is not fully understood.

Changes of Nutritional Status during a Phenological Cycle of Coffee under High Nitrogen Supply by Fertigation

High-technology coffee cultivation systems involving fertigation commonly apply high rates of nitrogen (N). However, there is little information on the plants' uptake of N under these conditions. The objective of this study was to evaluate the changes in the nutritional status of coffee plants during a phenological cycle in response to N applied by fertigation. The study was conducted with 7-year-old trees of Coffea arabica L., under pivot irrigation and fertigation, with five N rates (0, 200, 400, 600, and 800 kg ha−1) applied on the plants. The changes in nutritional status were monitored during the phenological cycle, and the yield was measured at the end of the cycle. The N concentration increased with the N rates and varied with the phenological period, with the greatest concentration occurring during anthesis, the same as for the sulfur level. However, N rate did not affect the concentrations of other nutrients. The greatest concentrations of phosphorus, calcium, and magnesium were obtained in the final fructification phases and for potassium in the initial phases. Micronutrient concentrations were greater in the vegetative phases and anthesis but were reduced in the fruit- formation phase and increased again when the berries started to mature. The maximum yield, considering a relative production of 90%, was obtained with application of 415 kg ha−1 of N. Leaf concentrations of N were directly related to the N rates, showing that the nutritional status of coffee plants can be evaluated in the ripening phase to adjust the fertilization parameters for the next year.

Down-regulation of Rubisco activity under combined increases of CO2 and temperature minimized by changes in Rubisco kcat in wheat

Increases in growth temperature have been observed to affect photosynthesis differently under long-term exposure to ambient- and twice ambient-air CO2 concentrations. This study investigates the causes of this interaction in wheat (Triticum aestivum L.) grown in the field over two consecutive years under temperature gradient chambers in ambient (370 μmol mol−1) or elevated (700 μmol mol−1) atmospheric CO2 concentrations and at ambient or ambient +4°C temperatures, with either a low or a high nitrogen supply. The photosynthesis-internal CO2 response curves and the activity, activation state, kcat and amount of Ribulose-1, 5-bisphosphate carboxylase/oxygenase (Rubisco) were measured, as well as the soluble protein concentration in flag leaves at ear emergence and 8–15 days after anthesis. A high nitrogen supply increased Vcmax, the Rubisco amount and activity and soluble protein contents, but did not significantly change the Rubisco kcat. Both elevated CO2 and above ambient temperatures had negative effects on Vcmax and Rubisco activity, but at elevated CO2, an increase in temperature did not decrease Vcmax or Rubisco activity in relation to ambient temperature. The amounts of Rubisco and soluble protein decreased with elevated CO2 and temperature. The negative impact of elevated CO2 on Rubisco properties was somewhat counteracted at elevated temperatures by an increase in kcat. This effect can diminish the detrimental effects on photosynthesis of combined increases of CO2 and temperature.

The effects of nitrogen addition on the growth of two exotic and two native forest understory plants

Many studies have linked the spread of exotic, invasive species to high nitrogen supply, but most of this work does not distinguish between various inorganic forms and different concentrations of available nitrogen. Previous research has suggested that exotic, invasive species common in eastern deciduous forests may preferentially utilize nitrate in contrast to native species that preferentially make use of ammonium. We tested this hypothesis by comparing the growth response of two common forest invaders, Berberis thunbergii and Microstegium vimineum, and two co-occurring native species (Vacciniumpallidum and Hamamelis virginiana) to different forms of nitrogen under varying concentrations in a greenhouse experiment. Two forms of nitrogen (nitrate or ammonium) were added at different concentrations (22, 106, and 212 mg N l−1) to all species. Growth response variables included survival, stem length, stem diameter, above and belowground biomass, and estimated seed production (Microstegium only). Unexpectedly the exotic species did not respond preferentially to nitrate addition. Microstegium responded most strongly to both nitrogen forms depending on the response variable. Berberis and Hamamelis surprisingly reacted similarly to nitrogen additions. As expected, Vaccinium fared poorly under most treatment conditions, but did show some growth in NH4+ treatments. Our findings suggest species response to nitrogen addition is complex, and that exotic species do not all respond similarly to nitrogen inputs. In this study, the response of exotic and native species to available nutrients does not provide a general mechanism of invasion success.

Why Nitrogen Use Efficiency Decreases Under High Nitrogen Supply in Rice (Oryza sativa L.) Seedlings

Hydroponic experiments were conducted in a greenhouse to examine the effects of different nitrogen (N) supply (low, 20 mg L−1; intermediate, 40 mg L−1; and high, 100 mg L−1) on the growth, nitrogen use efficiency, and photosynthetic characteristics of rice seedlings (Oryza sativa L., cv. “Shanyou 63” hybrid indica. China). Leaf gas exchange was conducted to identify the photosynthetic-limiting factors in plants with high N supply. The results showed that (1) shoot biomass, leaf area, and tiller numbers per plant under low N were lower than under intermediate and high N supplies. No significant differences were observed between plants supplied with intermediate and high N. (2) About a 35% increase in leaf N content in plants fed by high N resulted in about a 15% increase in carboxylation efficiency (CE) and photosynthetic rate. (3) The noncorresponding increases in photosynthetic rate in rice seedlings fed by high N relative to low N resulted from Rubisco activity and/or CE. (4) The decreased Rubisco activity was induced by a relatively insufficient CO2 supply under high N supply. These results indicated that insufficient CO2 supply under high N supply accounted for the decreased Rubisco activity and the noncorresponding increases in photosynthetic rate to leaf N content, and as a result, decreased (photosynthetic) nitrogen use efficiency.

Long-term effect of tillage, nitrogen fertilization and cover crops on soil organic carbon and total nitrogen content

No-tillage, N fertilization and cover crops are known to play an important role in conserving or increasing SOC and STN but the effects of their interactions are less known. In order to evaluate the single and combined effects of these techniques on SOC and STN content under Mediterranean climate, a long term experiment started in 1993 on a loam soil (Typic Xerofluvent) in Central Italy. The experimental variants are: conventional tillage (CT) and no-tillage (NT), four N fertilization rates (N0, N1, N2 and N3) and four soil cover crop (CC) types (C – no cover crop; NL – non-legume CC; LNL – low nitrogen supply legume CC, and HNL – high nitrogen supply legume CC). The nitrogen fertilization rates (N0, N1, N2 and N3) were: 0, 100, 200, 300 kg N ha −1 for maize ( Zea mays, L.); 0, 60, 120,180 kg N a −1 for durum wheat ( Triticum durum Desf.); 0, 50, 100, 150 kg N ha −1 for sunflower ( Helianthus annuus L.). From 1993 to 2008, under the NT system the SOC and STN content in the top 30 cm soil depth increased by 0.61 and 0.04 Mg ha −1 year −1 respectively. In the same period, the SOC and STN content under the CT system decreased by a rate of 0.06 and 0.04 Mg ha −1 year −1 respectively. During the experimental period, N1, N2 and N3 increased the SOC content in the 0–30 cm soil layer at a rate of 0.14, 0.45 and 0.49 Mg ha −1 year −1. Only the higher N fertilization levels (N2 and N3) increased STN content, at a rate of 0.03 and 0.05 Mg ha −1 year −1. NL, LNL and HNL cover crops increased SOC content by 0.17, 0.41 and 0.43 Mg C ha −1 year −1 and −0.01, +0.01 and +0.02 Mg N ha −1 year −1. Significant interactions among treatments were evident only in the case of the N fertilization by tillage system interaction on SOC and STN concentration in the 0–10 cm soil depth in 2008. The observed SOC and STN variations were correlated to C returned to the soil as crop residues, aboveground cover crop biomass and weeds (C input). We conclude that, under our Mediterranean climate, it is easier to conserve or increase SOC and STN by adopting NT than CT. To reach this objective, the CT system requires higher N fertilization rates and introduction of highly productive cover crops.

Heterotic Response for Grain Yield and Ecophysiological Related Traits to Nitrogen Availability in Maize

ABSTRACTMaize (Zea mays L.) hybrid vigor for plant grain yield (PGY) is associated with heterosis for plant biomass at maturity (aboveground biomass at physiological maturity [BiomassPM]), kernel number per plant (KNP), and harvest index (HI); however, no evidence of the effects of nitrogen (N) availability or combination of abiotic stresses on heterosis for physiological components of PGY has been reported. The objective of this study was to determine the response of heterosis for ecophysiological traits related to PGY at contrasting N supply levels in a set of six inbred lines and 12 derived hybrids. Field experiments were conducted in five growing seasons at low nitrogen (LN; no N added) and high nitrogen (HN) supply (200 or 400 kg N ha−1) under irrigation and dryland farming. Increased PGY (65% for hybrids and 30% for inbreds) was ascribed to similar increase in BiomassPM as no increase in HI was found. Heterosis for PGY was higher under HN (137%) than LN (87%). A similar response was observed for traits related to light capture and biomass accumulation. Heterosis for HI did not differ between HN (31%) and LN (28%). Heterosis for PGY was associated (p &lt; 0.01) with heterosis for KNP, BiomassPM, radiation use efficiency (RUE) during grain filling, HI, and traits related to maximum light capture. Heterosis for PGY at LN was also correlated with heterosis for RUE at critical period (i.e., 30 d bracketing silking) and kernel weight. Under the combined effect of N and drought, PGY heterosis was reduced and more affected at HN (59%) than at LN (70%).

Yield Response of Uniculm Wheat (Triticum aestivum L.) to Early and Late Application of Nitrogen: Flag Leaf Development and Senescence

Nitrogen (N) supply increased flag leaf area by increasing cell number. N promoted initiation and development of floret primordia. N availability upto ear emergence affected fertile floret number more than spikelet number and increased the number of grains. Late application of nitrogen at 5 days after anthesis increased percentage nitrogen in grains, grain weight and grain number due to its effect on ability of floret to set grain. Larger number of florets and grains provided sink not only for carbon but also for nitrogen accumulation with high nitrogen availability. The accumulation of grain protein depended on the accumulation and partitioning of reduced N accumulated during the vegetative stage of growth and the relative contributions of nitrate assimilation and N redistribution during grain development in low as well as high nitrogen supply. Flag leaf of ‘Gigas’ wheat retained the ability to synthesize RuBPCO on induction of nitrate reductase by substrate supply at post anthesis stage. The reductions in proteolytic enzymes were coincident with loss of Chl, total soluble protein and nitrate reductase activity from the flag leaves.

Feedback of carbon and nitrogen cycles enhances carbon sequestration in the terrestrial biosphere

AbstractThe efforts to explain the ‘missing sink’ for anthropogenic carbon dioxide (CO2) have included in recent years the role of nitrogen as an important constraint for biospheric carbon fluxes. We used the Nitrogen Carbon Interaction Model (NCIM) to investigate patterns of carbon and nitrogen storage in different compartments of the terrestrial biosphere as a consequence of a rising atmospheric CO2 concentration, in combination with varying levels of nitrogen availability. This model has separate but closely coupled carbon and nitrogen cycles with a focus on soil processes and soil–plant interactions, including an active compartment of soil microorganisms decomposing litter residues and competing with plants for available nitrogen. Biological nitrogen fixation is represented as a function of vegetation nitrogen demand. The model was validated against several global datasets of soil and vegetation carbon and nitrogen pools. Five model experiments were carried out for the modeling periods 1860–2002 and 2002–2100. In these experiments we varied the nitrogen availability using different combinations of biological nitrogen fixation, denitrification, leaching of soluble nitrogen compounds with constant or rising atmospheric CO2 concentrations. Oversupply with nitrogen, in an experiment with nitrogen fixation, but no nitrogen losses, together with constant atmospheric CO2, led to some carbon sequestration in organismic pools, which was nearly compensated by losses of C from soil organic carbon pools. Rising atmospheric CO2 always led to carbon sequestration in the biosphere. Considering an open nitrogen cycle including dynamic nitrogen fixation, and nitrogen losses from denitrification and leaching, the carbon sequestration in the biosphere is of a magnitude comparable to current observation based estimates of the ‘missing sink.’ A fertilization feedback between the carbon and nitrogen cycles occurred in this experiment, which was much stronger than the sum of separate influences of high nitrogen supply and rising atmospheric CO2. The demand‐driven biological nitrogen fixation was mainly responsible for this result. For the modeling period 2002–2100, NCIM predicts continued carbon sequestration in the low range of previously published estimates, combined with a plausible rate of CO2‐driven biological nitrogen fixation and substantial redistribution of nitrogen from soil to plant pools.

Nitriding of austenitic stainless steel by pulsed low energy ion implantation

Low energy ion implantation (LEII) of nitrogen into austenitic stainless steel was carried out using an electronic beam switch for a defined regulation of nitrogen ion flux and an additional external radiation heating for assuring a constant process temperature of 460 °C with the aim to investigate the influence of a varying ion energy and ion flux, respective particle flux on nitrogen diffusion, phase formation and hardness of the nitrided austenitic stainless steel, grade 1.4301, samples. No influence of both process parameter variations on the layer thickness was found as long as identical temperature profiles were maintained. This implies that the nitrogen diffusion is decoupled from nitrogen insertion at constant temperature for sufficiently high nitrogen supply. It was found that the pulsed mode does not influence the expended austenite formation, hardness of the nitrided layers as well as their corrosion resistance compared with a continuous LEII-mode at the same ion source plasma parameters.