Nitrogen Mobilization from Stubble and Roots during Re-growth of Defoliated Perennial Ryegrass

Nitrogen re-mobilization during ryegrass (Lolium perenne L.)re-growth was studied as a function of time. Roots and stubblecompounds were labelled with ¹⁵N before clipping. Experimentalresults clearly showed that ryegrass re-growth involves twoperiods of differing physiological significance. The first occursduring the first 6 d when nearly all the nitrogen of the newleaves comes from organic nitrogen re-mobilized from roots andstubble. At the same time, the uptake of nitrogen from the mediumis very low, no reduction of endogenous nitrate occurs and proteolysisand amino amido nitrogen re-mobilization in stubble are notfully compensated for by synthesis.Thus, the change in protein-Ncontent, expressed per plant, in stubble decreases from 998µg (uncut plant) to 866 µg and 661 µg for2 d and 4 d respectively after cutting. The second period (afterthe sixth day) may be more representative of stable behaviourof ryegrass, with assimilation of mineral nitrogen from themedium providing the predominant source of nitrogen for re-growth. Key words: Lolium perenne L., nitrogen, re-growth     

The Influence of Frequent Defoliation and of Drought on Nitrogen and Sulphur in the Roots of Perennial Ryegrass and White Clover

Frequent defoliation and drought, imposed individually overa period of 60 days, both reduced substantially the root weightsof white clover grown in the field, while causing no reductionin the root weights of perennial ryegrass. Concentrations ofN and S in the root organic matter of the clover were reducedby between 14 and 25 per cent by both treatments, but with theryegrass concentrations were not reduced. Perennial ryegrass, white clover, roots, nitrogen, sulphur, defoliation, drought     

Influence of Nitrogen Fertilizer and Endophyte Infection on Ecophysiological Parameters and Mineral Element Content of Perennial Ryegrass

An experiment was designed to determine the effect of the fungal endophyte Neotyphodium Iolii on the growth, physiological parameters and mineral element content of perennial ryegrass （Lolium perennel L.）, when growing at two N supply levels. Endophyte infection had a significant positive effect on both shoot and root growth of ryegrass, but this difference was only significant in the high N supply treatment. At high N supply, endophyte-infected （El） plants accumulated more soluble sugar in the sheath and the root than endophyte-free （EF） plants. Endophyte infection affected mineral element concentrations in the root more than in the shoot. We found a significant effect of endophyte infection on B, Mn and Mg in the root, but significant effect was only found on B in the shoot. El plants tended to accumulate less B in the shoot at both N levels, but accumulated more B, Mn and Mg in the root at low N levels. The difference of growth parameters in different periods was significant. The content of soluble sugar and crude protein in the sheath were also dependent on the growth stages of both El and EF plants.     

Influence of Nitrogen Fertilizer and Endophyte Infection on Ecophysiological Parameters and Mineral Element Content of Perennial Ryegrass

An expedment was designed to determine the effect of the fungal endophyte Neotyphodium lolii on the growth, physiological parameters and mineral element content of perennial ryegrass (Lolium perennel L.), when growing at two N supply levels. Endophyfe infection had a significant positive effect on both shoot and root growth of ryegrass, but this difference was only significant in the high N supply treatment. At high N supply, endophyte-infected (EI) plants accumulated more soluble sugar in the sheath and the root than endophyte-free (EF) plants. Endophyte infection affected mineral element concentrations In the root more than in the shoot. We found a significant effect of endophyte infection on B, Mn and Mg in the root, but significant effect was only found on B in the shoot. EI plants tended to accumulate less B in the shoot at both N levels, but accumulated more B, Mn and Mg in the root at low N levels. The difference of growth parameters in different periods was significant. The content of soluble sugar and crude protein in the sheath were also dependent on the growth stages of both EI and EF plants.     

Nitrogen Deficiency in Small Closed Communities of S24 Ryegrass. II. Changes in the Weight and Chemical Composition of Single Leaves During Their Growth and Death

Small communities of S24 ryegrass were grown under supplementarylights in a glasshouse at 20°C, and abundantly suppliedwith a complete nutrient solution containing 300 p.p.m. of nitrogen,until they had a leaf area index of 5 and were fully light intercepting.Half were then given a solution containing only 3 p.p.m. ofnitrogen (LN) while the rest were kept at 300 p.p.m. (HN). The HN plants subsequently produced marginally more leaves,which elongated more rapidly to a greater final length and area,on a third more tillers than did the LN plants. Leaves 5, 6 and 7 on the main stem were examined in more detail.In both the HN and the LN plants the d. wts of both laminaeand sheaths fell by about 30 per cent between their full expansionand death. Changes in acid extractable carbohydrate (AEC) verylargely accounted for the changes in leaf weight, particularlyin the LN plants. With increased nitrogen deficiency, AEC contentsrose from less than 10 per cent for leaf 5 to peak values of20 and 45 per cent for the lamina and sheath of leaf 7, as against10 and 15 per cent in the nitrogen sufficient leaves. Conversely,the nitrogen content of the deficient plants fell from valuesof 5·8 and 4·8 per cent for the lamina and sheathof leaf 5 to 3·0 and 1·2 per cent for leaf 7.It was striking that while the HN leaves lost nitrogen onlywhen they aged and died, the LN leaves started losing nitrogenbefore they had reached full expansion—70 per cent ofthe N initially present was remobilized by the time the leaveswere dead. The significance of these findinp to estimates of leaf deathand total biomass production in the field, and to our understandingof the achievement of ceiling yield, are discussed. Luliwn perenne, S24 ryegrass, carbohydrate content, nitrogen content, nitrogen deficiency     

The Volatilization of Ammonia from Perennial Ryegrass During Decomposition, Drying and Induced Senescence

The volatilization of gaseous ammonia was measured from cutherbage (leaf lamina + sheath) of perennial ryegrass (Loliumperenne L.), during a 70 d period of either decomposition ordrying, and also from intact plants of perennial ryegrass subjectedto induced senescence by shading. Volatilization during decompositionamounted to 20–47% of the herbage nitrogen, but volatilizationduring drying, and from intact plants during induced senescence,amounted to less than 1% of the herbage nitrogen. During decomposition, volatilization of ammonia was proportionallygreater from herbage containing 3.52% nitrogen than from herbagecontaining 2.32% nitrogen. Volatilization occurred more rapidlyat 20 °C than at 10 °C but, with both samples of herbageand at both temperatures, at least 4 d elapsed before appreciablevolatilization occurred. Ammonia, atmosphere, decomposition, leaves, Lolium perenne L, nitrogen, perennial ryegrass     

Regrowth by Swards of Subterranean Clover after Defoliation. 1. Growth, Non-structural Carbohydrate and Nitrogen Content

Swards of subterranean clover (Trifolium subterraneum L.) atLAl 6 grown in N-free nutrient solution were subjected to threedefoliation treatments which removed 30, 70 and 80% of shootdry weight. Subsequent regrowth and changes in the concentrationsof carbohydrate and nitrogen in plant components were measuredat 0, 1, 5, 9 and 13 d after defoliation and compared with thosein uncut swards. The rate of shoot regrowth declined with increasing severilyof defoliation. In all defoliation treatments, growth was confinedto leaves for up to 5 d. Root growth ceased in all treatmentsfor a longer period. Reestablishment of the leaf area in severely-defoliatedswards was facilitated by the rapid opening of developing leavesand by changes in the allocation of carbon which favoured leafover branch and root, and lamina over petiole growth. Loss of carbohydrate and nitrogen from roots and branches lasting5–9 d was observed in the more severe defoliation treatments.Loss of protein (N x 6.25) exceeded that of total non-structuralcarbohydrate, and could have accounted for the nitrogen contentof new leaf during this period. Branches lost 62% of their initialcarbohydrate content compared with 25% from roots in the 80%cut swards. In contrast, roots, by virtue of their greater mass,were the principle source of mobilized nitrogen. Nitrogen accumulationceased in 80% cut swards for 9 d. However, carbohydrate levelsin the crown nodules were not severely depleted. It was concluded that partitioning of growth to lamina and themobilization of carbohydrates and nitrogen were important forrecovery from defoliation. Carbohydrates, carbon partitioning, defoliation, nitrogen, mobilization, regrowth, subterranean clover, Trifolium subterraneum L     

Tillering Responses to the Light Environment and to Defoliation in Populations of Perennial Ryegrass (Lolium perenneL.) Selected for Contrasting Leaf Length

Tillering responses to the light environment and to defoliationwere studied in two populations of perennial ryegrass (LoliumperenneL.) selected for contrasting leaf lengths. The objectiveof this study was to determine whether differences in tilleringresponses between populations, as a result of management practices,affected their competitive ability. Young seedlings were exposed,under controlled conditions, to defoliation, neutral shading(decreased photosynthetic photon flux), low red:far-red ratioand/or decreased blue light. Selection for longer leaves reducedthe tillering rate. After defoliation, this difference betweenshort- and long-leaved populations was magnified. Defoliationdecreased both site filling and phyllochron of the long-leavedpopulation but had no effect on the short-leaved population.Lowering the photosynthetic photon flux reduced the phyllochronin both population. Decreasing the red:far-red ratio reducedtillering rate by reducing site filling, whereas decreasingblue light had no significant effects on tillering. Tilleringresponses to photosynthetic photon flux and to red:far-red ratiowere similar in the two populations selected for contrastingleaf length. The implication of these tillering responses indefining the competitive ability of the grass plants is discussedin relation to their management.Copyright 1999 Annals of BotanyCompany Blue light, defoliation, far-red, irradiance, leaf size,Lolium perenne(L.), perennial ryegrass, photomorphogenesis, phyllochron, shading, site filling, tiller production.     

低温贮藏期间百合鳞茎中的游离氨基酸组分和含量变化

百合鳞茎的游离氨基酸主要集中在顶芽和内部鳞片等幼嫩组织中,含量最高、变化最大的是精氨酸.谷氨酸族的氨基酸在鳞茎代谢中起重要作用.顶芽的氨基酸总量及精氨酸含量随贮藏温度的升高而增加.贮藏过程中,鳞茎盘的氨基酸含量下降,顶芽和贮备组织中其含量有明显升高的过程.贮藏前期34 d内游离氨基酸含量发生显著变化.     

Influx and Efflux of Nitrate and Ammonium in Italian Ryegrass and White Clover Roots: Comparisons Between Effects of Darkness and Defoliation

Seedlings of Italian ryegrass (Lolium multiflorum Lam. cv. RVP)and clonal stolon cuttings of white clover (Trifolium repensL. cv. Blanca) were grown for 19 d in flowing solution culture,with N supplied as either 250 mmol m^–3 NO₃^– or NH₃⁺.Rates of net uptake, influx and translocation of NO₃^–and NH₄⁺ were then determined using ¹⁵N and ¹³N labelling techniques:between 3–5 h into the photoperiod following 8 h darknessfor white clover (CL), and for ryegrass plants that were eitherentire (IL) or with shoots excised 90 min prior to ¹³N influx(IC); and 75 min into the photoperiod following 37–39h darkness for ryegrass (ID). Rates of net uptake, influx andefflux of NH₄⁺ exceeded those of NO₃^– in IL and IC ryegrassplants: the opposite occurred in white clover (CL). The decreasein net uptake following defoliation of ryegrass was greaterfor NH₄⁺ (62%) than NO₃^– (40%). For NH₄⁺ this was associatedwith a large decrease in influx from 110 to 6.0µmol h^–1g^–1 root fr. wt; but for NO₃^–, influx only decreasedfrom 42 to 37 µmol h^–1 g^–1. Prolonged exposureto darkness (ID plants) also lowered net uptake of NO₃^–and NH₄⁺ by, respectively, 86% and 95% of IL levels. For NH₄⁺this was characterized by a large decrease in influx and a smalldecrease in efflux; whilst for NO₃^– the effect of a largedecrease in influx was reinforced by a smaller increase in efflux. The data were used to estimate the translocatory fluxes of NO₃^–(03–20µmol h^–1 g^–1) and NH₄⁺ (003–0.4µmolh^–1 g^–1), assimilation in the roots of NO₃^–(02–26µmol h^–1 g^–1) and NH⁺⁴ (05–89 µmolh^–1 g^–1), and the concentrations of NO₃^– (9–15mol m^–3) in the cytoplasmic compartment of the roots.The relevance of variable influx and efflux to models for theregulation of N uptake is discussed. Key words: Lolium multiflorum, Trifolium repens, influx, efflux, nitrate, ammonium, ¹³N     

Changes in the Morphology of Roots and Leaves of Carob Seedlings Induced by Nitrogen Source and Atmospheric Carbon Dioxide

Carob seedlings were grown hydroponically for 9 weeks under360 and 800 µl l^-1CO₂. One of two nitrogen sources, nitrateor ammonium, was added to the nutrient medium at concentrationsof 3 mol m^-3. Root systems of the developing plants suppliedwith nitrate compared to those supplied with ammonium were characterizedby:(a)more biomass on the lower part of the root;(b)fewer lateralroots of first and second order;(c)longer roots;(d)higher specificroot length;(e)a smaller root diameter. The morphology of theroot systems of nitrate-fed plants changed in the presence ofelevated carbon dioxide concentrations, resembling, more closely,that of ammonium-fed plants. Total leaf area was higher in ammonium-than in nitrate-fed plants. Nitrate-fed plants had greater totalleaf area in the presence of high carbon dioxide than in normalCO₂, due to an increase in epidermal cell size that led to developmentof larger leaflets with lower stomatal frequency. The observedchanges in the morphology of roots and shoots agreed with theresults observed for total biomass production. Nitrate-fed plantsincreased their biomass production by 100% in the presence ofelevated CO₂compared to 15% in ammonium-fed plants, indicatingthat the response of carob to high CO₂concentrations is verydependent on the nitrogen source. Under elevated CO₂, nitrate-grownplants had a larger content of sucrose in both roots and shoots,while no significant difference was observed in the contentof sucrose in ammonium-grown plants, whether in ambient or enrichedcarbon dioxide. Hence, the differences in soluble carbohydratecontents can, at least partly, account for differences in rootand shoot morphology.Copyright 1997 Annals of Botany Company Ceratonia siliquaL.; carob; ammonium; carbohydrate; carbon dioxide; nitrate; morphology; sucrose     

Changes in the Activity of Antioxidant Enzymes in Wheat Leaves and Roots as a Function of Nitrogen Source and Supply

The activity of enzymes participating in the systems of antioxidant protection was assayed in the second leaf and roots of 21-day-old wheat seedlings (Triticum aestivum L.) grown in a medium with nitrate (NO^– ₃ treatment), ammonium (NH⁺ ₄ treatment), or without nitrogen added (N-deficiency treatment). The activities of superoxide dismutase (SOD), peroxidase, ascorbate peroxidase, glutathione reductase, and catalase in the leaves and roots of the NH⁺ ₄ plants was significantly higher than in the plants grown in the nitrate medium. The activity of SOD decreased and ascorbate peroxidase markedly increased in leaves, whereas the activity of ascorbate peroxidase increased in the roots of N-deficient plants, as compared to the plants grown in nitrate and ammonium. Low-temperature incubation (5°, 12 h) differentially affected the antioxidant activity of the studied plants. Whereas leaf enzyme activities did not change in the NH⁺ ₄ plants, the activities of SOD, peroxidase, ascorbate peroxidase, and catalase markedly increased in the NO^– ₃ plants. In leaves of the N-deficient plant, the activity of SOD decreased; however, the activity of other enzymes increased. In response to temperature decrease, catalase activity increased in the roots of NO^– ₃ and NH⁺ ₄-plants, whereas in the N-deficient plants, the activity of peroxidase increased. Thus, in wheat, both nitrogen form and nitrogen deficiency changed the time-course of antioxidant enzyme activities in response to low temperature.     

Interaction between Nitrogen Deficit of a Plant and Nitrogen Content in the Old Leaves

We examined changes in nitrogen content of the first leavesin relation to growth and nitrogen status of sunflower (Helianthusannuus L.) plants that were raised hydroponically at two irradiancelevels (high and low light, HL and LL) and at two nitrogen concentrations(high and low nitrogen, HN and LN). Initial increases in totaldry mass and total nitrogen of the whole plant were faster inHL-plants than in LL-plants irrespective of nitrogen supply,but in LN-plants the increase in total nitrogen was soon blunted.When plants grown under the same irradiance were compared, nitrogencontent of the first leaves (leaf N) decreased faster in LN-plantsthan in HN-plants, while for the plants grown at the same nitrogenconcentrations, it decreased faster in HL-plants than in LL-plants.Since these changes in leaf N were not explained solely by thechanges in plant dry mass or plant nitrogen, we introduced anindex, ‘nitrogen deficit (ND^*)’, to quantify nitrogendeficit of the whole plant. ND^* was expressed as ND^*(t)=[N_max–N(t)]xDM(t),where N_max and N(t) were nitrogen contents in the young, expandingleaves that had just unfolded to expand, at the initial stagewith sufficient nitrogen and at time t, respectively, and DM(t),plant dry mass at t. The decrease in leaf N was expressed asa liner function of ND^* irrespective of the growth conditions,which indicates validity of this index. Limitation of the useof ND^*, and mechanisms by which leaves sense nitrogen demandare also discussed. (Received June 17, 1996; Accepted August 30, 1996)     

The Influence of the Concentration of Gaseous Ammonia on its Uptake by the Leaves of Italian Ryegrass, with and without an Adequate Supply of Nitrogen to the Roots

Whitehead, D. C. and Lockyer, D. R. 1986. The influence of theconcentration of gaseous ammonia on its uptake by the leavesof Italian ryegrass, with and without an adequate supply ofnitrogen to the roots.—J. exp. Bot. 38: 818–827. Plants of Italian ryegrass (Lolium multiflorum Lam.) were grownin pots of soil with two rates of ¹⁵N-labclled nitrate, oneproviding adequate, and the other less than adequate, N formaximum growth. After 25 d in a controlled environment cabinet,the plants were transferred to chambers and exposed for 33 dto NH₃in the air at one of nine concentrations ranging from14 to 709 µg NH₃ m^–3. Increasing the concentrationof NH₃ in the air increased the dry weight of the shoots ofplants grown at the lower but not the higher rate of nitrate.The content of total N in the plant shoots (% dry weight) waslinearly related to NH₃ concentration; at 709 µg NH₃ andin both sets of plants it was more than double the content at14 µg NH₃ m^–3. Calculations, based on ¹⁵N enrichment,indicated that the amount of N taken up from the NH₃ per unitleaf area increased linearly with increasing concentration ofNH₃ in the air uptake (µg dm^–2 h^–1) = 0.1009xat the lower rate of nitrate and 0-0829x at the higher rateof nitrate, where x is the concentration of NH₃ in the air expressedas µg NH₃m^–3. The proportion of the total plant N that was derived from theNH₃ ranged from 4?0% at a concentration of 14 µg NH₃ m^–3with the higher rate of nitrate addition to 77?5% at a concentrationof 709 µg m^–3 with the lower rate of nitrate addition.The proportions of the total N in the water-insoluble proteinof the leaf tissue that were derived from nitrate and gaseousNH₃ were similar to the proportions in the whole leaf material. Key words: Ammonia, nitrogen, leaf sorption, Lolium multiflorum     

Ruminococcus flavefaciens Cell Coat and Adhesion to Cotton Cellulose and to Cell Walls in Leaves of Perennial Ryegrass (Lolium perenne)

Ruminococcus flavefaciens was shown to possess a prominent glycoprotein coat, which contained rhamnose, glucose, and galactose as its principal carbohydrates. Periodate-reactive carbohydrate occurred as a surface layer of the coat. The ruminococci adhered strongly by means of this coat to cotton cellulose and to cell walls in leaf sections of Lolium perenne L. (perennial ryegrass). The coat was diffuse at the point of contact so that the bacterial cell wall was in close contact with the substrate. Adhesion was influenced by the availability of damaged plant cell walls and by the cell wall type and occurred most rapidly to cell walls of the epidermis and sclerenchyma, followed by the phloem and mesophyll. Plaques of bacteria with filamentous coat extensions developed on all these tissues. The bacteria did not readily adhere to the walls of the bundle sheath cells or metaxylem or protoxylem vessels and did not adhere to the cuticle or chloroplasts. The epidermal and phloem cell walls were more rapidly digested than the walls of other cell types.     

叶施NO对NaCl胁迫下红砂幼苗叶片和根系中氮代谢酶及营养物质的影响

以当年生红砂(Reaumuria soongorica)幼苗为材料,采用盆栽实验,考察叶面喷施不同浓度(0、0.01、0.10、0.25、0.50、1.00 mmol·L^-1)NO供体硝普钠 (SNP) 对NaCl(300 mmol·L^-1)胁迫下红砂根、叶中可溶性蛋白、游离氨基酸和硝态氮含量,以及谷氨酰胺合成酶(GS)、谷氨酸合酶(GOGAT)、硝酸还原酶(NR)活性的影响,并采用主成分分析和隶属函数法筛选NO对NaCl胁迫缓解效应的氮代谢指标和最佳NO浓度,以探讨外源NO对NaCl 胁迫下红砂缓解效应的氮代谢响应机制。结果表明：(1)在300 mmol·L^-1 NaCl胁迫处理下,红砂幼苗根、叶中可溶性蛋白、硝态氮含量以及GS、GOGAT、NR活性均比对照显著下降。(2)外源NO能显著提高盐胁迫下红砂叶、根中GS、GOGAT、NR活性和硝态氮含量,增加根中可溶性蛋白和游离氨基酸含量。(3)NR和GOGAT活性可用于评价NO对NaCl胁迫下红砂幼苗的缓解作用,外源NO(SNP)对红砂幼苗在NaCl胁迫下的缓解效果强弱表现为0.25 mmol·L^-1> 0.50 mmol·L^-1> 0.10 mmol·L^-1> 1.00 mmol·L^-1> 0.01 mmol·L^-1。研究发现,300 mmol·L^-1 NaCl胁迫显著抑制了红砂幼苗氮代谢,外源NO(SNP)有助于提高盐胁迫下红砂NR活性,加快硝态氮转化为铵态氮,促进红砂叶片和根中GS/GOGAT对转化物的同化,从而增强红砂幼苗的耐盐性,并以0.25 mmol·L^-1SNP处理时缓解作用最佳;NR和GOGAT活性可作为NO缓解盐胁迫的评价指标。     

Ontogenetic Changes of Photosynthetic and Dark Respiration Rates in Relation to Nitrogen Content in Individual Leaves of Field Crops

Ontogenetic changes of rates of photon-saturated photosynthesis (P _sat) and dark respiration (R _D) of individual leaves were examined in relation to nitrogen content (Nc) in rice, winter wheat, maize, soybean, field bean, tomato, potato, and beet. P _sat was positively correlated with Nc as follows: P _sat = CfNc + P _sat0, where Cf and P _sat0 are coefficients. The value of Cf was high in maize, medium in rice and soybean, and low in field bean, potato, tomato, and beet, of which difference was not explained by ribulose-1,5-bisphoshate carboxylase/oxygenase (RuBPCO) content. R _D was explained by P _sat and/or Nc, however, two models must be applied according to plant species. R _D related linearly with P _sat and Nc in maize, field bean, and potato as follows: R _D = a P _sat + b, or R _D = aNc + b, where a, a, b and b are coefficients. In other species, the R _D/P _sat ratio increased exponentially with the decrease of Nc as follows: R _D/P _sat = a exp(b Nc), where a and b are coefficients. Therefore, R _D in these crops was expressed as follows: In(R _D) = ln(a P _sat) + b Nc, indicating that R _D in these crops was regulated by both P _sat and Nc.     

Changes in Amino Acid Content of Excised Leaves During Incubation. III. Role of Sugar in the Accumulation of Proline in Wilted Leaves

A previously reported accumulation of proline in wilted turnip leaves has been observed in 6 additional species representing 5 different families. The results of experiments on the conditions affecting the behavior of proline in wilted leaves were interpreted to mean that the supply and metabolism of available carbohydrate was essential for proline accumulation.     

冷害过程中黄瓜叶片SOD、CAT和POD活性的变化

实验选用3个耐冷力不同的黄瓜品种研究其叶片超氧化物歧化酶（SOD）、过氧化氢酶（CAT）和过氧化物酶（POD）等3种抗氧化酶活性在冷害过程中的变化。结果表明：低温胁迫期间的CAT和POD活性与黄瓜叶片的耐冷力表现一致,SOD活性则与其耐冷力表现相反。低温胁迫后,3个品种的所有3种抗氧化酶活性均降低,叶片表现出明显的冷害症状,但耐冷力较高的津优10号仍然具有相对较高的CAT活性。恢复期的SOD活性无显著性变化;耐冷力最弱的津研4号和耐冷力中等的津绿3号的CAT活性上升而津优10号的CAT活性降低;3个品种的POD活性都增高,但津研4号的上升幅度明显高于其它2个品种,可能与POD能催化活性氧（ROS）产生有关。