Polyamines in embryogenic cultures of Norway spruce (Picea abies) and red spruce (Picea rubens)

Embryogenic cultures of red spruce (Picea rubens Sarg.) and Norway spruce (Picea abies (L.) Karst.) were initiated from dissected mature zygotic embryos. The tissues were grown on either proliferation medium or maturation medium. On proliferation medium, the embryogenic tissue continued to produce early stage somatic embryos (organized meristems attached to elongated, suspensor-like cells), whereas on maturation medium fully mature embryos developed from the embryonic tissue. Analysis of polyamines in tissues grown on these two media showed that: (1) both putrescine and spermidine concentrations were always higher in cultures grown on proliferation medium than in cultures grown on maturation medium; (2) in both species, spermidine concentrations declined with time in the tissues grown on maturation medium; and (3) spermine was present in only minute quantities and showed only a small change with time. The presence of difluoromethylornithine in the culture medium had little effect on polyamine concentration, whereas the presence of difluoromethylarginine caused a decrease in putrescine concentrations in both red spruce and Norway spruce tissues grown on proliferation medium or maturation medium.     

蓝莓离体繁育新梢形态与抗氧化酶对营养元素的应答

为了研究营养元素硝酸铵、硝酸钾、葡萄糖酸钙对蓝莓离体繁育的影响,以蓝莓‘夏普蓝’继代增殖苗为试材,就添加了不同浓度的硝酸铵、硝酸钾、葡萄糖酸钙的改良培养基对蓝莓离体增殖的新梢形态及体内超氧化物歧化酶(Superoxide Dismutase,SOD)、过氧化物酶(Peroxidase,POD)、过氧化氢酶(catalase,CAT)活性的影响情况进行了试验研究。试验结果表明:当培养基中硝酸铵的浓度为600 mg·L~(-1)、硝酸钾的浓度为400 mg·L~(-1)、葡萄糖酸钙的浓度为600 mg·L~(-1)时,新梢植株发育良好,植株长势健壮,颜色正常;发育正常的新梢其SOD活性间不存在明显差异,其POD活性间不存在明显差异,其CAT活性间也不存在明显差异;而且其SOD、POD、CAT活性均明显高于发育不正常的新梢。分析结果表明:矿质营养元素能调节蓝莓不定芽抗氧化酶活性;而稳定、平衡的抗氧化酶活性又能促进不定芽的发育。     

转录因子CBF基因转化烟草抗寒性指标的检测

为了解棉花转录因子CBF基因转化烟草的抗寒性，将苗龄21d的转基因及其野生型T2代烟苗进行0、-1、-2、-3、-4℃低温处理4h，分别进行各处理材料的电解质渗透率、丙二醛含量和可溶性糖含量的检测。结果表明转基因烟草的电导率和丙二醛含量均低于非转基因烟草，而转基因烟草的可溶性糖含量高于非转基因烟草。证实转CBF基因可以提高烟株的抗寒性。     

大量元素组成对孝顺竹苗组培快繁的影响

为探索大量元素对竹子组培快繁的影响,以孝顺竹无菌苗为材料,采用L16(45)的正交试验设计,研究不同大量元素组成对孝顺竹组培苗扩繁效率的影响。结果表明,适宜孝顺竹增殖培养的大量元素组合为:1 650 mg.L-1NH4NO3+475 mg.L-1KNO3+220 mg.L-1CaCl2.2H2O+370 mg.L-1MgSO4.7H2O+85 mg.L-1KH2PO4;适宜孝顺竹生根培养的大量元素组合为:1 900 mg.L-1KNO3+220 mg.L-1CaCl2.2H2O+370 mg.L-1MgSO4.7H2O+85 mg.L-1KH2PO4。就不同成分而言,NH4NO3对孝顺竹继代增殖有促进作用,但抑制苗木的高生长。KH2PO4对苗木的增殖有抑制作用,KNO3对苗木的高生长有一定的抑制作用。     

影响苹果砧木M9组培苗玻璃化的因素与改善措施

以苹果砧木M9为材料,研究了琼脂、激素、NH4+与NO3-离子浓度、架温等对组培苗玻璃化的影响,结果表明:优化配方MS(其中NH4NO30.8g/L,KNO32.28g/L)+BA 0.6mg/L+IBA 0.3mg/L+琼脂8g/L,不仅使M9组培苗的玻璃化程度明显下降,同时还具有很好的分化系数,为M9继代培养的主要配方。     

Kinetics of nitrogen uptake by Populus tremuloides in relation to atmospheric CO(2) and soil nitrogen availability

Sustained increases in plant production in response to elevated atmospheric carbon dioxide (CO(2)) concentration may be constrained by the availability of soil nitrogen (N). However, it is possible that plants will respond to N limitation at elevated CO(2) concentration by increasing the specific N uptake capacity of their roots. To explore this possibility, we examined the kinetics of (15)NH(4) (+) and (15)NO(3) (-) uptake by excised roots of Populus tremuloides Michx. grown in ambient and twice-ambient CO(2) concentrations, and in soils of low- and high-N availability. Elevated CO(2) concentration had no effect on either NH(4) (+) or NO(3) (-) uptake, whereas high-N availability decreased the capacity of roots to take up both NH(4) (+) and NO(3) (-). The maximal rate of NH(4) (+) uptake decreased from 12 to 8 &mgr;mol g(-1) h(-1), and K(m) increased from 49 to 162 &mgr;mol l(-1), from low to high soil N availability.Because NO(3) (-) uptake exhibited mixedkinetics over the concentration range we used (10-500 &mgr;mol l( -1)), it was not possible to calculate V(max) and K(m). Instead, we used an uptake rate of 100 &mgr;mol g(-1) h(-1) as our metric of NO(3) (-) uptake capacity, which averaged 0.45 and 0.23 &mgr;mol g(-1) h(-1) at low- and high-N availability, respectively. The proximal mechanisms for decreased N uptake capacity at high-N availability appeared to be an increase in fine-root carbohydrate status and a decrease in fine-root N concentration. Both NH(4) (+) and NO(3) (-) uptake were inversely related to fine-root N concentration, and positively related to fine-root total nonstructural carbohydrate concentration. We conclude that soil N availability, through its effects on fine-root N and carbohydrate status, has a much greater influence on the specific uptake capacity of P. tremuloides fine roots than elevated atmospheric CO(2). In elevated atmospheric CO(2), changes in N acquisition by P. tremuloides appeared to be driven by changes in root architecture and biomass, rather than by changes in the amount or activity of N-uptake enzymes.     

模拟氮沉降对长白山兴安落叶松林土壤有机碳库的短期影响

以净月潭国家森林公园兴安落叶松林为研究对象,以NH4NO3为原料模拟4个强度的氮沉降,分析土壤总有机碳(TOC)、易氧化有机碳(ROC)、溶解性有机碳(DOC)和微生物量碳(MBC)的动态变化。研究结果表明:低氮沉降量(L,50 kg N yr^-1 ha^-1)提高了TOC、ROC、DOC和MBC浓度,但除MBC外均未达到显著性水平;中氮沉降量(M,100 kg N yr^-1 ha^-1)提高了TOC和DOC浓度,降低了ROC和MBC浓度;高氮沉降量(H,150 kg N yr^-1 ha^-1)提高了ROC和MBC浓度,降低了TOC和DOC浓度。     

糖和氮对白榆组织培养新梢生根的影响

研究糖和无机氮源对白榆组培新梢不定根形成的影响,结果表明,含有高浓度蔗糖的培养基比低浓度蔗糖的培养基新梢生根率高.新梢对糖的这种反应与糖代谢和物理渗透都有关,用甘露作为渗透代替剂在低浓度蔗糖存在下无作用,当蔗糖浓度达到一定程度时(86.65 mmol·L-1)能影响新梢的生根率.在培养基中分别加入NO-3或NH+4作为唯一氮源,或是在MS培养基中加入NO-3/NH+4比率为标准的混合氮源,在测试范围(0 mmol·L-1～120 mmol·L-1)内均降低新梢的生根率,三者对生根的抑制作用依次为NH+4>NO-3+NH+4-N>NO-3-N.NO-3/NH+4比率与生根之间呈现直线正相关.糖/氮比值高有利于生根.插穗中碳、氮的绝对量及碳/氮比率可作为白榆新梢生根的指标.     

Histology of magnesium-deficient Norway spruce needles influenced by nitrogen source

Effects of magnesium deficiency and variation in nitrate to ammonium ratio on needle histology and chlorophyll concentration were investigated in current-year and one-year-old needles of clonal Norway spruce trees (Picea abies (L.) Karst.). Six-year-old trees were grown for one year in sand culture with circulating nutrient solutions containing a sufficient (0.2 mM) or a limiting (0.04 mM) concentration of Mg. The nitrogen concentration was not varied (5 mM), but the NO(3) (-)/NH(4) (+)-ratio was adjusted to 0.76 in Mg-sufficient and to 1.86, 0.76 or 0.035 in Mg-limited plants. Visible symptoms of Mg deficiency occurred only in current-year needles, indicating adequate Mg nutrition before the experiment. Under conditions of Mg limitation, chlorophyll and Mg concentrations were lowest in needles of trees supplied with NH(4) (+) as the major nitrogen source and highest in needles of trees supplied with NO(3) (-) as the major nitrogen source. In current-year and one-year-old needles, starch accumulation induced by Mg deficiency was increased when NH(4) (+) was the major nitrogen source. The accumulation of tannin spherules in current-year needles, which occurred in response to Mg deficiency, also increased with decreasing NO(3) (-)/NH(4) (+)-ratios. Deficient Mg supply caused premature aging in tissues of the vascular bundle, as indicated by modifications of the cambium and increased amounts of collapsed sieve cells. The number of collapsed sieve cells was slightly lower in needles grown in a NH(4) (+)-dominated nutrient regime than in needles grown in a NO(3) (-)-dominated nutrient regime. We conclude that was not directly toxic to Norway spruce trees at the applied concentrations. However, effects of Mg deficiency were considerably greater in an NH(4) (+)-dominated nutrient regime than in a NO(3) (-)-dominated nutrient regime.     

Root system architecture and receptivity to mycorrhizal infection in seedlings of Cedrus atlantica as affected by nitrogen source and concentration

Effects of nitrogen (N) source and concentration on root system architecture and receptivity to mycorrhizal infection were studied in seedlings of Atlas cedar (Cedrus atlantica Manetti) grown in root observation boxes in a controlled-environment chamber. Nitrogen was supplied in a solution containing either NO3-; or NH4+ at a concentration of either 0.25 or 5.0 mM. Root extension was recorded twice weekly by tracing the roots growing in contact with the transparent face of the root observation box. Among treatments, lateral root production and branching density were greatest with 5.0 mM NO3-. Inoculation with mycelium of Tricholoma cedrorum Malencon was carried out 3 months after the start of the N treatments. The highest percentage of mycorrhizal roots, and the greatest amounts of living mycelium (estimated by the ergosterol assay) were observed in the NO3- treatments. Differences in root branching density among the N treatments were insufficient to explain the observed differences among treatments in the extent of mycorrhizal infection of seedlings.     

白刺花胚性愈伤组织诱导及体细胞胚发生

【目的】探讨不同植物生长调节剂对白刺花胚性愈伤组织诱导的作用,以及培养基中氮源和无机盐浓度对白刺花体细胞胚发生和植株再生的影响,以期建立白刺花体细胞胚发生、发育及调控技术体系,为白刺花种苗快速繁殖体系建立及遗传转化研究提供参考。【方法】以白刺花叶片为外植体,研究生长调节剂2,4-D(1.0、2.0、3.0、4.0 mg ·L -1 )、NAA(0、0.5、0.8、1.0 mg ·L -1 )、6-BA(0.2、0.5、1.0、2.0 mg ·L -1 )和TDZ(0、0.2、0.5、1.0 mg ·L -1 )组合对胚性愈伤组织诱导,及NAA(0、0.2、0.5 mg ·L -1 )、6-BA(0、0.5、1.0 mg ·L -1 )和TDZ(0、0.2、0.5 mg ·L -1 )组合对体细胞胚发生的调控作用,筛选最优生长调节剂组合;并研究培养基中KNO 3和NH 4NO 3比例对体细胞胚发生的作用,及MS培养基中无机盐浓度(1/5MS 、1/4MS、1/3MS、1/2MS)对体细胞胚萌发的影响,筛选最佳的体细胞胚发育及成熟萌发条件。【结果】白刺花叶片外植体胚性愈伤组织诱导适宜培养基为MS + 2,4-D 3.0 mg ·L -1 + NAA 0.5 mg ·L -1 + 6-BA 0.2 mg ·L -1 + TDZ 1.0 mg ·L -1 +蔗糖40 g ·L -1 +琼脂7.0 g ·L -1 ,诱导率为42.0%。采用MS基本培养基时,最佳的体细胞胚发生培养基为MS + NAA 0.5 mg ·L -1 + 6-BA 1.0 mg ·L -1 + TDZ 0.5 mg ·L -1 +蔗糖40 g ·L -1 +谷氨酰胺100 mg ·L -1 +琼脂7.0 g ·L -1 ,体细胞胚发生率为78.46%,总胚数为对照的3.6倍;MS培养基中,KNO 3浓度提高1倍、NH 4NO 3降至1/2时,体细胞胚发生率可提高至91.33%,总胚数为采用MS基本培养基时的1.4倍;1/3MS培养基有利于体细胞胚的萌发,萌发率为82.75%,幼苗长势良好,单株平均鲜质量为76 mg,幼苗驯化移栽1个月后成活率达90%以上。【结论】白刺花叶片接种于添加2,4-D、NAA、6-BA和TDZ不同组合的诱导培养基上,可脱分化形成愈伤组织或胚性愈伤组织,2,4-D浓度对愈伤组织形态和质地有较大影响。TDZ有利于体细胞胚的形成,适宜浓度的生长素与细胞分裂素组合及硝态氮和铵态氮的比例对体细胞胚的形成和发育具有调控作用,降低MS无机盐浓度可提高体细胞胚萌发率,本试验体系的再生植株移栽成活率达90%以上。     

Effects of aluminum on organic acid metabolism and secretion by red spruce cell suspension cultures and the reversal of Al effects on growth and polyamine metabolism by exogenous organic acids

In the absence of added Al, the concentration of succinate in cultured red spruce (Picea rubens Sarg.) cells was 15-20 times higher (> 600 nmol g-1FW) than that of citrate or oxalate and 4-6 times higher than that of malate. Addition of AlCl3 (effective monomeric Al concentrations of 0.23 and 0.48 mM) to 3-day-old suspension cultures significantly increased cellular succinate concentrations with a concomitant decrease in cellular oxalate concentrations. However, in the medium of Al-treated cell cultures, both succinate and oxalate concentrations were significantly higher than in the medium of cell cultures without added Al, and oxalate concentrations were several times higher than succinate concentrations. Aluminum did not significantly affect the cellular concentrations of malate, ascorbate and citrate, and none of these organic acids was present in detectable quantities in the medium. Exogenous succinate alone or with Al had no effect on cellular free polyamine concentrations or cell mass. Aluminum caused a significant increase in cellular putrescine concentrations. Addition of malate had a positive effect on growth and completely reversed the effects of Al on cell physiology. In contrast, the addition of oxalate and citrate only partly reversed the effects of Al.     

氮、磷、钾对若干种木本植物离体培养繁殖的影响

本文通过培养基中三个主要营养元素氮、磷、钾对若干种木本植物(如杉木、北美红杉等)离体培养繁殖影响的研究,提出了较适合于这些木本植物离体培养的改良MS基本培养基(其中大量元素氮、磷、钾水平修改为:NH_4NO_3 850mg/L,KNO_3 2000mg/L,KH_2LO_4 100mg/L)。在此基础上,讨论了工厂化组培繁殖木本植物特别是一些常规繁殖困难的林木树种的可能性,以及提高组培生产率和降低生产成本的有效措施。     

Influence of elevated CO2 and mycorrhizae on nitrogen acquisition: contrasting responses in Pinus taeda and Liquidambar styraciflua

An understanding of root system capacity to acquire nitrogen (N) is critical in assessing the long-term growth impact of rising atmospheric CO2 concentration ([CO2]) on trees and forest ecosystems. We examined the effects of mycorrhizal inoculation and elevated [CO2] on root ammonium (NH4+) and nitrate (NO3-) uptake capacity in sweetgum (Liquidambar styraciflua L.) and loblolly pine (Pinus taeda L.). Mycorrhizal treatments included inoculation of seedlings with the arbuscular mycorrhizal (AM) fungus Glomus intraradices Schenck & Smith in sweetgum and the ectomycorrhizal (EM) fungus Laccaria bicolor (Maire) Orton in loblolly pine. These plants were then equally divided between ambient and elevated [CO2] treatments. After 6 months of treatment, root systems of both species exhibited a greater uptake capacity for NH4+ than for NO3-. In both species, mycorrhizal inoculation significantly increased uptake capacity for NO3-, but not for NH4+. In sweetgum, the mycorrhizal effect on NO3- and NH4+ uptake capacity depended on growth [C02]. Similarly, in loblolly pine, the mycorrhizal effect on NO3- uptake capacity depended on growth [CO2], but the effect on NH4+ uptake capacity did not. Mycorrhizal inoculation significantly enhanced root nitrate reductase activity (NRA) in both species, but elevated [CO2] increased root NRA only in sweetgum. Leaf NRA in sweetgum did not change significantly with mycorrhizal inoculation, but increased in response to [CO2]. Leaf NRA in loblolly pine was unaffected by either treatment. The results indicate that the mycorrhizal effect on specific root N uptake in these species depends on both the form of inorganic N and the mycorrhizal type. However, our data show that in addressing N status of plants under high [CO2], reliable prediction is possible only when information about other root system adjustments (e.g., biomass allocation to fine roots) is simultaneously considered.     

KNO_3对猕猴桃组培苗形态及生理特性的影响

为研究MS培养基不同浓度的KNO_3对猕猴桃离体繁育的影响,以‘红阳’猕猴桃组培幼苗为试验材料,就培养基中添加不同浓度的KNO_3改良MS培养基对猕猴桃增殖的新梢形态,抗氧化酶活性、苯丙氨酸解氨酶活性及内源激素含量变化的影响进行了试验研究。结果表明:当KNO_3质量浓度从1 140 mg/L增加至2 660 mg/L时,猕猴桃幼苗中的抗氧化酶(SOD、POD和CAT)活性、PAL活性、内源激素(IAA、GA_3和CTK)含量、IAA/ABA、GA_3/ABA和CTK/ABA均呈先增大后减小的变化趋势;ABA含量则随KNO_3质量浓度的增大呈先减小后增大的趋势。当KNO_3质量浓度为1 900 mg/L时,体内氧化酶、苯丙氨酸解氨酶活性最高,内源激素IAA、GA_3、CTK含量较高,ABA含量较低,植株发育正常。     

Effects of nitrogen source and defoliation on growth and biological dinitrogen fixation of Gliricidia sepium seedlings

Effects of four N sources and two defoliation treatments on growth and nitrogenase activity of Gliricidia sepium (Jacq.) Walp seedlings were studied in a greenhouse. All nutrients were supplied in irrigation water to the sterile growing medium. The N sources were: (1) 100 mg l(-1) of N supplied as NO(3) (-) (high-NO(3) (-)), (2) 50 mg l(-1) of N supplied as NO(3) (-) and inoculation with Rhizobium spp. medium-NO(3) (-)), (3)100 mg l(-1) of N supplied as NH(4)NO(3), and (4) inoculation with Rhizobium spp without mineral N (N(2)). At 35 weeks after sowing, mean total biomass was 130.5, 50.5, 22.9 and 17.4 g seedling(-1) in the NH(4)NO(3), N(2), medium-NO(3) (-) and high-NO(3) (-) treatments, respectively. The root/shoot ratio was high in all of the N treatments (1.73-2.77) because the seedlings had big taproots. The medium-NO(3) (-) treatment completely inhibited nodulation, whereas seedlings in the N(2) treatment were profusely nodulated. At 32 weeks after sowing, groups of seedlings in the N(2) and high-NO(3) (-) treatments were subjected to 50 or 100% defoliation. Closed-chamber acetylene reduction assays of intact root systems were conducted to compare nitrogenase activity at 7, 14 and 28 days after defoliation (DAD). At 7 and 14 DAD, nitrogenase activity of completely and partially defoliated seedlings was about 10 and 60%, respectively, of that of undefoliated controls. At 28 DAD, nitrogenase activity of completely defoliated seedlings was twice the predefoliation value, whereas nitrogenase activity of partially defoliated seedlings was only 87% of the predefoliation value. Recovery of nitrogenase activity was strongly correlated with foliage regrowth in the completely defoliated seedlings, but not in the partially defoliated seedlings. Abundant belowground C and N reserves in the large taproot probably contributed to the rapid recovery from defoliation. Accumulation of belowground biomass may also improve defoliation tolerance of mature trees.     

Uptake and distribution of calcium and phosphorus in beech (Fagus sylvatica) as influenced by aluminum and nitrogen

We studied the effects of excess nitrogen added as nitrate (NO(3) (-)) or ammonium (NH(4) (+)), or both, on mineral nutrition and growth of beech (Fagus sylvatica L.) plants grown at pH 4.2 in Al-free nutrient solution or in solutions containing 0.1 or 1.0 mM AlCl(3). A high external concentration of NH(4) (+) increased the concentration of nitrogen in roots, stems and leaves. The root/shoot dry weight ratio was less in plants grown in the presence of NH(4) (+) than in plants grown in the presence of NO(3) (-). The concentration of phosphorus in the roots was increased and the concentration of potassium in all parts of the plant was decreased by NH(4) (+). A high external concentration of NO(3) (-) caused a decrease in phosphorus concentrations of the root, stem and leaf. Uptake of (45)Ca(2+) by roots was reduced in the presence of high concentrations of NH(4) (+) or NO(3) (-), and a combination of high concentrations of nitrogen and aluminum further reduced the uptake of (45)Ca(2+). Uptake of phosphate ((32)P) and concentrations of phosphorus in root and shoot were increased when plants were grown in the presence of 0.1 mM Al. Exposure to 1.0 mM Al, however, reduced the concentration of phosphorus in roots and shoots and the reduction was greater when plants were grown in the presence of a high external NO(3) (-) concentration. Aluminum binds to roots, and plants grown in the presence of 1.0 mM Al had a slightly higher concentration of aluminum in roots than plants grown in the presence of 0.1 mM Al, whereas the concentration of Al in the shoot was increased 2 to 3 times in plants exposed to 1.0 mm Al. Furthermore, the effects of 1.0 mM Al on uptake of other macronutrients were quite different from the effects of 0.1 mM Al. We conclude that 0.1 mM Al facilitates uptake and transport of phosphorus in beech and that between 0.1 and 1.0 mM Al there is a dramatic change in the effects of Al on uptake and transport of divalent cations and phosphorus.     

Effects of foliar potassium concentration on morphology, ultrastructure and polyamine concentrations of Scots pine needles

We examined the effects of three foliar potassium concentrations (high, intermediate and low) on the morphology, ultrastructure and polyamine concentrations of current-year and 1- and 2-year-old needles of 30-year-old Scots pine (Pinus sylvestris L.) trees. Foliar K concentration had only a slight effect on needle morphology. The sclerenchyma cell walls were thinner, the xylem area was larger, and the resin ducts were smaller in needles with a low K concentration than in needles with a high or intermediate K concentration. In addition, the bundle sheath cells were collapsed in needles having a low K concentration. The secondary growth of phloem tissue and the mesophyll area were greater in needles with a high or intermediate K concentration than in needles with a low K concentration, possibly indicating greater production of photoassimilates in these trees. At the ultrastructural level, mesophyll cells with enlarged central vacuoles and small vacuoles containing electron-dense material were common in needles having a low K concentration. Enlargement of the central vacuole coincided with an exponential increase in putrescine concentration in needles with a low K concentration, suggesting that the central vacuole may function as a storage site for putrescine.     

Regulation of organic and inorganic nitrogen uptake in Scots pine (Pinus sylvestris) seedlings

Plants possess regulatory mechanisms that enhance nitrogen (N) uptake under conditions of spatial and temporal variation in N availability. Study of regulatory mechanisms has focused almost exclusively on the uptake of inorganic N sources (i.e., ammonium (NH4+), nitrate (NO3-). Several lines of evidence, however, suggest that amino acids may constitute a potential source of N for a number of plant species, including conifers. In the present study, we investigated the uptake of amino acids and inorganic N in Scots pine (Pinus sylvestris L.) seedlings grown at different N concentrations. We compared the uptake rate of the individual N sources using U-[13C2], [15N]-glycine, U-[13C6], [15N4]-arginine, 15NH4, or 15NO3, and tested the short-term effect of N supply on the uptake rate of glycine, arginine and in field-grown Scots pine seedlings. Our data indicate that Scots pine seedlings can absorb substantial amounts of N in the form of intact arginine and glycine molecules. The data also suggest that Scots pine seedlings down-regulate their uptake of NH4+-N and arginine-N, but not of glycine-N in response to increased endogenous N concentrations.     

Growth response of cottonwood roots to varied NH4:NO3 ratios in enriched patches

Maximization of short-rotation forest plantation yield requires frequent applications of nutrients, especially nitrogen (N). Whole-plant growth is known to be sensitive to the proportion of ammonium to nitrate (NH4:NO3). However, the extent to which N form affects root growth, branching and morphology is poorly understood, and these variables may have substantial impacts on plant nutrient and water acquisition. We used rooted cuttings of cottonwood (Populus deltoides Bartr. ex Marsh.) to investigate the effect of various NH4:NO3 ratios on root growth in N-enriched patches. A sand culture study with split-root systems was carried out in which 1-3% of the total root system of each cutting was supplied with 2 mM N at NH4:NO3 ratios of 0:100, 20:80, 40:60, 60:40, 80:20 and 100:0 (molar basis), with the rest of the plant supplied with 0 mM N, resulting in the whole plant becoming N deficient. During the experiment, whole-plant growth was unaffected by the treatments. Of the NH4:NO3 ratios tested, greatest total root length, specific root length, and root N concentration of roots in enriched patches occurred in the 20:80 NH4:NO3 treatment. The largest response of roots in enriched patches was third- and fourth-order root production. We conclude that N form has a profound effect on root development and morphology in enriched patches.