Root morphology in response to nitrogen supply in mid-season indica rice cultivars released in different decades

正Dear Editor,Roots,as a major organ of plants,are involved in nutrient and water acquisition,and might play a vital role in yield increase and efficient N absorption with genetic improvement.Because of the great differences in growth period and pattern between the old and new rice cultivars,it is difficult to clarify how genetic improvements contribute to root growth in rice.For example,for a solution culture system,Wu et al.suggested that total root length increased with increasing year of release for maize hybrids,while shoot dry weight,     

Root response to CO2 enrichment and nitrogen supply in loblolly pine

This paper examines how elevated CO₂ and nitrogen (N) supply affect plant characteristics of loblolly pine (Pinus taeda L.) with an emphasis on root morphology. Seedlings were grown in greenhouses from seeds during one growing season at two atmospheric CO₂ concentrations (375 and 710 μL L^-1) and two N levels (High and Low). Root morphological characteristics were determined using a scanner and an image analysis program on a Macintosh computer. In the high N treatment, elevated CO₂ increased total plant dry weight by 80% and did not modify root to shoot (R/S) dry weight ratio, and leaf and plant N concentration at the end of the growing season. In the low N treatment, elevated CO₂ increased total dry weight by 60%. Plant and leaf N concentration declined and R/S ratio tended to increase. Nitrogen uptake rate on both a root length and a root dry weight basis was greater at elevated CO₂ in the high N treatment and lower in the low N treatment. We argue that N stress resulting from short exposures to nutrients might help explain the lower N concentrations observed at high CO₂ in other experiments; Nitrogen and CO₂ levels modified root morphology. High N increased the number of secondary lateral roots per length of first order lateral root and high CO₂ increased the length of secondary lateral roots per length of first order lateral root. Number and length of first order lateral roots were not modified by either treatment. Specific root length of main axis, and to a lower degree, of first order laterals, declined at high CO₂, especially at high N. Basal stem diameter and first order root diameters increased at high CO₂, especially at high N. Elevated CO₂ increased the proportion of upper lateral roots within the root system.     

Effects of nitrogen deficiency on photosynthetic traits of maize hybrids released in different years

BACKGROUND AND AIMS: New maize (Zea mays) hybrids outperformed old ones even at reduced N rates. Understanding the mechanisms of the differences in performance between newer and older hybrids under N deficiency could provide avenues for breeding maize cultivars with large yield under N deficiency, and reduce environmental pollution caused by N fertilizers. METHODS: N deficiency effects on grain weight, plant weight, harvest index, leaf area and photosynthetic traits were studied in the field for six maize hybrids released during the past 50 years to compare their tolerance and to explore their physiological mechanisms. KEY RESULTS: N deficiency decreased grain yield and plant weight in all hybrids, especially in the older hybrids. However, there was no significant difference in harvest index, rate of light-saturated photosynthesis (Psat) 20 d before flowering, leaf area or plant weight at flowering between the N-deficient and control plants of all hybrids. Dry matter production after flowering of the N-deficient plants was significantly lower than that of the control plants in all hybrids, especially in the older hybrids, and was mostly due to differences in the rate of decrease in photosynthetic capacity during this stage. The lower Psat of the older hybrids was not due to stomatal limitation, as there was no significant difference in stomatal conductance (gs) and intercellular CO2 concentration (Ci) between the hybrids. N deficiency accelerated senescence, i.e. decreased chlorophyll and soluble protein contents, after anthesis more for the earlier released hybrids than for the later ones. N deficiency decreased phosphoenolpyruvate carboxylase (PEPCase) activity significantly more in older hybrids than newer hybrids, and affected the maximal efficiency of PSII photochemistry (Fv/Fm) only in the old hybrids and at the late stage. CONCLUSIONS: Compared with older (earlier released) hybrids, newer (later released) hybrids maintained greater plant and grain weight under N deficiency because their photosynthetic capacity decreased more slowly after anthesis, associated with smaller non-stomatal limitations due to maintenance of PEPCase activity, and chlorophyll and soluble protein content.     

钾元素不同供应水平下玉米叶片的生长与发育

采用沙培法,以玉米品种V1和V2为试验材料,定量分析缺钾对玉米生长和发育的影响.从胚芽鞘叶完全展开时,设置营养液中钾的浓度为3个梯度,分别为KH＝8 mmol·L-1;KM＝4 mmol·L-1;KO＝0 mmol·L-1.从胚芽鞘叶完全展开到吐丝期经常浇这3种营养液.用有效积温来计算玉米生长期间所需热量,把每日完好的叶面积作为玉米生长的衡量指标;每天记录每株玉米的叶片数,不管叶片的大小,作为衡量植株生长发育的方法.在每一个钾元素供应水平上,品种V1和V2的叶片数和自播种以来的受热时间呈直线相关.在KO水平上,V1和V2的发育速率分别是10%和15%,相对于KH水平来说是低的.在11片叶子期间,KO水平上的叶面积大约比KH水平上的低46%,KM水平上的叶面积大约比KH水平上的低25%;在玉米抽雄期,KO水平上的叶面积相对于KH来说减少37%,比KM水平上的少26%.这种差异从抽穗期开始一直保持到吐丝期.     

Multi-trait genomic prediction for nitrogen response indices in tropical maize hybrids

In maize breeding, genomic prediction may be an efficient tool for selecting single-crosses evaluated under abiotic stress conditions. In addition, a promising strategy is applying multiple-trait genomic prediction using selection indices (SIs), increasing genetics gains and reducing time per cycles. In this study, we aimed (i) to compare accuracy of single- and multi-trait genomic prediction (STGP; MTGP) in two maize datasets, (ii) to evaluate prediction of four selection indices that could contribute to the selection of tropical maize hybrids under contrasting nitrogen conditions, and (iii) to compare the use of linear (GBLUP) and nonlinear (RKHS/GK) kernels in STGP and MTGP analyses. For either single-trait GBLUP and RKHS analyses, the highest values obtained for accuracy were 0.40 and 0.41 using harmonic mean (HM), respectively. From multi-trait GBLUP and GK, using the combination of selection indices in MTGP seems to be suitable, increasing the accuracy. Adding grain yield and plant height in MTGP showed a slight improvement in accuracy compared to STGP. In general, there was a modest benefit of using single-trait RKHS and GK multi-trait, rather than GBLUP.     

Root growth and nitrogen uptake in sycamore (Acer pseudoplantanus L.) seedlings in relation to nitrogen supply

Acer pseudoplatanus L. trees were grown in sand culture for 2 years and, in 1988, supplied with either 1.0 mol N m^-3 (low N) or 6.0 mol N m^-3 (high N) to precondition their growth. In 1989, the same trees received either high or low nitrogen, producing four treatments; High N in 1988/High N in 1989; High N in 1988/Low N in 1989; Low N in 1988/Low N in 1989; and Low N in 1988/High N in 1989. Plant growth was affected by N supply in both years. In 1989 the Low N/High N treated trees had the same overall mass, leaf mass and stem girth as the High N/High N treatment. Early spring growth of foliage and roots was conditional on nitrogen supplied in the previous season. Later, the rapid increases in leaf, stem and root growth under high N was through root uptake. Internal partitioning of growth was affected, with the Low N/High N treatment producing more new leaves on axillary shoots, and more new white roots on existing structures, than the Low N/Low N treatment. Despite effects of the N preconditioning on the structure of both canopy and root system, nitrogen uptake was solely dependent on the current nitrogen supply.     

水氮处理下不同品种水稻根系生长分布特征

为明确不同栽培条件下水稻(Oryza sativa)根系生长分布特征, 通过不同水氮处理和不同品种的水稻桶栽试验, 采用内置根架法, 于拔节期和抽穗期取样, 获取根系总干重(TRW)、不定根数(ARN)以及各类根(不定根、细分枝根和粗分枝根)的形态指标(长度、表面积和体积), 并分析植株根系生长状况和根系分布特征。结果显示: (1)各试验条件下抽穗期各项根系指标较拔节期均呈增长趋势。同一时期, 各项根系指标在3个施氮水平间均差异显著, 且随施氮量的增加而增加。不同水分处理下, 两个时期的ARN在湿润灌溉(W2)与保持水层(W1)之间差异均不显著, 而其他指标上W2处理均显著最高; 干旱处理 (W3)下, 仅拔节期的TRW和粗分枝形态指标与W1处理接近, 而在其他指标上均显著最低。不同品种间, ‘扬稻6号’ (V3)的各项根系指标均最高, 而‘日本晴’ (V1)和‘武香粳14’ (V2)间差异不显著。(2)各试验条件下, 抽穗期较拔节期根系下扎生长比例增加, 多分布于表层(0-5 cm)土中; 减少氮素和水分供应可提高根系在5 cm以下土层中的分布比例, 且分枝根反应最为明显; 品种V1和V2的深扎根性较V3明显。结果表明, 合理施氮与控水可优化水稻不同类型根的生长与分布特征, 但需考虑不同品种之间的差异。     

Root growth responses to lead in young maize seedlings

This work was undertaken to follow the appearance and development of symptoms of lead toxicity in growing roots of seedlings. The effects of lead nitrate (10^-2–10⁵ M) were studied on the roots of maize (Zea mays) seedlings, cvs. Diamant and Sterling. The roots were grown on filter paper either on glass in trays or in large Petri dishes. The following characteristics of root growth were studied: seed germination, length of primary and seminal roots, number of seminal and lateral roots, length of branching zone, length of meristem and fully-elongated cells and the number of fully-elongated cells along the daily length increment. 10^-2 M lead nitrate exerted a clear toxic effect on root elongation just after radicle emergence; its influence on shoot growth was weak. However 10^-2 M Pb solution did not affect either radicle emergence itself or seminal root emergence, which can be explained by the impermeability of seed testa to lead salt. The inhibitory effect of 10^-3 M lead nitrate appeared a day later and was not as toxic: the growth of primary and seminal roots proceeded at lower rate due to a partial inhibition of cell division and cell elongation in them. 10^-3 M lead nitrate modified the root system morphology: it exerted no effect on the emergence of lateral roots and their number, but induced a more compact distribution of lateral roots along a shorter branching zone due to a reduced length of mature cells in the primary root. As a result of the more prominent inhibition of primary root growth, a shorter branching zone with more compactly located lateral roots occupied a position much closer to the root tip than in roots grown without the influence of lead.     

Root hair phenotypes influence nitrogen acquisition in maize

Background and AimsThe utility of root hairs for nitrogen (N) acquisition is poorly understood.MethodsWe explored the utility of root hairs for N acquisition in the functional–structural model SimRoot and with maize genotypes with variable root hair length (RHL) in greenhouse and field environments.Key ResultsSimulation results indicate that long, dense root hairs can improve N acquisition under varying N availability. In the greenhouse, ammonium availability had no effect on RHL and low nitrate availability increased RHL, while in the field low N reduced RHL. Longer RHL was associated with 216 % increase in biomass and 237 % increase in plant N content under low-N conditions in the greenhouse and a 250 % increase in biomass and 200 % increase in plant N content in the field compared with short-RHL phenotypes. In a low-N field environment, genotypes with long RHL had 267 % greater yield than those with short RHL. We speculate that long root hairs improve N capture by increased root surface area and expanded soil exploration beyond the N depletion zone surrounding the root surface.ConclusionsWe conclude that root hairs play an important role in N acquisition. We suggest that root hairs merit consideration as a breeding target for improved N acquisition in maize and other crops.     

Tradeoffs between growth and reproduction in response to temporal variation in food supply

Allocating resources to growth or to reproduction is a fundamental tradeoff in evolutionary life history theory. In environments with unpredictable food resources, natural selection is expected to favor increased allocation to reproduction. Although effects of selection are realized only across generations, short-term changes in food predictability might influence intra-generational tradeoffs in resource allocation. We assessed the ability of fathead minnows, Pimephales promelas, to adjust allocation to growth and reproduction in response to predictable, unpredictable, and switched feeding schedules. Fish in the switched treatments were changed from unpredictable to predictable feeding schedules just after reaching sexual maturity. Egg production did not differ significantly among treatments despite the fact that females on the unpredictable and switched feeding schedules grew more slowly than those on the predictable schedule. Switched males were heavier and had proportionally larger testes than males in predictable and unpredictable treatments. Increased allocation to reproduction or growth by fish on unpredictable and switched feeding schedules was associated with changes in gut length relative to body mass. Both sexes showed a remarkable degree of phenotypic plasticity in response to resource availability and sex differences in allocation patterns were consistent with adaptive responses in the context of the fathead mating system.     

Maize and pigweed response to nitrogen supply and form

As nitrogen management practices change to achieve economic and environmental goals, effects on weed-crop competition must be examined. Two greenhouse experiments investigated the influence of N amount and form on growth of maize and redroot pigweed (Amaranthus retroflexus L.). In Experiment 1, maize and pigweed were grown together in a replacement series (maize: pigweed ratios of 0:4, 1:3, 2:2, 3:1, 4:0) under three NH₄NO₃-N supplies (0, 110, and 220 mg N kg^-1 soil). Maize was planted into established pigweed and plants were harvested 24 days after maize germination. Pigweed responded more to supplemental N than maize and accumulated 2.5 times as much N in shoots at the high N supply. Competition effects were not significant. Maize and pigweed were grown separately in Experiment 2 and supplied 220 mg N kg^-1 as either Ca(NO₃)₂ or (NH₄)₂SO₄ plus a nitrification inhibitor (enhanced ammonium supply, EAS). In maize, EAS treatment did not affect shoot growth and reduced root growth 25% relative to the NO₃-N treatment. In pigweed, shoot and root growth were restricted 23 and 86% by EAS treatment, respectively. Total plant N accumulation under EAS treatment was higher in maize, less in pigweed. Under EAS treatment, pigweed leaves were crinkled and chlorotic; leaf disks extracted in 70% ethanol, pH 3, contained less malate and oxalate but more NH₄ ⁺ compared to the NO₃-N treatment. Maize leaf disk malate levels were generally higher compared to pigweed but were less due to EAS treatment. Ammonium level in maize leaf disks was unaffected by N form and EAS treatment increased oxalate levels. Final bulk soil pH was generally lower in pots where pigweed were grown and tended to be lower due to EAS. Leaf disk malate levels and soil pH were positively associated. Results indicate that pigweed is more likely to compete with maize when high levels of NO₃-N are provided. Enhancing the proportion of N supplied as NH₄ ⁺ should restrict the growth of NH₄ ⁺-sensitive pigweed.     

Genotypic variation between maize (Zea mays L.) single cross hybrids in response to drought stress

Effects of soil drought on growth and productivity of 16 single cross maize hybrids were investigated under field and greenhouse experiments. The Drought Susceptibility Index (DSI) was evaluated in a three year field experiment by the determination of grain loss in conditions of two soil moisture levels (drought and irrigated) and in a pot experiment by the effects of periodical soil drought on seedling dry matter. In the greenhouse experiment response to drought in maize genotypes was also evaluated by root to shoot dry mater ratio, transpiration productivity index, indexes of kernel germination and index of leaf injury by drought and heat temperature. The obtained values of DSI enabled the ranking of the tested genotypes with respect to their drought tolerance. The values of DSI obtained in the field experiment allow to divide the examined genotypes into three, and in the greenhouse experiment into two groups of drought susceptibility. The correlation coefficients between the DSI of maize hybrids in the field and the greenhouse experiments was high and statistically significant, being equal to 0.876. The ranking of hybrids drought tolerance, identified on the basis of field experiments was generally in agreement with the ranking established on the basis of the greenhouse experiment. In the greenhouse experiment statistically significant coefficients of correlation with DSI values in hybrids were obtained for the ratio of dry matter of overground parts to dry matter of roots, both for control and drought treatments, whereas in the estimation of the transpiration productivity coefficient and total dry matter the correlation coefficients were not statistically significant. In this study several laboratory tests were carried out for the drought tolerance of plants (kernel germination, leaf injury) on 4 drought resistant and 4 drought sensitive maize hybrids. Statistically significant correlation coefficients between DSI and the examined parameter of grain germination and leaf injury were obtained for the determination of promptness index (PI), seedling survival index (SS) and leaf injuries indexes (IDS, ITS) as a result of exposure to 14 days of soil drought, osmotic drought −0.9 MPa and exposure to high temperature 45 ° or 50 °C. The results of laboratory tests show that in maize the genetic variation in the degree of drought tolerance is better manifested under severe conditions of water deficit in the soil.     

Response of enzymes and storage proteins of maize endosperm to nitrogen supply

To examine the effects of N nutrition upon endosperm development, maize (Zea mays) kernels were grown in vitro with either 0, 3.6, 7.1, 14.3, or 35.7 millimolar N. Kernels were harvested at 20 days after pollination for determination of enzyme activities and again at maturity for quantification of storage products and electrophoretic separation of zeins. Endosperm dry weight, starch, zein-N, and nonzein-N all increased in mature kernels as N supply increased from zero to 14.3 millimolar. The activities of sucrose synthase, aldolase, phosphoglucomutase, glutamate-pyruvate transaminase, glutamate-oxaloacetate transaminase, and acetolactate synthase increased from 1- to 2.5-fold with increasing N supply. Adenosine diphosphate-glucose pyrophosphorylase and both ATP- and PPi-dependent phosphofructokinases increased to lesser extents, while no significant response was detected for hexose kinases and glutamine synthetase. Nitrogen-induced changes in enzyme activities were often highly correlated with changes in final starch and/or zein-N contents. Separation of zeins indicated that these peptides were proportionately enhanced by N supply, with the exception of C-zein, which was relatively insensitive to N. These data indicate that at least a portion of the yield increase in maize produced by N fertilization is induced by a modification of kernel metabolism in response to N supply.     

Auxin transport in maize roots in response to localized nitrate supply

Background and Aims

Roots typically respond to localized nitrate by enhancing lateral-root growth. Polar auxin transport has important roles in lateral-root formation and growth; however, it is a matter of debate whether or how auxin plays a role in the localized response of lateral roots to nitrate.

Methods

Treating maize (Zea mays) in a split-root system, auxin levels were quantified directly and polar transport was assayed by the movement of [³H]IAA. The effects of exogenous auxin and polar auxin transport inhibitors were also examined.

Key Results

Auxin levels in roots decreased more in the nitrate-fed compartment than in the nitrate-free compartment and nitrate treatment appeared to inhibit shoot-to-root auxin transport. However, exogenous application of IAA only partially reduced the stimulatory effect of localized nitrate, and auxin level in the roots was similarly reduced by local applications of ammonium that did not stimulate lateral-root growth.

Conclusions

It is concluded that local applications of nitrate reduced shoot-to-root auxin transport and decreased auxin concentration in roots to a level more suitable for lateral-root growth. However, alteration of root auxin level alone is not sufficient to stimulate lateral-root growth.     

Root exudation from Hordeum vulgare in response to localized nitrate supply

Root proliferation as a response to exploit zones of nutrient enrichment in soil has been demonstrated for a wide range of plant species. However, the effectiveness of this as a strategy to acquire nutrients is also dependent on interactions with the soil microbial community. Specifically, C-flow from roots modifies microbial activity and probably the balance between nutrient mineralization and immobilization processes in the rhizosphere. In this study, near-natural abundance 13C-labelling and gene-reporter methods were applied to determine the effects of uneven nitrate supply to roots of Hordeum vulgare on assimilate partitioning and root exudation. Plants were initially grown in uniform nitrate supply in split-root, sand microcosms after which one treatment continued to receive uniform supply, and the other received nitrate to one root compartment only. At the time of imposing the treatments, the CO2 supplied to the plants was switched to a cylinder source, providing a distinct delta13C-signature and allowing the fate of new assimilate within the plants to be determined. The labelling approach allowed quantification of the expected preferential allocation of new C-assimilate to roots in enriched nitrate, prior to any measurable effect on whole biomass or root architecture. Biosensor (lux-marked Pseudomonas fluorescens 10586 pUCD607) bioluminescence, quantified spatially by CCD imaging, demonstrated that root exudation was significantly increased for roots in enriched nitrate. This response of root exudation, being primarily associated with root apices and concurrent with enhanced assimilate supply, strongly suggests that C-flow from roots is an integral component of the proliferation response to nitrate.     

Improving photosynthesis to increase grain yield potential: an analysis of maize hybrids released in different years in China

Photosynthesis Research - In this work, we sought to understand how breeding has affected photosynthesis and to identify key photosynthetic indices that are important for increasing maize yield in...     

Photosynthetic and growth responses of reciprocal hybrids to variation in water and nitrogen availability

? Premise of the study: Fitness of plant hybrids often depends upon the environment, but physiological mechanisms underlying the differential responses to habitat are poorly understood. We examined physiological responses of Ipomopsis species and hybrids, including reciprocal F(1)s and F(2)s, to variation in soil moisture and nitrogen. ? Methods: To examine responses to moisture, we subjected plants to a dry-down experiment. Nitrogen was manipulated in three independent experiments, one in the field and two in common environments. ? Key results: Plants with I. tenuituba cytoplasmic background had lower optimal soil moisture for photosynthesis, appearing better adapted to dry conditions, than plants with I. aggregata cytoplasm. This result supported a prediction from prior studies. The species and hybrids did not differ greatly in physiological responses to nitrogen. An increase in soil nitrogen increased leaf nitrogen, carbon assimilation, integrated water-use efficiency, and growth, but the increases in growth were not mediated primarily by an increase in photosynthesis. In neither the field, nor in common-garden studies, did physiological responses to soil nitrogen differ detectably across plant types, although only I. aggregata and hybrids increased seed production in the field. ? Conclusions: These results demonstrate differences in photosynthetic responses between reciprocal hybrids and suggest that water use is more important than nitrogen in explaining the relative photosynthetic performance of these hybrids compared to their parents.     

Effect of nitrogen form on maize response to drought stress

Two hybrids of maize (Zea mays L.) differing in resistance to drought, were grown in chernozem soil in a greenhouse and were fertilized with two different forms of nitrogen: Ca(NO₃)₂ and (NH₄)₂SO₄ in concentrations corresponding to 100 kg of N ha^-1. After emergence of the 4th leaf, plants were exposed to drought. During the drought period, the parameters of plant water status (water potential, osmotic potential, turgor pressure and relative water content) and chlorophyll a+b concentration were monitored every two days. N and K concentration and accumulation over the drought period were also monitored.Next to differences in adaptability of the two hybrids to drought, the results demonstrate different adaptability of NH₄ and NO₃-treated plants within each hybrid. NH₄-plants of each hybrid maintain higher turgor pressure during the drought by better osmotic adaptation. Especially significant differences appear between chlorophyll (a+b) values of NH₄ and NO₃-treated plants and as affected by drought. Chlorophyll concentrations of NH₄-plants are higher than those of NO₃-plants both in control and droughted plants. NH₄ plants show a characteristic initial chlorophyll increase at the beginning of the drought period while in NO₃ plants chlorophyll constantly decreases throughout the whole drought period. The influence of the nitrogen form on chlorophyll concentration changes during drought does not appear to be affected by regulation of the K concentration.