Growth and root responses of woody species to rocky substrate: implications for gully rehabilitation

Gullies formed in the Velhas River basin in Brazil have been filled with urban construction waste for physical stabilisation purposes. Aimed at rehabilitating gullies, we selected woody species from the Brazilian Cerrado that can grow on rocky substrates under greenhouse conditions. An assessment was made regarding plant growth in both rocky and natural soil substrates by analysing the height, diameter, fresh and dry weights of shoots and roots, plant water content, root occupation and architecture. Principal component analysis and Chi-squared tests segregated rock-tolerant species based on the specific influence on root dry and fresh weights. Fast-growing species reduced the emergence of their lateral roots under rocks, compromising their growth in height and biomass production. In contrast, slow-growing woody species were particularly suitable for gully rehabilitation because these species exhibited a genetic pattern of low lateral root emergence that prevented damage to their roots. Most slow-growing species demonstrated a similar growth pattern in both substrates, and some of them, such as Copaifera langsdorffii, achieved better growth in height and biomass production on rocks than on soil, a finding attributed to the root plastic response involving primary root elongation and lateral root emergence. Therefore, slow-growing species are recommended for gully rehabilitation procedures.     

Detailed quantitative analysis of architectural traits of basal roots of young seedlings of bean in response to auxin and ethylene

Vertical placement of roots within the soil determines their efficiency of acquisition of heterogeneous belowground resources. This study quantifies the architectural traits of seedling basal roots of bean (Phaseolus vulgaris), and shows that the distribution of root tips at different depths results from a combined effect of both basal root growth angle (BRGA) and root length. Based on emergence locations, the basal roots are classified in three zones, upper, middle, and lower, with each zone having distinct architectural traits. The genotypes characterized as shallow on BRGA alone produced basal roots with higher BRGA, greater length, and more vertically distributed roots than deep genotypes, thereby establishing root depth as a robust measure of root architecture. Although endogenous indole-3-acetic acid (IAA) levels were similar in all genotypes, IAA and 1-N-naphthylphthalamic acid treatments showed different root growth responses to auxin because shallow and deep genotypes tended to have optimal and supraoptimal auxin levels, respectively, for root growth in controls. While IAA increased ethylene production, ethylene also increased IAA content. Although differences in acropetal IAA transport to roots of different zones can account for some of the differences in auxin responsiveness among roots of different emergence positions, this study shows that mutually dependent ethylene-auxin interplay regulates BRGA and root growth differently in different genotypes. Root length inhibition by auxin was reversed by an ethylene synthesis inhibitor. However, IAA caused smaller BRGA in deep genotypes, but not in shallow genotypes, which only responded to IAA in the presence of an ethylene inhibitor.     

A novel image-analysis technique for kinematic study of growth and curvature

Kinematic analysis has provided important insights into the biology of growth by revealing the distribution of expansion within growing organs. Modern methods of kinematic analysis have made use of new image-tracking algorithms and computer-assisted evaluation, but these methods have yet to be adapted for examination of growth in a variety of plant species or for analysis of graviresponse. Therefore, a new image-analysis program, KineRoot, was developed to study spatio-temporal patterns of growth and curvature of roots. Graphite particles sprinkled on the roots create random patterns that can be followed by image analysis. KineRoot tracks the displacement of patterns created by the graphite particles over space and time using three search algorithms. Following pattern tracking, the edges of the roots are identified automatically by an edge detection algorithm that provides root diameter and root midline. Local growth rate of the root is measured by projecting the tracked points on the midline. From the shape of the root midline, root curvature is calculated. By combining curvature measurement with root diameter, the differential growth ratio between the greater and lesser curvature edges of a bending root is calculated. KineRoot is capable of analyzing a large number of images to generate local root growth and root curvature data over several hours, permitting kinematic analysis of growth and gravitropic responses for a variety of root types.     

The Initiation and Development of Lateral Meristems in the Pea Root: I. THE EFFECT OF YOUNG AND OF MATURE TISSUE

The effect of.distinct regions of the root on the initiationof lateral root primordia and the emergence of lateral rootshas been studied, using segments of roots from sterile 2-daygerminated pea seedlings. It is shown that the removal of the basal region causes a decreasein the number of primordia formed in the remainder of the root.On the other hand, the removal of the apical region causes alarger number of primordia to be formed in the remaining tissuethan in the corresponding tissue of roots where the apical regionis retained. It is suggested that a factor or a complex of factorsinvolved in primordium initiation is translocated from the oldertissue towards the potential site of primordium initiation inthe young tissue which has just completed extension growth. The removal of the apical region of the root is also shown tostimulate lateral root emergence. It is suggested that a factoror complex of factors involved in the development of the primordiasubsequent to initiation moves within the root in a similarmanner to the factor or factors involved in initiation.     

Spatio-temporal analysis of development of basal roots of common bean (Phaseolus vulgaris L.)

Temporal development of roots is key to the understanding of root system architecture of plants which influences nutrient uptake, anchorage and plant competition. Using time lapse imaging we analyzed developmental patterns of length, growth angle, depth and curvature of Phaseolus basal roots from emergence till 48 h in two genotypes, {"type":"entrez-nucleotide","attrs":{"text":"B98311","term_id":"3000390","term_text":"B98311"}}B98311 and TLP19 with contrasting growth angles. In both genotypes all basal roots appeared almost simultaneously, but their growth rates varied which accounted for differences in root length. The growth angles of the basal roots fluctuated rapidly during initial development due to oscillatory root growth causing local bends. Beyond 24 h, as the root curvature stabilized, so did the growth angle. Therefore growth angle of basal roots is not a very reliable quantity for characterizing root architecture, especially during early seedling development. Comparatively, tip depth is a more robust measure of vertical distribution of the basal roots even during early seedling development.Key words: basal root, kinematics, root architecture, root growth, spatiotemporal analysis, root imagingVertical and horizontal placements of the roots in the soil influence plant performance through acquisition of below ground resources like water and nutrients, plant anchorage and intra- and inter-plant competition.^1–4 Therefore the architecture of the root system plays important roles in regulating plant growth and yield, especially under abiotic stresses.⁵ As a seedling grows to become a mature plant, the root architecture develops continuously in response to various cues e.g., genotypic, environmental, hormonal, etc. Therefore studies of root architecture of plants of different ages are important for understanding the influence of these cues in regulating plant growth.The root scaffold of a plant is comprised of different types of roots with different functions. A mature common bean (Phaseolus vulgaris L.) plant has root system consisting of primary, adventitious, lateral and basal roots. Among these, the basal roots are typically the earliest emerging secondary roots from the hypocotyl⁶ forming a major part of the mature root system. We have recently demonstrated important differences in architectural traits of the basal roots of common bean in the early seedling stage between two contrasting class of genotypes and how auxin-ethylene interplay regulates these traits.⁷ While this study of basal roots at a fixed time allows assessment and comparison of root development up to that point of time, investigation of the temporal events of emergence and growth of the basal roots is important and complementary to the understanding of their architectural traits. Therefore in the present study, we examined the detailed developmental patterns of basal roots through time lapse imaging in two genotypes.We chose two bean genotypes with contrasting basal root growth angles (BRGA) relative to the gravity—{"type":"entrez-nucleotide","attrs":{"text":"B98311","term_id":"3000390","term_text":"B98311"}}B98311 producing basal roots of smaller BRGA (41.7° ± 14°) and TLP19 having roots of larger BRGA (56.4° ± 18°).⁸ The germinated seedling with 2–3 cm radical was transferred to the blue germination paper (Anchor Paper Co., St. Paul, MN), which was suspended in nutrient solution⁷ inside a growth chamber (ACMAS Technocracy Limited, Delhi, India) maintained at 25 ± 1°C. Time lapse photography was carried out for 48 h at 30 min intervals using Nikon D200 digital camera fitted with a macro lens to obtain high resolution digital images of the roots. Imaging started from the visibility of the protrusions of emerging basal root along the root-shoot interface. A computer program was developed in Matlab^® 7.8 (Mathworks, Natick) to analyze the images semi-automatically. From every image the computer program identified the basal roots using contrast of color between the roots (mostly white) and the germination paper (blue). Root midlines were determined following the methodology of Miller et al.⁹ and smoothed using the method of overlapping polynomials. Length of the midline is root length. The angle between gravity and the line connecting the root tip to the base is BRGA.⁷ The vertical distance of the root tip from the base of the lowest emerging root along the gravity vector is tip depth. From the midline, root curvature was also determined using the equation κ=x′y″−y′x″(x′2+y′2)3/2,(1) where [x(x), y(s)] is coordinate of any point along the root midline, s is normalized distance along the midline, and the primes denote derivatives with respect to s. Here positive curvature signifies bending upward and vice versa.     

Variation in the lag phase and uniformity of the length of the rooting phase prior to adventitious root production in cuttings of Agathis australis

Cuttings of Agathis australis (D. Don) Lindl passed through a well-defined series of morphological changes prior to root emergence. These phases were incorporated into a morphological index which can be used as a guide for the selection of cuttings at known developmental and anatomical stages. After a variable period (lag phase) during which no external change occurred there was an increase in stem diameter a few milimetres above the cut base. This swelling gradually increased in size and isolated bulges developed. Longitudinal splits then arose in the epidermis over the bulges, followed by root emergence through the splits. Root initiation occurred shortly after the sub-basal swelling commenced in cuttings that eventually rooted. Removal of the basal 8 mm of a rooted cutting (which included the roots) usually led to re-rooting of the cuttings. However, if the roots were merely trimmed off, the cutting never formed new roots and always died. The basal region apparently has the capacity to produce only one set of roots. Occasionally the stem diameter continued to increase and the swelling extended to include the basal region. Such cuttings never formed isolated wellings and never rooted.
In general the younger the plant from which the cutting was taken, the shorter the lag phase and the higher the final percentage rooting. Cuttings taken from older plants had a lower rooting percentage and a more variable lag phase, which was related to the time of year the cuttings were taken since root emergence always occurred in spring. Irrespective of the age of the original material there was a constant time period (3–4 weeks) from root initiation to root emergence.     

Growth rates,biomass and distribution of selected woody plant roots in Burkea africana-Ochna pulchra savanna

Woody plants in an African Burkea africana-Ochna pulchra savanna on deep sandy soil were found to have characteristically bimorphic root systems. The shallow lateral root component was often well developed and roots extended up to seven times the extent of the plant canopy in several species. Exponential tapering of lateral roots was found in Terminalia sericea. The wide-ranging roots, together with the high degree of multispecies root system interpenetration, result in the so-called, open grassy areas in the savanna mosaic often containing a competitively significant woody plant component. Root systems of Ochna pulchra were found to be relatively specialized and included: negatively geotropic, superficial roots; sinker roots to bedrock; high suckering response to damage in roots; belowground lignotuber-type organs; and sustained subterranean interconnections between some aboveground stems. These features are likely to contribute substantially to the resilience of this plant species to various climatic and veld management stress factors. Root/shoot mass ratios averaged unity but depended on plant size and aboveground growth form in Ochna pulchra. The dependence of these ratios on sizes of plant also applied to plant clones. Initiation of root tip growth occurred in early summer in one year and late spring in another. Main root tip growth occurred in late summer and early autumn, well after completion of most growth of leafy shoots in spring. It is suggested that some active uptake of water and nutrients by non-extending roots allows this form of phased growth in the plant. In an analysis of the seasonal growth of individual root tip systems, it was clear that transitory states of rest occur in fine root development but that these are far more frequent in the branching (and hence proliferation) of roots than in the continuing development of any root axis.Nomenclature follows the present system of the Botanical Research Institute, Pretoria, and the Flora of Southern Africa.I thank M.D. Panagos, P.S. Carr and J. Steyn for assistance at various stages of this work.     

Changes in root development of Arabidopsis promoted by organic matter from oxisols

The presence of ramified and abundant lateral roots is fundamental to plant growth on highly weathered soils. In this work, the effects of humic acid (HA), fulvic acid and hexanic–methanolic (HM) extract, after alkaline extraction from topsoil of seven different oxisols, on the development of roots of Arabidopsis thaliana was evaluated. Furthermore, we used another emergent plant model, that is, micro‐tom (MT) tomatoes with size similar to that of Arabidopsis to test the effects of HA. It was observed that both humic fractions and the HM extract were able to change the root development, improving the number of lateral roots and their development in comparison to control plants. The promotion of root growth by the three organic matter fractions was higher than that observed by 10^?6 mol L^?1 indole acetic acid. The treatment of MT tomato mutant, less sensitive to auxin, with HA did not promote the emergence of lateral roots, being an additional indication of auxin‐like activities of HA. However, some organic matter fractions exhibited, besides promotion of lateral roots number, increase in the length of principal root, which is not a typical auxin effect, indicating that these substances could contain other physiologically active substances.     

Architectural Tradeoffs between Adventitious and Basal Roots for Phosphorus Acquisition

Adventitious rooting contributes to efficient phosphorus acquisition by enhancing topsoil foraging. However, metabolic investment in adventitious roots may retard the development of other root classes such as basal roots, which are also important for phosphorus acquisition. In this study we quantitatively assessed the potential effects of adventitious rooting on basal root growth and whole plant phosphorus acquisition in young bean plants. The geometric simulation model SimRoot was used to dynamically model root systems with varying architecture and C availability growing for 21 days at 3 planting depths in 3 soil types with contrasting nutrient mobility. Simulated root architectures, tradeoffs between adventitious and basal root growth, and phosphorus acquisition were validated with empirical measurements. Phosphorus acquisition and phosphorus acquisition efficiency (defined as mol phosphorus acquired per mol C allocated to roots) were estimated for plants growing in soil in which phosphorus availability was uniform with depth or was greatest in the topsoil, as occurs in most natural soils. Phosphorus acquisition and acquisition efficiency increased with increasing allocation to adventitious roots in stratified soil, due to increased phosphorus depletion of surface soil. In uniform soil, increased adventitious rooting decreased phosphorus acquisition by reducing the growth of lateral roots arising from the tap root and basal roots. The benefit of adventitious roots for phosphorus acquisition was dependent on the specific respiration rate of adventitious roots as well as on whether overall C allocation to root growth was increased, as occurs in plants under phosphorus stress, or was lower, as observed in unstressed plants. In stratified soil, adventitious rooting reduced the growth of tap and basal lateral roots, yet phosphorus acquisition increased by up to 10% when total C allocation to roots was high and adventitious root respiration was similar to that in basal roots. With C allocation to roots decreased by 38%, adventitious roots still increased phosphorus acquisition by 5%. Allocation to adventitious roots enhanced phosphorus acquisition and efficiency as long as the specific respiration of adventitious roots was similar to that of basal roots and less than twice that of tap roots. When adventitious roots were assigned greater specific respiration rates, increased adventitious rooting reduced phosphorus acquisition and efficiency by diverting carbohydrate from other root types. Varying the phosphorus diffusion coefficient to reflect varying mobilities in different soil types had little effect on the value of adventitious rooting for phosphorus acquisition. Adventitious roots benefited plants regardless of basal root growth angle. Seed planting depth only affected phosphorus uptake and efficiency when seed was planted below the high phosphorus surface stratum. Our results confirm the importance of root respiration in nutrient foraging strategies, and demonstrate functional tradeoffs among distinct components of the root system. These results will be useful in developing ideotypes for more nutrient efficient crops.     

Growth direction of nodal roots in rice: its variation and contribution to root system formation

The root system of a rice plant (Oryza sativa L.) consists of numerous nodal roots and their laterals. The growth direction of these nodal roots affects the spatial distribution of the root system in soil, which seems to relate to yield and lodging resistance. The growth angle of a nodal root varies with the type and timing of emergence of the nodal root. The body of a rice plant can be recognized as an integrated set of shoot units, each unit consisting of an internode with a leaf and several roots. Nodal roots formed at the apical part of a shoot unit often elongate horizontally, whereas those formed at the basal part of the shoot unit show various growth directions depending on both the growth stages of the plant and the environmental conditions. Moreover, nodal roots that emerge from the most basal shoot unit of a tiller are usually thick and grow downwards. External factors such as planting density and nitrogen application affect the growth direction of nodal roots, probably partly because of the changing tillering pattern of the shoot. In addition to the growth angle of nodal roots, size of nodal roots may be another important factor determining the spatial distribution of the root system in soil.     

Light and decapitation effects on in vitro rooting in maize root segments

The effects of white light and decapitation on the initiation and subsequent emergence and elongation of lateral roots of apical maize (Zea mays L. cv LG 11) root segments have been examined. The formation of lateral root primordium was inhibited by the white light. This inhibition did not depend upon the presence of the primary root tip. However, root decapitation induced a shift of the site of appearance of the most apical primordium towards the root apex, and a strong disturbance of the distribution pattern of primordium volumes along the root axis. White light had a significant effect neither on the distribution pattern of primordium volumes, nor on the period of primordium development (time interval required for the smallest detectable primordia to grow out as secondary roots). Thus, considering the rooting initiation and emergence, the light effect was restricted to the initiation phase only. Moreover, white light reduced lateral root elongation as well as primary root growth.     

Complex physiological and molecular processes underlying root gravitropism

Gravitropism allows plant organs to guide their growth in relation to the gravity vector. For most roots, this response to gravity allows downward growth into soil where water and nutrients are available for plant growth and development. The primary site for gravity sensing in roots includes the root cap and appears to involve the sedimentation of amyloplasts within the columella cells. This process triggers a signal transduction pathway that promotes both an acidification of the wall around the columella cells, an alkalinization of the columella cytoplasm, and the development of a lateral polarity across the root cap that allows for the establishment of a lateral auxin gradient. This gradient is then transmitted to the elongation zones where it triggers a differential cellular elongation on opposite flanks of the central elongation zone, responsible for part of the gravitropic curvature. Recent findings also suggest the involvement of a secondary site/mechanism of gravity sensing for gravitropism in roots, and the possibility that the early phases of graviresponse, which involve differential elongation on opposite flanks of the distal elongation zone, might be independent of this auxin gradient. This review discusses our current understanding of the molecular and physiological mechanisms underlying these various phases of the gravitropic response in roots.     

Number,position, diameter and initial direction of growth of primary roots in Musa

To understand soil colonization by a root system, information is needed on the architecture of the root system. In monocotyledons, soil exploration is mainly due to the growth of adventitious primary roots. Primary root emergence in banana was quantified in relation to shoot and corm development. Root emergence kinetics were closely related to the development of aerial organs. Root position at emergence on the corm followed an asymptotic function of corm dry weight, so that the age of each root at a given time could be deduced from its position. Root diameter at emergence was related to the position of the roots on the corm, with younger roots being thicker than older ones. However, root diameters were not constant along a given root, but instead decreased with the distance to the base; roots appear to be conical in their basal and apical parts. Root growth directions at emergence were variable, but a high proportion of the primary roots emerged with a low angle to the horizontal. Further research is needed to evaluate whether these initial trajectories are conserved during root development. Results presented in this study are in good agreement with those reported for other monocotyledons such as maize and rice. They give quantitative information that will facilitate the development of models of root system architecture in banana.     

植物侧根发育的研究进展

侧根是植物根系的重要组成部分,其发生和发育受到内源植物激素和外界环境因素的共同影响。生长素在侧根发生起始、侧根原基的发育和侧根突破母体表皮等阶段均发挥关键作用。研究侧根的发育和形态解剖结构以及信号调控途径等,都具有重要的理论和实践意义。本文结合近年来的研究进展,综述了拟南芥和水稻侧根发育的详细过程和影响因素,重点关注生长素在侧根原基发生和发育过程中的作用。     

Rhizosphere microbial community structure in relation to root location and plant iron nutritional status

Root exudate composition and quantity vary in relation to plant nutritional status, but the impact of the differences on rhizosphere microbial communities is not known. To examine this question, we performed an experiment with barley (Hordeum vulgare) plants under iron-limiting and iron-sufficient growth conditions. Plants were grown in an iron-limiting soil in root box microcosms. One-half of the plants were treated with foliar iron every day to inhibit phytosiderophore production and to alter root exudate composition. After 30 days, the bacterial communities associated with different root zones, including the primary root tips, nonelongating secondary root tips, sites of lateral root emergence, and older roots distal from the tip, were characterized by using 16S ribosomal DNA (rDNA) fingerprints generated by PCR-denaturing gradient gel electrophoresis (DGGE). Our results showed that the microbial communities associated with the different root locations produced many common 16S rDNA bands but that the communities could be distinguished by using correspondence analysis. Approximately 40% of the variation between communities could be attributed to plant iron nutritional status. A sequence analysis of clones generated from a single 16S rDNA band obtained at all of the root locations revealed that there were taxonomically different species in the same band, suggesting that the resolving power of DGGE for characterization of community structure at the species level is limited. Our results suggest that the bacterial communities in the rhizosphere are substantially different in different root zones and that a rhizosphere community may be altered by changes in root exudate composition caused by changes in plant iron nutritional status.     

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.     

D‐Root: a system for cultivating plants with the roots in darkness or under different light conditions

In nature roots grow in the dark and away from light (negative phototropism). However, most current research in root biology has been carried out with the root system grown in the presence of light. Here, we have engineered a device, called Dark‐Root (D‐Root), to grow plants in vitro with the aerial part exposed to the normal light/dark photoperiod while the roots are in the dark or exposed to specific wavelengths or light intensities. D‐Root provides an efficient system for cultivating a large number of seedlings and easily characterizing root architecture in the dark. At the morphological level, root illumination shortens root length and promotes early emergence of lateral roots, therefore inducing expansion of the root system. Surprisingly, root illumination also affects shoot development, including flowering time. Our analyses also show that root illumination alters the proper response to hormones or abiotic stress (e.g. salt or osmotic stress) and nutrient starvation, enhancing inhibition of root growth. In conclusion, D‐Root provides a growing system closer to the natural one for assaying Arabidopsis plants, and therefore its use will contribute to a better understanding of the mechanisms involved in root development, hormonal signaling and stress responses.     

硝态氮（NO3^—）对水稻侧根生长及其氮吸收的影响

侧根是植物吸收利用土壤养分的重要器官 ,其生长发育受内部遗传因子和外部环境矿质养分的影响。通过琼脂分层培养发现 :局部供应NO-3 可以诱导水稻 (OryzasativaL .)主根或不定根上侧根的生长。为研究旱种条件下NO-3 对水稻侧根发育及其N吸收的影响 ,设置了 3个蛭石培养实验 :分根处理、全株缺N、全株供N处理。分根处理 (一半根系供应 3mmol/LKNO3,另一半根系供应 3mmol/LKCl)结果表明 :局部供应NO-3 能够促进水稻侧根生长。而在全株处理下 ,N饥饿诱导了侧根的伸长。水稻根系对NO-3 的这两种反应都存在着显著的基因型差异。同时对地上部N浓度、可溶性总糖含量及N含量分析表明 ,这些生理指标在分根处理与全株加N处理中的差异均不显著 ,表明分根处理也能基本满足植株正常生长对N的需求。在分根处理中 ,水稻的N含量与分根处理中供N一侧的平均侧根长度存在显著正相关 ,这表明在养分不均一的介质中 ,侧根长度对水稻N素吸收具有十分重要的作用。而在N素充足的条件下 ,两者之间的相关性并不显著 ,这暗示在养分充足的环境下 ,侧根长度可能并不是决定根系吸收N素的主要因素     

硝态氮(NO-3)对水稻侧根生长及其氮吸收的影响

侧根是植物吸收利用土壤养分的重要器官,其生长发育受内部遗传因子和外部环境矿质养分的影响.通过琼脂分层培养发现:局部供应NO-3可以诱导水稻( Oryza sativa L.)主根或不定根上侧根的生长.为研究旱种条件下NO-3对水稻侧根发育及其N吸收的影响,设置了3个蛭石培养实验:分根处理、全株缺N、全株供N处理.分根处理(一半根系供应3 mmol/L KNO3,另一半根系供应3 mmol/L KCl)结果表明:局部供应NO-3 能够促进水稻侧根生长.而在全株处理下,N饥饿诱导了侧根的伸长.水稻根系对NO-3的这两种反应都存在着显著的基因型差异.同时对地上部N浓度、可溶性总糖含量及N含量分析表明,这些生理指标在分根处理与全株加N处理中的差异均不显著,表明分根处理也能基本满足植株正常生长对N的需求.在分根处理中,水稻的N含量与分根处理中供N一侧的平均侧根长度存在显著正相关,这表明在养分不均一的介质中,侧根长度对水稻N素吸收具有十分重要的作用.而在N素充足的条件下,两者之间的相关性并不显著,这暗示在养分充足的环境下,侧根长度可能并不是决定根系吸收N素的主要因素.