Root Growth Patterns Research Articles

Growth and Alkaloid Patterns of Roots of Tabernaemontana pachysiphon and Rauvolfia mombasiana as Influenced by Environmental Factors

Abstract:The influence of environmental factors on the indole alkaloid content and biomass of the roots of Tabernaemontana pachysiphon and Rauvolfia mombasiana, two species of considerable local medicinal use in tropical East Africa, was investigated. Both species, belonging to the Apocynaceae, are frequent constituents of the residual tropical forests, prefering sites of different ecological conditions. Experimental plants, raised from seeds, were grown for 16 months in a temperature‐ and humidity‐controlled greenhouse. Environmental factors at variance were water and nutrient supply, and light intensity. At sufficient water and nutrient supply, the more drought and nutrient shortage‐tolerating heliophilous Rauvolfia mombasiana showed increased alkaloid accumulation, concurrently with reduced root biomass. Under the same conditions, the drought‐sensitive and higher levels of nutrient‐requiring ombrophilous Tabernaemontana pachysiphon produced more root biomass but accumulated less alkaloids in the roots. The results indicate that the accumulation of indole alkaloids in the roots, as well as biomass allocation to the roots, is influenced in an opposite manner by the nutrient and water supply to the heliophilous and the ombrophilous species.

Cell Cycle Duration in the Root Meristem of Sonoran Desert Cactaceae as Estimated by Cell-flow and Rate-of-cell-production Methods

Slow rates of cactus growth in the Sonoran Desert and high productivity of some Cactaceae under cultivation suggest that relatively low growth rates are not the consequence of a long cell division cycle but of short optimal periods for growth and adverse environmental factors. To verify this hypothesis, the duration of the cell division cycle (T)in the root apical meristem of seedlings of three sympatric species from the Sonoran Desert [Ferocactus peninsulae(F. A. C. Weber) Britton & Rose ‘Townsendianus’ (Britton & Rose) N. P. Taylor, stat. nov.,Stenocereus gummosus(Engelm.) Gibson & Horak andPachycereus pringlei(S. Watson) Britton & Rose] was estimated with the rate-of-cell-production (RCP) and the cell-flow (colchicine) methods. Both methods were applied during the steady-state growth phase, which was relatively short in the first two species because of the determinate pattern of root growth. The RCP method permitted estimation ofTin each root individually. Durations of the cell division cycle were inversely proportional to the rate of root growth (r2ranged from 0.42 to 0.88,P<0.05).T,determined by the cell-flow method, ranged from 14.4 to 19.3 h in these species and was within the same range asTdetermined by the RCP method. The averageTdetermined by the RCP method was 67 to 75% of that determined by the cell-flow method. Results obtained with both methods are compared and analysed. The proposed hypothesis appears to be correct, indicating that these species can be more productive under cultivation than in the wild due to the relatively short duration of the cell division cycle. Adaptive features of these findings are also considered.

Simulation in ecosys of root growth response to contrasting soil water and nitrogen

If mathematical models of plant growth are to perform reliably under diverse conditions of soil and climate, then the effects of these conditions on root growth must be represented. A mathematical model of root and mycorrhizal growth is proposed to represent the effects of soil and climate on growth using the hypothesis that a functional equilibrium exists among root axes and shoot branches. In this model access to growth resources (C, N, P, water) by different axes or branches depends upon (1) proximity of the axis or branch to the point of resource acquisition, and (2) the rate at which resources are consumed by the axis or branch in relation to that by other axes or branches. This model was coupled to a plant growth model as part of the ecosystem simulation model ecosys, and its sensitivity to changes in model parameters and soil boundary conditions was tested. Simulated root growth was less sensitive to changes in soil water and nitrogen than was simulated shoot growth. This lower sensitivity allowed the model to simulate changes in root:shoot ratios with changes in soil water and nitrogen that were consistent with those commonly reported in the literature. Changes in soil water also caused changes in vertical distributions of root length density to be simulated that were also consistent with those reported. Changes in root:shoot partitioning and in root density distributions allowed improved access by plants in the model to limiting growth resources. The root model was parameterized from basic root growth studies conducted independently of the model, and without reference to site-specific patterns of seasonal root growth. Consequently the model is likely to be of general value in the simulation of root growth under diverse soil conditions, although such generality needs to be established through further testing under different soils, climates and crops. The precision of some of the model parameters is uncertain and the sensitivity of the model to this uncertainty is discussed.

Citrus root responses to localized drying soil: A new approach to studying mycorrhizal effects on the roots of mature trees

Because fine roots tend to be concentrated at the soil surface, exposure to dry surface soil can have a large influence on patterns of root growth, death and respiration. We studied the effects of arbuscular mycorrhizas (AM) formation on specific root length (SRL), respiration and mortality of fine roots of bearing red grapefruit (Citrus paradisi Macf.) trees on Volkamer lemon (C. volkameriana Tan. & Pasq.) rootstock exposed to drying soil. For each tree, the fine roots were removed from two woody lateral roots, the roots were surface sterilized and then each woody root was placed in a separate pair of vertically divided and independently irrigated soil compartments. The two split-pot systems were filled with sterilized soil and one was inoculated with arbuscular mycorrhizal fungi (Glomus etunicatum/G. intraradices). New fine lateral roots that emerged from the woody laterals were permitted to grow inside the pots over a 10-month period. Irrigation was then removed from the top compartment for a 15-week period. At the end of the study, roots inoculated with AM fungi exhibited about 20% incidence of AM formation, whereas the uninoculated roots were completely void of AM fungi. Arbuscular mycorrhizal roots exhibited lower SRL, lower root/soil respiration and about 10% lower fine root mortality than nonmycorrhizal roots after 15 weeks of exposure to dry surface soil. This study demonstrates the feasibility of examining mycorrhizal effects on the fine roots of adult trees in the field using simple inexpensive methods.

Root growth, developmental changes in the apex, and hydraulic conductivity for Opuntia ficus‐indica during drought

Developmental changes in the root apex and accompanying changes in lateral root growth and root hydraulic conductivity were examined for Opuntia ficus‐indica (L.) Miller during rapid drying, as occurs for roots near the soil surface, and more gradual drying, as occurs in deeper soil layers. During 7 d of rapid drying (in containers with a 3‐cm depth of vermiculite), the rate of root growth decreased sharply and most root apices died; such a determinate pattern of root growth was not due to meristem exhaustion but rather to meristem mortality after 3 d of drying. The length of the meristem, the duration of the cell division cycle, and the length of the elongation zone were unchanged during rapid drying. During 14 d of gradual drying (in containers with a 6‐cm depth of vermiculite), root mortality was relatively low; the length of the elongation zone decreased by 70%, the number of meristematic cells decreased 30%, and the duration of the cell cycle increased by 36%. Root hydraulic conductivity (LP) decreased to one half during both drying treatments; LP was restored by 2 d of rewetting owing to the emergence of lateral roots following rapid drying and to renewed apical elongation following gradual drying. Thus, in response to drought, the apical meristems of roots of O. ficus‐indica near the surface die, whereas deeper in the substrate cell division and elongation in root apices continue. Water uptake in response to rainfall in the field can be enhanced by lateral root proliferation near the soil surface and additionally by resumption of apical growth for deeper roots.

Jasmonic acid affects mycorrhization of spruce seedlings with Laccaria laccata

Jasmonic acid (JA) was shown to be an important regulating molecule after wounding and pathogen attack, but it also conveys mycorrhizal signalling. It was therefore applied to the ectomycorrhizal system. Root growth patterns of 2-month-old spruce seedlings mycorrhized with Laccaria laccata after treatment with 0.5 μM JA, 5.0 μM JA, or none for the control, were studied using a paper-sandwich technique. Changes in plant weight, root length, the degree of branching, presence of root hairs, and infection parameters were monitored for 26 days. Data were analysed by means of Student’s t-test and ANOVA factorial. Shoot and root dry weights were significantly increased by mycorrhizal infection, especially when JA was applied. Lateral root formation and the presence of roots with hairs were dramatically decreased in the presence of the fungus. A synergistic effect of JA and mycorrhization on decrease of lateral root length was shown. The first mycorrhizal contact of fungal hyphae with roots was significantly accelerated after treatment with JA.

&lt;i&gt;In situ&lt;/i&gt; examination of white clover and perennial ryegrass roots inoculated with fungal pathogens

A minirhizotron-borescope system was used to directly measure the effect of two fungal pathogens, Cylindrocladium scoparium Morgan and Fusarium crookwellense Burgess Nelson & Tousson, on the root growth of white clover (Trifolium repens L.) and perennial ryegrass (Lolium perenne L.). This technique allowed roots to be counted in situ over a continuous time period without disturbing plant growth and function. Both fungal pathogens decreased clover and ryegrass root count numbers and reduced total plant dry weight. The pattern of clover root growth differed for each pathogen as C. scoparium decreased the total clover root count but F. crookwellense only reduced the rate of increase of the total clover root count.

Inheritance of Root Traits in Alfalfa

Root growth patterns influence nutrient uptake, productivity, and persistence in alfalfa (Medicago sativa L.). Inheritance of traits affecting root growth patterns in alfalfa are not well understood. Objectives of this research were to determine the affects of plant spacing and geographic location on root traits in alfalfa, to determine the inheritance of seven root morphological traits of alfalfa, and to evaluate the association between root traits, fall dormancy, and seedling year herbage yield. Progenies of diallels and design II matings were planted during May 1991 at two locations in 30‐cm rows with 2.5 cm between plants within the row. Plants were evaluated for seedling year herbage yield and fall dormancy. During October 1991, they were dug and evaluated for taproot diameter (TD), lateral root number (LRN), lateral root diameter (LRD), lateral root position (LRP), fibrous mass (FRM), percentage of determinate taproots (PDT), and determinate taproot position (DTP). Border effects were determined by evaluating single plants from the ends of the plots separately from plants in the middle of the plots. Extra space on plot borders affected root morphology, but few progeny × border interactions were found. Location affected root morphology, and a few location × cross interactions were observed for TD and LRP. Additive genetic effects were important in controlling inheritance for TD, LRN, LRD, LRP, and FRM. These traits had moderate (45) to high (87) heritabilities. genetic variances were detected for PDT or DTP. Taproot diameter was the root trait most highly correlated with fall dormancy (0.46–0.50) and seedling year herbage yield (0.61–0.75). Selection for LRN, LRD, and FRM at one location with uniform plant spacing should be successful. Multiple location selection programs may be more appropriate for TD and LRP.

Effects of elevated CO(2) and nitrogen on the synchrony of shoot and root growth in ponderosa pine.

We monitored effects of elevated CO(2) and N fertilization on shoot and fine root growth of Pinus ponderosa Dougl. ex P. Laws. and C. Laws. grown in native soil in open-top field-exposure chambers at Placerville, CA, over a 2-year period. The experimental design was a replicated 3 x 3 factorial with the center treatment missing; plants were exposed to ambient (~365 micro mol mol(-1)) air or ambient air plus either 175 or 350 micro mol mol(-1) CO(2) in combination with one of three rates of N addition (0, 100 or 200 kg ha(-1) year(-1)). All CO(2) by N interactions were nonsignificant. Both the CO(2) and N treatments increased plant height, stem diameter and leaf area index (LAI). Elevated CO(2) increased fine root area density and the occurrence of mycorrhizae, whereas N fertilization increased coarse root area density but had no effect on fine root area density. Spring flushes of shoot height and diameter growth were initiated concurrently with the increase in new root area density but height and diameter growth reached their maxima before that of fine roots. The temporal patterns of root and shoot growth were not altered by providing additional CO(2) or N. Greatest root loss occurred in the summer, immediately following the period of greatest new fine root growth. Elevated N initially reduced the fine root area density/LAI ratio independently of CO(2) treatment, indicating that the relationship between fine roots and needles was not changed by CO(2) exposure.

Root and Stem Growth Patterns of Young `Mauritius' Lychee Trees

`Mauritius' lychee (Litchi chinensis Sonn.) trees were planted in root observation chambers in July 1990 to determine the pattern of root and stem extension growth during 12 months. Root and stem lengths were measured at intervals ranging from 7 to 18 days from Aug. 1990 until Aug. 1991. During each period of active canopy growth, up to six stem tips were tagged and measured. Root growth was determined by measuring tracings of the extension of each root in a visible plane of the glass wall of the observation chambers. Stem growth was cyclic, with distinct periods of rapid extension followed by periods with no extension. In contrast, root growth was fairly continuous with only three periods of no visible root extension. Mean absolute extension rates were higher for stems than for roots. There were no consistent relationships between the timing of root and stem extension growth.

Statistical analysis of wheat root growth patterns under conventional and no-till systems

This is a preliminary study to find methods of quantifying and comparing root growth patterns in an agricultural soil under different tillage regimes. We tested the effectiveness of the use of variance-mean ratios and frequency histograms from counts in quadrats. Wheat plants ( Triticum aestivum L. cv. ‘Biggar’) were grown in undisturbed soil samples from two adjacent fields, one under no tillage for the previous 10 years, the other under conventional tillage for 9 years. Root contact points on horizontal plane sections of the samples were mapped. Statistical analysis of the root patterns indicated clustering; testing the hypotheses of pure-Poisson, Neyman type A and negative binomial distributions showed that the Neyman type A is the most suitable. Analysis of root distributions along with root and top biomass detected no significant difference between the two tillage treatments except a trend for increased rooting in the upper layer of the untilled soil.

Changes in root growth patterns of (Picea abies) spruce roots by inoculation with an ectomycorrhizal fungusPisolithus tinctorius and jasmonic acid treatment

Symbiosis between fungi and plant roots forming a mycorrhiza involves extensive interactions at the molecular level between both partners. The role of plant hormones in the regulation of mycorrhizal infection is not known to involve jasmonates. Their endogenous levels increase during pathogen attack; however, little has been done on their involvement in mycorrhizae. In our recent work, root growth patterns of 2-month-old spruce seedlings after inoculation withPisolithus tinctorius and/or jasmonic acid (JA) treatment were studied using a paper-sandwich technique. Changes in root length, the degree of branching, presence and length of root hairs, and infection parameters were followed using a stereomicroscope. The first mycorrhizal contact of hyphae with roots was significantly accelerated upon treatment with 0.5 μM JA. Interactions between root hairs and fungal hyphae were seen by scanning electron microscopy. The multiplication of root hairs of non-mycorrhized seedlings treated with 5.0 μM JA and changes of the root surface were observed by the same technique.

Root growth of triticale and barley grown for grain or for forage-plus-grain in a Mediterranean climate

Root systems of one triticale (x triticosecale Witt.) and one barley (Hordeum vulgare L.) cultivar grown for grain or for the dual purpose of winter forage-plus-grain were studied in a Mediterranean climate (Granada, Spain). The aim was to assess the effect of winter forage removal on root systems and to improve the knowledge of cereal root systems under Mediterranean conditions in relation to soil water use. After the forage was removed by clipping at the end of the winter period, cereal roots were shallower and lower in length densities, compared to the unclipped treatment. The largest differences occurred during the clipping-anthesis period and in the upper soil layers. At the end of the life cycle, the differences between the two systems regarding depth, density and dry matter of roots were small or nil. Moreover, there were no differences in total water use between clipped and unclipped cereals. Under both production systems (grain and forage plus grain), cereals demonstrated variable downward root extension (0.9 to 1.8 m) as a response to the wetting depth. Triticale roots continued growing after anthesis, especially in the deeper soil layers. In spite of that, root systems were not able to extract a notable amount of residual water (25 to 50 mm) apparently available from the subsoil. In semi-arid Mediterranean drylands, cereal root systems with greater phenotypic plasticity (deeper or larger in the subsoil) in response to subsoil water should be of interest in wetter areas or seasons. This does not necessarily imply a larger root system, but rather a root growth pattern with greater root growth in the subsoil.

Simulating root growth dynamics

We present a simple root-growth model that is capable of reproducing root distribution patterns as conditioned by varying soil conditions. The model assumes that the lateral growth of roots at any depth is governed by two factors: (i) the current root mass or root-length density at a given depth, and (ii) an environmental factor that may limit the further growth of roots at that depth. Using the relative soil-water content as the environmental factor, it is shown that an exponentially declining root distribution, commonly observed under wet soil profiles, can be reproduced by the model. Other non-exponentially declining root profiles observed under spatially varying soil-water contents can be simulated. The results indicate that the simple root model is capable of predicting differing root growth and distribution patterns, consistent with empirical observations under varying soil conditions.

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Changes in root growth patterns of (

Primary and Lateral Root Development of Dark‐ and Light‐Grown Cotton Seedlings under Salinity Stress*

AbstractPrimary root growth dynamics and lateral root development of dark‐ and light grown cotton seedlings (Gossypium hirsutum L., cv. Acala SJ‐2) were studied under control and salinity stress conditions. The seedlings were grown by two methods: A) in paper‐lined, vermiculite‐filled beakers with the plants growing between the paper and the glass wall (Gladish and Rost, 1993), and B) in hydroponics after germination and initial growth in germination paper rolls saturated with the treatment solutions (Kent and Läuchli, 1985). After germination, daily primary root elongation rate gradually incrased to a maximum, then gradually declined to close to zero for dark‐grown seedlings, or to sustained rates of about 10 mm per day for light‐grown control plants. Salinity stress delayed primary root growth and reduced peak elongation rates, without changing the general primary root growth pattern. These results suggest that salinity changed the time‐scale, but did not modify the normal developmental sequence. Lateral root growth was more inhibited by salinity than primary root growth. In addition, elongation of lateral roots was more inhibited by salinity than their initiation and emergence. Light exposure of the shoot favored both sustained primary root growth from 7 days after planting, and lateral root emergence and growth. Salinity effects were more severe on seedlings germinated and grown in hydroponics (method B) than on vermiculite‐grown plants (method A). These results emphasize the importance of growing conditions for the NaCl‐induced effects on cotton root development. In addition, the differential effects of salinity on primary and lateral roots became evident, pointing to diverse control mechanisms for the development of these root types.

Growth patterns of the lateral roots of young oak (Quercus robur) tree seedlings Relationship with apical diameter

The growth patterns of the first-order lateral roots of young oak (Quercus robur L.) tree seedlings were studied and related to variation in apical diameter. Seven seedlings were grown in root observation boxes and monitored daily for 6 wk. Apical diameters were measured daily on a sample of 48 lateral roots. A principal component analysis performed on the data set for 479 lateral roots showed that growth patterns were characterized by two major features. First, they could be described by a general growth potential (first factorial, 80% of the total variability) which was related to growth rate and growth duration. Second, but much less important (second factorial axis, 15% of the total variability), there was a distinction between early-growing roots (growing fast just after emergence and stopping early), and late-growing roots (having a low growth rate at emergence and a higher growth rate later). This growth pattern typology was related to the time-dependent variation in apical diameter. On almost all the roots, the apical diameter tended to decrease after emergence. On short roots (with a low growth potential) the initial apical diameter was low and its decrease was steep. Conversely, long roots had a greater initial diameter and tended to maintain it at a higher level. The so-called late-growing roots had a large apical diameter but a low growth rate in the early stages, possibly because of the between root competition for growth factors. The interest of the apical diameter as a morphological marker of sink strength, and the interactive relationships between growth rate, apical diameter and sucrose supply are discussed.

Root production and mortality under elevated atmospheric carbon dioxide

An essential component of an understanding of carbon flux is the quantification of movement through the root carbon pool. Although estimates have been made using radiocarbon, the use of minirhizotrons provides a direct measurement of rates of root birth and death. We have measured root demographic parameters under a semi-natural grassland and for wheat. The grassland was studied along a natural altitudinal gradient in northern England, and similar turf from the site was grown in elevated CO2 in solardomes. Root biomass was enhanced under elevated CO2. Root birth and death rates were both increased to a similar extent in elevated CO2, so that the throughput of carbon was greater than in ambient CO2, but root half-lives were shorter under elevated CO2 only under a Juncus/Nardus sward on a peaty gley soil, and not under a Festuca turf on a brown earth soil. In a separate experiment, wheat also responded to elevated CO2 by increased root production, and there was a marked shift towards surface rooting: root development at a depth of 80–85 cm was both reduced and delayed. In conjunction with published results for trees, these data suggest that the impact of elevated CO2 will be system-dependent, affecting the spatio-temporal pattern of root growth in some ecosystems and the rate of turnover in others. Turrnover is also sensitive to temperature, soil fertility and other environmental variables, all of which are likely to change in tandem with atmospheric CO2 concentrations. Differences in turnover and time and location of rhizodeposition may have a large effect on rates of carbon cycling.

Mineral Nitrogen in Plant Physiology and Plant Nutrition

Abstract Nitrogen (N) nutrition enhances metabolic processes that influences the physicochemical environment at the soil-root interface, modifies rhizosphere conditions, interferes with the uptake of cations and anions, and enhances or represses the activity of several enzyme systems. Also, it affects growth patterns, protein content, and protein quality of seeds. Ammonium (NH4)-N nutrition increases anion uptake, free amino-N/protein ratios, and acidity of root free space; it reduces carbohydrate levels in plant tissues. NO3-N nutrition results in higher cation uptake, higher carbohydrate content in tissues, and alkalinization of root free space. N-Assimilation interferes with the allocation of dry matter and energy, which causes different growth rates of plant parts. In this article we review the effects of mineral-N nutrition on uptake of cations and anions, activity of enzymes, growth patterns of roots and shoots, and water use efficiency, protein content, and protein quality of seeds.

Growth and yield response of barley and chickpea to water stress under three environments in southeast Queensland. II. Root growth and soil water extraction pattern

Root growth and water extraction of two barley cultivars, Corvette (early maturing), Triumph (late maturing) and one cultivar of chickpea (Amethyst at Redland Bay and Borwen at Hermitage) were compared under three environments: April sowing and July sowing at Redland Bay and June sowing at Hermitage Research Station, south-east Queensland. This work was designed to explain differences in dry matter production in terms of root growth and water uptake during the crop growth, which relied only on stored soil moisture. In the April sowing where all crops grew well during the early stages of growth, decline in soil water with time for the whole profile was similar among all crops. In the winter sowings (June, July), total water use was less in chickpea than in barley, particularly during early stages when chickpea growth was poor. Water extraction patterns of two barley cultivars were similar in all experiments, though the late-maturing Triumph extracted slightly more water than early maturing Corvette towards maturity. Water extraction front velocities of the three crops were similar in each experiment. At Redland Bay, the water extraction front velocities varied from 1.4 to 1.6 cm day-1 in the April sowing and 2.3 to 2.4 cm day-1 in the July sowing, while they varied from 2.0 to 2.3 cm day-1 at Hermitage. However, descent of the water extraction front commenced later in chickpea than in barley when sown in winter months, and this resulted in lower total water use in chickpea, particularly at Hermitage. In both sowings at Redland Bay total root length increased rapidly to about 60 days after sowing in barley, whereas the increase was slower in chickpea. Root length density was high in the upper soil layers, and this was associated with high extractable soil water. In deeper layers both root length density and extractable soil water decreased. For a given root length density chickpea extracted more water than barley. These results indicate that the differences in root growth and water extraction by the two barley crops were rather small and were unlikely to be the reason for the differences in total dry matter production. Chickpea on the other hand appeared to be susceptible to low temperatures during early stages of growth, and this caused poor growth of both shoots and roots.