Visible Root Research Articles

Decomposition of 13C-labelled wheat root systems following growth at different CO 2 concentrations

We tested whether the amounts of carbon (C) mineralized from decomposing wheat ( Triticum aestivum L. cv. Tonic) roots were related to the quantity (i.e. root dry weight per plant) or the chemical composition of material which had been grown at ambient or elevated CO 2 concentrations (350 or 700 μmol CO 2 mol −1). Plants were grown in 13C-depleted CO 2 to distinguish root-derived C from soil-derived C. Over periods of up to ca. 400 d, root C, soil C and nitrogen (N) mineralization were measured from: (i) root systems left in situ in soil; (ii) soil after removal of visible roots; and (iii) equal amounts of roots added to fresh soil. Root systems in situ showed transiently faster C mineralization rates after growth at elevated [CO 2] compared with ambient [CO 2]. Ultimately, there were no [CO 2]-related differences in the amounts of C or N mineralized from root systems in situ. Specific rates of C loss from extracted roots were not significantly different for roots from the two [CO 2] treatments. The potential accuracy of the 13C method was demonstrated and 13C/ 12C fractionation during root decomposition was negligible. We conclude that when wheat is grown under elevated [CO 2], subsequent root decomposition will not necessarily be affected. If it does, it is likely to do so via an effect of [CO 2] on the amounts of root material produced per unit of soil rather than on the chemical quality of that material.

Fabrication of Cr/Steel Graded-Boundary Material by Laser Beam and Electron Beam

With the purpose of developing thick metal/metal graded-boundary materials, the fabrication experiment of Cr/Steel graded-boundary materials was carried out using a laser beam and an electron beam. In order to produce a compositionally graded boundary region between the substrate steel and the added Cr metal, a series of surface alloying treatments were performed with both a CO2 laser beam and an electron beam. A Cr sheet was placed on a commercial low carbon steel, and then a CO2 laser beam was irradiated on the surface to produce a homogeneous alloyed layer. On this first surface-alloyed layer, another Cr sheet was placed and then the CO2 laser beam was used again to produce a second surface-alloyed layer. Four sequential repetitions of the laser surface alloying treatment resulted in a compositionally graded region with about a 2 mm thickness from 60%Cr and 40%Fe in the surface region to 0%Cr and 99%Fe in the substrate. Similar procedures were carried out by an electron beam surface alloying treatment to produce Cr/Steel graded-boundary material. Four sequential surface-alloying treatments resulted in a compositionally graded region with a thickness of about 1 mm from 60%Cr and 40%Fe in the surface region to 0%Cr and 99%Fe in the substrate. In both cases, no visible root porosities were found in the graded-boundary region. Since the structures of both the high Cr graded-boundary region and the substrate were both BCC, there was almost no volume change and thus no appreciable cracks were formed in the boundary region between the alloyed layers and the substrate even after rapid cooling.

THE UTILISATION OF AN EMBRYO BREEDER TECHNIQUE FOR MATURATION OF SOMATIC EMBRYOS

The formation of embryos from somatic tissue may require several transfers to different media before ripe embryos can be harvested. In a semiopen system, where fresh medium is delivered continuously to the cells through a semipermeable membrane, the problem of repeated transfer can be avoided or the number of transfers reduced. Two types of culture vessels were constructed for studying the growth and differentiation of cells on the membrane. Because cells and embryos are stationary, not moving around as in shaking cultures, it is called an embryo breeder (EB) system. This equipment allows culture periods of unlimited duration without transfer of cultured tissues and any kind of changes in nutrient composition during the culture period. In addition, selection of a membrane with an appropriate molecular weight cut-off (MWCO) enables control of molecule transfer through the membrane. The first prototype was made of Teflon® and the second one of polycarbonate. Both EBs are autoclavable and consist of upper and lower compartments separated by a semipermeable membrane. The cells to be cultured are located in the upper compartment and the nutrients are pumped slowly by a tubing pump through the lower compartment. In preliminary experiments, EBs were loaded with carrot somatic cells and globular embryos. During the culture period of 2 to 4 weeks, differentiation of so-called torpedo-stage embryos with clearly visible shoot and root initials could be observed.

Screening of 12 Festuca Cultivars for Rapid Root Development

ABSTRACT Establishment of cool season grass seedlings in sandy soils is difficult due to lack of sufficient water in the seed zone. Our objective was to quantify the root growth rate of two cultivars of each of six Festuca species in the greenhouse. Festuca cultivars differed in rooting depth, root elongation rates, root length density, root mass density, root area, shoot biomass, leaf area, leaf length, and leaf number. The deepest root system and greatest cumulative root elongation rates were observed for ‘Clemfine’ tall fescue (Festuca arundinacea Schreb.). Visible root depth within the tube wall was significantly correlated with the root length observed after soil washing. The results of this study show that plants with aggressive root elongation rates had the deepest and best developed root and shoot systems.

Growth and Flowering of Three Garden Chrysanthemum Cultivars Produced in Plastic or Copper-Impregnated Fiber Containers

Abstract A study was conducted with three garden chrysanthemum cultivars (Dendranthemum × grandiflorum (Ramat.) Kitamura), ‘Grenadine’, ‘Nicole’, and ‘Tolima’ to evaluate growth and flowering in 2.6 liter (#1) black plastic containers compared to copper hydroxide (Cu(OH)2) impregnated fiber containers. For all three cultivars, growth indices, shoot and root dry weights, and total biomass increased for plants grown in fiber containers. Total number of flower buds per plant increased 30 to 32% for ‘Grenadine’ and ‘Nicole’ and 53% for ‘Tolima’ in fiber containers. Plants grown in Cu(OH)2-impregnated fiber containers had less root coverage at the containensubstrate interface and no observable root circling in contrast to visible root circling of plants grown in black plastic containers. Foliar nutrient analysis on the cultivar ‘Grenadine’ showed that K decreased and Fe and Cu increased when grown in Cu(OH)2-impregnated fiber containers. No visible nutrient abnormalities were observed.

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.

Growth and Flowering of Garden Chrysanthemums Produced in Plastic or Copper-impregnated Fiber Containers

A study was conducted with Dendranthemum ×grandiflorum (Ramat.) Kitamura garden chrysanthemum (`Grenadine', `Nicole', and `Tolima') to evaluate the growth and flowering of these plants grown in 2.6-L (no. 1) black plastic containers compared to plants grown in fiber containers with Cu(OH)2 impregnated into the container walls. For all three cultivars, growth indices, shoot and root dry weights, and total biomass increased for plants grown in fiber containers. Total number of flower buds per plant increased 30% to 32% for `Grenadine' and `Nicole' and 53% for `Tolima' grown in fiber containers. Plants grown in Cu(OH)2-impregnated fiber containers had less root coverage at the container:growing medium interface and no observable root circling in contrast to visible root circling on plants grown in black plastic containers. Foliar nutrient analysis on `Grenadine' showed that K decreased and Fe and Cu increased when grown in Cu(OH)2-impregnated fiber containers. No visible nutrient abnormalities were seen in this study.

Rhizodeposition of N by pea and barley and its effect on soil N dynamics

Rhizodeposition of N during plant growth influences the microbial activity in the rhizosphere and constitutes a source of labile organic N, but has not been quantified to the same degree as the rhizodeposition of C. The rhizodeposition of N, defined as root-derived N present in the soil after removal of visible roots and root fragments, was determined during field pea ( Pisum sativum L.) and spring barley ( Hordeum vulgare L.) growth in a sandy soil at a low concentration of mineral N using a continuous split-root 15N-labelling technique. The N rhizodeposition constituted 15 and 48% of the below-ground N in pea when determined 7 and 14 (maturity) wk after planting (WAP), respectively. In barley 32 and 71% of the below-ground N were present in rhizodeposits at the two samplings. At maturity the rhizodeposition of N amounted to 19 mg N plant −1 (7% of total plant N) for pea and 17 mg N plant −1 (20% of total plant N) for barley. Incubation of soils, after removal of roots, showed that the N rhizodeposits were labile; 79% of the pea and 48% of the barley root-derived N present in soil at 7 WAP were mineralizable. The root-derived N present in soil at maturity was less labile, since only 30 and 23% of the N rhizodeposition from pea and barley, respectively, were mineralized upon incubation. The mineralization of N in soils was studied during 3 months after harvest of plants at maturity with roots in situ and was found to be greater after pea than after barley. This was due to differences in the net mineralization of N from roots and rhizodeposits, which was greater after pea than after barley. Rhizodeposits and roots contributed 35% of the N mineralized after pea and 12% of the N mineralized after barley. After removing roots and root fragments from the soil the total net mineralization of N was similar in soil previously grown to pea and barley.

A comparison of four methods for measuring roots of field crops in three contrasting soils

Rooting measurements have been made at different growth stages for sugar beets (1987) and for cereals (1988) on three different sites using four different root measurement techniques: (a) the core method where roots were extracted and root length is directly measured, (b) the core-break method where the visible roots were counted on the faces of a broken soil column, (c) the trench profile wall method where the number of visible roots were counted and the root length density was estimated on a profile wall, and (d) the monolith method where the roots were extracted from monoliths dug out from a profile wall. The calibration curves between the field methods and the extraction methods were not linear, and regression coefficients differed significantly between different sites, crops and between fields with different agronomic management, e.g. irrigation and liquid manure application. Differences between growth stages were comparably low compared with those found between locations. Root length densities obtained with the trench profile method were on average 10-fold lower in the sand brown earth, 6-fold lower in the vertisol and 4 times lower in the cambisol compared to data obtained with the core method. It is therefore concluded that the core-break method and the trench profile wall method deliver no reliable data for comparing rooting intensities between different soils and between different crops if they are not calibrated with an extraction method for each site and crop.

Gas Exchange, Water Relations, and Dry Weight Partitioning during Root Initiation and Development of Poinsettia Cuttings

Gas exchange, water relations, and dry weight partitioning of shoot tip cuttings of `Eckespoint Lilo Red' (`Lilo') and `Gutbier V-10 Amy Red' (`Amy') poinsettia (Euphorbia pulcherrima Wind. ex Klotzsch) were studied during the initiation and development of adventitious roots. Net photosynthesis (A) and stomatal conductance (g) of cuttings were initially low and remained low until root primordia formation. Foliar relative water content (RWC) and osmotic potential (ψπ) increased upon formation of root primordia. Following formation of root primordia (2 days before visible root emergence) and concurrent with increasing RWC and ψπ, g increased. As roots initially emerged, A and g increased rapidly and continued to increase with further root primordia development and subsequent emergence of adventitious roots. Cutting stem and leaf dry mass and leaf area increased during the first few days after sticking cuttings. During primordium development and initial root emergence, the highest percent increase in dry weight was accounted for by basal stem sections. AU cuttings of both cultivars rooted and had similar root numbers after 23 days, but `Lilo' cuttings had 15% better rooting and 44% more roots than `Amy' after 15 days. This research supports the hypothesis that formation and elongation of root primordia coincides with increased gas exchange in poinsettia cuttings, and that gas exchange can be used as a nondestructive indicator of adventitious root development.

Growth Dynamics of the Cotton Plant during Water‐Deficit Stress

AbstractInformation on the differential growth response of roots and shoots to water‐deficit stress will better describe root growth within the soil for purposes of modeling plant growth and assessment of drought resistant traits. Our aim was to investigate leaf expansion and changes in root elongation for field and growth‐chamber cotton (Gossypium hirsutum L.) during drought. Plants were grown in rhizotron containers and subjected to 6 d of water‐deficit stress followed by 6 d of recovery and compared with a well‐watered control. The stress period commenced when the plants were 55 to 65 d old. Leaf expansion was more sensitive to stress than root elongation, with curtailed growth after 2 d of withholding water compared with 6 d with roots. Stress reduced root elongation and root volume. About 85% of visible roots showed elongation growth under conditions of adequate water, which was reduced by stress to 50%. Small (0.30 mm mean diam.) roots were more abundant and gave the greatest cumulative length, but grew less on a mean length basis than medium roots (0.62 mm mean diam.). The rate of root growth increased during recovery, consisting of regrowth from stalled roots and followed later by initiation of new roots. Medium roots contributed the most to root volume initiated during recovery. Most growth for both root sizes occurred in the lower zone of the soil, where water was more available. Root size and position of roots within the soil profile are important factors to consider when studying root growth response to water‐deficit stress.

Activity of Grape Root Borer (Lepidoptera: Sesiidae) in Southern Mississippi

Muscadine grape vines were excavated from vineyards in southern Mississippi and examined for damage caused by the grape root borer, Vitacea polistiformis (Harris), and for the presence of borer larvae. Generally, young vines (<12 yr old) had no visible root borer damage and no borers were present; vines 12 to 15 yr old had moderate damage and borers were present; older vines had severe damage and borers were present. Grape root borer populations were monitored over 5 yr with pheromone traps. No moths were trapped before 15 June or after 2 October. Peak moth captures occurred from 15 July through 2 September. These data indicate that vineyards in southern Mississippi should be treated with an insecticide during the 2nd or 3rd wk of July for effective grape root borer control.

656 PB 040 PHOSPHORUS FERTILIZER ALTERS DEPTH OF ROOT SYSTEM DEVELOPMENT IN FOUR POTATO CULTIVARS

Phosphorus applications can increase potato yields in Michigan soils with over 400 kg·ha-1 Bray-Kurtz P1 extractable P. Four potato cultivars (Onaway (On), Kennebec (Ke), Russet Norkotah (RN), and Snowden (Sn)) were planted on 7 May 1993 to study P fertilizer effects on root growth and development. Each plot received adequate N &amp; K, and either 0 or 50 kg·ha-1 P. Two minirhizotrons (5 cm i.d.) were set 1.1 m deep at 45° to the soil surface into each plot. P treatment did not influence tuber yield. At 65 days after planting, root counts for On, RN and Sn averaged 72, 44 and 58%. respectively, of those in Ke plots. The P treatment did not significantly influence total root counts within or across cultivars on any of five sampling dates. More visible roots were produced in the first 0.4 m of soil by plants receiving P than by plants not receiving P. Below the first 0.4 m, plants not fertilized with P produced more visible roots than those receiving P.

Root demography in kiwifruit (Actinidia deliciosa)

ABSTRACTA rhizotron was used to study fine‐root demography in mature vines of kiwifruit (Actinidia deliciosa). The vines were grown in a deep, well drained, silt loam and received normal orchard management. Roots were measured from 10 to 160cm depth at biweekly intervals for 2 years. After an initial phase of rapid colonisation of the repacked soil behind the rhizotron windows, the total length of visible roots per vine remained quite steady. This apparent stability of the total belied fast and sustained localized turnover of the fine roots at all soil depths. Fifty‐one per cent of the roots survived ≤28d, 69% died at an age ≤56d and only 8% survived &gt;252d. For each year, the cumulative length of roots grown was equivalent to about 2·75 times the maximum net length of roots visible. These may be the largest annual rates of root turnover yet reported. This has important ramifications for the carbon balance, mineral nutrition and water relations of the plant.

Release of organic c from growing roots of meadow fescue ( Festuca pratensis L.)

A new method to estimate the amount of organic C released from roots during plant growth is described. The method is based on decomposing root-derived material left in the soil after plant growth and removal of all visible roots in a long-term incubation. The total amount of organic C released during plant growth is then calculated from the amount of root-derived material remaining in the soil after long-term decomposition and a stabilization factor for this material. An estimate of the total amount of organic C released from roots during plant growth allows the total rhizosphere respiration to be separated into root respiration and microbial respiration. In a previous cultivation of continuously 14C-labelled meadow fescue ( Festuca pratensis L.) the distribution of net assimilated 14C was determined. Root-derived material in root-free soil from the cultivation was allowed to decompose in a long-term incubation (61 weeks). The amount of stabilized root-derived material left in the soil after the incubation, representing a certain proportion of the fresh root-derived material released during growth, was calculated. The stabilization of root-derived material was approximated through comparison with stabilization of known organic materials (glucose, grass shoots and roots). Decomposition of root-derived material resulted in more acid-stable residues than decomposition of glucose but less than shoots and roots. From the relationship, for the known organic materials, between the amount of stabilized organic material remaining after decomposition and the amount of acid-stable residue, the amount of original root-derived material was estimated. This result was combined with data from the previous determination of distribution of net assimilated 14C in meadow fescue on shoots, roots, soil and rhizosphere respiration. It was found that, during 7 weeks from germination, about 10% of net fixed 14C was released as organic material from the roots. Microbial respiration, from decomposition of root-derived organic material during growth, was estimated to be 32% of the total rhizosphere respiration.

Phenology, Pathogenicity and Pathotypes of Cereal Cyst Nematodes, Heterodera a Venae and H. Latipons (Nematoda: Heteroderidae) in Israel

Cereal cyst nematodes were found in varying population densities in the majority of wheat fields surveyed in Israel. The dominant species was Heterodera avenae (Ha), while H. latipons (Hl) occurred mainly in the more arid (southern) areas. The phenology and life cycle of the two species was basically similar: both species completed a single generation per year, life-stage development being closely related to climate and plant development. The two species differed in their etiology; whereas Ha attacked the root tip region inducing typical branching and swelling of roots with ensuing adherence of soil particles, juveniles of Hl penetrated at sites along roots more distant from the apex and, therefore, did not produce clearly visible root symptoms in the early seedling stage. In field conditions, the presence of Hl could be recognized only when cysts appeared on the roots. Moreover, the growth inhibition caused by Ha was more severe than that due to Hl. All local wheat cultivars tested were found to be excellent hosts for both Ha and Hl, as were all tested cultivars of barley and Phalaris sp.; oat cultivars were extremely poor hosts of Ha, but good hosts of Hl. Seven Ha populations showed the predominance of two pathotypes: Ha21, in the northern and the coastal regions, and Ha41 in the southern areas. Soil temperature affected both Heterodera' species hatching and damage to roots: at 6 ° C, life-stage development took 4 months, and it shortened as temperature increased up to 18° C, when it took only 40 days. At 24° C, juveniles failed to penetrate the roots. The effects on plant growth of early vs later sowing in dry and wet soils were recorded and are discussed.

The Las Cruces Trench Site: Characterization, Experimental Results, and One‐Dimensional Flow Predictions

A comprehensive field trench study was conducted in a semiarid area of southern New Mexico to provide data to test deterministic and stochastic models of vadose zone flow and transport. A 4 m by 9 m area was irrigated with water containing a tracer using a carefully controlled drip irrigation system. The area was heavily instrumented with tensiometers and neutron probe access tubes to monitor water movement and with suction tubes to monitor solute transport. Approximately 600 disturbed and 600 core samples of soil were taken to support deterministic and stochastic characterization of the soil water hydraulic parameters. The core sample‐based saturated hydraulic conductivities ranged from 1.4 to 6731 cm/d with a mean of 533 cm/d and a standard deviation of 647 cm/d, indicating significant spatial variability. However, visual observation of the wetting front on the trench wall shows no indication of preferential flow or water flow through visible root channels and cracks. The tensiometer readings and the neutron probe measurements also suggest that the wetting front moves in a fairly homogeneous fashion despite the significant spatial variability of the saturated hydraulic conductivity. In addition to the description of the experiment and the presentation of the experimental results, predictions of simple one‐dimensional uniform and layered soil deterministic models for infiltration are presented and compared to field observations. These models are presented here to provide a base case against which more sophisticated deterministic and stochastic models can be compared in the future. The results indicate that the simple models give adequate predictions of the overall movement of the wetting front through the soil during infiltration. However, the models give poor predictions of point values for water content due to the spatial variability of the soil. Comparisons between the one‐dimensional infiltration model predictions and field observations show that the use of the layered soil model rather than the uniform soil model does not consistently improve the accuracy of the predictions for this particular field application. This result illustrates that increasing the spatial resolution of the deterministic characterization of the site in the vertical direction does not always improve the model predictions. Uncertainties due to horizontal spatial variability and due to other difficulties associated with experimental characterization appear to be more significant.

Hydrotropism and its interaction with gravitropism in maize roots.

We have partially characterized root hydrotropism and its interaction with gravitropism in maize (Zea mays L.). Roots of Golden Cross Bantam 70, which require light for orthogravitropism, showed positive hydrotropism; bending upward when placed horizontally below a hydrostimulant (moist cheesecloth) in 85% relative humidity (RH) and in total darkness. However, the light-exposed roots of Golden Cross Bantam 70 or roots of a normal maize cultivar, Burpee Snow Cross, showed positive gravitropism under the same conditions; bending downward when placed horizontally below the hydrostimulant in 85% RH. Light-exposed roots of Golden Cross Bantam 70 placed at 70 degrees below the horizontal plane responded positively hydrotropically, but gravitropism overcame the hydrotropism when the roots were placed at 45 degrees below the horizontal. Roots placed vertically with the tip down in 85% RH bent to the side toward the hydrostimulant in both cultivars, and light conditions did not affect the response. Such vertical roots did not respond when the humidity was maintained near saturation. These results suggest that hydrotropic and gravitropic responses interact with one another depending on the intensity of one or both factors. Removal of the approximately 1.5 millimeter root tip blocked both hydrotropic and gravitropic responses in the two cultivars. However, removal of visible root tip mucilage did not affect hydrotropism or gravitropism in either cultivar.

Coronal MR Imaging of the Normal 3rd 4th and 5th Lumbar and 1st Sacral Nerve Roots

Seven healthy volunteers underwent coronal MR imaging at 1.5 tesla of the normal 3rd, 4th, and 5th lumbar, and 1st sacral nerve roots. Coronal slices, 3-mm-thick with a 0.3-mm gap between the slices were obtained (TR/TE 600/22) through the lumbar spinal canal. All the nerve roots were visible on at least one image. One can routinely expect to demonstrate the 3rd, 4th, and 5th lumbar, and 1st sacral nerve roots on T1-weighted, 3-mm-thick coronal MR scans. We found no correlation between the degree of lumbar lordosis and the lengths of the visible nerve roots. Five patients with one of the following spinal problems: anomaly, tumor, disk herniation, and failed back surgery syndrome were examined according to our protocol. In all these cases coronal MR imaging gave the correct diagnosis.

Effect of Soil-Applied Chlorsulfuron on Canada Thistle (Cirsium arvense) Root and Root Bud Growth

Chlorsulfuron [2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)-amino] carbonyl] benzenesulfonamide], applied at 9 to 560 g ai/ha to the soil surface, stopped shoot elongation of well established Canada thistle [Cirsium arvense(L.) Scop. #4CIRAR] plants in the greenhouse. Root fresh weight decreased progressively as chlorsulfuron rate was increased when measured 1 month after treatment. In contrast, the number of visible root buds plus secondary shoots increased 1.9- to 2.3-fold between 9 and 67 g/ha chlorsulfuron 1 month after soil surface treatment. Despite more numerous root buds, the number of secondary shoots arising from adventitious root buds progressively decreased as chlorsulfuron rate was raised. Increases in the number of visible root buds were observed first between 3 and 4 weeks following soil application with 67 g/ha of chlorsulfuron, 2 weeks after shoot growth stopped.