Root Chamber Research Articles

Nonrecirculating Hydroponic System Suitable for Uptake Studies at Very Low Nutrient Concentrations

We describe the mechanical, electronic, hydraulic, and structural design of a nonrecirculating hydroponic system. The system is particularly suited to studies at very low nutrient concentrations, for which on-line concentration monitoring methods either do not exist or are costly and limited to monitoring relatively few individual plants. Solutions are mixed automatically to chosen concentrations, which can be set differently for every pump fed from a master supply of deionized water and nutrient concentrates. Pumping rates can be varied over a 50-fold range, up to 400 liters per day, which suffices to maintain a number of large, post-seedling plants in rapid growth at (sub)micromolar levels of N and P. The outflow of each pump is divided among as many as 12 separate root chambers. In each chamber one may monitor uptake by individual plant roots or segments thereof, by measuring nutrient depletion in batch samples of solution. The system is constructed from nontoxic materials that do not adsorb nutrient ions; no transient shifts of nitrate and phosphate concentrations are observable at the submicromolar level. Nonrecirculation of solutions limits problems of pH shifts, microbial contamination, and cumulative imbalances in unmonitored nutrients. We note several disadvantages, principally related to high consumption of deionized water and solutes. The reciprocating pumps can be constructed inexpensively, particularly by the researcher. We also report previously unattainable control of passive temperature rise of chambers exposed to full sunlight, by use of white epoxy paint.

Nitrogen release from roots of alfalfa and soybean grown in sand culture

An enclosed root chamber containing sterile sand medium was used to study net nitrogen (N) release from actively growing root systems of ‘Saranac’ alfalfa (Medicago sativa L.) and ‘Fiskeby V’ soybean (Glycine max L. Merr.). Plants were inoculated with a rhizobial strain appropriate to each host, irrigated with N-free nutrient solution, and grown either to 85 or to 173 d after germination (alfalfa) or to physiological maturity (soybean). Alfalfa released 4.5% of symbiotically-fixed plant N into the root zone over its growth period; soybean released 10.4% of plant N. Root zone leachates were analyzed for total N and for amino acid and ammonium content. Significant ammonium-N release occurred from the alfalfa but not the soybean root system; little amino-N was released by root systems of either species. Shoot harvest and water deficit caused increased release of N from alfalfa roots. The results provide evidence that alfalfa and soybean released significant proportions of their N into the root zone, and indicate that while substantial ammonium-N was released from alfalfa roots, passive leakage of amino-N was not a primary mechanism for N release from root systems of either species.

A root-mycocosm for growing ectomycorrhizal hyphae apart from host roots while maintaining symbiotic integrity

A culture system is described to grow mycorrhizal plants which allows experimental measurements to be made on mycorrhizae, and a portion of intact ectomycorrhizal fungi while in symbiosis, but growing apart from the rooting medium and host roots. A portion of the extramatrical hyphae is kept apart from the rooting medium by a restrictive passageway between the root and fungal chambers. The passageway is small enough to restrict coniferous fine roots to the root chamber, but large enough to allow fungal hyphae to grow out of the root chamber onto pre-weighed glass fiber filter paper situated in the fungal chambers. The pre-weighed filter paper allows for gravimetric estimation of the hyphal mass in the fungal chamber. The pieces of the modular Root-Mycocosm can be assembled in various configurations with one or two seedling chambers and one, two or three fungal chambers. Ponderosa pine (Pinus ponderosa Laws.) seedlings were inoculated withHebeloma crustuliniforme (Bull.: St. Amans) Quel in either commercial-vermiculite inoculum or in plastic growth-pouches and grown in the Root-Mycocosm. Hyphae were allowed to grow into the fungal chambers and after four weeks, amounted to 5.5±0.81 SE and 6.4±1.5 SE mg for pouch and commercial inoculum techniques, respectively.

Rates of rhizodeposition and ammonium depletion in the rhizosphere of axenic oat roots

A multiple split root chamber and artificial soil were developed which allowed for maintenance of axenic conditions and for the isolation of soil from specific regions of single roots. A sterile minirhizotron was used to measure patterns and rates of root extension under sterile conditions. Carbon and nitrogen distributions in the rhizosphere of sterile oat roots were measured in combination with rates of root elongation to calculate specific rates of rhizodeposition and ammonium nitrogen uptake. The highest rates of rhizodeposition C production and N depletion occurred at the root tip (first day segment). Rhizodeposited soluble and insoluble C compounds represented up to 50% of the standing root biomass C. Within 48 hours after root entry, levels of rhizosphere ammonium-N decreased by 40–50%. The results were summarized in a simple model of root growth, rhizodeposition, and NH 4 + −H uptake.

The uptake and distribution of 15N 2 into the various organs of Typha latifolia L.

Direct evidence of heterotrophic dinitrogen fixation associated with the emergent aquatic angiosperm, Typha latifolia L., was obtained through the exposure of actively growing plants to 15N 2 gas for 7 days in a gas-tight exposure vessel. Highest enrichments of 15N were found in roots/rhizomes and leaf bases. Slight enrichments were also found in the leaves due to translocation from the roots, rhizomes and leaf bases. Total fixed 15N values were 71.8 μg for the plant and 49.1 μg for the soil. Plants growing in silica sand, which received a nutrient solution containing combined nitrogen, exhibited higher enrichments and fixed 86% more 15N after exposure to 15N 2 gas than plants which received a nutrient solution lacking combined nitrogen. It is hypothesized that the concentration of combined nitrogen added was insufficient to repress nitrogen fixation and resulted in an increase in nitrogen fixation by associated microorganisms. Propane was used to trace the loss and movement of gases from the 15N 2 vessel and between the upper leaf chamber and the lower root chamber. Gas was rapidly exchanged between the upper and lower chambers through the leaves and roots of T. latifolia. Further investigations showed that propane moved at a rate of 1223 μmol day −1 from the leaves to the roots and 2652 μmol day −1 from the roots to the leaves. These data demonstrated that gases diffuse rapidly through the plant body of T. latifolia.

Effect of plant roots on carbon metabolism of soil microbial biomass

AbstractThe utilization of plant‐ and soil‐C by the microbial biomass in the rhizosphere of maize plants was investigated as a function of root proximity. The plants were cultivated in pots with divided root chambers and their shoots supplied with 14CO2 for 23 days. Subsequently the individual soil zones were analyzed for organic C, 14C, biomass C and biomass 14C.Plant roots induced a 197% increase in microbial biomass and a 5.4% decrease in soil organic C compared with an 1.2% decrease in the unplanted control soil. The contributions of plant‐ and soil‐C to this increased microbial growth amounted to 68% and 32% respectively. Biomass‐14C corresponded to 1.6% of the total photosynthetically fixed 14C, to about 15% of the organic 14C‐input into the rhizosphere and to 58% of the plant carbon remaining in soil after the removal of roots. 20% of this biomass‐14C was found outside the immediate root zone.These results demonstrate that growing roots are a significant C‐source for the microbial biomass and render an additional fraction of soil‐C available to microbial utilization. The efficiency of C‐utilization by the rhizosphere biomass is lower than values obtained with liquid cultures in laboratory experiments. The supply of plant‐C to the microbial biomass outside the immediate root vicinity indicates that the overall volume of the maize rhizosphere is greater than what has been supposed so far.

SOIL OXYGEN EFFECTS ON TWO DETERMINATE SOYBEAN ISOLINES1

Because a large portion of southern determinate soybean is grown on land frequently subject to poor soil aeration, an understanding of soybean responses to this condition is needed. It was hypothesized that soybean nutrient status, growth, and stomata would respond in a manner similar to that observed in many other species and, to test this hypothesis, grew soybean [Glycine max (L.) Merr., cv. Lee] in the greenhouse in sealed root chambers in equal volumes of soil and perlite. The soil was a Norfolk loamy sand (fine-loamy, siliceous, thermic, Typic Paleudult). Soil water was kept near field capacity; N, P, and K were added at equivalent field recommendation rates. Humidified gas containing 21, 4, 2, or 0% oxygen was passed over the soil at 500 ml/min beginning 46 d after planting. When soil-O2 diffusion rate (ODR) fell below 40 x 10-8 g cm-2 min-1, leaf diffusive resistance (R8) increased sharply. Plants were harvested 14, 22, and 29 d after treatment initiation. Adaxial stomatal density (SD) of 10/mm2 was unaffected by soil O2. Abaxial SD was inversely related to soil O2, rising from 55/mm2 at 21% O2 to 90/mm2 at 0%. All growth parameters were negatively affected by reduction in soil O2. The increase in SD was approximately proportional to the loss in leaf area in the absence of soil O2, indicating that changes in aperture rather than SD account for the rise in R, In general, concentrations of K and Ca declined in all tissue with declining soil O2. Magnesium concentrations were not consistently affected by O2 treatment.

Genetic and Hormonal Control of Shoot and Root Growth of Sorghum1

AbstractSorghum [Sorghum bicolor (L.) Moench] exhibits a large degree of genetic diversity far shoot development, but diversity in root development has heen virtually unexplored. Tall and short lines of ‘kafir’ and ‘milo’ sorghum that were near‐isogenic for height were examined to determine if genes which control height also exert a similar inlluence on root growth. Lines were compared both in hydroponics and in soil‐filled (fine sandy loam, Udic Paleustalf) root chambers in the field. Since dwarfing genes in sorghum appear to mediate their response through regulation of endogenous gibberellin (GA) levels, effects of exogenous GA3 applied to the shoot were also evaluated. In the field, differences in height of approximately 1 m developed between isolines of both kafir and milo, but the taller lines also developed 25 to 39% greater leaf areas. More roots were observed in the upper 60 cm of the soil profile in chambers containing the tall isolines, but when total root numbers were normalized with leaf area there were no differences between isolines. The GA3 application to tall and 3‐dwarf milo plants in hydroponic culture stimulated internode length of both cultivars, but reduced leaf area, root length, and root volume. Shoot dry weights of the tall and short isolines were increased by 19.6 and 9.9%, respectively, by GA3 treatment, while corresponding root dry weights decreased by 20.7 and 20.4 5%. These results are inconsistent with the hypothesis that gibberellins promote both shoot and root growth in sorghum, and further suggest that the genetic control of shoot growth in sorghum is largely independent from control of root growth.

A non-destructive field assay for soybean nitrogen fixation by acetylene reduction

A system for employing open-ended root chambers to measurein situ acetylene reduction rates under field conditions is described. Gas mixtures containing about 2 mbar acetylene were continuously flowed through the chambers providing a continuous record of acetylene reduction. These chambers have been used to measure acetylene reduction rates of soybeans during three growing seasons. The system has proved to be reliable with a high degree of precision. The large amount of plant-to-plant variability observed in N2 fixation research has been confirmed by the data collected with this system. However, such variability in physiological studies can be reduced by using a non-destructive system to compare the response of an individual plant with its rates before treatment.

Inlays for retaining composite resin in anterior tooth restorations

F requently, the dentist has to make esthetic restorations in anterior teeth where caries or trauma have involved a part of the incisal edge or angle. Often, such teeth are restored with a porcelain-faced or porcelain jacket crown. However, when the defect is minimal and the remaining tooth structure is sound, composite resin restorations with pin retention are generally used.‘-” Sometimes the shape of the root or pulp chamber makes it impossible to use a screw or cemented type of pin without involving the pulp or perforating the root. In such patients, a composite resin restoration placed in a gold-inlay-pin system is used. This technique is explained in this article.

The Relationship Between Oxygen and Water Uptake by Roots of Intact Bean Plants

To facilitate simultaneous measurements of root oxygen and water uptake, bean plants (Phaseolus vulgaris L. var. ‘Blue Lake’) were grown in washed sand in a root chamber which could be isolated from a chamber used to enclose the aerial portion of the plant. A continuous flow system was used in the root chamber and shoot chamber to measure oxygen consumption and transpiration, respectively. A good relationship between root oxygen uptake and transpiration was found during periods where the plants were subjected to gradual decreases in oxygen concentrations in the air in the root zone and during periods after some recovery had occurred as a result of reintroduction of 21% O2. The relationship failed, however, when plants were subjected to prolonged low oxygen concentrations, probably as a result of root injury, and when plants were abruptly given an ample supply of oxygen following a period of O2 deficiency, probably as a result of the need for oxygen to grow new roots before water uptake could begin again. For conditions other than those excluded, the correlation between root oxygen uptake and transpiration was 0.89. Transpiration decreased slightly as the oxygen concentration in the root zone decreased from 21 to 3%. Below 3%, the transpiration varied widely and depended on the length of time that the plant had been exposed to the decreased concentration. Recovery from damage resulting from low oxygen concentrations depended on the length of time the roots were subjected to the low concentrations. In some cases, full recovery was not achieved in 5 days. The ratio of the uptake of oxygen to water averaged 1:250 for the plants tested.

Carbon loss from roots of wheat cultivars

The amounts of organic materials released into soil from roots during the first 4 weeks of growth were determined for 11 cultivars of wheat ( Triticum aestivum L.). Carbon loss from roots was measured by supplying 14CO 2 continuously to the shoots and measuring the 14C content of the roots, root-free soil, water-soluble material and CO 2 flushed from the root chamber. Six cultivars were compared in each of two experiments, with the cultivar Condor common to both experiments. There were no significant differences between cultivars, relative to Condor, for 14C activity present in soil, roots, water-soluble material or rhizosphere CO 2. There was a significant difference between cultivars in experiment 1, but not in experiment 2, for the variate log 10 ( 14C lost from roots: 14C translocated to roots). There was evidence that a reduction in growth temperature, within the range 10–15°C, increased carbon loss from wheat roots into the rhizosphere.

Root Growth Along Plexiglas Surfaces by Sugarcane Under Different Soil Salinity Conditions1

AbstractRoot growth responses by sugarcane (Saccharum officinarum L.) to stress induced by salinity as a function of time or growth stage have not previously been investigated. This type of investigation is essential to a better understanding of the tolerance of plants such as sugarcane to salinity or stress. Root environment chambers seem to provide the best opportunity to study the growth interactions of roots and tops of plants and their environment. Root growth in soils irrigated with waters with electrical conductivities of 1.1, 5.0, and 8.0 mmhos/cm varied with stage of plant growth, time and salinity treatments. Root growth of sugarcane was greatest at soil depths of 20 to 60 cm in May, June, and July, a period of high growth rate and high evaporative conditions. During these months, average root intensities of sugarcane, irrigated with waters with salinities of 1.1, 5.0, and 8.0 mmhos/cm, were about 0.5, 1.0, and 1.5 mm/cm2, respectively. Moisture stress induced by osmotic potentials of about −1.8 and −2.9 bar and high evaporative conditions stimulated root intensities but reduced top growth by 22 and 50%, respectively. These studies using root chambers have contributed to a better understanding of the interactive influences of stages of plant growth, salinity, and environment on root growth by sugarcane.

Continuous, Automated Acetylene Reduction Assays Using Intact Plants

An automated method was developed for continuous, in situ determination of acetylene reduction (N(2) fixation) by intact soybean plants (Glycine max [L.]). The culture vessel containing the roots of intact plants grown in sand culture is sealed at the surface and an air-acetylene mixture continuously injected into the root chamber. The effluent gas is automatically sampled and injected into a gas chromatograph. Continuous acetylene assay at intervals as short as 3.5 min may be made over a period of several days, without attention, except for plant watering. Adverse effects of prolonged exposure of the root system to acetylene were mitigated by pulse injection of acetylene for 20 min followed by 40 min of acetylene-free air. Bare root systems can be suspended in a reaction chamber and sprayed with water or nutrient solution; this permits periodic removal of the root system for sampling nodules.In studies lasting several diurnal cycles, acetylene reduction did not decline more than 50% of the maximum rate in light, thus nitrogenase activity depends on concomitant photosynthesis and on carbohydrate from storage pools.

A root chamber for measuring the acetylene-reducing activity of intact soya beans

Abstract A technique is described enabling the N2 (C2H2)-fixing activity of intact soya beans to be measured repeatedly. Roots are enclosed in a perspex chamber containing aerated 0.5mM CaSO4 solution. At intervals the roots are exposed to acetylene in air and the ethylene production is measured Ethylene production was found to be linear for 90 minutes, and a standard assay period of 30 minutes was adopted. Assays during a 16-hour photoperiod showed no persistent increases or decreases in activity.

Soxlet Glassware Technique for Nutrient Culture Studies1

AbstractStandard Soxlet extraction glassware was used as plant containers for nutrient culture experiments. The thimble reservoir served as the root chamber. Fresh nutrient solution was continuously exchanged in the root growth chamber by a self‐pumping technique utilizing air injected into the bulk solution for lifting the newly aerated solution to the root growth chamber.