Flowing Nutrient Solutions Research Articles

Effect of Nutrient Solution Flow on Lettuce Root Morphology in Hydroponics: A Multi-Omics Analysis of Hormone Synthesis and Signal Transduction.

This study examined how the nutrient flow environment affects lettuce root morphology in hydroponics using multi-omics analysis. The results indicate that increasing the nutrient flow rate initially increased indicators such as fresh root weight, root length, surface area, volume, and average diameter before declining, which mirrors the trend observed for shoot fresh weight. Furthermore, a high-flow environment significantly increased root tissue density. Further analysis using Weighted Gene Co-expression Network Analysis (WGCNA) and Weighted Protein Co-expression Network Analysis (WPCNA) identified modules that were highly correlated with phenotypes and hormones. The analysis revealed a significant enrichment of hormone signal transduction pathways. Differences in the expression of genes and proteins related to hormone synthesis and transduction pathways were observed among the different flow conditions. These findings suggest that nutrient flow may regulate hormone levels and signal transmission by modulating the genes and proteins associated with hormone biosynthesis and signaling pathways, thereby influencing root morphology. These findings should support the development of effective methods for regulating the flow of nutrients in hydroponic contexts.

Nutrient flow environment as a eustress that promotes root growth by regulating phytohormone synthesis and signal transduction in hydroponics

The morphology of lettuce roots in hydroponics is affected by the flow environment of nutrient solutions. Regulating the flow rate therefore ensures quality and yield; however, the mechanisms underlying this impact have not been fully elucidated, and breakthroughs in regulatory methods are thus lacking. Herein, lettuce was grown in a hydroponic solution at three different flow rates, the root morphology indicators (such as root length and surface area) were evaluated, the hormone levels of roots grown under different flow conditions were measured, and the correlations between plant hormones and root morphology were analyzed. Transcriptomic analysis was conducted on roots at varying flow rates to investigate the differential expression of genes involved in the synthesis and signal transduction pathways of auxin, abscisic acid (ABA), ethylene, and jasmonic acid. Results showed that these plant hormones were closely related to root morphology. Compared to a non-flow environment, a flow environment promoted the synthesis of plant hormones in the roots and enhanced the signal transduction of certain hormones, such as auxin. However, it had a negative impact on the signal transduction of certain hormones, specifically ethylene. The flow of the nutrients regulated root morphogenesis by influencing the synthesis and transduction of plant hormones, which affected overall plant growth. During the same growth period, lettuce grown under suitable flow conditions had a higher fresh weight than lettuce grown under no-flow conditions. Although such flow would increase the electricity cost of operating water pumps, lettuce could be harvested in advance at appropriate flow rates, thereby reducing the energy consumed in plant factories through lighting and temperature regulation, which are the largest contributors to energy consumption. This study examined the impact of the nutrient solution flow environment as a positive stimulus for plant growth, and it provides a reference for strategically regulating the flow rate in plant factories to improve yield and save energy. Future research should explore the effects of other cultivation and flow methods on the growth of different plants and apply these findings to practical production.

Cell-Based Modeling of Tissue Developing in the Scaffold Pores of Varying Cross-Sections.

In this work, we present a mathematical model of cell growth in the pores of a perfusion bioreactor through which a nutrient solution is pumped. We have developed a 2-D vertex model that allows us to reproduce the microscopic dynamics of the microenvironment of cells and describe the occupation of the pore space with cells. In this model, each cell is represented by a polygon; the number of vertices and shapes may change over time. The model includes mitotic cell division and intercalation. We study the impact of two factors on cell growth. On the one hand, we consider a channel of variable cross-section, which models a scaffold with a porosity gradient. On the other hand, a cluster of cells grows under the influence of a nutrient solution flow, which establishes a non-uniform distribution of shear stresses in the pore space. We present the results of numerical simulation of the tissue growth in a wavy channel. The model allows us to obtain complete microscopic information that includes the dynamics of intracellular pressure, the local elastic energy, and the characteristics of cell populations. As we showed, in a functional-graded scaffold, the distribution of the shear stresses in the pore space has a complicated structure, which implies the possibility of controlling the growth zones by varying the pore geometry.

Short-term transplantation effect of a tissue-engineered meniscus constructed using drilled allogeneic acellular meniscus and BMSCs.

During the construction of tissue-engineered meniscus, the low porosity of extracellular matrix restricts the flow of nutrient solution and the migration and proliferation of cells, thus affecting the tissue remodeling after transplantation. In this study, the canine allogeneic meniscus was drilled first and then decellularized. The drilled tissue-engineered menisci (Drilled Allogeneic Acellular Meniscus + Bone Marrow Mesenchymal Stem Cells, BMSCs) were transplanted into the knee joints of model dogs. On the basis of ensuring the mechanical properties, the number of the porosity and the cells implanted in allogeneic acellular meniscus was significantly increased. The expression levels of glycosaminoglycans and type II collagen in the drilled tissue-engineered meniscus were also improved. It was determined that the animals in the experimental group recovered well-compared with those in the control group. The graft surface was covered with new cartilage, the retraction degree was small, and the tissue remodeling was good. The surface wear of the femoral condyle and tibial plateau cartilage was light. The results of this study showed that increasing the porosity of allogeneic meniscus by drilling could not only maintain the mechanical properties of the meniscus and increase the number of implanted cells but also promote cell proliferation and differentiation. After transplantation, the drilled tissue-engineered meniscus provided a good remodeling effect in vivo and played a positive role in repairing meniscal injury, protecting articular cartilage and restoring knee joint function.

The development of the multi-physical model for cell-laden nerve scaffolds and its bioprinting by stereolithography

3D bioprinting is a novel manufacturing technology that can directly stack biocompatible materials mixed with cells layer by layer to form parts, enabling complex shapes with high resolution, and has become a powerful tool for fabricating nerve scaffolds. During the in vitro culture of scaffolds, the growth of nerve cells is affected by factors such as nutrient solution flow, oxygen concentration and scaffold structure. In this paper, a multi-physical model that combines the oxygen diffusion effect, and substrate consumption kinetics in the pc-12 (the rat adrenal medullary pheochromocytoma) cell-laden nerve scaffold was established to simulate and predict the distribution of oxygen concentration and cell growth. The scaffold was fabricated by the stereolithography (SLA) method, and the cell distribution was observed by fluorescence staining experiments to verify the model. It is approved that the model could intuitively predict cell growth. And in the future, the environmental and structural parameters of the scaffold can be optimized based on the model to achieve high density and uniform distribution of cells.

Effect of Nutrient Solution Flow Rate on Hydroponic Plant Growth and Root Morphology.

Crop production under hydroponic environments has many advantages, yet the effects of solution flow rate on plant growth remain unclear. We conducted a hydroponic cultivation study using different flow rates under light-emitting diode lighting to investigate plant growth, nutrient uptake, and root morphology under different flow rates. Swiss chard plants were grown hydroponically under four nutrient solution flow rates (2 L/min, 4 L/min, 6 L/min, and 8 L/min). After 21 days, harvested plants were analyzed for root and shoot fresh weight, root and shoot dry weight, root morphology, and root cellulose and hemicellulose content. We found that suitable flow rates, acting as a eustress, gave the roots appropriate mechanical stimulation to promote root growth, absorb more nutrients, and increase overall plant growth. Conversely, excess flow rates acted as a distress that caused the roots to become compact and inhibited root surface area and root growth. Excess flow rate thereby resulted in a lower root surface area that translated to reduced nutrient ion absorption and poorer plant growth compared with plans cultured under a suitable flow rate. Our results indicate that regulating flow rate can regulate plant thigmomorphogenesis and nutrient uptake, ultimately affecting hydroponic crop quality.

Effect of the Flow Rate on Plant Growth and Flow Visualization of Nutrient Solution in Hydroponics

In hydroponics, the flow pattern of nutrient solution in a cultivation container affects the growth of plants. Even if the flow rate of nutrient solution is the same between containers, the flow pattern may differ based on the size and shape of the containers. Therefore, the flow pattern cannot be comprehensively described by flow rate alone. In order to identify the relationship between plant growth, root morphology, nutrient uptake, and flow pattern, a hydroponic cultivation of Swiss chard was carried out. In addition, in order to describe the flow pattern in a specific cultivation container, hydroponic flow patterns were observed via flow field visualization using particle image velocimetry. As a result, with the increase in flow rate, it was found that a specific flow rate can form an ideal flow pattern for plant growth. Under this flow pattern, nutrient absorption is promoted and roots are elongated, thereby absorbing more nutrients and further promoting plant growth. However, when the flow rate exceeds the ideal value, plant growth is hindered. In summary, identifying the ideal nutrient solution flow pattern in hydroponics can facilitate better crop production.

Performance Study of Grass-Derived Nano-Cellulose and Polycaprolactone Composites for 3D Printing

In recent years, 3D printing has received increasing attention from researchers. This technology overcomes the limitations of traditional technologies by printing precise and personalized scaffold with arbitrary shapes, pore structures, and porosities for the applications in various tissues. The cellulose nanocrystal (CNC) is extracted from Humulus Japonicus (HJS) and mixed with poly(ε-caprolactone) (PCL) to prepare a series of CNC/PCL composites for printing. Based on the analysis of the physical and chemical properties of the series of the CNC/PCL composites, an optimal mass ratio of CNC to PCL was obtained. The Solidworks was used to simulate the stretching and compression process of the scaffolds with three different patterns under an external force. The flow of nutrient solution in the scaffolds with different patterns was simulated by ANSYS FLUENT, and then a new optimization scaffold pattern with a concave hexagon shape was advised based on the simulation results. Collectively, the mechanical test results of the material and scaffold confirmed that the optimal filling amount of the CNC was 5%, and the scaffold pattern with concave hexagon shape exhibited better mechanical properties and suitable for the transport of cells and nutrients, which is expected to be more widely used in 3D printing.

Reducing Nitrate Accumulation and Fertilizer Use in Lettuce with Modified Intermittent Nutrient Film Technique (NFT) System

Lettuce (Lactuca sativa L.) is a leading greenhouse-grown vegetable. However, nitrate (NO3−) accumulation in leaves remains a major issue. The aims of this research were: (i) to test the modified intermittent Nutrient Film Technique (NFT) in the cultivation of soilless lettuce in which plants are grown on peat blocks in trays and supplied with an intermittent flow of nutrient solution, and (ii) to calibrate the fertilization scheme to increase yield performance, while keeping NO3− concentration under control. Two greenhouse trials were performed between autumn 2013 and spring 2014. Results showed that a 30-day cycle is the optimum duration in terms of fresh biomass yield, both for autumn and spring cultivation. Reducing N fertilization in the last cropping days never affected NO3− concentration in leaves during autumn trial, due to unfavourable growing conditions. Conversely, suspension of fertilization 2 days before harvest had a consistent effect during the spring trial, when NO3− concentration in leaves was highly reduced (from 20 to 36%) without yield penalties. Thus, suspending fertilization 2–4 days before harvesting in intermittent NFT may reduce, on average, NO3− accumulation by 29–58% and the fertilization rate by 7–16%, respectively. Yet, growing conditions are crucial to make this system effective.

PERIODICITY OF EXPOSURE OF HYDROPONIC LETTUCE PLANTS TO NUTRIENT SOLUTION1

ABSTRACT A balanced periodicity of the nutrient solution flow is essential for better agronomic performances and low production costs in hydroponic systems. Thus, the objective of this work was to evaluate the effect of periodicity of exposure of lettuce plants to the nutrient solution in an NFT hydroponic system on the production, nutrition, and profitability of this crop. The experiment was conducted in a randomized block design with five replications. The treatments consisted of four periodicities of exposure of lettuce plants to the nutrient solution, consisting of intervals of 60, 30, and 15 minutes between pumping periods of 15 minutes; and uninterrupted flow of the nutrient solution. The plants were harvested at 30 days after transplanting, and 15 lettuce plants of each experimental plot were used to determine total fresh weight; root fresh weight; shoot freshweight; and contents of N, P, K, Ca, Mg, S, B, Cu, Fe, Mn, and Zn in shoots, roots, and in the diagnostic leaf; accumulation of these nutrients in shoots and roots; and nitrate and ammonium contents in plant shoot. The highest production and profitability of lettuce were found using uninterrupted nutrient solution flow, which provided higher shoot and root nutrient contents to plants, and resulted in a better nutrient use efficiency.

Head lettuce production and nutrition in relation to nutrient solution flow

ABSTRACT The optimum flow rate of nutrient solution in hydroponic system can better nourish the crops, allowing healthy and faster growth of lettuce. However, flow also interferes with electric power consumption, so further researches are necessary, mainly on the effect of flow rate, nutrient accumulation and lettuce production. In this context, the aim of this study was to evaluate nutrition and production of head lettuce in relation to the nutrient solution flow in NFT hydroponic system. The treatments consisted of nutrient solution application at the flow rates 0.5; 1; 2, and 4 liters per minute in each cultivation channel. Five replicates per treatment consisted of 15 plants each. The flow in hydroponic systems to produce head lettuce alters the technical performance of the crop. Due to the greater nutrient accumulation in shoot and use efficiency of these elements, the highest production (g/plant) of head lettuce was obtained with a flow rate of 1 L/min of the nutrient solution.

EFFECT OF NUTRIENT SOLUTION FLOW INTERVAL ON GROWTH AND YIELD OF LETTUCE (Lactuca sativa) GROWN IN HYDROPONICALLY DEEP FLOW TECHNIQUE

Lettuce (Lactuca sativa L.) is one of the vegetables that are commonly cultivated by using hydroponic systems. Some hydroponic systems require high current expenses in particular for the electricity in order to circulate nutrient solution e.g. in the water culture system – deep flow technique (DFT) -. Electricity costs can be reduced by changing from continuous nutrient flow to intermittent nutrient flow. The aim of this research was to investigate the effect of interval nutrient flow on growth and yield of lettuce. The experiment was conducted in Cirebon from February to April 2018. The experiment was arranged by using randomized complete block design with four treatments: (i) continuous nutrient flow (control), intermittent nutrient flow (nutrient flow during (ii) 15 minutes, (iii) 30 minutes, and (iv) 45 minutes). For each intermittent treatment, the nutrient flow was interrupted for 60 minutes. Each treatment was repeated four times. The result showed nutrient flow interval affected to plant height, shoot diameter, and leaf area at 35 days after planting (DAP). Meanwhile, leaves number, root volume, and fresh weight of harvested crops were not significantly different in all nutrient interval treatments. The highest plant height and shoot diameter were detected in the treatment (ii) nutrient flow during 15 minutes and interruption for 60 minutes, the results were not significantly different to the control – continuous flow treatment. It can be concluded the interval nutrient flow can be used as an alternative of the continuous flow of nutrient solution in hydroponically DFT.

Turbulent Kinetic Energy Distribution of Nutrient Solution Flow in NFT Hydroponic Systems Using Computational Fluid Dynamics

Hydroponics is crucial for providing feasible and economical alternatives when soils are not available for conventional farming. Scholars have raised questions regarding the ideal nutrient solution flow rate to increase the weight and height of hydroponic crops. This paper presents the turbulent kinetic energy distribution of the nutrient solution flow in a nutrient film technique (NFT) hydroponic system using the computational fluid dynamics (CFD) method. Its main objective is to determine the dynamics of nutrient solution flow. To conduct this study, a virtual NFT hydroponic system was modeled. To determine the turbulent kinetic energy distribution in the virtual NFT hydroponic system, we conducted a CFD analysis with different pipe diameters (3.5, 9.5, and 15.5 mm) and flow rates (0.75, 1.5, 3, and 6 L min−1). The simulation results indicate that different pipe diameters and flow rates in NFT hydroponic systems vary the turbulent kinetic energy distribution of nutrient solution flow around plastic mesh pots.

Automated hydroponics nutrition plants systems using arduino uno microcontroller based on android

Technological developments today make the combination of science is very common, including in Computer Science and Agriculture to make both of science need each other. This paper aims to develop a control tool for the flow of nutrients of hydroponic plants automatically using Arduino microcontroller and controlled by smartphone. We use an Arduino Uno microcontroller to automatically control the flow of nutrient solution with logic if else. The microcontroller can also send data of fluid level (solution) and temperature around the plant to smartphone android of the owner of the hydroponics plant. The height of the nutrient solution (water) is detected by the Ultrasonic sensor HC-SR04 and the temperature is detected by the temperature sensor LM35. Data from the sensor will forward into Arduino Uno and displayed in liquid crystal display (LCD) then via wireless fidelity (WIFI) ESP8266 module will transmit the height of the nutrient solution and the temperature around of the plants to Android smartphone.

The Study of Turbulent Nutrient Solution Flows in Difference Hydroponics System Arrangements

This work studied the turbulent flow of the nutrient solution which affected the growth of plants in four hydroponic systems; the horizontal (traditional), the vertical cup-grown, the ladder and the droplet systems, which were connected with individual solution pumps which submerged in only one nutrient solution tank to supply the turbulent nutrient solution flow to all systems. Two experiments were done by planting Red Oak lettuce, fluid and ambient temperatures, fluid pH and sunlight intensity were measured 2 times a day from 4 systems placed in the same area and environment during 20 days of the experimental periods. From both result sets, the lower ambient and solution temperatures in the 2nd experiment yielded more productivity. The results also showed that adjusting pipe and hose sizes did not cause the nutrient solution overflow out of the systems, the turbulent flow occurred and the horizontal system could produce the highest productivity. However, the higher pump power was required to produce the turbulent solution, the higher pump power higher heat transfer from the pump to the nutrient solution in the tank since all pumps were placed in the same solution tank, this heated solution caused the lower productivity in this work.

Numerical simulation of the fluid dynamics within the tissue engineering scaffolds micro-tubes

The core of tissue engineering is the fabrication of a complex three-dimensional space with cells and biomaterials. In the development of porous scaffolds in vitro, no matter the seed cells ran into the scaffold, or its excretion of waste discharged scaffolds, they both need the nutrient solution to be brought into or taken out. Therefore, the flow of the nutrient solution, cells and metabolic waste for the profitable living in vitro culture plays a significant role. the paper constructed bone scaffold models of different geometric parameters, analog cells, and nutrient solution flow conditions in the scaffolds using the FLUENT software. By making a contrastive analysis with the simulated result, the internal organizational design parameters of scaffold for tissue engineering is optimized and a certain amount of data and a theoretical basis for the internal bone scaffold structure design is provided.

Reactions to cadmium stress in a cadmium-tolerant variety of cabbage (Brassica oleracea L.): is cadmium tolerance necessarily desirable in food crops?

Cadmium is a cumulative, chronic toxicant in humans for which the main exposure pathway is via plant foods. Cadmium-tolerant plants may be used to create healthier food products, provided that the tolerance is associated with the exclusion of Cd from the edible portion of the plant. An earlier study identified the cabbage (Brassica oleracea L.) variety, Pluto, as relatively Cd tolerant. We exposed the roots of intact, 4-week-old seedlings of Pluto to Cd (control ∼1 mg L(-1) treatment 500 μg L(-1)) for 4 weeks in flowing nutrient solutions and observed plant responses. Exposure began when leaf 3 started to emerge, plants were harvested after 4 weeks of Cd exposure and the high Cd treatment affected all measured parameters. The elongation rate of leaves 4-8, but not the duration of elongation was reduced; consequently, individual leaf area was also reduced (P < 0.001) and total leaf area and dry weight were approximately halved. A/C i curves immediately before harvest showed that Cd depressed the photosynthetic capacity of the last fully expanded leaf (leaf 5). Despite such large impairments of the source and sink capacities, specific leaf weight and the partitioning of photosynthate between roots, stems and leaves were unaffected (P > 0.1). Phytochelatins (PCs) and glutathione (GSH) were present in the roots even at the lowest Cd concentration in the nutrient medium, i.e. ∼1 μg Cd L(-1), which would not be considered contaminated if it were a soil solution. The Cd concentration in these roots was unexpectedly high (5 mg kg(-1) DW) and the molar ratio of -SH (in PCs plus GSH) to Cd was large (>100:1). In these control plants, the Cd concentration in the leaves was 1.1 mg kg(-1) DW, and PCs were undetectable. For the high Cd treatment, the concentration of Cd in roots exceeded 680 mg kg(-1) DW and the molar -SH to Cd ratio fell to ∼1.5:1. For these plants, Cd flooded into the leaves (107 mg kg(-1) DW) where it probably induced synthesis of PCs, and the molar -SH to Cd ratio was ∼3:1. Nonetheless, this was insufficient to sequester all the Cd, as evidenced by the toxic effects on photosynthesis and growth noted above. Lastly, Cd accumulation in the leaves was associated with lowered concentrations of some trace elements, such as Zn, a combination of traits that is highly undesirable in food plants.

THE STRUCTURAL CONTROL OF NUTRIENT SOLUTION FOR STABLE PRODUCTION OF HIGH-QUALITY VEGETABLES IN GREENHOUSES

With the increase in consumption of natural resources and energy, global environmental problems have appeared. On one hand, by eco-systemic agriculture, environmental preservation, and energy saving measures, the establishment of innovative techniques for year-round stable production of high-quality vegetables in green houses has been expected. On the other hand, the deterioration of water in the environment leads to an increase in health hazards because of active oxygen in living organisms, and raising the quality of water is an important issue to be addressed. In this study, efficient approaches to managing nutrient solution were developed. The upper and lower sides of a fluidized layer are sectioned with stainless steel nets. Sintered silicate mineral ceramics were inserted into the section. The flow of nutrient solution can be directed using a pump from the lower to the upper side so that the ceramic particles are fluidized. The nutrient solution allowed to flow through the fluidized layer would be fed back into a nutrient solution tank, and a structured nutrient solution with antioxidation property is induced by electrokinetic treatment. The nutrient solution was found to become positively charged by the formation of an electric double-layer interface between the ceramic surface and the nutrient solution. The structured nutrient solution was studied under thermally stimulated depolarized current (J), temperature profiles (TSDC analysis), and viscosity. Effects of surface activity were seen in the structured nutrient solution at similar temperature conditions. Effects of structured nutrient solution on plant growth were examined in Komatsuna (Brassica rapa L. nothovar) plants growing under NFT system. The structured nutrient solution was efficiently absorbed on contact with roots and the root mass significantly increased. Komatsuna plants grew fast and a larger root mass contributed to an increase of total free amino acid in leaves.

Growth and Phosphorus Uptake of Three Riparian Grass Species

Riparian buffers can significantly reduce sediment‐bound P entering surface water, but control of dissolved P inputs is more challenging. Because plant roots remove P from soil solution, it follows that plant uptake can reduce dissolved P losses. We evaluated P uptake of smooth bromegrass (Bromus inermis Leyss.), reed canarygrass (Phalaris arundinacea L.), and switchgrass (Panicum virgatum L.) grown in a flowing nutrient solution culture system with P concentrations of 1 or 100 μmol L−1 Plants were destructively sampled at approximately 0, 26, 40, and 53 days after transplanting (DAT). In a separate, concurrent experiment, we simulated the effect of an inflow of runoff with low or high dissolved P by switching a subset of pots approximately 40 DAT. When grown in 1 μmol L−1 P solution, shoot dry matter (DM) yield increased in the order bromegrass &lt; switchgrass &lt; canarygrass. When grown in 100 μmol L−1 P solution, shoot DM yield increased in the order bromegrass = canarygrass &lt; switchgrass. Shoot P content was correlated with shoot DM yield; however, switchgrass was the only species that had higher P content in plants grown in 100 μmol L−1 P solution than in 1 μmol L−1 P solution. When solution P concentration was abruptly increased or decreased, P uptake was affected more than plant growth. Shoot P concentration of canarygrass increased more than 3.5‐fold when the plants were switched from 1 μmol L−1 P solution to 100 μmol L−1 P solution. Shoot P concentration of switchgrass followed the same trend. The results of this solution‐culture experiment suggest that canarygrass and switchgrass would more effectively deplete dissolved P than would bromegrass.

Diurnal and ultradian rhythms in K+ uptake by Trifolium repens under natural light patterns: Evidence for segmentation at different root temperatures

The patterns and variability in the diurnal and ultradian fluctuations in net uptake of K+ by 85-day-old plants of white clover (Trifolium repens L. cv. Huia) were analysed during 21 days of vegetative growth under natural light conditions, at constant root temperaures of 13 and 25°C. Plants were established in flowing solution culture, and hourly rates of K+ uptake from solutions containing 2.5-6.5 µM K+ were automatically measured without physical disturbance. Total daily solar radiation ranged between 1.3 and 12.5 MJ m−2 day−1 over the 21 days of measurements. Substantial diurnal changes in rates of K+ uptake, both absolutely and proportionately, were recorded on all but the day of lowest radiation (day 19), during which there was a period of net efflux of K+ from the root system into the flowing nutrient solutions at both temperatures. Typically, uptake rates increased severalfold during the first half of the light period, followed by several hours of relative stability during the afternoon; then a rapid decline throughout the evening and first half of the night, and finally gradual decline during the second half of the night. The data from a sequence of typical days were normalised and indicated that the pattern could be resolved into 4 distinct and linear phases, successively: (1) rapid acceleration, (2) stable uptake, (3) rapid deceleration, and (4) slow deceleration. The full data set (days 1-21) of hourly K+ uptake rates was Fourier-transformed and subjected to time-series analysis to determine whether there were significant ultradian rhythms in K+ uptake. Periodograms indicated a strong 24 h periodicity for uptake at both root temperatures. In addition, there were strong ultradian periodicities of 7 h for uptake at 13°C and 4 h for uptake at 25°C. The results are interpreted in terms of the possible mechanisms responsible for diurnal fluctuations in nutrient uptake.