Effects Of Root Zone Temperature Research Articles

Kinetics of Root Ion Absorption Affected by Environmental Factors and Transpiration II. Environmental Effects and a Concentration-Dependent Model

Welsh onion plants (Allium fistulosum L.cv. Koutou) were grown under the different conditions of root zone temperature and dissolved O2 concentration. The absorptive functions in intact roots were analyzed by evaluating rates of water absorption, ion absorption, respiration and ion concentration in xylem sap simultaneously by applying the measurement system newly developed in the precedent study. The root water and ion absorption were activated with increase in root zone temperature, and the long term treatment with the high temperature and the low dissolved O2 concentration in the root zone significantly depressed water and ion absorption, while ion concentration in the xylem sap was not significantly affected by the root zone temperature. These suggest that the temperature dependence observed in root ion absorption is brought mainly through the temperature dependence of water absorption. A concentration-dependent model based on the theory of enzyme kinetics was applicable to kinetics of the root ion absorption responding to the root zone environment. The effects of root zone temperature and ion concentration on the root ion absorption were represented well by the concentration-dependent model which involves two parameters sensitive to changes in conditions of plants and the environment.

Integrated Effects of Root-Zone Temperatures and Phosphorus Levels on Aeroponically-Grown Lettuce (Lactuca sativa L.) in the Tropics

In this study, butterhead lettuce (Lactuca sativa L. cv. Baby Butter) plants were grown at three root-zone tem- peratures (RZTs): 25 o C, 30 o C and ambient-RZT (A-RZT) ranging from 26 o C-42 o C while their shoots were maintained at hot ambient temperature ranging from 26 o C-42 o C. Three phosphorus (P) concentrations: -25% P (minus P, 23.25ppm), control (31.00ppm) and +25% P (plus P, 38.75ppm) were supplied to the plants at each RZT using Netherlands Standard Nutrient Solution. Interactions between RZT and P concentrations on productivity, root morphology, maximum photosyn- thetic O2 evolution (Pmax), P uptake and its partitioning between shoot and root were studied. Lettuce plants grown with the plus P concentration at 25 o C-RZT had the highest productivity, highest Pmax, highest shoot and root P concentrations. However, all the root morphological parameters studied were the greatest in plants grown with the minus P at 25 o C-RZT. Higher P concentration in the solution and 25 o C-RZT resulted in higher portion of the absorbed P partitioned to the shoots. Integrated effects of RZT and P concentration on the productivity, root morphology, photosynthesis and P uptake were discussed.

Effects of root zone temperature and paraquat in the induction of oxidative stress in Trichosanthes cucumerina L.

We investigated the influence of root zone temperature (RZT) and the aerial application of paraquat on stress defence mechanisms of Trichosanthes cucumerina L. To achieve this objective, T. cucumerina cv Green was grown with roots at 25 and 30°C root zone temperature and maintained at 20 ± 1°C air temperature in a growth chamber. These RZT and air temperature had earlier been shown to favor growth and fruit production in T. cucumerina. Plants at each RZT were subjected to paraquat treatment (+P) and without paraquat treatment (−P). Paraquat (0.2 mmol/L) was applied as aerial spray. Results showed that the individual main effects of RZT and paraquat treatments significantly affected the chlorophyll fluorescence and gas exchange parameters, while the interaction of both treatments had no significant effect. Results showed that the total phenolics and ascorbic acid contents of T. cucumerina at 30°C were significantly higher than at 25°C. The T. cucumerina plants in +P treatment recorded significantly lower maximum photochemical efficiency (Fv/Fm), net photosynthesis (A), transpiration rate (E), intercellular CO2 concentration (Ci) and stomatal conductance (g1) compared to untreated plants. Also, plants raised at 30°C recorded significantly higher Fv/Fm, A, E, Ci and g1 compared to plants raised at 25°C. Plants that were sampled at 48 h after paraquat treatment recorded a higher degree of oxidative damage compared to those sampled at 24 h after treatment. We showed that the degree of damage suffered by T. cucumerina, when treated with paraquat either at 25 or 30°C RZT was similar at 48 h after treatment. We concluded that either at 25 or 30°C, exposure of T. cucumerina to paraquat would impose the same degree of oxidative damage.

Effects of plastic mulches on root zone temperature and on the manifestation of tomato spotted wilt symptoms and yield of tomato

Tomato spotted wilt (TSW) disease is a serious constraint to tomato production in various regions of the world. The effect of TSW on tomato yield is largely influenced by time of infection. Early infection usually results in severe stunting of the seedling and even death of the plant. Plastic film mulches affect both the incidence of TSW, and plant growth and yield of tomato. The objective of the present study was to determine the effect of root zone temperature (RZT) as affected by plastic film mulch on the manifestation of symptoms of TSW, and growth and yield of tomato plants either artificially inoculated with tomato spotted wilt virus (TSWV) or under natural TSW infection. In artificially inoculated plants as well as in plants under natural TSW infection, vegetative top fresh weight (FW) and fruit FW both increased with the length of time after transplanting that the plants remained free from TSW symptoms. The root zone temperature was highest under black mulch (seasonal mean = 27.5 °C), followed by gray (27.0 °C), silver (25.8 °C), and white (24.8 °C) mulches. The plants grown on black mulch showed the earliest appearance of TSW symptoms, and had significantly reduced vegetative growth and fruit yields compared to plants on the other mulches. In conclusion, utilization of plastic mulches that created conditions of high RZT stress resulted in reduced plant growth and yield and predisposed the plants to earlier expression of TSW symptoms compared to plants grown at RZTs more favorable to tomato plant growth (optimal RZT = 26.1 °C [Díaz-Pérez, J.C., Batal, K.D., Granberry, D., Bertrand, D., Giddings, D., Pappu, H., 2003. Vegetative top growth and yield of tomato grown on plastic film mulches as affected by the appearance of symptoms of Tomato spotted wilt virus. HortScience 38, 395–399]). Since these plant responses to TSW under heat stress occurred in artificially inoculated plants as well as in plants under natural TSW infection, high RZTs probably affected the plants directly, independently of any possible effects on the thrips vectors.

Growth and its partitioning in Prunus rootstocks in response to root zone temperature

Abstract Rootstocks for stone fruit varieties differentially influence tree physiology and one possible explanation for these differences is that varieties vary in their response to root zone temperature (RZT). To examine the effects of RZT, two trials using actively growing plants of five different Prunus rootstocks with chill requirements between 100 and 1100 h were undertaken. Plants were grown at RZTs of 5, 13 and 19 °C for 6 weeks after which total dry matter accumulation and its partitioning amongst roots, stems and leaves was determined. In general, the magnitude of total dry matter and its component parts positively correlated with RZT and significant differences were found among varieties in the magnitude of total dry matter accumulation. Individual varieties ranked differently at the three RZTs with respect to total dry matter: in general, the same ranking was also seen in the ranking of each growth component. RZT significantly influenced partitioning causing differences in leaf, stem and root mass ratios. These differences were greatest at low RZTs and became less as RZT increased. Several patterns of partitioning were found. Firstly, the low chill varieties (Okinawa and Flordagold) were little affected by RZT with similar partitioning occurring at each RZT. Secondly, the higher chill varieties, Green Leaf Nemaguard (GL), Golden Queen (GQ) and Fay Elberta (FE), reacted more strongly to RZT and were particularly affected by the lowest RZT. For these varieties, the root mass ratio rose and stem mass ratio fell as RZT increased. However, with respect to leaf mass ratio, two different trends were found: the leaf mass ratio for FE and GQ positively correlated with RZT whilst the relationship for GL was negative. These findings suggest that the response to RZT is related to a variety's chill requirement; offer an explanation for differences in performance of rootstock–scion combinations at different locations; and will aid the development of more accurate tree performance models by taking RZT into account.

Root Zone Temperature as Modified by Plastic Mulches Affect the Appearance of First Systemic Symptoms of Tomato Spotted Wilt and Fruit Yield in Tomato

Tomato spotted wilt (TSW) is a serious constraint to tomato production in various regions of the world. The effect of TSW on tomato yield is largely influenced by time of infection. Early infection usually results in severe stunting of the seedling and even death of the plant. Plastic mulches have been found to affect both the incidence of TSW, and plant growth and yield of tomato. The objective of this study was to determine the effect of root zone temperature (RZT) as affected by plastic mulch on the timing of appearance of first TSW symptoms, vegetative top fresh weight (FW) and fruit FW in tomato. Under natural TSW infection as well as in artificially inoculated plants, vegetative top FW and fruit FW were both linearly related with number of days after transplanting (DAT) the plants were free from TSW symptoms. The plants grown on black mulch during the fall showed earlier appearance of TSW symptoms, and had significantly reduced vegetative growth and fruit yields. The mean RZT during the first 42 DAT—the time before the plants reached full canopy closure—significantly affected the timing of first appearance of TSW symptoms, tomato plant growth and fruit yield. Vegetative top FW (optimal RZT = 24.1 °C) and fruit FW (26.9 °C) fitted the quadratic relationships with the mean RZT during the first 42 DAT. In conclusion, utilization of plastic mulches that created conditions of RZT stress, particularly heat stress, resulted in reduced plant growth and yield and may predispose the plants to earlier expression of TSW symptoms compared to plants grown under RZTs more favorable to tomato plant growth.

Effect of Root Zone Temperature on Oilseed Rape (Brassica napus) Response to Boron

Oilseed rape (Brassica napus) is sensitive to low boron (B) supply, and its growth response to B may be influenced by soil temperature. To test the relationship between B and temperature, oilseed rape (cv. Hyola 42) seedlings were grown at 10°C (low) root zone temperature (RZT) with B supply from deficient to adequate B levels until growth of low B plants just began to slow down. Half of the pots were then transferred to 20°C (warm) RZT for 11 days before they were moved back to 10°C RZT for the final 4 days. Both plant dry mass and B uptake increased after plants were exposed to warm RZT. However, plant B deficiency was exacerbated by warm RZT in low B plants because of increased relative growth rate and shoot–root ratio without a commensurate increase in B uptake rate. It is concluded that RZT above the critical threshold for chilling injury in oilseed rape can nevertheless affect the incidence of B deficiency by altering shoot–root ratio and hence the balance between shoot B demand and B uptake.

Root-zone temperatures affect phenology of bud break, flower cluster development, shoot extension growth and gas exchange of 'Braeburn' (Malus domestica) apple trees

We investigated the effects of root-zone temperature on bud break, flowering, shoot growth and gas exchange of potted mature apple (Malus domestica (Borkh.)) trees with undisturbed roots. Soil respiration was also determined. Potted 'Braeburn' apple trees on M.9 rootstock were grown for 70 days in a constant day/night temperature regime (25/18 degrees C) and one of three constant root-zone temperatures (7, 15 and 25 degrees C). Both the proportion and timing of bud break were significantly enhanced as root-zone temperature increased. Rate of floral cluster opening was also markedly increased with increasing root-zone temperature. Shoot length increased but shoot girth growth declined as root-zone temperatures increased. Soil respiration and leaf photosynthesis generally increased as root-zone temperatures increased. Results indicate that apple trees growing in regions where root zone temperatures are < or = 15 degrees C have delayed bud break and up to 20% fewer clusters than apple trees exposed to root zone temperatures of > or = 15 degrees C. The effect of root-zone temperature on shoot performance may be mediated through the mobilization of root reserves, although the role of phytohormones cannot be discounted. Variation in leaf photosynthesis across the temperature treatments was inadequately explained by stomatal conductance. Given that root growth increases with increasing temperature, changes in sink activity induced by the root-zone temperature treatments provide a possible explanation for the non-stomatal effect on photosynthesis. Irrespective of underlying mechanisms, root-zone temperatures influence bud break and flowering in apple trees.

Low root zone temperature effects on bean (Phaseolus vulgaris L.) plants inoculated with Rhizobium leguminosarum bv. phaseoli pre-incubated with methyl jasmonate and/or genistein

Methyl jasmonate (MeJA) has recently been shown to act as a plant-to-bacteria signal. We tested the hypothesis that pre-induction of Rhizobium leguminosarum bv. phaseoli cells with genistein and/or MeJA would at least partially overcome the negative effects of low root zone temperature (RZT) on bean nodulation, nitrogen fixation and plant growth. Otebo bean plants were grown at constant air temperature (25oC) and two RZT regimes (25 and 17oC) and inoculated with R. leguminosarum bv. phaseoli pre-induced with MeJA and/or genistein. Our results indicate that low RZT inhibited nodulation, nitrogen fixation and plant growth. The plants growing at low RZT began fixing nitrogen seven days later compared to those at higher RZT. The low RZT plants had fewer nodules, lower nodule weight, less N fixation, slower plant growth, fewer leaves, smaller leaf area, and less dry matter accumulation comared to plants at a higher RZT. Rhzobium leguminosarum bv. phaseoli cells induced with genistein and/or MeJA enhanced bean nodulation, nitrogen fixation and growth at both optimum and suboptimum RZTs. The results of this study indicate that MeJA improves bean nitrogen fixation and growth at both optimum and suboptimum RZTs, and can be used alone or in combination with genistein to partially overcome the low RZT induced inhibitory effects on nodulation and nitrogen fixation.

The Effects of Root Zone Temperature and Limestone on pH and Electrical Conductivity on New Guinea Impatiens `Celebration Orange'

The purpose of this experiment was to examine the effects of various root-zone temperatures and pH on Impatiens ×hybrida, New Guinea impatiens `Celebration Orange.' Greenhouse growers need to be cognizant of the root-zone medium pH, as New Guinea impatiens are sensitive to nutrient toxicities at low pH. It is thought that limestone at low root-zone medium temperatures is not quickly activated, leading to toxicities. The objectives of this project were to determine: the effect of root-zone medium pH on foliar symptoms of iron and manganese toxicity; and the effective rates and grind size of limestone on root-zone medium pH. Various rates of limestone and different grind sizes were incorporated into a sphagnum peat moss-based medium at a range of temperatures. This experiment used a two-way thermogradient plate to maintain varying, but stable root-zone medium temperatures, ranging from 12 to 42 °C. Plant growth as well as root-zone medium pH was monitored. Changes in root-zone medium pH were monitored over time. Results indicated that the addition of moderate or high rates of limestone, 6 or 3 kg·m-3, provided stable root-zone media pH over the course of time. Both limestone grind sizes at 325 and 100–200 mesh provided satisfactory starting and ending pH values for healthy New Guinea impatiens growth, especially between the root-zone temperatures of 30 and 18 °C. Higher and lower temperature extremes inhibited root growth, resulting in lower quality plants.

Flooding, root temperature, physiology and growth of two Annona species.

The effects of root zone temperature (RZT) and flooding on physiology and growth of Annona glabra L. (pond apple) and A. muricata L. (soursop) were investigated. Trees planted in containers were exposed to RZTs of 5, 10, 20, 25 or 35 degrees C in controlled root temperature chambers. Trees at each RZT were either non-flooded (control) or continuously flooded. There were four replications over time for each treatment combination. Pond apple was more flood-tolerant than soursop. A combination of flooding and RZTs of 5 and 10 degrees C resulted in tree mortality of both species by Week 4. Only trees that appeared to develop morphological adaptations survived continuous flooding. In both species, net CO2 assimilation (A) decreased to nearly zero within 1 week following exposure to RZTs of 5 or 10 degrees C and became consistently negative over the remaining experimental period. Flooding reduced leaf chlorophyll index (measured with a SPAD meter), A and plant growth, and increased root electrolyte leakage from soursop. Optimum growth occurred at RZTs of 25 to 35 degrees C for non-flooded pond apple trees and at 20 to 25 degrees C for flooded trees. Soursop exhibited maximum growth at RZTs of 35 degrees C under non-flooded conditions and at 25 degrees C under flooded conditions.

Photosynthetic Utilization of Radiant Energy by Temperate Lettuce Grown Under Natural Tropical Condition with Manipulation of Root-Zone Temperature

Photosynthetic utilization of radiant energy was studied by chlorophyll (Chl) fluorescence and maximum photosynthetic O2 evolution (Pmax) in temperate lettuce (Lactuca sativa L.) grown under natural tropical fluctuating ambient temperatures but with their roots exposed to two different root-zone temperatures (RZTs): a constant 20 °C-RZT (RZT20) and a fluctuating ambient RZT (RZTa) from 23 to 40 °C. On a sunny day, irrespective of RZT, ΔF/Fm′ [ratio of the variable to maximal fluorescence under irradiation (the maximal photosystem 2 quantum yield with “actinic light”)] decreased and non-photochemical quenching (NPQ) increased parallel to the increase of photosynthetic photon flux density (PPFD). However, RZTa plants showed lower ΔF/Fm′ and higher NPQ than RZT20 plants. The electron transport rate (ETR) was much higher in RZT20 plants than in RZTa plants especially during moderately sunny days. There were no significant diurnal changes in Pmax although these values of RZT20 plants were much higher than those of RZTa plants. On cloudy days, no significant diurnal changes in ΔF/Fm′ and NPQ occurred, but ΔF/Fm′ was higher and NPQ was lower in RZT20 plants than in RZTa plants. Diurnal changes in ETR were also observed in all plants while Pmax values throughout the whole cloudy days in both RZT20 and RZTa plants were constant. Again, RZT20 plants had much higher values of Pmax than RZTa plants. During RZT transfer period, all Chl fluorescence parameters measured at midday fluctuated with PPFD. Impact of RZT on these parameters was observed 2–3 d after RZT transfer. ETR and Pmax measured with saturating PPFD in the laboratory did not vary with the fluctuating PPFD in the greenhouse but the effects of RZT on these two parameters were observed 3–4 d after RZT transfer. Thus RZT affects photosynthetic utilization of photon energy in temperate lettuce grown under natural tropical condition.

Effects of temperature and nutrient availability on plasma membrane lipid composition in Scots pine roots during growth initiation.

We studied the effects of root zone temperature (RZT) and nutrient availability on free sterols and phospholipids in the plasma membrane (PM) and on PM-ATPase activity in roots of 1-year-old Scots pine (Pinus sylvestris L.) seedlings during growth initiation in the spring. Seedlings were grown for 6 weeks in hydroponic cultures with low (0.5 mM N; LN) or high (3 mM N; HN) nutrient availability. The root zone was subjected to slow warming (SW) and fast warming (FW) treatments while maintaining similar air temperatures in both treatments. Decreases in the amount of phospholipids and in the phospholipid/free sterol ratio, an increase in the degree of saturation of phospholipid fatty acids and changes in free sterol composition were observed during root growth initiation. Changes in lipid composition of the PM associated with the cold deacclimation process were detected at RZTs above 9 degrees C. Nutrient availability affected the lipid composition of the PM only when RZT was increased slowly. When RZT increased from 4 to 6 degrees C in the SW treatment, the degree of saturation of phospholipid fatty acids decreased, especially in HN seedlings. The sitosterol/stigmasterol ratio remained higher in HN seedlings than in LN seedlings. After an RZT of 9 degrees C had been reached in the SW treatment, HN caused increases in the saturation of phospholipid fatty acids and root PM-ATPase activity, and a decrease in the phospholipid/free sterol ratio. Possible effects of changes in PM lipid composition on root growth and PM-ATPase activity are discussed.

Does calcium determine water uptake under saline conditions in pepper plants, or is it water flux which determines calcium uptake?

Under saline conditions, we investigated the effects of root-zone temperature on pepper plants (Capsicum annumm L.) treated with extra calcium, in order to study the influence of this parameter on water and calcium uptake. The treatments, for plants cultivated hydroponically in a controlled environment chamber, were control, NaCl (50mM), Ca2+ (10mM) and Ca2+ (10mM) + NaCl (50mM), all at 25 and 35°C root temperature. After these treatments, it could be seen that salinity reduced the concentration of calcium in roots and leaves, which were restored when calcium was added to saline-stressed plants. This effect of calcium was increased when plants were grown at 35°C root-zone temperature. The effect of both high temperature and extra supply of calcium influenced plant water relations, involving functionality of aquaporins. Therefore, the negative effect of salinity, with respect to tissue calcium concentration and water relations, was mitigated if there was a supply of Ca2+, this effect being greater when the root-zone temperature was increased.

Arbuscular mycorrhiza colonization and development at suboptimal root zone temperature.

Temperature has a strong influence on the activity of living organisms. This study, involving two indoor experiments, evaluated the effects of root zone temperature (10, 15 and 23 degrees C) on the formation and development of arbuscular mycorrhizae (AM). In the first trial, greenhouse-grown sorghum [ Sorghum bicolor (L.) Moench] was either colonized by Glomus intraradices Schenck & Smith or left non-mycorrhizal. Root length, root and shoot weight and root colonization were measured after 5, 10 and 15 weeks of plant growth. Although suboptimal root zone temperatures reduced growth in both mycorrhizal and non-mycorrhizal plants, mycorrhizal plants were larger than non-mycorrhizal plants after 15 weeks at 15 and 23 degrees C. At suboptimal root zone temperatures, mycorrhizal inoculation sometimes slightly reduced root development. AM colonization was more affected than root growth at suboptimal root zone temperatures. Colonization was markedly reduced at 15 degrees C compared with 23 degrees C, and almost completely inhibited at 10 degrees C. The second experiment was conducted in vitro using transformed carrot ( Daucus carota L.) roots supporting G. intraradices. Mycelium length and spore number were measured weekly for 15 weeks. Spore metabolic activity (iodonitrotetrazolium reduction), root length and percentage root colonization were measured after 15 weeks. G. intraradices sporulation was reduced at temperatures below 23 degrees C, while spore metabolic activity was significantly reduced only at 10 degrees C. Root length and in particular percentage colonization were decreased at suboptimal temperatures. A negative interaction between AM hyphal growth and root growth resulting in reduced probability of contact at suboptimal root zone temperatures is proposed to explain the greater reduction observed in root colonization than in root and hyphal growth.

Effect of Root Zone Temperature on Accumulation of Molybdenum and Nitrogen Metabolism in Potato Plants

Changes in root temperature caused by the application of plastic covers were studied in relation to the uptake and content of molybdenum (Mo) in the different organs of potato (Solanum tuberosum L. var. Spunta) plants (roots, tubers, stems, and leaves) and in relation to nitrogen (N) metabolism. For the semi‐forcing technique of mulching, four different covers were used: T 1 (transparent polyethylene), T 2 (white polyethylene), T 3 (coextruded black and white polyethylene), and T 4 (black polythylene). The control treatment had no mulch. The results revealed a positive and significant effect of plastic covers on root temperatures: T 0 = 16°C, T 1 = 20°C, T 2 = 24°C, T 3 = 27°C, T 4 = 30°C. These thermal differences significantly influenced the Mo concentration, particularly in the T 2 and T 3 treatments in the leaves, roots, and tubers. The same temperatures significantly altered N metabolism in both the aerial and underground parts of the plants, and a strong interrelationship was found between Mo and nitrate reductase (NR) activity. The mulching of this crop proved to be a promising technique in phytoremediation.

Effect of root-zone temperatures on morphology, growth and development, yield, and yield components of annual medics

Annual medic pastures are an effective component of ley-farming systems (cereal–legume rotations) in Australian areas with a Mediterranean climate, but they have been unsuccessful in areas near the Mediterranean Sea. In some zones with a Mediterranean climate, like Iran and Syria, root-zone temperature is considered the major growth-limiting factor for annual medic early in the growing season. In order to study the effect of low root-zone temperature (RZT) on growth and development, yield, and yield components of some annual Medicago species, an experiment was conducted in a controlled-environment chamber. In this experiment, 3 species of annual medics, namely Medicago polymorpha, M. radiata, and M. rigidula, thought to be adapted to cold and temperate conditions, were used. Four root-zone temperatures (5, 10, 15, and 20�C) were considered. The experimental layout was a completely randomised block design with 4 replications. There were differences among the annual medics for dry matter and yield components. Two species, M. polymorpha and M. rigidula, had more leaf, stem, and root dry matter, plant height, leaf and stem to root ratio, leaf to stem ratio, and leaf area and yield than M. radiata. Therefore, M. polymorpha and M. rigidula may be better suited for ley-farming systems in cold and temperate zones. The results also showed that the 5�C RZT effectively decreased the yield and yield components of the annual medics. In conclusion, application of ley-farming is not likely to be successful when RZT is below 5�C, especially during vegetative development. Therefore, in the zones where soil temperature is greater than 10�C, annual medics have normal growth and produce average yields. Ley-farming (cereal–legume rotation) could be replaced with fallow–cereal rotation.

Effects of Root Zone Temperature on Growth, Fruit Yield and Mineral Composition of &apos;Toyonoka&apos; Strawberry.

Effects of Root Zone Temperature on Growth, Fruit Yield and Mineral Composition of &apos;Toyonoka&apos; Strawberry.

ROOT ZONE TEMPERATURE EFFECT IN HYDROPONICALLY GROWN CUCUMBER PLANTS: GROWTH AND CARBOHYDRATE METABOLISM

To investigate the effect of root zone temperature (RZT) on growth and carbohydrate metabolism in hydroponically grown cucumber plants, growth parameters and major carbon metabolites in plant tissues were analyzed at 2, 4, and 6 weeks after start of the RZT treatment (10°C, 18°C or 26°C). Shoot growth significantly increased with increasing RZT but not root growth until 4 weeks. Root activity at 18°C and 26°C continuously increased throughout the experimental period, while that at 10oC sharply decreased after 4 weeks. Chlorophyll content was less affected by RZT. The amount of hexose phosphate increased as RZT was lowered. Glyceraldehyde-phosphate (PGA) slightly increased within 18°C, but greatly fell down at 26°C RZT. Higher accumulation of soluble sugars was generally observed in both leaves and roots grown at 10°C RZT. Low RZT significantly depressed starch synthesis in leaves, but stimulated starch accumulation in roots.

Effects of Root Zone Temperature and N-K Nutrition on the Growth, Flower and Pod Abscissions, Pod Production and Mineral Contents of Bush Snap Bean.

Bush snap bean cv. Torukatto was used to investigate the effects of root zone temperatures (RZTs) and N-K levels on the growth, abscissions of flowers and pods, pod production and mineral contents. The effects of RZTs were more pronounced than N-K supply on the vegetative as well as reproductive performance in this cultivar. RZTs at 20, 25 and 30°C enhanced plant growth while 35°C RZT reduced it producing plants with less vegetative growth of vine, greener leaves and smaller leaf area. Moreover, photosynthetic activity tended to increase with an increase in RZT up to 30°C in combination with either of the N-K levels. Higher number of pods was obtained from plants grown with 20, 25 and 30°C RZT. Increased total-N, Ca and Mg contents were observed in leaf blades while P was higher in the pods and K was similar in both organs. The results suggest that maintaining the root zone temperature within the range of 20 to 30°C may act more effective for growth performance regardless of N-K supply in the nutrient solution. High RZT of 35°C has an adverse effect on root growth that can lead to the death of root tissues.