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1.
The response of carob (Ceratonia siliqua L.) seedlings grown at different root zone temperatures affected by nitrate and ammonium nutrition was studied. When root temperatures ranged from 10 to 35°C, ammonium‐fed plants were significantly larger than nitrate‐fed plants. Ammonium‐fed plants displayed toxicity symptoms and were much smaller at 40°C root temperature in comparison with the nitrate‐fed plants grown at the same root temperature. Root/shoot ratio slightly increase with root temperature in ammonium‐ and nitrate‐fed plants in a similar way, and shoot demand per root unit decreased with root temperature between 15 and 25°C. There was a general increase in net photosynthesis with root temperature, though nitrate‐fed plants were more sensitive to low and ammonium‐fed plants to high temperatures. Increasing the root temperature of ammonium fed plants from 10 to 40°C leads to a 30% increase in the amount of photosynthates sent to the roots. The presence of ammonium resulted in the distribution of newly fixed carbon away from carbohydrates and into nitrogen compounds. Potassium, calcium, and nitrogen content of the plants also increased with increasing root temperature.  相似文献   

2.
A thermotolerant strain AKM-P6 of Pseudomonas sp. possessing plant growth-promoting properties was isolated from rhizosphere of pigeon pea grown under semiarid conditions in India. The effect of inoculation with AKM-P6 on survival and growth of sorghum seedlings at elevated temperatures (ET) was investigated under sterile and nonsterile soil conditions. Inoculation with strain AKM-P6 helped sorghum (var CSV-15) seedlings to survive and to grow at elevated temperatures (47–50°C day/30–33°C night) up to 15 days while uninoculated plants died by the fifth day of exposure to elevated temperature. Under sterile and nonsterile conditions, significantly higher root and shoot biomass were recorded in inoculated seedlings as compared to uninoculated control at ET, but this difference was nonsignificant at ambient temperature. Inoculation induced the biosynthesis of high-molecular weight proteins in leaves under elevated temperature, reduced membrane injury, and improved the levels of cellular metabolites like proline, chlorophyll, sugars, amino acids, and proteins. Scanning electron microscopy studies confirmed the colonization and establishment of the organism on the root surface. The 16SrDNA sequence of the strain AMK-P6 showed 97% homology with that of Pseudomonas aeruginosa in the existing database. The results indicate that Pseudomonas sp. strain AKM-P6 can enhance tolerance of sorghum seedlings to elevated temperatures by inducing physiological and biochemical changes in the plant.  相似文献   

3.
Establishment of vesicular-arbuscular mycorrhizal fungi in plant roots involves a pre-infection phase of propagule germination, hyphal growth and appressorium formation, followed by growth of the fungus within the root. The effect of soil temperature on the pre-infection stage was examined by counting the numbers of fungal “entry-points” on the main roots of Medicago truncatula and Trifolium subterraneum, grown at soil temperatures of 12°, 16°, 20° and 25°C for periods up to 12 days. Increased root temperature was positively associated with increased numbers of “entry-points”. This effect was more marked between 12° and 16°C than at higher temperatures, as shown by comparing plants at the same stage of development (emergence of spade leaf) and by calculating the results as entry points per cm root.The first root nodules appeared sooner at higher temperatures (20° and 25°), but subsequent development of nodules (measured as nodule number and aggregate volume of nodules per plant, up to 21 days) was best at 16°C for both host Rhizobium combinations in non-sterile and autoclaved soil. There was no evidence that competition between mycorrhizal fungi and Rhizobium for infection sites occurred.A method of obtaining numbers of infective propagules of vesicular-arbuscular mycorrhizal fungi in soil is described.  相似文献   

4.
Seed treatment with thiamine mononitrate significantly increased germination rate of bean (Phasenius vulgaris L.) seedlings germinated at high soil moisture levels and low night-temperature (5° C). Beneficial effects of thiamine applications on germination were also observed in soil-free germination tests when the seeds were submerged in water for 1–4 d at 18°C. Optimum response was achieved at thiamine concentrations of 3 mM, applied during the first 24 h of imbibition. As an early response to the thiamine treatment, vital staining with triphenyltetrazolium chloride revealed a lower proportion of damaged tissue of the embryonic axes. In later stages of seedling development, thiamine seed treatment resulted in a lower proportion of abnormal seedlings with malformations of the shoot apex and of the primary leaves. The beneficial effect of thiamine was more pronounced when the temperature during submergence was kept at 25° C compared to 5° C. There was no response to thiamine applications when the germinating seeds were exposed to low temperature treatments only. The thiamine effect could be mimicked by raising the osmotic potential of the incubation medium, indicating a relationship to soaking injuries. The results suggest that normal seedling development may be impaired by thiamine deficiency in the embryonic tissue induced by soaking injury, whereas low temperatures are not involved as a stress-factor.  相似文献   

5.
Siberian C peach seedlings (Prunus persica L. Batsch) were grown for 35 days in all combinations of Long Ashton nutrient solution containing P concentrations of 0.05, 0.5, or 5.0 mM and root zone temperatures (RZT) of 8°C, 16°C, and 24°C. At harvest, a significant interaction between solution P concentration and RZT occurred for shoot and root dry weight, root length, shoot P concentration and shoot P uptake. At 8°C RZT, P concentration and uptake but not growth were increased by P. At 16°C and 24° C RZT, growth was depressed at the 5.0 mM P level with shoot P concentration and uptake lower at 24°C than 16°C. The inflow of P to the peach shoot per unit root length was increased at high P concentration and low temperatures but was lower than whole plant inflow rates for apples. The growth depression at high temperature‐high P was related to increased young leaf chlorosis, reduced shoot Fe and a possible P/Zn imbalance.  相似文献   

6.
Bleaching in stony-corals is the result of disruption of symbiosis between the coral hosts and photosynthetic microalgal endosymbionts (zooxanthellae). Coral bleaching events of unprecedented frequency and global extent have been reported during the last two decades. Recently, we demonstrated that bleaching of the coral Oculina patagonica in the Mediterranean Sea is caused by the bacterium Vibrio shiloi, when seawater temperature rises and allows the bacterium to become virulent. The first step in the infection process is host-specific adhesion of V. shiloi to O. patagonica via a β-galactoside receptor on the coral surface. The bacterium then penetrates into the coral tissue and produces extracellular materials which rapidly inhibit photosynthesis of zooxanthellae and bleach and lyse the algae. The inhibition of pothosynthesis is due to a low molecular weight, heat stable toxin and ammonia. Bleaching and lysis are due to a heat-labile, high molecular weight materials, probably lytic enzymes. Elevated temperature induces different virulence factors within the infectious agent of the disease, V. shiloi. Adhesion was found to be temperature-regulated. When the bacteria were grown at 16°C there was no adhesion to corals maintained at either 25°C or 16°. However, when the bacteria were grown at 25°C they adhered avidly to corals maintained at 16°C and 25°C. In addition, the production of lytic enzymes and the photosynthesis inhibitor was also found to be temperature dependent. Production of the latter toxin was ten times greater at 29°C than at 16°C, and extracellular protease was 5-fold higher in cultures grown at 29°C than at 16°C. The data presented here suggest an explanation for the correlation between elevated seawater temperatures and seasonal coral bleaching.  相似文献   

7.
The nutrient uptake and allocation of cucumber (Cucumis sativus L.) seedlings at different root-zone temperatures (RZT) and different concentrations of nitrogen (N), phosphorus (P), and potassium (K) nutrients were examined. Plants were grown in a nutrient solution for 30?d at two root-zone temperatures (a diurnally ?uctuating ambient 10°C-RZT and a constant 20°C-RZT) with the aerial parts of the plants maintained at ambient temperature (10°C–30°C). Based on a Hoagland nutrient solution, seven N, P, and K nutrient concentrations were supplied to the plants at each RZT. Results showed that total plant and shoot dry weights under each nutrient treatment were significantly lower at low root-zone temperature (10°C-RZT) than at elevated root-zone temperature (20°C-RZT). But higher root dry weights were obtained at 10°C-RZT than those at 20°C-RZT. Total plant dry weights at both 10°C-RZT and 20°C-RZT were increased with increased solution N concentration, but showed different responses under P and K treatments. All estimated nutrient concentrations (N, P, and K) and uptake by the plant were obviously influenced by RZT. Low root temperature (10°C-RZT) caused a remarkable reduction in total N, P, and K uptake of shoots in all nutrient treatments, and more nutrients were accumulated in roots at 10°C-RZT than those at 20°C-RZT. N, P, and K uptakes and distribution ratios in shoots were both improved at elevated root-zone temperature (20°C-RZT). N supplies were favorable to P and K uptake at both 10°C-RZT and 20°C-RZT, with no significantly positive correlation between N and P, or N and K uptake. In conclusion, higher RZT was more beneficial to increase of plant biomass and mineral nutrient absorption than was increase of nutrient concentration. Among the three element nutrients, increasing N nutrient concentration in solution promoted better tolerance to low RZT in cucumber seedlings than increasing P and K. In addition, appropriately decreased P concentration favors plant growth.  相似文献   

8.
Lactuca sativa L. plants were grown at three root-zone temperatures (RZTs): 25°C, 30°C and ambient RZT (A-RZT) on an aeroponic system. Three potassium (K) concentrations: ?25% (minus K), control (standard K), and +25% (plus K) were supplied to plants at each RZT. Plants grown at the plus K and 25°C-RZT had the highest productivity, largest root system and highest photosynthetic capacity. The minus K plants at 25°C-RZT had the highest shoot soluble carbohydrate (SC) concentration, but they had the highest root SC concentration in the plus K plants at A-RZT. However, the highest starch concentration was found in both shoots and roots of the plus K plants at 25°C-RZT. The plus K plants had the highest shoot K concentration at 25°C-RZT, but they had the highest root K concentration at A-RZT. Highest proportion of absorbed K was partitioned to shoots when the plants were grown with the plus K at 25°C-RZT.  相似文献   

9.
Uptake and translocation of sodium in two cultivars of Lolium perenne The uptake and translocation of Na was investigated in two Lolium perenne cultivars (Dolewi and NFG). With increasing Na+ concentration in the nutrient solution (0, 1, 2 and 4 mMNa) the Na+ uptake per pot increased from 1.4 to 11.9 me/1 Na+ for Dolewi and from 1.1 to 6.9 me/l Na+ for NFG. The higher Na uptake by Dolewi can only partly be explained by better growth, the higher Na+ selectivity playing also an important role. In another experiment plants of both types were grown in solution cultures for 41/2 weeks at 15°C and 25°C, respectively. Hereafter the plants were supplied with 1.25 mM 24NaCl for six hours under equal conditions. Again the higher Na uptake and also a higher Na translocation (of about 20%) was found in Dolewi, whereas only 10% of the 24Na uptake had been translocated by NFG. When plants were grown in a nutrient solution with a lower temperature (at 15°C) the root lipids showed a higher linolenic acid and oleic acid content than the plants grown in a medium at 25°C. At the same time the 24Na uptake was higher in the plants grown at the lower temperature, yet the relationship between root lipids and Na uptake still remains to be elucidated.  相似文献   

10.
The effect of a rhizosphere microflora on some morphological and physiological plant characteristics was studied with maize seedlings grown for five days in a mineral nutrient solution. In the presence of the microorganisms the root dry weight is lower than that of axenically grown plants due to a smaller diameter of the primary root. In addition, the root content of some vitamins and sugars is affected. Pure cultures of rhizosphere bacteria were isolated and their influence on morphological characteristics of the maize plant was classified. Whereas one culture retards the overall plant development, the remaining nine cultures exert a significant influence only on specific morphological parameters. These results are discussed as an indication of the participation of phytohormones in interactions between roots and bacteria.  相似文献   

11.
Influence of root temperature on the uptake of 28Mg, 86Rb and 45Ca by barley seedlings. The influence of root temperature on the uptake and transport of Mg(28Mg), K(86Rb) and Ca (45Ca) by barley seedlings was investigated. Rates of uptake and transport into barley shoots were lower at root temperatures of 5° and 15°C than at 25°C. This temperature effect was particularly pronounced with K. The uptake of Ca and its transport into the shoots was affected only at the low concentration of 0,25 meq/1 and was only noticeable after a period of 12 h exposure. The effect on Mg ranged between that of K and Ca. The length of time of the experiment, the concentration and composition of the nutrient solution influenced the temperature effect to a considerably greater extent with K than with Ca or Mg. The strong dependence of K uptake on root temperature is indicative of an active uptake and transport of K. In contrast to K the transport of Mg and Ca was apparently dependent on the transpiration stream. With decreasing root temperatures Mg but not Ca can take advantage of unutilized carrier capacities.  相似文献   

12.
Abstract

Milk thistle [Silybum marianum (L.) Gaertn] is an annual plant belonging to the Asteraceae family whose ripe seeds contain flavonoid substances, which are important in the modern pharmaceutical industry. Seed germination is a major factor limiting the establishment of plants under saline conditions. The effect of salinity and temperatures on germination and seedling establishment was studied in two genotypes of milk thistle, an Iranian wild type and German (Royston) type in the laboratory and in the field. Experiments were done with seven salt concentrations [0.1 (control), 1, 3, 6, 9, 12, and 15 dS/m] and three temperatures (15, 25, and 35°C). There were three replications for each treatment, and the experiment was run three times. The results showed that the percentage of germination and the number of normal seedlings at different salt treatment at 15°C were higher than at 25 or 35°C. The mean time to 50% germination was least at this temperature for both genotypes. Results suggested all germination indices and seedling emergence (50%) were achieved at levels up to 9 dS/m salinity at 15°C. Also, seeds at a salinity of 9–15 dS/m will germinate and up to 25% of the control nonstress treatment could emerge at the low temperature of 15°C.  相似文献   

13.
The effects of high growth temperature on sorghum starch structures were examined from the grains of three inbred lines (BTx623, IS8525, and Karper669), and the possible mechanism by which the growth of amylopectin molecules is terminated was discussed. Sorghum plants were grown at high temperature (38/21°C day/night) and control temperature (32/22°C day/night) from sowing to maturity. The grains sampled from plants grown at high temperature had significantly lower starch weights per grain (except BTx623) and smaller starch granule sizes than those grown at control temperature. Nevertheless, the amylose contents were similar. BTx623 and IS8525 samples grown at high temperature also had higher ratios of long to short amylopectin branches and lower degree of branching than their control counterparts. These results suggested that the activities of starch biosynthetic enzymes were evidently affected by elevated growth temperature. However, the weight‐average molecular weight and the z‐average radius of gyration of sorghum starch molecules were not significantly affected by the growth temperatures, suggesting that the effects of growth temperature on starch yield, starch granule size, and the branching structure of amylopectin molecules did not influence the events that stopped the overall growth of amylopectin molecules. This observation was consistent with the cessation of whole‐molecule growth being through increasing hindrance to enzyme access as the size of the starch molecule increases, controlled largely by the molecular density of the outermost part of an amylopectin molecule.  相似文献   

14.
The effects of different temperature treatments during the seedling stage on growth and nutrient absorbance of Gerbera jamesonii cv ‘Sunshine Coast’ growing in the organic substrate were investigated. The temperature treatments were conducted in growth chamber where the day/night temperature were set to 15/10, 20/15, 25/20, and 30/25°C individually. The results showed that the fresh and dry weight of aboveground part and that of roots, average number of leaves and lateral roots were greater at 30/25°C than other treatments. The highest level of macro elements nitrogen (N), phosphorus (P), and potassium (K) in the leaf samples were also detected at 25/20°C and 30/25°C. However, there was no significant influence of different temperatures on zinc (Zn) levels in leaves. In general, the day temperature 25～30°C and night temperature 20～25°C are thought to be the better temperature condition for gerbera growth as well as the nutrient uptake and accumulation in the plants during the seedling stage.  相似文献   

15.
The population dynamics of Salmonella enterica var. Typhimurium MAE 110 gfp, Escherichia coli O157:H7 gfp, and Pseudomonas fluorescens 32 gfp were investigated in their introduction to cattle excrements and subsequent entering the soil, plants of cress (Lepidium sativum L.), and migration through the gastroenteric tract of French snails (Helix pomatia L.). The survival of these bacteria in the excrements and soil was investigated at cyclically changing (day-night, 25–15 °C) and constant (18 °C) temperatures. The cyclically changing temperature adversely affected the survival of E. coli O157:H7 gfp, and P. fluorescens but did not influence S. enterica var. Typhimurium. All the bacteria and, especially, the analogues of enteropathogens showed high survival in the cattle and snail excrements, soil, and on the plants under the gradual decrease in their population. On the cress plants grown in a mixture of cattle excrements and soil, an increase in the number of the introduced bacteria was observed.  相似文献   

16.
The effect of nitrogen addition on the activity of rhizosphere bacteria was studied using barley seedlings. Three different nitrogen sources were added to the soil (nitrate, ammonium and ammonium+nitrate) at four different concentrations (0, 100, 300 and 500 mg N kg−1 soil) and the plants were allowed to grow for 6 weeks. The bacterial activity was estimated by measuring thymidine and leucine incorporation into bacteria extracted using homogenisation-centrifugation. Bulk soil bacterial activity was low compared with that of rhizosphere bacteria. Nitrogen addition did not affect the activity of the bulk soil bacteria, indicating that the activity was not nitrogen limited. The thymidine and leucine incorporation rates of rhizosphere bacteria decreased when ammonium or ammonium+nitrate was applied compared with the non-amended controls. No effect on bacterial activity was found following nitrate addition. There was a significant positive correlation between rhizosphere bacterial activity and rhizosphere pH. Shoot length following ammonium treatment was significant lower than in the non-amended control, while nitrate and ammonium+nitrate addition had no effect. This indicates that the varying effects due to nitrogen sources on rhizosphere bacterial activity were not due to effects on plant growth.  相似文献   

17.
Tomato (Lycopersicon esculuntum Mill.) grown in open fields in dry land areas or in non‐controlled greenhouses are subjected to substantial daily changes in root temperature. In the field, root‐zone temperatures fluctuate both diurnally and during the growing season. The purpose of this study was to monitor root‐zone temperature effects on tomato initial growth, transpiration, sap flow rate, leaf and air temperatures differences, nitrate accumulation, total nitrogen, and soluble carbohydrates in the shoot and roots as well as levels of endogenous cytokinins and gibberellins in xylem exudate. Tomato seedlings were grown in three growth cabinets with variable control of root temperatures. Three day/night root temperature regimes (12/12, 16/8 and 20/20°C) were employed. Low day root temperatures of 12 and 16°C reduced shoot dry weight by 47 and 26%, root dry weight by 36 and 14%, shoot nitrate by 79 and 50%, root nitrate by 49 and 16%, levels of cytokinins in root xylem exudate by 27 and 13% and gibberellins by 65 and 23%, in relation to the respective values of 20°C day root temperature. Soluble carbohydrates in the shoot and roots were increased significantly (18 and 111%) by 12°C root temperature. The main effects of low root temperatures on shoot growth stem from slow upward transport of plant hormones and nitrate rather than reduction in their rate of biosynthesis or entry to the root, respectively.  相似文献   

18.
Early season problems with growth of corn (Zea mays L.) under cool, wet conditions prompted a study of the effects of soil and environmental conditions on mineralization and plant uptake of phosphorus (P). Our objective was to determine the effect of soil test P, temperature, and soil fumigation on soil P availability and uptake during early corn growth. Corn was grown in growth chambers at temperatures of 14°C or 25°C. Soils were a high‐P Hastings silty clay loam (fine, montmorillonitic, mesic Udic Argiustoll) and a low‐P Sharpsburg clay loam (fine, montmorillonitic, mesic Typic Argiudoll). Plants grew for up to 42 d either in soil which had been fumigated with methyl bromide to reduce microbial populations or left unfumigated. We harvested whole pots for soil and plant analysis at 1, 14, 28, and 42 d after planting. Biomass carbon (C) and biomass P were lower in fumigated soils and biomass C increased with time. Fumigation increased Bray Pl‐extractable P at all times. Phosphatase activity and mycorrhizal colonization were both reduced by fumigation. Cumulative plant P uptake was highest in Hastings at 25°C. Higher temperature and higher initial P status increased plant P uptake during early growth. Plants grown in fumigated soil did not take up more P, despite greater extractable P.  相似文献   

19.
Six potato genotypes were tested to evaluate the effect of K nutrition on frost tolerance by measuring electrolyte leakage from leaves exposed to various freezing temperatures. Potato genotypes were selected through the known range of low temperature survival tolerance within tuber‐bearing Solanum species. An experiment was conducted using a soil high in K; and then nutrient solution experiments were conducted in the open environments of La Molina. Commercial K fertilizers, at different levels, were unable to increase significantly the frost tolerance in a common potato cultivar grown in a soil high in K. In nutrient solutions experiments, with plants grown without any hardening process, we found that there is a genetically related capacity to respond through K nutrition to increase frost tolerance among potatoes. The common commercial potato, S. tuberosum, did not change significantly its freezing sensitivity when K nutrition was varied. But S. curtilobum, which is grown by low income farmers in the Titicaca Lake area of Bolivia and Peru, especially reduced its sensitivity to frost tolerance when submitted to K deficiency by as much as 1.5 to 2°C. Leaf free proline does not accumulate as a result of K deficiency but all the K deficient plants had lower amounts of free proline. The K deficient plants also showed a lower induced nitrate reductase activity.  相似文献   

20.
Loss on ignition (LOI) is one of the most widely used methods for measuring organic matter content in soils but does not have a universal standard protocol. A large number of factors may influence its accuracy, such as furnace type, sample mass, duration and temperature of ignition and clay content of samples. We conducted a series of experiments to quantify these effects, which enabled us to derive (i) guidelines for ignition conditions (sample mass, duration and temperature), (ii) temperature‐specific soil organic matter (SOM) to soil organic carbon (SOC) conversion factors and (iii) clay content‐dependent correction factors for structural water loss (SWL). Bulk samples of a sandy soil (4% clay) and a silt loam soil (25% clay) were used to evaluate the effects of ignition conditions. Samples with a range of clay contents (0–50%) were used to quantify conversion and correction factors. Two furnaces, one without and one with pre‐heated air, did not show significant differences in terms of within‐batch LOI variability. In both furnaces less combustion occurred close to the door, which necessitated tray turning at half‐time as this reduced the standard deviation per batch significantly. Variation in mass loss declined exponentially with sample mass (range, 0.15–20 g). The LOI increased with duration at lower temperatures (≤ 550°C) for the sandy soil. At greater temperatures (600 and 650°C), no effect of duration was found. For the silt loam soil, LOI values increased with duration for each temperature, which was attributed to SWL. The SOM to SOC conversion factor decreased strongly with temperature at an ignition duration of 3 hours from 0.70 (350°C) to 0.57 (500°C) and stabilized around 0.55 between 550 and 650°C, indicating that at temperatures ≥ 550°C all SOM had been removed. The clay correction factor for SWL increased from 0.01 to 0.09 as the temperature of ignition increased from 350 to 650°C. To minimize within‐batch LOI variation we recommend a standard ignition duration of 3 hours, tray turning at half‐time, a sample mass ≥ 20 g and temperatures equal to or greater than 550 °C. To avoid over‐estimates of SOM through structural water loss, the presented SWL correction procedure should always be applied.  相似文献   

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