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1.
Tomato (Lycopersicon esculentum L. Mill. ‘Vendor') plants were grown for 21 days in flowing solution culture with N supplied as either 1.0 mM NO3 ‐ or 1.0 mM NH4 +. Acidity in the solutions was automatically maintained at pH 6.0. Accumulation and distribution of dry matter and total N and net photosynthetic rate were not affected by source of N. Thus, when rhizosphere acidity was controlled at pH 6.0 during uptake, either NO3 ‐ or NH4 + can be used efficiently by tomato. Uptake of K+ and Ca2+ were not altered by N source, but uptake of Mg2+ was reduced in NH4 +‐fed plants. This indicates that uptake of Mg2+ was regulated at least partially by ionic balance within the plant.  相似文献   

2.
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   

3.
The central moments of soil water content (SWC) variability at the field scale are determined by soil texture, considering both smooth topography and groundwater table position. The characteristics of variability are governed by other soil factors like soil structure, micro relief, preferred water flow paths, root system characteristics, rock content, etc. This paper shows the integral effect of all these hardly quantifiable factors on SWC variability simulated by the processes of evapotranspiration and groundwater–root zone interaction using the HYDRUS ET model. SWC and soil hydraulic characteristics were spatially determined over a 4.5 ha field during two sampling campaigns under different atmospheric and groundwater conditions, and data distributions were compared to SWC distributions provided by mathematical modeling. The entire spring–summer period of 2003 was then examined for changes of SWC spatial variability. It was found that evapotranspiration influences SWC spatial variability only if SWC is under the critical value when wetter parts of the field evaporate more water than drier parts, resulting in smoothed SWC variability. Under wet conditions the spatial variability of SWC increases by drainage, as those parts of the soil with coarser texture drain faster than finer-textured parts.  相似文献   

4.
Wheat (Triticum aestivum L. cv (9733) seedling (10 day) root length was decreased 60% when plants were watered with 0.01M sodium acetate (NaAc) pH 4.5 in comparison to plants exposed to the same NaAc concen‐ tration at pH 6.0. 3‐indoleacetic acid (IAA) (10‐10 and 10‐9M) (incorporated into the sand potting medium) reversed the excess hydrogen ions (H+) influence.  相似文献   

5.
One‐year‐old rooted cuttings of Vitis vinifera L. cv. Pinot blanc clone 55, grafted on “S.O.4” and “41 B” hybrid rootstocks, were grown in pots containing a calcareous soil. Before potting, the roots were infected by the VAM fungus (Glomus mosseae) and by a suspension of the following endophytic bacteria: Erwinia sp., Pseudomonas fluorescens, Enterobacter cloacae. The shoot growth was checked every ten days and leaf blade chlorophyll and mineral elements were assayed at the middle of the annual growing cycle as well as the mineral composition of the leaf petiole. Chlorosis was rated by visual screening as well in order to control the effect of the root treatments on the chlorosis occurrence. The most significant findings of the trial were: a) root infection with Erwinia sp. and Pseudomonas fluorescens increased the chlorophyll concentration over the untreated plants in both the graft combinations, b) the plants grafted on “S.O.4” rootstock did benefit from the treatment with Glomus mosseae as well, and c) root infection with Enterobacter cloacae depressed growth and chlorophyll concentration in both the graft combinations.  相似文献   

6.
The growth of sesame (Sesamum indicum L.) was studied at three root temperature regimes (25/25, 20/10 and 15/15°C day/night) factorially combined with three NO3 ‐: NH4 + ratios (mM ratios, 10:0, 8:2, or 6:4), as a source of nitrogen (N), in the irrigation solution. The air temperature was kept constant at 30°C. Transpiration, nutrient composition, and level of root‐born cytokinins and gibberellins in the xylem exudate were monitored. The two low root temperature regimes, 15/15 and 20/10°C, restricted the growth of sesame, reduced transpiration and increased the accumulation of soluble carbohydrates in the shoot and in the roots compared to the 25/25°C regime. The NO3:NH4 + ratios had no effect on growth. Nutrient contents in the shoot at low root temperatures, particularly K+, NO3 ‐, and H2PO4 ‐ were decreased markedly, but Na+ increased relative to it's content in the 25/25°C regime. Increasing NH4 + proportion in the irrigation solution raised total N concentration in the plant tissues at all root temperatures. The amounts of cytokinins and gibberellins in the xylem exudate decreased at the low root temperature regimes relative to the 25/25°C regime. Low root temperature reduced xylem transport of nutrients and root born‐phytohormones, most probably because of reduced water flow through the plant relative to the 25/25°C regime.  相似文献   

7.
Abstract

A method was devised in which plant roots can be easily and uniformly radiolabelled with 14C for use in soil decomposition studies. The roots were labelled from an exogenous sugar solution for a total period of 48 hours after which root decomposition studies could be performed. The method offers distinct advantages over the existing constant 14C‐CO2 atmosphere labelling method.  相似文献   

8.
Cassava is a root crop that serves as a primary caloric source for many African communities despite its low content of β-carotene (βC). Carotenoid content of roots from wild type (WT) and three transgenic lines with high βC were compared after cooking and preparation of nonfermented and fermented flours according to traditional African methods. The various methods of processing all decreased βC content per gram dry weight regardless of genotype. The greatest loss of βC occurred during preparation of gari (dry fermentation followed by roasting) from WT and transgenic lines. The quantities of βC in cooked transgenic cassava root that partitioned into mixed micelles during in vitro digestion and transported into Caco-2 cells were significantly greater than those for identically processed WT root. These results suggest that transgenic high βC cassava will provide individuals with greater quantities of bioaccessible βC.  相似文献   

9.
Abstract

Tobacco (Nicotiana tabacum L., cv. ‘Coker 319') plants were grown for 28 days in flowing nutrient culture containing either 1.0 mM NO3 ‐ or 1.0 mM NH4 + as the nitrogen source in a complete nutrient solution. Acidities of the solutions were controlled at pH 6.0 or 4.0 for each nitrogen source. Plants were sampled at intervals of 6 to 8 days for determination of dry matter and nitrogen accumulation. Specific rates of NO3 ‐ or NH4 + uptake (rate of uptake per unit root mass) were calculated from these data. Net photosynthetic rates per unit leaf area were measured on attached leaves by infrared gas analysis. When NO‐ was the sole nitrogen source, root growth and nitrogen uptake rate were unaffected by pH of the solution, and photosynthetic activity of leaves and accumulation of dry matter and nitrogen in the whole plant were similar. When NH4 + was the nitrogen source, photosynthetic rate of leaves and accumulation of dry matter and nitrogen in the whole plant were not statistically different from NO3 ‐ ‐fed plants when acidity of the solution was controlled at pH 6.0. When acidity for NH4 + ‐fed plants was increased to pH 4.0, however, specific rate of NH4 + uptake decreased by about 50% within the first 6 days of treatment. The effect of acidity on root function was associated with a decreased rate of accumulation of nitrogen in shoots that was accompanied by a rapid cessation of leaf development between days 6 and 13. The decline in leaf growth rate of NH4 + ‐fed plants at pH 4.0 was followed by reductions in photosynthetic rate per unit leaf area. These responses of NH4 + ‐fed plants to increased root‐zone acidity are characteristic of the sequence of responses that occur during onset of nitrogen stress.  相似文献   

10.
Abstract

Aluminum (Al)–humus complexes are abundant in the A horizons of non-allophanic Andosols and contribute to the unique properties of volcanic ash soils, such as high reactivity with phosphate ions and a low bulk density. Natural non-allophanic Andosols commonly show Al toxicity to plant roots. There have been very few studies examining the contribution of Al–humus complexes to the Al toxicity of plant roots, although the complexes are the probable source of the toxic Al. We extracted humic substances from the A horizon of a non-allophanic Andosol using NaOH solution and reacted the humic substances and partially neutralized the AlCl3 solution at three pH conditions (pH 4.0, 4.5 and 5.5) to prepare pure Al–humic substance complexes. The Al solubility study (equilibrium study in 10?2 mol L?1 CaCl2) and the Al release study (a stirred-flow method using 10?3 mol L?1 acetate buffer solution adjusted to pH 3.5) indicated that all the synthetic complexes easily and rapidly release monomeric Al into the liquid phase with slight changes in pH and ion strength, although the Al contents and their extent of polymerization are considerably different among the complexes. A plant growth test was conducted using a medium containing the Al–humic substance complexes and perlite mixture. Root growth in burdock (Arctium lappa) and barley (Hordeum vulgare L.) was reduced equally by all three complex media, and the roots showed the typical injury symptoms of Al toxicity. These results indicate that in soils dominated by Al–humus complexes the Al released from the Al–humus complexes, as well as the exchangeable Al adsorbed by soil minerals, is definitely toxic to plant roots.  相似文献   

11.
Controlled‐release urea is a fertilizer which meters out urea over a long period of time. It can provide a favorable nitrogen (N) concentration for root growth, especially at the early stage of plant development. The objective of this study was to determine the interactions of urea or controlled‐release urea granules with barley roots and the resultant N uptake by plants. Two experiments (Experiment I and Experiment II) with treatments of Nil, non‐coated urea, Coated I and Coated II (Coated I and Coated II are controlled‐release urea products) were conducted in a greenhouse at 23±5°C. In both experiments, one barley (Hordeum vulgare L. cv. Duke) seed and one granule of urea or controlled‐release urea were placed in a pot (5.2‐cm height and 8‐cm diameter) containing soil low in mineral N. In Experiment I, shoot and soil samples were taken at 14, 28, and 46 days after seeding. Roots and fertilizer interaction were visually examined and photographed. In Experiment II, root samples both around the fertilizer granule and away from the granule were taken only at 28 days after seeding. In both experiments, dry matter mass and total N content of shoot and root, and mineral N in soil were determined. In Experiment I, at the 28‐day sampling roots proliferated around the controlled‐release urea granule but not around the urea granule. Shoot N uptake since the 28 days was higher with controlled‐release urea than with urea because of the root proliferation. In Experiment II, root dry mass and N content around the granule was higher with controlled‐release urea than with urea. In the controlled‐release urea treatments, root mass and N content away from the granule were also increased in comparison to the Nil. This shows a stimulus relationship between the two portions of the roots in the same plant, i.e., the roots being accessed to the N source increased growth of the other roots with no access to the source. Because only a small portion of roots was involved in N uptake in the controlled‐release urea treatments, the intensity of N uptake per unit of root mass was much higher with controlled‐release urea as compared to urea. In conclusion, root growth was enhanced around controlled‐release urea granule, and that portion of roots around the fertilizer granule played a major role in absorbing N. In addition, a stimulus relationship existed between roots grown around the granule and those grown away from the granule.  相似文献   

12.
The diurnal pattern in concentrations of phytosiderophores (PS) and its precursor nicotianamine (NA) was studied in different root and shoot zones of iron (Fe)‐sufficient and Fe‐deficient barley (Hordeum vulgare L. cv. Europa) grown in nutrient solution. Roots were separated into apical (0–3 cm) and basal zones (>3 cm) and shoots into young (3 cm basal zones of youngest two leaves) and old (remaining zones of youngest two leaves and oldest leaf) parts. The main PS in barley was identified as epi‐hydroxymugineic acid (epi‐HMA). Regardless of the sampling zone and time of day, epi‐HMA concentrations were several times higher in Fe‐deficient than in Fe‐sufficient plants and several times higher in the roots than in the shoots. In roots and shoots, epi‐HMA concentrations were always higher in the younger compared with the older zones. In both root zones of Fe‐deficient plants, an inverse diurnal rhythm occurred in epi‐HMA concentrations and in its release by the roots. In contrast, such a rhythm was absent in roots of Fe‐sufficient plants and in the shoots regardless of the Fe nutritional status. Nicotianamine concentrations in roots were not affected by the Fe nutritional status in apical zones but slightly enhanced under Fe deficiency in basal zones. In contrast to roots, NA concentrations in both shoot parts were lower in Fe‐deficient than in Fe‐sufficient plants. Regardless of the Fe nutritional status in roots and shoots, NA concentrations were higher in young than in old parts and no consistent diurnal variations were observed. The results suggest that PS are also synthesized in the shoot, although at much lower rates than in roots. As with roots, PS synthesis in the shoot is enhanced under Fe deficiency and is mainly localized in young growing tissue. The distinct diurnal rhythm in PS release in roots is apparently not regulated by variation in the rate of PS synthesis during the day.  相似文献   

13.
Soybean plants (Glycine max L. cv Santa Rosa) grown hydroponically in nutrient solutions had reduced nodule mass and numbers in the presence of aluminum (Al). Reduced nodule number was attributed mainly to hydrogen (H) ion toxicity, whereas Al had a stronger effect on nodule growth. Using a vertical split‐root system with Al exclusively in the lower (hydroponic) layer also resulted in a significant reduction of nodulation and nodule growth in the surface compartment (vermiculite). This indirect effect could be attributed mainly to Al rather than H. Subsurface Al had no apparent effect on shoot growth or root growth of the upper compartment, but significantly limited root growth in the lower compartment where it was applied. The indirect effect of Al on nodulation could be a reflection of the abnormal root growth in the lower compartment. Split‐root experiments with a high Al soil, however, produced different effects. High Al in soil used exclusively in the lower compartment did not reduce nodule numbers or mass in the upper compartment despite being more harmful than the Al solutions to nodulation and growth of plants when used in a single compartment. Growth of roots in the subsurface compartment was also much less affected by the high soil Al compared with the Al‐containing nutrient solutions. Nodule activity, as estimated by xylem sap ureide levels, was only reduced after direct exposure of nodules to Al. A pronounced increase in the ratio of asparagine/glutamine occurred in all Al treatments where nodulation was reduced, and in some cases, there was an increase in total amino acid concentration of the xylem sap.  相似文献   

14.
Exposing 12‐day‐old soybean plants to 0.2 ppm nitrogen dioxide (NO2) for four weeks increased the nitrite concentration and acidity, and decreased the Leghemoglobin (LHb) concentration and the nitrogenase activity of root nodules. The supply of 1 mol.m‐3 nitrate to the roots intensified the nitrite accumulation, decreased the acidity of the nodules, and alleviated the inhibition of nitrogenase activity by NO2 fumigation. These results suggested that the inhibition of nitrogen (N2) fixation by N fertilizer supply might relate to the acid‐alkali balance in nodules.  相似文献   

15.
Abstract

Chemical and biological lime requirement (LR) reference values of 154 soils were obtained by six months of incubation of each soil with five levels of calcium carbonate (CaCO3). Levels of CaCO3 addition differed among soils according to their characteristics. Chemical LR values were based on the individual neutralization curves to achieve a desired pH (pHd) value of 5.5, 6.0, and 6.5 in water or 5.0, 5.5, and 6.0 in 0.01M calcium chloride (CaCl2). Biological LR values were estimated to achieve 90% relative root elongation on each soil after a growth period of 48 h using wheat cv Abe. Chemical values of LR suggest that SMP method is valid for a wide range of mineral soils from different geographic regions. However, the proportion of soil acidity reacting with the buffer is not constant. Results indicate that values obtained with the routine methods need to be calibrated with equations different from the originals. The use of curvilinear models to adjust one single pH of the soil‐buffer system improved substantially its accuracy, allowing the single‐buffer (SB) results to be comparable to the more time consuming and labourious double‐buffer (DB) technique. No advantage was noticed with the use of curvilinear equations for DB technique. The adoption of pHd in 0.01M CaCl2 leads to an increase of precision of the predicted LR. Regression equations are provided for calculating LR rates to different pHd values. Accuracy is high (r2=0.887) even for pH values (5.0 in 0.01M CaCl2) lower than normally considered in methods based on buffer solutions. An overestimation of biological LR values was observed with both SMP methods. Notwithstanding, a calibration can be also made with the root bioassay, adjusting the chemical values to lime rates based on biological constraints related with aluminum (Al) toxicity. Regression equations are provided. Once more, the use of quadratic model for SB method allows an accuracy (r2=0.836) comparable with the DB technique (r2=0.850).  相似文献   

16.
Abstract

Groups of “Kallar”; grass plants were subjected to various treatments of 100 mM NaCl simultaneously labelled with 22Na+ and 36Cl?. On the basis of the specific activity, the distribution of Na and Cl? in the tissue was followed during and after treatment, i.e. after transfer of some groups to an identical but inactive solution. Sequential collections of leaf washes showed that both Na and Cl? were extruded at a somewhat constant rate. Leaf sheaths accumulated more Na+ and Cl? than the leaf blades and the amounts of Na+ and Cl? in the leaf sheaths as a percentage of their total plant content (i.e. 28% and 31%) approximated the amounts of Na and Cl? extruded by the leaves (i.e. 23%). Moreover, almost equivalent amounts of Na+ (21%) and Cl? (29%) were removed by root efflux which continued even several days after transfer of the plants to the inactive, saline solution. Part of the Na+ and Cl? was retranslocated from the tops to the roots and was attributed to phloem export.

Tolerance of Kallar grass to NaCl was thus related to preventing the tissue from accumulating high concentration by extrusion of both Na+ and Cl? by the leaves and their efflux by the roots in addition to an equivalent retention in the leaf sheaths.  相似文献   

17.
Mineral nutrient absorption by 1‐cm root tips of Sorghum bicolor (L.) Moench. cv GP‐10, SC283, SC574, and/or Funk GS22DR from a 1‐hr exposure to Hoagland and Arnon complete mineral nutrient solution in the presence of diltiazem (0,10 mM), nifedipine (0,10 mM), or SITS (0, 1 mM) was evaluated using inductively coupled plasma emission photometry (ICP). Calcium (Ca2+) ‐ channel blockers (i.e. ‐ diltiazem, nifedipine, and verapamil) and PCMBS induced significantly decreased quantities of Ca2+ in root tips but the anion channel blocker, SITS, did not induce any response in Ca2+ uptake. Responses of phosphorus (P), zinc (Zn), boron (B), manganese (Mn), iron (Fe), magnesium (Mg), and copper (Cu) to all of the ion uptake modifiers were highly variable between the cultivars with increased, decreased, or no influence on ion uptake. As yet unrecognized multiple mechanisms of ion uptake through the root plasma membrane are necessary to explain the date.  相似文献   

18.
Tobacco plants (Nicotiana tabacum L. cv NC82) were supplied with (NH4)2SO4, or NH4Cl at root‐zone pH of 6.0 and 4.5 in hydroponic culture for 28 days. Dry matter accumulation, total N and C content, and leaf area and number were not affected by the NH4 + source or root‐zone pH. Plants supplied with NH4C1 accumulated up to 1.2 mM Cl g DW‐1, but accumulated 37% less inorganic H2PO4 ‐ and 47% less SO4 2‐ than plants supplied with (NH)2SO4. The large Cl‐ accumulation resulted in NH4C1 –supplied plants having a 31% higher inorganic anion (NO3 ‐, H2, PO4 ‐, SO4 2‐, and Cl‐) charge. This higher inorganic anion charge in the NH4C1‐supplied plants was balanced by a similar increase in K+ charge. Plants supplied with NH4Cl accumulated greater concentrations of Cl‐ in leaves (up to 5.1% of DW) than plants supplied with (NH4)2SO4 (less than ‐% DW). Despite the high Cl‐ concentration of leaves in NH4Cl supplied plants, these plants showed no symptoms of Cl‐ toxicity. This demonstrates that toxicity symptoms are not due solely to an interaction between high Cl‐ concentration in tissue and NH4 + nutrition. The increase in root‐zone acidity to pH 4.5 from 6.0 did not induce toxicity symptoms.  相似文献   

19.
Typical for the morainal landscape of NE‐Germany are catenas with pronounced gradients of abiotic factors, such as soil texture and organic matter content. For adequate management of these regions, their ecology must be better understood. In this context, the biological interactions in soil play an important role. The present study is based on the hypothesis that the gradients of abiotic factors across the catena are reflected in soil biota, i.e. earthworms and microarthropods, and root growth.

Sampling was carried out at selected positions across the catenary sequence of Boelkendorf, Brandenburg, for earthworms, Collembola and roots in April 1994. The soil physical analysis comprised measurements of soil bulk density and penetration resistance.

A positive correlation between earthworm abundance, numbers of Collembola and root growth at different catena positions was found. The top position especially, a calcaric regosol with low organic matter content, was markedly different with respect to soil biological and physical characteristics. High bulk densities and high soil resistance in the subsoil coincided with low earthworm densities, low microarthropod numbers and impeded rootability of the soil.  相似文献   

20.
The alterations brought about in the carbohydrate spectrum of root exudates of wheat in response to six foliar treatments, and their influence on the fungal population of the rhizosphere have been correlated. Pronounced suppression of ribose, maltose and raffinose exudation, which were liberated abundantly from root-rot infected roots, was recorded in response to foliar treatments with chloramphenicol and KCl. Chloramphenicol and to a lesser extent 2,4-D also reduced the rhizosphere population, including the test pathogen Helminthosporium saticiun. Previous and present investigations, therefore, indicate that the composition of root exudates could effectively be altered by foliar sprays, in an attempt to control the activity of Helminthosporium sativum, causing root-rot of wheat, in soil.  相似文献   

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