The influence of iron supply on toxic effects of manganese, molybdenum and vanadium on soybean, peas and flax

The investigations were carried out in nutrient solution with iron as ferric citrate and nitrogen in the form of nitrate. Addition of 2.5 p.p.m. vanadium to plants in which iron chlorosis was already-established, either by a lack of iron or by excess manganese, failed to counteract the condition, and caused toxic symptoms. Reduction of the standard iron supply to ½ or ? accentuated the toxicity of 2?5 or 5 p.p.m. V to soybean and flax, but a similar reduction in phosphorus had no influence. Toxicity to peas, however, was increased when the phosphorus was reduced to 1/10, provided the iron level was high (20 p.p.m. Fe). Raising the iron supply to 20 or 30 p.p.m. Fe counteracted the toxicity of manganese (10 p.p.m.), molybdenum (40 p.p.m.) and vanadium (2.5 p.p.m.), but the result was less marked when these three elements were combined. Iron supplied in successive, small doses proved less efficient in overcoming molybdenum or vanadium, but not manganese excess, than the same amount of iron supplied in fewer and larger quantities. Varying the iron supply had little effect when the concentration of the three elements was low. When increased iron supply had reduced the chlorosis caused by high manganese or vanadium, it also reduced the manganese and vanadium contents of the shoot (p.p.m./d.m.), but the molybdenum content was only lowered by high iron when given in non-toxic concentration (0.1 p.p.m. Mo) combined with excess manganese. The iron content of the shoot (%/d.m.) was scarcely affected by the amount of iron supplied, but was generally reduced by high concentrations of manganese, molybdenum or vanadium. Results regarding the effect of vanadium on the phosphorus content of the shoot were conflicting, and differences occurred only when the iron supply was low. Here the phosphorus content of soybean and peas was generally reduced, while that of flax was increased. Yield data for soybean and flax indicated an interaction between manganese with both molybdenum and vanadium if the iron supply was low, but none between molybdenum and vanadium. The effect of all three metals was additive in respect to iron

Some interrelationships between manganese, molybdenum and vanadium in the nutrition of soybean, flax and oats

Soybean and flax were grown in nutrient solutions containing high and low levels of molybdenum and vanadium, in combination with toxic (10?25 p.p.m.) and non-toxic (1 p.p.m.) manganese. Molybdenum (20 and to a less extent 10 p.p.m.) intensified the chlorosis induced by manganese excess, though these concentrations were harmless in the presence of 1 p.p.m. Mn. Vanadium (= 1.0, 5 and 10 p.p.m. Mo) counteracted some of the symptoms of manganese toxicity, but the two higher rates were harmful to growth irrespective of the manganese supply. Toxic concentrations of vanadium at first deepened the green colour of the shoot, though apical iron-deficiency chlorosis was generally induced later. Low molybdenum (0.1 p.p.m.) or equivalent vanadium had no influence on growth or iron nutrition at either level of manganese. Visual differences were corroborated by changes in the nitrogen, phosphorus and iron contents of the plants. There was no evidence of replaceability of molybdenum by vanadium. Oats were grown in nutrient solutions containing various combinations of manganese (nil?400 p.p.m.) and molybdenum (nil?20 p.p.m.). The appearance of manganese-deficiency symptoms was not affected by the quantity of molybdenum provided, and the manganese and molybdenum contents of the leaves were mutually independent of the quantity of each element supplied

Observations on the effect of molybdenum on plants with special reference to the solanaceae

In view of the similarity between certain cytological changes induced by virus disease and treatment with molybdenum, pot-and water-culture experiments were carried out to determine further the effect of this element on plant growth. Sodium molybdate was used throughout. 2 Toxic symptoms were produced with the larger dressings of molybdate, injury being shown at much lower concentrations in solanaceous species than in barley. 3 The shoots of tomato and Solanum nodiflorum turned a golden yellow, and potato tubers a reddish yellow colour when the plants were grown with the larger quantities of molybdate. 4 These colour changes were shown to be due to the presence of yellow globules of a tannin-molybdenum compound which had formed within the tissues. 5 Blue granular accumulations occurred in large numbers in molybdenum-treated plants. Their distribution was confined to tissues that contained anthocyanin pigment, and their composition was apparently of an anthocyanin-molybdenum nature

The influence of the pH of the nutrient solution and the form of iron supply on the counteraction of iron deficiency in peas, soybean and flax by high concentrations of molybdenum

The prevention of chlorosis in flax by high concentrations of molybdenum in a nutrient solution was associated with a delay in the precipitation of iron from ferric citrate, a slower drift of pH towards alkalinity and an increase in the iron content of the root. These effects were greater with ammonium than with sodium molybdate and occurred with solutions started at pH 4.6 but not at pH 6.6. When FeEDTA was the source of iron, a similar delay in pH drift in the solution and accumulation of iron in the root occurred, but there was no chlorosis or precipitation of iron in the control treatment, so the effect of high molybdenum could not be fully determined. When ferric chloride was used, high molybdenum did not prevent chlorosis nor delay iron precipitation or cause accumulation of iron in the root, though the rate of pH drift resembled that of solutions containing the organic forms of iron. Similar results were obtained with peas and soybeans receiving high molybdenum treatment, but suppression of chlorosis was only temporary. It is suggested that the capacity of molybdenum to offset chlorosis is due to the formation, in acid solution, of a complex with phosphorus which renders iron more available by delaying the formation of ferric phosphate. This seems to occur only when iron is supplied in the organic form

Investigations regarding the nature of the interaction between iron and molybdenum or vanadium in nutrient solutions with and without a growing plant

Iron offset the toxicity of molybdenum or vanadium in nutrient solutions more effectively when it was supplied at the same time as the molybdenum or vanadium than when it was given separately in alternate 3-day periods. Allowing nutrient solutions of pH 4.6 containing high concentrations of iron, with or without vanadium, to stand for 4 days before use did not delay the restoration of colour to chlorotic plants, but even 2 days' standing reduced the iron content of their roots and the vanadium content of both shoot and root. The presence of vanadium had little effect on iron uptake. In parallel experiments with molybdenum, standing the solutions for 7-9 days before use delayed colour recovery, but shorter periods had no effect. Standing for 2 days or longer greatly reduced the iron content of the root, butthemolybdenum content was unaffected or increased. High molybdenum greatly increased the iron in the root, but had little effect on that in the shoot. Precipitation of iron in the nutrient solution was delayed by high concentrations of either ammonium or sodium molybdate if the initial pH was 4.6, but not if it was 6.6. Vanadium had no influence on the precipitation of iron at pH 4.6. At least part of the compensating action of iron on molybdenum or vanadium toxicity would appear to take place outside the plant

The changes induced in the anatomical structure of Vicia faba by the absence of boron from the nutrient solution

The chemical. elements essential for the healthy growth of plants are now recognized to be more numerous than was originally supposed, and although some must be supplied in considerable quantity, of others only a trace is required. Boron is an example of the latter type of element. Experiments at Rothamsted have shown that Vicia Faba (broad bean) and several other leguminous plants fail to complete their development in water or sand culture unless a trace of this element is supplied, 1 part H3BO3 in 25,000—12,500,000 parts of nutrient solution being sufficient (1, 4). In its absence characteristic symptoms are exhibited in both shoot and root. In the case of the broad bean the flower buds shrivel and fall off and the stem withers and blackens at the apex, the injury gradually travelling down the plant; the root system is stunted, the laterals being few in number and often thickened. A comparison between the anatomical structure of such abnormal shoots and roots with those of the healthy plant is the subject of the present paper

Molybdenum as a factor in the nutrition of lettuce

Lettuce grown in nutrient solution sometimes showed slight benefit on a dry-weight basis from the addition of 0.1 p.p.m. Cr, Sr, Ti or V, while Zn was usually harmful. Addition of Mo at a similar concentration, however, exerted such a marked beneficial effect on both yield and appearance as to suggest that this element was essential for healthy growth. Confirmation of the response was not always obtained, and search was made for some factor which would account for the lack of uniformity in the results. Neither the season of the year, the variety, modifications in the nutrient solution, nor the addition of other trace elements appeared to be responsible, and further work is necessary for the elucidation of the problem