Molybdenum in Nitrogen Metabolism of Legumes and Non-Legumes

Abstract

SummaryA study was made of the growth and nitrogen metabolism of plants in relation to molybdenum supply. Four soils low in available molybdenum were used in pot cultures for this work.Subterranean· clover (Trifolium subterraneum L.) responded to molybdenum on each of the soils. Flax (Unum usitatis8imum L.) responded to molybdenum on only one of the soils in the presence of a heavy dressing of manganese sulphate, which reduced the uptake of molybdenum and induced molybdenum deficiency. Oats (Avena sativa L.) did not respond to molybdenum on any of the soils, even where manganese sulphate was added.Deficiency of molybdenum decreased the percentage protein nitrogen in the flax and in the clover, but in different ways. Molybdenum increased the yield of flax only where combined nitrogen, either as nitric acid or ammonium sulphate, was provided. High nitrate accumulation occurred in the flax provided with nitric acid but without molybdenum. The percentage total nitrogen in flax was unaffected by molybdenum, but deficiency of molybdenum decreased the percentage protein nitrogen and increased the percentage non-protein nitrogen. Thus molybdenum was needed by the non-legume for the utilization of absorbed nitrate nitrogen.Molybdenum markedly increased both the yield and percentage nitrogen of clover where no combined nitrogen was provided, but had little or no effect where nitrogen was supplied as nitric acid or ammonium sulphate. This was despite the fact that each of these nitrogen compounds decreased the uptake of molybdenum by the clover. Deficiency of molybdenum decreased both the percentage protein nitrogen and the percentage non-protein nitrogen in the clover. The evidence with clover shows that molybdenum is directly concerned in symbiotic nitrogen fixation, and that the molybdenum requirement for optimum symbiotic nitrogen fixation is appreciably greater than the requirement for optimum utilization of nitrate nitrogen.

Mineral constraints to nitrogen fixation

“…There is, however, a direct relationship between the degree of response shown and the involvement of the nutrient in nitrogen fixation. The most marked responses are observed for those nutrients whose requirements for symbiotic nitrogen fixation are much greater than their requirements for host plant growth, i.e., Co (Ahmed and Evans, 1960) and Mo (Anderson and Spencer, 1950a). Less clear results are observed for nutrients where requirements for symbiotic nitrogen fixation and host plant growth are similar, e.g.…”

“…If the nutrient is directly involved in nitrogen fixation then the proportion of protein nitrogen does not change between deficient and sufficient plants; examples are Mo (Anderson and Spencer, 1950a) and Cu (Snowball et al, 1980). However, in cases where the nutrient affects nitrogen metabolism rather than nitrogen fixation, there is a decrease in protein nitrogen under deficiency as in the case of severe S deficiency (Anderson and Spencer, 1950b;Andrew et al, 1952).…”

“…Specific involvement has been claimed in cases where nutrient applications increase both legume growth and nitrogen concentrations in plant tops. Examples of increases in nitrogen concentrations of symbiotic legumes following correction of nutrient deficiencies have been reported for Ca in T. subterraneum (Banath et al,, 1966;Loneragan, 1959); Co in Lupinus angustifolius (Chatel et al, 1978); Cu in T. subterraneum (Greenwood and Hallsworth, 1960;Snowball et al, 1980) and T. repens (Van der Elst et al, 1961); Mo in T. subterraneum (Anderson and Spencer, 1950a) and in Macroptilium atropurpureum, Glyeine wightii, Desmodium intortum and Lotononis bainesii (Johansen et al, 1977); P in T. subterraneum (McLachlan and Norman, 1961) and Stylosanthes humilis (Gates and Wilson, 1974); S in T. subterraneum (Anderson and Spencer, 1950b), D. intortum and L. bainesii (Andrew, 1977b), and S. humilis (Jones et al, 1971) and Zn in M. sativa (Lo and Reisenauer, 1968). However, such results should be interpreted with caution since increases in plant nitrogen concentrations may also reflect changes in plant structure (e.g.…”

“…If nutrient supply corrects nitrogen deficiency then there is strong evidence that the nutrient has a (Anderson and Spencer, 1950a); Ca in T. subterraneum (Loneragan, 1959); Co in Glycine max and in Medicago sativa (Delwiche et al, 1961); Cu in T. subterraneum (Snowball et at., 1980). In the latter case, the response need have no direct relationship to nitrogen fixation; such a response could occur if the addition of combined nitrogen increased the availability of the deficient nutrient either through a contamination of the fertilizer nitrogen or through some release of the nutrient in the soil.…”

The Effect of Molybdenum on the Organic and Inorganic Phosphorus of Plants

“…Molybdenum is known to be concerned in the nitrogen metabolism of legumes and non-legumes (Mulder 1948;Anderson and Spencer 1950), and many workers have attempted to elucidate this effect of molybdenum in plant metabolism (Hewitt, Jones, and Williams 1949;Agarwala 1951;Nicholas, Nason, and McElroy 1953).…”