Interactions Between Growth, Phosphate Content and Nitrogen Fixation in Mycorrhizal and Non-Mycorrhizal Medicago sativa

Abstract

Nodulated Medicago sativa cv. Europe plants, both non-mycorrhizal and mycorrhizal (inoculated with Glomus mosseae), were grown in sand or soil with a range of phosphate levels. The following parameters were measured: intensity of mycorrhizal infection, intensity of nodulation, growth, phosphate content, nitrogenase activity (acetylene reduction) and nitrogen content. Both nodulation and mycorrhizal infection had occurred within 2 weeks of inoculation with the appropriate endophytes. Major increases in dry weight of mycorrhizal plants were not apparent until approximately 10 weeks from inoculation. However, mycorrhizal plants showed more extensive nodulation, coupled with higher rates of nitrogenase activity from 2 weeks onwards, and at the final (12-week) harvest had higher values of % N. Phosphate content of mycorrhizal plants (�g P/g dry wt) was also greater than non-mycorrhizal plants at 7 weeks. By 10 or 12 weeks, when significant mycorrhizal enhancement of growth was apparent, the total nitrogen and total phosphorus per mycorrhizal plant were also higher, but nitrogenase activity and phosphate content measured on a dry weight basis showed no significant differences between mycorrhizal and non-mycorrhizal plants. It is clear that mycorrhizal enhancement of phosphate uptake and nitrogen fixation precedes any effect on growth and the results indicate the importance of the time factor in the development of this tripartite symbiosis between legume, Rhizobium and mycorrhizal fungus.

Underground transfer of nitrogen between pasture plants infected with vesicular‐arbuscular mycorrhizal fungi

“…The mycorrhizal effects are of greater significance in soils of low nitrifying capacity in which uptake of the ammonium ion predominates (Carrodus, 1966;France & Reid, 1978;Raven et al, 1978;Ames et al, 1983). Daft & El-Giahmi (1974) and Smith & Daft (1977), have reported marked increases in nodulation, nitrogen fixation and growth with mycorrhizal inoculation of legumes. Ames et al (1983) have shown that mycorrhizal roots can also derive more nitrogen from an organic source than can non-mycorrhizal plants.…”

MYCORRHIZAL INFECTION AND GROWTH OF TRIFOLIUM SUBTERRANEUM: USE OF STERILIZED SOIL AS A CONTROL TREATMENT

“…Furthermore, 0028-646X/81/060299-hll S02.00/0 ® 1981 The New Phytologist the method used to reintroduce mycorrhizal fungi poses new problems, not the least being the quantity and form of inoculum to add in order to give a level comparable to that in the original soil. In our studies of the effects of early endomycorrhizal infection on nodulation and growth of Trifolium subterraneum L. (Smith, Nicholas and Smith, 1979) we compared plants grown in sterilized and non-sterilized soil, and it has been suggested (e.g. by referees) that this approach is invalid.…”

Effects of endomycorrhizas and phosphorus fertiliser on nodulation and acetylene reduction activity of white clover seedlings

“…There have been claims of direct effects of mycorrhizas on nodulation and nitrogen fixation in legumes (Mosse 1977;Powell & Sithamparanathan 1977;Smith & Daft 1977;Munns & Mosse 1980). However, Robson et al (1981) suggest that the effects of mycorrhizal infection on nodulation and N fixation in subterranean clover are indirect, and result from the improved P uptake and plant growth which follow from mycorrhiza development.…”