Plant Growth Responses to Vesicular‐arbuscular Mycorrhiza

Abstract

SUMMARY Interactions between vesicular‐arbuscular (VA) mycorrhiza, utilization of rock phosphate and nodulation were examined in three legumes (clover, Stylosanthes and Centrosema) and in onions, grown in eight P‐deficient soils ranging from pH 8.1 to 5.3. Irrespective of pH, inoculation with VA endophytes increased P uptake in all host plants in all the soils when the indigenous endophytes had been removed by irradiation, but appreciable increases in plant dry weight only occurred when P concentrations of the uninoculated plants were low, generally below 0.15%. In the acid soils adding rock phosphate generally improved growth of the non‐mycorrhizal plants and inoculation with VA endophytes greatly improved its utilization. The effects persisted when the soil was used a second time. In neutral and alkaline soils rock phosphate was unavailable to non‐mycorrhizal plants and remained so after inoculation with VA endophytes. Legumes inoculated with the appropriate Rhizobium strain only nodulated in the most P‐deficient soils when they were also mycorrhizal, and added rock phosphate greatly improved nodulation and nitrogen fixation of the mycorrhizal plants. Some pilot experiments in unsterile soils are also described and the bearing of these results on field inoculation with VA endophytes is discussed.

MYCORRHIZAL INFECTION ON GROWTH AND NITROGEN FIXATION OF PUERARIA AND STYLOSANTHES AND UPTAKE OF PHOSPHORUS FROM TWO ROCK PHOSPHATES

“…(Unfortunately the phosphorus content in nodules was not estimated.) Mosse et al (1976) found that Stylosanthes and Centrosema nodules had twice as iiuieh phosphorus in nodules as in roots and Poschenrieder, Sammet and Fischer (1940) reported tive times more phosphorus in nodules than in roots of soybean.…”

“…In legumes, VAM not only stimulates plant growth but also nodulation and nitrogen fixation (Crush, 1974;Mosse, Powell and Hayman, 1976;Daft and El-Giahmi, 1976). This appears to be due to better phosphorus nutrition of legumes as a consequence of the mycorrhizal infection.…”

Influence of growth stage on the association between some tropical legumes and two variant species ofGlomusin an andosol

“…In groundnut, the increase in the production of shoot biomass may have resulted from maximum utilization of soil available P. Even though only groundnut showed clearly the VAM formation-P nutrition-growth-nitrogen fixation interdependency as reported by many authors for other crops (Mosse et al 1976;Subba Rao et al 1986), the findings reported here may be useful for fertilizer management. This is because information about the period of extensive VAM development and its contribution to P nutrition, growth, N2-fixation, etc., may enable to regulate phosphorus fertilizer applications so as to ensure rapid uptake by crop plants, thereby reducing loss through fixation especially in soils with high P fixation.…”

The response to phosphorus of white clover and lotus inoculated with rhizobia or given KNO3

“…In legumes, an increase in the supply of P, whether by fertilisation or mycorrhizae, can increase nodulation, N-fixing activity, and growth (van Schreven 1958;Crush 1974;Gates 1974; Mosse et al 1976; Smith & Daft 1977); increases in weight and P concentration are larger in the nodules than in the rest of the plant (Mosse et al, 1976; de S. Waidyanatha et at. 1979).…”