Importance of VA mycorrhizae for phosphorus supply to pasture plants in tropical Oxisols

Abstract

P utilization Sporulation of VA mycorrhizal fungi VA mycorrhiza Summary Inoculum of the VA mycorrhizal fungus Glomus manihotis was added to an Oxisol containing only a moderate inoculum potential of indigenous VA mycorrhizal fungi. Its effect on growth and P uptake of two pasture plant species was investigated in pot experiments. This effect was studied at a range of P applications, corresponding to 0, 9, 18, 35, 70 and 140kg P/ha. The plant species used were the grass Andropogon gayanus and the legume Pueraria phaseoloides, which were harvested four times, viz. at 70, 100, 130 and 160 days after planting.At first harvest, in the non-inoculated treatments, the first notable response to P application was found with 35 and 70 kg P/ha applied. Addition of inoculum resulted in growth response even at the lowest P application with both plant species. With successive harvests growth response to P application and inoculation disappeared rapidly. However, inoculation resulted in early and extensive development of mycorrhiza, in longer continued P uptake of plants and in a 2 to 4 times higher utilization of added P with both plant species. In the case of no inoculum being added a negative effect of medium and high P applications on mycorrhiza was found in the grass, but not in the legume. In both species the frequency of mycorrhiza increased with time. The slight negative growth response of both plants to the smallest P dressing (9 kg/ha) when no inoculum was applied could be related to the high level of sporulation of indigenous mycorrhizal fungi.

Growth responses of mycorrhizal and non-mycorrhizal tropical forage species to different levels of soil phosphate

“…After application of as little as 8 mg P k g -~ to the soil, growth of non-mycorrhizal plants was similar to that of mycorrhizal plants, suggesting a more efficient root system for P uptake and a low P requirement for growth in this host as compared to the legumes. Similar results in tropical forage legumes and grasses have been reported previously (Salinas et al, 1985).…”

“…Generally, P fertilizer depresses infection by VAMF (Powell, 1980a;Saif, 1986;Schubert and Hayman, 1986) but fertilization may not have any influence (Salinas et al, 1985). In our study, P fertilization inhibited fungal colonization in the grass (B. dictyoneura) and in one legume (S. capitata) but not in the other two legumes (C. macrocarpum and P. phaseoloides).…”

“…In our study, P fertilization inhibited fungal colonization in the grass (B. dictyoneura) and in one legume (S. capitata) but not in the other two legumes (C. macrocarpum and P. phaseoloides). Similarly Salinas et al (1985) reported high mycorrhizal infection in P. phaseoloides at a range of P concentrations (0 to 140kgPha-1). Our results support the suggestion that different plants exert different controls on the degree of root colonization by a given endophyte (Plenchette et al, 1983) and that the development of each VAM fungus, in our case G. manihotis, is related to the external P concentration depending on the host plant.…”

“…The ability of VAM fungi to colonize roots of plants is negatively correlated with increasing rates of phosphorus fertilization (Powell, 1980a;Saif, 1986;Schubert and Hayman, 1986), although there is now evidence of differences between VAM fungi in their sensitivity to phosphate (Plenchette et al, 1983;Salinas et al, 1985;Schubert and Hayman, 1986). Specificity to different sources of phosphorus has also been reported with VAMF which are effective with one phosphorus source being ineffective with other sources and vice versa (Jehne, 1980;Powell, 1980b).…”

Respuesta de cinco leguminosas de cobertura a la fertilización fosfórica

“…El aumento en esta variable es deseable, puesto que, una mayor biomasa aérea está relacionada con mayor fijación de nitrógeno (Divito y Sadras, 2014). Un efecto similar, aumento de la biomasa al aplicar fósforo, fue observado en un estudio realizado en plantas de esta leguminosa inoculadas con micorrizas específicas (Waidyanatha et al, 1979;Salinas et al, 1985). La inoculación de micorrizas vesículo-arbusculares, favorece la absorción del fósforo por parte de kudzú en comparación con plantas sin inocular (Waidyanatha et al, 1979).…”