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Accueil du site → Doctorat → États-Unis → 2004 → Role of arbuscular mycorrhizal fungi in subsistence agroecosystems in the semi-arid tropics of Zimbabwe

PENNSYLVANIA STATE UNIVERSITY (2004)

Role of arbuscular mycorrhizal fungi in subsistence agroecosystems in the semi-arid tropics of Zimbabwe

Besmer, Ylva

Titre  : Role of arbuscular mycorrhizal fungi in subsistence agroecosystems in the semi-arid tropics of Zimbabwe

Auteur  : Besmer, Ylva,

Université de soutenance : THE PENNSYLVANIA STATE UNIVERSITY

Grade : Doctor of Philosophy (PhD) 2004

Résumé
Arbuscular mycorrhizal fungi (AMF) are present in most soils and can increase plant P uptake by providing an increased surface uptake area. The sandy soil and black clay in Zimbabwe differed in their response to an increased AMF inoculum potential. In the sandy soil, increasing the AMF inoculum potential through an inoculation significantly increased nodule numbers and shoot N accumulation in greenhouse-grown groundnut and lablab. This indicates that plant P uptake was limited by low mycorrhizal inoculum potential and that AMF could, to a limited extent, substitute for P fertilizers. However, the increased colonization level did not result in increased shoot growth. Based on this, the additional P taken up by the fungi in the inoculated treatment was likely to be enough to promote nodule number and nodule weight but not to combat shoot P deficiencies.
The meta-analysis also showed that management practices affect mycorrhizal inoculum potentials differently. Inoculation was most effective in increasing mycorrhizal colonization followed by crop rotations with mycorrhizal plants (as opposed to non-mycorrhizal plants), shorter fallow and reduced disturbance. In our field trials, crop rotation affected the mycorrhizal inoculum potential, whereas tillage and fallow period had no effect. The lack of fallow and tillage effects in our experiments contradicts earlier findings in mesic temperate regions and could be due to climatic differences. A greenhouse study showed that fungal viability of two AMF species declined under moist warm conditions but remained high in dry soils or when the moist soil was frozen, regardless of whether the isolates were from tropical or temperate climates. Thus, minimal fallow periods may be necessary to maintain a high mycorrhizal inoculum potential only in certain regions where the soil is moist and above freezing.
In summary, our results showed that while legumes are limited by P, P uptake is not necessarily limited by low AMF inoculum potential. Where it is, increasing the AMF abundance with native fungi mimics the effects of modest P additions but due to generally high inoculum potential and low availability of soil P, the effect of an increased AMF inoculum potential is likely to be small. If benefits of an increased AMF inoculum potential are suspected, inoculum potential could be enhanced prior to the onset of the drought by growing vigorous mycorrhizal crops because fungal viability remains high during the fallow in the dry soils

Mots clés : BIOLOGY, ECOLOGY ; BIOLOGY, MICROBIOLOGY ; AGRICULTURE, AGRONOMY

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