Spatial difference in acquisition of soil phosphate between two arbuscular mycorrhizal fungi in symbiosis with Medicago truncatula
Date
2000
Authors
Smith, F.
Jakobsen, I.
Smith, S.
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Advisors
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Journal ISSN
Volume Title
Type:
Journal article
Citation
New Phytologist, 2000; 147(2):357-366
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Abstract
<jats:p>Responses of <jats:italic>Medicago truncatula</jats:italic> to colonization by two arbuscular mycorrhizal fungi, <jats:italic>Scutellospora calospora</jats:italic>
isolate WUM 12(2) and <jats:italic>Glomus caledonium</jats:italic> isolate RIS 42, were compared in the light of previous findings that
the former fungus can be ineffective as a beneficial microsymbiont with some host plants. The plants were grown
individually in two‐compartment systems in which a lateral side arm containing soil labelled with <jats:sup>33</jats:sup>P was
separated from the main soil compartment by a nylon mesh that prevented penetration by roots but not fungal
hyphae. Fungal inoculum was applied as a root–soil mixture in a band opposite the side arm. Nonmycorrhizal
controls were set up similarly, without inoculum. There were harvests at 28, 35, 42 and 49 d. Both sets of
mycorrhizal plants grew better than nonmycorrhizal plants and initially had higher concentrations of P in shoots
and roots. Plants grown with <jats:italic>S. calospora</jats:italic> grew better than plants grown with <jats:italic>G. caledonium</jats:italic>, and this was
associated with somewhat greater fungal colonization in terms of intraradical hyphae and numbers of arbuscules.
<jats:italic>Scutellospora calospora</jats:italic> formed denser hyphae at root surfaces than <jats:italic>G. caledonium</jats:italic>. By 28 d there were extensive
hyphae of both fungi in the side arms, and after 35 d <jats:italic>S. calospora</jats:italic> produced denser hyphae there than <jats:italic>G.
caledonium</jats:italic>. Nevertheless, there was very little transfer of <jats:sup>33</jats:sup>P via <jats:italic>S. calospora</jats:italic> to the plant at 28 d, and thereafter
its transfer increased at a rate only <jats:italic>c</jats:italic>. 33% of that via <jats:italic>G. caledonium</jats:italic>. The results showed that plants colonized by
<jats:italic>S. calospora</jats:italic> preferentially obtained P from sites in the main soil chamber relatively close to the roots, compared
with plants colonized by <jats:italic>G. caledonium</jats:italic>. Hence formation of a highly beneficial arbuscular mycorrhizal symbiosis
does not necessarily depend on development of hyphae at a distance from the roots or on large‐scale translocation
of P from distant sites. The results are discussed in relation to previous studies with compartmented systems that
have involved the same fungi. Possible causes of the variable effects of <jats:italic>S. calospora</jats:italic> in symbiosis with different host plants are briefly assessed. Differences in spatial abilities of individual arbuscular mycorrhizal fungi to acquire P might have strong ecological implications for plant growth in soils low in P.</jats:p>