permaculture

["Lawrence F. London, Jr." <lfl@intrex.net>]

<http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=16535730&itool=iconfft&query_hl=2&itool=pubmed_docsum>
 Appl Environ Microbiol. 1997 Nov;63(11):4408-4412.     Related Articles, 
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    Improvement of Arbuscular Mycorrhiza Development by Inoculation of Soil with Phosphate-Solubilizing Rhizobacteria 
To Improve Rock Phosphate Bioavailability ((sup32)P) and Nutrient Cycling.

    Toro M, Azcon R, Barea J.

    The interactive effect of phosphate-solubilizing bacteria and arbuscular mycorrhizal (AM) fungi on plant use of 
soil P sources of low bioavailability (endogenous or added as rock phosphate [RP] material) was evaluated by using soil 
microcosms which integrated (sup32)P isotopic dilution techniques. The microbial inocula consisted of the AM fungus 
Glomus intraradices and two phosphate-solubilizing rhizobacterial isolates: Enterobacter sp. and Bacillus subtilis. 
These rhizobacteria behaved as "mycorrhiza helper bacteria" promoting establishment of both the indigenous and the 
introduced AM endophytes despite a gradual decrease in bacterial population size, which dropped from 10(sup7) at 
planting to 10(sup3) CFU g(sup-1) of dry rhizosphere soil at harvest. Dual inoculation with G. intraradices and B. 
subtilis significantly increased biomass and N and P accumulation in plant tissues. Regardless of the rhizobacterium 
strain and of the addition of RP, AM plants displayed lower specific activity ((sup32)P/(sup31)P) than their comparable 
controls, suggesting that the plants used P sources not available in their absence. The inoculated rhizobacteria may 
have released phosphate ions ((sup31)P), either from the added RP or from the less-available indigenous P sources, which 
were effectively taken up by the external AM mycelium. Soluble Ca deficiency in the test soil may have benefited P 
solubilization. At least 75% of the P in dually inoculated plants derived from the added RP. It appears that these 
mycorrhizosphere interactions between bacterial and fungal plant associates contributed to the biogeochemical P cycling, 
thus promoting a sustainable nutrient supply to plants.

    PMID: 16535730 [PubMed - as supplied by publisher]