[permaculture] [Fwd: Re: [SANET-MG] Entrez PubMed Soil Quality & phosphate availability]

Lawrence F. London, Jr. lfl at intrex.net
Fri Mar 17 01:25:30 EST 2006

Improvement of Arbuscular Mycorrhiza Development by Inoculation of Soil with Phosphate-Solubilizing
Rhizobacteria To Improve Rock Phosphate Bioavailability ((sup32)P) and Nutrient Cycling.
"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 <...>"
"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"
"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."
I interpret this to mean that the researchers discovered that the presence of a specific AM fungus
innoculated with two phosphate-solubilizing ("helper") bacteria in soils with low phosphate bioavailability
resulted in higher levels of plant available phosphorus and "significantly increased
biomass and N and P accumulation in plant tissues". They had added rock phosphate to the soil tested and
"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."

Would the demise of colonies of the "two phosphate-solubilizing rhizobacterial isolates: Enterobacter sp. and Bacillus 
subtilis" described above, which, as the article says, released phosphate ions gleaned from "the external AM mycelium" 
which took up soil P, mean that benefits derived from adding the fungus and bacteria dual innoculants to soil would be 
limited to the lifespans of those rhizobacteria? Could the increase in available P be kickstarted by adding certain 
composts or compost tea to P deficient soils to reactivate the "helper bacteria" and thus the AM mycelium? How would you 
make compost with these properties?

More information about the permaculture mailing list