permaculture

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

Improvement of Arbuscular Mycorrhiza Development by Inoculation of Soil with 
Phosphate-Solubilizing
Rhizobacteria To Improve Rock Phosphate Bioavailability ((sup32)P) and 
Nutrient Cycling.
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
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"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."
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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?