Good post Philip, well worth building on.
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Originally Posted by Philip Small
I even emailed Dr. Lehman enthusiastically about glomalin a few weeks ago, thinking to pull my thoughts together on it for a blog post. He was not unaware of the rationale. His entirely neutral response reined me in a bit.
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I expect he is on the case but unwilling to say anything until he is safely published. Glomalin drives a coach and horses through much previous TP research, because its effects are so directly relevant that if not factored in, other results are, well, flaky. Give the man time.
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it's got to be more complicated than just AMF kicking up their glomalin production
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Certain to be true but is it important? Review what we know:
- Charcoal massively increases AMF growth, and is used extensively for this purpose in Japan. E.g. Saito & Marumoto (2002) 'Inoculation with arbuscular mycorrhizal fungi: the status quo in Japan and the future prospects', Plant and Soil 244(1-2), pp. 273-279.
- AMF inherently produce copious amounts of glomalin (Driver et al (2005) 'Characterization of glomalin as a hyphal wall component of arbuscular mycorrhizal fungi', Soil Biology & Biochemistry 37(1), pp. 101-106). This glomalin is recalcitrant and persists long after the hyphae have died.
- AMF are ubiquitous and are productive in tropical forest soil (Lovelock et al (2004) 'Soil stocks of glomalin produced by arbuscular mycorrhizal fungi across a tropical rain forest landscape', Journal of Ecology 92, pp. 278-287).
- Fire does not reduce AMF the way it does other fungi, leaving them as the dominant group for up to 15 years after a burn (Treseder et al (2004) 'Relationships among fires, fungi, and soil dynamics in Alaskan Boreal Forests', Ecological Applications 14(6), pp. 1826-1838). Terra preta soils were prabably continually burned during formation (Hecht in Amazonian Dark Earths).
- Glomalin forms water-stable soil aggregates (Rillig et al (2002) 'The role of arbuscular mycorrhizal fungi and glomalin in soil aggregation: comparing effects of five plant species', Plant and Soil 238(2), pp. 325-333).
- Water-stable aggregates of a similar size to those characteristic of glomalin bind and protect soil components (Teixera & Martins in Amazonian Dark Earths). This accounts for many of the properties of Dark Earth soils: stability; water retention; carbon retention; nutrient retention and reduced leaching; reduced CH4 and N2O emissions.
Perhaps you have heard of Occam’s Razor, or of Einstein’s “smallest possible number of hypotheses”? The important properties of terra preta do not need bacteria to explain them. Bacteria work with AMF (Rillig et al (2006) 'Phylogeny of arbuscular mycorrhizal fungi predicts community composition of symbiosis-associated bacteria',
Fems Microbiology Ecology 57(3), pp. 389-395), so as you say the reality will be found to be nonlinear, multi-staged, complex and inter-connected, but they aren’t needed as independent agents.
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there are pitfalls to fungi as an explanation for TP's self-replication once it has reached its full expression. By then the pH has come up, not so great for the fungi. By then the phosphorus levels have come up, not so great for mycorhhyzal mutualism.
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Self-replication of terra preta is reported by Amerindians but is there any scientific evidence for it? It seems to be one of several questionable beliefs (German in
Amazonian Dark Earths), in this case perhaps based on Dark Earth’s rapid recuperation under fallowing. Another such belief is that TP does not lose fertility or break down. It most definitely does if not maintained properly (German again).
pH up? The mean pH of terra preta is 5.7, and of terra mulata 5.3 (Kämpf et al in
Amazonian Dark Earths), higher than the awful common soil but nowhere near suppressing fungi.
Phosphorus up? The high P (and Ca) levels in terra preta are believed to be original, from the debris of habitation, not accumulated. They are reported to be the main features distinguishing terra preta from terra mulata, apart from the colour, which is probably due to bacterial decomposition of the debris but has no known beneficial effects. Terra mulata has low P and shows that P does not “come up” in Dark Earths. A useful hypothesis: more glomalin will be found in TM than in TP.
I had hoped that there was no link between TP and glomalin, because then we’d have two weapons against carbon dioxide instead of one. But the scientific evidence is too compelling for me right now. Nevertheless, I cling to the hope of a pleasant surprise when independent glomalin assays of Dark Earths are published.
M
