I recall a permaculturist suggesting that having a compost heap or animals inside/adjacently-heating a greenhouse has the added benefit of improving seed germination rates for tropical fruits due to the production of tiny amounts of ethylene, simulating a mass ripening of fruit in a tropical forest as a signal for germination.
A little research presently turned up studies showing that peak concentrations of ethylene are produced by many species of seeds at the moment the radicle germinates, ethylene affects the hormone signalling network within the seed which regulates dormancy.
Ethylene production in seeds is a consistent measure of seed vigor in many major crops and is a heritable trait (thus dormancy traits are heritable [though dormancy is exacerbated if ripening and storage conditions are sub-optimal]).
Interestingly, a close relationship between the ability to produce ethylene and seed vigor has been reported in various species including rape (Brassica napus; Takayanagi and Harrington, 1971), cotton (Gossypium spp.; Ketring et al., 1974), peanut (Arachis hypogaea; Ketring et al., 1974), cocklebur (Xanthium pennsylvanicum; Gorecki et al., 1991), snap bean (Phaseolus vulgaris; Samimy and Taylor, 1983), sunflower (Chonowski et al., 1997) and pea (Pisum sativum)
Exogenous sources of ethylene also affect seed dormancy, as well as improving germination rates in unfavorable conditions (higher temperatures, salinity, low-oxygen etc). [Ethylene and Seed Germination]
Chilling seeds and using gibberillins also affect seed dormancy mechanisms via the ethylene pathway.
The sensitivity of the seed to ethylene-induced germination decreases as its storage temperature rises (so frozen seeds need less ethylene to sprout at a given temperature than those stored in the fridge)
The quantity of ethylene necessary is minuscule, perhaps a single piece of ripe fruit would outgas enough ethylene for a greenhouse - making the chickens or compost overkill.
Breadfruit can take 8 months to ripen and could be put to use this way.
Humans and pets could also produce the ethylene if there is an airflow between the home and the greenhouse - or if the two are joined like in some earthship designs.
Now I think about it, seeds do seem to sprout most vigorously on the kitchen windowsill (next to the compost bucket) and out of the compost heap where ethylene concentrations are much higher than in a garden bed.
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