Part 1:
Frass (insect manure) has CO(NH2)2 urea, NH4+ ammonium, organic compounds with nitrogen (N) & fatty acids (carbon, hydrogen & oxygen) in it. In the soil the carbon causes those micro-organisms that can't fix carbon themselves (ex: fungi) to use the carbon for energy & propagate.
When frass is composted this increases the fungal proportion of that compost & alters the pH reaction. In general fungal predominant compost is best for lower pH favoring plants; meaning composted frass will do more good fed to perennials vegetation, shrubs & trees - which do better in fungal rich soils.
Of course the kind (geno-type) of insect making the frass influences the specific carbon to nitrogen ratio. So different genotypes of insects fed the same rate of green matter will themselves have different N ratios to carbon, even though insects fed on green matter will have higher N ratio.
As those kinds of carbon loving micro-organisms' (technically classified as hetero-trophs) mass increases they will want more N; which in turn ties up the frass N for a while. Thus frass may mean the soil has more N than without the frass, yet there is a decreased rate of total N that can be mineralized (not organic bound) which is the form plants take up N.
One analysis of decomposed plant matter (leaf litter) in the soil without frass added used for feeding some seedlings showed it can have 0.1% of it's N incorporated into the seedling stem, 0.2% of it's N incorporated into it's young roots & 0.7% of it's N incorporated into the leaves. In contrast only un-composted frass in the soil feeding the same kind of seedlings had 0.03% N in the seedling stem, 0.07% N in the seedling roots & 0.03% N in the seedling's leaves.
Another distinction appears between only (just) decomposed plant matter in soil & only (just) frass in soil regarding N is of interest. For some reason frass in soil also leads to bit more leaching of the N in the form of NO3- nitrate; although frass has no impact on the soil N in the form of ammonium NH4+ in comparison to decomposed plant matter. In other words frass makes normal fertilizing levels of NH4+ available & yet not as much NO3- as would otherwise be the case.
Nitrate NO3- is a negative charged an-ion & don't require an ion pump to transport it past the plant cell's gating portal (plasmo-lemma); it diffuses into plant cells without requiring the plant to expend energy. In contast positive charged cat-ions like ammonium NH4+ get through a plant cell's plasmo-lemma by shuttling out a H+ as the proton driver that gets taken from sequestration in that cell's internal vacuole organelle.
A plant cell unloading hydrogen H+ ions from it's interior (cytosol) risks overloading neighborhing cells with acidic pH provoking H+ ions. Plant cells must not get too acidic from H+ ions in order that it is ready at all times to re-uptake hydrogen through it channel protein & thus again have H+ ions available to swap out for allowing in positive cat-ion mineral nutrients. However, please don't jump to conclusions about frass' ammonium NH4+ positive ionic charges just yet.
Roots themselves have a negative charge due to the H+ ions put out to effect the postive cat-ions uptake (ex: potassium, calcium, copper, magnesium, manganes, molybdenum, etc.). Filamentous fungi growing in proximity to roots are attracted to the H+ ions pH & the fungi put out a hormone-like growth factor (auxin) as they grow hyphae which sheds some exo-genous (outside) auxin that in turn stimulates the plants root growth; which is part of why frass does fertilize already established (non-seedling) young plants.
The "natural" resultant H+ in the root zone gently lowers the local pH & not only helps attract symbiotic fungi, but also keeps local pH suitably low for iron uptake. Furthermore, since frass as the sole fertilizer alone reduces the level of nitrate NO3- ( with it's negative ion charge that would neutralize a H+ charge & otherwise lead to higher root zone pH) this allows trace minerals like copper, zinc & manganese (as well as iron) available for a maturing plant's growth.
But the lower nitrate N03- from frass not being around to raise the root zone pH does have the affect of reducing that root zone's ability to attract soil bacteria. A perennial doesn't want to attract bacteria as much as a new annual plant does.
Frass that is uncomposted for non-seedlings works because the ammonium NH4+ gets into plant cells through a plasmo-lemma & encounters an alkaline environment replete with more abundant OH- molecules than seedlings have.There is an ensuing shift of an H+ molecule (from the NH4+) to make both water H2O & a residual ammonia NH3; that ammonia NH3 is then processed into L-glutamate; the glutamate is what plant cells can use to cobble out amino acids that can actually be assembled into functional plant proteins.
Part 2:
Part of the reason uncomposted frass works for established growing plants & stymies seedlings is because of the difference in developed capacity. The non-seedling has had time to take in enough N to make proteins (chloroplast proteins & mesophyll chloroplasts should contain over 50% of all the N in that leaf) & also accumulate potassium.
Potassium is re-circulated from the top of the plant downward (inside the phloem) acting as a cyclical regulator for plant made organic acids (negative charged an-ions). The roots then excrete HC03- (a plant organic acid). It's OH- hydroxyl once out in the root zone raises the local root pH & when you water the plant (or it has enough moisture in the root zone) the plant nutrients with negative an-ion charges swap into the root (the OH- leaving makes the exchange possible).
And without adequate potassium there is poor regulation of CO2 (carbon dioxide gas) in the root & this lets CO2 gas out of that root. There is naturally CO2 outside the roots that reacts with some of the water H2O to form H2CO3, which in turn breaks down into CO3- & H+ (which drops the root zone pH).
Seedlings, unlike actively growing plants, have to deal with a low pH root zone without much counterbalancing from lots of spare potassium (20% of potassium is up-stream from the roots inside the xylem) holding down CO2 outgassing into the root zone that is by nature a bit low in pH. If the root zone of the seedling gets below 6pH they take in less potassium, magnesium, molybdenum & even calcium.
Without balanced amounts of potassium inside the plant to handle the developing root's CO2 the effect can make the root zone pH so low that some carbohydrates in the roots themselves ferment producing compounds that stunt the root; in other words the plant won't get as big as possible. Again, this is for seedlings fertilized with just frass alone.
Urea of frass in the soil undergoes bacterial hyro-lysis into ammonia NH3. However, NH3 decreases potassium absorption by the roots. The side effect is that without adequate potassium this itself can lead to stunted roots.
If look back at 5th paragraph & notice the low N content of seedling stems it may shed light on why pure frass fertilized seedlings make a tap root but less branched rootlets than plant litter does. The phyto-chromes (plant proteins that respond to light) in the developing plant's roots direct auxin (plant hormone) to the primary root; whereas phyto-chromes in the above ground shoot are responsible for the auxin that is directed to growth of lateral roots (which can end up performing more nutrient uptake).
Auxin has to cellularly move out (efflux) & in (influx) to do several things; when the efflux carrier of auxin naturally moves overnight from the plasmo-lemma portal of the plant cell into that internal plant cell's vacuole organelle structure some of that cell's auxin efflux carrier protein is degraded. Then without enough N in the seedling stem to regenerate efflux carrier protein to pass the maximum amount of auxin back out & around through that cell's plasmo-lemma portal the auxin isn't able to stimulate growth in other cells as much as a seedling stem with more N.
The pure frass fertilized seedling stem & primary root can still grow because there is no effect of the overnight darkness that causes the influx carrier protein of auxin to degrade. Unfortunately the initial cells of the plantlet that get a lot of light can also have their efflux carrier proteins of auxin simply stall at the plasmo-lemma portal to that cell & they can't cycle the carrier protein inside; most experimenters with pure frass fertilization give their seedlings the same amount of light as usual.
Then (with some efflux carriers stuck outside the plasmo-lemma portal) the next day a lot of the auxin that cell made, or had already brought in (via influx carrier proteins), can't be exported since the auxin efflux carrrier protein did not regenerate inside (where it should have been) to pass along to other less developed cells that are trying to grow. Should there be low available auxin the developing roots can lose their programming (gravi-tropism) to grow downward; too little auxin stalls a root cell's development cycle in a transitional phase (G1 cell phase) & getting auxin lets it progresss into the G1-S cell cycle needed to start becoming a lateral root.
Composted frass' fungal colonys are going to deliver enough auxin for seedling roots to grow downward; since filamentous fungi (& to some extent bacteria) supply the seedling with various auxin related compounds (indole-3-acetaldehyde/ethanol/acetic acid). Not only that, but the indoles-3-acetaldehyde/ethanol are stored inside plants as substrates to make into indole-3-acetic acid when needed to influx/efflux auxin around inside the plant; as for the roots under auxin the plant uses an endo-cytic (engulfing) vesicle type of secretion (specific to different plants) which cycles back & forth across the root apices.
Those cells which are having auxin at their plasmo-lemma cell portal can take that auxin in (influx) to stimulate growth; thus even pure frass fertilized plants will still grow. You want high auxin moved out & away, so to speak, because that up-regulates the elongation/roots forming hormone gibberellin; of course the established plant's pattern is to transport it's auxin upward.
L-glutamate & glutamate-like receptors under auxin's hormonal instigation is what makes root development go on & the plant's root pheno-type of plasticity occur. In fact the heading down of roots (gravi-tropism) occurs with the intermediary glutamate-like receptor called 3.3 functioning to regulate the calcium ionic shuttling required when calcium's action potentials (booster charge) are instigated by glutamate. (See 5th paragraph for how low the purely frass fertilized root N content is in comparison to decomposed organic matter & recall how N is needed to make L-glutamate.)
Of course this is a simplified explanation since auxin efflux carriers actually work with sub-sets of plasmo-lemma cell portal proteins. Depending on whether the efflux carrier forms an assymetrical or symetrical relationship with those subsets of proteins there are different orientation of the auxin sent out on it's way.
The plasmo-lemma cell portal have auxin binding proteins that are re-cycled inward to the interior of the cell (to the endo-plasmic reticulum & some gets to the golgi body before returning to the endo-plamic reticulum) & then re-cycling this binding protein to a plasmo-lemma portal. When auxin tags this protein there arises an action potential (jump start charge) from the hyper-polarization & in seconds the plamo-lemma undergoes changes.
Expansins (protein molecules in the plant cell) work with auxin to execute the hormonal signal; there are confusingexpansin classifications, different types working in phases/locations & so for frass fertilization relevance a generalization follows. Expansins act on the polymers of cellulose (& hemi-cellulose) where the internal plant cell micro-fibrils are being transitorily held together (by arabino-xylan & xylo-glucan) with no co-valent bond to cellulose.
The plant can elongate different growing parts because where the cellulose lacks co-valent bods the cell's micro-fibrils can "slip along" performing a co-ordinated separation of parallel micro-fibrils under the mediation of an expansin protein. When a plant cell matures growth vector creeping along stops because the cell wall has cross-linked (via hemi-cellulose, pectin &/or phenolic groups). Uncomposted frass only fertilizer doesn't give the seedling the same amount of cellular N to as promptly form the same amount of expansin proteins as other fertilization & so it's early growth is less.
Part 3:
Chitin from insects can also be added to the soil; about 40% of it will be "gone" in 5 months & about 60% of the chitin will be gone in 6 months. The soil's microbial denizens will have degraded it in a dynamic that is influenced by moisture (cool yet dry usually more enzymatic chitino-lysis cleaving than high temperature when soggy wet since maximum chitin breakdown occurs in soil's ideal basal pressure of -1.4 atmospheres), temperature (cool in forest more chitin cleaving than warm in forest, verses really hot in low desert like vegetation more chitin cleaving than merely warm, verses in agricultural fields more chitin cleaving as the growing season's temperature plateaus), pH & what phase the chitin is in when breaking apart.
Soil/dirt chitin's carbon will be incorporated into soil micro-organisms at a rate of 3 times more than the carbon lodged in organic matter in that soil; of course, as go deeper down in the soil profile there are less micro-organisms that break apart chitin. Native soil (as opposed to introduced) chitin degraders are more efficient that introduced microbes to a soil with chitin added in so if one is bringing in soil amendments (ex: bag of potting soil or top soil) the chitin cleaving micro-organisms will undergo a phase of adaptation (they'll experience what is called horizontal gene transfers).
Chitin added to soil first attracts local bacteria (& later local soil fungi) seeking to use it; some bacteria that themselves can not degrade chitin will come along to hijack some end products. As the chitin goes through break-down these colonize the chitin fibers & form a bio-film that then preps the chitin for real chitin cleaving microbes that are capable of putting out chitino-lytic enzymes.
In order to incorporate any chitin components for further break down inside themselves bacteria have to 1st hyro-lyse the chitin outside themselve. There are usually multiple chitin degrading genes for a micro-organism's chitin-ase enzymes & one sub-species has 18 of those genes.
Too high an amount of chitin added to the soil will find the gram negative bacteria responding (flourishing) faster than the gram positive bacteria; while those gram positive bacteria use the chitin carbohydrate (GlcNAc)for more anabolic(building themselves up) purposes. On the other hand gram negative bacteria use the chitin carbohydrate (GlcNAc) to drive reactions that are more catabolic (breaking down); soil gram negative bacteria have more of what is called the "2 partner secretion pathway" making them more capable of increasing aggregation/biofilm/iron uptake - however, if the gram negative bacteria has virulent potential these features can provoke pathogen-icity (goes from inactive to malign).
Moderation in the rate of chitin added to soil is a good practice & it has good effects on the soil population of proteo-bacteria & beneficial actino-bacteria sub-orders. Up to 46 genera of actino-bacteria, 9 genera of gamma proteo-bacteria, 3 genera of beta proteo-bacteria, 3 genera of firmicutes, 1 genera each of bacteroidetes & alpha as well as delta proteo-bacteria respond to chitin amended soil.
A low/moderate dose of chitin in soil 1st boosts the proteo-bacteria, although for the 1st 3 days their population slumps somewhat from original levels; if you add too much chitin the initial slump in numbers is greater. By the 6th day the proteo-bacteria have rebounded, reach peak numbers on the 10th day after exposure to chitin, start to fall back in numbers to original soil population by the 20th day & then experience another smaller scale surge in numbers for the next 15 days.
The response to chitin varies among the gamma, beta, alpha & delta proteo-bacteria species. Soil pH compounds the issue since it's role as a modifying factor can be over 75% on chitin degradation processes.
Actino-bacteria sub-orders don't ramp up their activity/population numbers as remarkably as do proteo-bacteria; however the actino-bacteria surge instigated by soil chitin goes on for a longer time than the proteo-bacteria. None-the-less if an excessive amount of chitin is placed in the soil the actino-bacteria will only be able to boost their numbers by about 38%.
The benefit from increased actino-bacteria in the soil is that all that extra mass in turn gives back more ammonium NH4+ into the soil & plants thrive with that mineralized nitrogen. Then too some actino-bacteria are symbiotic for the plant by controlling soil pathogens.
Now pH plays a shifting role in chitin degradation by most actino-bacteria's chitino-lytic enzymes; we can't simply say those enzymes are better functioning at a set pH. Generally speaking for the 1st 3 days of actino-bacteria exposure to soil chitin a higher pH will engender more chitin degrading enzyme genetic up-regulation, while after a week since exposure to soil chitin low pH will engender more chitino-lytic genetic expression. In terms of how much chitin degrading potential (enzymes elicited) there is not a vast difference whether the early soil pH level is high vs. low; but then by the 15th day of soil chitin exposure the actino-bacteria are putting out much more chitino-lytic enzymes to cleave the chitin (by 2nd month a 5.7 pH soil is way more active with actino-bacteria chitin degrading enzymes than their 15th days chitin degrading capability seen in a high pH soil).
Part 4:
Timing of a plants development cycle needs to be considered when applying chitin to soil; plants put out compounds into the soil as well. It takes some of the plants internal resources to exude molecules & one analysis estimates 23% of what roots put out are done for defensive purposes.
There are 2 recognized peak stages when the plant will exude it's own generated chitin degrading enzymes from their roots. The 1st happens when the plant is still a seedling (before 1.5 week old) & the other is when it in forming flowers (vegetative growth transitioning to flowering stage). One theory is these transitional times cause the plant to expend resources as root excreted chitin degrading enzymes to give a booster shot of immunity against root pathogens that might have adapted to the status quo & thus have renewed potential to be pathogenic to the plant roots.
Plant chitin-ase with more than 1 domain that can bind to chitin are capable of binding to select carbohydrates on the cell wall of pathogenic gram negative bacteria. That gram negative bacteria agglutinates due to multi-dimensional molecular changes on it's cell wall; this results in the loss of that bacteria's ability to move into the plant, as well as it's own capability to grow.
It is more common for plants to have only 1 chitin binding domain & this works for fungal defense. Multiple distinct chitin-ases (in theory from both plant & symbiotic micro-organisms) can work in synergy with their respective chitin "elicitor" binding protein at different fungal hyphae reactive sites on the same fungi; chitin-ase enzymes the hydro-lize the fungal cell wall component called beta-1,4-N-acetyl-glucosamine.
Another reason for the plant purging chitin degrading enzymes out of it's roots may(?) also be related to the fact that the ratio/blend of soil micro-organisms is changing with the different stages (age) of the plant. Which leads me to wonder if the plant root exudations of chitin degrading enzymes might also be a way to increase the amount of root zone fungal chitin being broken apart so that the local proteo-bacteria genera (or bacteroides/firmicutes/action-bacteria) can themselves thrive more & perform more of whatever symbiotic role they (it) plays for the plant. If the plant root enzymes exuded speed up the chitin break down the symbiotic micro-organisms uptake of extra chitin component(s)will be faster & their own population rise faster.
The question in my mind is if the period when plant roots are putting out a surge of chitin degrading enzymes is an ideal, less than ideal or even bad time to add chitin to the soil. Which brings me back to the plant hormone auxin (& cytokinin) since it is known that the plant chitin degrading enzyme (chitin-ase) responds to auxin (& cytokinin).
Messenger mRNA of plant chitin-ase is stymied by auxin (& cytokinin) while the age of the plant influences where the (those) plant hormone(s) are found. Auxin indole-3-acetic acid level is low in the bottom leaves yet higher in upper leaves; which corresponds with analysis showing the is not much plant made chitin-ase enzymes in the higher up leaves while there is notable chitin-ase in the lower leaves & even more plant chitin-ase enzyme mRNA in the roots of an established plant.
So, if a seedling wants a lot of auxin in it's developing roots then that root auxin is going to be inhibiting root chitin-ase enzyme levels. Which also means the seedling roots had to cut back it's auxin level temporarily (sometime before about 1.5 weeks old) in order to accumulate that root chitin-ase prior to exudation; the pause in root auxin level seems like a re-booting ploy to me.
Thus if you amended the soil with low dose chitin so that the proteo-bacteria had 10-20 days to work that chitin over (chitino-lysis) the week old seedling roots burst of chitin-ase will come along just as the proteo-bacteria capacity to degrade that chitin is flagging. And the root exuded chitin degrading enzymes will boost back up the amount of chitin converted into what soil microbes "like" to use(GlcNAc, etc.)until the proteo-bacteria get their 2nd surge (their day 21-35 of working over the added chitin).
I can't answer is if this is a good strategy or not; my inclination is that the seedling's root chitin-ase excretion is to liberate fungal chitin in the root zone & being a "blind shot" (there is not always pathogenic fungal chitin to attack) the seedling may really be performing this genetically programmed tactic to encourage the symbiotic micro-organism(s). Another thing to consider is if the purpose of the seedling maneuver is to knock back the ratio of fungi to bacteria; whose downstream effect may cause a staged phase of pH rise that is beneficial to the seedlings uptake of potassium (which maintains water balance as it is transported internally & a hyper-hydrated seedling won't develop ideal leaf photo-synthesis) at a key point in it's growth (& maybe restrict iron uptake rate at a key point in it's growth while storing the iron nearby in the extra microbial cells the degraded fungal chitin would feed). But I am speculating again.
Now if chitin was put in the soil far enough prior to seedling emergence so that actino-bacteria had a chance to bulk up then we can say it will provide the seedling with ammonium NH4+ mineralized nitrogen it can use. I don't envision any contra-indications to having added chitin 2 months before the seedling is a week old since the actino-bacteria should be effectively working on that chitin by then & have enough that died off whose carcass has nitrogen that is mineralized (technically organic ions are not taken up by plants & organic agriculture refers to something distinct). What happens to the residual extra chitin the actino-bacteria haven't degraded before the seedling roots dump their own chitin-ase enzymes out into the root zone I imagine is the actino-bacteria get to feed on even more chitin with less expenditure of their own resources.
Let me put it this way: I personally don't think the day the seed is planted is the appropriate time to put insect chitin in the root zone, nor right when the seedling roots exude their chitin degrading enzymes (apparently targeting the local fungal chitin). I am inclined to think the ideal time to put insect chitin into the planting area is sufficiently prior to seed emergence so that by the time the seedling is no more than 1.5 weeks old chitin loving micro-organisms have established their numbers by chitin degrading; whether it is better to promote proteo-bacteria (quicker) than actino-bacteria (slower) I do not know; my thinking is there will be less of a conflict (over degrading root's fungal chitin target) by timing for an actino-bactieria population - however, my hunch is that the seedling's root chitin-ase exudation is actually aimed at one or more of the 9 genera of proteo-bacteria(sort of a way for the seedling to get a proteo-bacterial "strike force" going).
Part 5:
Which leaves the issue of why roots once again explicitly expel chitin degrading enzymes into the soil when the plant transitions to flowering. All I can surmise is it deliberately intends to break up some fungal chitin at that time; whether it is purely a preventative "1st strike" against fungal pathogens before becoming vulnerable I can not say.
Personally I am willing to entertain the idea that it is another tactic to get more symbiotic micro-organisms active at that stage for whatever they might soon give to the flowering plant that the root zone fungi are not (a pH rise? chance to pump in specific ions?). Or it might simply be a way to kill off some fungi to free up the fungal bound phosphorus (although I doubt this & question the whole high phosphorus fertilizer for flowers regimen).
The chitin degrading instigated by the pre-flowering plant root exudation of chitin-ase is aimed at the soil microbial ratio. Flower cells are regulated by expansin protein(s) as the pollen tube grows toward the flower ovary; which makes for more pollen.
An ambient CO2 rise engenders enhanced elongation in a plant's life cycle because CO2 up-regulates the genetic expression of expansin(s). The soil microbes are the planets most prolific source of CO2 & if the root chitin-ase fosters micro-organisms that release more CO2 that gas is going to waft up to the plant's inflorescence. As far as whether that would be another opportune time to add insect chitin into the plant soil my inclination is to say no;(if I am correct) the plant doesn't want any time delay before the micro-organisms work on any chitin, but rather want the timely release of CO2 tied up at it's base.
Flowers have several different expansins mediating hormones for floral development when secreted into cell walls to "loosen" growing component parts; 3 beta-expansins are active mostly in early floral development & down-regulate precipitously as the florescence grows quicker. At least 7 alpha-expansins are part of flowering; these are low in small buds & become highly expressed when the floral tube develops the most.
The alpha-expansins' levels drop once the flower opens & rise again when the calyx folds in to collapse; correspondingly, the levels of proteins responsive to auxin change in tandem (paralleling the alpha expansins' levels at distinct phases). So conceivably if the root exudated chitin-ase(s) are causing a time lag of no more than 10 days for the proteo-bacteria to get busy & the purpose is to get a surge in CO2 volatilized up toward the floral expansin(s) we are forced to guess if it is the developmental beta- expansins that CO2 is supposed to stimulate or prior to floral opening alpha-expansin(s) that really benefits from CO2 boost.
