So, one of the (sometimes) downsides of being "US" (human), is that we can only perceive effects and not causes. Anything we see has already bounced of an item (light) and we are seeing the effect of the item upon which we are observing. With plants and differences in requirements, is also an effect. The cause would be related to the conditions it grew / evolved in.
We already know that differences in evolved cannabinoids relate to incident photo spectrum at varying latitude. As well that photoperiod effects hormone response and nitrate assimilation.
Something I've pondered on a bit, is relating to differences with strains and why plants evolved to require what they do. Plants in higher latitudes will tend to have more / longer / larger periods of cooler soil temps; which lower biological activity and thus lower nutrient conversion / availability. All the while the larger organisms that are introducing waste remain constant. When spring hits and biological activity increases; so does a large availability of "easily converted" products. This would mean that plants from higher latitudes would have to be more tolerant / resistant to higher salts (nutrients) than strains that developed in lower (mid) latitudes. I.E. Indicas.
Plants evolving in mid / equatorial latitudes would probably be exposed to a, in general, more stable level of nutrients / availability throughout the year. There would be no great periods of nutrient build up from lowered biological activity, so plants would not need as much resistance to salts. As well, there would most likely be a smaller variation in NPK and their relative ratios; so equatorial strains may well not need nor benefit as much from "dramatic" NPK shifts commonly seen in hydro and blooming. I.E sativas
As well differences in rooting should relate to evolved conditions. Northern latitudes will tend to have higher moisture periods and/or longer times of high moisture. Combined with periods of warming and high availability of salts, the root system should be more resistant to moisture as opposed to drought. There would not be a necessity to grow a huge root mass, but to retain the optimal health of the existing root mass.
Equatorial strains however would probably be more focused on large root systems that are more resistant to drought. Since seasonal availability varies to a smaller degree and (more or less) moisture tends to be lower / have longer periods of low moisture; the higher probability for survival here is to have more roots total than to preserve the quality of existing.
If we consider some element specifically:
Nitrate. Why would plants have evolved to "require" (used loosely) less nitrate in flower? Again if we look at latitudes with, at least, some seasonal variation in temperature (as largest percentage of total species are); we have spikes of nutrients during the warming periods. The first of these, most available and in the greatest quantity; would be forms of Nitrogen. However with new rapid spring growth and proliferation of biological activity, the fast arriving Nitrogen also becomes one of the first to lower as the season progresses. As a result of this, plants from seasonally dynamic locations and from a survival standpoint; must rely less on this element as the season progresses. Some plants may even use this lowering as a signal / trigger for seasonal blooming (i.e. orchids).
Phosphorus. This is one element that is still highly debated in all aspects of its' perceived properties (better blooming, rooting etc). However, P is something that is: very reactive in soils, generally always in medium in some form, often high in mediums and does not most technically vary to a large degree seasonally. Since P is always bouncing from one unavailable for to another and often requires exudates (along with root hairs) to be available in proper quantities; root structure via increase in hairs along with exudate modification, would be the best survival choices for evolution here. It would be of note though that latitudes with seasonal variations in temperature would cause marked changes to the N>P ratio throughout the season; much larger than equatorial. Note too, that the ratio change is merely a drop in N rather than an increase in available P throughout season.
Potassium. This element can be resolved relatively easily I suppose. The seasonal variable availability across many latitudes would be marginal for this element. Most plants have "no known toxicity" to potassium. Potassium is not as easily bound up as other elements. From all of this, it sorta makes sense that this would be the dependent element for transpiration and water uptake. I.E. plants have evolved to "expect" that this element is a Constant and not variable.
