Dear Lauw Some factors which no doubt play a part, are the qualities of light found in the southern hemisphere, you can get sun burnt even on cloudy days, differentiation of temperatures between day and night, less differentiation or more, depending on location, presence of absence of soil flora and bacteria. Depending on the species, I feel all of these have to be considered. One other factor which I often feel is overlooked, is the quality of the water supplied. I do not know the exact chemical formulae of the water however the light factor might play a role here, and in the northern hemisphere there is so much pollution it must also play a role. If pure distilled water is used, to avoid the pollution, it might also change the content of the rain water, soil water etc.. Indeed an interesting question, however logic dictates, at least to me, that in such natural occurring features the answers would be found. Cheers, John E. Bryan