Quote: >Of two identical plants >grown identically, the one receiving exogenous nutrients will grow at a rate >closer to its maximum capacity, all other things being equal.
Net primary productivity in almost any plant examined peaks at an environmentally-determined concentration of nutrients and then dips. That is, too much is harmful which is, of course, a tautology! However, quite aside from the affects of altered and raised soil microorganism levels, increased predation by insects and other consequences of high nutrient status, there is evidence that e.g. nitrate reductase inhibitor levels rise with very high levels of nitrate. (Plants cannot metabolise nitrate directly, and have to reduce it to the accessible NH4+ ion in the leaves, using the enzyme nitrate reductase and its spear carriers. The nitrate reductase inhibitor is a compound generated in the leaves which inhibits this, presumably thus managing nutrient inflow.) Symbiotic fungi that gather ions such as phosphate for the plant are eaten or their development is inhibited in nutrient-saturated media. (Or they are in onions, for which there are data. Such fungi are nevertheless probably crucial even for mature orchids.) And so on: I suspect that there may be a plant version of "metabolic syndrome", where too much is indeed too much. ______________________________ Oliver Sparrow +44 (0)1628 823187 www.chforum.org _______________________________________________ the OrchidGuide Digest (OGD) [email protected] http://orchidguide.com/mailman/listinfo/orchids_orchidguide.com
