Hang on just a sec. If K is antagonistic to Ca Mg Fe Mn Zn CU as Rick's table suggests, how could reduced K levels lead to reduced toxicitiy from the above elements? PS. not arguing just trying to clarify
What is the definition of a toxicant versus nutrient?
All of the above (including K) are required nutrients for plant growth, but that doesn't mean that the plant can take on unlimited amounts of any of them without them becoming toxic. Evolution to the world around us (which is pretty much the same for every terrestrial life form). Means that all of the above elements have been put to use at some relation to how common it is in the environment. Copper is a required nutrient at very low ppb levels, and is never encountered in the real world at much higher than it is used. What would be the competative advantage to require a nutrient that you had to spend a ton of energy and time to obtain almost nothing. Really is the same for K but it is a lot more common in the environment than copper (but still not as common as Ca or Na). So you either adapt to what is more than you need or develop a competative use for what you have the most of in your environment. You don't spend all your time coming up with great things to do with resources you don't have access too. But once that system is in place, its a shared system for many other things. K aquisition is a developed high priority system in plants, but because K is rare, no feedback loops are put in place. But the K aquisition mechanism is also hooked to aquistion and utilization of a ton of other mechanisms. So without checks and balances on K uptake it over loads on other things. If you added unnaturally high levels of Fe or Cu you would get the same disruptions, but natural for those ellements is <<<<than for K.
Some of the metal substitution work in bacteria is instructive. Particluar enzyme rates were measured for certain enzymes that typically have zinc as the operative metal in the enzyme structure. (say something like sugar metabolism). By growing the bacteria in a cobalt rich environment (still below toxic acutely toxic thresholds) they got the bacteri to substitute Co for Zn in the enzyme. That enzyme rate was sped up by a factor of 1000X, and then most of the bacteria burned out. But thats lab physiology stuff. You could also ask why did God come up with zinc requiring enzymes in the first place, or when would bacteria even see elevated levels of cobalt in the environment?
None of this is linear. Need to envision this as a big spider web, with a different ellement at the juncture of the different threads. As you pull on one it moves all of them. I can't possibly understand every last metabolic interconnection in a living organism now (after 40 years of study) let alone detail it in a 200 word paragraph post on a website. I guess this level of understanding is really cool to a lot of us. I never really thought of trying to grow bacteria in a cobalt enriched environment.
