Martin, I'm not dead certain of my memory either (experts please help), but if I recall correctly (and if the source(s) was/were correct), many "weeds" are non-mycorrhizal or facultatively so. I'm not sure of the Chenopodiaceae, but they seem to be notorious hyperaccumulators (as Popeye was famously aware), and I don't know whether or not they are ever mycorrhizal and what difference it may make.
Has anybody really sorted this out? I don't want to hit the books, but if I did I would dig out Stebbins' "The Genetics of Colonizing Species." Sounds like a peach of an idea for a dissertation. WT PS: The evolutionary history of mycorrhizal associations might hold a clue. What is it about root physiology that keeps some minerals in and some out? Semipermeable membranes? Something else (too)? How is the amount limited? Osmotic potential? Help! ----- Original Message ----- From: Martin Meiss To: Wayne Tyson Cc: [email protected] Sent: Wednesday, April 20, 2011 10:31 AM Subject: Re: [ECOLOG-L] where do edible plants retain lead and other contaminants? Wayne, Your comment on mineral uptake by the mustard family reminded me (correctly, I hope) that the the cruciferae are one family that does not use mycorrhizae to mediate mineral uptake. Maybe the mycorrhizal associations account for some of the variability in heavy-metal uptake in other families. Martin 2011/4/16 Wayne Tyson <[email protected]> The original post may be related to the "eat the weeds" movement, one I have long considered a good idea while suffering no illusions that it will have any real impact upon the weed "problem." I eat weeds because I prefer them to most of their highly developed or CMO'd relatives. The weeds often, in addition to being more tasty, contain more nutrition than their cultivated cousins. Chenopodium album, for example, a common roadside weed, is one of my favorites. It is an "accumulator" (what plant isn't), containing a lot of iron (iron is a vital nutrient; it also is a poison--dosage is important). I do, however, pay attention to the substrate upon which they are growing. I prefer hillsides to stream bottoms unless I know the watershed is pretty free of contamination. Stream bottoms, especially those into which contaminants, often in the form of raw sewage drain, often contain the "best" crops of the lushest weeds. In my ignorance of the specifics, I rely upon the precautionary principle, "the solution to pollution is dilution," and a smidgen of knowledge (which we all know can often get one into more trouble than ignorance), and perhaps some myths I have unwittingly adsorbed (or worse, absorbed) along the way. I avoid roadsides and vacant lots of unknown history too. I trust my own ignorance more than that of agribusiness, but that's far from perfect. WT ----- Original Message ----- From: "malcolm McCallum" <[email protected]> To: <[email protected]> Sent: Saturday, April 16, 2011 7:10 AM Subject: Re: [ECOLOG-L] where do edible plants retain lead and other contaminants? Wayne brings up a good point. The bioavailability of toxic compounds, including metals is affected by many things among which pH can be one. In fact, the issue of TMDLs in the clean water act is based on problem that each stream has its own water chemistry and organic load. This causes us to require specific total maximum daily loads (TMDLs) of each compound for each stream (or portions thereof). TMDLs were supposed to be completed for surface waters in most states a long time ago, unfortunately the process is not done everywhere! Malcolm On Fri, Apr 15, 2011 at 9:03 PM, Wayne Tyson <[email protected]> wrote: Ecolog: This rings a vague bell for me too. There was some work done in the British Isles (Scotland) on very crisp ecotones across pH differences using one grass species. Also, I seem to recall that the Dutch were using willows that were supposed to be hyperaccumulators and they were burning them for fuel, then disposing of (or "mining") the heavy-metal "laden" ash. There is, of course, considerable literature on "phytoprospecting." I, too, would like to be brought up to date in this area, and educated on the particulars. For example, I would like to know just how accumulation or "rejection" functions, and what processes are involved. For example, how does pH affect the rate and amount of absorption? What other chemical and physiological processes are involved? Why are some heavy metals (chromium, selenium, arsenic, etc.) apparently readily absorbed (by the Chenopodiaceae, for example--and the mustard family), and lead apparently not? Is it as simple as semipermeable membranes, whether or not they are soluble and under what conditions? Is something going on in the rhizosphere that evades some analytical procedures? WT ----- Original Message ----- From: "Martin Meiss" <[email protected]> To: <[email protected]> Sent: Friday, April 15, 2011 9:04 AM Subject: Re: [ECOLOG-L] where do edible plants retain lead and other contaminants? A long time ago, when I was learning about plant ecotypes, I heard of research on the adaptation of plants to high lead levels found in piles of mine tailings. If I remember correctly, local races of plants were forming that were able to adapt to toxic soils. This raises these questions: if plants ARE NOT taking up the heavy metals, what is the mode of toxicity? (Are ions in the soil blocking the uptake of needed substances?) What is the mechanism of resistance that was evolving? If it involved the blocking of uptake of lead and other metals, that implies that other, non-adapted plants DO take them up. Can any one comment on this aspect of the issue? Martin M. Meiss 2011/4/15 Judy Che-Castaldo <[email protected]> Hi Ben, In general you are unlikely to find lead in the shoots of plants, because it is not very soluble and most plants exclude heavy metals. The edible plants that may have Pb would likely be leafy vegetables (grown close to the ground) and root vegetables (as mentioned earlier) because of the associated soil particles containing Pb. There are some plants that uptake heavy metals into their shoots but few for Pb, and even those may only do so under rare circumstances (such as phosphorous deficiency - Chaney 2007 J. Environ. Qual. 36:1429–1443).. If you are interested in other contaminants you can look into the metal hyperaccumulation literature. Many of these plants are in the mustard family but probably are not normally eaten. best, Judy Judy Che-Castaldo BEES program, Biology Dept. University of Maryland (301)351-8290 http://www.life.umd.edu/grad/BEES/students/che.html ----- No virus found in this message. Checked by AVG - www.avg.com Version: 10.0.1204 / Virus Database: 1435/3511 - Release Date: 03/16/11 Internal Virus Database is out of date. -- Malcolm L. McCallum Managing Editor, Herpetological Conservation and Biology "Peer pressure is designed to contain anyone with a sense of drive" - Allan Nation 1880's: "There's lots of good fish in the sea" W.S. Gilbert 1990's: Many fish stocks depleted due to overfishing, habitat loss, and pollution. 2000: Marine reserves, ecosystem restoration, and pollution reduction MAY help restore populations. 2022: Soylent Green is People! 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