Post by brian on Dec 10, 2006 9:40:43 GMT -5
I’ve been wondering about temperature hardiness in CPs and how to look at the data I’ll hopefully have in the spring. There’s concepts here with analogies in occupational health & safety and toxicity testing.
The first is exposure time. For example, in noise testing, there is a limit for instantaneous noise beyond which your hearing is damaged. But there are other limits for various time weighted averages. A much lower level level would damage your hearing if sustained over an eight hour shift. So, a series of limits for various time intervals are published. In the case of plants would temperature tolerance vary with exposure time? On one extreme if anyone ever looked at impatience plants after a light frost they turn right to mush as if the high water content froze right at zero degrees and instantly burst the cells. With other plants there would likely be some antifreeze protection, or maybe substances that keep the ice crystals small enough to prevent damage. So basically, would there be one temperature that kills a plant, or could it take a much lower temperature over a day that would kill it if sustained for a month? In this case the initial freezing would not kill it but ice recrystallization for example could produce bigger shards that would eventually damage the cells. (On the flip side, this may be why hardy seeds need imbibation – thanx Tom! – followed by freezing; ice crystal formation would trigger viability).
The second analogy is the definition of lethal dose. In rainbow trout toxicity you basically toss the fish in different concentrations of industrial effluent, leave them there for a fixed time (five days I think) and count how many die. Yes I know it is cruel, I’ve never done it myself, but that’s how it is. (There are more ALF friendly tests that use daphnia magna or even fluorescent bacteria). The point is because of variations within a species the whole population does not simultaneously die at one concentration, so the toxicity is calculated as, say, an LD50 (the lethal dose that kills 50% of the population). Now, it could be that the temperature that kills 10% is only a degree away from the temperature that kills 90% so the concept is unimportant. Otherwise, ultimately one would want to look at what constitutes a sustainable survival rate for plants, maybe LD5, or perhaps the point at which their natural propagation rate via self seeding and expansion equals the loss rate. As a bonus, knowing something like the LD50 could be used to breed hardier plants by crossing survivors in an artificially chilled environment.
One more trout toxicity analogy. The test reports include a comments column where they record the number of floaters, not yet dead but obviously distressed. I’ve wondered if some plants suffer some cellular damage to the growth centre but manage to self propagate from surviving root tissue, which would explain small leaf growth and lack of flowering. Just wondering if they could be “floaters”.
Too bad I didn’t go to Guelph and study botany – could’ve been a thesis project!
The first is exposure time. For example, in noise testing, there is a limit for instantaneous noise beyond which your hearing is damaged. But there are other limits for various time weighted averages. A much lower level level would damage your hearing if sustained over an eight hour shift. So, a series of limits for various time intervals are published. In the case of plants would temperature tolerance vary with exposure time? On one extreme if anyone ever looked at impatience plants after a light frost they turn right to mush as if the high water content froze right at zero degrees and instantly burst the cells. With other plants there would likely be some antifreeze protection, or maybe substances that keep the ice crystals small enough to prevent damage. So basically, would there be one temperature that kills a plant, or could it take a much lower temperature over a day that would kill it if sustained for a month? In this case the initial freezing would not kill it but ice recrystallization for example could produce bigger shards that would eventually damage the cells. (On the flip side, this may be why hardy seeds need imbibation – thanx Tom! – followed by freezing; ice crystal formation would trigger viability).
The second analogy is the definition of lethal dose. In rainbow trout toxicity you basically toss the fish in different concentrations of industrial effluent, leave them there for a fixed time (five days I think) and count how many die. Yes I know it is cruel, I’ve never done it myself, but that’s how it is. (There are more ALF friendly tests that use daphnia magna or even fluorescent bacteria). The point is because of variations within a species the whole population does not simultaneously die at one concentration, so the toxicity is calculated as, say, an LD50 (the lethal dose that kills 50% of the population). Now, it could be that the temperature that kills 10% is only a degree away from the temperature that kills 90% so the concept is unimportant. Otherwise, ultimately one would want to look at what constitutes a sustainable survival rate for plants, maybe LD5, or perhaps the point at which their natural propagation rate via self seeding and expansion equals the loss rate. As a bonus, knowing something like the LD50 could be used to breed hardier plants by crossing survivors in an artificially chilled environment.
One more trout toxicity analogy. The test reports include a comments column where they record the number of floaters, not yet dead but obviously distressed. I’ve wondered if some plants suffer some cellular damage to the growth centre but manage to self propagate from surviving root tissue, which would explain small leaf growth and lack of flowering. Just wondering if they could be “floaters”.
Too bad I didn’t go to Guelph and study botany – could’ve been a thesis project!