The archetypal dose-response curve is the one described by Mitscherlich (1909), with at the left a part (marked by an A)
where a given environmental factor (e.g. Nutrient supply) is limiting the plant trait of interest (e.g. Yield),
then a region (B) where the environmental factor is optimal,
and subsequently a range (C) where the environmental factor is supra-optimal for that trait:
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The above graph also illustrates an interesting problem. Suppose that two experiments are carried out, one with species X by investigator M,
and one with species Y by investigator N, both with two levels of the same environmental factor. The results for the first experiment are the
brown points in the graph, the results for the second are the blue points.
When we try to generalise across these experiments, we would conclude from the 1st experiment
that the environmental factor has a positive effect on the trait of interest, whereas the 2nd experiment suggests that
there was no effect at all. In reality, it might be that the species X and Y respond exactly in the same way, following the same dose-response curve,
but that the two experiments comprised rather different parts of this curve.
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Of course, it could also be that the two species behave differently because they were grown at very different other conditions
(e.g. growth chamber versus glasshouse) or behave differently because they occupy different ecological niches, or simply
because the two species have evolved from different ancestors. Also these alternatives can be analysed with the MetaPhenomics
approach. |