In this report we consider the application of growth analysis techniques in environmental physiology, with particular concern for their ability to produce results which can be integrated with studies of short-term metabolic responses at finer levels of organization. For purposes of illustration, we use responses of Spergularia marina (L.) Griseb. and lettuce (Lactuca sativa L. cv. Black-seeded Simpson) to changes (environmental discontinuities) in the composition of a solution culture medium. Initial emphasis is on the use of cubic spline methods. It is concluded that while these may give apparently good fits to growth data, differentiation for determination of relative growth rate (RGR), and further transformation for such parameters as net uptake rate (NUR), are of questionable applicability. An alternative analysis based on the discrete estimation of RGR is considered.
In any study, the requirements for both statistical and physiological confidence must be reconciled. In practice, and in the absence of mechanistic frameworks to which the results can be modeled, this is best accomplished by strictly adhering to the mathematical guideline that no more elaborate a description be applied than can be statistically justified.