Multifactorial Growth Responses in Holcus lanatus: Optima and Limiting Factors

Abstract

A factorial, controlled-environment experiment employing four levels each of photosynthetically-active radiation (PAR), nutrient supply and ambient temperature was conducted on the grass Holcus lanatus L. (Yorkshire fog).The back-transformed means of log total dry weight per plant at 28 d for the highest- and lowest-yielding treatments were 533 mg and 1·8 mg respectively. An analysis of variance showed that all three environmental variables have strong and complex interaction with one another. Multivariable, polynomial response surfaces were fitted to answered questions such as: Where does maximal yield lie? How curved is the response? How steep are the gradients of yield against the three environmental variables? How sensitive are individual response curves to background levels of other factors?The direction of change in the logarithms of total dry weight and total leaf area was positive throughout with changes in PAR, nutrient supply and temperature, except at certain extreme combinations of factor values. For leaf area ratio, the direction of change with nutrient supply and temperature was also consistently positive, but with PAR it was consistently negative, creating saddle-point in the response surface.For all three yields variables, the response to all three factors considered individually was relatively independent of variations in the background levels of the remaining two. The ranking of percentage yields was particularly stable to such variations in background, even under markedly sub-optimal combinations of conditions.General conclusions regarding the significance of multivariate tests were drawn, with particular reference to the conduct of inter-specific screening operations and the interpretation of multi-factor environment scenarios such as those involved in climate change research.