Articles
SIMULATION OF PLANT GROWTH BASED ON METHODS OF PLANT GROWTH ANALYSIS EXEMPLARY FOR RADISH
The functional approach of plant growth analysis must be used for separating the effect of ontogenetic drift and the one of medium-term climatic fluctuations.
As growth functions (equation 1 and 2) and the Intransformation of these ones do not meet all requirements, especially the exact description of the whole growth period (tab.1), a compound function had to be developed.
Using equation 1 the fit of untransformed data was connected with the fit of transformed data as a function of time (equation 3, tab.1).
Instantaneous values of growth components like Absolute Growth Rate (G), Relative Growth Rate (RGR), Net Assimilation Rate (NAR), Leaf Area Ratio (LAR) and the ratio of Leaf Weight and Tuber Weight (LW/TW) were derived from function 3. Marked points like maxima of growth components indicate changes in the metabolism of plants.
They are used for dividing growth period in physiological founded domains (growth phases) in comparing to formal weight classes (fig.1 and 2), since up to now it is impossible to describe physiological age in a functional way.
Following from the assumption of constant values of RGR, NAR and LAR within the growth phases the continuous process of age is described in a stepwise manner (fig.3).
The central relationship "RGR=NARxLAR" takes into account that dry matter gain depends on photosynthesis and morphogenesis and that the reaction of these both components on climatic conditions may be different.
The assumption of constant RGR values in growth phases implies an exponential gain of dry matter and the daily weight (Wn) can be calculated after the equation Wn= Wn-1 exp (RGR). Daily RGR values are determined by the age, equivalent to the level of RGR values in growth phases, and by the reaction of RGR to daily mean values of radiation and temperature derived from response surfaces.
Simulation of radish growth was best with four growth phases with slight superiority of the formal founded phases.
The simulated growth is in accordance with the real one (fig.4). The direct relation between RGR and radiation is obvious.
The effect of age is remarkable from different levels of RGR values during growth.
Further details are described by Liebig and Lederle in the article "Strategy for modelling plant growth" of the same issue.