IDENTIFICATION OF DYNAMIC PLANT GROWTH AS A FUNCTION OF LIGHT QUANTITY

The dynamic responses of the shoot growth of Hedera helix L. ‘Mein Herz’ in relation to changes in photosynthetic photon flux density (PPFD) is identified. For the identification a growth experiment was conducted in a climate chamber from August to October 1997. The shoots from three pot plants were placed on three balances and the fresh weight was continuously measured together with the PPFD level. The measurements were sampled at 10 min intervals. The daily increase in fresh weight was determinated over a period of 45 days and related to the daily mean PPFD. During the experiment a two level and random strategy of the daily PPFD level was used, i.e. random 60 or 260 μmolm^-2s^-1.

A discrete dynamic model of growth response to PPFD was estimated. The results show that not only the current PPFD level at the actual day is related to the daily increase in the fresh weight, but also the PPFD given at previous days. For the previous days the effect of PPFD is described as an exponential decay; whereby from one day to the previous one, the effect of PPFD is reduced to 67%, 66% and 80%, respectively for plant 1, 2 and 3.