%0 Research article
%T Utilizing a multipoint measuring system of photosynthetically active radiation in photosynthetic studies within canopies
%A Palva, Lauri
%A Garam, Eero
%A Palmroth, Sari
%A Sepponen, Raimo
%A Hari, Pertti
%D 1998
%J Silva Fennica
%V 32
%N 4
%R doi:10.14214/sf.673
%U https://silvafennica.fi/article/673
%X A novel multipoint measuring system of photosynthetically active  radiation (PAR) has been constructed and operated within a Scots pine  canopy. A regular grid of 800 measuring points has been incorporated  into a cuvette to observe the spatial and temporal distribution of PAR  incident on the needles of a twig along with simultaneous measurements  of the CO2 exchange in order to determine the dependence of  photosynthesis on PAR. It was shown that large errors can result if the  photosynthetic rate is estimated using the mean value of PAR instead of  the instantaneous values of PAR detected at given points in the region  of the needles. The results demonstrate that the obtained regression  between the CO2 exchange rate estimated using the multipoint PAR  measuring system and the measured CO2 exchange rate is as good within a  canopy as in unshaded conditions.