Abstract: According to the principles of photochemical reaction and the ecophysioiogical characteristics of photosynthesis of tree leaves, the relative distribution of photosynthetic effective, radiation (PAR) in any position of tree canopy is detected by photochemical reaction actinometer with a solution of 0.01M Reinecke salt {ammonium reineckate, ammonium tetrathiocyanodiammonochromate, NH₄[Cr(NH₃)₂(SCN)₄] ·H₂O}. The effective absorption wavelengths are as wide as 350—750nm and meet the demand for PARin tree leaf photosynthesis. The new technique is reliable, simple, convenient, and practical without any damage to the vegetative or reproductive organs of tree canopy. It is superior to the traditional methods (e. g. using photometer, radiometer, quantometer) in representativeness and repeatability. Therefore, it is appropriate for studying the photosynthetic eeophysiological phenomenon in tree population.

Key words: Photosynthetic effective radiation, Tree canopy, Photochemical reaction, Reinecke salt solution, Tamarix chinensis, IsoSource model, water use strategy, coastal zone, oxygen stable isotope