EFFECTS OF SIMULATED ACID-RAIN ON PINUS-DENSIFLORA - INHIBITION OF NET PHOTOSYNTHESIS BY THE PHEOPHYTIZATION OF CHLOROPHYLL

This research addressed the effects of simulated acid rain on the chlo rophyll contents of leaves of Pinus densiflora, on the net photosynthe tic rate on a unit chlorophyll basis, and on chlorophyll degradation. When NO3- concentrations in rain water increased, the chlorophyll(a+b) contents of the leaves increased in parallel, even though the pH of t he simulated rain decreased. The nitrogen content of the rain was suff icient to stimulate the production of chlorophyll and was able to over ride any degradative effect expected due to the H+ input from acid rai n. The absorption spectrum of chlorophyll extracted from the leaves ex posed to acid rain showed peaks at 665, 606 and 535 nm, characteristic of pheophytin a, indicating degradation of chlorophyll to pheophytin. Net photosynthetic rate on the basis of chlorophyll content was reduc ed by acid rain, even though the total chlorophyll content of the leav es was increased. The acid rain does, therefore, simultaneously increa se chlorophyll content and reduce the efficiency of the use of chlorop hyll in photosynthesis. This reduced efficiency may be linked to the i ncrease in the rate of degradation of chlorophyll to pheophytin.