Plant Photosynthesis

Plant photosynthesis requires light, normally light from thesun. When the sun is high in the sky more of its light penetrates through the atmosphere to the earth's surface. Knowing this, I have never understood why it is claimed that plant growth during the summer in the far north is faster than at lower latitude. It would seem that the long summer days would not compensate for the low sun angle.

The error in my thinking was corrected by Dr. Don Dinkel of the University's Institute of Agricultural Sciences at Fairbanks during one of his recent lectures. He showed that the rate of plant photosynthesis is not proportional to the intensity of the sun's rays reaching the plant. Instead, photosynthesis begins as soon as the sun comes up and continues until sunset. The rate of photosynthesis does not necessarily increase as the sun gets higher in the sky. Quite the contrary if the plant leaves get too hot, the rate of photosynthesis actually decreases.

Thus it really is true that some plants grow more rapidly and produce more useful food in Alaska than in other states. Further emphasizing the point is Dr. Dinkel's statement that, figured over the summer growing months, the area around Circle in northcentral Alaska has the highest potential for photosynthesis of any region in the world.