Photosynthesis declined in all treatments over time from the start of the treatment (data not shown) similar to the decline in leaf nitrogen levels. The decline,however, was mush steeper in the ON() treatment compared to the 20N() and 100N () treatments. The photosynthesis of 100N,20N and ON treatments was 40,35and 24 ,respectively, when averaged across measuring times.The 20N treatment was not statistically different from that of 100N,but the ON treament was statistically different from the 100N,20N treatment.