Abstract: Tomato seedlings were treated with 15 ℃ (control), 12 ℃, 9 ℃, and 6 ℃ at night for seven days to study the changes of their leaf photosynthesis an d chloroplast ultrastructure, aimed to make sure the recovery effect of the phot osynthesis of tomato leaves after a short-term low nocturnal temperature. The r esults showed that short-term low nocturnal temperature was favorable to the ph otosynthesis of tomato leaves at recovery stage. The chlorophyll content could r ecover to the normal level as control under the treatments of 12 ℃ and 9 ℃, bu t not under the treatment of 6 ℃. The formation of stoma was not seriously inhi bited by low nocturnal temperature. On the contrary, the stoma formation and its growth were stimulated at recovery stage. Under the treatment of 6 ℃, chloropl ast grana layers arranged loosely, and their number reduced. In the seven days o f recovery, the lower the treatment temperature, the smaller and the fewer the s tarch grains were, and the more compact and tidy the chloroplast grana became. I n addition, the transportation of photosynthesis products was promoted after sho rt-term low nocturnal temperature.

Key words: hedgerow, soil aggregates, destruction rate of soil structure, slope, soil and water loss.