Abstract:

The high salinization character of coastal saline soil affected the plant colonization and growth. In this paper, the effects of different method of using composed sewage sludge were compared. And the photosynthetic characteristic of some plant species was measured periodically for the purpose of reflecting the effects of different ratio of composed sewage sludge in time gradient. The results showed that: (1) Using composed sewage sludge in the coastal saline soil could improve the photosynthetic efficiency of plant species. The comprehensive effects of adding composed sewage sludge was not only related to the added concentration, but also the plant growth condition and adaptability. The effect duration of adding composed sewage sludge was proportional to the added concentration. (2)Adding composed sewage sludge may cause stress effect in early period, and some plant species with strong adaptability showed that the net photosynthetic rate was higher than control group in adding 5% amount of composed sewage sludge, such as Nerium indicum, Pittosporum tobira and also. The effects of adding 2.5% and 5.0% amount of composed sewage sludge was better than that of 7.5% or higher amount in normal growth period of plant species. And the effects of adding 2.5% and 5.0% amount of composed sewage sludge was significantly weakened in about 500 days since the adding day, but adding 7.5% amount of composed sewage sludge was also showed a significant promotion effect. It was suggested that adding composed sewage sludge should be many times but small amount for once. (3) The stomatal conductance and intercellular CO2 concentration of adding composed sewage sludge group was higher than control group, but its net photosynthetic rate was lower than control group. The photosynthetic efficiency of new or excellent plants didn’t change significantly in condition of adding 5.0% amount composed sewage sludge group in about 180 days since the adding day. (4)While using composed sewage sludge for improving soil condition, the main factor that affected the plant net photosynthetic rate was plant adaptability in a relative long time scale, but the using amount of sludge would have more significant affects in the short time scale. It was suggested that the main application ratio of composed sewage sludge might be 5% and below when using sludge for improving coastal saline soil.