Effect Of Natural Brassinolide On Drought Resistance Of Three Tree Species' Seedlings On The Loess Plateau

Robinia pseudo-acacia, Pinus tabulae formis, Platycladus orientalis are mainly tree species on the Loess Plateau. Effect of brassinolide on drought resistance of three tree seedlings were studied in potted-plant. Roots of three arbor seedlings were dipped with different concentrations of natural brassinolide when cultivated and the seedlings were sprayed same concentrations of natural brassinolide one year later. At the same time, three soil water treatments were set by artificially controlling soil moisture. The results are as follows. 1. The growth development of three seedlings was decreased under soil water deficit. The plant height and base diameter were increased under different NBR treatment. Especially under severe soil water deficit, root growth was increased to that in normal soil water maintained, suggesting that NBR treatment may relieve soil water deficit and increase absorbing area of seedlings. Biomass was accumulated under light soil water deficit. The growth development of Pinus tabulae formis and Platycladus orientalis seedlings under 0.1mg/L NBR treatment was better than other concentration NBR treatment. 0.2mg/L NBR treatment was the best to Robinia pseudo-acacia seedlings. 2. The leaf water potential and RWC of three arbor seedlings was increased on severe soil water deficit after NBR treatment. The Platycladus orientalis seedlings'RWC was more increased under severe soil water deficit than normal soil water condition. The natural saturation deficit of three arbor seedlings was decreased after NBR treatment, implying that NBR treatment can increase the leaf water content and decline water loss of seedlings under soil water deficit. 0.1mg/L,0.2mg/L NBR treatment were better than other concentration to Pinus tabulae formis and Platycladus orientalis seedlings, respectively,0.2mg/L NBR treatment was the best to Robinia pseudo-acacia seedlings. 3. Proline contents, soluble sugar contents and the activities of superoxide dismutase, peroxidase and catalase of three arbor seedlings were enhanced under NBR treatment on soil water deficit. The conductivity of relativity and the accumulation of MDA were decreased after NBR treatment. These showed that using NBR handling could increase the protection substance and raised the drought resistance of three arbor seedlings. 0.1mg/L NBR treatment was better than other concentration to Pinus tabulae formis and Platycladus orientalis seedlings, and 0.2mg/L NBR treatment was the best to Robinia pseudo-acacia seedlings. 4. Chlorophyll a and b contents, chlorophyll total contents and carotenoids contents of three arbor seedlings were efficiently increased after 0.1mg/L NBR treatment. The net photosynthetic rate and the water use efficiency were rise under NBR handling. The transpiration rate and the stomatal conductance were decreased on severe soil water deficit using NBR treatment. 0.1mg/L NBR treatment was better than other concentration to Pinus tabulae formis and Platycladus orientalis seedlings, and 0.2mg/L NBR treatment was the best to Robinia pseudo-acacia seedlings. 5. The effects of different concentration NBR treatment on drought resistance of three arbor seedlings were comprehensive evaluated by principal component analysis. To Robinia pseudo-acacia seedlings, effect of concentration of natural brassinolide is 0.2mg/L> 0.1mg/L>0.3mg/L> 0mg/L>0.4mg/L. To Pinus tabulae formis seedlings, it is 0.1mg/L> 0.2mg/L>0.3mg/L>0.4mg/L>0mg/L. To Platycladus orientalis seedlings, it is 0.1mg/L> 0.2mg/L>0mg/L>0.3mg/L>0.4mg/L, suggesting that the drought resistance of three arbor seedlings were more raised by lower concentration NBR treatment than higher concentration NBR treatment.