Abstract:

This paper studied the seasonal characteristics to resist the drought stress of Haloxylon persicum photosynthetic shoots at habitat. The results showed that the predominant drought resistance factors were varied at the different stage from growth to development. In the blooming season (from 31 May to 29 June), endogenous ABA contents were rare; stomatal conductance and photosynthesis intensity were the highest at the whole stage from growth to development; soluble sugar contents had a decreasing trend and proline contents increased a little that made proline become the predominant factor to resist the drought under this light water stress. In the hot summer (from 29 June to 26 July), ABA contents accumulated rapidly; stomatal conductance dropped to the lowest level of the growth and development; chlorophyll was also decomposed; both soluble sugar and proline contents showed the trend of quickly accumulating, but the former was faster than the latter. It was due to stomatal limition and osmotic organic molecules accumulation that would affect the photosynthetic shoots to resist severe drought stress. At the late period of the development (from 9 Aug. to 22 Aug.), ABA rapidly accumulated, its contents got to the highest level of whole life-span; stomatal conductance increased a little; proline and soluble sugar contents changed little at high level; while the ratios of ABA to CTK content and ABA to IAA content got up obviously, the effect to resist drought stress on high content ABA was inhibited by endogenous hormone CTK and IAA, then the continuing accumulation of proline and soluble sugar would be prevented. Osmosis of organic molecules was the most important factor to adjust leaves to severe water stress at this period.

Key words: Haloxylon persicum, drought stress, endogenous hormone, stomatal conductance, osmotic organic substance