Abstract:

The effect of drought on photosynthesis and physiological response of Pinus massoniana seedlings and the underlying mechanisms were investigated. One-year-old P. massoniana seedlings were used as materials, and greenhouse soil potting was used to carry out drought stress treatment. After treatment for 0, 15, 30, 45 and 60 days, some indexes were determined to study the effects of continuous drought on the growth of P. massoniana seedlings. The results showed that with the intensification of drought stress degree and the extension of stress time, the seedling root-shoot ratio increased slightly. Under severe stress, the seedling height growth, ground diameter growth and dry matter accumulation decreased by 69.89%, 70.73% and 75.58%, respectively. The activity of peroxides dismutase and peroxidase in P. massoniana seedlings increased at first and then decreased, and reached the peak values of 699.81 and 817.82 U/g, until thirtieth day of medium and severe stress, which increased by 75.57% and 104.01% than normal water supply. At 45 ^th day, the activity of peroxidase was still high, under severe stress, while the peroxidase content reached a peak of 319.00 U/(g·min), which was 171.88% higher than that of normal watering and showed a significant difference from normal watering. The content of malondialdehyde and proline increased gradually. The index of root-shoot ratio and physiological indicators of malondialdehyde, transpiration rate, stem biomass, stomatal conductance, stomatal conductance and root biomass showed a strong positive correlation (r=1); however, proline had a strong negative correlation with net photosynthetic rate (r=-1). P. massoniana seedlings resisted drought stress by adjusting growth and biomass distribution. Transpiration and photosynthesis were weakened by water deficit. In the early stage of drought, antioxidant enzyme activity was rapidly increased to protect the peroxidation damage of seedlings. In the middle and later stages, osmotic substances were added to maintain the osmotic pressure in cells to alleviate the membrane damage. P. massoniana restricted and coordinated various tissues and organs to deal with drought stress by adjusting photosynthesis and the related physiological mechanism.

Key words: Pinus massoniana seedlings, drought stress, photosynthetic characteristics, physiological and biochemical properties, correlation