Studies On The Seedling Physiological Characteristics In Different Pinus Massoniana Provenance Under Drought Stress

One-year masson pine seedlings, whose seeds were separately from Lechang, Guangdong province, Yuan'an, Hubei province, Rucheng, Hunan province, Jiangshan, Zhejiang province and Huoshan, Anhui province, were subjected to different degrees of water stress in a three-circle drought stress treatment. Through the studies on the characteristics of growth, physiology and biochemistry of masson pine young seedlings under artificial drought stress treatments, especially the studies on the organic substances with low molecular weight, the purposes of this thesis were to reveal the mechanisms of osmotic adjustment in drought stress, choose the main morphological and physiological indexes for determining the ability of drought resistance of masson pine seedlings, and select the drought resistant masson pine provenance. The results of these studies will provide theoretical basis for guiding the selection of drought resistant masson pine provenance and improving the ability of drought resistance of masson pine seedlings. Through the determination and analysis of morphological and physiochemical indexes in the experiments, the main results were shown as followes:1. The young seedlings of all masson pine provenances were injured along with the decrease of soil water content. The seedling growth of the masson pine provenance from Lechang, Guangdong province was best under mild drought stress, but most needles of the same provenance was withered and yellow under severe drought stress. The seedling growth of other four provenances was poor, and there were no significant difference in needle appearance among these four provenances at the same water condition.2. The height growth and total biomass of all seedlings from different provenances decreased under drought stress. The seedlings from Yuan'an, Hubei province and Lechang, Guandong province were less affected by water stress among five provenances, followed by provenances of Huoshan, Anhui province, Rucheng, Hunan province and Jiangshan, Zhejiang province.3. The seedling photosynthesis of all masson pine provenances was affected under water stress. The initial chlorophyll fluorescence (F0) increased. But Fm, Fv, light conversion efficiency (Fm/Fv) and potential activity (Fv/F0) of PSII had a trend of decrease along with the aggravation of drought stress. The value of Fm and Fv decreased first and then increased thereafter. The change of Fv value was little and there were no big differences among different provenances. But the Fm and Fv value of the provenance from Lechang, Guandong province was higher than that of the other four provenances. The variation of Fv/Fm value was big and the variation of Fv/F0 value was small among different provenances at the beginning of drought stress. But the changes of Fv/Fm and Fv/F0 value became stable at the later stage of drought stress. As a whole, the seedling of provenance from Lechang, Guandong province had higher light conversion efficiency, followed by that of Jiangshan, Zhejiang province, Rucheng, Hunan province, Yuan'an, Hubei province and Huoshan, Anhui province.4. The seedling root vigor of all provenances had a significant trend of decrease. And the range of seedling root vigor from weak to strong was Jiangshan, Zhejiang province, Huoshan, Anhui province, Yuan'an, Hubei province, Rucheng, Hunan province and Lechang, Guandong province. 5. The variation of seedling proline content among different provenances was big and the seedling proline content had an increasing trend along with the aggravation and duration of drought stress. But the seedling proline content would not increase after the stress reached a certain level and even decreased at some extent. The accumulation of total content of free amino acids in severe drought stress was much more than that of mild drought stress. And the changes of total content of free amino acids in different provenances were similar. There were no significant differences in the total content of free amino acids among different provenances.6. It was found that there were mannose, glucose, galactose and maltose in the needle of masson pine seedlings under drought stress, especially mannose and glucose were found to be accumulated. Further, more mannose and glucose would be accumulated under severe drought than under mild drought stress. The mannose and glucose were accumulated more rapidly at the later stage of drought stress, and the trend of accumulation of mannose and glucose content was similar among different provenances. Galatose content had no stable trend of changing and there were no significant difference among provenances. But the galatose content had an increasing trend after a relatively long period of drought stress. Maltose content had a decreasing trend under drought stress. In general, the contents of above four sugars accumulated in the seedlings of the provenance from Huoshan, Anhui province were the highest, followed by Lechang provenance, Guandong province. And those of Yuan'an provenance, Hubei province, Jiangshan provenance, Zhejiang province and Rucheng provenance, Hunan province were relatively less.7. The ABA content of masson pine seedlings from all different provenances was sensitive to drought stress at the early stage of stress treatment. And GA3 content had no regular changing pattern at the early stage but it increased at the later stage in all provenances. The content of IAA and ZR in the seedlings of masson pine from different provenance decreased under drought stress. IAA was not sensitive to drought stress and its reaction to drought stress would be obvious after a relatively long period of stress. ZR was sensitive to drought stress and it decreased along with the aggravation of drought stress. ZR/ABA also decreased under drought stress. According to the hypothesis of phytohormone balance adjustment to stress resistance of plants, a conclusion could be reached as follows: The seedlings from Huoshan, Anhui province and Lechang, Guandong province were stronger in drought resistance and seedlings from Yuan'an, Hubei province, Jiangshan, Zhejiang province and Rucheng, Hunan province were weaker in drought resistance.8. Based on the comprehensive analysis of all indexes, principal component analysis and a general evaluation of membership function, following conclusions were reached: the correlations among different indexes were not significant, and chlorophyll fluorescence, the content of osmotic solutes and endogenous hormones were good indexes for appraisal of the drought resistance of Masson pine. According to a comprehensive evaluation of drought resistance for all provenances, it was concluded that the range of drought resistance from strong to weak could be Lechang provenance>Huoshan provenance>Yuan'an provenance>Jiangshan provenance>Rucheng provenance.