| This paper take three different districts nine provenances(Yuan jiang dry-hot valley(DHV), Xishuangbanna and Lincang) of Bombax ceiba which possesses different hydrothermal condition and representes the dry-hot, humid-hot and semi-humid-hot environment condition respectively as research marerial. Adopts pot experiment and field investigation methods to analysis the soil nutrition of different sites and roots and leaves anatomical structure of different provenances, and combined the comprehensive research of moisture physiological characteristics, photosynthetic characteristics, osmotic regulation substance and protective enzyme activity of different seedlings under drought stress to explore the physiological response of different provenance seedling on drought stress. Meantime, analyse the biomass and root characteristic value difference of different provenances seedlings under drought stress. The main results were shown as follows:(1) The kapok growth situation of different provenances had a difference, which was subjected to the mutual influence of soil nutrient, rainfall and annual average temperature, etc. The soil N nutrient and water condition of Xishuangbanna humid-hot district were better than that of Lincang semi-humid-hot and DHV districts, which showed the better high growth and leaf area. Whereas K nutrient and P nutrient in Lincang semi-humid-hot district was prior to DHV and Xishuangbanna humid-hot districts, which manifested stronger drought resistance.(2) Seed germination rate and index of Lincang semi-humid-hot district provenance were higher than DHV and Xishuangbanna humid-hot ditrict in PEG concentration 0 g·L-1—0.2 g·L-1, when the concentration is greater than 0.2 g·L-1, the germination rate represented DHV ditrict >Lincang semi-humid-hot ditrict >Xishuangbanna humid-hot ditrict, and Xishuangbanna humid-hot ditrict seed cannot germinate in PEG concentration 0.3 g·L-1; When soil water content was 10%, only Yuanyang county of DHV district had 8.0% seeds germination rate, and other provenances cannot germinate. When water content was 15%, seed can germinate in Lincang semi-humid-hot and DHV region, but can not germinate in Xishuangbanna humid-hot. When the soil moisture content was 60%, there were 1-8.5% germination rate in Xishuangbanna humid-hot region, while other provenances can hardly germinate. The seedling ground diameter and height growth showed DHV ditrict >Lincang semi-humid-hot ditrict >Xishuangbanna humid-hot ditrict under natural conditions in DHV.(3) Kapok tree belonged to low water consumption tree species that water consumption per plant was 392.0 g·d-1, but the water consumption rate was relatively higher(328.9 g·m-2·h-1), which were characterized by high photosynthetic rate and adaptability to the drought environment. Leaf water potential and water consumption rate decreased gradually with increasing of drought stress, which presented the stoma closing, transpiration falling, osmotic regulation substances accumulation and other ways to adapt the drought stress conditions. But the change range of each indicators had significant difference, which embodied the differences of genotypes of three districts nine provenances. Leaf water potential, net photosynthetic rate, chlorophyll fluorescence parameters and enzyme activity of Yuanjiang DHV district provenance were less affected by the drought stress, and osmotic regulation substances content was higher, which showed stronger drought resistance for DHV district provenance. Followed by the Lincang semi-humid-hot district provenance, which the root-shoot ratio reached much than two times under severe stress. The taproot length, primary fibrous root number and secondary fibrous root number of Lincang semi-humid-hot provenances were higher than DHV district and Xishuangbanna humid-hot district, which showed that the root of Lincang semi-humid-hot provenances had the strong ability to absorb water. The ground and underground biomass of Xishuangbanna humid-hot district was impacted serious by stress condition, and it embodied the poorer drought-resistant ability.(4) The leaves anatomical structure research displayed that the leaf of kapok is bifacial leaf,which had the developed vein and succulent system. The thickness of upper and lower epidermis showed Lincang semi-humid-hot >Xishuangbanna humid-hot >DHV, and Lincang semi-humid-hot > DHV>Xishuangbanna humid-hot district for the thickness of cuticle and stockade tissue, which it made the Lincang semi-humid-hot provenance have strong ability for water storage and prevent effectively moisture loss, and the size of CTR and SR showed DHV>Lincang semi-humid-hot >Xishuangbanna humid-hot, which indicated that the DHV provenance can better use light energy, and avoid high temperature and light to damage the plant. The developed xylem and vascular cylinder of DHV provenance showed that it conveyed efficiently water. The size of vessel diameter showed Xishuangbanna humid-hot >Lincang semi-humid-hot >DHV district, which showed the large vessel diameter of Xishuangbanna humid-hot facilitate water to upward transportation for long distance under moisture adequate condition. The number of catheter showed DHV >Lincang semi-humid-hot >Xishuangbanna humid-hot, which showed smaller catheter diameter of DHV district and Lincang semi-humid-hot ensure to carry efficiently water on one hand, and to improve the efficiency of transporting water on other hand.Taking above conclusion into consideration, the DHV district provenances showed stronger drought resistance ability for drought stress although the biomass was affected seriously by drought stress, water-saving index and drought index were better than others. Secondly, anatomical structure of Lincang semi-humid-hot reflected strong drought resistance ability, at the same time, the more biomass of Lincang semi-humid-hot provenance was allocated to root system which was in favor of absorbing moisture effectively. The ground and underground biomass allocation of Xishuangbanna humid-hot provenances are affected serious by drought stress, and the seedling growth condition of Xishuangbanna humid-hot is inferior to the DHV district and Lincang semi-humid-hot provenance under natural condition in Yuanjiang DHV, which showed the drought resistance is relatively poor for Xishuangbanna provenance.Therefore, the size of drought resistance for different districts performed for Yuanjiang DHV > Lincang semi-humid-hot >Xishuangbanna humid-hot regions, and the order of the various sources of drought resistance of Yuanyang county > Yuanjiang county > Gengma county > Linxiang county > Honghe county > Mengding county > Jinghong county >Mengla county >Menghai county. |
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