| Allelopathy exists extensively in agricultural ecosystem, and it brings significant effects to agricultural production. Now, it is a key project to overcome its disadvantageous effects. Hot pepper yield and quality fell because of continuous cropping obstacles, for which allelopathy was an important reason. Now, the research on hot pepper allelopathy was little and not comprehensive. So allelopathy of hot pepper was researched systemically in this experiment. Allelochemicals were separated and identified. The mechanism of allelopathy was discussed by synthesized allelochemicals. The main results were as follows. The allelopathy of donor materials on receiver materials was researched by bioassay. The results showed that donor materials affected the seed germination and seedling growth of receiver materials. Receiver material for further study was selected with integrate subjection value, which was lettuce. The sequence of donor material allelopathy was Chinese cabbage > cucumber > hot pepper > radish > watermelon > tomato. The sequence of donor material allelopathy on lettuce was cucumber > watermelon > hot pepper > tomato > Chinese cabbage, which was studied by tissue culture method. The two results suggested that hot pepper was very feasible as receiver material for further research. Effect of microorganisms on hot pepper allelopathy was researched through the two methods, which were seed germination with aqueous extracts of hot pepper and sponge culture. The results showed that microorganisms affected hot pepper allelopathy. Allelopathy of hot pepper on lettuce was promoted by microorganisms when the concentrations of allelochemicals were lower, which was beneficial to lettuce seed germination and seedling growth. Microorganisms could decrease allelopathy of hot pepper when the concentrations of allelochemicals were higher. This inhibition of allelochemicals on lettuce seed germination and seedling growth was weakened. In the allelopathic system, allelochemicals were dominating, microorganisms were subsidiary. Allelopathy of hot pepper on lettuce was promoted when the concentrations of aqueous extracts, methanol soluble components and root exudates were low. It was prohibitive under high concentrations. Main prohibitive effects on lettuce seeds were that they reduced seed vigor and deferred seed germination. The sensitivity to allelochemicals was different with the different parts of lettuce seedlings. The root sensitivity was higher than that of top. The sensitivity to allelochemicals varied with different growth stages too, and seedling stage was higher than germination stage. Allelopathy of various components and contents of allelochemicals on lettuce was studied by aqueous extracts and methanol soluble components of hot pepper. The results showed that the contents and components of allelochemicals were higher, and allelopathy was stronger, vice versa. Allelochemicals of hot pepper was obtained from aqueous extracts, nutrient solution and medium of culture. It was collected by XAD-4 resin, then XAD-4 resin was washed by aether, 50% aether + 50% ethyl acetate, ethyl acetate, 50% ethyl acetate + 50% methanol, methanol and distilled water, and separated step by step. Culture medium was washed by distilled water, passed XAD-4 resin, then washed. Acid, alkaline and water fractions were separated. The results of each fraction bioassay showed that allelopathy of aether fraction in aqueous extracts and nutrient solution and distilled water fraction in culture medium were the strongest. Aether fraction was further separated, then bioassay. The results showed that allelopathy of 80% aether + 20% ethyl acetate fraction was the strongest. GC-MS analysis showed dominating allelochemicals were dibutyl phthalate, 1,2-Benzenedicarboxylic acid ramification, Diphenylamine, 1,2-Benzenedicarboxylic acid, N-phenyl-1-Naphthalenamine. Dibutyl phthalate was the most in these solutions. Allelochemicals were different with different releasing pathways. Allelochemicals in aqueous extracts were the most, they were the least in culture medium. Finally, 1,2-benzenedicarboxylic acid, dibutyl phthalate and diphenylamine, which were synthesized, were proved to be allelochemicals by bioassay. Allelopathy of diphenylamine was the strongest, and allelopathy of 1,2-benzenedicarboxylic acid was the least. 1,2-Benzenedicarboxylic acid , dibutyl phthalate, diphenylamine and vanillin affected N, P, K absorption of tomato roots. Inhibition effect of 1,2-benzenedicarboxylic acid on N, P, K absorption rised with the concentration increasing. K absorption ability increased when vanillin concentration was at 1×10-4 mol.L-1. Vanillin inhibited N, P, K absorption at other concentrations. When dibutyl phthalate concentration was low, N absorption was promoted, but P, K absorption was inhibited. Dibutyl phthalate reduced N, P, K absorption when the concentrations were high. N and K absorption was promoted, but P absorption was reduced when its concentration was low. These allelochemicals affected P absorption ability more than that of N and K. The research results of allelopathy mechanism showed that SOD activity fell in lettuce, POD activity rised with the concentration of methanol soluble components in hot pepper aqueous extracts becoming higher. MDA content increased when the concentration exceeded 0.02 mol.L-1, and peroxibation of membrane lipids increased. 1,2-Benzenedicarboxylic acid ,dibutyl phthalate, diphenylamine and vanillin affected SOD, POD, CAT activity significantly. Effect of different allelochemicals was different on these enzymes. When lettuce was dealt with different concentrations of the same allelochemical, SOD, POD and CAT activity fell while the concentration was up to a certain value. MDA content increased with the concentration increasing. Ca2+-ATPase activity increased when the concentration of allelochemical was low in lettuce. When the concentration reached a certain value, Ca2+-ATPase activity began to fall. Then Ca2+ was accumulated in cells, so cells were damaged. Finally, plant growth and development were affected.
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