The Effect Of Aqueous Extract Of Zanthoxylum Piperitum On Plants' Seed Germination And Seedling Growth

Zanthoxylum piperitum is one of the most important cash crops and has been extensively cultivated in Eastern Tibetan Plateau, especially in the fragile dry valley areas. Allelopathic effects could be a reason for Z piperitum's continuous cropping impediment. Systemmatically research of the effect of Z piperitum allelopathy could help to comprehend the continuous cropping impediment. The allelopathic effects of Da Hongpao(DHP), the most common varieties of Z piperitum in this area, on other plants' growth were investigated with different concentrations of different DHP organs and plantation soil. The treatments with soil covered by residues of Z. piperitum were designed for exploring its self-noxious effects. Components of the four aqueous extracts were also analyzed with HPLC. The main results showed that:1. The aqueous extracts of different organs of DHP and soil of plantation had the allelopathic effects on seed germination and root length, it were significantly inhibited at high concentration while stimulated at low. At the same concentration level, the order of the inhibitory effects of different organs aqueous extracts was : leaf>stem≈ root>soil. 40g/L leaf aqueous extracts made the main root shorter and wider, decreased fibril number and inhabited stem growth. Vascular cylinder cell specialization delayed. At the saturation pot of seed water-absorbing (8hours), 40 and 30g/L leaf aqueous extract significantly decreased the water-absorbing rate.2. Illumination could stimulate alfalfa seed germination rate significantly, and strengthened the inhibitory effect of leaf extract on alfalfa seed germination. 40g/L leaf extract could inhibited alfalfa seedling growth significantly with the illumination condition of 12hs/d and kept stably, while 20g/L extract stimulated it in 48~84hs. Theallelopathic effect of two kinds of leaf extracts changed from inhabitation to stimulation during 36~96hs without illumination. The seed germination and seedling growth of alfalfa was more sensitive with the illumination condition of 12hs/d.3. Aqueous extracts of Z. piperitum and residue covering treatment significantly inhabited the increment rate of height, radical diameter, crown size and net photosynthetic rate of DHP seedling. At the same concentration level, leaf extract had the highest inhibitory effect, there was no obvious disciplinarian among the other extracts. The DHPseedling tended to increase the proportion of above-ground part when it was inhabited.4. The main allelopathic components of four kind of aqueous extracts included: Leaf and stem extract (Ferulic acid and p -coumaric acid); root extract (Herniarin); the concentration of components in the soil aqueous extract was low and not higher than 10"5mol/L.