| The allelopathy of VOCs from some plants played an important role in enhancing existence and enlarging multiplication of emitter. In order to find out whether the degeneration of pastures was induced by allelopathic effects of VOCs from A. frigida. The main compounds of VOCs from undamaged, damaged and restoring after damaged A. frigida were determined with GC-MS, and the overground microstructures of A. frigida were observed. Those can be used to reveal the releasing mechanism of its VOCs. The allelopathy of VOCs from A. frigida was reflected by its effects on seeds germination, seedlings growth and photosynthesis. The results were as follows:1. The VOCs from A. frigida mainly included terpenoids, alcohols, esters, aldehydes and ketones. Terpenoids and alcohols were the main kinds in the 5 kinds of VOCs. The major compounds were eucalyptol,α-terpineol, camphene, p-cymene, (E)-3-hexen-1-ol acetate and camphor among the all compounds. The relative content of those 6 major compounds in undamaged A. frigida VOCs was 39.80%, 10.04%, 14.27%, 9.05%, 10.85% and 5.66%, respectively.2. There were lots of big air chambers in the leaves of A. frigida, which can reserve a lot of secondary metabolites. A lot of VOCs released from the open air chambers, besides some GLVs and terpenoids were composed and released when A. frigida was damaged, so the concentration and kinds of VOCs were increased.3. The germination energy, germination rate and germination index were reduced differently; buds and roots growth, fibres (lateral roots) development, total biomass and biomass allocation were inhibited by VOCs from A. frigida. In the treatment of VOCs from undamaged A. frigida, the germination rate of P. sativus, P. radiatus, C. sativus, M. sativa, M. suaveolens, S. sudanense, E. dahuricus and A. cristatum was reduced by 45.83%, 30.00%, 12.77%, 5.08%, 10.42%, 42.11%, 24.49% and 0.00%, respectively, and the dry mass of one plant in germination was reduced by 26.04%, 33.48%, 18.61%, 26.55%, 24.47%, 9.46 %, 20.12% and 20.44%, respectively.4. The content of chlorophyll a, b and total chlorophyll was reduced, and the photosynthesis was changed by VOCs from A. frigida. The Pn of P. radiatus, M. sativa, and M. suaveolens was reduced, however the Pn of P. sativus, C. sativus, S. sudanense, E. dahuricus, A. cristatum and L. chinensis was increased in the treatment of VOCs from A. frigida. The AQY of P. radiatus, M. sativa and M. suaveolens was reduced, however the AQY of P. sativus, C. sativus, S. sudanense, E. dahuricus, A. cristatum and L. chinensis was increased in the treatment of VOCs from damaged A. frigida.5. The inhibition of VOCs from damaged A. frigida was stronger than the undamaged.6. The structure of stele in roots was developed well in CK, and the xylem, phloem, cambium and Casparian strip were very clear and integrity. But the development of every part of stele was inhibited differently by VOCs from damaged A. frigida.The main compounds and releasing mechanism of VOCs from A. frigida, and its allelopathy to the seeds germination and seedlings growth were exposed in the above results. That not only revealed the relationship in plant-plant, but also was helpful for revealing the degeneration, recovering after degeneration and continual development of pastures.
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