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Eucalyptus trees and Ageratina adenophora complex system, a new ecological phenomenon that is worthy of attention, was proposed firstly in this paper, and some scientific problems were summarized from the new phenomenon. Causes of the new phenomenon were analyzed tentatively from the perspective of ecology. It was pointed out that ecological degradation of Eucalyptus plantation and strong invasiveness of A. adenophora are two apparent reasons for formation of Eucalyptus trees and A. adenophora complex system. Basic view of the authors on causes of the new phenomenon was put forward that resistance unbalance between chemical defensive potential of Eucalyptus trees and chemical invasive potential of A. adenophora might be the fundamental reason for formation of Eucalyptus trees and A. adenophora complex system, based on the two apparent reasons respectively connected with allelopathic effects of Eucalyptus trees and A. adenophora as dominant species of the complex system. Some proofs from studies on chemical components and biological activities of Eucalyptus species and A. adenophora have proved the basic view of the authors. It was discussed that formation of the complex system would influence some environmental elements such as soil environment, hydrology environment, and biology environment. It was proposed that three key scientific issues, namely chemical mechanism of formation of the complex system, ecological effects of formation of the complex system, and succession trends and impact factors of the complex system should be mainly studied as special researches to probe ecological relationship of exotic species because of absence study on the complex system and objective requirements of production practice in future. It was emphasized that the proposed researches might be of guidance significance to scientific management and sustainable operation of Eucalyptus plantation under the condition of biological invasion. [ABSTRACT FROM AUTHOR]

By using orthogonal design, this paper investigated the growth of cultured prairie milk vetch (Astragalus adsurgens) root on the B5 medium with different contents of sucrose, macro-and microelements and organic supplements, and adopting the method of filter paper-culture in Petri-dish, studied the effects of A. adsurgens culture filtrate on the seedling growth of radish (Raphanus sativus) and wheat (Triticum aestivum). The results showed that the effect of A. adsurgens culture filtrate on R. sativus and T. aestivum seedling growth was of allelopathic, and nutritional stress might be the important cause of A. adsurgens allelopathy.