| Ageratina adenophora Sprengel is an invasive weed in China, which has caused serious economic losses and ecological damage in many countries. Up to now, some measures have been carried out to control A. adenophora, most of the control methods being used obviously do not match the present status of the expansion. In recent years, studies on the invasive mechanism of A. adenophora have become a hotspot in the research of this weed. A few studies have pointed out that allelopathy plays an important role in the process of invasion and it’s establishing monocultures. Meanwhile, some allelochemicals and their action mechanism have been reported. Procecidochares utilis Stone, a natural enemy of A. adenophora, has been introduced into China since 1984 and has established some stable natural populations, does show a poor control effect. Parasitism of the fly couldn’t cause an effective lethal effect to A. adenophora, so does that of manual control. Thus, these control factors could be defined as sublethal factors to A. adenophora. Evaluation changes of the allelopathy of A. adenophora under these sublethal factors will help us to better understand the role of these controlling factors during its expansion. So, we designed experiments in order to investigate the effects of abiotic control factors (mechanical damage) and biological control factor (P. utilis) on the content changes of rhizosphere allelochemicals. The main research contents were as follows:1. With the method of nutrient solution cultivation, effects of leaves holing and plants cutting at different level on the contents of main three allelochemicals (DEHP, DBP, and DTD) of Ageratina adenophora were investigated in this paper. Our results showed that, treatments of leaves holing and plants cutting increased the contents of DBP and DTD from exudates of A. adenophora significantly, among which the contents of both DBP and DTD treated by leaves holing at the highest density of 6 hole/leaf increased by more than 2 times than that of control; the treatment of plants aboveground part all cut off caused a obvious enhancement of DBP by 253.6% than that of control. Both of the leaves holing and plants cutting decreased the contents of three allelochemicals in roots of A. adenophora in different degree, and the content of DTD attained the most significant vary compared with control. Therefore, this study suggest that leaves holing and plants cutting treatment enhances the allelopathic effect of A. Adenophora rhizosphere, future more the abiotic factor may contribute to the enhance of allelopathic and accelerate the expansion of A. adenophora.2.With the methods of single A. adenophora plant with gauze combine with resin adsorption, effects of P. utilis parasitic (specialist natural enemy) and MEJA treatment (simulation generalist natural enemy) on the contents of three main allelochemicals (DTD, HHO and o-coumaric acid) of A. adenophora were investigated. Results indicate that the contents of DTD and HHO significantly reduced under the parasitical stress when P. utilis completely hatched. No significant content changes of these two allelochemicals at the other two stages of gall appear and gall growth for the largest when compared with control The content of o-coumaric acid in insect gall appear, gall growth for the largest and P. utilis completely hatch the three stages are reduced, especially in a lesser parasitic. MEJA treatment significantly increased the o-coumaric acid content, e.g. the content of o-coumaric acid with treated concentration at 5mmol/L was more than 5 times than that of control. Meanwhile, MEJA treatment promoted the contents of DTD and HHO of the four months age A. adenophora. Therefore, this study suggest that the prevention and control is different of specialist natural enemy and generalist natural enemy, while the specialist natural enemy may inhibit the effect of allelopathy and the generalist natural enemy may promote the effect of allelopathy. |
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