| Ageratina adenophora Sprengel, being one kind of the invasive weeds, has been widely spread in the world, and has caused serious economic loss and even danger to the health of human beings and animals. Recent studies have confirmed that allelopathy arised from rhizosphere played an important role during the development of A. adenophora forming as a single dominant population in invasived areas. Based on the reported information of allelochemicals from the root secretiona and leachates of A. adenophora, this study was carried out to analyze the allelochemicals from rhizosphere soil of A. adenophora qualitatively and quantitatively, and to compare the productive and degradative dynamics of these allelochemicals and their effects on the content of available phosphorus between the invasived soil and non-invasived soil around, which should improve our understanding on the more roles, eg. regulation of soil nutrients and autotoxicity, of allelochemicals from A. adenophora in invasived soil compared with non-invasived soil. Furthermore, Procecidochares utilis Stone, a parasitical natural enemy of the A. adenophora, has been introduced into China since1980s, and has established some stable natural populations, but showed a poor control effect. So, the changes of contents of allelochemicals from rhizosphere and anti-herbivore substance of A. adenophora under the parasitical stress of P. utilis were also examined in this paper, which will help us better understand whether the sub-lethal stress of nature enemy can enhance the allelopathic effect of invasive plants, and the physiological mechanism of adaptability of A. adenophora under the stress of nature enemy. The results are as follows:1. With the methods of direct extraction from soil and PDMS (polydimethylsiloxane) probe, the main four allelochemicals from rhizosphere of A. adenophora were found, and their temporal and spatial dynamics in fields were analyzed quantitatively. The results showed that, bis (2-ethylhexyl)phthalate (DEHP), Dibutyl phthalate (DBP),4,7-dimethyl-l-(propan-2-ylidene)-1,4,4a,8a-tetradronaphthalene-2,6(1H,7H)-dione(DTD), and6-hydroxy-5-isopropyl-3,8-dimethyl-4a,5,6,7,8,8a-hexahydraphthalen-2(1H)-one (HHO) are the the main four allelochemicals. Among them, the DEHP, DBP, and DTD were found as the allelochemicals from root exudations, and the DTD and HHO were the allelochemicals from leachates of A. adenophora. Based on creating the appropriate analytical conditions, one method of ethyl acetate extraction was constructed and used to quantitative analyze the contents of these four allelochemicals of rhizosphere soil of A. adenophora sampled from multiple sites including different invasived levels and times. We found that all the four allelochemicals were measurable from some samples, and the contents of DTD and DBP were relatively higher than the other two, among which the highest content of DTD achieved1.2ug/g. Similarly, the analytical results from PDMS (polydimethylsiloxane) probe indicated a detectable content of these allelochemicals consisting in rhizosphere soil of A. adenophora. Whereas, there has been some differences of contents of these allelochemicals between soil extraction and PDMS probe, which maybe due to the different adsorptive efficiency to some substances of this probe, and also connected with the different sampling sites.2. The effects of these four allelochemicals on contents of available phosphorus from the invasived soil and non-invasived soil around were investigated in lab. The results showed that, before the treatments of allelochemicals, the content of available phosphorus from the invasived soil was higher significantly than that from non-invasived soil around. However, an obvious increased content of available phosphorus from the invasived soil were found when treated with these allelochemicals, e.g. the treatments of DTD and50and100ppm concentrations, compared with an tiny changes of contents of available phosphorus from non-invasived soil around with the same treatment. Especially, the content of available phosphorus from the invasived soil enhanced markedly when the treatment was a mixed allelochemicals according to the examined proportion of these four allelochemicals from natural soil, which indicated that A. adenophora could cause a more high efficient of nutritional activation in invasived soil promoting the population growth of itself. Meanwhile, the results of productive and degradative dynamics of these allelochemicals showed that, there was no obvious different productive content of DEHP, DBP, and DTD, besides the productive content of HHO in the non-invasived soil around was higher than that in invasived soil obviously. The degradative rate of four allelochemicals in the invasived soil was significant lager than that in non-invasived soil around, which increased with the enhancing temperature. Thus, the accelerated degradation of allelochemicals in the invasived soil of A. adenophora will benefit it from reduced autotoxicity.3. With the methods of single A. adenophora plant vestured with gauze and adsorption resin, changes of the contents of allelochemicals from rhizosphere and anti-herbivore substance from A. adenophora under the parasitical stress of P. utilis were examined in lab. We found that, the contents of the four allelochemicals decreased in different degree after the A. adenophora plant parasited by P. utilis, and the contents of DTD reached a significant reduction under the parasitical stress. The contents of total flavanone and phenolic acid from A. adenophora planted in invasived soil were significant lager than that in non-invasived soil around, when with no parasitical stress. And, the contents of total flavanone and phenolic acid enhanced at different extents when treated with P. utilis, but which was no obvious variation compared with no parasite. |
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