| Xanthium italicum Moretti is an annual herb of the genus Xanthium(Asteraceae)origining from North America and South Europe.It invaded China in the 1990 s,and now is widely distributed in northern Xinjiang and Wuqia County in southern Xinjiang.The plant is easy to form a single dominant species community in the invaded land,because of its strong adaptability,high reproductive capacity,and strong individual competitiveness.Thus,the expansion rate of the population is very fast,causing serious damages to the local indigenous plant diversity,animal husbandry,and agricultural production.In this study,soils in the range of the 40-50 cm from the taproot of Xanthium italicum was set as the control,we studied the effects of Xanthium italicum on the soil microbial community species richness,soil physicochemical properties,soil enzyme activity,and soil microbial functional and structural diversity(0-5 cm and 10-20 cm from the taproot),intending to reveal the invasion mechanism of the plant.The results of the study were as follows:1.Compared with the bacteria,fungi,and actinomycetes counts in the range of 40-50 cm from the taproot,Xanthium italicum increased the bacteria and fungi counts within the 0-5cm and 10-20 cm range from the taproot system,and reduced the actinomycetes count.The bacteria count in the range of 0-5 cm and 10-20 cm from the taproot increased by 47.40% and24.28%,respectively;the fungi count increased by 354.29% and 48.57%,respectively;and the bacteria count decreased by 43.08% and 36.48%,respectively.The effect of X.italicum on the bacteria,fungi,and actinomycetes counts in the 0-5 cm range was the most significant.2.X.italicum increased the content of soil organic matter,total nitrogen,total potassium,total phosphorus,available phosphorus,and alkali-hydrolyzable nitrogen,and reduced the available potassium content within the range of 0-5 cm from the taproot;it also increased the content of soil organic matter,total nitrogen,total potassium,and available phosphorus,and reduced the content of available potassium,total phosphorus,and alkaline dissolved nitrogen within the range of 10-20 cm from the taproot,compared with those of the range of 40-50 cm from the taproot.In general,the effect of X.italicum on soil nutrients decreased with the distance increased.3.X.italicum increased soil sucrase,urease,and phosphatase activities within the 0-5 cm and 10-20 cm range from the taproot,compared with those of the 40-50 cm range from the taproot,and the degree of increase was greater in the 0-5 cm range than in the 10-20 cm range.X.italicum decreased the activity of cellulase and hydrogen peroxide in the 0-5 cm and 10-20 cm range from the taproot,and the degree of reduction in the 0-5 cm range was greater than inthe 10-20 cm range.The activities of sucrase,urease and phosphatase decreased with the distance increased.and the activities of cellulase and hydrogen peroxide increased with the distance increased.4.The utilizing rate of total carbon source of soil microorganisms decreased with the distance increased.Compared with that of CK,in the range of 0-5 cm and 10-20 cm from the taproot,the Shannon diversity index(H)of soil microbes increased by 5.10% and 2.61%,respectively,the Shannon dominance index(D)increased by 1.70% and 1.06%,respectively,the richness index(S)increased by 18.85% and 9.39%,respectively,and the Shannon evenness index(E)decreased by 2.09% and 0.71%,respectively.Carbon fingerprinting metabologram analysis showed that X.italicum increased the utilization of 16 and 10 carbon sources in the 0-5 cm and 10-20 cm range from the taproot,respectively,and the effect on that of the 0-5 cm range was the most significant.Principal component analysis showed that carbohydrates,carboxylic acids,amino acids,and polymers were the main carbon sources for soil microbial utilization.5.In the bacterial community,the result of the number of OTUs obtained by soil bacterial communities in the 0-5 cm,10-20 cm,and 40-50 cm from the taproot showed that:0-5 cm > 10-20 cm > 40-50 cm.Compared with thoes of the 40-50 cm from the taproot,specific OTUs in the 0-5 cm range from the taproot significantly increased by 61.02%(P<0.01);specific OTUs in the 10-20 cm range from the taproot increased by 29.07%.Ten phyla contributed higher to the soil bacterial community,and the relative abundance of actinobacteria and proteobacteria were the highest.The relative abundance of proteobacteria,gemmatimonadetes,and bacteroidetes in the range of 0-5 cm,10-20 cm and 40-50 cm from the taproot showed that: 0-5 cm > 10-20 cm > 40-50 cm.Correlation analysis showed that urease(NE),phosphatase(PE),and total nitrogen(N)were the main environmental driving factors affecting the distribution of soil bacterial communities in the range of 0-5 cm from the taproot.Cellulase(XE),available potassium(AK),and electrical conductivity(D)were the main environmental driving factors affecting the distribution of soil bacterial communities in the range of 10-20 cm and 40-50 cm from the taproot.In the fungal community,compared with those of the 40-50 cm range from the taproot,specific OTUs in the 0-5 cm range from the taproot significantly increased by 256.10%(P<0.01).Seven phyla contributed higher to the soil fungi community,and the relative abundance of ascomycota and basidiomycota were the highest.Redundancy analysis showed that phytase community(PE),total nitrogen(N),and urease(NE)were the most importantenvironmental factors affecting the distribution of soil fungal communities in the range of 0-5cm from the taproot;available AP,total potassium(K),and electrical conductivity(D)were the most important environmental factors affecting the distribution of soil fungal communities in the range of 10-20 cm from the taproot;and available potassium(AK)and cellulase(XE)were the most important environmental factors affecting the distribution of soil fungal communities in the range of 40-50 cm from the taproot.In summary,the effect of X.italicum on the soil microorganisms in the invaded land decreased with the horizontal distance from the taproot increased.X.italicum increased the number of soil microorganisms,soil enzyme activity,and soil nutrients,and improved the soil microbial functional diversity and structure,building an environment that is beneficial to self-growth and to improve competitive advantages and invasive ability. |
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