The Competition Strategy Of Invasive Plants Solidago Canadensis L. For Phosphorus

The invasion of alien plants change community structure and function of the native ecosystem,especially the reduction of the biodiversity in the native ecosystem,and poses a series of ecological and environmental problems.Therefore,the invasion of alien plants is considered as one of the major challenges for the global ecological and environmental protection.In order to deal with the threat of invasive plants and reduce the ecological risk of the native ecosystem,deeply exploring the driving factors of invasive plants and interaction with invasive and native plants is a key to successful plant invasion control.When an invasive plant is introduced into a new habitat,it will face the different level interspecific competition with native plants for limited resources,invasive potential of alien plants may be benefited from its competitive advantage for limited resources.Competitive advantages of invasive plants depend not only on their biological characteristics,but also on the effects of biological and non-biological factors in the environment on invasive plants.However,most previous studies on the competition of invasive plants resources only focus on one aspect,either focusing on the invasiveness of invasive plants,or focusing on the invasibility of local environments,which usually leads to one-sided results.In this research,the role of biological characteristics of invasive plants,microorganism and resources changes in the environment on interspecific competition for resource,especial phosphorus?P?resource,were comprehensively considered the mechanism of successful invasion of invasive plants.In this research,invasive plant Solidago canadensis L.,which has posed serious ecological and economic damages in the most parts of China,was selected as the research object.We developed greenhouse-potted experiments to comprehensively analyze the growth and competitive response of S.canadensis grown in sparingly soluble P sources for resources from biological characteristics,arbuscular mycorrhizal fungi?AMF?symbiosis and nitrogen?N?and P resource changes in the environment.This research aims to clarify the competition strategy of S.canadensis for P resource which will provide strong theoretical support and practical guidance for the management and control of its potential invasion.The innovation points of this study mainly include:?1?This research directly and simply reflected the competitiveness of invasive plant and native plant by taking the efficiency of clonal integration under the competition which provides a new research method for the verification of competitive advantages of other invasive plants;?2?This research clarifies the effects of plant biological characteristics,arborescent mycorrhizal symbiosis and nitrogen deposition on the growth and competition of S.canadensis in sparingly soluble P sources,which could provide important information for the regional distribution and diffusion prediction of S.canadensis in China.The main results were as follows:1.A comparative analysis was conducted about the competitive ability of invasive plant S.canadensis and native plant Pterocypsela laciniata depending on the effects of competition on the clonal integration of the native clonal plant Alternanthera sessilis.The results showed that the clonal integration of A.sessilis was not significant when there was no competition at the apex of A.sessilis.The growth of the apex of A.sessilis was significantly inhibited whether the competitor was S.canadensis or P.laciniata.However,clonal integration improved the growth of the apex of A.sessilis under the competition.Compared to competitor P.laciniata,the benefits of clonal integration was significantly less when the competitor was S.canadensis than that when the competitor was P.laciniata.This research clarifies that the invasive plant has stronger competitive advantages than the native plant according to the effects of the competition from S.canadensis or P.laciniata on the clonal integration of A.sessilis.2.In order to explore the causes of competitive advantage of invasive plants,this research did further work from the perspective of resource competition strategy by taking P as the competitive resource.This research tested the growth response of S.canadensis to increased nitrogen?N?supply grown in different phosphorus source.The results showed that:?1?S.canadensis was able to selectively utilize P from AlPO₄ but not from FePO₄ or Ca₅?OH??PO₄?₃;?2?S.canadensis grown in AlPO₄ improved the efficiency of P uptake by increasing root number and length under N additions,which was significantly positively correlated with total biomass;?3?When the P source is available to S.canadensis,the amount of P absorbed by the plant significantly increased with increased in N levels.This research suggests that the growth response of S.canadensis grown different P sources depends not only on the availability of the inorganic P source,but also has close relation with biological characteristics and N resource level.3.S.Canadensis has also widely distributed in northern China,where P source mainly is Ca₅?OH??PO₄?₃?HAP?.However,according to the results of this research in the above chapter,it is difficult for S.canadensis to make use of HAP through its own biological characteristics.A large number of studies have reported that arbuscular mycorrhizal fungi?AMF?can promote the P acquisition of plant,and S.canadensis is a typical AMF symbiotic plant.Therefore,the aseptic seedlings of invasive plant S.canadensis grown in the HAP was inoculated with the monoxenic culture of AMF to explore the important roles of AMF on the P acquisition and the growth of S.canadensis.The results showed that AMF colonization rate of S.canadensis grown in the HAP was significantly higher,and the P acquisition and the growth of S.canadensis was promoted by AMF.The experiment is sterile culture system in this research,the results is the direct reflection of contribution AMF colonization to the P acquisition and the growth of S.canadensis,because the sterile culture system avoids the interference with the results from other factors promoting the solubilization of HAP from endophytic bacteria or other soil microorganisms.The results of this research provide theoretical support for the colonization and spread of S.canadensis in northern China.4.Soil acidification due to N deposition,which is conducive to the dissolution of HAP,improves the availability of HAP.According to the results in chapter ii,that is,when the availability of P source is increased,the amount of P uptake by plants significantly increases with increased in N.Therefore,the effects of current and projected N deposition on the growth,the intra-and interspecific competitive ability of invasive plants in calcareous soils with low P availability were discussed.The results showed that the P acquisition and the growth of both S.canadensis and P.laciniata growing alone significantly increased with increasing N level.However,the effect of N addition was reduced when intra-or interspecific competition existed.N addition altered the competitive relationship between S.canadensis and P.laciniata allowing S.canadensis to out-compete P.laciniata due to variation in P acquisition from HAP.Elevated N deposition maybe one important driving factors of the invasion of S.canadensis in the widely distributed calcareous soils in the context of environmental changes according to the results of this research.5.Based on the results of previous studies and the above chapter,S.canadensis shows a stronger competitive advantage under low P conditions,and it can be speculated that the S.canadensis may be a super competitor for P resources compared with P.laciniata.Therefore,the increased P supply can induce a high demand for biotic N according to the demand of the balance N:P ratio.The results showed that the growth of P.laciniata was significantly inhibited by S.canadensis under the ambient conditions.The P⁺N^-treatment promoted the growth of P.laciniata,but did not promote the growth of S.canadensis.The competition between S.canadensis and P.laciniata was alleviated under the ambient N condition after P addition.The N requirement of P.laciniata was higher than that of S.canadensis,and P.laciniata outcompeted S.canadensis under the P⁺N⁺treatment.We concluded that P addition may reduce the competitive ability of the invasive plant S.canadensis,especially under a high N condition.The ratio of N and P might be a critical factor for determining the competitive abilities of S.canadensis and P.laciniata.To sum up,S.canadensis can have stronger P resource competitiveness in different P resource environments through its biological characteristics,AMF symbiosis and environmental changes,which is conducive to its distribution and spread in multiple environments.