Effects of enhanced UV-B radiation and nitrogen addition and their interaction on competition between Alternanthera philoxeroides and Digitaria sanguinalis
[Objective]The present paper aimed to examine the effects of enhanced UV-B radiation,nitrogen addition and their interaction on the interspecific competition between invasive weed Alternanthera philoxeroides and its native accompanying species Digitaria sanguinalis,providing reference for the control of invasive plants under the global change.[Method]According to the de Wit substitution test method,we totally set two experimental factors that contained the treatment method(nitrogen addition,UV-B radiation,nitrogen × UV-B)and the spe-cies(A.philoxeroides,D.sanguinalis)on the mono and mixed potting cultures,measured the total biomass,morphology,pigment,and photosynthetic fluorescence of these two studied plant species,and then used the two-way ANOVA and the least significant difference(LSD)multiple comparisons to examine the differences of above indicators with different treatment combinations.[Result](i)In the monoculture,nitrogen addition led to a significant increase in the maximum stem length of plants and leaf area of D.sanguinalis by 207.154％and 297.643％,and a significant decrease in the total biomass and qp_Lss of A.philoxeroides by 40.612％and 52.381％,respectively.UV-B radiation led to a significant increase in the maximum stem length of plants,QY_max and QY_Lss of A.philoxeroides by 117.607％,404.459％and 835.714％,respectively,and a significant decrease in the QY_Lss of D.sanguinalis by 45.605％.The interaction effect led to a significant decrease in the total biomass of A.philoxeroides and QY_max of D.sanguinalis by 79.310％and 18.984％,and a sig-nificant increase in the QY_max of A.philoxeroides by 685.350％,respectively.The interaction effect also led to an opposite trade-off of F0 and QY_Lss between these two studied plant species.(ii)In the mixed culture,nitrogen addition led to a significant increase in the leaf ar-ea and Chla of D.sanguinalis by 254.259％and 53.018％,respectively,and a significant decrease in the root length and Chla of A.phi-loxeroides by 76.051％and 12.084％,respectively.UV-B radiation led to a significant increase in the Chla of A.philoxeroides by 45.434％.The interaction effect led to a significant decrease in the root length of A.philoxeroides by 58.824％.[Conclusion]Nitrogen ad-dition relatively increased the competitive advantage of D.sanguinalis in terms of biomass and morphology,but UV-B radiation weakened its photosynthetic activity and increased the chlorophyll content of A.philoxeroides.Furthermore,UV-B radiation and its interaction with nitro-gen addition significantly increased the actual photochemical efficiency of A.philoxeroides.Thus,we should strengthen the monitoring of A.philoxeroides invasion under global change,to prevent the interaction of multiple factors aggravating the competitive substitution of native plants by this invader.
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