| Solidago canadensis is an invasive plant,which could pose a serious threat such as reduction of biodiversity,disturbance to community structure as well as restriction to ecosystem services to the regions they invaded,causes considerable economic loss every year throughout the world.A variety of methods are used to control this alien species;on account of physical control is of low efficiency and high cost,and biological control needs further study to guarantee long-term ecological safety,chemical control is still widely chosen.Herbicide glyphosate,which of high efficiency and low toxicity,is most widely used both at home and abroad at present.Intraspecific and interspecific interactions are common among plant individuals,the nature and strength of plant-plant interactions are often affected by environmental factors.The extensive use of herbicides not only inhibits weeds growth but also affects the growth of neighboring plants,which means that herbicide usage could change the relationship between alien and neighboring plants.From this the usage of herbicide may cause unfriendly consequences to local ecosystems,for instance,interfere with the natural succession of local communities and destroy the dynamic balance of ecosystem.Researches related to impacts of glyphosate on alien plants mostly focus on the effects of glyphosate to control weeds,the effects of this chemical on plant physiology as well as the sensitivity of resistant or non-resistant crops to glyphosate treatment.Further studies are needed to determine whether the application of glyphosate affect the relationship between invasive and native plants.In order to explore the variation relationship between invasive and local plants after spraying glyphosate,a replacement series experiment was conducted in Wetland Ecosystem Research Station of Hangzhou Bay by using the alien plant S.canadensis invaded in Hangzhou Bay and the native plant Imperata cylindrica as study objects to examine the effects of seven different concentrations of glyphosate(0,0.3,0.6,0.9,1.2,1.5,1.8mL/L)on the RII/and RY index of S.canadensis and I.cylindrica,which can reflect the changed interactions of these two species.Besides,in order to explore the underlying mechanism of glyphosate on interspecific interactions,controlled experiments were also conducted to study the change of hydrolyzed amino acid content,growth indexes,photosynthesis and chlorophyll fluorescence parameters of both S.canadensis and I.cylindrica after different glyphosate treatments,as well as the allelopathy of S.canadensis and allelochemicals content in the rhizosphere soil.The aim was to provide data which can support rational use of herbicide and theoretical reference to further studies on ecological effects of glyphosate.The results are as following:(1)Effects of glyphosate on the growth of S.canadensis and I.cylindrica.Glyphosate had significantly inhibited the growth of S.canadensis and I.cylindrica,the latter one turned yellow first.The above and below ground biomass as well as the content of hydrolytic amino acid of S.canadensis had reduced,with glyphosate concentration increasing.Accumulative plant height of S.canadensis had gradually reduced with 0.3?0.9mL/L treatment,while individual growth had ceased with 1.2?1.8mL/L;green leaves of S.canadensis turned to increase with time when sprayed under 0.3?1.5mL/L concentration,while those treated with 1.8mL/L were almost perished.The length of leaves and tiller number of I.cylindrica had decreased as concentration of glyphosate increasing,so did the above and below ground biomass as well as the content of hydrolytic amino acid of this species.The tiller number and the length of leaves of I.cylindrica treated with 0?0.6mL/L tended to increase with time.Effects of the same concentration treatment on I.cylindrica was much higher than that on S.canadensis.(2)Effects of glyphosate on the photosynthesis and chlorophyll fluorescence parameters of S.canadensis and I.cylindrica.Glyphosate had significantly inhibited the net photosynthetic rate(Pn),stomatal conductance(Gs),transpiration rate(Tr)and intercellular CO2 concentration(Ci)of S.canadensis and I.cylindrica.In accordance with the growth state,the influence of the same concentration on photosynthetic and chlorophyll fluorescence parameters of I.cylindrica was higher than that on S.canadensis.Compared with S.canadensis,the maximum net photosynthetic rate(Pnmax)and light saturation point(LSP)of I.cylindrica decreased more,and the light compensation point(LCP)of this species increased more,while glyphosate had no obvious effect on dark respiration rate(Rd)and the apparent quantum yield(AQY)of these two species.The photosynthesis response of these two species to glyphosate differed in different planting patterns.Influence of 0.6mL/L treatment on the photosynthesis of S.canadensis and I.cylindrica grown in mixture was higher than those grown in monoculture,while the effect on the photosynthesis of these two species grown both in mixture and in monoculture became similar with glyphosate concentration increasing.Similarly,glyphosate had apparently influenced NPQ and Fv/Fo of the two species.Chlorophyll fluorescence parameters such as Yield,ETR and Fv/Fm of I.cylindrica were affected higher than that of S.canadensis.(3)Effects of glyphosate on the allelopathy of S.canadensis.The allelopathy of aqueous extract of S.canadensis had the tendency of decrease under glyphosate treatment.With concentration increasing,the length of leaves,tiller number and total biomass of I.cylindrica tended to increase after spraying the corresponding aqueous extract of S.canadensis.Besides,the content of total flavonoids,total polyphenols in rhizosphere soil were decreased after glyphosate treatment,while the content of total saponins tested in soil remained unchanged.Overall,glyphosate had decreased the allelopathy of S.canadensis on the associated plant I.cylindrica,along with the intraspecific competition gradually larger than the intensity of interspecific competition;as a consequence,I.cylindrica grew better in mixed planting than in monoculture.(4)Effects of glyphosate on the interspecific interaction between S.canadensis and I.cylindrica.Glyphosate had significantly influenced on interspecific competition between S.canadensis and I.cylindrica.RII index was negative naturally,which mean these two species were in competition condition;the intensity of competition between S.canadensis and I.cylindrica had gradually weakened as glyphosate concentration increasing.On the one hand,glyphosate had inhibited the normal growth of S.canadensis and I.cylindrica,from which the competition of these two species for survival resources such as space,light,nutrient and water weakened.On the other hand,glyphosate had influenced the synthesis of some secondary metabolites of S.canadensis,which leaded to the reducing of total flavonoids,polyphenol that released from the root of S.canadensis to soil environment;the allelopathic effect of this invasive species on I.cylindrica thus reduced.RY index increased after glyphosate treatment,which showed that the intraspecific competition of I.cylindrica was gradually greater than the intensity of interspecific competition,so I.cylindrica grown in mixture tended to grow better than those grown in monoculture.Compared with the native plant I.cylindrica,the alien plant S.canadensis which invaded successfully showed stronger tolerance to glyphosate treatment.Based on the study results,in order to reduce the impact on the indigenous I.cylindrica community,glyphosate should be avoided in the early invasion stage of S.canadensis.The further study will try to determine the element which play the role rule in reducing competition between invasive and native plants in the processing of glyphosate treatment. |
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