The Mechanism Of Competition-allelopathy Trade-off Mediating Niche Differentiation In Sphagnum

In recent years,the research on allelopathy is increasing with the help of the biochemical tools for ecology.Allelopathy and resource competition are two important types of inter-specific interactions,which refers to a form of interference competition mediated by releasing chemical substance compounds into the environment,and competing for water,nutrients,light and space,respectively.Due to allelopathy often occurs simultaneously with resource competition,it is hard to separate the effect of resource competition from allelopathy which undoubtedly hinder further the exploration of the mechanism concerning the inter-specific interaction.Recent researches have mainly focused on allelopathy involved in agriculture and biological invasion areas,but very few studies on the inter-specific interaction among mosses in peatlands.In peatland ecosystems,there are strong competitions and niche differentiation amongSphagnum species.The traditional view argues that competition and tolerant are the underlying causes of niche differentiation and divergence of peatland plants.However,the allelopathy roles in the niche differentiation and divergence of Sphagnum species remain unclear,and the relevant research is still an open problem.This study aims to thoroughly assess the contribution of resource competition and allelopathy to interspecific interaction and niche differentiation of Sphagnum.One hollow?S.angustifolium?and two hummock species?S.fuscum,S.magellanicum?that were with distinct niche differentiation were chosen as study species.Furthermore,we also set up mono-culture and mixed culture of Sphagnum separately along water table level and light gradients to simulate different inter-specific interactions.Besides,activated carbon?AC?was performed to weaken allelopathic effect of neighbors.In addition,a ¹⁴N labelled experiment was employed to determine the effect of competition and allelopathy on nitrogen reabsorption of Sphagnum,which provided new insight into the mechanism of species interaction.The main contributions and conclusions of our research are as follows:?1?The addition of activated carbon reduced the released phenolics of Sphagnum,and successfully separated the allelopathy and resource competition between Sphagnum.At low water level,hummock species inhibited the growth of hollow species by its allelopathy whereas the growth of hummock species is inhibited by resource competition of hollow species.At high water level,the allelopathic effect of hummock species on the growth of hollow species disappeared,while its growth was inhibited by the allelopathy of hollow species.Thus,in the case of water table level gradient for niche differentiation,it showed that,the competitive advantage of Sphagnum is determined by resource competition and allelopathy.Allelopathy weighs more importance than resource competition among the mechanism of niche differentiation among Sphagnum.?2?Under the low light condition,the allelopathy of S.magellanicum?stress tolerant competitor species?and S.fuscum?stress tolerator?could inhibit the growth of neighbors.Under the condition of low and high light,the resource competition of S.angustifolium?competitor?decreased the growth of its neighbors.The results suggested that the niche differentiation of Sphagnum on the light resource gradient is also driven by resource competition and allelopathy.During such process,the life history strategy of sphagnum affects the type of interspecific interaction acting on its neighbors.?3?The N reabsorption of S.angustifolium was inhibited by the resource competition but promoted by the allelopathy of S.magellanicum.Moreover,the N reabsorption of S.magellanicum was inhibited by the resource competition of S.angustifolium.Our experiments have shown that the capacity of N reabsorption of Sphagnum is related to the two inter-specific interactions,resource competition and allelopathic effect.?4?When water and light are unavailable,there is a clear negative correlation between the biomass production and released phenolics of S.magellanicum,indicating that bryophytes increase the allelochemicals but reduce resource competitiveness.In other word,there is a trade-off between resource competition and allelopathy.In addition,the allelopathic effect intensity of Sphagnum is determined by its own total released phenolics.?5?Contrary to the common knowledge,under the condition of abundant water,the competitor does not gain the advantage through resource competition in the coexistence with stress-tolerant competitor.For the stress tolerator or stress tolerant competitor species,the lack of water and light resource is beneficial to stimulate their allelopathy that could balance the depression effect of the competitors'resource competition on them,then occupy a dominant position when they influenced.In conclusion,based on a series of indoor and outdoor plant inter-specific interaction experiments,the feasibility of separating allelopathy and resource competition in bryophytes have been proved successfully and the intensity of allelopathy changing along resource gradients have been clarified.Furthermore,as best to our knowledge we are the first to show the important contribution of allelopathy and reveal its mechanism in the niche differentiation of Sphagnum.In future research,we should not only pay attention to the resource competition,but also focus more on the role of allelopathy in plant distribution pattern,species coexistence and community stability maintenance in peatlands.