Response Of Seedling Regeneration And Interspecific Competition Of Phyllostachys Edulis And Broad-leaved Tree Species To Altered Soil Nitrogen

The process of Phyllostachys edulis continuous expansion to the surrounding evergreen broad-leaved forest through underground stems（bamboo whip）is accompanied by the soil nitrogen mineralization effect of"increasing ammonium and suppressing nitrate".Competition is an important factor of affecting population development and community dynamics.However,the response of the soil nitrogen supply changes of evergreen broad-leaved forest tree species and the competition of P.edulis invasion are still poorly understood.In this paper,P.edulis is the representative of bamboo plants,Sapium sebiferum and Camellia oleifera are the representatives of broad-leaved trees,through indoor controlled pot experiment,the update of P.edulis broad-tree species seedlings,the way of competition（symmetrical competition or non-symmetrical competition）and the response of the above-ground and underground competition effects towards nitrogen supply changes are studied,with a view to revealing the internal connection and regulation mechanism between soil nitrogen conversion and community replacement caused by P.edulis invasion.The main findings are as follows:1.A certain concentration of NH₄⁺-N can promote the germination of P.edulis seeds,while the increase of NO₃^--N concentration has an inhibitory effect on the germination;the nitrogen concentration and form have no obvious effect on the germination of S.sebiferum and C.oleifera seeds.NH₄⁺-N can promote the growth of P.edulis and C.oleifera seedling height,root architecture,biomass,etc.High concentration（8m M）NO₃^--N can inhibit the growth of P.edulis seedling height and biomass;The promoting effect of NO₃^--N on the growth of S.sebiferum seedlings is better than that of NH₄⁺-N.2.Under ammonium enrichment condition,the growth of P.edulis has similar dynamics and biomass between pure culture of P.edulis and mixed culture of P.edulis-S.sebiferum and P.edulis-C.oleifera.Compared with pure culture,the mixed culture of S.sebiferum and C.oleifera seedling height and biomass are significantly inhibited.It shows that under ammonium-rich conditions,the P.edulis is in a dominant position in the growth competition with broad-leaved trees.3.The growth response and the competition relationship of the tree species under different nitrogen forms are:in a short time,the growth of P.edulis is not much different under different nitrogen forms,as the treatment time increases,it shows a preference for NH₄⁺-N;S.sebiferum is no obvious preference for nitrogen form,and it grows best when it is supplied with NH₄⁺+NO₃^--N;C.oleifera has no obvious preference for nitrogen form.The growth rate of S.sebiferum is higher than that of P.edulis in the beginning of the experiment.In mixed culture of P.edulis-S.sebiferum,the growth of P.edulis is inhibited while the growth of S.sebiferum is promoted in NH₄⁺-N and NH₄⁺+NO₃^--N;In mixed culture of P.edulis-C.oleifera,compared with pure culture,the biomass of P.edulis increases significantly,while the biomass accumulation of C.oleifera decreases significantly.In addition,by calculating the relative competitiveness index,P.edulis has the strongest competitiveness under NH₄⁺-N,the weakest under NO₃^--N,S.sebiferum has the strongest competitiveness under NO₃^--N,and the weakest under NH₄⁺-N.C.oleifera competitive ability under NH₄⁺-N is greater than that under NO₃^--N.4.Through the analysis of the aboveground and belowground competition effects in the ammonium enrichment condition,in the mixed culture of P.edulis-S.sebiferum,P.edulis grows better in the belowground competition and perfect competition,while the S.sebiferum grows better in the aboveground competition and is in an advantageous position;the mixed culture of the P.edulis-C.oleifera,P.edulis has an advantage in competition on the aboveground,belowground,and perfect competition,while C.oleifera is inhibited under all three competitions.The competition between P.edulis and broad-leaved trees mainly occurs belowground.In summary,a certain concentration of NH₄⁺-N is beneficial to the seed germination and seedling growth of P.edulis,while nitrogen has little effect on the broad-leaved tree seedlings update.Under ammonium enrichment condition,P.edulis is in a dominant position mainly through belowground competitive advantages when it competes with broad-leaved trees.Therefore,the soil nitrogen nutrient habitat of"increasing ammonium and suppressing nitrate"during the P.edulis continuous expansion to the surrounding evergreen broad-leaved forest is beneficial to the growth and interspecific competition of P.edulis,which is speculated to be one of the mechanisms for the successful expansion and community replacement of P.edulis.