The Study Of Allelopathic Effect In The Plant Succession On The Typical Steppe Of The Losses Plateau

The typical steppe in Loess Plateau, Ningxia Yunwu Mountain has had be enclosure inthe past30years, its constructive species are Thymus mongolicus, Artemisi asacrorum andStipa bungeana. By the succession, S. bungeana has become the main community in the area.There are many studies about the relationship between changes in biodiversity, soil physicaland chemical properties and vegetation succession in the past30years. However, research onthe drive factors of the regional vegetation succession was rarely weak. There are lack of thetheoretical basis on the relates among the succession and soil environment, ecology, naturalrecovery, artificial interference or induced.Therefore, an urgent work is to prove the dynamicchanges of soil biochemical properties in the different successional stages of typical steppein the Loess Plateau; meanwhile the relationship between vegetation succession andallelopathy, the dynamic response mechanism are addressed which reveals the grasslandvegetation succession intrinsic motivation, and provides a theoretical basis on rehabilitationand reconstruction for the grasslands of the arid areas.This research studies the steppe that has three different constructive species withdifferent succession stages in Yunwu Mountain natural reserve as the research object, andtheir extracts of rhizosphere soil, leaves and stem, their ether extract, and the root exudates ofhydroponic experiments were used to test allelopathic effects on seed germination, radiclelength, and coleoptile length of the dominant species. Simultaneously, the chemiecologyrelationship among the species is addressed and, the role of allelopathy in the typical steppevegetation succession is revealed as well.The results as follows:(1) T. mongolicus grass was due to overgrazing S. bungeana grass,. The growth of S.bungeana was best under the extracts of rhizosphere soil from T. mongolicus and its radiclelength was promoted significantly than other acceptor plants. The extracts of leaves and stemsinhibited the growth of all test plants (T. mongolicus, S. bungeana, S. grandis, and L.secalinus), though inhibition rate (IR) of S. bungeana was smallest, T. mongolicus's biggest.The inhibition of phenolic substances from extracts of leaves and stems was significantly stronger than the other three chemical compounds. With the same compound, S. bungeanaseedling growth was pronounced promoted than other test species (T. mongolicus, A.asacrorum, S. grandis, and L. secalinus). The seed germination of A. asacrorum was lowestdue to the influence of root exudates from T. mongolicus. Root exudates promoted S.bungeana strongest and with increasing concentration, the allelopathic promotion effectenhancement.(2) Under the conditions of Yuwu Mountain area, A. sacrorum community replaced T.mongolicus community and would continue the succession to S. bungeana, and was a veryimportant phase in the vegetation succession process of T. mongolicus-A. sacrorum-S.bungeana. The seeding growth of T. mongolicus was limited by the extract of A. asacrorumrhizosphere soil, however, S. bungeana S. grandis and L. secalinus was promoted, but thedifference was not significant. On the same concentration, the growth of S. bungeana and S.grandis was significantly better than L. secalinus.The four test plant performances were not identical as for extracts of leaves and stems:the seeding growth of test plants were inhibited increased with the increase of concentration.under the same concentration, the inhibition rate (IR) were, in order, S. bungeana<L.secalinus<S. grandis <T. mongolicus. The extracts (extracts of rhizosphere soil, leaves andstems) had the property that the methanol extracts had stronger effects than the aqueousextracts. The property could attribute that methanol extracts contain more chemicalcompounds or allelochemicals which work on the acceptor species than aqueous extracts.Alkaloids from leaves and stems extracts of A. asacrorum, the seeding growth of T.mongolicus, A. asacrorum, S. bungeana, S. grandis, and L. secalinus were significantlydifferent from the phenols, neutral compounds and organic acids. Four compounds promotedthe seeding growth of S. bungeana but restricted the other four test plants.The seed germination and growth of S. bungeana was promoted significantly strongerthan the other four test plants (T. mongolicus, A. asacrorum, S. grandis, and L. secalinus),and at the200mg/L concentration, the growth of four test plants were restricted.(3) The germination rate of S. bungeana was significantly higher than T. mongolicus's, A.asacrorum's, S. grandis's, and L. secalinus's under the extracts of rhizosphere soil, leavesand stem and their ether extract, and the root exudates.The methanol extract of rhizosphere soil from S. bungeana significantly promoted theseeding growth of S. bungeana and S. grandis, but limited the growth of T. mongolicus and L.secalinus. The aqueous extracts of rhizosphere soil had significantly stronger allelopathiceffects than the methanol extract.Neutral compounds extracted by ether from the extracts of leaves and stems of S. bungeana significantly inhibited the radicle length of the A. asacrorum and T. mongolicus.The growth of S. bungeana was facilitated by neutral compounds, phenols and alkaloids. Thecoleoptile length of S. bungeana was significantly better than T. mongolicus's, A.asacrorum's, S. grandis's, and L. secalinus's under the four kinds of compounds. Thepromotion effect of phenols on S. grandis was significantly lower than the neutral compounds,organic acids and alkaloids.The seeding growth, especially the radicle length of A. asacrorum was significantlyrestricted by the root exudates of S. bungeana. The seeding growth of S. bungeana and S.grandis had been promoted significantly.