The Research On The Change Of Plant-Soil Characteristics And Allelopathic Mechanism In The Process Of Degradation Succession In The Typical Grassland Northern China

It is well known that the long-term overgrazing is the major reasons for the degradation succession. In Inner Mongolia typical grassland, the vegetation succession pattern is from Leymus chinensis or Stipa krylovii or Stipa grandis to Artemisia frigida to Potentilla acaulis. And A. frigida and P. acaulis were seen as the indicator species of degraded grassland, and it is easy to form the mono-dominant community for them. Researcheres had studied on degradation mechanism including overgrazing, selectively foraging by sheep, reproduction strategies and the resources redistribution of plant. Recent years, more reaearches have suggested that plant allelopathy mechanism is the important factor to affect the vegetation distribution pattern in the process of succession. Secondary metabolites produced by plant affect the normal growth of plants, which affect the plant community structure and species composition, but also influence the microenvironment of the soil. In essence, vegetation community succession process is the coordination development of the vegetation and soil. So, it owns important ecological significance to research the soil characteristics responces to the vegetation succession in typical grassland north China.This research determined two hypothesises:(1) the allelopathy mechanism of P. acaulis affects the vegetation community structure and succession process in typical grassland;(2) Along the vegetation degradation succession order, soil condition deteriorated with grassland degradation. We explored the allelopathy of P. acaulis leaves, root and root soil leaching solution to the seed germination and seedling growth of its associated species, L. chinensis, S. krylovii and A. frigida through the laboratory biological detection method, and investigated community composition of different vegetation succession communities, and studies patches soil characteristics responding to vegetation change. The main results were as follows:1. P. acaulis leaves, root and root soil leaching solution showed the "dose effect" in inhibitory the seed germination rate, delaying germination time. The leaf and root soil water extract had no significant effect on seed germination rate at lower concentration (≤0.025g ml-1), however, inhibition enhanced with increasing concentration.2. P. acaulis leaves, root and root soil leaching solution showed the phenomenon of "promotion at lower and suppression at higher concentration"on the seedling growth of L. chinensis and A. frigida. When extract concentration of leaf≤2mg ml-1and root and root soil≤4mg ml-1, significantly promoted the stem growth of A. frigida seedling. When extract concentration of leaf, root and root soil leaching solution≤4mg ml-1, significantly promoted the stem growth of L. chinensis seedlings. The inhibition strengthened significantly with the increasing concentration. The extraction showed "dose effect" on stem growth of S. krylovii seedling and the radical growth of3receports seedlings. The sensitivity of radical growth of receptor seedling was stronger than stem growth. Generally, S. krylovii is the most sensitive species for allelopathy of P. acaulis, followed by L. chinensis and A. frigida.3. In natural grassland ecosystem, the A. frigida and P. acaulis vegetation communities significantly inhibited the normal growth of L. chinensis and S. krylovii.4. During the process of plant community succession, soil conditions under different vegetation communities would not deteriorate following the vegetation degradation. Soil characteristics of P. acaulis have been significant increased and improved, especially in the surface soil of0to10cm, mainly including significantly increasement of soil moisture, SOC and MBC content, the content of bacteria and fungi, and significantly reduced soil PH, temperature and buld density.5. The soil respiration fluxe of P. acaulis was higher than S. krylovii and A. frigia community soil, which may be related with higher SOC, MBC and soil microflora. In the arid and degraded grassland, soil CO2emissions fluxes and soil temperature had no significant correction.and appear positive correlation with soil moisture.In conclusion, the allelopathy affected vegetation regeneration and structure by inhibiting the seed germination and seedling growth of associated species, which may be the factor to promote the vegetation community succession in typical grassland. However, P. acaulis community, as the last succession stage, plays an important role in maintain stability of the degraded grassland ecosystem by improving the quality of the surface soil fertility and protecting soil from wind erosion.