Study On Impact Of Grazing And Nowing On Soil’s Microbial Properties And Aboveground Vegetation

Soil microbial community is sensitive index for soil quality and ecosystem functional changes. In this study, the impacts of cattle grazing intensity and mowing freqency on soil microbial community structures were examined by phospholipid fatty acid(PLFA) in temperate meadow steppe of the Hulunber grasslands, Northeastern China. Four grazing intensities(0, 0.23, 0.46 and 0.92 Au/ha) and five mowing freqencies were analyzed, and observations were conducted from 2013. The main results are follows:(1) Grazing changed the composition of soil microbial community, but no significant affect the predominant position of functional bacterias. Soil total microbial biomass was highest in control grazing G0.00, then in the heavy grazing(G0.92), was lowest in the moderate grazing(G0.46). The biomass of Bacteria, Gram-negative bacteria, Saprophytic fungi, and Arbuscular mycorrhizal fungi(AMF) also displayed the same change respectively. And there was extremely significantly difference for AMF between different grazing intensities. The biomass of Gram-positive bacteria and Actinomyces showed a upward trend with increased grazing intensity. In addition, we found that soil microbial community structure was almost similar in the control grazing G0.00 and light grazing G0.23, whereas intermediate grazing G0.46 and heavy grazing G0.92 could lead to substantial changes in the microbial community structure. And our findings demonstrate that soil organic matter and available phosphorus were important nutrient factors for influence microbial species and biomass.(2) The maximum number of Ammonifying bacteria, Oligotrophic Azotobacter microorganisms, Oligotrophic Cellulolytic microorganisms appeared when it was light grazing G0.23; the maximum number of Aerobe Azotobacter, Oligotrophic azotobacter appeared when it was moderate grazing G0.46. Except for Catalase, the activities of Alkaline Phosphatase, Urease and Invertase decreased significantly as grazing intensity increased(P<0.05). The tendency of vegetation coverage, biomass and vegetation diversity indexes obviously decreased with the increase of grazing gradient. The soil bacterial physiological functional groups(except Nitrifying bacteria) positively correlate with the species richness of aboveground vegetation, vegetation coverage, community diversity indexes and biomass; the soil Alkaline Phosphatase and Urease activities showed significant positive correlation with vegetation coverage, community diversity indexes and biomass(P<0.05). The temperate meadow steppe soil’s biological properties show different degrees of change under different grazing intensities, soil enzyme activities represent the current state of soil ecological system better than the microorganism community, and it has better correlation with aboveground vegetation indexes.(3) Mowing also changed the composition of soil microbial community and promoted the growth of microorganisms.The microbial biomass was highest in the M2 and M3 processing. In addition, we found that the community structure was almost similar in the mowing M2 and M3, the community structure under the M6 and CK processing was similar, whereas the mowing M1 lead to substantial changes in the microbial community structure. Bacteria, Gram-negative bacteria and Gram-positive bacteria were the key factors of the soil microbial community structure. And our findings demonstrate that available phosphorus, available potassium and pH were the important nutrient factors for influence the microbial species and biomass.(4) The microbial number of M1 mowing processing(Oligotrophic Azotobacter microorganisms, Oligotrophic Cellulolytic microorganisms) and M3 mowing processing(Nitrifying bacteria, Ammonifying bacteria, Oligotrophic azotobacter) were more than the microbial number of the control area. The number of Alkaline Phosphatas showed a trend of decrease as mowing intensity increased; Under the heavy mowing frequency, the activity of Urease and Invertase were high, and the activity were reduced in the low intensity. The mowing changed the composition of vegetation community, and promoted the growth of constructive species Leymus chinensis; also reduced species richness and diversity index, vegetation biomass. The analysis showed that the number of Aerobe azotobacter, Cellulolytic microorganisms were negative correlation with the species richness and community diversity, vegetation biomass, the number of denitrifying bacteria are positively correlated with aboveground vegetation. The temperate meadow steppe soil’s biological properties show different degrees of change under different mowing intensities, soil enzyme activities represent the current state of soil ecological system better than the microorganism community, and it has better correlation with aboveground vegetation indexes.