Relationship Between Degraded Grassland And Microorganism Of Steppe In Gansu East As Well As Phylogenetic Analysis And Identification Of The Dominant Microbes

The soil microorganisms, a main part of the agricultural ecosystem of grassland, play vital roles in energy conversion,substance cycling, and soil development and maturation.They are sensitive indicatives of any variation in environmental conditions. Both constitution and quantity of each member come to be the key parameters for evaluating the soil quality. Thus investigatina the diversity and member quantity of microorganisms in grassland soil as well as effects of pathogenic ones on grassland productivity are of indispensably significance.In this paper, aiming a solution to the serious degradation of present grassland, based on principles of soil microbiology and plant pathologic ecology, combined technologies such as, field test, lab isolation and cultivation,physiochemical analysis and molecular confirmation based on 16S rDNA were employed. plots of steppe grassland at different level of degradation in the east of Gansu Province were selected and administered with three different treatments. Treatment No 1 (CG), enclosed grassland in 2001 after a 7-year-cultivation-withdrawal; No 2 (WS), enclosed natural grassland in 2001; and No 3 (CK), natural grassland free to graze. Systematic studies on seasonal quantitative kinetics of soil microorganisms, physiological flora,dominant genera species and effects of pathogenic ones on productivity of grassland were conducted. Findings of the 3-year researches are as follows:1. Physicochemical properties and yearly variation of grassland soil General characteristics such as low content of organic substance, total nitrogen and phosphorus, medium of alkaline hydrolytic nitrogen, extreme low of available phosphorus, and accompanying unbalanced ratio of C/N, C/P and N/P were detected. Water content detection of sample soil collected in 2003 showed, compared with 2002, no obvious variation in sample CG, an increase from 5.23% to 7.25% in WS, while a decrease from 7.04% to 2.56% in CK. During the same period, tests revealed an rise by 2.15g/kg of organics content, 0.181g/kg of total nitrogen, 0.274g/kg of total phosphorus, and 3.3 mg/kg of alkaline hydrolytic nitrogen in sample WS, whereas little change in CG and CK. These data suggest that enclosed natural grassland is significantly effective in humidity improvement and fertility rehabilitation of grassland soil.2.Yearly and seasonal variation pattern of soil microorganism In 2002, flourishing of soil microorganisms in June and September is contrasted with their small quantity May and October, while in 2003, a peak showed in May and July contrasted with their nadir in September. Quantitative pattern of various microorganisms among different samples and years were compared. (1) Bacteria were dominant regardless of the months and samples in 2002. Its annual average proportion against total soil related microorganisms reached 76.16%, 84.51% and 69.45% in CG, WS and CK samples respectively. However in 2003, it slightly reduced to 52.75%, 62.07% and 58.28% with relatively a smaller fluctuation against different time periods compared with 2002. (2) Actinomyces, with a quantitatively steep change between years, peaked its proportion as 30.40% in CK sample grassland and showed its least as 17.5% in WS in 2002, meanwhile with its inter-monthly fluctuation range as 11.47～33.23 %, 8.15～29.99% and 8.05～39.80% in CG, WS and CK respectively. However, in 2003, Actinomyces showed a great rise in its proportion against total soil microorganisms, even became dominant by accounting for about 50% or more both in CG and CK in July and September. (3) Fungi comprised only 0.09～0.20% against total soil microorganisms, always higher in CK than either CG or WS in both 2002 and 2003, showing a resemble variation patterns as bacteria except for peak showed in June and July and lowest in October in 2002. Kinetics of microorganisms either yearly or quarterly were affected by various factors including soil physiochemical conditions, microbiological ecosystem, vegetation flora, and mainly by rainfall and temperature. The humidity exerted a restriction to quantity of microorganism.