Effects Of Typical Plant Roots Decomposition On Soil Nutrients And Soil Microbial Diversity Of Southern Area In Ningxia

The loess plateau region has attracted wide concerns in recent years for its bad natural conditions, strenuous water loss,soil erosion and biggest Loess gully region in the world. A serious of measure included Grain for Green Project and sealing off mountainous areas to facilitate afforestation were used to restore the vegatation and ecological environment of the region at 20 th century and get a good effect. The temperate grass zones in Loess hilly-gulled was selected as the research object. Three kinds of typical plant roots of stipa bungeana Trin(St.B), Artemisia sacrorum Ledeb.(Ar.S), Thymus mongolicus( Th.M) were used as experimental material. The decomposition speed of plant roots in grassland ecosystem are studied,and the main factors that effect the decompostion speed, soil microorganisms,soil enzymes activities,soil microbial diversity and content of soil nutrition fluctuated are discussed in this paper. The thesis wants to make sure the resond of roots decomposition to golbal change,provide proof for grassland vegetations recovery and soil fertility quality evaluation, and improve the theory of material and energy cycle in grassland ecosystem.The main results as followed:(1)For different decomposition phase of roots,the increase of quality loss is different.After the decomposition, the quality loss of St.B, Ar.S, Th.M were 9.22, 12.57, 12.47, weight loss ratio were 18.44%, 25.14%, 24,94%. It needed about 66.95, 48.34, 44.13 months for St.B,Ar.S, Th.M to decompose 50% of plant roots, and about 317.78, 245.14, 206.97 months to decompose 95% of plant roots. Significant positive correlations were found between the K and initial phosphorus content in roots, and significant negative correlations were found between the K and lignin in roots. P content and lignin content can predict the decomposition rate excellently. When root decomposition is ends, St.B, Ar.S, Th.M oganic carbon and total nitrogen show the release process, oganic carbon is about 103.34,57.05,124.40g/kg, total nitrogen is about 4.77, 2.93, 0.19g/kg. In first 90 days, the P content declined rapidly and enriched phosphorus. The content of ligin and cellulose declined and reached the nadir in the135 th and 305 th days increased and reached the peak in the 470 th and 425 th days.(2)In the decompostion proces in field, content of organic carbon was decreasing. Afterone years soil organic carbon is 0.81-0.85 times at 0-5cm soi layer than the early times,while0.86-0.92 times at 5-20 soil layer. The concentrations of soil organic carbon in the surface soil under St.B, Ar.S, Th.M root decomosition increased to 0.33, 0.53, 0.22g/kg than control,while the increase is about 0.36,0.11,0.06g/kg at 5-20 cm soil layer. The content of soil carbon could be improved efficiently after root decomposition. After one years soil total nitrogen is1.03-1.06 times at 0-5cm soi layer than the early times,while 1.02-1.05 times at 5-20 soil layer,The concentrations of soil total nitrogen in the surface soil under St.B, Ar.S, Th.M root decomosition increased to 0.032, 0.035, 0.019g/kg than control, root decomposition can increase the total nitrogen in a certain degree. The concentrations of soil nitrate nitrogen in the surface soil under St.B, Ar.S, Th.M root decomosition increased to 0.34-1.09mg/kg than control, butwas not significant difference in ammonium nitrogen.(3)Soil microbial carbon showed obvious season change with root decomposition. The mircrobial carbon in treatment is always below than control except in the initial 45 days. After one year, The concentrations of soil microbial carbon in the surface soil under St.B, Ar.S,Th.M root decomosition decreased to 194.02,197.10,258.87mg/kg than control. The improvment of soil microbial nitrogen at surface mainly in the initial stage(5-8months) of the decomposition, and it is always higher than control at 5-20 cm soil player. Roots decomposition had the opposite effects to soil microbial nitrogen.(4)Soil urease showed the same trend both in the treatment and control. Urease activity in treatment is higer than control slightly at the early decomposition, while the urease activities in treatment were similiar to control. The soil urease reached peak in following 9month and reached minimum in following 3month. Soil sucrase activity of treatment was vasically the same as that of control, but is inconsistent in different layers.soil sucrase were rising slowly in surface soil at eraly stage of the decomposition and showed flucuation changes then. It quickly reached a maximum at eralier stage and slowly reached tis minimum,and then slowly incresed. Soil phosphatese activity reached maximum in next march and may in surface soil, and recached maximum in next july of 0-5cm soil player.(5)To explore the root decomposition by using the method of Miseq sequencing influence on soil microbial community diversity, the results show that under the 97%similarity level, there were 30 divisions, 78 classes, 131 orders, 222 families and 344 genera in soil samples of bacteria. In soil samples there were 18 divisions, 32 classes, 56 orders,72families and 76 genera of fungi. Percentage of actinomycetes to total microbe is38.35-45.39 as dominant bacterial community. Community structure is same between treatment and control at the levle of the division, but in any quantity. Roots decompositionincreased the quantity of actinobacteria and decreased the quantity of cyanobacteria.