| In this paper,the methods of field observation,soil seed bank germination,field water excitation and soil microbial in situ mineralization were used to observe and analysis the Characteristics of herbs communities,soil carbon and nitrogen,soil seed bank diversity,and soil microorganisms mineralization in the antropogetic introduced Caragana Korshinskii shrublands with different years(14 years enclosed grassland/FY,Grazed grassland/F,3-year shrubland/NT3,12-year shrubland/NT 12,22-year shrubland/NT22)and different spaces(14 years enclosed grassland/FY,Grazed grassland/F,40 m interval shrubland/NT40,8 m interval shrubland/NT8,2 m interval Shrubland/NT2),and to elucidate the response of these indexes to the Desert Grassland with Anthropoogenic Introduced shrub,especially responses of soil seed bank and soil microorganisms mineralization to soil moisture influenced by shrubland encrochment in the Eastern of Ningxia Area.The aim of this paper to provide a theoretical basis and reference data for the sustainability vegetation recovery of arid and semi-arid desert grassland.Mainly obtained the following results and conclusions:1)With the Anthropogenic introduction of shrubs with different planting years and spaces,soil water in deep soil moisture was accelerated to be consumed.The soil water content in 0-200cm soil was in the range of 4.44%-13.32%in shrubland,which was significantly lower than that of FY and F,and soil water content of the NT22 and NT2 was the lowest.Due to the depletion of deep soil moisture,the seasonal dynamics of soil moisture in different years and spaces introduced shrublands showed that the soil water content in the spring and early wet seasons was also significantly lower than enclosed grassland and grazedgrassland(P<0.05).The soil organic carbon content showed an overall trend of increasing,showing the content of soil organic carbon in shrubland was higher than that of enclosed grassland and grazing land,which was between 0.5063-4.2293 g/kg.With the introduction of different ages and spaces shrubs,the soil total nitrogen content showed an increasing trend.The total soil nitrogen ranged from 0.0504-0.5080 g/kg.2)With the increase of the planting age and density of the shrublands in the desert steppe,the diversity and richness of above-ground herbaceous plants showed a downward trend.The density of annual herb was significantly higher than that of other perennial herbs,with a density of 83-429 strains/m3,accounting for 92.3%the density of the entire species and the density of NT40 is highest.The number of species only 12 species,the proportion of Compositae is significantly higher than other family genus plants,and the dominant species in all plots are Artemisia selengensis.The species composition of the soil seed bank and the density of the soil seed bank showed a trend of increasing with different planting years and spaces.There was a significant difference between different shrublands(NT22,NT 12 and NT3)and F and FY(P<0.05).The number of seeds increased in different year and spaces shrublands,ranging 6200-19400 grains/M-2,6200-17700 grains/m-2,respectively,mainlythe annual Artemisia herbaceous species,Artemisia frondosa.The number of species in soil seed bankdecreased with introduction of the different ages and spaces shrub,ranging 5-7 species and 2-7 species,respectively.The simila,rity between the plant characteristics of the soil seed bank and aboveground vegetation was low in all plots.3)With the increase of rainfall gradient,the germination number of soil seed bank increased and then decreased during the introduction of shrubs,but there were no significant effect on the variation of number of seed species.Compared with other rainfall gradients the number of soil species and soil seed bank density is highest in the annual rainfall 348mm,Among germinating seeds,Artemisia selengensis was suitable for all rainfall gradients and increased more than other species with increasing rainfall gradients.Other species,T.mongolica and S.mongolica,geminated only in the rainfall of 116 mm,wherea Lespedeza potaninii can germinate in the precipitation 232 mm and 348 mm.4)The amount of bacteria in the soil was greater than the number of fungi in the process of shrub introduction,and the number of bacteria increased with the increasing years of introduction.The highest amount of fungi was 112.83x 103/g in NT3 plot,and the lowest was 13.79x 103/g in FY.The number of actinomycetes in the process of shrub introduction was higher compared with other microbials,and there no significant difference between plots(P>0.05).Soil respiration peaked of all plots were in August,showing the trend of increasing first and then decreasing.With the increase of the planting age and density of the shrublands,Soil respiration intensity ranged from 0.016 to 0.544 CO2/m2/h,0.016 to 0.506 CO2/m2/h,respectively,and the highest amount of different year introduction were 0.544 CO2/m2/h in NT12 plot and the highest amount of different spaces introduction 0.506 CO2/m2/h in FY plot.Soil respiration was positively correlated with soil moisture,microbial biomass carbon(MBC)and microbial biomass nitrogen(MBN).5)The change of MBC and MBN was highest in summer season June(in situ culture and mineralization for 2 months),and the range of MBC and MBN of soil microorganisms in different years and spaces of introduction were 27.67-54.88 mg/kg and 0.0045-0.1841 mg/kg,59.33-637.93 mg/kg and 0.0045-0.1841 mg/kg,respectively.MBC and MBN in situ mineralization of 2-4 months gradually increased and decreased After incubation of six months,indicating that soil carbon was in the process of accumulation in the process of shrub introduction,while soil microbial mineralization was greater than the accumulation of soil microbial biomass in grazing grassland.The soil NH4+-N and NO3--N during the introduction of shrubs at different ages under different water gradients showed a slow depletion process after the introduction of shrubs.The net ammonification rate in different years and spaces shrublands were-0.26-0.03 mg/g/d,-0.19-0.05 mg/g/d,respectively,and the net nitrification rate were-0.37-0.25 mg/g/d,-0.55-0.23 mg/g/d and the net mineralization rate were-0.41-0.22 mg/g/d,-0.29-0.1 mg/g/d.The net mineralization rate ofafter introduction of shrubs was higher than that of enclosed grassland and grazed grassland. |
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