Effects Of Revegetation Engineering On Soil Microbial Activity And Community Structure During In-situ Mineralization In The Mountain Area Of Southern Ningxia

The mountainous area of southern Ningxia locates inland, with dry climate and complexunderlying surface, having fragile ecological environment.. The ecological environment andsoil quality were improved because of the implementation of the “Grain for Green” projectfrom the end of last century. In order to study the effects of vegetation engineering on thedynamics of soil microbial comunity and activities during soil mineralization process, sixtypical vegetation types lands in a mountainous area of southern Ningxia were taken as testobjects and soil mineralization process in a year was carried out by the methods of in situclosed-top PVC tube incubation. Soil samples were taken every2month in each study plotsand the basic soil physicochemical properties, microbial activity and microbial phospholipidfatty acid (PLFA) were measured. The results showed that:（1）The soil organic carbon and dissolved organic carbon of different vegetation typeswere highest in summer, followed by spring and autumn, and winter. Soil moisture washigher in winter, but the soil total nitrogen, organic nitrogen, the ratio of C/N and soil pH hadno significant change during the mineralization period. The soil organic carbon, dissolvedorganic carbon, total nitrogen and organic nitrogen were highest in natural grassland,followed by artificial woodland and abandoned land, and artificial grassland. The physicaland chemical properties of natural grassland was superior to artificial grassland, which wassimilar with abandoned land. However, the soil nutrient content of Caragana korshinskiiwoodland was highest amang three artificial woodland. Soil moisture was higher inArmeniaca sibirica woodland and lower in Caragana korshinskii woodland and artificialgrassland. The fish-scale pits of Armeniaca sibirica woodland is conducive to holds moisturein the soil. The soil ratio of C/N in different vegetation types was highest in Caraganakorshinskii woodland, followed by natural grassland, Armeniaca sibirica woodland, Prunusdavidiana woodland and abandoned land, and artificial grassland. There was no significantdifference between the soil pH of different vegetation types. The results revealed that thenatural and artificial restoration was be beneficial to improve the physical and chemicalproperties and hold the soil nutrient content, moreover, the natural restoration had a better effect.（2）The soil microbial biomass carbon of different vegetation types was closely linkedto microbial activity. They had similar change during the mineralization period, which washighest in summer, followed by spring and autumn, and winter. However, soil microbialmetabolic quotients had no obvious change and was less affected by the seasons. There weresignificant difference among the soil microbial biomass carbon, soil microbial respiration andmetabolic quotients in different vegetation types. The soil microbial biomass carbon andmicrobial respiration were highest in the natural grassland, lowest in the artificial grassland.Howerver, the soil microbial metabolic quotients was highest in the artificial grassland,lowest in the natural grassland. The soil microbial biomass carbon and microbial respirationcorrelated or significantly correlated with soil organic carbon, dissolved organic carbon, totalnitrogen, organic nitrogen, and soil moisture, but negatively correlated with the soil pH. Thesoil microbial metabolic quotients negatively correlated with the soil organic carbon and pH,but no correlation with the dissolved organic carbon,total nitrogen, organic nitrogen, and soilmoisture.This showed that the physical and chemical properties of soil were closelyassociated with the soil microbial biomass and microbial respiration, but the soil microbialmetabolism entropy was relatively stable, which was less affected by the growth condition ofvegetation.（3）The microorganism PLFAs content in different vegetation types had significantdifference during the mineralization period (P <0.05). The microorganism PLFAs content ofsoil were highest in the natural grassland, which were lowest in the artificial grassland. Thesoil microbial community structure in different vegetation types has obvious seasonalvariation. Meanwhile, changes of microbial community structure mainly were caused by thechanges of bacteria with16:0,16:1ω9c,16:1ω9t,17:0,10Me18:0, cy19:0and fungi with18:2ω9,12c. The soil microbial biomass correlated or significantly correlated with soilmicrobial respiration, microbial biomass carbon, organic C, dissolved organic carbon, organicnitrogen, and soil moisture, but negatively correlated with the soil pH and metabolic quotients.This showed that the physical and chemical properties of soil were closely associated with thesoil microbial community structures.