Biological Characteristics And Soil Quality Changes On Different Land Use Soils From Tanggu District In Tianjin

With the development of human society, ecosystem has evolved from natural ecosystem into artificial ecosystem under the influence of human activities. Tanggu, the core area of New Coastal Region of Tianjin, is one of the typical urbanizing coastal regions in China. Because of the special soil conditions, the unique soil-forming conditions and diverse landuse types, soil fertility conditions, especially the biological properties, were not very clear. In this study, soil samples were collected from different landuse types, including farmlands, vegetable fields, orchards, artificial plantation and wetlands in Tanggu. By means of outdoor investigation, laboratory analysis and consulting relevant information, we systematically compared the characteristics of fertility conditions, enzyme activities, microbial biomass, microbial quantity, and microbial activity and function in different landuse type soils. The main research results are as follows.(1) Microbial biomass carbon and nitrogen in different landuse soils had the same variation tendency. Sequence of soil microbial biomass carbon from the high to the low was below: vegetable field, orchard, farmland, artificial plantation, and wetland. Bacteria quantity had no obvious differences in farmland, vegetable field, orchard and artificial plantation soils. Sequence of fungi quantities from the high to the low was below: vegetable field, farmland, artificial plantation, orchard, and wetland. Actinomycetes quantity in wetland was relatively low, and there were no significant differences of actinomycetes quantity in other landuse soils.(2) There were no significant differences of soil basal respiration among different landuse soils. The soil basal respiration in artificial plantation was relatively high. In wetland soil, microbial quotient was relatively low, however, the respiration quotient was much higher than that in the other landuse soils.(3) Enzyme activity in different landuse soils varied. Soil urease activity in farmland and vegetable field had significant differences. Sequence of soil alkaline phosphatase activity from high to low was below: orchard, vegetable filed, farmland, artificial plantation, and wetland. Sequence of catalase activity from high to low was below: farmland, artificial plantation, vegetable filed, wetland, and orchard. Invertase activity in wetland soil was very low. (4) Principal component analysis showed that microbial biomass carbon, microbial biomass nitrogen, microbial community quantity and invertase activity were characteristic soil biological indicators in New Coastal Region of Tianjin. Wetland soil biological quality of wetlands was relatively poor, with a low principal component evaluation comprehensive score. The clustering results between biological indicators and principal component scores were similar to the rate of 85.71%, which indicated that principal component scores can be used as a basis for soil biology evaluation.(5) Nutrient contents had obvious differences in different soils. Variation coefficient of soil organic matter and total nitrogen were medium-sensitive indicators. Average organic matter content was 21.15 g kg^-1, medium level. Average total nitrogen content was 1.04 g kg^-1, reaching the intermediate level of the average national survey grading standards. Sequence of soil organic matter and total nitrogen content from the high to the low was below: orchard, vegetable field, farmland, artificial plantation, and wetlands. Average total phosphorus content was 0.75 g kg^-1, much higher than the national rich soil nutrient level, 0.44 g kg^-1. Available phosphorus was abundant. Sequence of average available phosphorus content from the high to the low was below: orchard, artificial green, vegetable field, farmland, and wetland.(6) Soil organic matter had positive correlation with soil total nitrogen and total phosphorus (P<0.01). Total nitrogen had positive correlation with total phosphorus and available phosphorus (P <0.01). Soil organic matter, total nitrogen and total phosphorus could be used as a sensitive indicator in soil quality evaluation.(7) Comprehensive quality of different landuse soils in Tanggu had significant differences by calculating the soil quality index. Sequence of soil fertility and biological activity from high to low was below: vegetable field, orchard, farmland, artificial plantation, and wetland. Vegetable field effected largely by land management and fertilization had the highest soil comprehensive quality. SQI of farmland was at the middle level, indicating that there would be room for improvement through proper land management. Due to comparatively large environmental stress, SQI of wetlands was the lowest. However, it should be considered carefully to how to improve and utilize wetlands as a potential exploitable soil.