[Effects of Converting Farmland into Forest and Grassland on Soil Nitrogen Component and Conversion Enzyme Activity in the Mountainous Area of Southern Ningxia].

The effects of the policy of converting farmland to forest and grassland on soil nitrogen content and conversion enzyme activity were studied. Caragana intermedia, Prunus davidiana, Medicago spp., and Stipa bungeana and a corn control were examined to determine the concentrations of seven soil nitrogen components and the activity of two nitrogen conversion enzymes. The main factors affecting soil nitrogen distributions and transformation was also explored using redundancy analysis (RDA). The results showed that:① Compared with the corn soil, the content of particulate organic nitrogen, light fraction organic nitrogen, microbial biomass nitrogen, and ammonium nitrogen in the Stipa bungeana soil increased by 35.3%, 83.3%, 64.2%, and 110.0%, respectively; soluble organic nitrogen and ammonium in the Medicago spp. soil increased by 0.7% and 67.5%, respectively; the asparaginase and protease activities in the Stipa bungeana soil increased by 360% and 144.8%, respectively, indicating that conversion of farmland to forest and grassland has a promoting effect on nitrogen components and conversion enzyme activity; ②The content of organic nitrogen, light organic nitrogen, particulate organic nitrogen, and soluble organic nitrogen in the Prunus davidiana soil was 3.7%, 133.3%, 70.6%, and 28.1% higher than that of the corn soil, respectively. The light fraction organic nitrogen content of the Caragana intermedia soil and microbial biomass nitrogen content of the Prunus davidiana soil was 16.7% and 49.6% higher than that of the corn soil, respectively. Protease activity in the Caragana intermedia and Prunus davidiana soils was higher than in the corn soil, further indicating that the conversion of farmland to forest and grassland promotes the accumulation of nitrogen components and enhances conversion enzyme activity; ③ The RDA and environmental factor explanation rate results indicated that soil water content, pH, and soil organic carbon were the key factors affecting nitrogen distribution and transformation in the mountainous area of southern Ningxia. Overall, the results show that converting farmland into forest and grassland has changed conversion enzyme activity and has promoted the accumulation of nitrogen components in soils. This provides a theoretical basis for ecological restoration and soil quality management in the Loess Plateau.

[Effects of the Farmland-to-Forest/Grassland Conversion Program on the Soil Bacterial Community in the Loess Hilly Region].

This study investigated the effects of the program aimed at converting farmland into forest or grassland on the soil bacterial diversity in the Loess Hilly region. Corn land was selected as the experimental control, and Caragana intermedia land and Stipa bungeana land were selected as the experimental lands. Soil from three different land use types were selected as subjects. The soil bacterial communities were analyzed using a high throughput sequencing technique (MiSeq). The sequence region was 16S rRNA V3-V4 variable region. The α diversity, community composition, and relative abundances of the soil bacterial groups were analyzed, in order to explore the effects of soil physical and chemical properties on the bacterial community structure. The results showed that the structure and diversity of the microbial communities differed under the different land use types. At the phylum level, the dominant phyla were Proteobacteria, Actinobacteria, Acidobacteria, Chloroflexi, Gemmatimonadetes, and Firmicutes. At the class level, α-Proteobacteria, Actinobacteria, Acidobacteria, ß-Proteobacteria, Thermoleophilia, Gemmatimonadetes, Bacilli, and δ-Proteobacteria were predominant. Compared to the corn land, Proteobacteria and Actinobacteria were the dominant bacteria in the Caragana intermedia land, while Actinobacteria and Acidobacteria were the dominant bacteria in the Stipa bungeana land. Soil bacterial diversity was the highest in the shrub land. RDA analysis revealed that soil organic matters and total nitrogen were the most influential environmental factors. It was shown thus that the program of converting farmland into forest or grassland has significantly improved the soil fertility and environmental conditions, and the composition of the soil bacterial community has also been appreciably changed.

[Characteristics and Coupling Relationship of Soil Carbon and Nitrogen Transformation During In-situ Mineralization Cultivation in Forestlands in the Mountain Area of Southern Ningxia].

The study aimed to investigate the characteristics and relationship between soil carbon and nitrogen transformation of artificial forestlands, which is one type of vegetation restoration in the mountain area of Southern Ningxia. Soil samples were collected every two months in a year from three forestlands, and the characteristics of soil organic carbon, dissolved carbon, microbial biomass carbon, organic nitrogen, inorganic nitrogen, soil ammonification, nitrification and mineralization rates, microbial immobilization rates and coupling of soil carbon and nitrogen were studied by the in-situ closed-top PVC tube incubation methods. The results showed that: in the process of in-situ incubation, the most obvious changes of carbon and nitrogen were in 61-120 days which was mainly affected by soil moisture; There were significantly positive correlations between the soil organic carbon and the total nitrogen, microbial biomass carbon and microbial biomass nitrogen, dissolved carbon and dissolved nitrogen; Transformation rates of soil organic carbon had significant effects on the soil ammonification, nitrification and microbial immobilization rates. It can be well simulated by model of linear regression equation; Microbial quotient, MBN/SON were significantly increased in soil of Caragana korshinskii land. Net nitrification rates, net mineralization rates in Caragana korshinskii land were significantly higher than that in Prunus davidiana and Prunus mandshurica lands.