Soil organic nitrogen (SON) components are a key indicator of soil fertility and plant growth. The Danxia degraded region (DDR) is an ecologically fragile area in southern China, where the “Grain for Green” project has been implemented to prevent further land degradation. However, little is known about the effects of vegetation restoration on SON components in the DDR or the factors that influence them. We compared three vegetation restoration types, namely, grassland, shrubland, and arbor forest, with cropland to determine the relationship between SON components and N−cycling enzyme activities. Vegetation restoration increased the soil amino sugar N and amino acid N and reduced the proportion of non−hydrolyzable N. Compared with forest restoration measures, restoration to grassland was more beneficial to SON levels and N−fixation capacity. Vegetation restoration also increased soil nitrate reductase, denitrifying enzyme, protease, β−1,4−N−acetylglucosaminidase activities, and soil microbial biomass. Vegetation restoration in the DDR changed the SON components through the “mineralization−fixation” of organic matter via amorphous iron and proteases, which, in turn, affected the level of available soil N. Vegetation restoration improved the soil N structure and promoted the intrinsic soil N cycle, providing a scientific basis for soil quality restoration in the DDR.

Combining rice cultivation and aquaculture into an integrated cropping system is a management approach that enhances the sustainability of rice fields. However, how soil characteristics influence soil microbial community characteristics following implementation of such an integrated system, particularly in the waterlogged paddies of the Pearl River Delta, is poorly understood. An integrated cropping system (rice–fish–duck integrated cropping system, RFD) and a rice–pepper rotation system (RPS) were compared using a conventional rice cropping system (CRS) as a reference. We used phospholipid-derived fatty acid (PLFA) analysis to assess soil microbial community structure and function and measured soil nutrient content and organic carbon fractions. Our results indicated that the soil nutrient content, organic carbon fractions, and C-hydrolyzing activities differed among the cropping systems. The RFD resulted in higher microbial PLFA concentrations and a lower ratio of Gram-positive to Gram-negative bacteria than CRS. Additionally, the integrated system reduced microbial nutrient stress by increasing soil pH. Further analysis revealed that active soil organic carbon significantly affected the soil microbial community. Thus, the RFD integrated cropping systems that alter the combined actions of pH and active organic carbon fractions can be used to improve soil microbial communities.