In the context of global change, anthropogenic activities, either their forms or levels, constantly transform the land use patterns 1. The most typical example is converting natural forests or pasture to farmland around the world 2. It has been well recognized that land-use strategies significantly impact soil health status 3–5. As the essential indicators, soil physicochemical and microbial properties have received the most attention 6–8. Various related parameters, such as soil pH, electrical conductivity, organic matter, total nitrogen, and biomass and metabolic profiles of soil microbiome, are measured to assess the effects of land-use type on soil quality 9,10.
Facing the growing demands for food and bioenergy, countries worldwide need to continuously increase their arable lands and agricultural yields 10. Subsequently, excessive cultivation practices, however, adversely influence soil physicochemical conditions, inhibit the local soil microbial activities, and threaten soil function ultimately 11. Tillage operations physically disturb the soil structure, causing changes in soil physical properties (e.g., bulk density and soil moisture), losses of nitrogen contents and organic carbon in soils, and reductions in soil microbial biomass and enzyme activity 12,13. Fertilization may induce nutrient disorders and microbial community structure shifts 11. For instance, a higher N fertilization rate significantly decreases the amount of several extractable soil nutrients (e.g., P, K, and Ca) and lowers the relative abundance of the mycorrhizal fungi 7.
Rice, one of the most widely consumed cereal crops globally, is the staple food for more than half the world’s population 14. China plays a leading role in global rice-producing and meanwhile consumes more rice than any other country 15,16. China’s rice-growing region can be further subdivided into six first-grade regions, i.e., South China double rice cropping region (I), Central China double and single rice cropping region (II), Southwestern plateau region of single and double rice cropping (III), North China single rice cropping region (IV), Northeast China early maturing and single rice cropping region (V), and Northwest China single rice cropping region in dry areas (VI) 17. Northeastern China, 6comprising Heilongjiang, Jilin, and parts of Liaoning and Inner Mongolia, is a traditional high-quality rice planting area18. In particular, Wuchang rice (Oryza sativa spp. japonica), a geographical indication protection product in China, has been planted in the meadow soil of Wuchang City in Heilongjiang province with a history exceeding 200 years 19,20.
Rice monoculture is a rice-cropping strategy adopted world-widely, and a double or triple sequential cropping method is even implemented in the lowland tropics and subtropics of Asia 21. However, the continuous monoculture system is questioned for its adverse effects on agricultural sustainability23. In concretely, such practices induce increased soil compaction, reduced soil nutrient availability, and deteriorated soil physicochemical quality 21,22. Likewise, it slashes the abundance and diversity of soil bacterial communities and reshapes the soil microbial community structures, hence fluctuating a series of soil microbiological indicators 24,25. Moreover, intensive rice cultivation elevates the risk of rice diseases and pests and the build-up of soil-borne pathogens26.
Due to the low winter temperature and short growing season, single-cropped rice with winter fallow is the predominant cultivation mode in Wuchang City, southern Heilongjiang 16,18. As indicated in the previous paragraphs, the cultivated soil is presumed to degrade after experiencing a long-term–more than 200 years–cultivation practice. In this study, conducted in a seed breeding farm in Wuchang City, China, we measured the physicochemical parameters (soil pH, soil organic matter (SOM), total nitrogen (TN), and alkali-hydrolyzed nitrogen (AHN)) and microbial profiles (microbial biomass (MB) and carbon metabolism characteristics (CMC)) of meadow soils managed with local rice-cropping strategies, and further compared it with that in an uncultivated control. Besides, the seasonal variance of preceding indices was observed as well. Our main hypotheses are: (H1) rice cultivation practices reduce nutrient-related soil physicochemical indicators. (H2) MB is higher in uncultivated soil; MB in the rhizosphere exceeds bulk soil in cultivated areas. (H3) CMC varies with cultivation status and presents seasonal dynamics.