Effects of different land-use types on soil microbial metabolic limitation and carbon use efficiency in the Yellow River floodplain

Field investigations and sampling were conducted in April and September 2024 across three representative sites of the lower Yellow River floodplain: Taohuayu, Wantan, and Langchenggang. At each site, three distinct land-use types were selected: first floodplain , grassland, and farmland. Within each land-use type, three replicate plots were randomly established, yielding a total of 27 plots (3 sites × 3 land-use types × 3 replicates). In each plot, five soil cores (0–20 cm depth) were collected using a soil auger (3.6 cm inner diameter) and composited to form one representative soil sample. A total of 54 composite samples were collected across both sampling seasons. After removing visible roots and stones, fresh soil samples were sieved through a 2 mm mesh and divided into two subsamples: one stored at -20 °C for extracellular enzyme activity analysis (completed within one month), and the other air-dried for subsequent physicochemical property measurements.