Biocrusts are key components of dryland ecosystems that strongly influence soil nitrogen (N) cycling. In semiarid regions, they often coexist with xerophytic shrubs, forming stable shrub-biocrust patches. Yet their links to subsurface N processes and shrub nutrient uptake remain unclear. Here, we compared shrub patches (Artemisia ordosica) with and without well-developed biocrusts in a semiarid shrubland on the Chinese Loess Plateau, combining field and laboratory incubations with molecular and isotopic analyses to quantify soil N fixation potential, N mineralization, and shrub N acquisition. Our results showed that shrub-biocrust patches harbored distinct nifH-bearing bacterial communities and exhibited higher nifH gene abundances, with cyanobacterial diazotrophs dominating the 0-5 cm layer (69.7% vs. 0.5% in shrub soils). In deeper layers (10-20 cm), heterotrophic Azotobacter became increasingly abundant (14.3% vs. 0.1%). Shrub-biocrust patches also showed substantially higher rates of net ammonification (+4%-133%), nitrification (+18%-31%), and total N mineralization (+10%-56%), accompanied by 20%-47% higher inorganic N contents throughout the growing season. These patterns were associated with biocrust-induced changes in soil properties that enhanced substrate availability and enzyme activity, thereby promoting N turnover. Soil moisture-temperature interactions jointly regulated these processes, with biocrust presence strengthening this coupling. The temperature sensitivity was numerically lower in shrub-biocrust soils, although the difference was not statistically significant. Moreover, shrub-biocrust patches exhibited higher leaf N content and more depleted delta 15N values, consistent with greater plant access to biologically fixed N and a shift in plant N sources toward newly fixed N inputs. Collectively, our findings indicate that biocrust presence is closely linked to enhanced N-fixation potential and mineralization beneath shrub canopies, thereby increasing soil N availability and shrub N uptake. While manipulative experiments are required to confirm causality, the mechanistically consistent patterns observed here support a key role of biocrusts in strengthening soil-plant N coupling in semiarid ecosystems.