Nutrient resorption represents a key adaptive strategy for plants in nutrient-poor environments. Grazing exclusion is widely used to restore degraded grasslands; its success ultimately hinges on the population dynamics of dominant species, which drive community structural changes. However, our understanding remains limited regarding how plant nutrient utilization strategies mediated by nutrient resorption regulate these critical population dynamics. A three-year consecutive study investigated the nutrient utilization strategies of dominant species (Stipa breviflora and Cleistogenes songorica) in a desert steppe of northern China across three grazing exclusion durations: long-term (17 years), short-term (5 years), and control (0 years). The results revealed that long-term grazing exclusion significantly increased soil moisture and soil available nitrogen (N) and phosphorus (P) concentrations but decreased soil temperature, indicating that the soil microenvironment is significantly altered in fenced desert steppes. Long-term grazing exclusion significantly reduced N and P concentrations in green leaves of the two species, decreasing nitrogen resorption efficiency (NRE) and phosphorus resorption efficiency (PRE), indicating plants had reduced dependence on nutrient resorption after long-term grazing exclusion. Consequently, the reduced relative aboveground biomass of both species demonstrated a weakening of population dominance, indicating that shifts in population dynamics alter community structure in fenced desert steppes. Structural equation modeling showed that grazing exclusion indirectly decreased plant NRE and PRE through increased soil available nutrients, while directly regulating these processes via soil moisture improvement. These ecological processes ultimately decreased the species' importance values, indicating that grazing exclusion-mediated nutrient supply restructuring reshapes ecosystem structure and function. This study reveals a shift in plant nutrient strategy in fenced desert grasslands from an internal cycling-dominated model to an external access-dominated model and provides a theoretical framework for understanding community succession in fenced grasslands from the perspectives of micro-physiological processes and macro-population dynamics.