Background and aims <p>Nutrient resorption (NR), a critical strategy for improving plant nutrient use efficiency, plays a pivotal role in seed yield formation, particularly in nutrient-limited environments. Furthermore, the combined effects of elevated CO₂ and night warming, are projected to modify NR strategies, with consequent impacts on seed yield. However, the interactive effects of elevated CO₂ and night temperature on NR dynamics and their linkage to seed yield remain poorly characterized.</p> Methods <p>We conducted a two-year open- field experiment using common vetch (<i>Vicia sativa</i> L.) as a model system to examine the response of nitrogen resorption efficiency (NRE) and phosphorus resorption efficiency (PRE) under four treatments: ambient conditions (CC), elevated CO₂ (eCO₂), elevated night temperature (eNT) and their combination (eCO₂ + eNT). Structural equation modeling quantified the direct and indirect effects of climate treatments on seed yield through NRE/PRE.</p> Results <p>The results showed that compared with CC and eNT, eCO₂ and eCO₂ + eNT increased NRE by approximately 40% and 90% in 2020, respectively. However, these NRE enhancements were attenuated or reversed in the subsequent growing season. In contrast, PRE showed more consistent enhancement across both experimental years. The eCO₂ + eNT treatment achieved maximal PRE values of 50% and 39% in 2020 and 2021, respectively. Structural equation modeling identified PRE as the primary driver of seed yield under P-limited conditions. This relationship is clearly demonstrated by the concurrent &gt; 50% increase in seed yield and the highest PRE (50%) under the combined (eCO₂ + eNT) treatment, where the NRE: PRE ratio was minimized.</p> Conclusions <p>These results suggested that the increase in PRE under combined climate stressors was conducive to improving seed yield. The study provides critical insights into climate-resilient legume cultivation in nutrient-constrained ecosystems.</p>