<p>Desert ecosystems are constrained by both moisture and nitrogen, with leguminous plants serving as crucial nitrogen sources and showing high sensitivity to fluctuations in these factors. This study hypothesizes that the combined effects of moisture and nitrogen will alter the growth and physiological functions of ephemeral leguminous plants in desert ecosystems. We conducted a greenhouse pot experiment using ¹⁵N tracing to investigate the responses of two desert leguminous species (<i>Trigonella arcuata</i> and <i>Astragalus arpilobus</i>) to different moisture and nitrogen levels. The experiment followed a full-factorial design with four moisture levels (W1: 5%, W2: 7%, W3: 9%, W4: 11% soil moisture) and three nitrogen levels (N1: 0 mmol L⁻¹, N2: 18 mmol L⁻¹, N3: 72 mmol L⁻¹ ¹⁵NH₄¹⁵NO₃). Results showed that: (1) Both moisture and nitrogen treatments similarly affected growth and chlorophyll fluorescence, with optimal growth at W3N3 and minimal growth at W4N1. (2) Under severe stress, plants enhanced stress tolerance through osmoregulatory substances, lipid peroxidation, and antioxidant enzyme activities, with osmoregulatory substances most sensitive to moisture stress and lipid peroxidation/enzymes to nitrogen stress. (3) Seasonal adaptation was observed in physiological processes, with growth traits, lipid peroxidation, and antioxidant activities lower during rapid growth, while chlorophyll and osmoregulatory substances were higher. Our findings suggest that drought limits nitrogen absorption, while adequate moisture accelerates metabolism, but excessive moisture dilutes nutrients. Moisture-nitrogen interactions significantly influence physiological responses, varying across growth seasons. This study provides insights into the nutrient utilization and adaptation mechanisms of desert legumes under climate change.</p>