Abstract
<title>Abstract</title> <p> Bckground and aims Intensive agriculture in arid oases relies heavily on excessive nitrogen (N) inputs, driving environmental degradation and resource depletion. While agroforestry systems enhance resource sharing, their ecological potential is often constrained by a lack of targeted nutrient management. This study elucidates how targeting N reduction exclusively to the understory crop regulates plant-soil synergies in a juvenile apricot-soybean intercropping system. Methods Through a two-year field experiment systematically conducted in Shihezi, Xinjiang, four treatments were evaluated: monoculture with conventional N (MS) and reduced N (MSN), alongside intercropping with conventional N (IS) and reduced N (ISN). Results Targeted N reduction dynamically regulated soil inorganic N, facilitating early-stage N retention to mitigate monoculture nutrient imbalances. Furthermore, during the critical pod-filling stage (R6), it significantly stimulated belowground microecological potential. Compared to IS, the R6 activities of soil β-glucosidase, N-acetyl-β-D-glucosaminidase, and nitrite reductase increased by 59.87%, 50.03%, and up to 121.96%, respectively. Physiologically, this late-stage enzymatic mineralization alleviated stomatal limitations. At the R6 stage, soybean stomatal conductance was 131.99% higher than MSN, maintaining intercellular CO <sub>2</sub> > 300.00 µmol/mol. This compensatory effect increased R6 dry matter accumulation by 19.98% relative to IS, allocating 28.40%-28.70% of photosynthates to grains. Although interspecific competition reduced absolute soybean yields, the land equivalent ratio of the ISN system consistently exceeded 1.00, and its income equivalent ratio reached 1.25–1.35, demonstrating robust system-level resource synergy. Conclusion By coupling belowground enzymatic mineralization with aboveground compensation, targeted N reduction provides a highly efficient and sustainable agroforestry paradigm for fragile arid ecosystems. </p>