Background and Aims <p>Plant species may use one nutrient to facilitate uptake of another, which could explain nutrient uptake advantage in intercropping systems. This study determined whether intercropping enhances N uptake under P addition and P uptake under N addition, as well as to explore the mechanisms driving these diversity-related effects.</p> Methods <p>From 2012 to 2014, aboveground N (or P) uptake was measured using two long-term experiments (established in 2009) involving maize-based intercrops and monocultures. One experiment tested three P rates, and the other tested five N rates. To assess N (or P) complementarity/facilitation and the effects of dominant species, the relative complementarity effect (rCE) and relative selection effect (rSE) were calculated.</p> Results <p>The addition of N (or P) increased aboveground P (or N) uptake in both monocultures and intercrops, indicating a nutrient reciprocal facilitation mechanism between N and P. The relative increase in N (or P) uptake due to P (or N) addition was greater in intercropping systems than in monocultures, with variations depending on crop combinations. Enhanced nutrient uptake in intercropping systems was positively correlated with rCE but not rSE.</p> Conclusions <p>Intercropping promoted the reciprocal facilitation of N and P uptake compared to monoculture, leading to improved overall plant nutrient uptake. The increased N (or P) uptake in intercropping systems was driven by nutrient complementarity and/or facilitation. This finding contributes to the understanding that multiple mechanisms for complementarity may reinforce one another in intercropping systems.</p>