IntroductionThe production of root exudates with biological nitrification inhibition (BNI) effects is a strategy adopted by ammonium-N (NH4+‐N) tolerant plant species that occur in N-limited environments. Most knowledge on BNI comes from plant species that occur in acidic soils.MethodsHere, combining field sampling and laboratory culture, we assessed the BNI-capacity ofLeymus chinensis, a dominant grass species in alkaline grasslands in eastern Asia, and explored whyL. chinensishas BNI ability.Results and discussionThe results showed thatL. chinensishas strong BNI-capacity. At a concentration of 1 mg mL-1,L. chinensis’ root exudates inhibited nitrification in soils influenced byPuccinellia tenuifloraby 72.44%, while DCD only inhibited it by 68.29%. The nitrification potential of the soil ofL. chinensiscommunity was only 53% of theP. tenuifloraor 41% of theSuaeda salsacommunity. We also showed that the supply ofNH4+‐Ndriven byL. chinensis’ BNI can meet its requirements . In addition,NH4+‐Ncan enhance plant adaptation to alkaline stress by regulating pH, and in turn, the uptake of nitrate-N (NO3‐‐N). We further demonstrated that the regulatory function ofNH4+‐Nis greater than its nutritional function in alkaline environment. The results offer novel insights into howL. chinensisadapts to high pH and nutrient deficiency stress by secreting BNIs, and reveal, for the first time, differences in the functional roles ofNH4+‐NandNO3‐‐Nin growth and adaptation under alkaline conditions in a grass species.