Limited direct impact of long-term phosphorus addition on soil respiration with simulated nitrogen deposition in a saline-alkaline desert steppe

While phosphorus (P) addition alleviates nitrogen (N)-induced P limitation and thereby alters soil respiration rate (SR) in acidic to slightly alkaline grasslands, its effects may differ substantially in moderate to severe alkaline grasslands (pH > 8.5) due to the immobilization of added P by Ca2+ and its consequent unavailability. To address this uncertainty, we conducted a five-year field experiment in a moderately saline-alkaline desert steppe. The study applied a consistent background N (5 g m⁻2 yr⁻1) alongside a gradient of seven P levels (0-16 g m⁻2 yr⁻1).