Nutrient resorption tightens plant nitrogen and phosphorus coupling and decreases with sulfur deposition as mediated by interannual precipitation in a meadow

Purpose Sulfur (S) deposition as a global change issue causes worldwide soil acidification, nutrient mobilization and marked changes in plant nutrition. Here, we investigated how S deposition would affect leaf nutrient resorption and how this effect varies with yearly fluctuations in precipitation. Methods In a semiarid meadow exposed to S addition, we measured nitrogen (N), phosphorus (P) and S concentrations in green and senescent leaves of a grass and a sedge and calculated nutrient resorption efficiencies (NuRE) across two years with contrasting precipitation (13% higher and 27% lower than long-term mean annual precipitation). Results Concentrations of N, P, and S in green and senescent leaves generally increased with S addition across the two years, with the exception of N and P concentrations in green leaves of the grass that showed no response or even decreased with S addition. The coupling relationships between N and P concentrations showed interannual variations and tightened by nutrient resorption, as evidenced by stronger N and P correlations in senescent leaves than in green leaves in the wet year. Leaf NuRE convergently decreased with S addition across the two years congruent with soil acidification and increased soil N, P and S availability, while NuRE was higher in the wet year due to lower soil nutrient availability herein. Conclusions This study provides new evidence on the role of nutrient resorption in tightening stoichiometric N:P relationships, and a three-dimensional feedback framework that plant nutrient resorption was favored by higher precipitation to sharpen its tradeoff with soil nutrient availability.