Productivity of Leymus chinensis grassland is co-limited by water and nitrogen and resilient to climate change

Aims: Changes in both rainfall patterns and nitrogen (N) deposition affect plant productivity. However, the knowledge of the interactions between reduced rainfall amount, reduced rainfall frequency, and increased atmospheric N deposition in grasslands is limited. Methods: A three-factorial mesocosm experiment was conducted with monocultures of Leymus chinensis (Trin.) Tzvel. Treatments of rainfall amount (control, −30%), rainfall frequency (control, −50%) and N (0, 10 g N m⁻² yr⁻¹) were included. Results: In the Songnen grassland, the aboveground net primary productivity (ANPP) of L. chinensis increased by 137% with N addition, decreased by 22% with reduced rainfall amount and increased by 74% with reduced rainfall frequency. Rainfall amount, but not frequency, had significant interaction with N treatment. The combined treatment of N addition and reduced rainfall amount increased ANPP by 46%. The shoot density was decreased by 35% with reduced rainfall amount, but increased by 45% with reduced rainfall frequency and by 67% with N addition. Nitrogen addition increased net carbon assimilation rate and water use efficiency (WUE), but they showed no significant response to main factors of altered rainfall changes except the increased WUE under reduced rainfall amount. Conclusions: Shoot density rather than shoot biomass of L. Chinensis, is the key factor affecting ANPP in response to changes in rainfall pattern and N deposition, and ANPP was co-limited by water and N. The Songnen grassland will be resilient in ANPP in future climate change scenarios, because deeper water infiltration following reduced rainfall frequency can offset the reduced ANPP caused by reduced rainfall. This offset will be further enhanced by the higher WUE caused by increased atmospheric N deposition.