Increased nitrate uptake by plants in response to nitrogen addition and mowing in a temperate grassland

Plants absorb different forms of nitrogen (N) from the soil, which influences biodiversity and ecosystem functioning. However, how N uptake responds to different N addition rates and traditional mowing practices remains largely unexplored.

A field experiment was carried out to examine the effects of six N addition rates (0, 2, 5, 10, 20 and 50 g N m-2 yr-1) and mowing on N uptake. Using a 15N labelling method, we quantified ammonium, nitrate and glycine absorption by the dominant rhizomatous grass (Leymus chinensis) and three common bunchgrass species (Stipa grandis, Agropyron cristatum and Achnatherum sibiricum) in a temperate grassland.

Our results showed an overall N acquisition pattern across all species in the control: ammonium (46-51 %) > nitrate (27-41 %) > glycine (10-26 %). Nitrogen addition increased nitrate uptake while decreasing glycine uptake, with ammonium uptake enhanced only in the rhizomatous grass, L. chinensis. Mowing increased nitrate uptake by 5-12 %. However, the interactions between N addition and mowing had no significant effect on plant N uptake. Structural equation modelling revealed that both N addition and mowing reduced the NH4+/NO3- ratio, thereby promoting nitrate uptake.

These findings highlight distinct N acquisition strategies between rhizomatous and bunchgrass species in response to N addition and mowing. The greater uptake of nitrate compared to ammonium aligns with the increasing trend of nitrate deposition. Future rises in nitrate deposition may favour the succession of common plant species, especially dominant ones, potentially enhancing ecosystem stability and mitigating the negative effects of N deposition.