Effects of clipping and shading on 15NO3− and 15NH4+ recovery by plants in grazed and ungrazed temperate grasslands

aimsin natural ecosystems, plants generally promote the acquisition of nitrogen (n) through the input of carbon (c) into the soil. the present study aimed to clarify how changes in c input affect n uptake by plants. methods:in situ 15n labeling ((15nh4)2so4 and k15no3) was performed in grazed and ungrazed leymus chinensis grasslands located in inner mongolia, northern china. clipping and shading treatments were used to reduce c allocation to roots by limiting photosynthesis because grazing can produce such similar effect through defoliation. results:grazing increased the allocation of photosynthate to roots and the relative biomass of carex duriuscula but decreased the relative biomass of l. chinensis. grazing decreased 15n-nh4+ recovery (grazed: 30.9% vs. ungrazed: 39.3%) but increased 15n-no3− recovery (grazed: 26.9% vs. ungrazed: 17.6%), which may be due to changes in the nh4+/no3− ratio and species composition. clipping and shading reduced 15n recovery, mainly because they decreased c supply for n uptake by reducing photosynthesis. conclusion:sthese findings indicate that the reduction of the c input to soil decreases 15n recovery by plants in temperate grasslands, which contributes to our understanding of the trade-off between c and n and grassland n cycles.