Atmospheric nitrogen （N） deposition caused by anthropogenic activities may alter litter decomposition and species composition, and then affect N cycling and carbon （C） sequestration in an ecosystem. Using the litterbag method, we studied the effects of N addition （CK： no N addition; low-N： 1 g N m-2 y-l; high-N： 2 g N m-2 y-l） on changes in mass remaining of shoot litter decomposition of three grasses （Stipa baicalensis, Carex pediformis and Leymus chinensis） over 28 months in the Hulun Buir meadow steppe of Inner Mongolia. The results showed that the addition of high and low N had no significant effect on the decomposition of single-species litter, but low N addition slightly inhibited the decomposition of litter mixtures. In addition, litter decomposition was strongly species dependent. Our results suggest that species type is likely the main determinant of litter decomposition, and low N deposition in natural ecosystems does not influence single-species litter decomposition.
Atmospheric nitrogen （N） deposition may affect carbon （C） sequestration in terrestrial ecosystem. The main objective of this paper was to test the hypothesis that N addition would increase CO2 emission in the N limited meadow steppe in Inner Mongolia, China. Response of CO2 fluxes to simulated N deposition was studied in the growing season of 2008 and 2009 by static chamber and gas chromatograph techniques. Parallel to the flux mea- surements, soil temperature, soil moisture, TOC, DOC, soil NH4~ and NO3- were measured at the same time. The results indicated that two-year N additions had no significant effect on NH4＋, but slightly increased NO3- in the later period. The HN treatment tended to increase CO2 fluxes in the two years, and LN treatment tended to decrease CO2 fluxes in 2008, and shifted to increase CO2 fluxes in later growing season of 2009. N addition significantly in- creased the aboveground biomass and root biomass. The correlation between CO2 fluxes and moisture or tempera- ture factors did not significantly change due to N addition, but N addition enhanced the moisture sensitivity of CO2 fluxes as well as the temperature sensitivity of CO2 fluxes. These results suggest that the increasing ammonium N deposition would be likely to stimulate CO2 fluxes in the meadow steppe of Inner Mongolia, China.
