Atmospheric nitrogen (N) deposition greatly affects grassland soil respiration (Rs)
and its components. However, whether there exists a similar pattern in the response
of Rs and its components to N deposition among the grasslands with varying degradation
status remains unclear. We established a 3-year field experiment with six N addition
levels on three grassland sites (non-degraded, moderately degraded and severely degraded)
and measured autotrophic respiration (Ra), heterotrophic respiration (Rh), Rs and
their influencing factors, including abiotic and biotic variables. Our results showed
that Ra had an increasing tendency, whereas Rh and Rs had decreasing tendencies, in
response to increasing N addition in the non-degraded and moderately degraded grasslands.
In the severely degraded grassland, Ra, Rh and Rs exhibited increasing tendencies
under lower N addition levels and decreasing tendencies under higher N addition levels.
In the non-degraded grassland, N addition mainly affected Rs by directly increasing
Ra and decreasing Rh. Conversely, in the moderately degraded grassland, N addition
tended to indirectly affect Ra through increased aboveground biomass. In the severely
degraded grassland, Rh was influenced indirectly by an increase in aboveground biomass.
The findings of this research highlight the importance of considering the degradation
level of grasslands when assessing grassland soil carbon emissions under N deposition