Effects of nitrogen deposition and litter dynamics on soil respiration in a semiarid sandy grassland.

Soil respiration (Rs) is the second-largest carbon dioxide flux from terrestrial ecosystems to the atmosphere, and increasing atmospheric nitrogen (N) deposition affects terrestrial carbon fluxes by altering plant productivity and litter input. However, few studies have examined the effects of N deposition and litter management on Rs and its components in sandy grassland ecosystems of semiarid regions, or the associated drivers. After 9 years of continuous field treatments combining N addition [non-N addition (N0) and N addition (N1)] with litter manipulation [litter left on the soil (L1, control), litter removal (L0) and litter doubled (L2)], we investigated the seasonal dynamics of Rs, microbial respiration (Rm), and root respiration (Rt) in the Horqin Sandy Land in 2022. Four key findings emerged: (1) Seasonal patterns of Rs components remained consistent across treatments, and litter removal significantly reduced Rm by 25.34% through substrate limitation. (2) Compared with our earlier work (after 3 consecutive years of field treatments), after 9-year continuous nitrogen addition in the current study weakened the stimulation of Rt via soil acidification in 2022. Similarly, while litter doubled after 3 years previously stimulated Rs and its components in our previous study, litter doubled after 9 years shifted this effect to inhibition. (3) Temperature sensitivity (Q10) analysis revealed differential responses, with N addition reducing the Q10 of Rt and litter manipulation lowering the Q10 values across components. (4) The random forest analysis indicated that, under N addition and litter manipulation, soil moisture is the primary driver of the seasonal dynamics of Rs, Rm, and Rt. These results highlight the critical role of treatment duration in evaluating the impacts of litter manipulation on soil C dynamics in wind-eroded grasslands under chronic N deposition.