Soil respiration (Rs), the efflux of CO₂ from soils to the atmosphere driven by root and microbial activity, is one of the largest terrestrial carbon fluxes and a primary determinant of net carbon sequestration.
The important role of nitrogen in driving terrestrial carbon sequestration has long been recognized. However, the role of nitrogen in temporal dynamics of Rs has not been well understood.
Now, new research led by Profs. FANG Jingyun and SHEN Haihua at the Institute of Botany of the Chinese Academy of Sciences highlights the role of nitrogen deposition in Rs and how it changes over time.
The study was published in PNAS on November 4.
In this study, the researchers compiled data from manipulation experiments conducted in forests and grasslands worldwide to gauge the effects of nitrogen addition on Rs.
They found that the effect of nitrogen addition changed systematically over time from short-term stimulation of Rs to its long-term suppression. This shift toward Rs suppression followed a nonlinear temporal trajectory: Rs declined rapidly at first, with the rate of decline gradually leveling off.
They discovered that the rate of nitrogen addition did not significantly change the pace of decline, but an increase in nitrogen inputs produced stronger overall suppression.
When treatments were classified into low- and high-rate categories based on the median addition rate in the analyzed dataset (50 kg N ha-1 y-1), high-rate nitrogen addition reduced Rs by approximately 11%, whereas low-rate addition had no significant overall effect.
This study extends the prevailing static-response paradigm by showing that the effects of nitrogen enrichment on soil carbon fluxes are strongly dependent on exposure duration and cumulative nitrogen input.
The findings suggest that models need to capture these temporal dynamics, rather than assume a constant response, to accurately predict land–atmosphere carbon exchange under global change.
