Progressive shifts in soil respiration response to long-term nitrogen enrichment across global forests and grasslands.

Across 38 long-term forest and grassland experiments, soil respiration’s response to nitrogen addition shifts from a ~2-year transient increase to sustained suppression (mean effect = -6%; 95% CI = [-10%, -3%]).

• Why it matters: Nitrogen deposition has risen substantially, yet how prolonged inputs reshape soil carbon emissions over time remains unclear, limiting climate feedback projections.
• What they did: The study analyzed a global time-series dataset from 38 long-term experiments, tracking nonlinear Rs trajectories under N addition and linking shifts to soil acidification and microbial property changes.
• The result: Suppression became evident once cumulative N inputs exceeded ~100 kg N ha -1 and was stronger and faster under high-level additions (>50 kg N ha -1 y -1), implying models must represent these temporal dynamics.

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