Abstract
Grassland ecosystems account for more than 10% of the global CH4 sink
in soils. A 4-year field experiment found that addition of P alone did
not affect CH4 uptake and experimental addition of N alone significantly
suppressed CH4 uptake, while concurrent N and P additions suppressed CH4
uptake to a lesser degree. A meta-analysis including 382 data points in
global grasslands corroborated these findings. Global extrapolation with
an empirical modeling approach estimated that contemporary N addition
suppresses CH4 sink in global grassland by 11% and concurrent N and P
deposition alleviates this suppression by 6%. The P alleviation of
N-suppressed CH4 sink is primarily attributed to substrate competition,
defined as the competition between ammonium and CH4 for the methane
monooxygenase enzyme. The N and P impacts on CH4 uptake indicate that
projected increases in N and P depositions might substantially affect
CH4 uptake and alter the global CH4 cycle.