Data from: Soil acidification exerts a greater control on soil respiration than soil nitrogen availability in grasslands subjected to long-term nitrogen enrichment

Terrestrial ecosystems worldwide are receiving increasing amounts of
biologically reactive nitrogen (N) as a consequence of anthropogenic
activities. This intended or unintended fertilization can have a
wide-range of impacts on biotic communities and hence on soil respiration.
Reduction in below-ground carbon (C) allocation induced by high N
availability has been assumed to be a major mechanism determining the
effects of N enrichment on soil respiration. In addition to increasing
available N, however, N enrichment causes soil acidification, which may
also affect root and microbial activities. The relative importance of
increased N availability vs. soil acidification on soil respiration in
natural ecosystems experiencing N enrichment is unclear. We conducted a
12-year N enrichment experiment and a 4-year complementary acid addition
experiment in a semi-arid Inner Mongolian grassland. We found that N
enrichment had contrasting effects on root and microbial respiration. N
enrichment significantly increased root biomass, root N content and
specific root respiration, thereby promoting root respiration. In
contrast, N enrichment significantly suppressed microbial respiration
likely by reducing total microbial biomass and changing the microbial
community composition. The effect on root activities was due to both soil
acidity and increased available N, while the effect on microbes primarily
stemmed from soil acidity, which was further confirmed by results from the
acid addition experiment. Our results indicate that soil acidification
exerts a greater control than soil N availability on soil respiration in
grasslands experiencing long-term N enrichment. These findings suggest
that N-induced soil acidification should be included in predicting
terrestrial ecosystem C balance under future N deposition scenarios.