Abstract
The feedback between soil carbon (C) and climate has the potential to
decrease in magnitude over time due to the thermal acclimation of
microbial respiration, while, whose strength is highly uncertain, partly
because the response of microbial respiration is regulated by multiple
environmental factors simultaneously rather than by temperature alone.
Using a 9-year two-way factorial experiment involving warming and
multilevel nitrogen enrichment treatments from an alpine grassland, we
show that microbial respiration acclimates to warming only under
nitrogen enrichment and that the strength of thermal acclimation
increases as nitrogen enrichment. We identified two contrasting
pathways—via an enhancement of acclimation by soil acidification and a
weakening of acclimation by the inhibition of soil C availability and
stimulation of soil C-degrading enzymes—with a net positive effect of
nitrogen enrichment on microbial thermal acclimation. Our findings
emphasize the importance of considering multiple environmental factors
in shaping the strength of thermal acclimation.