Liming modifies greenhouse gas fluxes from soils: A meta-analysis of biological drivers

Acidic soils cover about 30% of the world's land. Liming is a management practice applied worldwide to reduce the negative effects of acidification on soil fertility and plant growth. Liming also affects the biotic and abiotic soil properties controlling the production and consumption of the greenhouse gases (GHGs) carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4). Although our understanding of how liming regulates net GHG emissions is increasing, the impact of liming on soil biological drivers of GHG emissions has not been quantitatively synthesized. Here we conducted a global meta-analysis using 1474 paired observations from 124 studies to explore the responses of GHG emissions to liming, with a focus on soil biological factors. We show that the N2O mitigation capacity of liming could be linked to (i) increases in bacterial abundance of N2O reductase genes (NosZ) and decreases in fungi:bacteria ratio, both contributing to a lower N2O:N-2 product ratio of denitrification; and (ii) reductions in soil mineral nitrogen (N) via stimulation of plant N uptake. The limited evidence available indicates that liming reduced CH4 emissions and the abundance of methanogens, but it had no effect on CH4 uptake and abundance of methanotrophs. Liming-induced increases in soil CO2 emissions can be explained by higher heterotrophic and/or autotrophic respiration. The strong coupling between liming effects on GHG emissions and on soil microbial communities involved in GHG production and consumption can be used to identify strategies to reduce GHGs in response to liming, and to improve process-based models for better pre-dictions of soil GHG emissions.