Warming effects on carbon dynamics and microbial communities in soils of diverse texture

Abstract Climate change may profoundly influence soil organic carbon (SOC) dynamics through effects on soil temperature and water, but the mechanisms and magnitude of those effects remain uncertain. We measured the response of residue-C and native SOC in six soils with diverse texture subjected to artificial heating after transplanting to a common field site. The soils, three from each of two climatic zones in Canada, were amended with 13C labelled oat (Avena sativa) residue to distinguish turnover of recently-applied C and native SOC. The soils were either kept at ambient temperature or heated to 5 °C above ambient and CO2 emission was monitored over two growing seasons. Temperature was the primary factor regulating soil respiration across all six soils; water content did not have any additional explanatory effect, probably because the study site conditions were generally wet and thus decomposition was not limited by water. Soil aggregation and loss of residue-C (68% after 295 days) were not affected by warming. Compared to residue-C, native-SOC was more sensitive to loss by warming. The effect of physical aggregate protection against loss of SOC under warming was not evident. Bacterial community structure (16S rRNA gene sequencing) showed that there was a strong and persistent legacy effect on microbial communities. These differences among soils were far greater than those between heating and ambient treatments despite transplanting to a common location. Our results show that decomposition of residue-C and SOC were strongly governed by soil temperature rather than water content, even among transplanted soils with different textures and bacterial communities.