Diversity–function relationship of ammonia-oxidizing bacteria in soils among functional groups of grassland species under climate warming

Although warming and plant diversity losses have important effects on aboveground ecosystem functioning, their belowground effects remain largely unknown. We studied the impact of a 3 °C warming and of three plant functional groups (forbs, grasses, legumes) on ammonia-oxidizing bacteria (AOB) diversity (polymerase chain reaction-denaturing gradient gel electrophoresis, PCR-DGGE) and their function (potential nitrification) in artificial grasslands. Warming did not influence AOB diversity and function. Sequencing of 16S rRNA gene fragments retrieved from DGGE gel revealed that they were all related to Nitrosospira-like sequences. Clustering analysis of DGGE profiles resulted in two nodes, separating AOB community structure under legumes from all other samples. Decreased AOB richness (number of DGGE bands) and concurrent increased potential nitrification were also observed under legumes. We hypothesized that ammonium availability was the driving force regulating the link between aboveground and belowground communities, as well as the AOB diversity and function link. The results document that the physiology of AOB might be an important regulator of AOB community structure and function under plant functional groups. This study highlights the major role of the microbial community composition in soil process responses to changes in the functional composition of plant communities.