6533b836fe1ef96bd12a1aef

RESEARCH PRODUCT

Responses of soil bacterial and fungal communities to extreme soil drought and rewetting

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description

Question: The patterns of resource allocation and activity of the soil microbial community over the dry summer in Mediterranean grasslands are still largely unknown. The microbial response to summer desiccation reflects adaptation strategies, setting the stage for a large rainfall-induced soil CO2 pulse upon rewetting, an important component of the ecosystem carbon budget. Methods: In three California annual grasslands, the present (DNA-based) and potentially active (RNA-based) soil bacterial and fungal communities were tracked over a summer season and in response to controlled rewetting of intact soil cores. Phylogenetic marker genes for bacterial (16S) and fungal (28S) RNA and DNA were sequenced and the abundance of these genes and transcripts were measured. Results: While bacterial community composition differed between sites, all sites shared a similar response pattern of the present and potentially active bacterial community to dry-down and wet-up. In contrast, the fungal community was not detectably different between sites, and largely unaffected by drought, showing a marked resistance to dessication. The potentially active bacterial community changed significantly as summer drought progressed, then returned to pre-drought composition within several hours of rewetting, displaying spectacular resilience. Upon rewetting, transcript copies of bacterial rpoB genes increased consistently, reflecting rapid activity resumption. Changes in relative abundance of the most dominant potentially active bacterial taxa reflected a differential response of phyla, which was consistent across sites and conserved at high taxonomic level. Conclusions: These contrasting drought-related bacterial life-strategies suggest that predicted changes in precipitation patterns may affect soil nutrient and carbon cycling by impacting activity patterns of microbial communities.