Microbial respiratory preferences linked to C and dissimilatory N metabolism follow ecohydrological patterns at the landscape scale

Abstract:

The Pacific Coastal Temperate Rainforest (PCTR) of Southeast Alaska is one of the most carbon-rich ecosystems on earth, and can be partitioned into a subset of representative ecosystem types characterized by differing plant communities and hydrological conditions. However, comparisons of microbial functional capacity associated with key biogeochemical processes which result in production of (GHGs) have not been assessed within the context of the region’s ecohydrological gradient. To address this research gap, we used metagenomics to quantify the abundance of genes encoding crucial proteins involved in GHG producing metabolic pathways across ecosystem types ranging from oxic upland to suboxic emergent wetland environments. This information was used to test the hypothesis that the master variables that define ecosystem type also control the distribution of genes linking C oxidation and N oxide reduction to energy conservation. This analysis provides evidence that hydrologic, biological and soil characteristics are significant predictors of the occurrence of a critical subset of respiratory genes within the soil microbial community across the PCTR. Additionally, the dominant hydrologic regime in each ecosystem type appears sufficiently consistent over time to allow for the differentiation of preferred modes of microbial respiration and other bioenergetics pathways among the site types, most likely to maximize energy production. The results of this study produce new insights into ecosystem level biogeography of microbial functional diversity driving C and N metabolism. With regional temperatures rising, this information is critically important for developing models of how climate change-dependent shifts in distribution of particular ecosystems within the PCTR could impact soil C and N storage, transformation, and GHG production.