Sources: Eoin L. Brodie, Nicholas J. Bouskill
A significant proportion of the turnover rate of terrestrial carbon pools may be determined by the structure of the microbial communities responsible for catalyzing numerous different reactions. Not all carbon is alike, and microbial species within an ecosystem play fundamental and complementary roles in this cycle by harboring the genetic capability to breakdown different kinds of carbon, including recalcitrant compounds. Any loss of microbial biodiversity, brought about through anthropogenic perturbation, can thus have a large effect on the efficiency of this cycle. There is, therefore, clear impetus to understand and predict how microbial communities might respond to changes (projected by the Intergovernmental Panel on Climate Change) in gross environmental factors, such as precipitation.
The ability of microbial communities to withstand environmental perturbation is largely determined by the genetic capacity and functional traits of member species. It is largely unknown how the environment determines an organism’s ability to adapt; however, it is possible that organisms stringently adapted to an environment such as a tropical rainforest, with very little annual variability in precipitation, might have a reduced capacity to adapt to long-term excursions from standard conditions.
In their ongoing LDRD project, ESD’s Eoin Brodie and Nicholas Bouskill address this issue through rainfall manipulation experiments in three geographically distinct environments, each with contrasting precipitation regimes (desert, Mediterranean grassland, and tropical rainforest). These three soil microbial populations have evolved under different rainfall regimes, allowing for a comparison of the evolutionary constraints upon community adaptation to climate change. The workflow takes a bottom-up, three-pronged approach to this question by focusing on the properties of individual organisms, microbial communities, and the biogeochemical processes they mediate.
Brodie and Bouskill have used next-generation DNA sequencing technologies to initially characterize the response of the microbial communities to manipulated rainfall regimes (both increases and decreases). Functional traits important in responding to osmotic stress are being identified by following changes in the community gene expression (meta-transcriptomics). Simultaneously, a range of phylogenetically related Actinobacteria, major contributors to the degradation of recalcitrant carbon, has been isolated from these soils. These isolates are now being used to answer the question of whether the genetic capacity to adapt to changing rainfall regimes is contingent on long-term evolutionary (phylogenetic) history or more recent climate history (i.e., origin of isolates). For this, Brodie and Bouskill are using a combination of genetic (genome sequencing and transcriptomics) and metabolomic techniques to identify specific pathways and compounds mediating adaptation.
This work is in collaboration with research teams at UC Berkeley, the USDA Forest Service International Institute of Tropical Forestry (IITF), and Brown University.