Priorities, opportunities, and challenges for integrating microorganisms into Earth system models for climate change prediction

Abstract

Climate change jeopardizes human health, global biodiversity, and sustainability of the biosphere. To make reliable predictions about climate change, scientists use Earth system models (ESMs) that integrate physical, chemical, and biological processes occurring on land, the oceans, and the atmosphere. Although critical for catalyzing coupled biogeochemical processes, microorganisms have traditionally been left out of ESMs. Here, we generate a "top 10" list of priorities, opportunities, and challenges for the explicit integration of microorganisms into ESMs. We discuss the need for coarse-graining microbial information into functionally relevant categories, as well as the capacity for microorganisms to rapidly evolve in response to climate-change drivers. Microbiologists are uniquely positioned to collect novel and valuable information necessary for next-generation ESMs, but this requires data harmonization and transdisciplinary collaboration to effectively guide adaptation strategies and mitigation policy.

Keywords: biogeochemistry; climate change; modeling; traits.

Fig 1

Microbes in models. (A) ESMs consist of submodels that represent physical, chemical, and biological interactions that control processes on land, in the ocean, and in the atmosphere with grid scales that are typically 100 km × 100 km, or approximately one degree of latitude and longitude. (Map image from reference .) (B) A microbially informed ESM might contain equations that describe how cells process carbon (C) which includes estimates for uptake (U), respiration (R), exudation (E), and growth (G), which can also include categorical or continuous traits, such as enzyme kinetics or temperature sensitivities that act as rate modifiers with effects on ecosystem functioning that can generate potential feedback. (C) Equations in ESM need to be parameterized, ideally with information collected from experiments and comparative studies that capture key environmental drivers associated with climate change on relevant temporal and spatial scales. Pictured here in the winter are plots from a long-term warming experiment at the Harvard Forest in Massachusetts, USA (copyright Audrey Barker Plotkin), where microbial data have been critical for understanding soil carbon feedback to climate systems (5). (D) The incorporation of microbes into ESMs can provide mechanistic insight into how traits and functional groups affect biogeochemical processes. For example, lignin is a complex polymer derived from the cell wall of plants that is important for understanding soil carbon dynamics. Comprising cross-linked lignols (L), its degradation is initiated by microbial depolymerization followed by funneling pathways that catabolize different aromatic compounds depending on distinct classes of fungal and bacterial enzymes (6), which can be affected by environmental conditions that are associated with climate change.