Ecological stoichiometry as a foundation for omics-enabled biogeochemical models of soil organic matter decomposition

Abstract

Coupled biogeochemical cycles drive ecosystem ecology by influencing individual-to-community scale behaviors; yet the development of process-based models that accurately capture these dynamics remains elusive. Soil organic matter (SOM) decomposition in particular is influenced by resource stoichiometry that dictates microbial nutrient acquisition (‘ecological stoichiometry’). Despite its basis in biogeochemical modeling, ecological stoichiometry is only implicitly considered in high-resolution microbial investigations and the metabolic models they inform. State-of-science SOM decomposition models in both fields have advanced largely separately, but they agree on a need to move beyond seminal pool-based models. This presents an opportunity and a challenge to maximize the strengths of various models across different scales and environmental contexts. To address this challenge, we contend that ecological stoichiometry provides a framework for merging biogeochemical and microbiological models, as both explicitly consider substrate chemistries that are the basis of ecological stoichiometry as applied to SOM decomposition. We highlight two gaps that limit our understanding of SOM decomposition: (1) understanding how individual microorganisms alter metabolic strategies in response to substrate stoichiometry and (2) translating this knowledge to the scale of biogeochemical models. We suggest iterative information exchange to refine the objectives of high-resolution investigations and to specify limited dynamics for representation in large-scale models, resulting in a new class of omics-enabled biogeochemical models. Assimilating theoretical and modelling frameworks from different scientific domains is the next frontier in SOM decomposition modelling; advancing technologies in the context of stoichiometric theory provides a consistent framework for interpreting molecular data, and further distilling this information into tractable SOM decomposition models.

Rethinking Aerobic Respiration in the Hyporheic Zone under Variation in Carbon and Nitrogen Stoichiometry

“…34,71,72 However, the current understanding of the relationships between C, N, DOM quantity and quality, and metabolism in rivers has mostly been derived from batch reactors, flowthrough columns, or field-scale experiments and observations. Taking advantage of the elemental stoichiometry of C and N (C/N) as a proxy for microbial nutrient limitations, 29,30,34 this work investigates the spatiotemporal relationships between aerobic metabolism, DOM, and the importance of C and N in the HZ. While we acknowledge that other elements may also constrain biological processes, we focused on N limitations due to recent work highlighting its possible interactions with DOM cycling in the river corridor.…”

“…29−33 While we acknowledge that other elements such as phosphorus and sulfur may also limit biological activities, we focus on N because it is a predominant limiting nutrient in temperate inland rivers and because field observations of interactions between several limiting elements are exceedingly difficult without experimentally disrupting natural dynamics. 34 This is evident from a recent small-scale, short-duration study by Garayburu-Caruso et al, 35 which proposed that integrated DOM and nutrient cycles are critical to regulating aerobic respiration (AR) in hyporheic environments through a trade-off between C and N limitations. The authors suggest that under C limitation, AR is regulated by DOM thermodynamics and that under N limitation, AR is regulated by organic N availability.…”

“…The role of microbial nutrient limitations in regulating C turnover in natural environments remains an active area of research, largely because they are challenging to measure in situ . Considering that true measurements of nutrient limitations involve assessing the abilities of individuals to adjust to nutrient availability, relative changes in the ratio of C/N (i.e., elemental stoichiometry) are often used to infer the balance of C and N limitations. − While we acknowledge that other elements such as phosphorus and sulfur may also limit biological activities, we focus on N because it is a predominant limiting nutrient in temperate inland rivers and because field observations of interactions between several limiting elements are exceedingly difficult without experimentally disrupting natural dynamics …”

Potential bioavailability of pyrogenic organic matter resembles natural dissolved organic matter pools

“…Interestingly, the relative equivalence of predicted CUE across PyOM and DOM pools suggests that PyOM decomposition in rivers could emit comparable amounts of CO2 per mole of C to extant DOM pools. CUE is used in many microbially-explicit decomposition models to constrain organic matter bioavailability (reviewed in Graham and Hofmockel, 2022). Therefore, predicted CUE offers a path for assimilating PyOM in microbially-explicit models.…”

One thousand soils for molecular understanding of belowground carbon cycling

“…Soil organic matter (SOM) is a critical part of the global carbon (C) cycle. Belowground ecosystems contain more C than stored in terrestrial vegetation and the atmosphere combined (Crowther et al, 2019; Crowther et al, 2016; Jobbágy and Jackson, 2000), and SOM is the largest and most biologically active portion of soil C. SOM decomposition is regulated by a complex and interacting set of factors including soil structure, moisture distribution, temperature, pH, and nutrient status; collectively, these factors determine accessibility, bioavailability, and rate kinetics of SOM (Graham and Hofmockel, 2022). Despite the importance of SOM in the global C cycle, the drivers of SOM decomposition from molecular to continental scales are not well understood.…”