Isothermal Microcalorimetry Provides New Insight into Terrestrial Carbon Cycling

Abstract

Energy is continuously transformed in environmental systems through the metabolic activities of living organisms, but little is known about the relationship between the two. In this study, we tested the hypothesis that microbial energetics are controlled by microbial community composition in terrestrial ecosystems. We determined the functional diversity profiles of the soil biota (i.e., multiple substrate-induced respiration and microbial energetics) in soils from an arable ecosystem with contrasting long-term management regimes (54 years). These two functional profiling methods were then related to the soils’ microbial community composition. Using isothermal microcalorimetry, we show that direct measures of energetics provide a functional link between energy flows and the composition of below-ground microbial communities at a high taxonomic level (Mantel R = 0.4602, P = 0.006). In contrast, this link was not apparent when carbon dioxide (CO2) was used as an aggregate measure of microbial metabolism (Mantel R = 0.2291, P = 0.11). Our work advocates that the microbial energetics approach provides complementary information to soil respiration for investigating the involvement of microbial communities in below-ground carbon dynamics. Empirical data of our proposed microbial energetics approach can feed into carbon-climate based ecosystem feedback modeling with the suggested conceptual ecological model as a base.

Microbial carbon use efficiency: accounting for population, community, and ecosystem-scale controls over the fate of metabolized organic matter

“…Microbes metabolize a wide variety of compounds to satisfy heterotrophic demands for carbon (C) and energy, thereby influencing the accumulation/loss dynamics of soil organic matter stocks and ecosystem carbon dioxide efflux (Frey et al 2013;Karhu et al 2014). CUE is therefore an important concept for understanding the future trajectory of soil-climate feedbacks, recognition of which has led to recent reviews of the topic (Manzoni et al 2012;Sinsabaugh et al 2013), application in ecosystem models (Wang et al 2013;Allison 2014;Wieder et al 2014), and the development of new methods to estimate microbial efficiency in environmental samples (Blazewicz and Schwartz 2011;Dijkstra et al 2011b;Herrmann et al 2014). However, progress in this field is hampered by chronic issues symptomatic of a divide among research approaches and disciplinespecific terminologies.…”

Differences in substrate use efficiency: impacts of microbial community composition, land use management, and substrate complexity

“…This partitioning is often referred 47 to as substrate use efficiency or C use efficiency, and it is an important microbial physiological feature in 48 determining the fate of C during organic matter decomposition in soils. This property is often assumed to be 49 constant in process-based models, but research indicates that substrate use efficiency is (i) temperature dependent 50 Recent research suggests that differences in substrate use efficiencies may be linked to the relative 58 abundance of fungi and Gram-negative bacteria in an arable ecosystem (Harris et al 2012;Herrmann et al 2014) or 59 a forest ecosystem (Creamer et al 2015). These studies emphasize that microbial community composition may play 60 a significant role in determining substrate use efficiencies within one land use management system.…”

Simultaneous screening of microbial energetics and CO2 respiration in soil samples from different ecosystems

“…Isothermal calorimetry measures the net outcome of heat flows derived from all catabolic and anabolic reactions in soils; it quantifies all microbial metabolic processes, not only those accounted for by CO 2 respiration measurements. Recent research (Herrmann et al, 2014) therefore has demonstrated that such an approach is a more comprehensive methodology, providing complementary information for investigating soil microbial metabolism than the respiratory approach alone. Although very little is known about the link between soil microbial energetics and CO 2 respiration, changes in calorespirometric ratios may indicate differences in microbial C use efficiencies and metabolic pathways (Hansen et al, 2004;Herrmann et al, 2014) or a change in organic material undergoing decomposition (Hansen et al, 2004).…”

“…Recent research (Herrmann et al, 2014) therefore has demonstrated that such an approach is a more comprehensive methodology, providing complementary information for investigating soil microbial metabolism than the respiratory approach alone. Although very little is known about the link between soil microbial energetics and CO 2 respiration, changes in calorespirometric ratios may indicate differences in microbial C use efficiencies and metabolic pathways (Hansen et al, 2004;Herrmann et al, 2014) or a change in organic material undergoing decomposition (Hansen et al, 2004). However, respiration and microbial energetics are often obtained by separate samples and methods (Sparling, 1983;Herrmann et al, 2014) which often results in highly varying calorespirometric ratios.…”