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The article titled "Gibbs energy or enthalpy—What is relevant for microbial C‐turnover in soils?" discusses the relationship between microbial carbon utilization and energy transformation in soil. The authors argue that a consolidated concept for coupled carbon use efficiency (CUE) and energy use efficiency (EUE) in soil systems requires the correct application of thermodynamic principles and state variables. They criticize the oversimplifications and inconsistencies in a previous review on the topic, pointing out errors in the understanding of Gibbs energy, the use of the NOSC approach, and the comparison of activation energy and reaction enthalpy. The authors conclude that the previous review's statements and equations lack validity and are not supported by data. The article is authored by Matthias Kästner, Thomas Maskow, Anja Miltner, Marcel Lorenz, Sören Thiele‐Bruhn, Tobias Bölscher, Sergey Blagodatsky, Thilo Streck, Holger Pagel, and Evgenia Blagodatskaya. [Extracted from the article]

Mechanisms controlling carbon stabilisation in soil and its feedback to climate change are of considerable importance. Microbial substrate-use efficiency is an important property during decomposition of soil organic matter. It determines the allocation of substrate towards biosynthetic stabilisation of carbon and for respiratory losses into the atmosphere. Previously, it was observed that substrate-use efficiency declines with an increase in temperature and that it varies across organic substrates. Yet, our mechanistic understanding of processes causing the temperature sensitivity of substrate-use efficiency is limited. Changes in substrate-use efficiency could be triggered by (i) shifts in the active components of microbial communities, (ii) changes in microbial physiology within the same community, or (iii) a combination of both. In the present study, we evaluated the link between microbial community composition and substrate-use efficiency, combining measurements of carbon mineralisation and microbial energetics. We found only minor shifts in microbial community composition, despite large differences in substrate-use efficiencies across incubation temperatures and substrate additions. We conclude that short-term changes in substrate-use efficiency were mainly caused by changes in microbial physiology, but emphasize that future studies should focus on resolving long-term trade-offs between physiological and community influences on substrate-use efficiency. [ABSTRACT FROM AUTHOR]

Climate studies show high likelihood of changing hydrological regimes in European rivers. Concerned authorities increasingly question the sustainability of current river management strategies. The aim of this paper is to apply the adaptation turning point (ATP) approach and demonstrates its potential for analysing turning points in river management strategies as a method to support authorities in decisions on adaptation to climate change. Two management strategies in the Rhine River basin were selected as case studies: (1) reintroduction of a sustainable population of Atlantic salmon and (2) inland shipping in relation to water depth variability. By applying the turning point approach, we search for answers to the following questions: when will these management strategies fail due to climate change impacts on the river's hydrology? What adaptation measures exist to delay or avoid failure? The identification of adaption turning points is not easy, due to large scenario and model uncertainties in transient future projections of low-flow discharges and water temperatures. But the case studies demonstrate that the ATP approach is salient from a decision-maker's perspective, because it addresses the timing of possible failure of current management strategies. Analysis of results allows policy makers to assess risks and the urgency for action and provides them with a time horizon for adaptation planning. It is also a valuable first step in the application of methods of formal appraisal of adaptation options when flexibility in planning is required. [ABSTRACT FROM AUTHOR]

Soil organic carbon (SOC) is a substantial source of atmospheric CO 2 , but also a large cause of uncertainties in Earth-system models. A principal control on soil CO 2 release is the carbon-use efficiency (CUE) of microbial communities, which partitions the carbon (C) allocation between biosynthetic stabilization and CO 2 respiration during SOC decomposition. In Earth-system models, CUE is commonly considered as a constant, although it should be susceptible to environmental factors such as temperature. We explored CUE across a set of land-uses and temperatures, and we show the hitherto neglected phenomenon that land-use can alter the temperature response of CUE. In arable soils, CUE was constant over a temperature range between 5 and 20 °C, but it decreased with temperature in ley farming, grassland, and forest soils at temperatures above 12.5 °C. The decrease in CUE was strongest for forest soils. Implementing our findings into a soil-C model revealed substantial differences in projected SOC losses: Assuming an increase of mean annual temperature of 2 or 4 °C, soils were projected to lose up to 6 or 15% of their current SOC, respectively, until they reach a new steady-state. These projections varied among land-uses. Our findings confront the current representation of CUE in global C models and challenges C sequestration strategies based on land-use changes, because land-uses such as e.g. forest ecosystems with current high C storage may lose substantially more C than agricultural soils due to strong declines of CUE. Image 1 • Temperature responses of carbon-use efficiency (CUE) differed across land-uses. • CUE decreased strongly in ley farming, grassland, and forest soils beyond 12.5 °C. • Land-use specific CUE temperature responses have profound impact on SOC projection. • Novel consumption-based thermodynamic approach ensures similar microbial workloads. • Microbial community composition was not a major driver of differences in CUE. [ABSTRACT FROM AUTHOR]