Reviews and syntheses: Carbon use efficiency from organisms to ecosystems – definitions, theories, and empirical evidence

Manzoni, S.; Capek, P., Porada, P.; Thurner, M.; Winterdahl, M.; Beer, C.; Brüchert, V.; Frouz, J.; Hermann, A.M.; Lindahl, B.D.; Lyon, S.W.; Santruckova, H.; Vico, G.; Way, D.
2018 | Biogeosciences | 15 (5929-5949)

The cycling of carbon (C) between the Earth surface and the atmosphere is controlled by biological and abiotic processes that regulate C storage in biogeochemical compartments and release to the atmosphere. This partitioning is quantified using various forms of C-use efficiency (CUE) – the ratio of C remaining in a system to C entering that system. Biological CUE is the fraction of C taken up allocated to biosynthesis. In soils and sediments, C storage depends also on abiotic processes, so the term C-storage efficiency (CSE) can be used. Here we first review and reconcile CUE and CSE definitions proposed for autotrophic and heterotrophic organisms and communities, food webs, whole ecosystems and watersheds, and soils and sediments using a common mathematical framework. Second, we identify general CUE patterns; for example, the actual CUE increases with improving growth conditions, and apparent CUE decreases with increasing turnover. We then synthesize >5000CUE estimates showing that CUE decreases with increasing biological and ecological organization – from unicellular to multicellular organisms and from individuals to ecosystems. We conclude that CUE is an emergent property of coupled biological–abiotic systems, and it should be regarded as a flexible and scale-dependent index of the capacity of a given system to effectively retain C.

Analytically tractable climate–carbon cycle feedbacks under 21st century anthropogenic forcing

Lade, S. J.; Donges, J. F.; Fetzer, I.; Anderies, J. M.; Beer, C.; Cornell, S. E.; Gasser, T.; Norberg, J.; Richardson, K.; Rockström, J.; Steffen, W.
2018 | Earth Syst. Dynam. | 9 (507-523)

Year-round simulated methane emissions from a permafrost ecosystem in Northeast Siberia

Castro-Morales, K.; Kleinen, T.; Kaiser, S.; Zaehle, S.; Kittler, F.; Kwon, M. J.; Beer, C.; Göckede, M.
2018 | Biogeosciences | 15 (2691-2722)

Methane production as key to the greenhouse gas budget of thawing permafrost

Knoblauch, C.; Beer, C.; Liebner, S.; Grigoriev, M.N.; Pfeiffer, E.-M.
2018 | Nat. Clim. Change | 8 (4) (309-312)

Effects of short-term variability of meteorological variables on soil temperature in permafrost regions

Beer, C.; Porada, P.; Ekici, A.; Brakebusch, M.
2018 | TC | 12 (741-757)

Carbon stocks and fluxes in the high latitudes: using site-level data to evaluate Earth system models

Chadburn, S. E.; Krinner, G.; Porada, P.; Bartsch, A.; Beer, C.; Belelli Marchesini, L.; Boike, J.; Ekici, A.; Elberling, B.; Friborg, T.; Hugelius, G.; Johansson, M.; Kuhry, P.; Kutzbach, L.; Langer, M.; Lund, M.; Parmentier, F.-J. W.; Peng, S.; Van Huissteden, K.; Wang, T.; Westermann, S.; Zhu, D.; Burke, E. J.
2017 | Biogeosciences | 14 (22) (5143-5169)

Estimating global nitrous oxide emissions by lichens and bryophytes with a process-based productivity model

Porada, P.; Pöschl, U.; Kleidon, A.; Beer, C.; Weber, B.
2017 | Biogeosciences | 14 (1593-1602)

Evaluation of climate-related carbon turnover processes in global vegetation models for boreal and temperate forests

Thurner, M.; Beer, C.; Ciais, P.; Friend, A. D.; Ito, A.; Kleidon, A.; Lomas, M. R.; Quegan, S.; Rademacher, T. T.; Schaphoff, S.; Tum, M.; Wiltshire, A.; Carvalhais, N.
2017 | Glob. Change Biol. | 23 (8) (3076-3091)

Turnover concepts in state-of-the-art global vegetation models (GVMs) account for various processes, but are often highly simplified and may not include an adequate representation of the dominant processes that shape vegetation carbon turnover rates in real forest ecosystems at a large spatial scale. Here we evaluate vegetation carbon turnover processes in GVMs participating in the Inter-Sectoral Impact Model Intercomparison Project (ISI-MIP; including HYBRID4, JeDi, JULES, LPJml, ORCHIDEE, SDGVM, and VISIT) using estimates of vegetation carbon turnover rate (k) derived from a combination of remote sensing based products of biomass and net primary production (NPP). We find that current model limitations lead to considerable biases in the simulated biomass and in k (severe underestimations by all models except JeDi and VISIT compared to observation-based average k), likely contributing to underestimation of positive feedbacks of the northern forest carbon balance to climate change caused by changes in forest mortality. A need for improved turnover concepts related to frost damage, drought and insect outbreaks in order to better reproduce observation-based spatial patterns in k is identified. Since direct frost damage effects on mortality are usually not accounted for in these GVMs, simulated relationships between k and winter length in boreal forests are not consistent between different regions and strongly biased compared to the observation-based relationships. Some models show a response of k to drought in temperate forests as a result of impacts of water availability on NPP, growth efficiency or carbon balance dependent mortality as well as soil or litter moisture effects on leaf turnover or fire. However, further direct drought effects like carbon starvation (only in HYBRID4) or hydraulic failure are usually not taken into account by the investigated GVMs. While they are considered dominant large-scale mortality agents, mortality mechanisms related to insects and pathogens are not explicitly treated in these models.

Process-based modelling of the methane balance in periglacial landscapes (JSBACH-methane)

Kaiser, S.; Göckede, M.; Castro-Morales, K.; Knoblauch, C.; Ekici, A.; Kleinen, T.; Zubrzycki, S.; Sachs, T.; Wille, C.; Beer, C.
2017 | Geosci. Model Dev. | 10 (333-358)

Effects of bryophyte and lichen cover on permafrost soil temperature at large scale

Porada, P.; Ekici, A.; Beer, C.
2016 | TC | 10 (2291-2315)

Permafrost Sub-grid Heterogeneity of Soil Properties Key for 3-D Soil Processes and Future Climate Projections

2016 | Front. Earth Sci | 4:81

There are massive carbon stocks stored in permafrost-affected soils due to the 3-D soil movement process called cryoturbation. For a reliable projection of the past, recent and future Arctic carbon balance, and hence climate, a reliable concept for representing cryoturbation in a land surface model (LSM) is required. The basis of the underlying transport processes is pedon-scale heterogeneity of soil hydrological and thermal properties as well as insulating layers, such as snow and vegetation. Today we still lack a concept of how to reliably represent pedon-scale properties and processes in a LSM. One possibility could be a statistical approach. This perspective paper demonstrates the importance of sub-grid heterogeneity in permafrost soils as a pre-requisite to implement any lateral transport parametrization. Representing such heterogeneity at the sub-pixel size of a LSM is the next logical step of model advancements. As a result of a theoretical experiment, heterogeneity of thermal and hydrological soil properties alone lead to a remarkable initial sub-grid range of subsoil temperature of 2°C, and active-layer thickness of 150 cm in East Siberia. These results show the way forward in representing combined lateral and vertical transport of water and soil in LSMs.

Soil-frost-enabled soil-moisture–precipitation feedback over northern high latitudes

Hagemann, S.; Blome, T.; Ekici, A.; Beer, C.
2016 | Earth Syst. Dynam. | 7 (611-625)

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