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.

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)

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

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

Earliest land plants created modern levels of atmospheric oxygen

T. M. Lenton; T. W. Dahl; S. J. Daines; B. J. W. Mills; K. Ozaki; M. R. Saltzman; P. Porada
2016 | Proc. Natl. Acad. Sci. U.S.A. | 113 (35) (9704-9709)

The progressive oxygenation of the Earth’s atmosphere was pivotal to the evolution of life, but the puzzle of when and how atmospheric oxygen (O2) first approached modern levels (∼21%) remains unresolved. Redox proxy data indicate the deep oceans were oxygenated during 435–392 Ma, and the appearance of fossil charcoal indicates O2 >15–17% by 420–400 Ma. However, existing models have failed to predict oxygenation at this time. Here we show that the earliest plants, which colonized the land surface from ∼470 Ma onward, were responsible for this mid-Paleozoic oxygenation event, through greatly increasing global organic carbon burial—the net long-term source of O2. We use a trait-based ecophysiological model to predict that cryptogamic vegetation cover could have achieved ∼30% of today’s global terrestrial net primary productivity by ∼445 Ma. Data from modern bryophytes suggests this plentiful early plant material had a much higher molar C:P ratio (∼2,000) than marine biomass (∼100), such that a given weathering flux of phosphorus could support more organic carbon burial. Furthermore, recent experiments suggest that early plants selectively increased the flux of phosphorus (relative to alkalinity) weathered from rocks. Combining these effects in a model of long-term biogeochemical cycling, we reproduce a sustained +2‰ increase in the carbonate carbon isotope (δ13C) record by ∼445 Ma, and predict a corresponding rise in O2 to present levels by 420–400 Ma, consistent with geochemical data. This oxygen rise represents a permanent shift in regulatory regime to one where fire-mediated negative feedbacks stabilize high O2 levels.

High potential for weathering and climate effects of non-vascular vegetation in the Late Ordovician

Porada, P.; Lenton, T. M.; Pohl, A.; Weber, B.; Mander, L.; Donnadieu, Y.; Beer, C.; Pöschl, U.; Kleidon, A.
2016 | Nat. Commun. | 7:12113

It has been hypothesized that predecessors of today’s bryophytes significantly increased global chemical weathering in the Late Ordovician, thus reducing atmospheric CO2 concentration and contributing to climate cooling and an interval of glaciations. Studies that try to quantify the enhancement of weathering by non-vascular vegetation, however, are usually limited to small areas and low numbers of species, which hampers extrapolating to the global scale and to past climatic conditions. Here we present a spatially explicit modelling approach to simulate global weathering by non-vascular vegetation in the Late Ordovician. We estimate a potential global weathering flux of 2.8 (km3 rock) yr−1, defined here as volume of primary minerals affected by chemical transformation. This is around three times larger than today’s global chemical weathering flux. Moreover, we find that simulated weathering is highly sensitive to atmospheric CO2 concentration. This implies a strong negative feedback between weathering by non-vascular vegetation and Ordovician climate.

On the potential vegetation feedbacks that enhance phosphorus availability – insights from a process-based model linking geological and ecological timescales

C. Buendía; S. Arens; T. Hickler; S. I. Higgins; P. Porada; A. Kleidon;
2014 | Biogeosciences | 11 (13) (3661-3683)

Estimating Impacts of Lichens and Bryophytes on Global Biogeochemical Cycles of Nitrogen and Phosphorus and on Chemical Weathering

Porada, P.; Weber, B.; Elbert, W.; Pöschl, U.; Kleidon, A.
2014 | Global Biogeochem Cycles | 10 (1-15)

Lichens and bryophytes may significantly affect global biogeochemical cycles by fixation of nitrogen and biotic enhancement of surface weathering rates. Most of the studies suggesting these effects, however, are either conceptual or rely on upscaling of regional estimates to obtain global numbers. Here we use a different method, based on estimates of net carbon uptake, to quantify the impacts of lichens and bryophytes on biogeochemical cycles at the global scale. We focus on three processes, namely, nitrogen fixation, phosphorus uptake, and chemical weathering. Our estimates have the form of potential rates, which means that we quantify the amount of nitrogen and phosphorus needed by the organisms to build up biomass, also accounting for resorption and leaching of nutrients. Subsequently, we use potential phosphorus uptake on bare ground to estimate chemical weathering by the organisms, assuming that they release weathering agents to obtain phosphorus. The predicted requirement for nitrogen ranges from 3.5 to 34 Tg yr −1 and for phosphorus it ranges from 0.46 to 4.6 Tg yr −1 . Estimates of chemical weathering are between 0.058 and 1.1 km 3 yr −1 of rock. These values seem to have a realistic order of magnitude, and they support the notion that lichens and bryophytes have the potential to play an important role for biogeochemical cycles.

Estimates of the climatological land surface energy and water balance derived from maximum convective power

Kleidon, A.; Renner, M.; Porada, P.
2014 | Hydrol. Earth Syst. Sci. | 18 (2201-2218)

The land surface energy and water balances are tightly coupled by the partitioning of absorbed solar radiation into terrestrial radiation and the turbulent fluxes of sensible and latent heat, as well as the partitioning of precipitation into evaporation and runoff. Evaporation forms the critical link between these two balances. Its rate is strongly affected by turbulent exchange as it provides the means to efficiently exchange moisture between the heated, moist surface and the cooled, dry atmosphere. Here, we use the constraint that this mass exchange operates at the thermodynamic limit of maximum power to derive analytical expressions for the partitioning of the surface energy and water balances on land. We use satellite-derived forcing of absorbed solar radiation, surface temperature and precipitation to derive simple spatial estimates for the annual mean fluxes of sensible and latent heat and evaluate these estimates with the ERA-Interim reanalysis data set and observations of the discharge of large river basins. Given the extremely simple approach, we find that our estimates explain the climatic mean variations in net radiation, evaporation, and river discharge reasonably well. We conclude that our analytical, minimum approach provides adequate first order estimates of the surface energy and water balance on land and that the thermodynamic limit of maximum power provides a useful closure assumption to constrain the energy partitioning at the land surface.

Estimating global carbon uptake by Lichens and Bryophytes with a process-based model

Porada, P.; Weber, B.; Elbert, W.; Pöschl, U.; Kleidon, A.
2013 | Biogeosciences | 10 (6989-7033)

Lichens and bryophytes are abundant globally and they may even form the dominant autotrophs in (sub)polar ecosystems, in deserts and at high altitudes. Moreover, they can be found in large amounts as epiphytes in old-growth forests. Here, we present the first process-based model which
estimates the net carbon uptake by these organisms at the global scale, thus assessing their significance for biogeochemical cycles. The model uses gridded climate data and key properties of the habitat (e.g. disturbance intervals) to predict processes which control net carbon uptake, namely
photosynthesis, respiration, water uptake and evaporation. It relies on equations used in many dynamical vegetation models, which are combined with concepts specific to lichens and bryophytes, such as poikilohydry or the effect of water content on CO 2 diffusivity. To incorporate the great functional variation of lichens and bryophytes at the global scale, the model parameters are characterised by broad ranges of possible values instead of a single, globally uniform value. The predicted terrestrial net uptake of 0.34 to 3.3 Gt yr −1 of carbon and global patterns of productivity are in accordance with empirically-derived estimates. Considering that the assimilated carbon can be invested in processes such as weathering or nitrogen fixation, lichens and bryophytes may play a
significant role in biogeochemical cycles.

Entropy production of soil hydrological processes and its maximisation

Porada, P.; Kleidon, A.; Schymanski, S. J.
2011 | Earth Syst. Dynam. | 2 (179-190)

Hydrological processes are irreversible and produce entropy. Hence, the framework of non-equilibrium thermodynamics is used here to describe them mathematically. This means flows of water are written as functions of gradients in the gravitational and chemical potential of water
between two parts of the hydrological system. Such a framework facilitates a consistent thermodynamic representation of the hydrological processes in the model. Furthermore, it allows for the calculation of the entropy production associated with a flow of water, which is proportional to the product of gradient and flow. Thus, an entropy budget of the hydrological cycle at the land surface is quantified, illustrating the contribution of different processes to the overall entropy production. Moreover, the proposed Principle of Maximum Entropy Production (MEP) can be applied to the model. This means, unknown parameters can be determined by setting them to values which lead to a maximisation of the entropy production in the model. The model used in this study is parametrised according to MEP and evaluated by means of several observational datasets describing terrestrial fluxes of water and carbon. The model reproduces the data with good accuracy which is a promising result with regard to the application of MEP to hydrological processes at the land surface.

Contact information

Visiting addresses:

Geovetenskapens Hus,
Svante Arrhenius väg 8, Stockholm

Arrheniuslaboratoriet, Svante Arrhenius väg 16, Stockholm (Unit for Analytical and Toxicological Chemistry)

Mailing address:
Department of Environmental Science and Analytical Chemistry (ACES)
Stockholm University
106 91 Stockholm

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