Carbon Cycle

Carbon cycle: The carbon cycle refers to the biogeochemical cycle by which carbon is exchanged between the biosphere (which usually includes animals, plants and bacteria), geosphere (soil and soil bacteria), hydrosphere (which includes dissolved inorganic carbon and living and non-living marine biota) and atmosphere (mostly CO2).

From: Engineered Nanoparticles , 2016

Carbon Cycle

John Grace , in Encyclopedia of Biodiversity (Second Edition), 2013

Abstract

The carbon cycle is one of several key biogeochemical cycles linking the biosphere, atmosphere, geosphere, and hydrosphere. It is no longer in a state of equilibrium as a result of burning fossil fuels and converting forested land into low-carbon alternatives. These perturbations result in an accumulation of greenhouse gases in the atmosphere and associated warming. We review the current rates of change in the fluxes of carbon and discuss the critical processes in the cycle. Finally, we examine how the carbon cycle might be managed by reducing deforestation, finding alternative energy supplies and geo-engineering.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780123847195003063

Carbon Cycle

John Grace , in Encyclopedia of Biodiversity, 2001

I.A. Atmospheric Analysis

Some of the best information about the carbon cycle comes from the analysis of the CO 2 concentration in the atmosphere, pioneered in the 1950s by Keeling, who established a CO2 observatory at Mauna Loa in Hawaii and first demonstrated the upward trend in the CO2 concentration (Fig. 2). Superimposed on the trend, there is an annual cycle whereby the concentration decreases during summer in the Northern Hemisphere and increases in the winter, with a minimum in October and a maximum in May. This summer decline is attributable to strong summertime uptake by photosynthesis of terrestrial vegetation (in the Southern Hemisphere, there is much less land and so a corresponding photosynthetic signal is not evident during the southern summer). Now, there is a network of remote stations whereby air samples are regularly taken in glass flasks and sent to a common laboratory for analysis. An important component of the analysis is the isotopic signal of CO2. This enables us to distinguish between ocean uptake and the photosynthetic uptake by C3 plants because the latter discriminates against 13C, whereas the former does not. Recently, it has become technically possible to detect small changes between oxygen and nitrogen concentrations. This also provides a signal of photosynthesis because photosynthesis releases one molecule of O2 for every CO2 taken up, whereas dissolution in the ocean has no influence on O2. In fact, just as the CO2 concentration is increasing by a few parts per million (ppm) each year so also the O2 concentration is decreasing. Fortunately, this is not cause for alarm because the O2 concentration is very high (about 210,000   ppm). Ultimately, this technique of measuring changes in O2 may prove to be the most sensitive method of detecting trends in photosynthesis at a global scale. Currently, most of the inferences have been made from CO2 concentrations and isotopic fractions of 13C and 12C. Using data from the flask network coupled with knowledge of the anthropogenic emissions and atmospheric circulation, it is possible to calculate the latitudinal distribution of the terrestrial and oceanic carbon sink. Currently, there is not complete agreement between different groups of workers on the point of detail because each group uses its own approach to the calculation, but three conclusions emerge:

Figure 2. The increase in CO2 concentration (parts per million by volume) as measured over 40 years at Mauna Loa in Hawaii.
1.

There is a large northern net sink of carbon, associated with uptake by the terrestrial vegetation and the ocean, usually estimated as 1 or 2   Gt of carbon per year.

2.

In the equatorial latitudes there is a small net sink, but because deforestation accounts for an efflux of about 1.5   Gt of carbon per year there must be a biotic sink of opposite sign and about the same magnitude.

3.

The pattern of sink distribution is not the same each year, being influenced by climatic phenomena and possibly by major volcanic eruptions (droughts associated with the El Niño–Southern Oscillation have been implicated as the main influence).

Overall, we can conclude from these studies that the net terrestrial sink is 2 or 3   GtC of carbon per year, and the ocean sink is likely to be about 2   GtC a −1. In addition to the flask measurements mentioned previously, there is independent evidence for terrestrial carbon sinks. For example, temperate forests in Europe and North America are growing faster than ever before, and in the equatorial region it has been found that undisturbed, mature forests are accumulating carbon.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B0122268652000420

Carbon Relations, the Role in Plant Diversification of

B. Oberle , in Encyclopedia of Evolutionary Biology, 2016

Abstract

The carbon cycle pulses with life. Each year, atmospheric CO 2 concentrations rise and fall as the balance of photosynthesis and respiration shifts with the seasons. The related exchanges of carbon between atmosphere, land, and oceans may balance such that atmospheric CO2 and the greenhouse effect change little between years. Over long time scales, geological processes and evolutionary change can shift the controls on the carbon cycle with major impacts on climate and biodiversity. Recent syntheses of comparative paleoclimatic and biogeochemical data document several episodes during earth's history which illustrate how the carbon cycle can mediate feedback between biodiversity and climate.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780128000496002614

Comparison of Element Cycles

T. Fenchel , ... T.H. Blackburn , in Bacterial Biogeochemistry (Third Edition), 2012

The Carbon Cycle

The carbon cycle ( Fig. 4.1) is unique in its dominance over other element cycles. Organic C mineralization results in major changes at degradation loci, particularly with respect to oxidant consumption. Due to its prevalence in the atmosphere and the high energy yield associated with aerobic respiration, oxygen is the primary (and ultimate) oxidant for organic C. At sites where access to oxygen is limited, usually by diffusion through water, it disappears first and usually rapidly. When they are available, other electron acceptors are then consumed in the order NO3 −, Mn4+, Fe3+, and SO4 2−. When all of these oxidants have been consumed or are otherwise unavailable, detrital carbon is converted to a mixture of CO2 and CH4. Once particulate detritus has been hydrolyzed, the soluble hydrolytic products are almost inevitably and rapidly catabolized to CO2 only or to CO2+CH4 in the absence of electron acceptors. Methane can later be oxidized by O2 or by reverse methanogenesis under anaerobic conditions in the presence of hydrogen utilizing bacteria such as sulfate reducers (Chapter 1.3). Methane oxidation is not directly coupled to electron acceptors such as nitrate, sulfate or oxidized Fe and Mn, although thermodynamic considerations suggest that these processes should be possible.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780124158368000049

Global Warming Potential and the Net Carbon Balance☆

F.M. Pulselli , M. Marchi , in Reference Module in Earth Systems and Environmental Sciences, 2015

Net Carbon Balance

Global Carbon Cycle

The carbon cycle is a fundamental component of the biogeochemical dynamics of Earth. Carbon is exchanged and cycled between atmosphere, ocean layers, land and lithosphere through processes such as photosynthesis, decomposition, respiration, and mineralization. In the atmosphere, carbon exists in the form of gaseous atmospheric CO 2, which constitutes a small but very important portion of total terrestrial carbon.

On land, living biota and decaying organic matter are phases of the cycle. A significant fraction of carbon occurs in minerals, especially in calcium and magnesium carbonates (CaCO3). A fraction has been buried in the Earth in the form of solid coal, liquid petroleum and natural gas by biogeochemical processes. Photosynthesis is the milestone for life on Earth. Early organisms developed the capacity, aided by sunlight, to use CO2 and water from their surroundings to build the organic molecules they required for growth. Land hosts a large percentage of the photosynthesis, and the biggest contribution comes from forests in the tropical belt. Carbon is fixed by plants as CO2 and is sooner or later returned to the air as CO2 or to the sea as organic material. This return occurs by two pathways: respiration of consuming organisms (including humans) and the action of organisms that decompose dead organic matter and eventually return it to the mineral state. Photosynthesis and respiration cause daily fluctuations of carbon dioxide in the atmospheric reservoir.

In the ocean, the carbon is dissolved as HCO3 − or exists in form of molecular CO2 or in microscopic plants such as phytoplankton. The carbon cycle is somewhat different in oceans where the agent of photosynthesis is phytoplankton. CO2 fixed in the surface layers of water initiates a downward flow of carbon. Organic sediment is used by the decomposing organisms of the ocean floor, again producing CO2 which is partly absorbed in the depths of the sea and partly released to the atmosphere. The marine reservoir absorbs CO2 from the other two systems (the earth and atmosphere) through the rain cycle and surface absorption.

About 38   000–40   000   Pg of carbon is stored in the ocean depths, 5000   Pg on land and in soil, 750–850   Pg in the atmosphere, and 900   Pg in the surface layer of the ocean (1   Pg C   =   1015  g C).

The atmosphere, biota, soil, and surface layer of the ocean are closely linked, continuous, relatively rapid exchanges of carbon occurring between them. Exchange of carbon between this fast-responding system and the ocean depths takes much longer (of the order of thousands of years). In other words, exchange with the depths of the ocean limits absorption of CO2; the overall result is accumulation of CO2 in the atmosphere. This means that the ocean depths cannot help to mitigate CO2 build-up.

Although all these fluxes, mostly driven by solar energy, are approximately balanced each year, imbalances are possible and feedbacks may occur, that significantly affect atmospheric CO2 concentration in the time horizon ranging from years to centuries. This variability is mainly caused by variations in land and ocean uptake, by climatic phenomena such as El Niño, as well as by human behavior. It is often difficult to distinguish changes due to human activity from natural variations.

Human activities contribute to CO2 accumulation in two main ways: through combustion of fossil fuels (coal, oil, natural gas) and through deforestation, especially of tropical rain forests. Biomass and fossil fuels are burned to meet humanity's growing demand of energy, releasing CO2 into atmosphere. Moreover, livestock breeding, as well as solid waste and wastewater management, release to the atmosphere relevant amounts of CH4 and N2O, further altering the climate change. All these inputs cause a significant perturbation in the delicate equilibria of the biosphere, especially fossil fuels which are being burned in an infinitesimal time compared to the aeons taken by slow sedimentary processes to form this resource.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780124095489095269

The Carbon Cycle in Lakes: A Biogeochemical Perspective*

Yves T. Prairie , Jonathan J. Cole , in Reference Module in Earth Systems and Environmental Sciences, 2021

Introduction

The lake carbon cycle encompasses all the processes that transport, transform, use, exchange or recycle any form of carbon found in lakes. As the common currency of all life, the flow of carbon through lake ecosystems is thus considered a general metric of the intensity of biological activity within, although some carbon transformation also may also occur through abiotic mechanisms. While this biological activity occurs within the lake's shoreline, lake ecosystems are largely a reflection of what they receive and are inextricably linked with the terrestrial catchment they drain. This paradigm of lakes as receptor funnels and reactors is not unique to carbon and is necessary to account for their observed responses to changes in external loadings, be it of nutrients in the case of eutrophication, or of sulfur or nitrogen oxides for acidification. For carbon, this terrestrial-aquatic linkage is even more pronounced because carbon processing is not only a function of the amount and form lakes receive but also by the input of other substances such as nutrients or, in some cases, of pollutants as well.

At its simplest level, the lacustrine carbon cycle is the study of how lakes react to the external loads of carbon and nutrients they receive from upstream, how the various carbon pools interact with—and are transformed into—one another, and how and in what form they are lost from the lakes, all of which are constrained or augmented by physical, chemical and biological processes. In this chapter, we review the main transformation and transport processes of the largest carbon pools and fluxes and how carbon ultimately leaves the lake at the ecosystem main interfaces: the outflow, the air-water surface and the sediments.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780128191668000554

Forests in the Global Carbon Balance: From Stand to Region

Paul G. Jarvis , Roddy C. Dewar , in Scaling Physiological Processes, 1993

I Introduction

In the global carbon cycle, carbon is transported bidirectionally between the atmosphere and terrestrial ecosystems (vegetation and soils) and the oceans. The amounts of carbon estimated to be stored in the main compartments (atmosphere, terrestrial biota, soils, and oceans) are large. The annual fluxes between the compartments are also large, although net fluxes are much smaller ( Fig. 12.1).

Figure 12.1. A diagram to show 1990 conceptions of the sizes of the carbon reservoirs (Pg) and of the carbon fluxes (Pg/year) in the global cycle. The fluxes resulting from land use change (2.8   Pg/year), gross primary productivity of terrestrial plants (117.3   Pg/year), and ocean uptake (103   Pg/year) have been assigned artificially precise values consistent with Table 12.1 As the question mark indicates, these fluxes are, in fact, highly uncertain.

 Adapted from King et al. (1987).

This cycle has been perturbed substantially by humans over the last 130   years through large changes in land use and through the burning of fossil fuels. These changes continue today at an accelerating rate. The resultant anthropogenically induced fluxes of carbon dioxide are very small in relation to the gross fluxes that occur naturally, but are large enough to modify the net fluxes, leading to an increase in the CO2 content of the atmosphere at a current rate of 3.2   gigatonnes (Pg) of carbon per year (3.2 × 1015 g/year).

This increase in CO2 content of the atmosphere has been the largest single contributor to the enhanced "greenhouse effect," cumulatively, about 55% of the total effect up to the present. It is, therefore, vital to know whether the atmospheric CO2 content is likely to continue to increase proportionately with increases in the consumption of fossil fuels.

The current annual increase in CO2 content of the atmosphere accounts for a little more than half the known current release of CO2 through the burning of fossil fuels (5.7   Pg carbon per year). The fate of the remainder of this CO2 released, in addition to any released in land-use changes, is poorly known. The airborne fraction of future CO2 releases must depend on the continuing capacity of the sinks for CO2 to take up a substantial part of the CO2 released. To be able to evaluate this ability and, indeed, possibly manage the sinks to diminish the "greenhouse effect," we first must know the size and locations of the major sinks for CO2 at the present time and, second, must interpret the nature of these sinks and predict their likely role in response to future changes in CO2, land use, and climate.

There are, however, considerable uncertainties in our knowledge of the present magnitude and spatial distribution of the sinks for the anthropogenically produced CO2, other than the atmospheric sink. These uncertainties arise from lack of atmospheric CO2 data of adequate spatial resolution, so the sinks are poorly defined. Also, there is inadequate understanding of the physiological processes governing the responses of plants and soils to, for example, the fertilization effect of the rise in atmospheric CO2 concentration, so the nature of the sinks is uncertain. The major sources arising from land-use changes are also poorly known because of inadequate survey data.

A tentative global carbon balance sheet is given in Table 12.1. It must be emphasized that the only quantities known with any degree of certainty are the annual fossil fuel emission and the increase in atmospheric content of carbon. The likely errors attached to the other terms are of the order of ±100%.

Table 12.1. Projected Annual Global Balance Sheet for Enhanced CO2 Sources and Sinks in 1990

Sources Carbon dioxide (Gt/year) Reference Sinks Carbon dioxide (Gt/year) Reference
Fossil fuels 5.7 Houghton et al. (1990) Atmosphere 3.2 Houghton et al. (1990)
Tropical deforestation 2.1? a Hammond (1990), Houghton (1991a) Oceans 1.0? Tans et al. (1990)
CO and CH4 from burning vegetation and soil changes 0.7? Enting and Mansbridge (1991) Temperate and boreal forests 1.8? Enting and Mansbridge (1991)
Tropical forests and grasslands 2.5? Enting and Mansbridge (1991)
Total sources 8.5? Total sinks 8.5?
a
Values followed by ? are uncertain.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780122334405500191

Dynamic Global Vegetation Models

Iain Colin Prentice , Sharon A. Cowling , in Encyclopedia of Biodiversity (Second Edition), 2013

Carbon Cycle

The story of modern carbon cycle science begins with the first precise measurement of annually and seasonally varying CO 2 concentrations by Keeling (1958), who was thus able to confirm a hypothesis (that CO2 concentration was rising) which had first been put forward more than half a century earlier. Since the 1980s, several overlapping networks of remote atmospheric measurement stations (for CO2, other trace gases and valuable tracers of the carbon cycle such as the stable carbon isotope composition of atmospheric CO2) have been maintained. The resulting global network of measurement stations contains far more information than could be extracted from Keeling's original two, at Mauna Loa (Hawaii) and the South Pole. These records already showed that in addition to the year-on-year increase of CO2 concentration, there is a seasonal cycle, which is much stronger at Mauna Loa than at the South Pole and which shows opposite phase in the two hemispheres. Keeling quickly realized that this cycle is caused by the 'breathing' (seasonal CO2 uptake and release) of the terrestrial biosphere. The great value of the more extensive CO2 observation network that exists today is that it provides more highly resolved information about the latitudinal variations in this seasonal cycle, and even about longitudinal patterns (albeit these are smoothed by rapid mixing), which give information about the spatial patterns of sources and sinks of CO2.

This information is valuable as a test of DGVMs, since they explicitly predict a spatial and seasonal pattern of CO2 uptake and release. To use this information, however, it is necessary to involve an atmospheric transport model to translate the signals at grid cells to a combined signal at a remote place in the atmosphere. A simple recipe for this comparison, presented by Heimann et al. (1998), provides a powerful (but under-used) benchmark for DGVMs and coupled climate–carbon cycle models (Prentice et al., 2000a, Cadule et al. 2010). The ability to reproduce this seasonal signal at different latitudes is a major achievement of DGVMs.

The rate of increase in CO2 concentration varies greatly from year to year. These variations bear the imprint of the El Niño-Southern Oscillation (Bacastow, 1976), and of large volcanic eruptions such as Mount Pinatubo that have significant transient effects on climate (Mercado et al., 2009). The interannual variability of the CO2 growth rate has been shown to be dominated by variations in the fraction of anthropogenic CO2 that is taken up by the land (McGuire et al., 2001; Denman et al., 2007). Thereby it provides a further test and demonstration of the capabilities of DGVMs (Cadule et al. 2010).

The longer term mean rate of uptake of CO2 by the land, which can be separated from the ocean component by independent measurements of O2 concentration or the stable isotope composition of atmospheric CO2 (Keeling and Shertz, 1992; Keeling et al., 1996; Battle et al., 2000; Prentice et al., 2001), is a further quantity that can be predicted by DGVMs. It is modeled as a direct consequence of the continuing CO2 rise and its fertilizing effect, combined with the residence time of carbon in the biosphere (Friedlingstein et al., 1995; Kicklighter et al., 1999; McGuire et al., 2001; Prentice et al., 2001). The residence time is long enough to ensure that the size of the carbon pool does not keep up with the rate of increase in growth. This historical rate of carbon uptake by the land is potentially an important constraint on models' future projections of carbon uptake (Arora et al., 2009). In Friedlingstein et al. (2006), the models with the lowest and highest uptake rate of atmospheric CO2 in the future, respectively, under- and overpredicted the rate of CO2 uptake during recent decades, suggesting that this very simple carbon budget criterion could provide one way to identify poorly performing models.

The IPCC Fourth Assessment Report (Denman et al., 2007) highlighted the uncertainty in the modeled terrestrial carbon cycle feedbacks, represented by these coupled climate–carbon cycles. It is a matter of urgency that the uncertainty be reduced, which will be possible through systematic comparison of model outputs with the most relevant observations – i.e., atmospheric carbon cycle measurements.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780123847195004123

Carbon Dioxide

S. Goel , D. Agarwal , in Encyclopedia of Toxicology (Third Edition), 2014

Environmental Fate and Behavior

The CO2 cycle is part of carbon cycle in the ecosystem. Carbon dioxide cycles in the environment (atmospheric air and surface water) through respiration (aerobic and anaerobic), photosynthesis, decomposition, and release from earth's carbon sinks (fossil fuels – coal, petroleum, methane; and calcium carbonate rocks) during combustion. In water, dissolved CO 2 reacts with calcium to form calcium carbonate and precipitates to the ocean floor. Few examples of most common reactions in the CO2 and carbon cycles in animals, plants, and the environment are presented below. Most of these reactions either use or produce energy.

Aerobic Metabolism: Glucose (C6H12O6) + Oxygen (O2) ↔ Carbon Dioxide (CO2) + Water (H2O).

Reaction in the Water (including body fluids): Carbon Dioxide (CO2) + Water (H2O) ↔ Carbonic Acid (H2CO3) and Carbonic Acid (H2CO3) ↔ Proton (H+) + Bicarbonate (HCO3 −).

Reaction in Water in Oceans: Calcium Carbonate + Carbon Dioxide (CO2) + Water (H2O) ↔ Calcium ion (Ca2+) + Bicarbonate (HCO3 −).

Anaerobic Decomposition: Carbon Dioxide (CO2) + Hydrogen (H2) ↔ Methane (CH4) + Water (H2O).

Combustion: Methane (CH4) + Oxygen (O2) ↔ Carbon Dioxide (CO2) + Water (H2O).

Carbon dioxide is transported over long distances across the globe in air by winds and in water with ocean currents, polluting the environment in distant places from its source of origin. The general concerns about greenhouse gases and climate changes are well known, through our ability to model the climate. However, the timing and magnitude of these effects are uncertain. The major greenhouse gases are CO2 and methane, which together represent 92% of all US greenhouse gas emissions (CO2 accounts for 82%). There is a clear trend of increasing concentrations of greenhouse gases in the atmosphere. The impact of further increases in concentrations of these gases will lead to ever-increasing warming of the climate, leading to a serious impact on human health and the environment. Many scientists believe that these impacts could include an increase in severe weather events such as hurricanes and floods, sea level rise, and increase in heat waves. These weather changes would trigger an increase in heat strokes, which may cause a migration of tree and plant species, and initiate the penetration of airborne diseases in areas that do not currently experience these. Little attention has also been directed to investigating the possibility that escalating levels of CO2 may serve as a selection pressure altering the genetic diversity of plant populations.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780123864543002694

Fungi and Their Role in the Biosphere☆

G.M. Gadd , in Reference Module in Earth Systems and Environmental Sciences, 2013

Organic Matter Degradation and Biogeochemical Cycling

Most attention has been given to carbon and nitrogen cycles, and the ability of fungi to utilize a wide spectrum of organic compounds is well known. The latter range from simple compounds such as sugars, organic acids, and amino acids, which can be easily transported into the cell, to more complex molecules that are first broken down to smaller molecules by extracellular enzymes before cellular entry. Such compounds include natural substances such as cellulose, pectin, lignin, lignocellulose, chitin, and starch to anthropogenic products such as hydrocarbons, pesticides, and other xenobiotics. Utilization of these substances results in redistribution of the component elements, primarily C, H, and O, as well as N, P, S, and other elements that may be constituents.

Some fungi have remarkable degradative properties, and lignin-degrading white rot fungi, such as Phanerochaete chrysosporium, can degrade several xenobiotics including aromatic hydrocarbons, chlorinated organics, polychlorinated biphenyls, nitrogen-containing aromatics, and many other pesticides, dyes, and xenobiotics. Such activities are of potential use in bioremediation where appropriate ligninolytic fungi have been used to treat soil contaminated with substances such as pentachlorophenol and polynuclear aromatic hydrocarbons (PAHs), the latter being constituents of creosote. In many cases, xenobiotic-transforming fungi need additional utilizable carbon sources because, although they are capable of degradation, they cannot utilize these substrates as an energy source for growth. Therefore, inexpensive utilizable lignicellulosic wastes such as corn cobs, straw, and sawdust can be used as nutrients to obtain enhanced pollutant degradation. Wood-rotting and other fungi are also receiving attention for the bleaching of dyes and industrial effluents, and the biotreatment of various agricultural wastes such as forestry, pulp and paper by-products, sugar cane bagasse, coffee pulp, sugar beet pulp, apple and tomato pulp, and cyanide.

Fungi are also important in the degradation of naturally occurring complex molecules in the soil, an environment where the hyphal mode of growth provides several advantages, and also in aquatic habitats. Since 95% of plant tissue is composed of carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur, the decomposition activities of fungi are clearly important in relation to redistribution of these elements between organisms and environmental compartments. In addition to C, H, O, N, P, and S, another 15 elements are typically found in living plant tissues – K, Ca, Mg, B, Cl, Fe, Mn, Zn, Cu, Mo, Ni, Co, Se, Na, and Si. However, all 90 or so naturally occurring elements may be found in plants, most of them at low concentrations although this may be highly dependent on the environmental conditions. They include Au, As, Hg, Pb, and U, and there are even plants that accumulate relatively high concentrations of metals such as Ni and Cd. In fact, plant metal concentrations may reflect environmental conditions and provide an indication of toxic metal pollution or metalliferous ores. Such plants are also receiving attention in bioremediation contexts (double bond  phytoremediation). Animals likewise contain a plethora of elements in varying amounts. For example, the human body is mostly water and so 99% of the mass comprises oxygen, carbon, hydrogen, nitrogen, calcium, and phosphorus. However, many other elements are present in lower amounts including substances taken up from contaminants in food and water. A similar situation occurs throughout the plant, animal, and microbial world and therefore, any decomposition, degradative, and pathogenic activities of fungi must be linked to the redistribution and cycling of all these constituent elements, on both local and global scales ( Figure 2 ).

Figure 2. Simplified elemental biogeochemical cycle in a vegetated ecosystem where organic matter decomposition processes, and therefore a prime fungal role, lead to cycling of many other elements besides C. The cycle depicted could be of Ca or K, for example. Organic matter could also arise from anthropogenic sources.

Organometals (compounds with at least one metal–carbon bond) can also be attacked by fungi, with the organic moieties being degraded and the metal compound undergoing changes in speciation. Degradation of organometallic compounds can be carried out by fungi, either by direct biotic action (enzymes) or by facilitating abiotic degradation, for instance, by alteration of pH and excretion of metabolites. Organotin compounds, such as tributyltin oxide and tributyltin naphthenate, may be degraded to mono- and dibutyltins by fungal action, inorganic Sn(ii) being the ultimate degradation product. Organomercury compounds may be detoxified by conversion to Hg(ii) by fungal organomercury lyase, the Hg(ii) being subsequently reduced to Hg(0) by mercuric reductase, a system broadly analogous to that found in mercury-resistant bacteria. Degradation of persistent carbon sources, such as charcoal and black shale, can be accelerated by fungal activity, which in turn may accelerate the release of toxic metals as organic metal complexes.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780124095489009337