We review measured rates of soil respiration from terrestrial and wetland ecosystems to define the annual global CO 2 flux from soils, to identify uncertainties in the global flux estimate, and to investigate the influences of temperature, precipitation, and vegetation on soil respiration rates. The annual global CO 2 flux from soils is estimated to average (± S.D.) 68 ± 4 PgC/ yr, based on extrapolations from biome land areas. Relatively few measurements of soil respiration exist from arid, semi-arid, and tropical regions; these regions should be priorities for additional research. On a global scale, soil respiration rates are positively correlated with mean annual air temperatures and mean annual precipitation. There is a close correlation between mean annual net primary productivity (NPP) of different vegetation biomes and their mean annual soil respiration rates, with soil respiration averaging 24% higher than mean annual NPP. This difference represents a minimum estimate of the contribution of root respiration to the total soil CO 2 efflux. Estimates of soil C turnover rates range from 500 years in tundra and peaty wetlands to 10 years in tropical savannas. We also evaluate the potential impacts of human activities on soil respiration rates, with particular focus on land use changes, soil fertilization, irrigation and drainage, and climate changes. The impacts of human activities on soil respiration rates are poorly documented, and vary among sites. Of particular importance are potential changes in temperatures and precipitation. Based on a review of in situ measurements, the Q 10 value for total soil respiration has a median value of 2.4. Increased soil respiration with global warming is likely to provide a positive feedback to the greenhouse effect. DOI: 10.1034/j.1600-0889.1992.t01-1-00001.x

https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=1225&context=eeob_ag_pubs

The global carbon dioxide flux in soil respiration and its relationship to vegetation and climate

If stretched end to end, the estimated 1030viruses in the oceans would span farther than the nearest 60 galaxies. This reservoir of genetic and biological diversity continues to yield exciting discoveries and, in this Review, Curtis A. Suttle highlights the areas that are likely to be of greatest interest in the next few years. Viruses are by far the most abundant 'lifeforms' in the oceans and are the reservoir of most of the genetic diversity in the sea. The estimated 1030 viruses in the ocean, if stretched end to end, would span farther than the nearest 60 galaxies. Every second, approximately 1023 viral infections occur in the ocean. These infections are a major source of mortality, and cause disease in a range of organisms, from shrimp to whales. As a result, viruses influence the composition of marine communities and are a major force behind biogeochemical cycles. Each infection has the potential to introduce new genetic information into an organism or progeny virus, thereby driving the evolution of both host and viral assemblages. Probing this vast reservoir of genetic and biological diversity continues to yield exciting discoveries.

Marine viruses — major players in the global ecosystem

Viruses are the most common biological agents in the sea, typically numbering ten billion per litre. They probably infect all organisms, can undergo rapid decay and replenishment, and influence many biogeochemical and ecological processes, including nutrient cycling, system respiration, particle size-distributions and sinking rates, bacterial and algal biodiversity and species distributions, algal bloom control, dimethyl sulphide formation and genetic transfer. Newly developed fluorescence and molecular techniques leave the field poised to make significant advances towards evaluating and quantifying such effects.

/pdf/marine-viruses-and-their-biogeochemical-and-ecological-1lkd7mtgjc.pdf

Marine viruses and their biogeochemical and ecological effects

 Many atmospheric chemicals occur in the gas phase as well as in liquid cloud droplets and aerosol particles Therefore, it is necessary to understand the distribution between the phases According to Henry's law, the equilibrium ratio between the abundances in the gas phase and in the aqueous phase is constant for a dilute solution Henry's law constants of trace gases of potential importance in environmental chemistry have been collected and converted into a uniform format The compilation contains 17 350 values of Henry's law constants for 4632 species, collected from 689 references It is also available at http://wwwhenrys-laworg 

/pdf/compilation-of-henry-s-law-constants-version-4-0-for-water-58il9q0ogv.pdf

Compilation of Henry's law constants (version 4.0) for water as solvent

https://horizon.documentation.ird.fr/exl-doc/pleins_textes/pleins_textes_7/b_fdi_57-58/010025232.pdf

Production, oxidation, emission and consumption of methane by soils: A review

About half the biogenic sulfur flux to the earth's atmosphere each year arises from the oceans. Dimethylsulfide (DMS), which constitutes about 90% of this marine sulfur flux, is presumed to originate from the decomposition of dimethylsulfoniopropionate produced by marine organisms, particularly phytoplankton. The rate of DMS release by phytoplankton is greatly increased when the phytoplankton are subjected to grazing by zooplankton. DMS production associated with such grazing may be the major mechanism of DMS production in many marine settings.

https://science.sciencemag.org/content/sci/233/4770/1314.full.pdf

Oceanic Dimethylsulfide: Production During Zooplankton Grazing on Phytoplankton

An intriguing example of genome reduction has been found in SAR11 marine bacteria, the ubiquitous clade with the smallest known genome of all free-living heterotrophic cells. 'Normal' marine aerobic bacteria are known to use assimilatory sulphate reduction to acquire sulphur from the environment. But Candidatus Pelagibacter ubique, and other SAR11 microbes, are deficient in this key metabolic pathway. Instead they rely on reduced sulphur compounds in the environment. This identifies compounds such as DMSP and methionine as essential growth requirements for these large plankton populations, a potentially important factor in microbial population dynamics in the oceans. Marine aerobic bacteria are known to use assimilatory sulphate reduction to acquire sulphur from the environment. The abundant and ubiquitous SAR11 clade is shown to be deficient in this pathway and instead to rely on reduced sulphur components such as DMSP for growth. Sulphur is a universally required cell nutrient found in two amino acids and other small organic molecules. All aerobic marine bacteria are known to use assimilatory sulphate reduction to supply sulphur for biosynthesis, although many can assimilate sulphur from organic compounds that contain reduced sulphur atoms1,2,3. An analysis of three complete ‘Candidatus Pelagibacter ubique’ genomes, and public ocean metagenomic data sets, suggested that members of the ubiquitous and abundant SAR11 alphaproteobacterial clade are deficient in assimilatory sulphate reduction genes. Here we show that SAR11 requires exogenous sources of reduced sulphur, such as methionine or 3-dimethylsulphoniopropionate (DMSP) for growth. Titrations of the algal osmolyte DMSP in seawater medium containing all other macronutrients in excess showed that 1.5 × 108 SAR11 cells are produced per nanomole of DMSP. Although it has been shown that other marine alphaproteobacteria use sulphur from DMSP in preference to sulphate1,2, our results indicate that ‘Cand. P. ubique’ relies exclusively on reduced sulphur compounds that originate from other plankton.

SAR11 marine bacteria require exogenous reduced sulphur for growth

[1] Air-water gas transfer influences CO 2 and other climatically important trace gas fluxes on regional and global scales, yet the magnitude of the transfer is not well known. Widely used models of gas exchange rates are based on empirical relationships linked to wind speed, even though physical processes other than wind are known to play important roles. Here the first field investigations are described supporting a new mechanistic model based on surface water turbulence that predicts gas exchange for a range of aquatic and marine processes. Findings indicate that the gas transfer rate varies linearly with the turbulent dissipation rate to the 1/4 power in a range of systems with different types of forcing - in the coastal ocean, in a macro-tidal river estuary, in a large tidal freshwater river, and in a model (i.e., artificial) ocean. These results have important implications for understanding carbon cycling.

/pdf/environmental-turbulent-mixing-controls-on-air-water-gas-34m6hh0rtw.pdf

Environmental turbulent mixing controls on air-water gas exchange in marine and aquatic systems

The kinetics of DMS production resulting from reaction of OH(-) with DMSP were investigated as a function of hydroxide concentration and temperature. The reaction was first-order with respect to DMSP and OH(-). The second order rate constant at 20+/-1 C is 0.0044/M/sec. The activation energy for this reaction is 14.4 kcal/mode. The investigation indicates that the rate of reaction of DMSP with OH(-) is very slow at the pH of seawater, suggesting that DMSP, which may be a major precursor of DMS in seawater, decomposes in the ocean by other mechanisms. A bacterium which produces DMS from DMSP quantitatively at rates many orders of magnitude higher than indicated by OH(-1) decomposition has been cultured, suggesting that enzymatic processes accelerate the production of DMS from DMSP in seawater.

Hydroxide decomposition of dimethylsulfoniopropionate to form dimethylsulfide

Surface oxygen uptake, sulfate reduction and total sediment metabolism were measured in sediments (0-30 cm) supporting stands of short Spartina alterniflora in a New England salt marsh. Surface oxygen uptake varied seasonally and was highly correlated with total sediment metabolism. Rates of oxygen uptake ranged from about 75 to 121 mmol/sq m/day during winter to a maximum in August of 363. Total carbon dioxide production followed the same trend with a winter low of 65 mmol/sq m/day and a maximum in August of 415. The sulfate concentration in porewater from the 0-2 cm interval was about that expected from seawater at the salinity of the interstitial water. Below this depth sulfate decreased to values of about 21.6 mmol/liter. Time-course experiments using carbon dioxide production and sulfate reduction indicate that the aqua regia technique is not reliable for measuring sulfate reaction and that the rate of sulfate reduction is much less than previously reported for this marsh. Carbon mineralization is estimated to average about 180 mmol C/sq m/day, among the highest measured for marine sediments. Simultaneous measurements of oxygen uptake, carbon dioxide production and sulfate reduction suggest that at least half of this decomposition occurs via sulfate reduction. 54 references, 7more » figures.« less

https://aslopubs.onlinelibrary.wiley.com/doi/pdf/10.4319/lo.1984.29.5.1037

John W. H. Dacey

Papers

Oceanic Dimethylsulfide: Production During Zooplankton Grazing on Phytoplankton

SAR11 marine bacteria require exogenous reduced sulphur for growth

Environmental turbulent mixing controls on air-water gas exchange in marine and aquatic systems

Hydroxide decomposition of dimethylsulfoniopropionate to form dimethylsulfide

Carbon flow through oxygen and sulfate reduction pathways in salt marsh sediments1