Coupled changes in western South Atlantic carbon sequestration and particle reactive element cycling during millennial-scale Holocene climate variability

AbstractContinental shelves have the potential to remove atmospheric carbon dioxide via the biological pump, burying it in seafloor sediments. The efficiency of marine carbon sequestration changes rapidly due to variations in biological productivity, organic carbon oxidation, and burial rate. Here we present a high temporal resolution record of marine carbon sequestration changes from a western South Atlantic shelf site sensitive to Brazil Current-driven upwelling. The comparison of biological records to rare earth element (REE) patterns from authigenic oxides shows a strong relationship between higher biological productivity and stronger particle reactive element cycling (i.e. REE cycling) during rapid climate change events. This is the first evidence that authigenic oxides archive past changes in upper ocean REE cycling by the exported organic carbon. In addition, our data suggest that Brazil Current-driven upwelling varies on millennial-scales and in time with continental precipitation anomalies as registered in Brazilian speleothems during the Holocene. This indicates an ocean–atmosphere control on the biological pump, most probably related to South American monsoon system variability.

The relationship between land cover and microbial community composition in European lakes

Microbes such as bacteria, archaea, and protists are essential for element cycling and ecosystem functioning, but many questions central to the understanding of the role of microbes in ecology are still open. Here, we analyze the relationship between lake microbiomes and the land cover surrounding the lakes. By applying machine learning methods, we quantify the covariance between land cover categories and the microbial community composition recorded in the largest amplicon sequencing dataset of European lakes available to date. We identify microbial bioindicators for these land cover categories. Combining land cover and physico-chemical bioindicators identified from the same amplicon sequencing dataset, we develop two novel similarity metrics that facilitate insights into the ecology of the lake microbiome. We show that the bioindicator network, i.e., the graph linking OTUs indicative of the same environmental parameters, corresponds to microbial co-occurrence patterns. Taken together, we demonstrate the strength of machine learning approaches to identify correlations between microbial diversity and environmental factors, potentially opening new approaches to integrate environmental molecular diversity into monitoring and water quality assessments.

Roles of Arbuscular Mycorrhizal Fungi on Soil Fertility and Its Importance in Phytoremediation of Polluted Soil

A single paragraph Arbuscular mycorrhizal fungi (AMF) establish symbiotic relationships with many crops. These soil microbiotas improve the soil fertility through the soil physical, chemical and biological properties. extending the root absorbing area. In return, the symbiont receives plant carbohydrates for the completion of its life cycle. AMF also helps plants to cope with biotic and abiotic stresses such as extreme temperature, heavy metal, diseases, and pathogens. For soil physical properties, the mechanisms used by AMF are the production of a glycoprotein, glomalin, which creates a high quality of soil macro-aggregations. These macro-aggregations control soil erosion, nutrients and organic matter losses. For soil chemical properties, AMF produce acids and an enzyme called phosphatase. This enzyme hydrolyzes the inorganic phosphorus and the rock phosphate (RP) hence making P available in the soil for plant uptake. AMF also are involved in soil nitrogen, carbon and trace element cycling. Regarding the biological component of the soil, AMF influence the composition, diversity and activity of microbial communities in the hydrosphere. They also work in synergy with others soil microorganisms to improve soil fertility, plant growth and resistance against some diseases. In this review, we present the contribution of AMF on soil fertility and importance in polluted soils.

Factors Governing Biodegradability of Dissolved Natural Organic Matter in Lake Water

Dissolved Natural Organic Matter (DNOM) is a heterogeneous mixture of partly degraded, oxidised and resynthesised organic compounds of terrestrial or aquatic origin. In the boreal biome, it plays a central role in element cycling and practically all biogeochemical processes governing the physico-chemistry of surface waters. Because it plays a central role in multiple aquatic processes, especially microbial respiration, an improved understanding of the biodegradability of the DNOM in surface water is needed. Here the current study, we used a relatively cheap and non-laborious analytical method to determine the biodegradability of DNOM, based on the rate and the time lapse at which it is decomposed. This was achieved by monitoring the rate of oxygen consumption during incubation with addition of nutrients. A synoptic method study, using a set of lake water samples from southeast Norway, showed that the maximum respiration rate (RR) and the normalised RR (respiration rate per unit of carbon) of the DNOM in the lakes varied significantly. This RR is conceived as a proxy for the biodegradability of the DNOM. The sUVa of the DNOM and the C:N ratio were the main predictors of the RR. This implies that the biodegradability of DNOM in these predominantly oligotrophic and dystrophic lake waters was mainly governed by their molecular size and aromaticity, in addition to its C:N ratio in the same manner as found for soil organic matter. The normalised RR (independently of the overall concentration of DOC) was predicted by the molecular weight and by the origin of the organic matter. The duration of the first phase of rapid biodegradation of the DNOM (BdgT) was found to be higher in lakes with a mixture of autochthonous and allochthonous DNOM, in addition to the amount of biodegradable DNOM.

How C: N: P stoichiometry in soils and carbon distribution in plants respond to forest age in a Pinus tabuliformis plantation in the mountainous area of eastern Liaoning Province, China

Carbon distribution in plants and ecological stoichiometry in soils are important indicators of element cycling and ecosystem stability. In this study, five forest ages, young forest (YF), middle-aged forest (MAF), near-mature forest (NMF), mature forest (MF), and over-mature forest (OMF) in a Pinus tabuliformis plantation were chosen to illustrate interactions among the C: N: P stoichiometry in soils and carbon distribution in plants, in the mountainous area of eastern Liaoning, China. Carbon content was highest in the leaves of MAF (505.90 g⋅kg−1) and NMF (509.00 g⋅kg−1) and the trunks of YF (503.72 g⋅kg−1), MF (509.73 g⋅kg−1), and OMF (504.90 g⋅kg−1), and was lowest in the branches over the entire life cycle of the aboveground components (335.00 g⋅kg−1). The carbon content of the fine roots decreased with soil layer depth. In YF, MAF, and NMF carbon content of fine roots at 0.5 m was always higher than that of fine roots at 1 m; however, it was the opposite in MF and OMF. The carbon content of the leaves changed with forest age; however, carbon content of branches, trunks and fine roots did not change significantly. Soil total carbon (TC), total nitrogen (TN), total phosphorus (TP), and available phosphorus (AP) content was highest in the OMF. Soil TC, TN and AP content, and TC: TN, TC: TP and TN: TP ratio decreased with increasing soil depth. Soil TC, TN, and TP content had a significant effect on the carbon content of fine roots (p < 0.05). The leaf carbon content and soil element content changed obviously with forest age, and the soil TN, TP and AP increased, which might reduce the carbon content allocation of fine roots.

Marine Gel Interactions with Hydrophilic and Hydrophobic Pollutants

Microgels play critical roles in a variety of processes in the ocean, including element cycling, particle interactions, microbial ecology, food web dynamics, air–sea exchange, and pollutant distribution and transport. Exopolymeric substances (EPS) from various marine microbes are one of the major sources for marine microgels. Due to their amphiphilic nature, many types of pollutants, especially hydrophobic ones, have been found to preferentially associate with marine microgels. The interactions between pollutants and microgels can significantly impact the transport, sedimentation, distribution, and the ultimate fate of these pollutants in the ocean. This review on marine gels focuses on the discussion of the interactions between gel-forming EPS and pollutants, such as oil and other hydrophobic pollutants, nanoparticles, and metal ions.

Geographical and Seasonal Thermal Sensitivity of Grazing Pressure by Microzooplankton in Contrasting Marine Ecosystems

Grazing pressure, estimated as the ratio between microzooplankton grazing and phytoplankton growth rates (g:μ), is a strong determinant of microbial food-web structure and element cycling in the upper ocean. It is generally accepted that g is more sensitive to temperature than μ, but it remains unknown how the thermal dependence (activation energy, Ea) of g:μ varies over spatial and temporal scales. To tackle this uncertainty, we used an extensive literature analysis obtaining 751 paired rate estimates of μ and g from dilution experiments performed throughout the world’s marine environments. On a geographical scale, we found a stimulatory effect of temperature in polar open-ocean (∼0.5 eV) and tropical coastal (∼0.2 eV) regions, and an inhibitory one in the remaining biomes (values between −0.1 and −0.4 eV). On a seasonal scale, the temperature effect on g:μ ratios was stimulatory, particularly in polar environments; however, the large variability existing between estimates resulted in non-significant differences among biomes. We observed that increases in nitrate availability stimulated the temperature dependence of grazing pressure (i.e., led to more positive Ea of g:μ) in open-ocean ecosystems and inhibited it in coastal ones, particularly in polar environments. The percentage of primary production grazed by microzooplankton (∼56%) was similar in all regions. Our results suggest that warming of surface ocean waters could exert a highly variable impact, in terms of both magnitude and direction (stimulation or inhibition), on microzooplankton grazing pressure in different ocean regions.

Limitation of microbial processes at saturation-level salinities in a microbial mat covering a coastal saltflat

Hypersaline microbial mats are dense microbial ecosystems capable of performing complete element cycling and are considered analogs of Early Earth and hypothetical extraterrestrial ecosystems. We studied the functionality and limits of key biogeochemical processes, such as photosynthesis, aerobic respiration, and sulfur cycling in salt crust-covered microbial mats from a tidal flat at the coast of Oman. We measured light, oxygen, and sulfide microprofiles as well as sulfate-reduction rates at salt saturation and in flood conditions and determined fine-scale stratification of pigments, biomass, and microbial taxa in the resident microbial community. The salt crust did not protect the mats against irradiation or evaporation. Although some oxygen production was measurable at salinity ≤ 30% (w/v) in situ , at saturation-level salinity (40%), oxygenic photosynthesis was completely inhibited and only resumed two days after reducing the pore water salinity to 12%. Aerobic respiration and active sulfur cycling occurred at low rates under salt saturation and increased strongly upon salinity reduction. Apart from high relative abundances of Chloroflexi, photoheterotrophic Alphaproteobacteria , Bacteroidetes , and Archaea, the mat contained a distinct layer harboring filamentous Cyanobacteria , which is unusual for such high salinities. Our results show that the diverse microbial community inhabiting this saltflat mat ultimately depends on periodic salt dilution to be self-sustaining and is rather adapted to merely survive salt saturation than to thrive under the salt crust. Importance Due to their abilities to survive intense radiation and low water availability hypersaline microbial mats are often suggested to be analogs of potential extraterrestrial life. However, even on Earth the limitations imposed on microbial processes by saturation-level salinity have rarely been studied in situ . While abundance and diversity of microbial life in salt-saturated environments is well documented, most of our knowledge on process limitations stems from culture-based studies, few in situ studies, and theoretical calculations. Especially oxygenic photosynthesis has barely been explored beyond 5M NaCl (28% w/v). By applying a variety of biogeochemical and molecular methods we show that despite abundance of photoautotrophic microorganisms, oxygenic photosynthesis is inhibited in salt-crust covered microbial mats at saturation salinities, while rates of other energy generation processes are decreased several fold. Hence, the complete element cycling required for self-sustaining microbial communities only occurs at lower salt concentrations.