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In this work, molecular diversity of two hypersaline microbial mats was compared by Whole Genome Shotgun (WGS) sequencing of environmental DNA from the mats. Brava and Tebenquiche are lakes in the Salar de Atacama, Chile, where microbial communities are growing in extreme conditions, including high salinity, high solar irradiance, and high levels of toxic metals and metaloids. Evaporation creates hypersaline conditions in these lakes and mineral precipitation is a characteristic geomicrobiological feature of these benthic ecosystems. The mat from Brava was more rich and diverse, with a higher number of different taxa and with species more evenly distributed. At the phylum level, Proteobacteria, Cyanobacteria, Chloroflexi, Bacteroidetes and Firmicutes were the most abundant, including ~75% of total sequences. At the genus level, the most abundant sequences were affilitated to anoxygenic phototropic and cyanobacterial genera. In Tebenquiche mats, Proteobacteria and Bacteroidetes covered ~70% of the sequences, and 13% of the sequences were affiliated to Salinibacter genus, thus addressing the lower diversity. Regardless of the differences at the taxonomic level, functionally the two mats were similar. Thus, similar roles could be fulfilled by different organisms. Carbon fixation through the Wood-Ljungdahl pathway was well represented in these datasets, and also in other mats from Andean lakes. In spite of presenting less taxonomic diversity, Tebenquiche mats showed increased abundance and variety of rhodopsin genes. Comparison with other metagenomes allowed identifying xantorhodopsins as hallmark genes not only from Brava and Tebenquiche mats, but also for other mats developing at high altitudes in similar environmental conditions.

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Introducción: Los cultivos de café, cacao y pasturas para la ganadería son actividades agropecuarias de interés económico en Colombia. Cuando estas actividades se desarrollan bajo sistemas agroforestales (SAF) promueven la conservación e incrementan la fijación de carbono y, por ende, la mitigación del cambio climático. Objetivo: El estudio estimó el almacenamiento de carbono en la biomasa aérea, necromasa y carbono orgánico del suelo bajo SAF con cacao (SAF cacao), SAF con café (café SAF), sistemas silvopastoriles (SSP) y bosque en el municipio de Mesetas, Meta (Colombia). Métodos: Se establecieron 44 parcelas de muestreo, en donde se tomaron medidas dasométricas a individuos con un diámetro del tronco a la altura del pecho (dap) ≥ 2.5 cm (latizales, fustales y fustales grandes), cuyos valores fueron transformados a carbono con modelos de biomasa y una fracción de carbono default. En los tres sistemas agropecuarios, se contó el número de árboles de cacao, café, plantas asociadas y se identificó el tipo de uso (maderable, alimento, combustión). Resultados: El almacenamiento de carbono presentó diferencias significativas (P < 0.0001) entre usos del suelo. La mayor acumulación se encontró en bosque, con 216.6 t C ha-1, superando en 59, 72 y 73 % a SAF cacao, SSP y SAF café, respectivamente. Fabaceae, Lauraceae y Primulaceae presentaron el mayor almacenamiento de carbono. En SAF cacao, la mayor acumulación de carbono fue encontrada en especies para alimento humano; en SAF café y SSP, el mayor almacenamiento fue presentado en las especies maderables. Conclusión: Estos resultados resaltan el potencial de almacenamiento de carbono en los sistemas productivos de mayor importancia en el departamento del Meta, lo cual es importante para el diseño de estrategias que permitan integrar acciones de mitigación de emisiones de gases de efecto invernadero y promover la economía campesina local.

Introduction: Coffee, cocoa crops and pastures for livestock are agricultural activities of economic interest in Colombia. When these activities are developed under agroforestry systems (AFS), they promote conservation and increase carbon fixation and, therefore, climate change mitigation. Objective: The study estimated carbon storage in aboveground biomass, necromass and soil organic carbon under SAF with cocoa (SAF cocoa), SAF with coffee (SAF coffee), silvopastoral systems (SPS) and forest in Mesetas, Meta (Colombia). Methods: Forty-four sampling plots were established, where dasometric measurements were taken from individuals with a trunk diameter at breast height (dbh) ≥ 2.5 cm (saplings, trees and large trees), whose values were transformed to carbon with biomass models and a default carbon fraction. In the three agricultural systems, the number of cocoa and coffee trees and associated plants was counted, and the type of use (timber, food, combustion) was identified. Results: Carbon storage showed significant differences (P < 0.0001) among land uses. The highest accumulation was found in forest, with 216.6 t C ha-1, exceeding in 59, 72 and 73 % to SAF cocoa, SSP and SAF coffee, respectively. The botanical families Fabaceae, Lauraceae and Primulaceae presented the greatest carbon storage. In SAF cocoa, the greatest accumulation of carbon was found in species for human food; in SAF coffee and SSP, the greatest storage was presented by timber species. Conclusion: These results highlight the potential for carbon storage in the most important productive systems in the Meta department, which is important for designing strategies that allow for integrating actions to mitigate greenhouse gas emissions and to promote the local peasant economy.

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The present study was aimed to develop a membrane sparger (MS) integrated into a tubular photobioreactor to promote the increase of the carbon dioxide (CO2 ) fixation by Spirulina sp. LEB 18 cultures. The use of MS for the CO2 supply in Spirulina cultures resulted not only in the increase of DIC concentrations but also in the highest accumulated DIC concentration in the liquid medium (127.4 mg L-1 d-1 ). The highest values of biomass concentration (1.98 g L-1 ), biomass productivity (131.8 mg L-1 d-1 ), carbon in biomass (47.9% w w-1 ), CO2 fixation rate (231.6 mg L-1 d-1 ), and CO2 use efficiency (80.5% w w-1 ) by Spirulina were verified with MS, compared to the culture with conventional sparger for CO2 supply. Spirulina biomass in both culture conditions had high protein contents varying from 64.9 to 69% (w w-1 ). MS can be considered an innovative system for the supply of carbon for the microalgae cultivation and biomass production. Moreover, the use of membrane system might contribute to increased process efficiency with a reduced cost of biomass production.

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Analyses of the integrated seagrass response to depth support the previously documented low plasticity and consistent shade-adapted leaf physiology of a habitat-builder that dominates well-illuminated reef environments. Two structural responses, "canopy-opening" and "below-ground-mass-depletion", govern the photoacclimatory response and facilitate, respectively, light penetration within the canopy and functional adjustments in whole-plant carbon balances. Conversely, "canopy-closing" may also explain dense canopies formed close to the waterline, as they provide shade and photoprotection to a susceptible leaf physiology under high-light. Canopy light attenuation is primarily regulated by the leaf area index (LAI), which is governed by changes in shoot size and density. Shoot density diminishes non-linearly with depth, while shoot size increases to a maximum followed by a decline. The initial increase in shoot size, which resembles a self-thinning response, increases LAI and meadow production in shallow depths. These seagrass structural adjustments have relevant ecological implications. Canopy-thinning allows macrophyte diversity to increase with depth, while seagrass production and carbon storage diminish exponentially, and are maximal only in a shallow coastal fringe. The results support the universality of plant self-thinning, from phytoplankton to complex canopies, likely the consequence of simple physical laws related to light limitation and pigment self-shading within photosynthetic structures and communities.

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OBJECTIVE: To construct Pseudomonas aeruginosa PA14 derivatives that overproduce rhamnolipids (RL) by blocking the synthesis of the carbon-storage polymer polyhydroxyalkanoates (PHA) and by overexpressing the rhlAB-R operon that encodes for enzymes of RL synthesis and the RhlR transcriptional regulator. RESULTS: In contrast to previous results showing that overexpression of rhlAB-R genes in two P. aeruginosa strains (PAO1 and ATCC 9027) is sufficient to overproduce RL, we show that a PA14 derivative overexpressing the rhlAB-R operon did not increase the synthesis of these biosurfactants. In addition, PA14 mutants deficient in PHA production did not overproduce RL either. However, if the rhlAB-R genes were expressed in a mutant that is completely impaired in PHA synthesis, a significant increase in RL production was observed (59%). These results show that RL production in PA14 is limited both by the availability of fatty acid precursors and by the levels of the RhlA and RhlB enzymes that are involved in the synthesis of mono-RL. CONCLUSIONS: The limitation of RL production by P. aeruginosa PA14 is multifactorial and diverse from the results obtained with other strains. Thus, the factors that limit RL production are particular to each P. aeruginosa strain, so strain-specific strategies should be developed to increase their production.

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Few studies have shown the importance of different pasture management practices on C storage and the reduction of CO2-C emissions in tropical conditions. The objective of the present study was to determine short-term changes in C pools and C balance from different pasture management practices established in the Atlantic Rainforest. A field study was carried out in Alegre, ES, Brazil from September 2013 to August 2014 to investigate the first-year effect of pasture management practices on a Udult clayey soil. The different pasture management practices studied included the following: control (CON), chiseled (CHI), fertilized (FER), burned (BUR), integrated with crop-livestock (iCL) systems, and plowed and harrowed (PH). Monthly disturbed and undisturbed soil samples were taken at two different layers (0.00-0.05 and 0.05-0.20 m) for chemical, physical, and organic matter characterization. C inputs monitored in aboveground pools included plant aerial parts and litter, and belowground pools included roots and soil C stocks. C outputs monitored were CO2-C emissions, erosion water, and sediment. C balance was considered the difference between inputs and outputs in each treatment during four seasons. The spring and summer seasons had a strong influence on C inputs and outputs where there is significant difference between spring and summer, while the autumn and winter seasons had less influence. All pasture management practices exhibited positive C balance after 1 year. High values of C balance were verified in pastures fertilized (FER) (53.04 Mg ha-1 year-1. Intermediate C balance was found in the burned (BUR) (40.84 Mg ha-1 year-1), traditional control (CON) (40.31 Mg ha-1 year-1), and in the plowing and harrowing (PH) (40.02 Mg ha-1 year-1) management practices. The practices of chiseled (40.00 Mg ha-1 year-1) and integrated crop-livestock systems (iCL) (59.06 Mg ha-1 year-1) resulted in low C balance.

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Oxygen availability drives changes in microbial diversity and biogeochemical cycling between the aerobic surface layer and the anaerobic core in nitrite-rich anoxic marine zones (AMZs), which constitute huge oxygen-depleted regions in the tropical oceans. The current paradigm is that primary production and nitrification within the oxic surface layer fuel anaerobic processes in the anoxic core of AMZs, where 30-50% of global marine nitrogen loss takes place. Here we demonstrate that oxygenic photosynthesis in the secondary chlorophyll maximum (SCM) releases significant amounts of O2 to the otherwise anoxic environment. The SCM, commonly found within AMZs, was dominated by the picocyanobacteria Prochlorococcus spp. Free O2 levels in this layer were, however, undetectable by conventional techniques, reflecting a tight coupling between O2 production and consumption by aerobic processes under apparent anoxic conditions. Transcriptomic analysis of the microbial community in the seemingly anoxic SCM revealed the enhanced expression of genes for aerobic processes, such as nitrite oxidation. The rates of gross O2 production and carbon fixation in the SCM were found to be similar to those reported for nitrite oxidation, as well as for anaerobic dissimilatory nitrate reduction and sulfate reduction, suggesting a significant effect of local oxygenic photosynthesis on Pacific AMZ biogeochemical cycling.

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Predictions from forest ecosystem models are limited in part by large uncertainties in the current state of the land surface, as previous disturbances have important and lasting influences on ecosystem structure and fluxes that can be difficult to detect. Likewise, future disturbances also present a challenge to prediction as their dynamics are episodic and complex and occur across a range of spatial and temporal scales. While large extreme events such as tropical cyclones, fires, or pest outbreaks can produce dramatic consequences, small fine-scale disturbance events are typically much more common and may be as or even more important. This study focuses on the impacts of these smaller disturbance events on the predictability of vegetation dynamics and carbon flux. Using data on vegetation structure collected for the same domain at two different times, i.e. "repeat lidar data", we test high-resolution model predictions of vegetation dynamics and carbon flux across a range of spatial scales at an important tropical forest site at La Selva Biological Station, Costa Rica. We found that predicted height change from a height-structured ecosystem model compared well to lidar measured height change at the domain scale (~150 ha), but that the model-data mismatch increased exponentially as the spatial scale of evaluation decreased below 20 ha. We demonstrate that such scale-dependent errors can be attributed to errors predicting the pattern of fine-scale forest disturbances. The results of this study illustrate the strong impact fine-scale forest disturbances have on forest dynamics, ultimately limiting the spatial resolution of accurate model predictions.

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Betaproteobacteria were the most common isolates from the water-filled tank of a Costa Rican bromeliad. Isolates included eight species from the orders Neisseriales and Burkholderiales, with close relatives recovered previously from tropical soils, wetlands, freshwater, or in association with plants. Compared to close relatives, the isolates displayed high temperature and comparatively low pH optima, reflecting the tropical, acidic nature of the bromeliad tank. Bromeliad-associated bacteria most closely related to Chromobacterium, Herbaspirillum, and Aquitalea were all isolated exclusively at pH 6, while Ralstonia, Cupriavidus, and three species of Burkholderia were isolated mostly at pH 4. Activity profiles for the isolates suggest pervasive capabilities for the breakdown of plant-sourced organics, including d-galacturonic acid, mannitol, d-xylose, and l-phenylalanine, also reflecting a niche dominated by decomposition of leaves from the overlying canopy, which become entrained in the tanks. Metabolic activity profiles were overlapping between the Burkholderiales, isolated at pH 4, and the Neisseriales, isolated at pH 6, suggesting that plant material decomposition, which is presumably the underlying process sustaining the tank community and possibly the plant itself, occurs in the tanks at both pH extremes. These results suggest that bromeliad-associated betaproteobacteria may play an important role in the cycling of carbon in this unusual aquatic habitat.

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Tropical forests store vast quantities of carbon, account for one-third of the carbon fixed by photosynthesis, and are a major sink in the global carbon cycle. Recent evidence suggests that competition between lianas (woody vines) and trees may reduce forest-wide carbon uptake; however, estimates of the impact of lianas on carbon dynamics of tropical forests are crucially lacking. Here we used a large-scale liana removal experiment and found that, at 3 y after liana removal, lianas reduced net above-ground carbon uptake (growth and recruitment minus mortality) by ∼76% per year, mostly by reducing tree growth. The loss of carbon uptake due to liana-induced mortality was four times greater in the control plots in which lianas were present, but high variation among plots prevented a significant difference among the treatments. Lianas altered how aboveground carbon was stored. In forests where lianas were present, the partitioning of forest aboveground net primary production was dominated by leaves (53.2%, compared with 39.2% in liana-free forests) at the expense of woody stems (from 28.9%, compared with 43.9%), resulting in a more rapid return of fixed carbon to the atmosphere. After 3 y of experimental liana removal, our results clearly demonstrate large differences in carbon cycling between forests with and without lianas. Combined with the recently reported increases in liana abundance, these results indicate that lianas are an important and increasing agent of change in the carbon dynamics of tropical forests.

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