Disturbance alters relationships between soil carbon pools and aboveground vegetation attributes in an anthropogenic peatland in Patagonia

1 Vegetation attributes derived from species and plant functional types (PFTs) directly or indirectly drive the carbon (C) cycle in peatlands. However, anthropogenic-based disturbances may alter petland soil-plant interactions and their ability to sequester carbon. Likewise, it is unclear how the soil-plant linkages among different soil C decomposition-based pools and plant attributes vary under disturbance conditions. 2 We aimed to assess how anthropogenic disturbances affect the relationships between aboveground vegetation attributes and belowground C pools in a peatland located in Northern Patagonia, Chile. We further evaluated if attributes derived from PFTs are better suited to predict soil C pools than attributes derived from species. We used structural equation modeling and regression analyses to explore these differences. 3 We found that undisturbed peatland has more soil-plant significant relationships between soil C pools and vegetation attributes, yielding higher predictive accuracies than disturbed areas. The species-based attributes yielded consistently better results predicting soil C pools than PFT-based attributes. However, PFT-based information showed significant interactions with the highly-decomposed C pools in the undisturbed peatland. Likewise, plant height and diversity were only significant with C pools in the undisturbed peatland. 4 We observed that water-logged plant communities have different soil-plant interactions than dryer communities. These differences were observed in both areas but were higher in the disturbed peatland, making it impossible to find meaningful soil-plant relationships across vegetation types and taxa. 5 Our results highlight the importance of accounting for disturbance or management when linking vegetation attributes to soil C pools in peatlands. This implies that up-to-date extensive monitoring of peatland disturbances is needed to accurately monitor soil C attributes at the regional level using vegetation as proxies. We also need to aggregate species into specific plant functional types that hold these soil-plant interactions across landscapes, regions, and disturbances to generalize the soil-plant relationships accurately.

Simulation of soil carbon dynamics in Australia with {\sc Roth C}

<p>We simulated soil organic carbon (C) dynamics across Australia with the Rothamsted carbon model ({\sc Roth C}) by connecting new spatially-explicit soil measurements and data with the model. This helped us to bridge the disconnection that exists between datasets used to inform the model and the processes that it depicts. We compiled publicly available continental-scale datasets and pre-processed, standardised and configured them to the required spatial and temporal resolutions. We then calibrated {\sc Roth C} and run simulations to estimate the baseline soil organic C stocks and composition in the 0--0.3~m layer at 4,043 sites in cropping, modified grazing, native grazing, and natural environments across Australia. We used data on the C fractions, the particulate, mineral associated, and resistant organic C (POC, MAOC and ROC, respectively) to represent the three main C pools in the {\sc Roth C} model's structure.<span class="Apple-converted-space">  </span>The model explained 97--98\% of the variation in measured total organic C in soils under cropping and grazing, and 65\% in soils under natural environments. We optimised the model at each site and experimented with different amounts of C inputs to simulate the potential for C accumulation under constant and chainging climate in a 100-year simulation. Soils under native grazing were the most potentially vulnerable to C decomposition and loss, while soils under natural environments were the least vulnerable. An empirical assessment of the controls on the C change showed that climate, pH, total N, the C:N ratio, and cropping were the most important controls on POC change. Clay content and climate were dominant controls on MAOC change. Consistent and explicit soil organic C simulations improve confidence in the model's estimations, contributing to the development of sustainable soil management under global change.<span class="Apple-converted-space"> </span></p>

Stochiometric control of SOM and plant derived soil C pools dynamics under elevated CO2

<p>Elevated carbon dioxide in the atmosphere (eCO<sub>2</sub>) has been found to influence soil C by altering the belowground balance between the decomposition of existing soil organic matter (SOM) and the accumulation of plant-derived C inputs. Even small changes in this balance can have a potentially large effect on future climate. The relative availability of soil nutrients, particularly N and P, are crucial mediators of both decomposition and new C accumulation, but both these two processes are rarely assessed simultaneously. We asked if the effect of eCO<sub>2 </sub>on soil C decomposition was mediated by soil N and P availability, and if the effect of CO<sub>2 </sub>and soil N and P availability on soil C decomposition was dependent on C pools (existing SOM C, newly added C). We grew Eucalyptus grandis and a C3 grass (Microlaena stipoides) from seed in an experimentally manipulated atmosphere with altered δ<sup>13</sup>C signature of CO<sub>2</sub>, which allowed the separation of plant derived C, from the existing SOM C. Then we manipulated N and P relative abundance via nutrient additions. We evaluated how the existing SOM and the new plant-derived C pool, and their respiration responded to eCO<sub>2</sub> conditions and nutrient treatments. SOM respiration significantly increased in the eucalypts when N was added but was not affected by CO<sub>2</sub>. In the grass the SOM respiration increased with eCO<sub>2</sub> and added N and SOM respiration per unit of SOM-derived microbial was significantly higher in both the added P and added N+P nutrient treatments. The rhizosphere priming of SOM was suppressed in both the added P and added N+P nutrient treatments. The heterotrophic respiration of plant-derived C was contingent on nutrient availability rather than eCO<sub>2</sub> and differed by species. The grass-derived respiration was significantly higher than the eucalypt and was higher in both added P and added N+P nutrient treatments. Thus, nutrient stoichiometry had similar effects on SOM and plant derived C, but e CO<sub>2</sub> only affected SOM and only for the Eucalyptus.  This study shows how species differences have large effects on rhizosphere C cycling responses to eCO2 and stoichiometric conditions.      </p>

Synthesis of a Biodegradable Polymer of Poly (Sodium Alginate/Ethyl Acrylate)

The objective of the study was to obtain a new biodegradable graft polymer by performing two chemical processes: first, a transesterification reaction between carboxylic acid’s salt and ethyl acrylate’s ester, followed by polymerization of the vinyl group from the ethyl acrylate monomer via free radicals. The copolymer’s FTIR shows an absence of ethyl bands, while the characteristic band of pyranose is maintained, which confirms the monomer’s graft. TGA analysis shows that sodium alginate had three decomposition temperatures: 103 °C due to dehydration, 212 °C associated with the destruction of glycosidic bonds, and 426 °C due to conversion of alginate into Na2CO3. The copolymer presents four processes at different temperatures, i.e., evaporation of alcohol at 65 °C, decomposition of ungrafted alginate at 220 °C, copolymer decomposition at 298 °C, and degradation of fragments into carbonate at 423 °C. The evaluation of the action of fungal growth on the copolymer was higher than 50%, which means it is an excellent material to be biodegraded.

Influence of Carbon Nanotubes on Phase Composition, Thermal and Post-Heating Behavior of Cementitious Composites

This paper experimentally investigates the influence of carbon nanotubes (CNTs) on phase composition, microstructure deterioration, thermal behavior, and residual mechanical strengths of cementitious composites exposed to elevated temperatures. Cement mortars with small dosages of CNTs, 0.05% and 0.2% by weight of cement, were prepared and then heated at 25 °C, 150 °C, 200 °C, 450 °C, and 600 °C for two hours before being tested. The results show positive impact of the CNTs on the hydration process of cement mortar at room temperature and at higher temperatures up to 200 °C. Decomposition of the hydration products is obvious at 450 °C, whereas sever deterioration in the microstructure occurs at 600 °C. The nano reinforcement and bridging effect of the CNTs are obvious up to 450 °C. Thermal behavior characterization shows that CNTs incorporation enhances the thermal conductivity of the unheated and heat-treated mortar specimens. The decomposition of the hydration products needs more heat in the presence of CNTs. Finally, presence of CNTs significantly enhances the residual compressive and flexural strengths of heated mortar specimens for all studied temperatures.

Correlation between silane concentration and temperature operated toward conductivity of well-synthesized chitosan-fly ash composite membrane

Composite membrane is synthesized using well-synthesized chitosan as matrix crosslink with fly ash as filler and modified using 3-glicydyloxypro-pyltrimetoxy silane coupling agent. XRD analysis is carried out to characterize fly ash. While, FTIR characterization is conducted to determine the interaction between chitosan matrix and fly ash that has been modified using silane. The emergence of a new absorption at wave numbers 1118.64 cm-1 shows the inter-action between silane and fly ash. In addition, the widening of OH absorption shows that hydrogen bonds are formed between the silane and chitosan. The interaction is also demonstrated by the evenly distributed hills and valleys on AFM topography analysis. Characterizing the composite membrane with TGA analysis is done to determine thermal stability. While, proton conductivity of the composite membranes are measured using EIS. The highest conductivity values are obtained with the addition of 5 % silane concentration of 2.75x10-4 S cm-1 at room temperature, 3.995x10-4 S cm-1 at 40?C, and 3.909x10-4 S cm-1 at 60?C. On the contrary, measurements at 80?C, decomposition in all composite membranes occur. Thus, the crosslinked composite membrane chitosan - fly ash prepared by silane-crosslinking technique has potential to be applied with polymer electrolyte membrane fuel cell (PEMFC).

Peculiarities of doping of ZnO:Mn nanocrystals during their synthesis by the aerosol pyrolysis method

Samples of ZnO:Mn nanocrystals with Mn concentrations of 2 and 4 at.% were synthesized by ultrasonic aerosol pyrolysis. The synthesis was carried out at 550°C using aqueous solutions of zinc and manganese nitrates. The samples obtained were subjected to heat treatment at 550°C and 850°C in air for 1 hour. The study of the samples by XRD and EPR methods shows that during the synthesis the process of doping ZnO nanocrystals with manganese occurs only partially, on the surface, in the near-surface layer. Residues of the Mn impurity are located on the surface of nanocrystals and appear during annealing at 550°С in the form of manganese oxides (Mn2O3). During heat treatment at 850°C, decomposition of Mn2O3 and bulk doping of ZnO:Mn nanocrystals occur.

Wildfire-driven release of metal(loid)s from topsoils in a smelter-polluted semi-arid area: an experimental approach

<p>Wildfires contribute to global emissions of trace elements. This study focuses on highly polluted areas near an operating copper smelter and old mine-tailing disposal sites in Tsumeb (semi-arid north of Namibia), where wildfires frequently occur. Capturing of particulates windblown from the ore processing and smelting areas by vegetation (trees, grass) leads to the topsoil enrichment with metal(loid) contaminants (up to 7090 mg/kg Cu, 2070 mg/kg As, 4820 mg/kg Pb, 3480 mg/kg Zn, 75 mg/kg Cd, 7.66 mg/kg Hg). Experimental samples corresponding to representative biomass-rich topsoils (bushland with acacia and marula trees, grassland) were investigated using a combination of mineralogical and geochemical methods. Wildfires were simulated using a thermodesorption (TD) technique (75-670 °C; Hg) and an experimental setup composed of a temperature-controlled furnace (250-850 °C), an aerosol-filtering unit and a gas-trapping device (As, Cd, Cu, Pb, Zn). The obtained ashes were investigated to depict any mineralogical and chemical transformations in order to understand temperature-dependent release of metal(loid) contaminants during the simulated wildfire.</p><p>Thermodesorption experiments indicated that more than 90% of Hg was released at ~340 °C, which corresponded to predominant grassland-fire conditions. A comparison with the TD curves of the Hg reference compounds confirmed that the Hg in the biomass-rich topsoils occurs as a mixture of Hg bound to the organic matter and metacinnabar (black HgS), which exhibited similarities with the TD pattern of smelter flue dust residue. Temperature-dependent release of other metal(loid)s (As, Cd, Cu, Pb, Zn) is dependent on their solid-state speciation. Cadmium is released at ~750 °C, corresponding to the thermal decomposition of carbonates, in which Cd is mainly bound. Arsenic exhibits first remobilization step at <350 °C (decomposition of arsenolite, As<sub>2</sub>O<sub>3</sub>) and the second step at >650 °C corresponding to the instability of arsenates and As-rich slag glass. Other contaminants (Cu, Pb, Zn) were mainly bound in carbonates, slag particles and sulfides/sulfosalts. During the simulated wildfire, they were mainly retained in the ash and were remobilized to a lesser degree at >650 °C. Calculations indicated that at 850 °C (worse-case wildfire scenario) 2-17 % of total As, Cu, Pb and Zn, 27-79 % of total Cd and 100 % of Hg can be volatilized from these biomass-rich contaminated topsoils.</p><p>This study was supported by the Czech Science Foundation (GACR project no. 19-18513S) and a student grant from the Grant Agency of Charles University (GAUK no. 1598218).</p>