This study investigated seasonal changes in litter and soil organic carbon contents of deciduous and coniferous forests at two altitudes (500 and 1000 m a.s.l.), which were used as proxies for temperature changes. To this aim, adjacent pine (P500 and P1000) and deciduous forests (downy oak forest at 500 m a.s.l. and beech forest at 1000 m a.s.l., D500 and D1000, respectively) were selected within two areas along the western slope of a calcareous massif of the Apennine chain (central Italy). Periodic sampling was carried out within each site (a total of 19 sampling dates: 6 in autumn, 4 in winter and spring, and 5 in summer), taking each time an aliquot of the upper mineral soil horizon and measuring litter thickness and CO2 emission from the soil. The samples were then analyzed for their content of organic C, total N, water-soluble organic C and N (WEOC and WEN, respectively), and the natural abundance of 13C and 15N. Soil and litter C and N stocks were calculated. The chemical and isotopic data suggested that organic C and N transformations from litter to the upper mineral soil horizon were controlled not only by temperature but also by the quality (i.e. C:N ratio) of the plant material. In particular, the more the temperature decreased, the more the quality of the organic matter would influence the process. This was clearly showed by the greater 13C fractionation from litter to soil organic matter (SOM) in D1000 than in P1000, which would indicate a higher degree of transformation under the same thermal condition of the plant residues from the deciduous forest, which were characterized by a more balanced C:N ratio than the pine litter. However, while at 500 m altitude a significant SOM 13C fractionation and a parallel increase in soil CO2 emissions occurred in the warmer seasons, no seasonal delta 13C variation was observed at 1000 m for both forests, despite the different quality of SOM derived from deciduous and coniferous forests. Our findings suggested that organic C and N transformations from litter to the upper soil mineral horizon were greatly controlled by the quality of the plant residues, whereas soil temperature would seem to be the major driver for the seasonal evolution of SOM. This study, by considering two different vegetation types (deciduous and coniferous), allowed to evaluate the combined interactions between the plant residue quality and temperature in controlling litter and SOM mineralisation/accumulation processes.

In this article, the mechanical properties and frost resistance of soil solidification rock (SSR) recycled coarse aggregate concrete (RCAC) prepared by using SSR as a total replacement for ordinary silicate cement were investigated, based on which bio-mineralisation was used to improve the properties of recycled aggregate (RCA) in SSR RCAC as a means of improving the performance of SSR RCAC. The results showed that the mineralisation modification by Bacillus pasteurii enhanced the apparent density of RCA by 3.5%, reduced the water absorption by 20.4% and decreased the crushing value by 17.6%. SSR RCAC prepared using mineralised RCA increased its compressive and flexural strengths by 91.2% and 33.3%, respectively, at the age of 28 days, and maintained 93.5% relative dynamic elastic modulus after 225FTCs, with a 100% enhancement in frost durability factor compared with the untreated group. Although the slow early hydration of SSR resulted in low initial concrete strength, the combination of biomineralisation enhanced the early compressive strength growth by about 140%. It increased the post-freeze-thaw compressive strength residual to 67%. The SSR RCAC proposed in this study provides a solution with both environmental benefits and engineering applicability for infrastructure such as roads and bridges in seasonal permafrost regions.

Vegetated blue carbon environments have the potential to sequester large amounts of carbon due to their high productivity and typically saturated, anaerobic soils that promote carbon accumulation. Despite this, and the coupling of Fe-S-C cycling processes, the influence of iron (Fe) in acid sulfate soils (ASSs) on carbon sequestration in blue carbon environments has yet to be systematically explored. To address this knowledge gap, this review provides an overview linking the current state of blue carbon studies with the influence of Fe on soil organic carbon (SOC), as well as the potential influence ASSs have on carbon sequestration. A systematic literature review on SOC stock in blue carbon studies using the Web of Science database yielded 1477 results. Studies that investigated the drivers of carbon accumulation in blue carbon studies were restricted to vegetation species/structure and geomorphic setting, and few focused on soil properties and type. Iron both protects and enhances SOC decomposition depending on its redox state. Under oxic conditions, Fe oxyhydroxides can protect SOC via adsorption, co-precipitation and by acting as a cement in soil aggregates. Iron can also increase SOC decomposition under oxic conditions due to Fenton reactions. However, under anoxic conditions, SOC mineralisation can also occur as Fe acts as an electron transporter in dissimilatory reductions. ASSs contain a range of Fe minerals, but the oxidation of Fe sulfides can result in soil acidification (pH < 4) and subsequent impacts, such as a decline in vegetation health, poor water quality and infrastructure damage. Therefore, potential SOC protection by Fe under oxic conditions may come at the cost of soil acidification in ASSs, while maintaining anoxic conditions prevents acidification but may enhance SOC decomposition. Future studies on the influence of ASSs on Fe-S-C cycling and carbon sequestration in blue carbon environments are important, particularly for 'hotspots' such as Australia.

This study aimed to enhance the efficiency of microbial-induced carbonate precipitation (MICP) for reinforcing sandy soil by inspiring natural processes involving microbial-induced carbon cycling and carbonation. The experiment focused on enhancing MICP curing of sandy soil using carbonic anhydrase (CA), which significantly increases the reaction rate of CO2 hydration (10(8) times faster) and facilitates the rapid hydration of CO2 (produced by urease (UA) decomposition of urea) to form a substantial amount of carbonate. The effect of carbonic anhydrase on MICP-reinforced sandy soil and its underlying mechanism were systematically examined through a combination of macroscopic physical and mechanical tests and microfabrication tests. The results showed that: (1) CA significantly increases the production of cement during the microbial consolidation of sandy soils, and the optimum dose of carbonic anhydrase producing bacteria is reached at about 4%, which increases the production of cement by 105.3%, compared with conventional MICP. (2) The incorporation of CA improves the compressive strength and resistance of the cured body. In the range 0.25-4.00%, the unconfined compressive strength of the solidified soil sample increases with the increase of the CA bacteria content. The strength of the cured soil sample reaches 1.915 MPa when the content is 4%, which is 8.54 times the strength of the conventional MICP cured sample. (3) CA does not change the product of the MICP process, it is still calcite, but after adding CA, the grain size of the calcite is larger, the shape of the hexahedron is more standardised, and the mechanical properties are improved. (4) In the process of MICP, urease and CA co-precipitate calcium carbonate-cured sandy soil. CA can significantly accelerate the rate of urea-generated CO2 hydrate and form HCO3- and CO32-, providing more favourable conditions for mineralisation.

Palsa peatlands, permafrost-affected peatlands characteristic of the outer margin of the discontinuous permafrost zone, form unique ecosystems in northern-boreal and arctic regions, but are now degrading throughout their distributional range due to climate warming. Permafrost thaw and the degradation of palsa mounds are likely to affect the biogeochemical stability of soil organic matter (that is, SOM resistance to microbial decomposition), which may change the net C source/sink character of palsa peatland ecosystems. In this study, we have assessed both biological and chemical proxies for SOM stability, and we have investigated SOM bulk chemistry with mid-infrared spectroscopy, in surface peat of three distinct peatland features in a palsa peatland in northern Norway. Our results show that the stability of SOM in surface peat as determined by both biological and chemical proxies is consistently higher in the permafrost-associated palsa mounds than in the surrounding internal lawns and bog hummocks. Our results also suggest that differences in SOM bulk chemistry is a main factor explaining the present SOM stability in surface peat of palsa peatlands, with selective preservation of recalcitrant and highly oxidized SOM components in the active layer of palsa mounds during intense aerobic decomposition over time, whereas SOM in the wetter areas of the peatland remains stabilized mainly by anaerobic conditions. The continued degradation of palsa mounds and the expansion of wetter peat areas are likely to modify the bulk SOM chemistry of palsa peatlands, but the effect on the future net C source/sink character of palsa peatlands will largely depend on moisture conditions and oxygen availability in peat.