Soil Organic Carbon and Geochemical Characteristics on Different Rocks and Their Significance for Carbon Cycles

Soil organic carbon (SOC) is significant for soil quality and global carbon cycles. SOC was observed to be related to soil geochemistry, and soils originating from different bedrocks have different geochemical properties, but the effect of bedrock on SOC is still undefined. Soils overlying different bedrocks in Zhenxiong County and Weixin County were sampled. Specifically, soils in the mineral horizon, which are less affected by the external environment than surface soils, are focused on to reveal the effect of bedrock on SOC. Al/Ti, Fe/Ti, and Al/Fe indicate a soil–rock successive relationship. SOC contents in the mineral horizon are 0.19–2.74% (1.24% on average), and those in the surface horizon are 1.26–4.01% (2.63% on average). SOC contents in the surface and mineral horizons of the same bedrock are significantly positively correlated, implying that the bedrock is an important factor affecting SOC. SOC in the mineral horizon is related to the first transition metal ions. Significantly, positive correlations of SOC (p < 0.01) with Co, Cu, Ti, V, and Zn, and a positive correlation (p < 0.05) with Ni were observed in the mineral horizon. Organic transition metal complexation seems to play an important role in governing SOC in the mineral horizon. That is, the complexation maintains organic carbon stability, slows down its decomposition rate, and accumulates organic carbon. The Ca–SOC positive correlation in the mineral horizon exits because Ca also can complex with organic carbon. Co, Cu, and V–SOC positive correlations (p < 0.05) were also observed, but there were no significant positive correlations (p < 0.01) in the surface horizon because surface SOC had diversified sources. An SOC evolution model influenced by the bedrock was forwarded. Thus, the different soil geochemistry originating from different bedrocks should be noticed when SOC and global carbon cycles are discussed.

Effects of a simulated drying-rewetting cycle on microbial activity in soils degraded by post-fire erosion

<p>Large forest fires are expected to occur more frequently in some areas in the Iberian Peninsula with the current climate change predictions. Post-fire soil erosion is an important issue because of its potential large impact on soil carbon stocks and functioning. Addition of mulching to burnt soils has been proved as an effective measure to reduce post-fire erosion. This measure could also increase the stability of microbial activity to drought events, which are also expected to be more frequent in the region.</p><p>This study analyzes the response of three measurements of soil microbial activity (dehydrogenase activity, respiration rates and DNA concentration, as an index of microbial biomass) to a drying-rewetting cycle in soils that were burnt during large wildfires and that have been treated with different mitigation measures to prevent post-fire erosion.</p><p>Soil samples were collected from two field experiments on post-fire mitigation in Portugal, one in a Maritime Pine plantation over a Humic cambisol and one in a Strawberry tree stand over a Umbric leptosol. These sites were affected by large wildfires in june and october 2017, respectively. At the pine site, three treatments were compared: 1) control plots, where no treatment was applied and post-fire erosion rates were highest; 2) SM plots (Spontaneuos Mulching), in which spontaneous needle cast from the scorched pine crowns occurred (at an average rate of 0.5 kg m<sup>-2</sup>); 3) HM plots (Human Mulching), in which pine needles (were applied manually at a rate of 0.2 kg m<sup>-2</sup>. In addition, a nearby unburned Maritime Pine plantation was sampled (Unburnt). At the Strawberry tree site, control plots were compared with plots mulched with wheat straw (WM) at an application rate of 0.2 kg m<sup>-2</sup>. Sampling involved the organic surface horizon as well as the upper 15 cm of the Ah horizon.</p><p>Samples were preincubated during 28 days at 25°C and at 70% of field capacity. Afterwards, they were divided into two sets; one set was subjected to a drought event for 30 days that reduced soil moisture contents to 5-10% of field capacity. Subsequently, the drought replicates were rehydrated until they reached their initial moisture content, which was maintained for 14 days.</p><p>Dehydrogenase activity differed significantly between the burnt and unburnt soils, both for the drying and the re-wetting period. The burnt soils generally were more vulnerable to the drought episode than the unburnt soil. By contrast, dehydrogenase activity did not reveal significant impacts of the different mulching treatments compared to the untreated burnt soils. This was the case for both the organic surface horizon and the subsurface horizon. Respiration rates and DNA concentrations revealed basically the same results.</p><p>The three indicators of microbial activity studied here discriminated between burnt and unburnt soils, but they did not suggest any significant improvement in the response to drought by any of the post-fire emergency stabilization measures. Further research on the impacts of such measures on the resistance and resilience of microbial activity to drought should consider other soil quality indicators such as labile organic matter fractions.</p>

Assessing the role of soil microbial communities of natural forest ecosystem

In forests, edaphic microbial communities are involved in litter decomposition and soil forming processes, with major contribution to humification, especially bacteria and fungi being responsible for the main ecosystem services fulfilled by the soil. Research has been carried out aiming to characterize the structure and diversity of microbial communities in the Rendzic Leptosols (WRB) under natural deciduous forest from Visterna, Babadag Plateau and to assess their contribution to ecosystem services provided by soil. The paper presents the results of quantitative estimations and taxonomic composition of soil and litter communities of heterotrophic bacteria and fungi, identification of cellulolytic species, as well as the microbial biomass and global physiological activities expressed as soil respiration potential. More than a half of bacterial species were common in litter and soil (SI=57.14%) and were represented by dominant species of fluorescent or non-fluorescent pseudomonads and Bacillus subtilis but no similarity was found between the two fungal communities. Fungal populations included cosmopolitan species, such as antagonists and strong cellulolytic representatives of genera Penicillium, Trichoderma, Mortierella, Chaetomium, Epicoccum, Aspergillus. Microbial density and microbial biomass presented the highest values in the litter (684 mg C x kg-1 d.s.) and in surface horizon Am1 of soil profile than in the bottom layers. The highest diversity was found in Am1 horizon (0-5 cm) H’=1.983 bits and ε=0.869 for cellulolytic community. Soil respiration reflected the intense physiological activity of microbiome, with high values associated to numerous effectives of bacteria and fungi especially in surface horizon. Microorganisms identified contribute to formation of soil by recycling of nutrients, cellulose decomposition, the synthesis of stable organic matter (humic acids), aggregation of soil particles, biological control of pathogens by antagonistic activity. They improve plant uptake of water and nutrients by forming symbioses (ectomycorrhizae), thus modelling the structure of vegetation.

Phytoplankton production during austral summer in the Bransfield strait

Production characteristics of summer phytoplankton in the Bransfield Strait were studied in January 2020 during the 79th cruise of the R/V «Akademik Mstislav Keldysh» in the Atlantic sector of the Southern Ocean. The primary production, concentration of chlorophyll «a» and the relative content of pheophytin «a» in the sum of chlorophyll «a» and pheophytin «a» were determined. The concentration of chlorophyll «a» within the upper 125 m layer varied from 0.04 to 1.29 mg/m3 with an average value of 0.61 mg/m3. The maximal values were detected in the upper 20 m layer in the northwestern part of the section. The integral content of chlorophyll in the photic layer ranged from 16.67 to 62.43 mg/m2 with an average content of 36.66 mg/m2, decreasing from west to east. The relative content of pheophytin «a» in the euphotic layer varied from 20 % to 68 % with an average value of 42 %. The lowest values of pheophytin, indicating active photosynthetic processes, were observed in the northwestern part of the section at depths of up to 30 m, in the surface horizon in the central part of the strait, and at depths up to 80 m at the southeastern stations. The depth-integrated primary production was equal to 116–206 mg C/m2 per day, the most active synthesis of organic matter was revealed in the surface horizon. The assimilation number was 0.33–0.45 μg C/μg Chl/hour*L, reaching maximum values in the upper ten-meter layer of water. The northwestern part of the Bransfield Strait was the most productive.

Modeling of Infiltration Characteristics by the Modified Kostiakov Method: A Case Study in Thuong River Alluvial Soil in Vietnam

The purpose of this study was to apply the modified Kostiakov method to determine the soil infiltration rate and permeated water amount of Thuong River alluvial soil for orange plantations in Lang Giang district, Bac Giang province, Vietnam. The soil particle size ranged from 0.02 to 2.00mm mainly found in the surface horizon (>77.7%). The soil was slightly acidic in the surface horizon, and highly acidic in the subsurface horizons (pHKCl from 3.42 to 4.79). The organic matter content of the surface horizon was mederate, while it was very low in the other horizons. The total nitrogen (N) content was low (0.15%) in the surface horizon and very low in the subsurface horizons (0.02-0.06%) while the available N was medium. The total phosphorus (P) content in the surface horizon was high (0.4%) and medium in the other horizons. Available P in the surface horizon was high (18.6mg per 100g soil) and decreased in lower depths to only 0.3mg per 100g soil in the deepest (5th) horizon. The total and available potassium measurements were very low. A filtration characteristic model was developed by using the modified Kostiakov method for alluvial soil. The constant values a, a, and b of the equation y = ata + b were 0.8035, 0.758, and 0.00346, respectively, which were smaller than 1. The average percentage difference between the actual and calculated values by the model was only 0.141%, indicating that the calculated values can accurately predict the actual data measurements in the field.

Modeling of Infiltration Characteristics by the Modified Kostiakov Method: A Case Study in Thuong River Alluvial Soil in Vietnam

The purpose of this study was to apply the modified Kostiakov method to determine the soil infiltration rate and permeated water amount of Thuong River alluvial soil for orange plantations in Lang Giang district, Bac Giang province, Vietnam. The soil particle size ranged from 0.02 to 2.00mm mainly found in the surface horizon (>77.7%). The soil was slightly acidic in the surface horizon, and highly acidic in the subsurface horizons (pHKCl from 3.42 to 4.79). The organic matter content of the surface horizon was mederate, while it was very low in the other horizons. The total nitrogen (N) content was low (0.15%) in the surface horizon and very low in the subsurface horizons (0.02-0.06%) while the available N was medium. The total phosphorus (P) content in the surface horizon was high (0.4%) and medium in the other horizons. Available P in the surface horizon was high (18.6mg per 100g soil) and decreased in lower depths to only 0.3mg per 100g soil in the deepest (5th) horizon. The total and available potassium measurements were very low. A filtration characteristic model was developed by using the modified Kostiakov method for alluvial soil. The constant values a, a, and b of the equation y = ata + b were 0.8035, 0.758, and 0.00346, respectively, which were smaller than 1. The average percentage difference between the actual and calculated values by the model was only 0.141%, indicating that the calculated values can accurately predict the actual data measurements in the field.

Mytilidae fouling of some hydraulic structures in the coastals water areas of Sevastopol (Crimea, Black sea)

The conditions assessment of hydrobiont`s settlements in a various water area is of great theoretical and practical importance. This issue is particularly relevant for organisms that create abundant settlements on the artificial substrates in a coastal water areas. The evaluation of the modern (2015) condition of mytilidae fouling of some hydraulic structures of various coastal waters of Sevastopol was made. Based on these data, the calculation of the biofilters capacity formed by mussels and mytilasters in the surface horizon of hydraulic structures was made. It was assigned that on the underwater part of the embankment of the Sevastopol Bay, a biofilter 3 times exceled in those in the water area Kruglaya bay and park Pobedy. The assessment of the current state metilenovoj fouling of some hydraulic structures for various coastal water areas of the Sevastopol found that the investigated structures mytilaster was prevalent. The number of mussels ranged from 403 to 14726 specimens∙m–2. The number of mytilaster ranged from 5690 to 33802 ind.∙m–2.