Soil Organic Carbon Availability Research Articles

Soil Carbon Storage in Forest and Agriculture Land Use in the Tanralili Watershed

Soil is a long-term store of carbon in terrestrial ecosystems and plays an important role in the global carbon cycle. Sequestration of soil organic carbon is considered as one of the climate change mitigation strategies and is related to carbon storage in the soil. This study aims to determine soil carbon storage based on land use in forest areas and dry land agriculture in the Tanralili watershed.Soil samples were taken at a depth of 0-10 cm, 10-20 cm, and 20-30 cm, repeated three times in succession purposive sampling on the use of forest land and dry land agriculture. Soil chemical properties observed are bulk density, soil organic carbon, nitrogen, and C:N ratio. Research results show that soil carbon storage is higher in forest land use compared to dry land farming. Forest land with mixed tree crop species had the highest carbon store, namely 96 tons/ha, while dry land with horticultural crop types rotated with various crops had the lowest carbon store, namely 43 tons/ha. Soil carbon accumulation is most abundant in the topsoil layer of 0-10 cm. The availability of soil organic carbon can be seen from the C:N ratio, increasing C:N will reduce the ability to absorb soil carbon.

Woolly beech aphid infestation reduces soil organic carbon availability and alters phyllosphere and rhizosphere bacterial microbiomes

PurposeThe woolly beech aphid thrives on European beech leaves, which has complex direct and indirect impacts on above- and belowground processes. A mechanistic understanding of insect-mediated changes in organic carbon (OC) availability for microbial life and its implications for element cycling is still lacking. This study aims at disentangling aphid-induced effects on phyllosphere and rhizosphere bacterial communities, as well as investigating feedbacks to OC transfer from the canopy to the mineral soil.MethodsFollowing 2.5 months of infestation, we tracked the fate of OC (13CO2 pulse-labelling) in several compartments of beech sapling – soil mesocosms over 5 days. In ecosystem solutions, water extracts and soil/plant compartments we determined OC and N and solid δ13C. Bacterial community structure (16S rRNA gene targeted amplicon sequencing and quantitative PCR) and metabolite profiles (LC-qTOF-MS) were analysed.ResultsWe found significantly higher aphid-mediated inputs of OC within throughfall. Honeydew-derived C on infested leaves was inconsequential for total phyllosphere bacterial abundances, but verifiably affected the community structure. In all soil compartments, cold-water extractable OC pools declined significantly by frequent inputs of readily available OC. This pattern might relate to reductions in rhizodepositions and altered microbial processing by accelerated soil C-mineralization. As a result, the abundance of metabolites changed significantly in different ecosystem solutions.ConclusionsOur findings attest that insect infestations induce distinct direct and indirect effects on plant-insect-microbiome interactions leading to marked alterations in C dynamics. This integrated approach improves our understanding on microbial dynamics and biogeochemistry and evaluates the role of insects for ecosystem processes.

Increased Litter Greatly Enhancing Soil Respiration in Betula platyphylla Forests of Permafrost Region, Northeast China

The change of litter input can affect soil respiration (Rs) by influencing the availability of soil organic carbon and nutrients, regulating soil microenvironments, thus resulting in a profound influence on soil carbon cycle of the forest ecosystem. We conducted an aboveground litterfall manipulation experiment in different-aged Betula platyphylla forests (25-, 40- and 61-year-old) of the permafrost region, located in the northeast of China, during May to October in 2018, with each stand treated with doubling litter (litter addition, DL), litter exclusion (no-litter, NL) and control litter (CK). Our results indicated that Rs decreased under NL treatment compared with CK treatment. The effect size lessened with the increase in the stand age; the greatest reduction was found for young Betula platyphylla forest (24.46% for 25-year-old stand) and tended to stabilize with the growth of forest with the reduction of 15.65% and 15.23% for 40-and 61- year-old stands, respectively. Meanwhile, under DL treatment, Rs increased by 27.38%, 23.83% and 23.58% on 25-, 40- and 61-year-old stands, respectively. Our results also showed that the increase caused by DL treatment was larger than the reduction caused by NL treatment, leading to a priming effect, especially on 40- and 61-year-old stands. The change in litter input was the principal factor affecting the change of Rs under litter manipulation. The soil temperature was also a main factor affecting the contribution rate of litter to Rs of different-aged stands, which had a significant positive exponential correlation with Rs. This suggests that there is a significant relationship between litter and Rs, which consequently influences the soil carbon cycle in Betula platyphylla forests of the permafrost region, Northeast China. Our finding indicated the increased litter enhanced the Rs in Betula platyphylla forest, which may consequently increase the carbon emission in a warming climate in the future. It is of great importance for future forest management in the permafrost region, Northeast China.

Changes in Microbial Community as Affected by Soil Compaction and Organic Matter Amendment

Soil compaction may threaten agricultural sustainability through its impact on altering soil microbial structure and function. This occurs as a result of the limitation of air permeability and oxygen availability, which has implications for soil nutrition and soil-borne disease. The present study aimed to assess compaction effect on changes of soil microbial communities over time and whether these changes were influenced by organic matter (OM) amendment. An experiment consisted of two levels of compaction (1.1 and 1.4 g cm-3) and two levels of OM (0 and 10 g kg-1). Soil microbial community attributes investigated were soil respiration, microbial biomass, activity and diversity. Data on microbial attributes were obtained from three-sampling times (10; 20; 80 days). The results showed that microbial respiration, biomass, activity and diversity changes over time and were higher in compacted soil than uncompacted soil in day-10, but then higher in uncompacted soil at day-20. An increase in microbial biomass, activity and diversity in uncompacted soil within 20 days were presumably associated with the availability of soil organic carbon (SOC), void space and aeration. However, microbial biomass, activity and diversity across the treatments declined in day-80, where bacteria and fungi performed a different pattern. Bacterial community was lower in compacted soil at day-80 and this might be an indicator of the effect of compaction and of the reduction in SOC availability. Meanwhile, fungal community was found to be higher in compacted soil over 80 days confirming the ability of fungal communities to survive under such an environment.

Influence of Altered Microbes on Soil Organic Carbon Availability in Karst Agricultural Soils Contaminated by Pb-Zn Tailings.

Soil organic carbon (SOC) availability is determined via a complex bio-mediated process, and Pb-Zn tailings are toxic to the soil microbes that are involved in this process. Here, Pb-Zn-tailings- contaminated karst soils with different levels (paddy field > corn field > citrus field > control group) were collected to explore the intrinsic relationship between Pb-Zn tailings and microbes due to the limited microbial abundance in these soils. The SOC concentration in the paddy fields is the highest. However, based on the soil microbial diversity and sole-carbon-source utilization profiles, the rate of SOC availability, McIntosh index, Shannon-Wiener diversity index, Simpson’s diversity index and species richness are the lowest in the rice paddy soils. According to the results of Illumina sequencing of the 16S rRNA gene, Acidobacteria and Proteobacteria are the dominant phyla in all samples, accounting for more than 70% of the reads, while the majority of the remaining reads belong to the phyla Verrucomicrobia, Chloroflexi, Actinobacteria, Bacteroidetes, and Nitrospirae. We also observed that their class, order, family, genus and operational taxonomic units (OTUs) were dependent on SOC availability. Pearson correlation analysis reveals that L-asparagine utilization profiles show significant positive correlation with OTUs 24, 75, and 109 (r = 0.383, 0.350, and 0.292, respectively), and malic acid utilization profiles show significant positive correlation with OTUs 4, 5, 19, 27 (Bradyrhizobium), 32 (Burkholderia), 75 and 109 (r = 0.286, 0.361, 0.387, 0.384, 0.363, 0.285, and 0.301, respectively), as also evidenced by the redundancy analysis (RDA) biplot and heat map. These results indicate that the most abundant groups of bacteria, especially the uncultured facultative Deltaproteobacteria GR-WP33-30 (OTU 24), after long-term acclimation in heavy metal-contaminated soil, are associated with the variance of labile carbon source such as L-asparagine and may have considerable control over the stability of the vast SOC pool in karst surface soils with different agricultural land-use practices. These findings can expand our understanding of global soil-carbon sequestration and storage via changes in microbial community structure of the most abundant species.

Ameliorating Effects of Fungus Chaff and Its Biochar on Soil Acidity

A biochar was generated from fungus chaff at 300 °C, and the ameliorating effects of fungus chaff and its biochar on an acidic Ultisol were compared using incubation experiments. Incorporation of fungus chaff and its biochar significantly increased soil pH and soil exchangeable base cations but decreased soil exchangeable acidity. The ameliorating effect was greater for the biochar than the fungus chaff, and thus the biochar was a better amendment for acidic soil than its feedstock of fungus chaff. The biochar ameliorated soil acidity mainly through the release of its contained alkaline substances, while fungus chaff increased pH of acidic soils through two mechanisms: release of alkaline substances and inhibition of soil nitrification. The incorporation of fungus chaff increased soil-available organic carbon and thus accelerated the microbial assimilation of inorganic nitrogen, while incorporation of fungus chaff biochar enhanced nitrification due to increased soil pH.

Turnover and availability of soil organic carbon under differentMediterranean land‐uses as estimated by13Cnatural abundance

SummarySoil organic matter (SOM) is an important factor in ecosystem stability and productivity. This is especially the case for Mediterranean soils suffering from the impact of human degradation as well as harsh climatic conditions. We used the carbon (C) exchange resulting fromC3‐C4andC4‐C3vegetation change under field conditions combined with incubations under controlled conditions to evaluate the turnover and availability of soil organicCunder different land‐uses. The 40‐year succession ofHyparrenia hirtaL. (C4photosynthesis) after more than 85 years of olive tree (Olea europaeaL.;C3photosynthesis) growth led to the exchange of 54% of soil organic C fromC3toC4forms. In contrast, 21 years of vine (Vitis viniferaL.) growing afterH. hirtadecreased the organic C content to 57%. Considering this exchange and decrease as well as the periods after the land‐use changes, we calculated the mean residence time (MRT) of soil C of different ages. TheMRTof C under grassland dominated byH. hirtawas about 19 years, but was 180 years under the vineyard. The rates of C accumulation under theH. hirtagrassland were about 0.36 Mg C ha−1 year−1. In contrast, the rates ofClosses after conversion from natural grassland to a vineyard were 1.8 times greater and amounted to 0.65 Mg C ha−1 year−1. We conclude that changes of land use from naturalMediterranean grassland to a vineyard lead to very largeClosses that cannot be compensated for over the same periods.

Silicate fertilization in no-tillage rice farming for mitigation of methane emission and increasing rice productivity

Agricultural practices mostly influence methane (CH4) emissions from rice field, which must be controlled for maintaining the ecosystem balance. No-tillage farming with chemical amendments having electron acceptors could be an effective mitigation strategy in CH4 emissions from irrigated rice (Oryza sativa L.) field. An experiment was conducted in Korean paddy field under tillage and no-tillage farming practices with silicate iron slag amendments (1–4Mgha−1) for suppressing CH4 emissions and maintaining rice productivity. It was found that CH4 emissions from the no-tillage rice field significantly decreased as compared to that of tilled field, irrespective of silicate amendments. The total seasonal CH4 flux from the control tillage and control no-tillage plots were recorded 38.1 and 27.9gm−2, respectively, which were decreased by 20% and 36% with 4Mgha−1 silicate amendment. Silicate fertilization (4Mgha−1) with no-tillage system decreased total seasonal CH4 flux by 54% as compared to that of control tillage plot. This is most likely due to the higher concentrations of active iron and free iron oxides in the no-tilled rice field as compared to that of tilled field under silicate fertilization, which acted as electron acceptors and contributed to decrease CH4 emission. In addition, the improved soil porosity and redox potential, rice plant growth parameters such as active tillering rate, root volume and porosity, etc. in combination increased the rhizosphere oxygen concentrations and eventually suppressed CH4 emission during the rice growing season. The leaf photosynthetic rate was significantly increased with 4Mgha−1 silicate amendment, which ultimately increased grain yield by 18% and 13% in the tilled and no-tilled rice field, respectively. CH4 flux showed a strong positive correlation with the availability of soil organic carbon, while there were negative correlations with soil porosity, soil pH, soil Eh, and the content of active iron and free iron oxides in soil.

Regulators of heterotrophic microbial potentials in wetland soils

Potential rates of aerobic respiration, denitrification, sulfate reduction and methanogenesis were investigated in 10 different wetland soils with a wide range of biogeochemical characteristics, with the objective of determining relationships between process rates and soil properties. Electron acceptor amendments to methanogenic soils caused gradual (1–13 d) to immediate transitions in electron flow from methanogenesis to alternate electron acceptors. Rates of organic C mineralization ranged between 0.2 and 34 μmol C g −1 d −1 and averaged three times faster with O 2 as compared to alternate electron acceptors. There was no significant difference between rates of organic C mineralization (CO 2+CH 4 production) under denitrifying, sulfate-reducing and methanogenic conditions, indicating that soil organic carbon availability was similar under the different anaerobic conditions. Rates of electron acceptor consumption ranged between 1 and 107 μmol g −1 d −1 for O 2, 0.5 and 9.3 μmol g −1 d −1 for NO 3 −, 0.1 and 11.1 μmol g −1 d −1 for SO 4 2− and 0.1 and 6.2 μmol g −1 d −1 for CO 2. Heterotrophic potentials in wetland soils were strongly correlated with inorganic N and several available C indices (total, dissolved and microbial C), but not with pH or dissolved nutrients (P, Ca 2+, Mg 2+, Fe(II)). Microbial activity–soil property relationships determined in this study may be useful for predicting the fate of pollutants that are influenced by microbial oxidation–reduction reactions in different types of wetland soils.

The influence of soil compaction on microbial biomass and organic carbon turnover in micro-and macroaggregates

Agricultural practices with high traffic and with low input of organic material into the soil result in the deterioration of soil structure leading to soil compaction. It is accompanied by the reduction of gas exchange and by limited colonizable habitats. The changes in microbial biomass and its activity cannot be readily explained by interactions of altered gas and water exchange. In order to explain the differences in biological activity of compacted and uncompacted soils, the soil structure related microbial turnover was observed. The content and the availability of soil organic carbon, microbial biomass and respiration activity in micro- (< 0.2 mm) and macroaggregates (2–5 mm) from the plots with different wheel induced compactive treatments were measured in the layers 0–10, 10–20 and 20–30 cm. In the topsoil (0–30 cm) of the wheel tract plot the higher content of total carbon (0.942% C org) and higher availability of C than in the no traffic (0.907% C org) and high traffic (0.908% C org) plots were established. The compacted plots contained less total carbohydrates in macroaggregates. The average value of microbial biomass was lower only in the high traffic plot — 99 μg C g −1 against 159 in the no traffic plot. The compacted plots differed from the other treatments in the distribution of microbial biomass in soil layers; the maximum of microbial biomass was in the lower layers (20–30 cm) instead of in the surface layer. The “potential” activity of microbial biomass reached maximal values in the high traffic plot.

Effects of storing soils at various temperatures on their capacity for denitrification

The effects of storing soils at various temperatures on their capacity for denitrification of nitrate were studied by determining the influence of storage of field-moist soils at −4, 4 or 30°C for 2. 10 or 30 days on their ability to reduce nitrate to nitrous oxide when incubated anaerobically with nitrate for various times in the presence of acetylene. The data obtained showed that storage of soils at 4°C for 2, 10 or 30 days did not significantly affect their capacity for denitrification, whereas storage at −4°C for 2, 10 or 30 days led to a marked increase in denitrification capacity. Storage at 30°C for 2 days did not have a significant effect on the denitrification capacity of the soils studied, but storage of these soils at 30°C for 10 or 30 days led to a decrease in their denitrification capacity. The effects of storing soils at −4°C on their capacity for denitrification cannot be attributed solely to changes in the availability of soil organic carbon to denitrifying microorganisms as a result of storage because they were evident even when soils stored at −4°C were treated with readily-available organic carbon (as mannitol) before anaerobic incubation with nitrate.