Soil Carbon Mineralization Research Articles

Drying-rewetting of permanent pasture and agricultural soils induces a shift towards microbial use of more C-rich organic matter

Rewetting dry soil induces enormous dynamics in microbial growth and biogeochemistry. The temporal dynamics of soil carbon (C) mineralization following drying-rewetting (D/RW) have been widely documented. However, there have been far fewer assessments of gross nitrogen (N) mineralization, and it remains unclear how C and N mineralization dynamics are linked following D/RW events. To address this, soils were sampled from permanent pasture and tilled-and-cropped agricultural fields at two depths (“shallow” soils from 0 to 5 cm depth and “deep” soils from >15 cm depth), with soil C mineralization and gross N mineralization, along with responses in bacterial and fungal growth, measured at high temporal resolution after D/RW. Although soil C mineralization and gross N mineralization were both stimulated by D/RW, the dynamics in C and N mineralization were transiently decoupled. In the cropland soils from both depths, C mineralization peaked immediately and then declined, while N mineralization was sustained at a high level. Similarly, in the deep pasture soil, N mineralization peaked immediately and then declined while C mineralization was maintained at a high level. The shallow pasture was the only soil where C mineralization and N mineralization dynamics were clearly linked after D/RW, both during the first 24 hours, and throughout the 7-day study. Interestingly, in all cases, the ratio of soil C mineralization to N mineralization after D/RW was higher than in moist control soils, suggesting a consistent shift towards microbial use of more C-rich organic matter. The shift was especially pronounced in the pasture soils, where the C-to-N ratio of substrate used after D/RW was more indicative of plant-residues than microbial necromass. The δ13C-signature of respired CO2 was also consistently lower after D/RW compared to that of the moist control – particularly for the pasture soils – providing further evidence that the organic matter used by microorganisms after D/RW was more recently plant-derived than that targeted by microorganisms under optimal moisture conditions. Together, these results highlight that while C and N mineralization are both stimulated by D/RW, changes in mineralization rates do not necessarily occur in parallel, with shifts in the ratio of C-to-N mineralization reflecting shifts in the source of organic matter being used by microorganisms.

Evaluating the Effect on Cultivation of Replacing Soil with Typical Soilless Growing Media: A Microbial Perspective

Bacteria and fungi are good indicators for soil health as well as soilless growing media (SGM) health. However, there is very limited information about the fungal and bacterial communities for SGM. In the present study, coir substrate and peat-based substrate were used as typical SGM under drip irrigation and tidal irrigation to understand the situation of fungal and bacterial communities by high-throughput sequencing technology. In this study, both environmental factors and microbial communities were significantly affected by SGM type and irrigation pattern, in which SGM type played a major role and irrigation pattern played a minor role. The bacterial phyla Actinobacteriota and Proteobacteria and the fungal phyla Ascomycota were more closely related to environmental factors including EC, pH, NO3−, NH4+ and ω as well as urease and phosphatase. The bacterial and fungal communities in the two SGM had some similarities with those in soil. In addition, the functions of the soil, including key soil organisms, carbon mineralization, wood decomposition, nitrification, denitrification, carbon fixation, nitrogen fixation and methanotrophy, could be basically performed by the two SGM. In general, the SGM should possess common soil capabilities according to bacterial and fungal analyses, but there are numerous fungi of unknown function that need be addressed in the future. Meanwhile, these results improve our understanding of the correlation between the environmental factors and the microbiome, and provide basic guidance for management and research on SGM in the future.

Hydrodynamic and geochemical controls on soil carbon mineralization upon entry into aquatic systems

Erosion is the most widespread form of soil degradation and an important pathway of carbon transfer from land into aquatic systems, with significant impact on water quality and carbon cycle. However, it remains debatable whether erosion induces a carbon source or sink, and the fate of eroded soil carbon in aquatic systems remains poorly constrained. Here, we collect 41 representative soils from seven erosion-influenced basins and conduct microcosm simulation experiments to examine the fate of soil carbon under three different scenarios. We showed that soil carbon mineralization was generally promoted (by up to 10 times) in water under turbulence relative to in soils, but suppressed under static conditions upon entering into aquatic systems. Moreover, the enhancement of mineralization in turbulent systems is primarily related to soil aggregate content, while suppression in static systems positively relates to macromolecule abundance, indicating that soil geochemistry affects the magnitude of hydrodynamic effects on carbon mineralization. Random forest model further predicts that erosion may induce significant carbon sources in basins dominated by turbulent waters and aggregate-rich soils. Our findings demonstrate hydrodynamic and geochemical controls on soil carbon mineralization upon delivery into aquatic systems, which is a non-negligible part of the boundless carbon cycle and must be considered when making region-specific conservation strategies to reduce CO2 emissions from inland waters.

Dependence of cumulative CO2 emission and microbial diversity on the wetting intensity in drying-rewetting cycles in agriculture soil on the Loess Plateau

Altered drying-rewetting (DRW) procedures due to climate change may influence soil microbial properties and microbially-mediated carbon cycling in arid and semi-arid regions. However, the effects of DRW of different intensities on the microbial properties and respiration are not well understood. Thus, the responsive patterns of microbial communities and carbon mineralization in agriculture soil on the Chinese Loess Plateau to DRW treatments with different wetting intensities (5%–25% and 5%–36%) and frequency (1-cycle to 4-cycle) were investigated. Continuous moisture levels of 5%, 25% and 36% were used as control. Results revealed that the reduction of bacterial diversity and richness were greater for 5%–36% than 5%–25% treatment, while diversity of fungi was similar for different wetting intensities. Bacterial communities became clustered by wetting intensity rather than cycle number, however fungal community was unaffected by DRW. The complexity of bacterial co-occurrence network increased because of higher nodes, edges, average degree, diameter and average cluster coefficient after 4-cycles, and the interaction was more complex after 1-cycle for fungi. Rewetting caused a pulse-like increase of respiration rate, and the pulse amplitude was greater for DRW with high rewetting intensity and decreased with the increase of cycle number. The cumulative CO2 emission for DRW treatments was lower than that for the continuous moisture conditions. The net reduction of carbon release for 5%–36% treatment was 1.18 times higher than that for 5%–25% treatment. Our study provides experimental evidence of the positive potential of DRW processes for maintaining soil carbon stock in an agriculture system on the Loess Plateau.

Responses of soil carbon and nitrogen mineralization to nitrogen addition in a semiarid grassland: The role of season

Elevated atmospheric N deposition can profoundly alter soil carbon (C) mineralization (Cmin) and nitrogen (N) mineralization (Nmin), which could severely impact long-term productivity of grassland ecosystem. However, little is known about how N addition, season, and their interaction affect soil Cmin and Nmin rates and their relationships by regulating soil abiotic and biotic factors. Here we investigated the seasonal variations in soil Cmin and Nmin rates and their relationship in response to multi-level N additions in a semiarid grassland in 2014–2015, and further identified direct and indirect pathways by which soil abiotic and biotic factors regulated these variations using structural equation modeling. We documented the statistically significant impacts of N addition and its interaction with season on soil Cmin rates. In contrast, only a significant seasonal effect on the soil Nmin rate was observed. Random forest analysis revealed that across all seasons, dissolved organic carbon (DOC), soil water content (SWC), catalase, urease, sucrase, microbial biomass carbon (MBC), soil organic carbon (SOC) to total nitrogen (TN) ratio, and TN were the most pivotal predictors of the soil Cmin rate. Comparatively, catalase, MBC, DOC, NO3–-N, urease, TN, NH4+-N, SWC, and the MBC to microbial biomass nitrogen (MBN) ratio were the most dominant drivers of the soil Nmin rate. SEM results indicated that the identified potential drivers that regulated the soil Cmin and Nmin rates in response to N addition varied seasonally. Additionally, N addition decoupled the soil Cmin and Nmin rates, which was a consistent relationship among most seasons. In summary, our results show that, in this semiarid grassland, current N additions can enhance soil N immobilization across all seasons; however, its impacts on soil C sequestration were seasonally variable. These findings provide evidence that season and its interactions with elevated atmospheric N deposition have important implications for the grassland biogeochemical cycling.

Responses of soil microbial carbon use efficiency to short-term nitrogen addition in Castanopsis fabri forest

As an important parameter regulating soil carbon mineralization, microbial carbon use efficiency (CUE) is essential for the understanding of carbon (C) cycle in terrestrial ecosystems. Three nitrogen supplemental levels, including control (0 kg N·hm-2·a-1), low nitrogen (40 kg N·hm-2·a-1), and high nitrogen (80 kg N·hm-2·a-1), were set up in a Castanopsis fabri forest in the Daiyun Mountain. The basic physical and chemical properties, organic carbon fractions, microbial biomass, and enzyme activities of the soil surface layer (0-10 cm) were measured. To examine the effects of increasing N deposition on microbial CUE and its influencing factors, soil microbial CUE was measured by the 18O-labelled-water approach. The results showed that short-term N addition significantly reduced microbial respiration rate and the activities of C and N acquisition enzymes, but significantly increased soil microbial CUE. β-N-acetyl amino acid glucosidase (NAG)/microbial biomass carbon (MBC), microbial respiration rate, β-glucosidase (BG)/MBC, cellulose hydrolase (CBH)/MBC, and soil organic carbon content were the main factors affecting CUE. Moreover, CUE significantly and negatively correlated with NAG/MBC, microbial respiration rate, BG/MBC, and CBH/MBC, but significantly and positively correlated with soil organic carbon. In summary, short-term N addition reduced the cost of soil microbial acquisition of C and N and microbial respiration, and thus increased soil microbial CUE, which would increase soil carbon sequestration potential of the C. fabri forest.

Effects of Different Organic Amendments on Soil Improvement, Bacterial Composition, and Functional Diversity in Saline–Sodic Soil

The agricultural productivity of farmland in Northeast China’s Liaohe Plain is restricted by the salinity and sodicity of the soils, which have additionally low organic matter content. In order to improve saline–sodic soils, organic amendments are frequently applied. Our objective was to clarify how different organic amendments affect the diversity and composition of soil microbes, as well as how these factors are related to crop yield. In 2020–2021, we conducted an experiment with different organic amendments. The treatments included the application of crop residue incorporation (SR), lignite humic acid (LHA; 6 ton/ha), or cow manure (FM; 30 ton/ha), and a control (CK). The results show that, compared with CK, the content of SOM in soil treated with organic amendments increased by 5.3–7.4 g/kg; the available potassium (AK) of the LHA treatment was significantly higher than that of the FM and SR treatments by 32.17 and 42.79 mg/kg, respectively; and the available phosphorus (AP) of the LHA treatment was significantly higher than that of the SR treatment by 7.19 mg/kg. The pH and EC1:5 values of the LHA treatment were significantly lower than those of CK by 1.36 units and 0.2 mS/cm, respectively. The application of organic amendments and changes in environmental conditions also significantly affected community structure and increased soil microbial richness and diversity. SR treatment increased the abundance of Acidobacteria. Further FAPROTAX (Functional Annotation of Prokaryotic Taxa) analysis showed that organic amendments can increase the abundance of microbes involved in the carbon and nitrogen cycle processes, such as aerobic_ammonia_oxidation, aerobic_chemoheterotrophy, nitrification, etc., which increases the kernel number per row and increases crop yield. LHA can increase the microbial abundance of the nitrogen cycle and reduce soil carbon mineralization, while also increasing soil nutrients and crop yield. This study provides a comprehensive understanding of the application of organic amendments in saline–sodic cultivated land.

Progressive freeze-thaw redistributes water, solute and CO2 emissions across soil layers – The role of soil particle size

Progressive freeze-thaw redistributes water and solute among soil layers, and thus perturbs soil carbon mineralization. This potentially introduces variations when differently-sized soil aggregates experience progressive thawing and detachment. In this study, a Mollisol was dry-sieved into three particle sizes (<0.125, 0.125–0.5 and 0.5–1 mm). Each was refilled into a soil column, rewetted to saturation, frozen at −15 °C for 12 h, and then thawed at ambient temperature. During thawing, the soil columns were peeled by layers from the outermost to the inner core into six layers (T1 ∼ T6), to simulate soil detachment while progressive thawing. Our results show that: 1) The outermost layer T1, thawed earlier and thus peeled off first, had the highest water content (102.1–151.2 %) but the lowest electrical conductivity (EC, 63.2–68.3 μS·cm−1). On the contrary, the inner core T6, thawed the last, was driest with merely 24.1–28.4 % water content yet higher EC of 61.0–87.0 μS·cm−1. Such polarized distributions were most pronounced among the soil layers composed of fine aggregates. 2) The CO2 emission rates from the T1 were in general lower than that from the T6 (on average 56.1–65.6 vs. 70.0–84.8 μg CO2-C·g soil −1 7d −1). The soil columns composed of fine aggregates released significantly less CO2 than the coarser aggregates. Overall, the convection of free water during freezing and the diffusion of ice-insoluble materials from freezing front to unfrozen zones, collectively resulted in the polarized patterns of soil water, solute and CO2 emissions. This challenges the conventional investigations based on complete freeze-thaw, highlighting the necessity to distinguish inter-layer heterogeneity during progressive thawing. The varying responses of differently-sized aggregates call for systematic investigations on how progressively thawing and detachment affect slope-scale carbon biogeochemical processes.

Comparison of nonlinear models for the description of carbon mineralization in degraded pasture soil and in soils with plant cover

Tree planting is an important way to restore degraded areas, however, the quality of the plant residue added to the soil influences the organic matter decomposition rate and, consequently, carbon availability. Carbon mineralization curves over time make it possible to understand the decomposition of organic residues and improve soil management. Nonlinear regression models have been used to describe the dynamics of carbon mineralization over time, as they summarize the information contained in the data in just a few parameters with practical interpretations. Thus, this study aimed at evaluating the nonlinear models Cabrera, Juma and Stanford &amp; Smith to describe the soil carbon mineralization in the following plantations: Secondary forest, Acacia auriculiformis, Mimosa caesalpiniifolia and Pasture, obtained from the first to the twentieth week. All the computational part involved in the adjustments and analyses was performed using the R statistical software. The most suitable regression model was selected for the description of soil carbon mineralization for each vegetation cover based on the following criteria: adjusted coefficient of determination (R2adj), residual standard deviation (RSD) and Akaike information criterion (AIC). For Acacia, the Cabrera model was indicated as the best to describe this treatment. For Forest and Pasture, the Juma model had the best fit, and the Stanford &amp; Smith model best described the Mimosa treatment.

Forests have a higher soil C sequestration benefit due to lower C mineralization efficiency: Evidence from the central loess plateau case

Soil carbon (C) mineralization varies with vegetation restoration and plays an essential role in the soil C cycle. However, the response of soil C mineralization to different vegetation restoration types remains unclear. In this study, three vegetation restoration types for the restoration of cropland, namely forestland (Robinia pseudoacacia), shrubland (Caragana korshinskii), and grassland (Artemisia sacrorum and Stipa bungeana), were selected to determine how vegetation restoration types affect soil C mineralization. The vegetation in the assessed areas had been restored 20 years before this study. The results showed that vegetation restoration significantly increased soil CO2 efflux, whereas soil C mineralization efficiency (CME) decreased after cropland conversion. The lowest soil CO2 efflux and CME were observed in forestland, with the highest stable soil organic carbon (SOC) pool. Vegetation restoration significantly increased SOC and its C fraction stocks, and the variation in soil C fractions was regulated by vegetation restoration type. Soil microbial biomass carbon (MBC) and dissolved organic carbon (DOC) effectively reflected the variation in soil C mineralization and stability of the SOC pool, respectively. Soil CO2 efflux was controlled by litter biomass, macroaggregates, particulate organic C, MBC, and DOC, whereas CME was mainly influenced by aboveground biomass, pH, silt and clay content, macroaggregates and DOC. The study suggested that forestland should be selected as the preferred vegetation restoration type in the central Loess Plateau owing to its lower CME with similar C stocks.

Changes in soil carbon mineralization related to earthworm activity depend on the time since inoculation and their density in soil

Earthworms play a key role in soil carbon mineralization, but their effect is highly uncertain and suspected to vary as a function of several factors, particularly the earthworm density and time from earthworm inoculation. We conducted a meta-analysis considering these factors based on 42 experiments comparing carbon mineralization in the absence and presence of earthworms at different times. The results reveal an average carbon mineralization increase of 24% (sd 41%) in the presence of earthworms with an initial median earthworm density of 1.95 mg/g soil DM (Dry Mass) (sd 48%). We show that carbon mineralization due to earthworms was related to their density and time from inoculation. From a simple regression model using these two variables, the estimated impact of earthworms on carbon mineralization was 20% increase from 0 to 60 days and 14% decrease at day 350 for a density of worms commonly found in soils (0.5 mg/g soil DM). Finally, we proposed a simple equation that could be used in organic matter decomposition models that do not take macrofauna into account.

Bacterial community dynamics explain carbon mineralization and assimilation in soils of different land-use history.

Soil dwelling microorganisms are key players in the terrestrial carbon cycle, driving both the degradation and stabilization of soil organic matter. Bacterial community structure and function vary with respect to land use; yet the ecological drivers of this variation remain poorly described and difficult to predict. We conducted a multi-substrate DNA-stable isotope probing experiment across cropland, old-field, and forest habitats to link carbon mineralization dynamics with the dynamics of bacterial growth and carbon assimilation. We tracked the movement of 13 C derived from five distinct carbon sources as it was assimilated into bacterial DNA over time. We show that carbon mineralization, community composition, and carbon assimilation dynamics all differed with respect to land use. We also show that microbial community dynamics affect carbon assimilation dynamics and are associated with soil DNA content. Soil DNA yield is easy to measure and may be useful in predicting microbial community dynamics linked to soil carbon cycling. Soil dwelling microorganisms are key players in the terrestrial carbon cycle, driving both the degradation and stabilization of soil organic matter. Microbial communities vary with respect to land use, but we still have an incomplete understanding of how variation in community structure links to variation in community function. DNA stable isotope probing (DNA-SIP) is a high-resolution method that can identify specific microbial taxa that assimilate carbon in situ. We conducted a large-scale multi-substrate DNA-SIP experiment to explore differences in bacterial activity across land-use regimes. We show that microbial community dynamics vary with land use, that these dynamics are linked to soil carbon cycling, and that they are associated with easily measured soil properties.

Coupled of carbon and nitrogen mineralization in rhizosphere soils along a temperate forest altitudinal gradient

Coupled of carbon and nitrogen mineralization in rhizosphere soils along a temperate forest altitudinal gradient

Long‐term cultivation of Miscanthus and switchgrass accelerates soil organic carbon accumulation by decreasing carbon mineralization in infertile red soil

AbstractPerennial energy crops (PECs) such as Miscanthus spp. and switchgrass (Panicum virgatum L.) may have particular influence on microbial communities and their functions in soil organic carbon (C) utilization and mineralization (Cm). In this study, long‐term effects of PECs on Cm and soil hydrolase activities were examined in bulk and rhizosphere soils of Miscanthus and switchgrass grown on a red soil in South China. Long‐term cultivation (10 years) of PECs led to increases in soil organic C (SOC) and the absolute Cm of bulk and rhizosphere soils. Total Cm was correlated with dissolved organic C and dissolved organic nitrogen (N) in red soils. The specific Cm in bulk soils of switchgrass and Miscanthus were decreased by 11.73% and 20.67% comparing with the control group, respectively. Cultivation of PECs led to a relatively high C/N ratio. There was a difference in priming effect on activities of β‐glucosidase (BG), leucine amin peptidase, N‐acetyl‐β‐glucosaminidase (NAG), and phosphatase between rhizosphere and bulk soils. Compared with the control without PECs, BG activity did not change significantly in bulk soils of PECs, whereas NAG activity decreased significantly. Soil microorganisms were generally limited by soil C and phosphorus (P) in the red soil. The C and P limitations were significantly linearly related with relative Cm (p &lt; 0.05). Phosphorus limitations in microbial communities were lower with PECs than in the control, indicating that cultivation of PECs could provide an optimal nutrient environment for both plants and microorganisms. Thus, long‐term cultivation of PECs increased SOC content but decreased specific Cm rates. However, because C and P limitations remain for plants and soil microbial communities, optimum fertilization is also necessary for sustainable growth of PECs on red soils.

Deep carbon dioxide flows substantially contributes to soil-atmosphere carbon flux from Robinia pseudoacacia forests

Alterations in land use and vegetation cover cause CO2 transfer not only to the soil surface but also across soil profiles. To explore the vertical diffusion characteristics of CO2 in deep soil profiles and their driving factors, we calculated CO2 flux and measured environmental factors in sections situated from 0 to 200 cm in Robinia pseudoacacia forests (Loess Hilly Region, China). The results found that (1) Deep soils (>80 cm) exhibited a stable contribution to the soil-atomosphere CO2 flux, ranging from 21.81% to 24.42%. (2) The total CO2 storage within deep layers accounted for 55.03–79.98% of the total storage in the layer at 0–200 cm. The stable storage of CO2 at deep layers helped suppress the mineralization of organic carbon in deep soil; (3) Soil temperature, moisture, CO2 concentration, aerated porosity, SOC content, bulk density, total porosity, root density, microbial biomass carbon (MBC), pH, and profile depth explained 86.0% and 89.1% of the variance in CO2 flux at shallow and deep layers, respectively. Soil moisture was the key limiting factor for vertical differentiation of CO2 fluxes in deep and shallow layers. The sensitivity of temperature and aerated porosity on CO2 flux increased with soil depth increasing. While the soil microbial biomass carbon had a weaker effect on CO2 flux both in the deep and shallow layers. Root stimulation was more likely to induce CO2 emission in deep layers. However, increase of pH was more conducive to CO2 fixation and flux reduction in deep layers. Our results help to further clarify the mechanisms of carbon emission in deep soil carbon pools, and provide a theoretical basis for scientific evaluation of soil carbon emissions.

Soil carbon mineralization affected by hot water and ultrasound pretreatment

Paddy soil has attracted several studies; however, the effects of pretreatment on soil carbon mineralization remain unclear. This study aimed at validating the effects of soil pretreatment by performing anaerobic incubation of 15 soil samples before treating at room temperature water boiling at 80°C or ultrasound assist at 37Hz and combining (hereafter are control, hot water, ultrasound, mixed hot water, and mixed ultrasound treatments) conducted with three replications. Results showed that initial extracted carbohydrate and incubation extracted carbohydrate (Ini-ECH and Incu-ECH) ranged from 211 to 691 mg kg&lt;sup&gt;−1&lt;/sup&gt; and 229 to 961 mg kg&lt;sup&gt;−1&lt;/sup&gt;, respectively, and reached the highest values with hot water. control, ultrasound, and mixed ultrasound treatments showed the lowest Ini-ECH (211–269 mg kg&lt;sup&gt;−1&lt;/sup&gt;), while the lowest Incu-ECH was linked to both mixed soil treatments with similar amounts (229–264 mg kg&lt;sup&gt;−1&lt;/sup&gt;). Conversely, soil carbon mineralization (generated extracted carbohydrates during anaerobic incubation, Min-ECH) was similar in control, hot water, and ultrasound treatments (ranged from 271 to 393 mg kg&lt;sup&gt;−1&lt;/sup&gt;) but tended to be a negative value in mixed soil treatments. Therefore, we conclude that hot water and ultrasound pretreatments do not increase soil carbohydrate potential but likely promote carbon decomposition.

Characterization of Soil Pores Through X-Ray Computed Microtomography and Carbon Mineralization Under Contrasting Tillage and Land Configurations in the Indo-Gangetic Plains of India

Contrasting tillage and land configuration have important roles in porosity and pore size distribution (PSD), which in turn affects the carbon mineralization in soil. Information on the effects of these treatments on PSD and subsequent carbon mineralization is very limited. Hence, an attempt was made to evaluate the long-term impact of soil tillage and land configurations on the distribution of soil pores and its relationship with soil carbon mineralization under a maize (Zea mays)-wheat (Triticum aestivum) rotation. There were five treatments, that is, conventional tillage, (CT); permanent broad bed, (PBB); PBB + residue (R); zero tillage, (ZT); and ZT + R. Soil pores were quantified by X-ray computed tomography (μ-CT). The conversion of CT to ZT and PBB with or without residue retention (+R) resulted in the reduction of pores &amp;gt;60 μm diameter and was mostly due to a reduction in the number of larger size macro-pores (&amp;gt;110 μm). This resulted in restricted drainage. However, under these practices, pores with larger diameters (60–110 μm) facilitated soil aeration. The total organic carbon (TOC) was 15–48% and 17–47% higher under PBB, PBB + R, ZT, and ZT + R than that under CT in the 0–5 and 5–15 cm layers. The highest MWD (1.01 mm) was in the plots under PBB + R, and the lowest was in the CT plots, and all residue-retained plots (ZT + R and PBB + R) had a higher MWD than residue removal plots (ZT and PBB). Relative to CT, soil C mineralization rates in 0–5 and 5–15 cm soil depths were 63 and 55% higher in the alternate tillage practices, respectively, and the highest value occurred in PPB + R treatments. Increased labile C concentrations were indicative of greater mineralization and were correlated with pores &amp;gt;60 μm, particularly in the size range 110–500 μm and TOC concentrations of 0–15 cm soil layer. Thus, the transition to alternate tillage from the conventional tillage enhanced soil organic carbon concentration (16–47.5%), improved soil structure, reduced the diameter of pores up to &amp;gt;60 μm, and facilitated C mineralization by altering the pore size distribution of soil under a maize-wheat system in the IGP.

Effects of Byproduct Amendments and Nitrogen on Carbon Mineralization and Soil Enzyme Activities in Acidic Brown Soil from Jiaodong Peninsula of China

ABSTRACT It has been proposed strategy that acidic soil quality can be improved by addition of alkaline byproduct amendments containing silicon, calcium, magnesium and potassium. The effects of amendments and three different forms of nitrogen [(NH2)2CO, NaNO3 and NH4Cl] on quality of acidic soil were investigated in Jiaodong Peninsula of China. A 120-day incubation test was carried out to assess the effect of amendments and nitrogen on soil physicochemical properties, soil carbon (C) mineralization and enzyme activities. The results showed that the addition of alkaline amendments can increase soil pH from 5.93 to 6.99 at the beginning of cultivation, while when amendments combined with urea or NH4Cl, soil pH decreased with incubation time. The response of C mineralization was inversely proportional to soil pH value. The addition of amendments could improve soil C content via decreasing soil C-CO2 emissions, and the mineralization rate was reduced by 26%. Addition of amendments in combination with urea or NH4Cl, which could decrease soil pH, stimulated soil C mineralization and increased soil microbial biomass carbon (MBC) and dissolved organic carbon (DOC) fractions in acidic brown soil. However, when amendments were applied with NaNO3, the soil C mineralization could be inhibited. The addition of amendments or combination of amendments and nitrogen increased the soil invertase and phenol oxidase activities, and inhibited soil urease activity. Therefore, the chemical and biological properties of the acidic brown soil in Jiaodong Peninsula of China might be better improved by combination of amendments and NaNO3.

A legacy of fire emerges from multiple disturbances to most shape microbial and nitrogen dynamics in a deciduous forest

Healthy forests are vital components of terrestrial ecosystems for their raw materials, high biodiversity, cycling of nutrients, and potential to sequester carbon. However, these ecosystems are sensitive to disturbances, and anthropogenic activities pose a serious threat to forest ecosystems globally. For example, human activities have dramatically altered multiple historical disturbance regimes in forests, including suppressing fire, increasing the density of large herbivores, and reducing the size of canopy gaps, among other disturbances. Such disturbances can have dramatic impacts on microbially-mediated forest soil functions, but more research is needed to determine the collective impacts of these disturbances. In this study, we investigated the interactive effects of disturbances, namely the legacies of fire, large herbivore densities, and canopy gap creation, in a deciduous forest soil. We determined that forest floor and mineral soil carbon and nitrogen pools were shaped by multiple disturbances, but fire was more influential than the other disturbances. The abundance of several functionally-relevant microbial taxa were significantly impacted by fire, and the effect was more pronounced in the mineral soil than in the forest floor. Together, these findings demonstrate that multiple disturbances, especially a legacy of fire, exerts long-term control over soil carbon, nitrogen and microbial dynamics in a deciduous forest system.

Continuous Cover Forestry and Cost of Carbon Abatement on Mineral Soils and Peatlands

Continuous cover forestry (CCF) has proven to financially outperform rotation forestry (RF) with low or even moderate social price of carbon in mineral soils. However, to date there are no studies to compare financial performance of joint production (timber and carbon sequestration) between mineral soils and peatlands when CCF is applied. A vast variety of harvest intervals and intensity (expressed as post-harvest basal area) for a mature spruce-dominated [Picea abies (L.) Karst.] stand on both mineral and peat soils was simulated with process-based ecosystem model, EFIMOD. In addition, four levels of carbon price (0, 25, 50 and 75€/tCO2) were applied in assessing the profitability of joint production (timber and carbon sequestration) associated with CCF. Mineral soil turned out to be superior to peatland in cost-efficiency of carbon sequestration. For instance, the cost of additional ton of CO2 was only €2/tCO2 with a carbon price of €25/tCO2 for a private forest owner (through carbon trading), while on peatland it fluctuated between €30 and €39.5/tCO2, depending on the carbon price applied for a private forest owner (€25-€75/tCO2). In general, mineral soil was more sensitive to harvest interval and intensity than peatland, with respect to cost-efficiency in climate change mitigation.