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Globally, soil temperature to 1 m depth is predicted to be up to 4 °C warmer by the end of this century, with pronounced effects expected in temperate forest regions. Increased soil temperatures will potentially increase the release of CO2 from temperate forest soils, resulting in important positive feedback on climate change. Dark CO2 fixation by microbes can recycle some of the released soil CO2, and CO2 fixation rates are reported to increase under higher temperatures. However, research on the influence of temperature on dark CO2 fixation rates, particularly in comparison to the temperature sensitivity of respiration in soils of temperate forest regions is missing. To determine the temperature sensitivity (Q10) of dark CO2 fixation and respiration rates, we investigated soil profiles to 1 m depth from beech (deciduous) and spruce (coniferous) forest plots of the Hummelshain forest, Germany. We used 13C-CO2 labelling and incubations of soils at 4 and 14°C to determine CO2 fixation and net soil respiration rates and derived the Q10 values for both processes with depth. The average Q10 for dark CO2 fixation rates normalized to soil dry weight was 2.07 for beech and spruce profiles, and this was lower than the measured average Q10 of net soil respiration rates with ~2.98. Assuming these Q10 values, we extrapolated that net soil respiration might increase 1.16 times more than CO2 fixation under a projected 4 °C warming. In the beech soil, a proportionally larger fraction of the label CO2 was fixed into soil organic carbon than into microbial biomass compared to the spruce soil. This suggests primarily higher turnover (i.e. growth and death) of microbial cells, and we speculate that this is related to lower clay content in the beech soil. Despite a similar abundance of the total bacterial community in the beech and spruce soils, the beech soil also had a lower abundance of autotrophs, implying a higher proportion of heterotrophs when compared to the spruce soil, hence might partly explain the higher biomass turnover. Furthermore, higher temperatures in general lead to higher microbial biomass turnover in both soils. Our findings suggest that in temperate forest soils, CO2 fixation might be less responsive to future warming than net soil respiration and that variations in site-specific parameters might affect microbial biomass turnover and resultantly, dark CO2 fixation rates and its temperature sensitivity in temperate forest soils. [ABSTRACT FROM AUTHOR]

Protecting soil fertility represents a fundamental effort of sustainable development. In this study we investigate how different altitudes affect soil microbial biomass carbon (MBC) and soil organic carbon (SOC), and their ratio, MBC/SOC in Hyperalic Alisol. MBC and SOC are well established and widely accepted microbial quotients in soil science. Our work hypothesis was that a decrease in MBC and SOC should be observed at higher altitudes. This initial assumption has been verified by our measurements, being attributed to the increase in MBC and SOC at low altitudes. Our approach should contribute to the better understanding of MBC and SOC distribution in soil and changes in MBC/SOC at various altitudes in the region.

In order to assess the suitability of sludge application for maize (Zea mays L.) soil ecosystems, this study aimed to evaluate soil microbial properties over three consecutive years using treated municipal sewage sludge (TSS) amendment in the Typic Xerofluvent Mediterranean soils of Turkey. Soil microbial properties and biochemical activities significantly increased with increasing TSS amounts. Microbial biomass carbon peaked following amendment with 30 Mg ha−1 a−1 of TSS, while basal soil respiration was not significantly affected by TSS doses. Moreover, soil enzyme activity increased significantly with increasing TSS amounts. A significant increase in the grain yield of 7% and 9% was found with 10 and 20 Mg TSS ha−1 a−1 applications respectively, whereas a significant decrease of 5% was found with 30 Mg TSS ha−1 a−1. Our results suggest that if the goal is to achieve plant yield in the short-term, it seems that TSS application of 20 Mg ha−1 a−1 can be recommended as organic fertilizer without causing potential risks. On the other hand, if the primary aim is to ensure the sustainability of the soil organic matter, the use of TSS as organic soil conditioner at a rate of 30 Mg ha−1 a−1 can be recommended. [ABSTRACT FROM AUTHOR]

Abstract Understanding soil organic carbon (SOC) mineralization under different temperature regimes is critical for predicting SOC responses to climate change. Yet, the effects of altering temperature regimes on SOC mineralization remain poorly understood in forest plantations converted from natural forests. Forest conversion is extensive and could have major impact on SOC dynamics, so that this knowledge limits our ability of predicting the consequences of such land use change on carbon cycling. To fill this knowledge gap, we conducted a 360-day incubation experiment under constant and varying temperature regimes for soils of a natural forest and a Chinese fir (Cunninghamia lanceolata) plantation. Results showed that SOC mineralization was greater in the forest plantation soil than in the natural forest soil in both temperature treatments, possibly due to greater labile SOC in the forest plantation soil by 27–28%. The results suggested that replacing natural forests with forest plantations may increase CO 2 emission via the mineralization of SOC. In the natural forest soil, SOC mineralization was greater in the varying temperature treatment relative to the constant temperature treatment but no difference was found in the forest plantation soil. Moreover, temperature sensitivity (Q 10) of SOC mineralization was greater in the natural forest soil than the Chinese fir soil for the 0–180 day of the incubation. The difference in the response to the two temperature treatments between the two forest soils which was accompanied by difference in soil microbial communities. It was likely that soil microbes of the closed-canopy natural forest were less adapted to temperature fluctuations than soil microbes of the forest plantation soil as the canopy was rarely closed. Our results highlight that soil incubation experiments need to take temperature fluctuations into consideration to more accurately reflect SOC dynamics in the field, especially when evaluating the impacts of replacing natural forests with forest plantations on soil carbon dynamics. Highlights • SOC mineralization was greater in a natural forest than a plantation forest. • Converting natural forests to forest plantations may enhance respirational CO 2 loss. • Varying temperature elevated SOC mineralization only in the natural forest soil. • Microbial community differed between the two forests and two temperature treatments. [ABSTRACT FROM AUTHOR]

Experiments were conducted in two phases, first under in vitro condition to study the stress tolerant ability and then in pot experiment to study the effect of Rhizobium isolates on rhizospheric microbial activity. The strain CHRS-7 could tolerate the pH 4.0, whereas RAN-1 and RAB-1 could not. The growth of all the strains was luxuriant in 1% NaCl solution and decreased with increase in the concentration of NaCl. All the strains could produce the phytohormone indole acetic acid (IAA) by metabolizing different carbon sources. The highest amount of IAA was produced by RAB-1 (81 μg/mL), CHRS-7 (78 μg/mL) and RAN-1 (72 μg/mL) by metabolizing mannitol, glucose, and sucrose, respectively. The higher bacteria and rhizobial population was enumerated in the treatment with inoculation of Rhizobium strains and added with 50% of soil test dose of nitrogen whereas higher fungi population was enumerated with the treatment receiving 150% of a soil test dose of nitrogen. The soil enzymes activity, microbial biomass carbon and nitrogen were also higher with a lower dose of external sources of N (50% of a soil test dose) and decreased with increase in nitrogen dose. [ABSTRACT FROM AUTHOR]

Taking surrounding woodland soils of Cedrus deodara (Roxb.) G. Don, Prunus ceraifera cv. Pissardii, Ginkgo biloba L. and Ligustrum lucidum in Zhoushan Forest Park of Henan Province as the research objects, the physicochemical properties of sample plots were investigated, and the contents of soil microbial biomass carbon, nitrogen, phosphorus and total soil nutrients were determined. The results showed that the carbon-nitrogen ratios and carbon-phosphorus ratios were 8.0-11.4 and 17.1-25.3, respectively; the percentages of carbon, nitrogen and phosphorus in soil organic carbon (SOC), total nitrogen (TN) and total phosphorus (TP) were 2.84%-5.1%, 2.69%-4.44% and 2.19%-5.62%, respectively. The carbon-nitrogen ratio and carbon-phosphorus ratio of P. ceraifera, G. biloba and L. lucidum forests were significantly lower than that of C. deodara forest (P < 0.05). The MBC/SOC, MBN/TN and MBP/TP ratios of G. biloba forest were the highest, which had significant difference with those of other tree species (P < 0.05). The contents of carbon, nitrogen and phosphorus were extremely or significantly correlated with SOC, TN, TP, tree species and human disturbance, but had no correlation with soil pH, slope, slope direction, etc. Tree species and human disturbance also significantly affected the physical and chemical properties closely related to soil microbial biomass. [ABSTRACT FROM AUTHOR]

Nitrogen (N) fertilization affects the rate of soil organic carbon (SOC) decomposition by regulating extracellular enzyme activities (EEA). Extracellular enzymes have not been represented in global biogeochemical models. Understanding the relationships among EEA and SOC, soil N (TN), and soil microbial biomass carbon (MBC) under N fertilization would enable modeling of the influence of EEA on SOC decomposition. Based on 65 published studies, we synthesized the activities of α-1,4-glucosidase (AG), β-1,4-glucosidase (BG), β- d -cellobiosidase (CBH), β-1,4-xylosidase (BX), β-1,4- N -acetyl-glucosaminidase (NAG), leucine amino peptidase (LAP), urease (UREA), acid phosphatase (AP), phenol oxidase (PHO), and peroxidase (PEO) in response to N fertilization. The proxy variables for hydrolytic C acquisition enzymes ( C-acq ), N acquisition ( N-acq ), and oxidative decomposition ( OX ) were calculated as the sum of AG, BG, CBH and BX; AG and LAP; PHO and PEO, respectively. The relationships between response ratios (RRs) of EEA and SOC, TN, or MBC were explored when they were reported simultaneously. Results showed that N fertilization significantly increased CBH, C-acq , AP, BX, BG, AG, and UREA activities by 6.4, 9.1, 10.6, 11.0, 11.2, 12.0, and 18.6%, but decreased PEO, OX and PHO by 6.1, 7.9 and 11.1%, respectively. N fertilization enhanced SOC and TN by 7.6% and 15.3%, respectively, but inhibited MBC by 9.5%. Significant positive correlations were found only between the RRs of C-acq and MBC, suggesting that changes in combined hydrolase activities might act as a proxy for MBC under N fertilization. In contrast with other variables, the RRs of AP, MBC, and TN showed unidirectional trends under different edaphic, environmental, and physiological conditions. Our results provide the first comprehensive set of evidence of how hydrolase and oxidase activities respond to N fertilization in various ecosystems. Future large-scale model projections could incorporate the observed relationship between hydrolases and microbial biomass as a proxy for C acquisition under global N enrichment scenarios in different ecosystems. [ABSTRACT FROM AUTHOR]

The current experiment was conducted to examine the influence of compost on the growth of vetiver grass (Vetiveria zizanioides) in the artificially diesel contaminated soil. Collected soil samples were spiked with different diesel concentrations (0.5% and 1% v/w) and also amended with compost then stored in polythene bags for 15 days. Vetiver grass (Vetiveria zizanioides) was grown as a test plant species to examine the effect of soil diesel contamination and compost amendment on plant growth and nutrient uptake for four months under controlled conditions. The physico-chemical characteristics such as pH, organic matter (OM), total organic carbon (TOC), total nitrogen (TN), microbial biomass carbon (MBC) and microbial biomass nitrogen (MBN), were analyzed after two weeks of spiking and afterthe harvesting of the grasscrop. Significant variation was observed in pH in contaminated soil. It ranged from 7.3 (control soil) to 8.7(contaminated soil). Concentration of total organic carbon significantly increased in treated soils. MBC and MBN were not influenced by diesel contamination. Application of compost improved the soil characteristics and plant growth due to its remediation potential. Our results indicated a buffering effect of compost in diesel contaminated soil which resulted in improving soil health of contaminated soil. [ABSTRACT FROM AUTHOR]

Effect of biochar addition on soil CO2 efflux in a typical Chinese chestnut (Castanea mollissima) plantation in Lin'an, Zhejiang Province, China was investigated from July 2012 to July 2013 by the static closed chamber-GC technique. Soil temperature, soil moisture, WSOC and MBC concentrations were determined as well. Results showed that soil CO2 efflux exhibited a strong seasonal pattern. Compared with the control (without biochar application), the biochar treatment increased the soil CO2 efflux only in the first month since application, and then the effect diminished thereafter. There were no significant differences in the annual cumulative value of soil CO2 efflux between the biochar and control treatments. The annual mean value in soil MBC concentration (362 mg.kg-1) in the biochar treatment was higher than that (322 mg.kg-1) in the control. However, no significant difference in the soil WSOC concentration was found between the biochar and control treatments. Strong exponential relationships between soil temperature and soil CO2 efflux were observed regardless of the treatment and soil layer. The apparent temperature sensitivity (Q10) of soil CO2 efflux in the biochar treatment was higher than that in the control. Soil CO2 efflux was related to soil WSOC concentration but not with soil MBC or moisture content. To conclude, the application of bamboo leaf biochar did not affect the annual cumulative CO2 emission in the Chinese chestnut plantation but increased the Q10, and the CO2 efflux was predominantly controlled by the soil temperature and soil WSOC level. [ABSTRACT FROM AUTHOR]

The wetlands on the Qinghai-Tibet Plateau are experiencing serious degradation, with more than 90,000 hectares of marshland converted to wet meadow or meadow after 40 years of drainage. However, little is known about the effects of wetland conversion on soil C stocks and the quality of soil organic carbon (SOC) (defined by the proportion of labile versus more resistant organic carbon compounds). SOC, microbial biomass carbon, light fraction organic carbon (LFOC), dissolved organic carbon, and the chemical composition of SOC in the soil surface layer (0-10 cm), were investigated along a wetland degradation gradient (marsh, wet meadow, and meadow). Wetland degradation caused a 16 % reduction in the carbon stocks from marsh (178.7 ± 15.2 kg C m) to wet meadow (150.6 ± 21.5 kg C m), and a 32 % reduction in C stocks of the 0-10 cm soil layer from marsh to meadow (122.2 ± 2.6 kg C m). Wetland degradation also led to a significant reduction in SOC quality, represented by the lability of the carbon pool as determined by a density fractionation method ( L), and a significant increase in the stability of the carbon pool as reflected by the alkyl-C: O-alkyl-C ratio. C NMR spectroscopy showed that the labile form of C ( O-alkyl-C) declined significantly after wetland degradation. These results assist in explaining the transformation of organic C in these plateau wetland soils and suggest that wetland degradation not only caused SOC loss, but also decreased the quality of the SOC of the surface soil. [ABSTRACT FROM AUTHOR]

Land use changes are known to alter soil organic carbon (SOC) and microbial properties, however, information about how conversion of natural forest to agricultural land use as well as plantations affects SOC and microbial properties in the Changbai Mountains of Northeast China is meager. Soil carbon content, microbial biomass carbon (MBC), basal respiration and soil carbon mineralization were studied in five selected types of land use: natural old-growth broad-leaved Korean pine mixed forest (NF); spruce plantation (SP) established following clear-cutting of NF; cropland (CL); ginseng farmland (GF) previously under NF; and a five-year Mongolian oak young forest (YF) reforested on an abandoned GF, in the Changbai Mountains of Northeast China in 2011. Results showed that SOC content was significantly lower in SP, CL, GF, and YF than in NF. MBC ranged from 304.4 mg/kg in CL to 1350.3 mg/kg in NF, which was significantly higher in the soil of NF than any soil of the other four land use types. The SOC and MBC contents were higher in SP soil than in CL, GF, and YF soils, yielding a significant difference between SP and CL. The value of basal respiration was also higher in NF than in SP, CL, GF, and YF. Simultaneously, higher values of the metabolic quotient were detected in CL, GF, and YF soils, indicating low substrate utilization of the soil microbial community compared with that in NF and SP soil. The values of cumulative mineralized carbon and potentially mineralized carbon ( C) in NF were significantly higher than those in CL and GF, while no significant difference was observed between NF and SP. In addition, YF had higher values of C and C mineralization rate compared with GF. The results indicate that conversion from NF into agricultural land (CL and GF) uses and plantation may lead to a reduction in soil nutrients (SOC and MBC) and substrate utilization efficiency of the microbial community. By contrast, soils below SP were more conducive to the preservation of soil organic matter, which was reflected in the comparison of microbial indicators among CL, GF, and YF land uses. This study can provide data for evaluating soils nutrients under different land use types, and serve as references for the rational land use of natural forest in the study area. [ABSTRACT FROM AUTHOR]

Highlights: [•] 100× recommended application rate reduced soil microbial activity. [•] 100× recommended application rate changed soil microbial community composition. [•] 100× recommended application rate changed microbial functional diversity. [•] Nitrogen-fixing gene abundance was reduced by high fomesafen application. [ABSTRACT FROM AUTHOR]

Highlights: [•] 5-year-old exclosure increased soil C and N stocks for meadow. [•] Soil C increase was attributed to increases in both labile and non-labile OC. [•] No exclosure effects on soil C and N stocks were found for marsh and wet meadow. [•] Changes in soil bulk density, N, dissolved C explain soil C change after exclosure. [ABSTRACT FROM AUTHOR]

Abstract: Urbanization degrades soil by surface soil removal and subsoil compaction. Subsoiling and organic matter incorporation offer potential to increase soil carbon (C) storage over time. We evaluated the effects of urban land development practices and post-development soil rehabilitation on soil C pools and microbial biomass carbon (MBC). In 2007, four treatments [typical development practice (A horizon removed, subsoil compacted, and A horizon soil partially replaced), enhanced topsoil (same as typical practice plus tillage), profile rebuilding (compost incorporation to 60-cm depth in subsoil; A horizon soil partially replaced plus tillage), and undisturbed soil] were applied to 24 plots in Virginia, USA. In 2011, soil C pools and MBC were measured at 0–5, 5–10 and 15–30 cm depths. In surface soils, undisturbed soils had greater total soil C (12.10 and 7.73 Mg C ha−1 at 0–5 and 5–10 cm depths, respectively) than the three practices where A horizon soils were disturbed. However, profile rebuilding had higher total soil C (6.12 Mg C ha−1) and larger available and aggregate-protected C pools (1.59 and 2.04 Mg C ha−1, respectively) at 15–30 cm depth than other treatments, including undisturbed. In surface soils, MBC ranged from 185.3 to 287.3 mg C kg−1 soil among all practices. At the 15–30 cm soil depth, profile rebuilding had the greatest MBC (149.5 mg C kg−1 soil). Total soil C, available, aggregate-protected and mineral-bound C pools had positive relationships with MBC at the 15–30 cm depth (r = 0.85, 0.71, 0.77, and 0.69, respectively). We found typical land development practices led to soil C loss during construction processes even when topsoil is replaced. Soil rehabilitation that includes compost additions and subsoiling has potential to increase soil C storage below the surface horizons. [Copyright &y& Elsevier]

Highlights: [•] Influence of wood size, type, amount and quality on denitrification rate and adverse effects in denitrification walls. [•] Denitrification rate in denitrification walls most strongly affected by temperature. [•] Wood carbon quality, surface area and amount significantly influence denitrification rate but not wood type (pine, oak). [•] Increases in hydraulic loading rate increased TKN and DOC losses and wood amount increased DOC loss. [•] Multivariate model of denitrification rate predictors was developed. [ABSTRACT FROM AUTHOR]

Highlights: [•] We reported changes in microbial community under biochar amendment in a field study. [•] Biochar soil amendment (BSA) increased bacterial but decreased fungal gene abundance. [•] Both bacterial and fungal community structure were clearly affected by BSA. [•] Changes in soil enzyme activities could partially support the above findings. [•] BSA could potentially affect the soil C and N cycling of the rice soil ecosystem. [Copyright &y& Elsevier]

Earthworms as ecosystem engineers partially improve soil properties by egesting casts. Our previous study confirmed that soil pollution affects the physico-chemical properties of earthworm casts. It is still unclear whether the biological properties (e.g. cellulase, urease, and acid and alkaline phosphatase activities, as well as microbial biomass carbon) of casts are affected by foreign substances in soil. The present study aimed to investigate the effect of phenanthrene (PHE) on the biological characteristics of earthworm (Eisenia fetida) casts. Furthermore, correlations between cast properties and the digestive and antioxidant systems were explored by the determination of digestive enzyme (urease, protease, acid and alkaline phosphatase) activities, antioxidant indexes [superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD)], as well as malondialdehyde (MDA) content. Exposure at a range of PHE doses (0, 2, 5, 10, and 20 mg kg−1) for 15 d resulted in the following observations: (1) Compared with urease, as well as acid and alkaline phosphatase activities, cellulase activities in both soil and casts were sensitive to PHE, and could potentially act as biomarkers to provide early-warning signals for soil pollution. (2) Microbial biomass carbon in casts was modified, but with no clear pattern. (3) Cellulase and POD activities, as well as MDA content in earthworms, increased with elevated exposure to PHE in soil. Protease, SOD, and CAT activities exhibited a biphasic dose response to PHE, while acid and alkaline phosphatase activities were inhibited under treatment conditions. (4) Correlation analysis suggested that microbial biomass carbon in casts significantly and positively correlated with cellulase and acid phosphatase activities of earthworms, but negatively correlated with protease activities. A significant but weak negative correlation between alkaline phosphatase activities in casts and POD activities was also observed. Based on these results, we concluded that PHE content in soil modified some biological properties of casts, by partially affecting the earthworm's digestive and antioxidant systems. This study advances our knowledge of earthworm ecology in polluted soil by providing a better understanding of their ecological functions. Image 1 • PHE negatively affects cellulase activities and MBC in casts at low exposure levels. • Cellulase activities in soil and casts could be potential biomarkers. • PHE differentially affects earthworms' digestive and antioxidant enzyme activities. • PHE alters cast properties by affecting the digestive and antioxidant systems. [ABSTRACT FROM AUTHOR]

Protecting soil fertility represents a fundamental effort of sustainable development. In this study we investigate how different altitudes affect soil microbial biomass carbon (MBC) and soil organic carbon (SOC), and their ratio, MBC/SOC in Hyperalic Alisol. MBC and SOC are well established and widely accepted microbial quotients in soil science. Our work hypothesis was that a decrease in MBC and SOC should be observed at higher altitudes. This initial assumption has been verified by our measurements, being attributed to the increase in MBC and SOC at low altitudes. Our approach should contribute to the better understanding of MBC and SOC distribution in soil and changes in MBC/SOC at various altitudes in the region., Competing Interests: No competing interests were disclosed., (Copyright: © 2020 Mendoza B et al.)

To assess the effects of long-term intensive management on soil carbon cycle and microbial functional diversity, we sampled soil in Chinese hickory (Carya cathayensis Sarg.) stands managed intensively for 5, 10, 15, and 20 years, and in reference Chinese hickory–broad-leaved mixed forest (NMF) stands. We analyzed soil total organic carbon (TOC), microbial biomass carbon (MBC), and water-soluble organic carbon (WSOC) contents, applied 13C-nuclear magnetic resonance analysis for structural analysis, and determined microbial carbon source usage. TOC, MBC, and WSOC contents and the MBC to TOC ratios were lower in the intensively managed stands than in the NMF stands. The organic carbon pool in the stands managed intensively for twenty years was more stable, indicating that the easily degraded compounds had been decomposed. Diversity and evenness in carbon source usage by the microbial communities were lower in the stands managed intensively for 15 and 20 years. Based on carbon source usage, the longer the management time, the less similar the samples from the monospecific Chinese hickory stands were with the NMF samples, indicating that the microbial community compositions became more different with increased management time. The results call for changes in the management of the hickory stands to increase the soil carbon content and restore microbial diversity. [ABSTRACT FROM AUTHOR]