Observations of a seasonally shifting thermal optimum in peatland carbon-cycling processes; implications for the global carbon cycle and soil enzyme methodologies

Thermal gradient apparatus has been used to study enzyme activity and carbon cycling in peat collected seasonally from a Northern upland peatland. A thermal optimum was observed in the peat where maximum carbon-cycling enzyme activities (phenol oxidase and β-glucosidase), phenolic compound concentrations, dissolved organic carbon (DOC) concentrations and microbial respiration (CO₂ efflux) were all found in a given season. The thermal optimum for these carbon-cycling processes coincided with the highest ambient soil temperature recorded at the time of peat collection, suggesting microbial acclimation to the external conditions. Under the waterlogged conditions of this experiment, phenol oxidase activites correlated positively with phenolic compounds (winter 0.96, P<0.01; spring 0.92, P<0.001; summer 0.94, P<0.001; autumn 0.88, P<0.001) and β-glucosidase activities with DOC (winter 0.91, P<0.01; spring 0.85, P<0.01; summer 0.92, P<0.001; autumn 0.72, P<0.05). We propose, therefore, that the relative activities of these enzymes is crucial in mobilising DOC from the peat matrix, with implications for carbon exports to the receiving waters (magnitude and molecular weight distribution) and CO₂ efflux to the atmosphere. The pronounced seasonality in carbon processing found here, must be taken into account when modelling carbon flux in and from these systems, if responses to climate change are to be predicted satisfactorily. Furthermore, because the optimum activity of these carbon-cycling enzymes shifted with seasonal changes in temperature, it is essential to perform enzyme assays in soil ecological investigations at field temperatures (rather than standardised temperatures), when information on natural process rates is required.     

Contribution of plant photosynthate to soil respiration and dissolved organic carbon in a naturally recolonising cutover peatland

The aim of this study was to investigate how three vascular plant species (Calluna vulgaris, Eriophorum angustifolium and Eriophorum vaginatum) colonising an abandoned cutover peatland affect fluxes of recent photosynthate to dissolved organic carbon (DOC), soil and plant respiration and shoot biomass. We used in situ ¹³CO₂ pulse labelling to trace carbon (C) throughout a 65 day pulse chase period. Between 16 and 35% of the pulse of ¹³C remained in shoot biomass after 65 days with significant differences between C. vulgaris and E. angustifolium (P = 0.009) and between C. vulgaris and E. vaginatum (P = 0.04). A maximum of 29% was detected in DOC beneath labelled plants and losses of ¹³C from peat respiration never exceeded 0.16% of the original pulse, showing that little newly fixed C was allocated to this pool. There were no significant differences between the different plant species with respect to ¹³C recovered from DOC or via peat respiration. More C was lost via shoot respiration; although amounts varied between the three plant species, with 4.94–27.33% of the ¹³C pulse respired by the end of the experiment. Significant differences in ¹³C recovered from shoot respiration were found between C. vulgaris and E. angustifolium (P = 0.001) and between E. angustifolium and E. vaginatum (P = 0.032). Analysis of δ¹³C of microbial biomass indicated that recently assimilated C was allocated to this pool within 1 day of pulse labelling but there were no significant differences in the ¹³C enrichment of the microbial biomass associated with the different plant species. The data suggest that peat respiration represents a small flux of recent assimilate compared to other fluxes and pools and that different vascular plant species show considerable variation in the quantities and dynamics of C allocated to DOC.     

Temperature and soil moisture effects on dissolved organic matter release from a moorland Podzol O horizon under field and controlled laboratory conditions

Organic upland soils store large amounts of humified organic matter. The mechanisms controlling the leaching of this C pool are not completely understood. To examine the effects of temperature and microbial cycling on C leaching, we incubated five unvegetated soil cores from a Podzol O horizon (from NE Scotland), over a simulated natural temperature cycle for 1 year, whilst maintaining a constant soil moisture content. Soil cores were leached with artificial rain (177 mm each, monthly) and the leachates analysed for dissolved organic carbon (DOC) and their specific C‐normalized UV absorbance determined (SUVA, 285 nm). Monthly values of respiration of the incubated soils were determined as CO₂ efflux. To examine the effects of vegetation C inputs and soil moisture, in addition to temperature, we sampled O horizon pore waters in situ and collected five additional field soil cores every month. The field cores were leached under controlled laboratory conditions. Hysteresis in the monthly amount of DOC leached from field cores resulted in greater DOC on the rising, than falling temperature phases. This hysteresis suggested that photosynthetic C stimulated greater DOC losses in early summer, whereas limitations in the availability of soil moisture in late summer suppressed microbial decomposition and DOC loss. Greater DOC concentrations of in‐situ pore waters than for any core leachates were attributed to the effects of soil drying and physico‐chemical processes in the field. Variation in the respiration rates for the incubated soils was related to temperature, and respiration provided a greater pathway of C loss (44 g C m⁻² year⁻¹) than DOC (7.2 g C m⁻² year⁻¹). Changes in SUVA over spring and summer observed in all experimental systems were related to the period of increased temperature. During this time, DOC became less aromatic, which suggests that lower molecular weight labile compounds were not completely mineralized. The ultimate DOC source appears to be the incomplete microbial decomposition of recalcitrant humified C. In warmer periods, any labile C that is not respired is leached, but in autumn either labile C production ceases, or it is sequestered in soil biomass.     

Carbon dioxide production and oxygen consumption during the early decomposition of different litter types over a range of temperatures in soil‐inoculated quartz sand

Oat straw, hay, and alfalfa litter, differing in microbial colonization and recalcitrance, were added to organic matter–free quartz sand (5 mg C [g material]^–1) and incubated in the laboratory at 5°C, 10°C, 15°C, 20°C, and 25°C. Different incubation periods were chosen so that theoretically the same amounts of CO₂ would be produced and the same amounts of O₂ would be consumed for each litter type. It was investigated whether Q₁₀ values (change in respiration rate between two temperatures) increase with decreasing temperature and how much these Q₁₀ values and also the respiratory quotient (RQ: mol CO₂/mol O₂) depend on the litter type. The sums of CO₂‐C evolved and O₂ consumed, but also the contents of microbial biomass C and microbial biomass N showed a nearly 7‐fold increase in the order oat straw < hay < alfalfa litter. In contrast, the ratio of the fungal cell‐membrane component ergosterol to microbial biomass C was highest in the oat straw (4.1‰) and lowest in the alfalfa litter (0.2‰). This ratio reached a similar level between 5°C and 15°C (1.9‰), significantly higher (p = 0.01) than the level at 20°C (0.9‰). Respiration was similar between 20°C and 25°C, with a mean Q₁₀ value of 1.9. The use of temperature rate‐modifying factors suggested by the carbon‐turnover model ROTHC revealed that the incubation period for similar respiration rates was underestimated at 5°C and overestimated at 25°C. The lignin‐poor and protein‐rich alfalfa litter showed the highest Q₁₀ values of the three litter types in the medium temperature range of 10°C to 20°C. In contrast, the lignin‐rich and protein‐poor oat straw showed significantly highest Q₁₀ values at 5°C and 25°C in comparison with the other two litter types. The RQ was significantly highest in the hay litter (1.05) and in comparison with alfalfa litter (0.97) and oat straw (0.92). Strong temperature‐dependent variations in Q₁₀ values and respiratory quotients suggest interactions between litter quality, microbial colonization of litter, and temperature, which warrants further investigation.     

Seasonal fluctuation in microbial biomass and activity along a natural nitrogen gradient in a drained peatland

The effects of peat total N on the dissolved N and C concentrations and microbial biomass and activity and their range of seasonal fluctuation were studied in a drained peatland forest in Finland. Seasonal fluctuations in the concentrations of extractable dissolved organic (DON) and inorganic nitrogen (DIN) compounds and extractable dissolved organic carbon (DOC), microbial C and N, ergosterol, net and gross N mineralisation rates were investigated during two growing seasons along a natural peat N gradient in a drained peatland. Significant seasonal fluctuations in NH₄⁺ and DOC concentrations, microbial C and N, but not in ergosterol or microbial C-to-N ratios in the peat, were observed during the 1999 and 2000 growing seasons. The peat total N concentration affected extractable DON and DOC, but not DIN concentrations in the peat. A negative correlation was found between total N concentration in peat and microbial N and C, and a positive correlation between total N and ergosterol, in peat with N concentrations of up to 2%. Gross mineralisation rates did not show any correlation, whereas net mineralisation rates showed a significant positive correlation with the total N concentration of the peat in both 1999 and 2000.     

Optimizing fen peatland water-table depth for romaine lettuce growth to reduce peat wastage under future climate warming

Forty percentage of UK peatlands have been drained for agricultural use, which has caused serious peat wastage and associated greenhouse gas emissions (carbon dioxide (CO₂) and methane (CH₄)). In this study, we evaluated potential trade-offs between water-table management practices for minimizing peat wastage and greenhouse gas emissions, while seeking to sustain romaine lettuce production: one of the most economically relevant crop in the East Anglian Fenlands. In a controlled environment experiment, we measured lettuce yield, CO_2, CH₄ fluxes and dissolved organic carbon (DOC) released from an agricultural fen soil at two temperatures (ambient and +2°C) and three water-table levels (−30 cm, −40 cm and −50 cm below the surface). We showed that increasing the water table from the currently used field level of −50 cm to −40 cm and −30 cm reduced CO₂ emissions, did not affect CH₄ fluxes, but significantly reduced yield and increased DOC leaching. Warming of 2°C increased both lettuce yield (fresh leaf biomass) and peat decomposition through the loss of carbon as CO₂ and DOC. However, there was no difference in the dry leaf biomass between the intermediate (−40 cm) and the low (−50 cm) water table, suggesting that romaine lettuce grown at this higher water level should have similar energetic value as the crop cultivated at −50 cm, representing a possible compromise to decrease peat oxidation and maintain agricultural production.     

Determination of the soil microbial biomass carbon using the method of substrate-induced respiration

Specific features of determining the carbon content in the soil microbial biomass using the method of substrate-induced respiration (MB_SIR) were studied as related to the conditions of the incubation (the glucose concentration and temperature) and pre-incubation (the duration and temperature) of the soil samples collected in the summer (tundra gley and soddy-podzolic soils and chernozems) and in different seasons (for the gray forest soil). The glucose concentration providing the highest substrate-induced respiration (SIR) in the soils studied was shown to be 2–15 mg/g. The MB_SIR in the soil samples collected in summer and in the soils pre-incubated for 10 and 22°C (7 days) did not significantly differ. The MB_SIR in the gray forest soil pre-incubated at 3, 6, and 10°C (winter, spring/autumn, and summer, respectively) and at 22°C (recommended by the authors of the SIR method) was similar for the cropland in all the seasons. For the meadow, it was the same in the winter, summer, and autumn, and, in summer, it did not differ only for the forest. For the comparative assessment of the MB_SIR, soil samples from different ecosystems are recommended to be collected in the autumn or in the summer. Soil samples of 100–500 g should be pre-incubated for 7 days at 22°C and moisture of 60% of the total water capacity; then, 1-2 g soil should be incubated with glucose (10 mg/g) at 22°C for 3–5 hours.     

Grasses, litter, and their interaction affect microbial biomass and soil enzyme activity

Plant effects on ecosystem processes are mediated through plant-microbial interactions belowground and soil enzyme assays are commonly used to directly relate microbial activity to ecosystem processes. Live plants influence microbial biomass and activity via differences in rhizosphere processes and detrital inputs. I utilized six grass species of varying litter chemistry in a factorial greenhouse experiment to evaluate the relative effect of live plants and detrital inputs on substrate-induced respiration (SIR, a measure of active microbial biomass), basal respiration, dissolved organic carbon (DOC), and the activities of β-glucosidase, β-glucosaminidase, and acid phosphatase. To minimize confounding variables, I used organic-free potting media, held soil moisture constant, and fertilized weekly. SIR and enzyme activities were 2-15 times greater in litter-addition than plant-addition treatments. Combining live plants with litter did not stimulate microbial biomass or activity above that in litter-only treatments, and β-glucosidase activity was significantly lower. Species-specific differences in litter N (%) and plant biomass were related to differences in β-glucosaminidase and acid phosphatase activity, respectively, but had no apparent effect on β-glucosidase, SIR, or basal respiration. DOC was negatively related to litter C:N, and positively related to plant biomass. Species identity and living plants were not as important as litter additions in stimulating microbial activity, suggesting that plant effects on soil enzymatic activity were driven primarily by detrital inputs, although the strength of litter effects may be moderated by the effect of growing plants.     

Release of Carbon in Different Molecule Size Fractions from Decomposing Boreal Mor and Peat as Affected by Enchytraeid Worms

Terrestrial export of dissolved organic carbon (DOC) to watercourses has increased in boreal zone. Effect of decomposing material and soil food webs on the release rate and quality of DOC are poorly known. We quantified carbon (C) release in CO₂, and DOC in different molecular weights from the most common organic soils in boreal zone; and explored the effect of soil type and enchytraeid worms on the release rates. Two types of mor and four types of peat were incubated in laboratory with and without enchytraeid worms for 154 days at +?15 °C. Carbon was mostly released as CO₂; DOC contributed to 2–9% of C release. The share of DOC was higher in peat than in mor. The release rate of CO₂ was three times higher in mor than in highly decomposed peat. Enchytraeids enhanced the release of CO₂ by 31–43% and of DOC by 46–77% in mor. High molecular weight fraction dominated the DOC release. Upscaling the laboratory results into catchment level allowed us to conclude that peatlands are the main source of DOC, low molecular weight DOC originates close to watercourse, and that enchytraeids substantially influence DOC leaching to watercourse and ultimately to aquatic CO₂ emissions.     

Effect of N addition,moisture, and temperature on soil microbial respiration and microbial biomass in forest soil at different stages of litter decomposition

Purpose

The objective of the present study was to investigate the interactive effects of nitrogen (N) addition, temperature, and moisture on soil microbial respiration, microbial biomass, and metabolic quotient (qCO₂) at different decomposition stages of different tree leaf litters.

Materials and methods

A laboratory incubation experiment with and without litter addition was conducted for 80 days at two temperatures (15 and 25 °C), two wetting intensities (35 and 50 % water-filled porosity space (WFPS)) and two doses of N addition (0 and 4.5 g N m^?2, as NH₄NO₃). The tree leaf litters included three types of broadleaf litters, a needle litter, and a mixed litter of them. Soil microbial respiration, microbial biomass, and qCO₂ along with other soil properties were measured at two decomposition stages of tree leaf litters.

Results and discussion

The increase in soil cumulative carbon dioxide (CO₂) flux and microbial biomass during the incubation depended on types of tree leaf litters, N addition, and hydrothermal conditions. Soil microbial biomass carbon (C) and N and qCO₂ were significantly greater in all litter-amended than in non-amended soils. However, the difference in the qCO₂ became smaller during the late period of incubation, especially at 25 °C. The interactive effect of temperature with soil moisture and N addition was significant for affecting the cumulative litter-derived CO₂-C flux at the early and late stages of litter decomposition. Furthermore, the interactive effect of soil moisture and N addition was significant for affecting the cumulative CO₂ flux at the late stage of litter decomposition but not early in the experiment.

Conclusions

This present study indicated that the effects of addition of N and hydrothermal conditions on soil microbial respiration, qCO₂, and concentrations of labile C and N depended on types of tree leaf litters and the development of litter decomposition. The results highlight the importance of N availability and hydrothermal conditions in interactively regulating soil microbial respiration and microbial C utilization during litter decomposition under forest ecosystems.

     

Spatial structure of microbial biomass and activity in prairie soil ecosystems

Management of soil ecosystems requires assessment of key soil physicochemical and microbial properties and the spatial scale over which they operate. The objectives were to determine the spatial structure of microbial biomass and activity and related soil properties, and to identify spatial relationships of these properties in prairie soils under different management histories. Soil were sampled along a transect at 0.2 m intervals in each of five long-term treatments, namely, undisturbed, cattle grazed at two intensities, and cultivated with either wheat (Triticum aestivum L.) or cotton (Gossypium hirsutum L.). Contents of organic carbon (C_org), dissolved organic C (DOC), soluble nitrogen (N_sol), and microbial biomass C (C_mic) and N (N_mic) as well as dehydrogenase activity (DH) in 70 samples were evaluated. Results showed that long-term soil management altered the spatial structure and dependence of C_org and microbial biomass and activity. Cultivation has contributed to high nugget variance for C_org, C_mic, N_mic and DH which interfered with detection of spatial structure at the sampling scale used. Contents of C_org were spatially connected to microbial biomass and activity and to DOC in the uncultivated but not in the cultivated soils, indicating that various factors affected by management may operate at different spatial scales.     

Microbial immobilisation of C rhizodeposits in rhizosphere and root-free soil under continuous C labelling of oats

A greenhouse experiment was conducted by growing oats (Avenasativa L.) in a continuously ¹³CO₂ labeled atmosphere. The allocation of ¹³C-labeled photosynthates in plants, microbial biomass in rhizosphere and root-free soil, pools of soil organic C, and CO₂ emissions were examined over the plant's life cycle. To isolate rhizosphere from root-free soil, plant seedlings were placed into bags made of nylon monofilament screen tissue (16 μm mesh) filled with soil. Two peaks of ¹³C in rhizosphere pools of microbial biomass and dissolved organic carbon (DOC), as well as in CO₂ emissions at the earing and ripeness stages were revealed. These ¹³C maxima corresponded to: (i) the end of rapid root growth and (ii) beginning of root decomposition, respectively. The δ¹³C values of microbial biomass were higher than those of DOC and of soil organic matter (SOM). The microbial biomass C accounted for up to 56 and 39% of ¹³C recovered in the rhizosphere and root-free soil, respectively. Between 4 and 28% of ¹³C assimilated was recovered in the root-free soil. Depending on the phenological stage, the contribution of root-derived C to total CO₂ emission from soil varied from 61 to 92% of total CO₂ evolved, including 4-23% attributed to rhizomicrobial respiration. While 81-91% of C substrates used for microbial growth in the root-free soil and rhizosphere came from SOM, the remaining 9-19% of C substrates utilized by the microbial biomass was attributable to rhizodeposition. The use of continuous isotopic labelling and physical separation of root-free and rhizosphere soil, combined with natural ¹³C abundance were effective in gaining new insight on soil and rhizosphere C-cycling.     

Controls on soil nitrogen cycling and microbial community composition across land use and incubation temperature

We conducted a laboratory incubation of forest (Scots pine (Pinus sylvestris) or beech (Fagus sylvatica)), grassland (Trifolium repens/Lolium perenne) and arable (organic and conventional) soils at 5 and 25 °C. We aimed to clarify the mechanisms of short-term (2-weeks) nitrogen (N) cycling processes and microbial community composition in relation to dissolved organic carbon (DOC) and N (DON) availability and selected soil properties. N cycling was measured by ¹⁵N pool dilution and microbial community composition by denaturing gradient gel electrophoresis (DGGE), phospholipid fatty acid (PLFA) and community level physiological profiles (CLPP). Soil DOC increased in the order of arable<grassland<forest soil while DON and gross N fluxes increased in the order of forest<arable<grassland soil; land use had no affect on respiration rate. Soil DOC was lower, while respiration, DON and gross N fluxes were higher at 25 than 5 °C. Gross N fluxes, respiration and bacterial biomass were all positively correlated with each other. Gross N fluxes were positively correlated with pH and DON, and negatively correlated with organic matter, fungal biomass, DOC and DOC/DON ratio. Respiration rate was positively correlated with bacterial biomass, DON and DOC/DON ratio. Multiple linear modelling indicated that soil pH, organic matter, bacterial biomass, DON and DOC/DON ratio were important in predicting gross N mineralization. Incubation temperature, pH and total-C were important in predicting gross nitrification, while gross N mineralization, gross nitrification and pH were important in predicting gross N immobilization. Permutation multivariate analysis of variance indicated that DGGE, CLPP and PLFA profiles were all significantly (P<0.05) affected by land use and incubation temperature. Multivariate regressions indicated that incubation temperature, pH and organic matter content were important in predicting DGGE, CLPP and PLFA profiles. PLFA and CLPP were also related to DON, DOC, ammonium and nitrate contents. Canonical correlation analysis showed that PLFA and CLPP were related to differences in the rates of gross N mineralization, gross nitrification and soil respiration. Our study indicates that vegetation type and/or management practices which control soil pH and mediate dissolved organic matter availability were important predictors of gross N fluxes and microbial composition in this short-term experiment.     

Effect of paclobutrazol on microbial biomass,respiration and cellulose decomposition in soil

Paclobutrazol is a plant growth regulator largely utilized in mango cultivation and usually applied directly to soil. The aim of this study was to examine the effect of paclobutrazol on soil microbial biomass, soil respiration and cellulose decomposition in Brazilian soils under laboratory conditions. Soil samples were collected from fields with and without a reported history of paclobutrazol application. A solution of paclobutrazol (8 mg of active ingredient kg^?1 of soil) was added to soils, which were then incubated at 28 °C for 30 days. Paclobutrazol decreased soil microbial biomass, soil respiration and cellulose decomposition in soil with and without a report of paclobutrazol application, while significant increase was observed in the respiratory quotient (qCO₂). Our results show that the soil microbiological attributes were negatively affected by paclobutrazol in short-term experiment.     

黄土高原中国松人工林演替过程中的土壤微生物和酶活性

Successional and seasonal effects on soil microbial and enzymatic properties were studied in Chinese pine (Pinus tabu- laeformis) plantations in an age sequence of 3-, 7-, 13-, 21- and 28-year-old in northern Ziwuling region in the middle of Loess Plateau, China. The results indicated that plantation age and season affected soil microbial and enzymatic parameters significantly. Soil organic C, total N, microbial biomass C, microbial quotient, basal respiration, dehydrogenase, N-α-benzoyl-L-argininamide (BAA)-protease, urease and β-glucosidase increased quickly and tended to be highest at PF21 (21-year plantation), thereafter they remained nearly at a constant level, whereas the metabolic quotient (qCO 2 ) showed an initial increase and then decreased gradually. Measures of these soil properties showed significant seasonal fluctuations except for organic C and total N, which were found to be relatively stable throughout the study period, and the seasonal distributions were autumn spring summer winter for microbial biomass C, microbial quotient, dehydrogenase, and β-glucosidase; autumn summer spring winter for BAA-protease and urease; and summer autumn spring winter for basal respiration and qCO 2 . Significant season × age interaction was observed for biomass C, basal respiration, dehydrogenase and BAA-protease.     

Nickel regulation of photoautotrophy in a cyanobacterium

Ni inhibited photoautotrophic growth, nitrogenase activity, oxygenic photosynthesis (O₂-evolution, ¹⁴CO₂-uptake) and respiratory O₂-uptake in the diazotrophic cyanobacterium, Nostoc muscorum. ¹⁴CO₂-uptake was more sensitive to Ni compared to nitrogenase activity, O₂evolution or respiratory O₂-uptake. Lower Ni concentrations (1 μ.M and 5 μM) stimulated N₂ase as well as RuBPcase (ribulose bisphosphate carboxylase) activity. It is proposed that Ni inhibition is mainly through the regulation of RuBPcase activity in the cyanobacterium.     

Effects of collembola on nutrient cycling and microbial biomass on intact soil microcosm

(Jpn. J. Soil Sci.Plant Nutr., 77, 299–306, 2006)

The effects of Collembola (Folsomia candida Willem) on nutrient cycling, microbial biomass, and soil respiration were studied using intact soil microcosms. Intact soil microcosms (dia. 10·6 cm and depth 15 cm) were taken from pine forest soil, and were divided into four treatments · the unmanipulated control and three Collembolan manipulations in which microcosms were defaunated by deep-freezing, and then F. candida were introduced at three densities (0, 50, 100 per microcosm). The microcosms were incubated on forest floor with a roof. At 3- to 4-week intervals the microcosms were irrigated with deionized water for analyses of nutrients (Na+, K+, NH4+, Ca2+, Mg2+, Cl?, NO3?, SO42?) in the leachate. Soil respiration was measured using an infrared gas analyser. After 13 and 34 weeks of exposure, microcosms were destructively sampled. Collembola did not significantly affect microbial biomass C, N, and P nor soil respiration. Because the experiment was started in winter, nutrient leaching increased from spring to summer with increasing microbial activity. At the end of the experiment, leached nitrate from microcosms was significantly different between the 0 and 50 Collembolan treatments. Total established Collembolan biomass was under 4% of the soil microbial biomass in the microcosms, while manipulation of Collembola affected soil nitrogen dynamics at high microbial and collembolan activity.     

Decomposition of peat,biogenic municipal waste compost,and shrub/grass compost added in different rates to a silt loam

An incubation experiment was carried out to test the effects of biogenic municipal waste (compost I) and shrub/grass (compost II) composts in comparison to peat on respiration and microbial biomass in soil. The amounts of these three substrates added were linearly increased in the range of field application rates (0.5%, 1.0%, 1.5%, 2.0%). The sum of CO₂ evolved during the incubation was markedly raised by the three substrates and increased with the rate of substrate concentration. However, the percentage of substrate mineralized to CO₂ decreased with the addition rate from 103 to 56% for compost I, from 81 to 56% for compost II, and from 21 to 8% for peat. During the first 25 days of incubation, compost I enlarged the biomass C content, which remained constant until the end. In contrast, compost II did not raise biomass C initially. But at the end of the incubation, the biomass C content of all 4 compost II treatments almost reached the level of the respective compost I treatment. The increase was significantly larger the more of the two composts was added. In contrast to the two composts, the addition of peat did not have any significant effect on microbial biomass C. The average qCO₂ values at day 25 declined in the order compost I > compost II > peat, at day 92 the order was changed to compost II > peat > compost 1. This change in the order was caused by a significant decrease in qCO₂ values of the compost I treatments, a significant increase in qCO₂ values of the peat treatments and constant qCO₂ values in the compost II treatments.     

The effect of geocryological conditions and soil properties on the spatial variation in the CO<Subscript>2</Subscript> emission from flat-topped peat mounds in the isolated permafrost zone of Western Siberia

The active layer thickness, CO2 emission, and contents of organic substances (including the total organic carbon, labile carbon, and the carbon of microbial biomass) in the soils of flat-topped peat mounds in the area of the Nadym Experimental Station in the north of Western Siberia (experimental site CALM R1) are characterized by considerable spatial variability. The low values of the CО₂ emission are confined to the microelevations on the peatland surface. The high values of the emission (>200 mg CO₂/(m² h)) are typical of the soils with the highest content of the carbon of microbial biomass and the lowest content of the labile organic carbon. The soils of elevated flat-topped peat mounds statistically differ from the soils of waterlogged mires in the contents of total, labile, and microbial carbon and in the CO₂ emission values. Though the soils of elevated flat-topped peat mounds are characterized by the high content of the carbon of microbial biomass (4260 ± 880 mg С/kg soil), the CO₂ emission from them is low (158 ± 23 mg CO₂/(m² h)), which is explained by the structure of microbial communities in the cryogenic soils and by the effect of specific hydrothermic conditions.     

Soluble organic C and N and their relationships with soil organic C and N and microbial characteristics in moso bamboo (Phyllostachys edulis) plantations along an elevation gradient in Central Taiwan

Purpose

Moso bamboo (Phyllostachys edulis), an important economic crop, is distributed from low- to medium-elevation mountains in Taiwan. Bamboo is a fast-growing herbaceous species with an extensive rhizome structure. With the hypothesis that the characteristics of soil organic matter and microbes might change after long-term bamboo plantation, we investigated different fractions of organic C and N as well as soil microbial biomass and activities in five moso bamboo plantations along an elevation gradient in Central Taiwan.

Materials and methods

Five soil samples (top 10 cm of soil) were collected from each bamboo plantation (600, 800, 1,000, 1,200, and 1,400 m above sea level (asl)) in January 2011. Soil was processed and analyzed for soil total C and N contents, biologically available C, potentially mineralizable N, soil microbial biomass and soil respiration (CO₂). Two extraction methods (2 M KCl and hot-water extraction) were used to estimate soil soluble organic C and N (S_bOC and S_bON) and soil inorganic N (NH₄ ⁺ and NO₃ ^?) concentrations to evaluate the relationship with soil organic matter and microbe characteristics in bamboo plantations.

Results and discussion

Soil total C and N contents as well as soil microbial biomass and soil respiration (CO₂) of the bamboo plantations increased along the elevation gradient. Temperature changes along elevation contributed to such variations observed among the selected bamboo plantations. The S_bON in hot-water extracts was highest in the 1,200-m plantation, then in the 1,400-m plantation, and lowest in the low-elevation plantations (600, 800, and 1,000 m). However, S_bON in 2 M KCl extracts did not differ by elevation. The S_bON was strongly correlated with soil total N in both 2 M KCl and hot-water extracts, but only S_bON in hot-water extracts was strongly correlated with microbial biomass N and potentially mineralizable N. S_bOC was strongly correlated with soil total C content, microbial biomass C, and biologically available C in both 2 M KCl and hot-water extracts.

Conclusions

Soil total C and N, S_bOC and S_bON, and microbial biomass characteristics increased in the moso bamboo plantations with increasing elevation. No altitudinal difference in specific soil respiration (CO₂) rate suggested that the enhanced potentially mineralizable N and soil respiration (CO₂) in the high-elevation plantations were associated with increased microbial biomass rather than microbial activities.