Responses of ethylene and methane consumption to temperature and pH in temperate volcanic forest soils

There is limited knowledge about the consumption and interaction of methane (CH₄) and ethylene (C₂H₄) in forest soils under disturbances of temperature and acidification. Temperate volcanic forest topsoils (0‐5 cm) sampled under different tree species (e.g. Pinus sylvestris, Cryptomeria japonica and Quercus serrata) were used to study the capacities for CH₄ and C₂H₄ consumption and their sensitivity to temperature and pH. We also studied the responses of soil nitrogen (N) transformations to temperature and relationships to consumption of both CH₄ and C₂H₄. The C₂H₄ consumption rates increased with temperature up to 35^oC, whereas the optimum temperature for CH₄ consumption rates was approximately 25^oC. Both Q₁₀ values and activation energies for CH₄ consumption rates over the range 5 to 25^oC were larger than corresponding values for C₂H₄ consumption rates. The rates of nitrous oxide (N₂O) and nitric oxide (NO) evolution and net N mineralization in the soils increased exponentially with temperature up to 35^oC, with relatively large Q₁₀ values and activation energies for NO evolution. In these forest topsoils, rates of CH₄ and C₂H₄ consumption at pH < 4.0 were negligible, and the pH optimum for both consumptions varied from 5.5 to 6.2. Most of the tested forest soils had an optimum pH for CH₄ and C₂H₄ consumption that was above natural pH values, which indicated that soil acidification would inhibit CH₄ and C₂H₄ consumption in situ. There was a high rate of net C₂H₄ evolution from forest soils acidified experimentally to pH < 4.0, particularly from Cryptomeria japonica forest soil, and 67% of the variation in C₂H₄ evolution rates could be accounted for by the increase in soil water‐soluble organic carbon concentrations. Previous studies have shown that addition of C₂H₄ in headspace gases can inhibit atmospheric CH₄ consumption in such forest soils. Hence, the evolution of C₂H₄ from temperate volcanic forest soils at decreasing pH can exacerbate inhibition of the soil atmospheric CH₄ consumption in situ.     

Ethylene oxidation,atmospheric methane consumption,and ammonium oxidation in temperate volcanic forest soils

Temperate volcanic forest surface soils under different forest stands (e.g., Pinus sylvestris L., Cryptomeria japonica, and Quercus serrata) were sampled to study the kinetics of ethylene (C₂H₄) oxidation and the C₂H₄ concentrations that effectively inhibit oxidation of atmospheric methane (CH₄) and nitrification. The kinetics of C₂H₄ oxidation in temperate volcanic forest soils was biphasic, indicating that at least two different microbial populations, one with low and another with high apparent K _m values, were responsible for ethylene oxidation. Methane consumption activity and ammonium oxidation of soil were inhibited by adding ethylene. Added C₂H₄ at concentrations of 3, 10, and 20 μl C₂H₄ per liter in the headspace gas respectively reduced by 20%, 50%, and 100% atmospheric CH₄ consumption by soil, and these values were much smaller than those inhibiting ammonium oxidation in these forest soils; thus, the CH₄ consumption activity was more sensitive to the addition of C₂H₄ than ammonium oxidation. Previous studies have shown that accumulation of C₂H₄ in such volcanic forest soils within 3 days of aerobic and anaerobic incubations can reach a range from 0.2 to 0.3 and from 1.0 to 3.0 μl C₂H₄ per liter in the headspace gas, respectively. It is suggested that C₂H₄ production beneath forest floors, particularly after heavy rain, can to some extent affect the capacity of forest surface soils to consume atmospheric CH₄, but probably, it has no impact on ammonium oxidation.     

Soluble organic nitrogen in temperate forest soils

Very few studies have been related to soluble organic nitrogen (SON) in forest soils. However, this nitrogen pool could be a sensitive indicator to evaluate the soil nitrogen status. The current study was conducted in temperate forests of Thuringia, Germany, where soils had SON (extracted in 0.5 M K₂SO₄) varying from 0.3 to 2.2% of total N, which was about one-third of the soil microbial biomass N by CFE. SON in study soils were positively correlated to microbial biomass N and soil total N. Multiple regression analysis also showed that mineral N negatively affected SON pool. The dynamics of the SON was significantly affected by mineralization and immobilization. During the 2 months of aerobic incubation, the SON were significantly correlated with net N mineralization and microbial biomass N. SON extracted by two different salt solution (i.e. 1 M KCl and 0.5 M K₂SO₄₎ were highly correlated. In mineral soil, SON concentrations extracted by 1 M KCl and 0.5 M K₂SO₄ solutions were similar. In contrast, in organic soil layer the amount of KCl-extractable SON was about 1.2-1.4 times higher than the K₂SO₄-extractable SON. Further studies such as the differences of organic N form and pool size between SON and dissolved organic N (DON) are recommended.     

Effect of dry-wet cycles on carbon dioxide release from two different volcanic ash soils in a Japanese temperate forest

ABSTRACT

In the present study, two volcanic ash soils (soil A and B) from a temperate broad-leaved forest in eastern Japan were aerobically incubated under repeated dry-wet cycles and continuously constant moisture conditions. The primary aims were to quantify the potential for enhancement of carbon dioxide (CO₂) release owing to increased water fluctuation and to examine differences in the responses of volcanic ash soils with different physicochemical properties. Soil B, rather than soil A, was a typical Andosol. During incubation at 20°C for 120 days with five dry-wet cycles, the CO₂ release rate was measured periodically. Abundance of the stable carbon isotope in CO₂ (δ¹³C-CO₂) was measured to capture changes in the origin of decomposed soil organic matter (SOM) owing to the dry-wet cycles. The CO₂ release rate under the dry-wet cycles was up to 49% higher than the values predicted from a parabolic relationship between CO₂ release and water content during incubation under the continuously constant moisture condition. The magnitude of CO₂ release enhancement was 2.7-fold higher in soil B relative to that in soil A. The δ¹³C-CO₂ value in the dry-wet cycles was enriched by 0.3–2.3‰ compared to that during incubation under the continuously constant moisture conditions, suggesting that the decomposition of well-metabolized and/or old SOM was enhanced by the dry-wet cycles. Thus, the present study suggests that Andosols, which have been believed to have a strong SOM stabilization ability, are vulnerable to dry-wet cycles. Then, increased water fluctuation in a future warmer world would have significant potential to stimulate CO₂ release from soils.     

Influence of vegetation types and soil properties on microbial biomass carbon and metabolic quotients in temperate volcanic and tropical forest soils

Abstract

There is limited knowledge about the differences in carbon availability and metabolic quotients in temperate volcanic and tropical forest soils, and associated key influencing factors. Forest soils at various depths were sampled under a tropical rainforest and adjacent tea garden after clear-cutting, and under three temperate forests developed on a volcanic soil (e.g. Betula ermanii and Picea jezoensis, and Pinus koraiensis mainly mixed with Tilia amurensis, Fraxinus mandshurica and Quercus mongolica), to study soil microbial biomass carbon (MBC) concentration and metabolic quotients (qCO₂, CO₂-C/biomass-C). Soil MBC concentration and CO₂ evolution were measured over 7-day and 21-day incubation periods, respectively, along with the main properties of the soils. On the basis of soil total C, both CO₂ evolution and MBC concentrations appeared to decrease with increasing soil depth. There was a maximal qCO₂ in the 0–2.5 cm soil under each forest stand. Neither incubation period affected the CO₂ evolution rates, but incubation period did induce a significant difference in MBC concentration and qCO₂ in tea soil and Picea jezoensis forest soil. The conversion of a tropical rainforest to a tea garden reduced the CO₂ evolution and increased the qCO₂ in soil. Comparing temperate and tropical forests, the results show that both Pinus koraiensis mixed with hardwoods and rainforest soil at less than 20 cm depth had a larger MBC concentration relative to soil total C and a lower qCO₂ during both incubation periods, suggesting that microbial communities in both soils were more efficient in carbon use than communities in the other soils. Factor and regression analysis indicated that the 85% variation of the qCO₂ in forest soils could be explained by soil properties such as the C:N ratio and the concentration of water soluble organic C and exchangeable Al (P < 0.001). The qCO₂ values in forest soils, particularly in temperate volcanic forest soils, decreased with an increasing Al/C ratio in water-soluble organic matter. Soil properties, such as exchangeable Ca, Mg and Al and water-soluble organic C:N ratio, were associated with the variation of MBC. Thus, MBC concentrations and qCO₂ of the soils are useful soil parameters for studying soil C availability and microbial utilization efficiency under temperate and tropical forests.     

Biological degradation of pyrogenic organic matter in temperate forest soils

Pyrogenic organic matter (PyOM), derived from the incomplete combustion of plant biomass and fossil fuels, has been considered one of the most stable pools of soil organic matter (SOM) and a potentially important terrestrial sink for atmospheric CO₂. Recent evidence suggests that PyOM may degrade faster in soil than previously thought, and can affect native SOM turnover rates. We conducted a six-month laboratory incubation study to better understand the processes controlling the degradation of PyOM in soils using dual-enriched (¹³C/¹⁵N) PyOM and its precursor wood (Pinus ponderosa). We examined the effects of soil type and inorganic N addition on PyOM and wood C and N mineralization rates, microbial C utilization patterns, and native SOM turnover rates. PyOM charred at 450 °C or its precursor pine wood was incubated in two temperate forest subsoils with contrasting short range order (SRO) clay mineralogy (granite versus andesite parent material). Duplicates of experimental treatments with and without PyOM added were sterilized and abiotic C mineralization was quantified. In a second incubation, PyOM or wood was incubated in granitic soil with and without added NH₄NO₃ (20 kg N ha⁻¹). The fate of ¹³C/¹⁵N-enriched PyOM and wood was followed as soil-respired ¹³CO₂ and total extractable inorganic ¹⁵N. The uptake of ¹³C from PyOM and wood by soil microbial community groups was quantified using ¹³C-phospholipids fatty acids (PLFA). We found that (1) The mean residence time (MRT) of PyOM-C was on a centennial time scale (390–600 yr) in both soil types; (2) PyOM-C mineralization was mainly biologically mediated; (3) Fungi more actively utilized wood-C than PyOM-C, which was utilized by all bacteria groups, especially gram (+) bacteria in the andesite (AN) soil; (4) PyOM-N mineralization was 2 times greater in granite (GR) than in AN soils; (5) PyOM additions did not affect native soil C or N mineralization rates, microbial biomass, or PLFA-defined microbial community composition in either soil; (6) The addition of N to GR soil had no effect on the MRT of C from PyOM, wood, or native SOM. The centennial scale MRT for PyOM-C was 32 times slower than that for the precursor pine wood-C or native soil C, which is faster than the MRT used in ecosystem models. Our results show that PyOM-C is readily utilized by all heterotrophic microbial groups, and PyOM-C and -N may be more dynamic in soils than previously thought.     

Origin of cristobalite in soils derived from volcanic ash in temperate and tropical regions

Cristobalite was isolated from four Ando soils and a Podzolic soil developed on volcanic ashes in French West Indies, Indonesia and Japan by selective chemical dissolution with 6 M HCl, 0.5 M NaOH and H₂SiF₆ treatments followed by specific gravity separation. All the cristobalite isolates give X-ray diffractograms with a strong and sharp peak at 4.10–4.11 Å and associated peaks at 2.8 and 2.5 Å, which are characteristic for cristobalite of high-temperature origin. Four out of five isolates show a peak at 4.06–4.07 Å ascribed to low-temperature cristobalite. The oxygen isotopic ratios (δ¹⁸O_SMOW) of cristobalite isolates show a range of +5.3 to +11.0%. which suggests a high-temperature igneous origin. These X-ray diffraction and oxygen isotopic data indicate that the cristobalite was inherited from primary volcanic ash rather than formed during pedogenesis.     

Earthworm communities in temperate beech wood forest soils affected by liming

To monitor the effects of liming on forest ecosystems, experimental plots were installed in forests in mid-western Germany. In addition to soil chemical indices, earthworm communities were investigated on these plots about 15 years after first lime applications took place. As a “natural reference”, communities were compared to earthworm records that derived from a beech forest on limestone. In the non-acidified plots that had never been limed only epigeic earthworms were detected in small numbers and low species richness. Forest liming caused higher pH and a higher base saturation in the mineral topsoils. To a large extent, epigeic earthworm species seemed to benefit from this and had increased in number and biomass at all three different locations selected for the investigations. The epigeic dominated communities were completed by anecic Lumbricus terrestris that was rarely found in some of the samples from one location and a number of endogeic species that showed a very patchy distribution in limed plots. In contrast to this, the soil of the beech forest on limestone showed a different community composition. It was dominated by endogeic species in abundance and by anecic species in biomass. On limestone the total biomass of earthworms clearly exceeded the biomass values from all other plots. In conclusion, a long-term support of forest earthworm fauna due to liming was detected. This support was mainly effective for epigeic species, but in some cases for endogeic and anecic species, too.     

Substantial net N mineralization during the dormant season in temperate forest soils

In temperate forest soils, N net mineralization has been extensively investigated during the growing season, whereas N cycling during winter was barely addressed. Here, we quantified net ammonification and nitrification during the dormant season by in situ and laboratory incubations in soils of a temperate European beech and a Norway spruce forest. Further, we compared temperature dependency of N net mineralization in in situ field incubations with those from laboratory incubations at controlled temperatures. From November to April, in situ N net mineralization of the organic and upper mineral horizons amounted to 10.9 kg N (ha · 6 months)^–1 in the spruce soil and to 44.3 kg N (ha · 6 months)^–1 in the beech soil, representing 65% (beech) and 26% (spruce) of the annual above ground litterfall. N net mineralization was largest in the Oi/Oe horizon and lowest in the A and EA horizons. Net nitrification in the beech soil [1.5 kg N (ha · 6 months)^–1] was less than in the spruce soil [5.9 kg N (ha · 6 months)^–1]. In the range of soil temperatures observed in the field (0–8°C), the temperature dependency of N net mineralization was generally high for both soils and more pronounced in the laboratory incubations than in the in situ incubations. We suggest that homogenization of laboratory samples increased substrate availability and, thus, enhanced the temperature response of N net mineralization. In temperate forest soils, N net mineralization during the dormant season contributes substantially to the annual N cycling, especially in deciduous sites with large amounts of litterfall immediately before the dormant season. High Q₁₀ values of N net mineralization at low temperatures suggest a huge effect of future increasing winter temperature on the N cycle in temperate forests.     

Nitrous oxide production by denitrification and nitrification in temperate forest, grassland and agricultural soils

Nitrous oxide is produced in soils by biological denitrification and nitrification. To improve the fundamental understanding of the processes leading to N₂O fluxes from soils, the production of N₂O from denitrification and nitrification in spruce forest, beech forest, riparian grassland, coastal grassland and an agricultural field were studied. Samples were taken at a high and a low position along a topographic gradient in each site in the spring and autumn when the largest N₂O fluxes were expected. They were incubated after being amended with N, and C₂H₂ was used as biological inhibitor to distinguish nitrification and denitrification. The N₂O production in the low landscape position varied between 32 and 121 ng N cm^?3 h^?1 in the riparian grassland. 9 and 26 ng N cm^?3 h^?1 in the coastal grassland, and 135 and 195 ng N cm^?3 h^?1 in the agricultural field which was 10–100 times more than in the high positions where rates ranged between 3 and 5 ng N cm^?3 h^?1, 0.3 and 0.4 ng N cm^?3 h^?1, and 7 and 10 ng N cm^?3 h^?1, respectively. These differences almost certainly arose because the soil in the low positions was wetter and contained more organic matter. In the two forests N₂O production was less than 1 ng N cm^?3 h^?1, strongly inhibited by O₂, and not influenced by landscape position. Nitrification contributed to more than 60% of total N₂O production in the riparian grassland. In the agricultural field nitrification produced 13–74% of the total N₂O in the low position, and 10–88% in the high position. Denitrification was the dominant source of N₂O in the coastal grassland except at the low position in the autumn where nitrification produced 60% of the total N₂O. In the two forests where the soil had small nitrification potentials denitrification was the only source of N₂O. In the other sites nitrification and denitrification potentials were large and of identical magnitude. The results emphasize the need to separate nitrification and denitrification at the process level and to recognize topography at the field scale when modelling N₂O effluxes from soil.     

Consequences of nitrogen fertilization on soil methane consumption in a productive temperate deciduous forest

To investigate the consequences of long-term N additions on soil CH₄ dynamics, we measured in situ CH₄ uptake rates, soil profiles and kinetics parameters during the growing season in a temperate deciduous forest in northwestern Pennsylvania (Allegheny College Bousson Environmental Forest). Measurements were made in control and adjacent plots amended with 100 kg N ha^–1 year^–1 for 8 years. We found that the in situ consumption rates were 0.19±0.02 (mean±SE) for the control and 0.12±0.01 mg CH₄–C m^–2 h^–1 for the N treatment, indicating that consumption had been reduced by 35% after 8 years of N amendments. Despite the large difference in rates of consumption, there were no differences in the CH₄ concentration profiles between the control and N-amended plots. Laboratory incubations of CH₄ consumption throughout the soil column (organic horizon and mineral soil depths) showed that rates were greatest in the organic horizon of both control and N-amended soils, although consumption was reduced by 42% in the N-amended plot. However, the rate in the organic horizon was only about 50% the rate measured in organic horizons at other temperate forests. The apparent K_m [K_m(app)] value in the organic horizon of the control plot was fourfold less than the K_m(app) value in the organic horizon of another temperate forest, but similar to the K_m(app) values in adjacent plots amended with N for a decade. Unlike results for other temperate forests, K_m(app) values at Bousson generally did not decrease with soil depth. These results indicate that N cycling strongly controls the CH₄-consuming community, and suggest that alterations of the N cycle due to N deposition or addition may alter rates and the location of CH₄ consumption by soils, even in soils with high N content and cycling rates.     

Stoichiometric responses of soil microflora to nutrient additions for two temperate forest soils

The ratios of soil carbon (C) to nitrogen (N) and C to phosphorus (P) are much higher in Chinese temperate forest soils than in other forest soils, implying that N and P might limit microbial growth and activities. The objective of this study was to assess stoichiometric responses of microbial biomass, enzyme activities, and respiration to N and P additions. We conducted a nutrient (N, P, and N + P) addition experiment in two temperate soils under Korean pine (Pinus koraiensis) plantation and natural broadleaf forest in Northeast China and measured the microbial biomass C, N, P; the activities of β-glucosidase (BG), N-acetyl-β-glucosaminidase (NAG), and acid and alkaline phosphomonoesterase (AP); and the microbial respiration in the two soils. Nitrogen addition increased microbial biomass N and decreased microbial biomass C-to-N ratio and microbial respiration in the two soils. Nitrogen addition decreased NAG activity to microbial biomass N ratio, P addition decreased AP activity to microbial biomass P ratio, and N, P, and N + P additions all increased BG activity to microbial biomass C ratio. These results suggest that microbial stoichiometry is not strictly homeostatic in response to nutrient additions, especially for N addition. The responses of enzyme activities to nutrient additions support the resource allocation theory. The N addition induced a decline in microbial respiration, implying that atmospheric N deposition may reduce microbial respiration, and consequently increase soil C sequestration in the temperate region.     

Effect of water tension on ethylene production and consumption in montane and lowland soils in Austria

The trace gas ethylene affects plant growth and atmospheric chemistry and it interferes with soil restoration. In soil ethylene is simultaneously produced and consumed by different microorganisms. The effects of land use and soil moisture conditions on processes leading to an accumulation of ethylene are still unclear. We measured the rates at which montane and lowland soils from Austria produced and consumed ethylene over a range of water tensions and oxygen supply. Complete anaerobiosis (waterlogging, zero tension) favoured ethylene production, whereas ethylene degradation rates were greatest in soils at 30 kPa water tension. Soils from the lowland region of eastern Austria produced ethylene at rates of up to 12 pmol C₂H₄ g^–1 h^–1 under anaerobic conditions, and they consumed ethylene at rates reaching 231 pmol C₂H₄ g^–1 h^–1, after addition of 20 μl l^–1 ethylene. Deciduous forest soils consumed ethylene fastest. Ethylene formed rapidly and was also consumed rapidly in soils rich in humus and total nitrogen. Soils taken from the mountains both produced and consumed ethylene more rapidly than lowland soils did. Production rates reached 146 pmol C₂H₄ g^–1 h^–1 under anaerobic conditions. Spruce forest soils produced significantly more ethylene than pastures. Ethylene formation was negatively correlated with soil pH. In montane soils ethylene production was related to the availability of simple carbon sources, expressed by the amount of extractable glucose equivalents. Maximum ethylene degradation amounted to 895 pmol g^–1 h^–1. Most of the soils were net sinks for ethylene at a water tension of 30 kPa and drier.     

A comparative study on chemical characteristics of tropical soils from volcanic material under forest and agriculture

Abstract

An investigation was conducted to compare differences in chemical characteristics of Costa Rica soils under continuous cultivation and under forest vegetation. Inceptisols from young volcanic material under forest, sugar cane, coffee and pasture, respectively, were sampled in the San Carlos region of Costa Rica, and analysed for pH, organic matter, N, Ca, Mg, K, Na, Al, Fe, Zn and Mn contents. Indications were obtained that continuous cropping for 1 to 22 years with sugar cane resulted in a decrease in Ca and Mg content and an increase in acid extractable Al concentrations, compared to amounts found in forest soils. In soils under coffee the only significant changes were a reduction in soil organic matter, N and Al contents. Exchangeable bases decreased slightly during the first two years, but in fields 15 years under coffee, the content of exchangeable bases was affected slightly, except for a relatively marked decrease in amounts of Mg. Conversion into pasture maintained soil fertility at a level comparable to that found in the forest soil ecosystem. It was concluded that differences in vegetational ecosystems caused soil chemical changes, but deforestation in the tropics did not necessarily result in rapid soil degradation processes. The magnitude of the data showed that the soil in the San Carlos region of Costa Rica had been cultivated for at least 10 to 20 years without producing evidence of excessive deterioration.     

Production and consumption of N2O during denitrification in subtropical soils of China

Purpose

Nitrous oxide (N₂O) production and reduction rates are dependent on the interactions with each other and it is therefore important to evaluate them within the context of simultaneously operating N₂O emission and reduction. The objective of this study was to quantify the simultaneously occurring N₂O emission and reduction across a range of subtropical soils in China, to gain a mechanistic understanding of potential N₂O dynamics under the denitrification condition and their important drivers, and to evaluate the potential role of the subtropical soils as either sources or sinks of N₂O through denitrification.

Materials and methods

Soils (45, from a range of different land uses and soil parent materials) were collected from the subtropical region of Jiangxi Province, China, and tested for their potential capacity for N₂O emission and N₂O reduction to N₂ during denitrification. N₂O emission and reduction were determined in a closed system under N₂ headspace after the soils were treated with 200?mg?kg^?1 NO ₃ ^? -N and incubation at 30?°C for 28?days. The soil physical and chemical properties, the temporal variations in headspace N₂O concentration, and NO ₃ ^? -N and NH ₄ ⁺ -N concentrations in the soil slurry were measured.

Results and discussion

Variations in N₂O concentration (N) over incubation time (t) were consistent with an equation in which average R ²?=?0.84?±?0.11 (p?<?0.05): $ N = A \times \left( {1 - \exp \left( { - {k_1} \times t} \right)} \right) - B \times \exp \left( {{k_2} \times t} \right) $ , where A is the total N₂O emission during the incubation, B is a constant, and k ₁ and k ₂ are the N₂O emission constant and reduction constants, respectively. The results of the simulation showed that k ₁ was greater than k ₂. The reduced amount of NO ₃ ^? -N in the first 7?days of incubation and the N₂O emission rate (the percentage of A value relative to the amount of NO ₃ ^? -N reduced during the 28-day incubation, R _n) were able to explain 82.9?% (p?<?0.01) of the variation in total N₂O emission (A) during the incubation for the soil samples studied, indicating that the total amount of N₂O emitted was determined predominately by denitrification capacity. Soil organic carbon content and soil nitrogen mineralization are the key factors that determine differences in the amounts of reduced NO ₃ ^? -N among the soil samples. The R _n value decreased with increasing k ₂ (p?<?0.01), indicating that soils with higher N₂O reduction capacity under these incubation conditions would emit less N₂O per unit of denitrified NO ₃ ^? -N than the other soils. Results are valuable in the evaluation of net N₂O emissions in the subtropical soils and the global N budget.

Conclusions

In a closed, anaerobic system, variations in N₂O concentration in the headspace over the incubation time were found to be compatible with a nonlinear equation. Soil organic carbon and the amount of NH ₄ ⁺ -N mineralized from the organic N during the first 7?days of incubation are the key factors that determine differences in the N₂O emission constant (k ₁), the N₂O reduction constant (k ₂), the total N₂O emission during the incubation (A) and the N₂O emission rate (R _n).     

Available potassium in volcanic soils of Kamchatka

The distribution of available potassium in the profiles of synlithogenic volcanic soils of Kamchatka has been studied. Most of the soils in the Central Kamchatka Depression and the Western Kamchatka Lowland are characterized by a medium content of nonexchangeable potassium and a high content of exchangeable potassium. The soils of the east coast are less rich in potassium. The reserves of available potassium in the root layer of the virgin and cultivated soils of Kamchatka have been calculated. It is shown that differences in the reserves of potassium are related to different degrees of the soil tolerance toward the depletion of potassium and to the uneven application of potassium fertilizers. In most cases, soil cultivation is accompanied by a general rise in the reserves of available potassium with an increase in the portion of exchangeable potassium relative to its nonexchangeable forms.     

Effects of changes in pH, ionic strength, and sulphate concentration on the CEC of temperate acid forest soils

As the acidity of rain diminishes, changes in the pH, ionic strength, and ion activities of the soil solution will influence the charge characteristics of soil. We have investigated the response of cation exchange capacity (CEC) of three acid forest soils of variable charge to small changes in pH, ionic strength, and SO^2?₄ concentration. The variable charge for these temperate soils has the same significance as for tropical soils and those from volcanic ash. Maximum absolute increase in CEC on increasing pH by 0·2–0·5 units reached 5 cmol_c kg^-1 in O horizons. The increase in CEC on doubling ionic strength in EA and Bsh horizons of a Cambic Podzol was about half that amount, but relative gains compared to effective CEC were 65 and 46%, respectively. For other soil horizons, absolute changes were smaller, and relative changes were between 10 and 30%. Halving the SO^2?₄ concentration significantly influenced CEC only in some samples. Both pH and ionic strength must be adjusted with care when determining CEC_c of acid forest soils. Decreasing acid deposition will not inevitably increase CEC_c because in some soils pH effects may be balanced by simultaneous decrease in ionic strength.     

Speciation of phosphorus in temperate zone forest soils as assessed by combined wet‐chemical fractionation and XANES spectroscopy

Phosphorus availability in terrestrial ecosystems is strongly dependent on soil P speciation. Here we present information on the P speciation of 10 forest soils in Germany developed from different parent materials as assessed by combined wet‐chemical P fractionation and synchrotron‐based X‐ray absorption near‐edge structure (XANES) spectroscopy. Soil P speciation showed clear differences among different parent materials and changed systematically with soil depth. In soils formed from silicate bedrock or loess, Fe‐bound P species (FePO₄, organic and inorganic phosphate adsorbed to Fe oxyhydroxides) and Al‐bound P species (AlPO₄, organic and inorganic phosphate adsorbed to Al oxyhydroxides, Al‐saturated clay minerals and Al‐saturated soil organic matter) were most dominant. In contrast, the P speciation of soils formed from calcareous bedrock was dominated (40–70% of total P) by Ca‐bound organic P, which most likely primarily is inositol hexakisphosphate (IHP) precipitated as Ca₃‐IHP. The second largest portion of total P in all calcareous soils was organic P not bound to Ca, Al, or Fe. The relevance of this P form decreased with soil depth. Additionally, apatite (relevance increasing with depth) and Al‐bound P were present. The most relevant soil properties governing the P speciation of the investigated soils were soil stocks of Fe oxyhydroxides, organic matter, and carbonate. Different types of P speciation in soils on silicate and calcareous parent material suggest different ecosystem P nutrition strategies and biogeochemical P cycling patterns in the respective ecosystems. Our study demonstrates that combined wet‐chemical soil P fractionation and synchrotron‐based XANES spectroscopy provides substantial novel information on the P speciation of forest soils.