Carbon pools and fluxes of 25-year old coniferous and deciduous stands in middle Siberia

Between 72 and 88% of carbon (C) loss in forest litter decomposition returns to the atmosphere in the form of carbon dioxide. The share of water-soluble organic products does not exceed 3–4%. Between 8% under spruce and 25% under aspen and pine of the total C loss from litter organic matter goes to the formation of humus. Decomposition intensity of the dead organic matter on the soil surface is close to annual litterfall income (except under cedar). The specific rate of decomposition processes among the coniferous litters is minimum for cedar (167 mgC g^?1yr^?1) and maximum for larch (249 mg C g^?1 yr^?1). The specific rate of decomposition of organic residues under aspen and birch canopies are 344 and 362 mg C g^?1yr^?1.     

Nutrient balance in Scots pine (Pinus sylvestris L.) forest 1. Design of experiments

The main objectives of the project described in the present and four following papers are:

1. To study tree growth and nutrient status of forest soil as influenced by atmospheric depositions of S and N.
2. To study the influence of plant growth, litter decomposition and atmospheric depositions on soil acidity.
3. To study the influence of atmospheric deposition on the release of N₂O from soil.

One field plot experiment in a Scots pine forest and one lysimeter experiment were established in 1990 on weakly podzolized soils (Cambic arenosol). The experiment was established in a young Scots pine forest. N, Mg and P were applied in a factorial design. The experiment includes 12 treatments and three blocks. Soil was collected in a long-term field experiment with acid rain and filled into lysimeters (bucket type) by horizon. Under each horizon tension lysimeters were installed. The lysimeters were under a roof to avoid input of natural precipitation. S was applied as sulphuric acid diluted to pH levels of 5.5, 4.0, 3.5 and 3.0 and applied in a quantity of 1000 mm ”rain” yr^?1. Nitrogen (NH₄NO₃) was applied in three quantities: 0, 30 and 90 kg N ha^?1 yr^?1. Seedlings of Scots pine were planted in the lysimeters. Lysimeters with no trees were also established. The experiment includes four replicates.     

Riverine transport of atmospheric carbon: Sources,global typology and budget

Atmospheric C (TAC) is continuously transported by rivers at the continents’ surface as soil dissolved and particulate organic C (DOC, POC) and dissolved inorganic C (DIC) used in rock weathering reactions. Global typology of the C export rates (g.m^?2.yr^?1) for 14 river classes from tundra rivers to monsoon rivers is used to calculate global TAC flux to oceans estimated to 542 Tg.yr^?1, of which 37 % is as DOC, 18 % as soil POC and 45 % as DIC. TAC originates mostly from humid tropics (46 %) and temperate forest and grassland (31 %), compared to boreal forest (14 %), savannah and sub-arid regions (5 %), and tundra (4 %). Rivers also carry to oceans 80 Tg. yr^?1 of POC and 137 TG.yr^?1 of DIC originating from rock erosion. Permanent TAC storage on land is estimated to 52 Tg.yr^?1 in lakes and 17 Tg.yr^?1 in internal regions of the continents.     

Effect of surface-casting earthworms on the transport of phosphorus and nitrogen in surface runoff from pasture

Treatment of a soil under permanent pasture with carbaryl (a broad spectrum carbamate biocide) resulted in a 2-fold increase in the volume of surface runoff. This was attributed to a 3-fold reduction in infiltration rate as a result of litter accumulation at the soil surface in the absence of surface-casting earthworm activity. The amounts of dissolved inorganic P (DIP), NH⁺₄-N, and NO^?₃-N in surface runoff from pasture treated with carbaryl (1.18, 9.53 and 4.25 kg ha^?1 yr^?1, respectively) were appreciably greater than those from untreated pasture (0.31, 1.63 and 0.52 kg ha^?1 yr^?1). This was attributed to the large amounts of DIP, NH⁺₄-N, and NO^?1₃-N released from decomposing litter. Following incubation at 4°C for 18 days the release of DIP, NH⁺₄-N and NO^?₃-N from litter was 160, 1600 and 950 μg g^?1, respectively. Losses of particulate P and sediment in surface runoff were lower in the absence (0.31 and 290 kg ha^?1 yr^?1, respectively) than in the presence (0.56 and 1120 kg ha^? yr^?1) of surface casts, pointing to the importance of surface casts as a source of sediment. Surface casts accounted for 45 and 75%, respectively, of the annual loading of particulate P and sediment in surface runoff. Nevertheless, the total loss in surface runoff of P and N forms was increased substantially when the production of earthworm casts was eliminated     

Importance of biological processes in the sulfur budget of a northern hardwood ecosystem

Summary Total S, organic S and sulfate were measured in foliage, litter, roots, soil and solutions at a hardwood site within the Adirondack Mountains of New York. Sulfate as a percentage of total S was similar in foliage and litter (10%), but was greater in roots (30%). Sulfur constituents in the hardwood forest ecosystem were dominated by C-bonded S (60 g m^–2) and ester sulfate (16 g m^–2) which are formed by biological processes. Because sulfur mineralization (1.42 g m^–2 yr^–1) was greater than wet precipitation inputs (0.82 g m^–2 yr^–1), those factors that influence mineralization-immobilization processes are important in evaluating S cycling and sulfate fluxes in this ecosystem. Ester sulfate was formed within the forest floor by the soil biota and was leached to mineral horizons. Annual turnover of this pool was high (25%) within the mineral forest floor. Forest-floor C-bonded S was derived from root and above-ground litter, and substantial amounts were leached to mineral horizons. Calculated storage + outputs (1.64 g m^–2 yr^–1) was much greater than wet inputs (0.82 g m^–2 yr^–1).     

Influence of elevated ecosystems levels on litter decomposition and mineralization

Litter decomposition was studied at two forested watersheds in east Tennessee which differed primarily in their past history of atmospheric S input. Cross Creek Watershed, located near a large coal-fired power plant, has received greater S inputs than the more remote Camp Branch Watershed. Decomposition was estimated through the measurement of forest floor respiration, litter microflora populations, litter and soil microarthropod populations, and litter nutrient status. Average forest floor respiration rates were very similar, 6.78 g CO₂ m^?2 day^?1 or 2472 g m^?2 yr^?1 at Camp Branch and 6.86 g CO₂ m^?2 day^?1 or 2505 g M^?2 yr^?1 at Cross Creek. Fractional loss rates provided estimates of annual decay rates (k) of 0.35 and 0.39 for Camp Branch and Cross Creek, respectively. Litter decomposition was estimated to contribute 23% of the total CO₂ output at Camp Branch and 26% at Cross Creek, while root respiration accounts for about 43 to 46%. Bacterial and fungal populations were about equal in size at both watersheds, with bacteria averaging 100 × 106 g^?1 of litter and fungi 23 × 106 g^?1 of litter. Total numbers of arthropods averaged 34% greater at Camp Branch. Acarina populations averaged 59% higher at Camp Branch, while Collembola numbers were about equal at the two watersheds. Nutrient mobility in the litter and soil was similar at both watersheds. The order of decreasing mobility was K, Mg, Ca, S, N, and P. Litterfall nutrient concentrations were slightly higher for all elements at Cross Creek, resulting in greater litter concentrations of Ca and Mg. Litter concentrations of S and N, however, were significantly greater at Camp Branch, indicating watershed differences in the loss rates and cycling processes of these elements. There were no differences between the loss rates or litter concentrations of P, K, and Na at either site. Overall, decomposition was similar at the two watersheds. Historic S inputs do not appear to have had a major effect on decomposition rate or decomposer organisms with the possible exception of lowered arthropod populations at Cross Creek.     

Silvopasture Switchgrass Fertilized with Poultry Litter: Nutrient Removal,Soil Fertility,and Runoff Water Quality

Alternative use of poultry litter (PL) for forest rather than pasture fertilization would improve forest soil fertility and reduce nutrient build-up in pasture. Yield and nutrient uptake of Alamo switchgrass (Panicum virgatum L.) in a loblolly pine (Pinus taeda L.) silvopasture annually fertilized with PL or urea at 80 and 160 kg N ha^?1 for four years, and without fertilization were compared. Treatment effects on soil fertility and effect of PL on runoff water quality were also determined. Fertilization with N increased yields 120% to an average of 3.8 Mg ha^?1 yr^?1. Since nutrient removal was small, P, base cations and pH increased in the ≤30 cm depth soil with PL. Total P in edge-of-plot runoff was increased by 0.31 kg ha^?1 y^?1 at the higher PL rate. Two applications at this rate per tree rotation might be justified based on increased soil fertility and infrequently increased P load.     

Carbon dioxide, nitrous oxide and methane dynamics in boreal organic agricultural soils with different soil characteristics

The annual carbon dioxide (CO₂), nitrous oxide (N₂O) and methane (CH₄) dynamics were measured with static chambers on two organic agricultural soils with different soil characteristics. Site 1 had a peat layer of 30 cm, with an organic matter (OM) content of 74% in the top 20 cm. Site 2 had a peat layer of 70 cm but an OM content of only 40% in the top 20 cm. On both sites there were plots under barley and grass and also plots where the vegetation was removed. All soils were net sources of CO₂ and N₂O, but they consumed atmospheric CH₄. Soils under barley had higher net CO₂ emissions (830 g CO₂-C m⁻² yr⁻¹) and N₂O emissions (848 mg N₂O-N m⁻² yr⁻¹) than those under grass (395 g CO₂-C m⁻³ yr⁻¹ and 275 mg N₂O-N m⁻² yr⁻¹). Bare soils had the highest N₂O emissions, mean 2350 mg N₂O-N m⁻² yr⁻¹. The mean CH₄ uptake rate from vegetated soils was 100 mg CH₄-C m⁻³ yr⁻¹ and from bare soils 55 mg CH₄-C m⁻² yr⁻¹. The net CO₂ emissions were higher from Site 2, which had a high peat bulk density and a low OM content derived from the addition of mineral soil to the peat during the cultivation history of that site. Despite the differences in soil characteristics, the mean N₂O emissions were similar from vegetated peat soils from both sites. However, bare soils from Site 2 with mineral soil addition had N₂O emissions of 2-9 times greater than those from Site 1. Site 1 consumed atmospheric CH₄ at a higher rate than Site 2 with additional mineral soil. N₂O emissions during winter were an important component of the N₂O budget even though they varied greatly, ranging from 2 to 99% (mean 26%) of the annual emission.     

Effects of Nitrogen Deposition on Nitrous Oxide Emissions from the Forest Floor

Increasing nitrogen deposition due to human activity might have a serious impact on ecosystem functions such as the nitrogen transformations conducted by microbes. We therefore focused on nitrous oxide (N₂O) production as an indicator of soil microbial activity. The rates of N₂O emission from the forest floor were measured every two weeks in two forest stands in the central part of Japan: a red pine stand at Kannondai and a deciduous stand at Yasato. Nitrogen deposition rates by throughfall were 30.6 kg N ha^?1 y^?1 at Kannondai and 15.7 at Yasato. The rates of N₂O emission ranged from 0.5 to 14.2 µg N m^?2 h^?1 (mean 4.5) at Kannondai and from 0.2 to 7.0 µg N m^?2 h^?1 (mean 2.3) at Yasato. The N₂O emission rate showed significant positive relationships with soil temperature and nitrogen deposition during the preceding two weeks. The annual emission rates of N₂O were 0.38 kg N ha^?1 y^?1 at Kannondai and 0.20 at Yasato. As a the annual nitrogen deposition, these rates were 1.23% at Kannondai and 1.27% at Yasato.     

Calculating critical loads of acid deposition with PROFILE — A steady-state soil chemistry model

A steady state soil chemistry model was used to calculate the critical load of acidity for forest soils and surface waters at Lake GÄrdsjön in S.W. Sweden. The critical load of all acid precursors (potential acidity) for the forest soil is 1.64 kmol_c ha^?1 yr^?1, and 1.225 kmol_c ha^?1 yr^?1 for surface waters. For the most sensitive receptor, the critical load is exceeded by 1.0 kmol_c ha^?1 yr^?1, and a 80% reduction in S deposition is required, if N deposition remains unchanged. The critical load is largely affected by the present immobilization of N in the terrestrial ecosystem which is higher than the base cation uptake. The model, PROFILE, is based on mass balance calculations for the different soil layers. From measurable soil properties, PROFILE reproduces the present stream water composition as well as present soil solution chemistry. The model calculates the weathering rate from independent geophysical properties such as soil texture and mineral composition.     

Fluxes and production pathways of nitrous oxide in different types of tropical forest soils in Thailand

Nitrous oxide (N₂O) emissions from the soil surface of five different forest types in Thailand were measured using the closed chamber method. Soil samples were also taken to study the N₂O production pathways. The monthly average emissions (±SD, n?=?12) of N₂O from dry evergreen forest (DEF), hill evergreen forest (HEF), moist evergreen forest (MEF), mixed deciduous forest (MDF) and acacia reforestation (ARF) were 13.0?±?8.2, 5.7?±?7.1, 1.2?±?12.1, 7.3?±?8.5 and 16.7?±?9.2?µg N m^?2 h^?1, respectively. Large seasonal variations in fluxes were observed. Emission was relatively higher during the wet season than during the dry season, indicating that soil moisture and denitrification were probably the main controlling factors. Net N₂O uptake was also observed occasionally. Laboratory studies were conducted to further investigate the influence of moisture and the N₂O production pathways. Production rates at 30% water holding capacity (WHC) were 3.9?±?0.2, 0.5?±?0.06 and 0.87?±?0.01?ng N₂O-nitrogen (N) g-dw^?1day^?1 in DEF, HEF and MEF respectively. At 60% WHC, N₂O production rates in DEF, HEF and MEF soils increased by factors of 68, 9 and 502, respectively. Denitrification was found to be the main N₂O production pathway in these soils except in MEF.     

Comparison of two methods to assess the carbon budget of forest biomes in the Former Soviet Union

The sink of CO₂ and the C budget of forest biomes of the Former Soviet Union (FSU) were assessed with two distinct methods: (1) ecosystem/ecoregional, and (2) forest statistical data. The ecosystem/ecoregional method was based on the integration of ecoregions (defined with a GIS analysis of several maps) with soil/vegetation C data bases. The forest statistical approach was based on data on growing stock, annual increment of timber, and FSU yield tables. Applying the ecosystem/ecoregional method, the area of forest biomes in the FSU was estimated at 1426.1 Mha (10⁶ ha); forest ecosystems comprised 799.9 Mha, non-forest ecosystems and arable land comprised 506.1 and 119.9 Mha, respectively. The FSU forested area was 28% of the global area of closed forests. Forest phytomass (i.e., live plant mass), mortmass (i.e., coarse woody debris), total forest plant mass, and net increment in vegetation (NIV) were estimated at 57.9 t C ha^?1, 15.5 t C ha^?1, 73.4 t C ha^?1, and 1.0 t C ha^?1 yr^?1, respectively. The 799.9 Mha area of forest ecosystems calculated in the ecosystem/ecoregional method was close to the 814.2 Mha reported in the FSU forest statistical data. Based on forest statistical data forest phytomass was estimated at 62.7 t C ha^?1, mortmass at 37.6 t C ha^?1; thus the total forest plant mass C pool was 100.3 t C ha^?1. The NIV was estimated at 1.1 t C ha^?1 yr^?1. These estimates compared well with the estimates for phytomass, total forest plant mass, and NIV obtained from the ecosystem/ecoregional method. Mortmass estimated from the forest statistical data method exceeded the estimate based on the ecosystem/ecoregional method by a factor of 2.4. The ecosystem/ecoregional method allowed the estimation of litter, soil organic matter, NPP (net primary productivity), foliage formation, total and stable soil organic matter accumulation, and peat accumulation (13.9 t C ha^?1, 125.0 t C ha^?1, 3.1 t C ha^?1 yr^?1, 1.4 t C ha^?1 yr^?1, 0.11, and 0.056 t C ha^?1 yr^?1, respectively). Based on an average value of NEP (net ecosystem productivity) from the two methods, and following a consideration of anthropogenic influences, FSU forests were estimated to be a net sink of approximately 0.5 Gt C yr^?1 of atmospheric C.     

Litter decomposition reduces either N2O or NO production in strongly acidic coniferous and broad-leaved forest soils under anaerobic conditions

Purpose

The beneficial effect to the environment of nitrate (NO₃ ^?) removal by denitrification depends on the partitioning of its end products into nitrous oxide (N₂O), nitric oxide (NO), and dinitrogen (N₂). However, in subtropical China, acidic forest mineral soils are characterized by negligible denitrification capacity and thus reactive forms of N could not be effectively converted to inert N₂, resulting in a negative environmental consequence. In this study, the influences of C input from litter decomposition on denitrification rate and its gaseous products under anoxic conditions in the acidic coniferous and broad-leaved forest soils in subtropical China were investigated using the acetylene (C₂H₂) blockage technique in the laboratory.

Materials and methods

The coniferous and broad-leaved forest soils with and without litter addition were incubated under anaerobic conditions for 244 h. There were three treatments for each forest soil including addition of 0.5 and 1% corresponding litter (gram of litter per gram of soil) and the control without addition of litter.

Results and discussion

The results showed that litter addition into the broad-leaved forest soil had no effect on average rates of denitrification (calculated as the sum of NO, N₂O, and N₂), whereas in the coniferous forest soil, the addition resulted in a significant increase in average denitrification rate. In the broad-leaved forest soil, both rates of litter addition decreased the production of NO but increased the production of N₂, and high rates of litter addition into the coniferous forest soil promoted the reduction of N₂O to N₂.

Conclusions

Increased decomposition of litter in the forest soils could effectively reduce N₂O and NO production through denitrification under anaerobic conditions.     

Depletion of soil organic carbon and nitrogen under Pinus taeda plantations in Southern Brazilian grasslands (Campos)

Establishment of pine (Pinus spp.) plantations on grasslands could increase carbon (C) sequestration to counteract increased atmospheric carbon dioxide concentrations. In the grasslands of the southern Brazilian highland (Campos), large areas have been converted to Pinus plantations over the last 30 years. In order to assess the impact of this land‐use change on the amount and composition of soil organic matter (SOM), we investigated a grassland pasture site (G), and both an 8‐year‐old (P8) and a 30‐year‐old (P30) plantation with Pinus taeda. Soil samples down to 45 cm were analysed for texture, pH, soil organic carbon (SOC) and total nitrogen (N_tot) concentrations. Chemical composition of SOM was determined by using cross‐polarization magic angle spinning (CPMAS) ¹³C NMR spectroscopy. We analysed for stable C isotope (δ¹³C) and assessed the lignin composition by CuO oxidation. Additionally, contents of pyrogenic organic material (PyOM) were determined because the Campos is regularly burnt. Both pine plantations revealed relatively small SOC concentrations in the mineral soil of 72.6 mg g^?1 (P8) and 56.8 mg g^?1 (P30) and N_tot concentrations of 4.0 mg g^?1 (P8) and 2.9 mg g^?1 (P30) for the A horizon, while grassland showed significantly (P < 0.01) larger contents of 100.2 mg g^?1 for SOC and 5.9 mg g^?1 for N_tot. Accumulation of litter layers suggests decreased input of organic material into the mineral soil under pine, which was confirmed by the δ¹³C values and lignin composition. Smaller contents of vanillyl‐ (V), syringyl‐ (S), and cinnamyl (C)‐phenols, smaller ratios of S/V and C/V, and smaller ratios of acidic to aldehydic forms of V and S phenols indicated a high degree of decomposition of residual grass‐derived SOM in the upper part of the mineral soil (0–10 cm) under pine plantations. This was confirmed by CPMAS ¹³C NMR spectroscopy, showing an increasing Alkyl C/O‐Alkyl C ratio at the same depth. No significant changes in the contents of PyOM could be detected, but all sites tended to show the greatest concentrations at deeper soil depths > 15 cm, indicating a vertical relocation of PyOM. The results suggest that decomposition of residual SOM originating from grassland species contributes to the decrease of SOC and N_tot and to an acidification in the topsoil under pine plantations. We also suggest that slow litter decomposition and incorporation and the absence of fires at the plantations are additional reasons for the reduced amount of SOM. Depletion of SOM and the acidification of the topsoil may reduce the availability and supply of nutrients and diminish the C sequestration potential of the mineral soil.     

Controls on carbon accumulation and storage in the mineral subsoil beneath peat in Lakkasuo mire, central Finland

What processes control the accumulation and storage of carbon (C) in the mineral subsoil beneath peat? To find out we investigated four podzolic mineral subsoil profiles from forest and beneath peat in Lakkasuo mire in central boreal Finland. The amount of C in the mineral subsoil ranged from 3.9 to 8.1 kg m^?2 over a thickness of 70 cm and that in the organic horizons ranged from 1.8 to 144 kg m^?2. Rates of increase of subsoil C were initially large (14 g m^?2 year^?1) as the upland forest soil was paludified, but decreased to < 2 g m^?2 year^?1 from 150 to 3000 years. The subsoils retained extractable aluminium (Al) but lost iron (Fe) as the surrounding forest podzols were paludified beneath the peat. A stepwise, ordinary least‐squares regression indicated a strong relation (R² = 0.91) between organic C concentration of 26 podzolic subsoil samples and dithionite–citrate–bicarbonate‐extractable Fe (negative), ammonium oxalate‐extractable Al (positive) and null‐point concentration of dissolved organic C (DOC_np) (positive). We examined the ability of the subsoil samples to sorb dissolved organic C from a solution derived from peat. Null‐point concentration of dissolved C (DOC_np) ranged from 35 to 83 mg l^?1, and generally decreased from the upper to the lower parts of the profiles (average E, B and C horizon DOC_np concentrations of 64, 47 and 42 mg l^?1). The DOC_np was positively correlated with percentage of soil C and silt and clay content. The concentration of dissolved organic C in pore water in the peat ranged from 12 to 60 mg l^?1 (average 33 mg l^?1), suggesting that the sorptive capacity of the subsoil horizons for C had been exhausted. We suggest that the increase of C contents in the subsoil beneath mires is related to adsorption of dissolved organic C and slow mineralization under anaerobic conditions.     

Chemical effects of pH 3 sulphuric acid on a soil profile

Cores of podzolic soil (monolith lysimeters) were treated for 4.8 yr with 1500 mm yr^?1 of either 0.5 mM H₂SO₄ at pH 3, equivalent to 24 g S m^?2 yr^?1 (acid treated) or distilled water (controls). The acid treatment was about 37 times greater than the average annual input of H₃O⁺ from rain at the site from which the monoliths were taken. Acid treatment acidified the litter (from pH(CaCl₂)3.4 to pH(CaCl₂)2.6) and the mineral soil to a depth of 80 cm (mean pH(CaCl₂) decrease of 0.2 unit). In the litter and upper A horizon, ion-exchange reactions provided the main neutralizing mechanism, resulting in a decrease in the reserves of extractable (in 2.5 % acetic acid) Ca, Mg, and Mn of about 70 to 80 %. Dissolution of solid phase Al from hydrous oxides provided most neutralization below this depth. Al3⁺ was the principal soluble Al species throughout the profile. In the litter and upper A horizon, some of the mobilized Al³⁺ was retained on cation exchange sites resulting in an increase in exchangeable Al. Deeper in the profile, where the exchange sites were effectively saturated with Al³⁺, no increase in exchangeable Al occurred, and Al³⁺ was, therefore, available for leaching. Some reversible adsorption of SO₄ ^2?, associated with hydrous Al oxides, occurred in the Bs and C horizons. The results are discussed in relation to possible effects of acid deposition over regions of Europe and N. America.     

Nitrification and Methane Oxidation in Forest Soil: Acid Deposition, Nitrogen Input and Plant Effects

In a laboratory incubation experiment, nitrification potential, methane oxidation, N₂O and CO₂ release were studied in the organic soil layer (0–10 cm) of field lysimeters containing re-established soil profiles from a 100-year-old Scots pine (Pinus sylvestris) forest of Norway. The experiment was designed as a full factorial (3 factors; N fertilisation rates, soil acidification, and plants), with three replicates. The more acidic irrigation (pH 3) significantly reduced nitrification potential and N₂O fluxes, methane oxidation and CO₂ release. We concluded that the reduction in soil N₂O release by severe acid deposition is partly due to reduction in nitrification potential. The highest N₂O fluxes were observed in the combination of fertilised planted and less acidic pH treatment. N fertilisation (90 kg N ha^?1 y^?1 with NH₄NO₃) increased soil N₂O release by a factor of 8 and decreased CH₄ oxidation by 60–80%. Plant effects on soil nitrification potential and methane oxidation rates are discussed.     

Fluxes of CO2, CH4 and N2O from drained organic soils in deciduous forests

We examined net greenhouse gas exchange at the soil surface in deciduous forests on soils with high organic contents. Fluxes of CO₂, CH₄ and N₂O were measured using dark static chambers for two consecutive years in three different forest types; (i) a drained and medium productivity site dominated by birch, (ii) a drained and highly productive site dominated by alder and (iii) an undrained and highly productive site dominated by alder. Although the drained sites had shallow mean groundwater tables (15 and 18 cm, respectively) their average annual rates of forest floor CO₂ release were almost twice as high compared to the undrained site (1.9±0.4 and 1.7±0.3, compared to 1.0±0.2 kg CO₂ m⁻² yr⁻¹). The average annual CH₄ emission was almost 10 times larger at the undrained site (7.6±3.1 compared to 0.9±0.5 g CH₄ m⁻² yr⁻¹ for the two drained sites). The average annual N₂O emissions at the undrained site (0.1±0.05 g N₂O m⁻² yr⁻¹) were lower than at the drained sites, and the emissions were almost five times higher at the drained alder site than at the drained birch site (0.9±0.35 compared to 0.2±0.11 g N₂O m⁻² yr⁻¹). The temporal variation in forest floor CO₂ release could be explained to a large extent by differences in groundwater table and air temperature, but little of the variation in the CH₄ and N₂O fluxes could be explained by these variables. The measured soil variables were only significant to explain for the within-site spatial variation in CH₄ and N₂O fluxes at the undrained swamp, and dark forest floor CO₂ release was not explained by these variables at any site. The between-site spatial variation was attributed to variations in drainage, groundwater level position, productivity and tree species for all three gases. The results indicate that N₂O emissions are of greater importance for the net greenhouse gas exchange at deciduous drained forest sites than at coniferous drained forest sites.     

Soil Acidification and Solute Budgets for Forested Lysimeters in Nordrhein-Westfalen

Solute budgets and nitrogen use were quantified in two 400 m² forested lysimeters in St. Arnold, Nordrhein-Westfalen. The lysimeters are covered by a mixture of oak-beech and Weymouth pine, respectively. The average bulk deposition between May 1985 and May 1987 of NH, SO and NO₃ was 1.1, 1.7, and 0.4 kmol_c ha^?1 yr^?1 in the deciduous stand and 2.1, 2.1, and 0.8 kmol_c ha^?1 yr^?1 in the coniferous stand. The input of N is almost completely retained in the deciduous stand. In the coniferous stand about 30% of this N-input is leached as NO₃. Due to N-transformations, total proton turnover is 4.4 kmol_c ha^?1 yr^?1 in the coniferous stand and only 2.5 kmol_c ha^?1 yr^?1 in the deciduous stand. Ca-mobilization is the major acid buffering process in both lysimeters. Only the deciduous stand was limed in 1980 (90 kmol_c/ha). Mobilization of Al is only relevant down to a soil depth of 30 cm. Below a 30 cm depth, Al is immobilized. The amounts of exchangeable and silicate-bound Ca in the soil underlying the coniferous stand are very small, but no evidence was found for explanation of the observed high Ca-mobilization by artificial Ca-sources.     

Potential hazards of lime application in a damaged pine forest ecosystem in Berlin,Germany

Ninety percent of the pines (P. Sylvestris) in the forests of Berlin (West) are classified as damaged. Needle and leaf analyses do not indicate nutrient deficiencies. In site of high S-inputs (55 kg ha^?1 yr^?1 with throughfall) total acid inputs are moderate (2.4 kmol ha^?1 yr^?1) due to their neutralization by carbonatic dusts. Heavy metal depositions have led to accumulations in the forest floor (e.g. Pb 150 mg kg^?1, Cd 0.5 mg kg^?1). The dominating soil type, a cambic arenosol (Ustipsamment) is strongly acidified (pH 3.2 – 4.0) and poor in available nutrients. On an experimental plot, the application of dolomitic lime (6.1 tons ha^?1) and fertilizer (145 kg ha^?1 K₂SO₄) led to a significant increase m pH and base saturation in the top 10 cm of the mineral soil after 2 yr. The data on element fluxes give evidence for increased mineralization rates, enhanced heavy metal accumulation in the forest floor and increased soil solution concentrations of potentially hazardous substances (Al, Cd, NO₃). The lime application is discussed in terms of site specific effects on ecosystem stability and groundwater quality.