Soil carbon and nitrogen budget in Scots pine (Pinus sylvestris L.) stands along an air pollution gradient in eastern Germany

Litterfall, bio- and necromass of the forest floor vegetation, decomposition of recent organic material, soil respiration and humus stocks were examined in 3 Scots pine stands along an air pollution gradient in eastern Germany. High nitrogen loads and increased pH values due to Ca deposition caused shifts in the vegetation structure, and higher biomass production of the forest floor vegetation, whereas needle litter production was not impacted. Simultaneously, decomposition rates of the recently harvested forest floor vegetation decreased with increasing pollutant loads, but needle litter and soil organic matter decomposition rates did not differ between the sites. Consequently, soil carbon and nitrogen stocks increased with increasing pollutant input.     

Effects of coniferous resin on fungal biomass and mineralisation processes in wood ant nest materials

 Wood ants (Formica rufa group) often bring large quantities of conifer resin to their mounds. The aim of this study was to test the hypothesis that the resin acts as a fungicide and thereby reduces C and N mineralisation. Two laboratory incubation experiments were carried out using two different materials: F/H layer from a Scots pine (Pinus sylvestris) stand and mixed litter from Scots pine and Norway spruce (Picea abies) stands. We estimated the effects of resin addition on fungal biomass and on the rates of C and N mineralisation. Addition of resin to the F/H material caused an increase in fungal biomass and C mineralisation, whereas N mineralisation decreased. Addition of resin to litter material did not significantly affect fungal biomass or C and N mineralisation. The results indicate that rather than having a fungicidal effect, resin acts as a C source that increases C mineralisation (mainly from the resin itself) and decreases net N mineralisation. The latter factor might be important in preventing plants dependent on inorganic N from invading and covering the ant mounds. Received: 17 December 1998     

Humusveränderungen nach Einbringung von Buche und Eiche in Kiefernreinbestände

Humus changes after introduction of beech and oak into Scots‐pine monocultures Medium‐ and long‐term (16 to 83 years) effects of an introduction of broadleaf‐tree species (Common beech [Fagus sylvatica] and European‐Sessile Oak [Quercus robur/petraea]) into mature Scots‐pine (Pinus sylvestris) stands on humus type and chemical properties of the Oh layer (pH value, base saturation, C : N ratio) were studied on 16 sites in Bavaria/Germany. The sites investigated covered a large range with respect to elevation, climate, parent material, and soil type. At most sites, the introduction of beech resulted in a significant change of the soil humus type from biologically inactive humus types to more active ones. The strongest changes occurred on the poorest sites, where forest floors under pure pine were particularly biologically inactive. In most cases, the changes in humus type were accompanied by significant increases in the pH value and the base saturation and significant decreases in the C : N ratio of the Oh layer. However, the latter effect was not noticed at most sites with initial C : N ratios higher than 30. In contrast to beech, the introduction of oak did not result in a systematic change of the humus type, the pH value, or the base saturation of the Oh layer. In spite of the considerable change of humus type under beech to biologically more active types, the introduction of broadleaf trees did not result in a systematic change of the thickness or the mass of the forest floor. A decrease in the mass of the Of layer was compensated by an increase of the Oh‐layer mass. All studied sites considered, the introduction of broadleaf trees into Scots‐pine monocultures resulted on average in an 8% decrease of the total amount of organic carbon (C_org) in the forest floor; the C_org amount in the uppermost 10 cm mineral soil increased by 9%. At 35% of all investigated sites, broadleaf tree introduction resulted in increased (+5% to +18%) topsoil (forest floor and uppermost 10 cm mineral soil) C_org stocks. At 30% of the sites, the stock changes were less than ±5%, and on 35% of all sites, soil C_org stocks decreased by –5% to –36%. The average change in the topsoil C_org stock for all studied sites was –5%. The introduction of beech into Scots‐pine monocultures resulted in an ecologically desired translocation of soil organic matter from the forest floor into the mineral topsoil. It is an effective and sustainable silvicultural measure to restore and revitalize acidified, nutrient‐depleted topsoils with biologically inactive humus types.     

DOC leaching from a coniferous forest floor: modeling a manipulation experiment

The DyDOC model simulates the C dynamics of forest soils, including the production and transport of dissolved organic matter (DOM), on the basis of soil hydrology, metabolic processes, and sorption reactions. The model recognizes three main pools of soil C: litter, substrate (an intermediate transformation product), and humic substances. The model was used to simulate the behavior of C in the O horizon of soil under a Norway spruce stand at Asa, Sweden, that had been subjected to experimental manipulations (addition and removal) of above‐ground litter inputs and to removal of the Oi and Oe layers. Initially, the model was calibrated using results for the control plots and was able to reproduce the observed total soil C pool and ¹⁴C content, DOC flux and DO¹⁴C content, and the pool of litter C, together with the assumed content of C in humic substances (20% of the total soil C), and the assumed distribution of DOC between hydrophilic and hydrophobic fractions. The constant describing DOC exchange between micro‐ and macropores was estimated from short‐term variations in DOC concentration. When the calibrated model was used to predict the effects of litter and soil manipulations, it underestimated the additional DOC export (up to 33%) caused by litter addition, and underestimated the 22% reduction in DOC export caused by litter withdrawal. Therefore, an additional metabolic process, the direct conversion of litter to DOC, was added to the model. The addition of this process permitted reasonably accurate simulation of the results of the manipulation experiments, without affecting the goodness‐of‐fit in the model calibration. The results suggest that, under normal conditions, DOC exported from the Asa forest floor is a mixture of compounds derived from soil C pools with a range of residence times. Approximately equal amounts come from the litter pool (turnover time 4.6 yr), the substrate pool (26 yr), and the humic‐substances pool (36 yr).     

Montezuma pine nutrient status as affected by alder densities nitrogen fertilization

Literature reports both positive and negative effects of N‐fixing alders on conifer growth in alder‐conifer stands. Such divergent effects probably result from poorly understood species interactions. The aim of this work was to examine how varying alder‐to‐pine ratios (APRs) and N fertilization affect pine nutrient status. A pseudo‐experiment was installed in each of two areas of regeneration (AR) with different amounts of radiation reaching alder. The experimental approach consisted of a series of pseudoreplicated plots with five APRs within each AR. Half of each plot received 200 kg N ha^–1. Data were interpreted by vector analysis. Alders in the AR 1987 induced needle‐biomass reductions, K deficiency, and P accumulation in pine needles. However, nutrient availability increased with the proportion of alders in the AR 1989, where alders received high sunlight due to a less dense pine stand. Nitrogen fertilization increased needle biomass and N in three out of five alder proportions where alders were sunlight‐limited. In the other stand, with the exception of the no‐alder and A4 plots, positive effects of N fertilization increased with decreasing alder density. We conclude that sunlight‐limited alders may not positively affect associated‐species growth even in N‐limited sites.     

Nitrogen cycling in two Norway spruce (Picea abies) ecosystems and effects of a (NH4)2SO4 addition

Nitrogen cycling in two Norway spruce (Picea abies (L.) Karst.) ecosystems in the ARINUS experimental watershed areas Schluchsee and Villingen (Black Forest, SW Germany) and initial effects of a (NH₄)₂SO₄ treatment are discussed. Although N reserves in the soils are similar and atmospheric N input is the same low to moderate level characteristic for many forested areas in SW Germany, N export by both seepage and streamwater differs considerably. At Villingen, deposited N is almost totally retained in the ecosystem, whereas at Schluchsee N export is the order of the input. This is explained by differences in forest management history. The Villingen site had been subject to excessive biomass export (e.g., litter raking) leading to unfavorable microbial transformations in the soil. In contrast, as a ‘relic’ of the former beech stand, the Schluchsee site is characterized by high biological activity in the soil with vigorous nitrification despite low pH values. Accordingly, the two ecosystems responded differently to the additional N input (150 kg NH₄ ⁺ -N ha^?1 as (NH₄)₂SO₄). Nitrification starting immediately in the Schluchsee soils led to continued Al mobilization and leaching of basic cations and NO₃ ^?. The availability of Mg, already deficient before treatment, further decreased due to Mg leaching and marked N uptake by the stand. In contrast, most of the added N in Villingen was immobilized in the soil. Hence, uptake by the stand and leaching of NO₃ ^? and cations was correspondingly lower than at Schluchsee. The results emphasize the problems associated with the definition of generally applicable values for ‘critical loads’ of N deposition.     

Analytical pyrolysis of a soil profile under Scots pine

The chemical properties of pine needle litter cause slow decomposition, which results in an accumulation of highly lignocellulosic material on the forest floor. Decomposition of organic matter is important for the nutrient turnover in pine forests on nutrient-poor soils. We studied the biodegradation of needles in an organic layer focusing on the various stages of lignin degradation by fungi. Samples were obtained from pine needle litter and a stratified organic layer over nutrient-poor sand under a 60-year-old Scots pine (Pinus sylvestris forest stand. Pyrolysis mass spectrometry (PyMS) and pyrolysis gas chromatography mass spectrometry (PyGCMS) were used to characterize the chemical composition of the needles and the soil. The pyrolysis data show that diterpenoid acids are a main component in fresh needles, but rapidly decrease in the organic layer of the soil, as a result of decomposition. The chemical composition of the soil profile is dominated by guaiacyl lignin and polysaccharides from needle litter. The hexose/pentose ratio increases with depth in the soil profile. The partial preservation of hexose polymers is the result of the preferential decomposition of pentose polymers by white-rot fungi, and points to the input of microbially synthesized polysaccharides. Indications for the degradation of guaiacyl lignin are also found in the soil profile. Oxidative reactions by soil fungi result in a shortening of the side chain of the guaiacyl lignin derivatives and an increase of carbonyl and carboxyl groups. These degradational patterns of lignin in the soil profile under Scots pine are similar to those observed in lignin model compounds and wood lignin degraded by fungi under controlled laboratory conditions.     

Chronic N deposition does not apparently alter the biochemical composition of forest floor and soil organic matter

Future rates of atmospheric N deposition have the potential to slow litter decay and increase the accumulation of soil organic matter by repressing the activity of lignolytic soil microorganisms. We investigated the relationship between soil biochemical characteristics and enzymatic responses in a series of sugar maple (Acer saccharum)-dominated forests that have been subjected to 16 yrs of chronic N deposition (ambient + 3 g NO₃⁻–N m⁻² yr⁻¹), in which litter decay has slowed and soil organic matter has accumulated in sandy spodosols. Cupric-oxide-extractable lignin-derived phenols were quantified to determine the presence, source, and relative oxidation state of lignin-like compounds under ambient and experimental N deposition. Pools of respired C and mineralized N, along with rate constants for these processes, were used to quantify biochemically labile substrate pools during a 16-week laboratory incubation. Extracellular enzymes mediating cellulose and lignin metabolism also were measured under ambient and experimental N deposition, and these values were compared with proxies for the relative oxidation of lignin in forest floor and surface mineral soil. Chronic N deposition had no influence on the pools or rate constants for respired C and mineralized N. Moreover, neither the total amount of extractable lignin (forest floor, P = 0.260; mineral soil, P = 0.479), nor the relative degree of lignin oxidation in the forest floor or mineral soil (forest floor P = 0.680; mineral soil P = 0.934) was influenced by experimental N deposition. Given their biochemical attributes, lignin-derived molecules in forest floor and mineral soil appear to originate from fine roots, rather than leaf litter. Under none of the studied circumstances was the presence or relative oxidation of lignin correlated with the activity of cellulolytic and lignolytic extracellular enzymes. Although chronic atmospheric N deposition has slowed litter decay and increased organic matter in our experiment, it had little effect on biochemical composition of lignin-derived molecules in forest floor and surface mineral soil suggesting organic matter has accumulated by other means. Moreover, the specific dynamics of lignin phenol decay is decoupled from short-term organic matter accumulation under chronic N deposition in this ecosystem.     

Mycorrhizal status of a Scots pine (Pinus sylvestris L.) plantation affected by pollution from a phosphate fertilizer plant

Ectomycorrhizas are an integral, functioning part of many conifer tree species root systems and often considered a link in the causal chain leading to forest decline. In our experiment 12-year-old Scots pine trees grown for 10 years on a polluted acid soil with high aluminium content were compared to a control stand in western Poland. Soil at the polluted site had lower pH than the control site, increased aluminium availability and very low microbial activity. Roots analysed over two years showed lower number of mycorrhizal tips at the polluted site, but only when calculated per soil volume. Differences between sites were not significant when number of mycorrhizal tips was expressed per root mass. There was no significant reduction in the occurrence of any mycorrhizal morphotype. The number of mycorrhizas on trees from the polluted stand was negatively correlated with aluminium content in the needles. Our results showed no clear pollution effect on mycorrhizas in a young stand of Scots pine.     

Organisms,decomposition, and growth of pine seedlings in boreal forest soil affected by sod cutting and trenching

In an experiment with factorial design performed in a mature, mixed Norway spruce (Picea abies (L.) Karst.) and Scots pine (Pinus sylvestris L.) stand in central Finland, we studied the effects of sod cutting (exposing the mineral soil simulating mechanical site preparation) and trenching the study plot (excluding root-mycorrhizal connections) on soil organisms, decomposition rate and pine seedling performance. During two growing seasons after sod cutting, the growth of pine seedlings was significantly enhanced compared to plots with the organic layer left intact. Some epiedaphic soil animals, such as ants, spiders and certain entomobryid collembolan, were more active (pitfall sampling) on sod-cut plots. By the end of the second growing season numbers of enchytraeids were greater in the exposed mineral soil than in the mineral soil under the forest floor. Trenching induced changes in microbial phospholipid fatty acid (PLFA) pattern and collembolan community structure with decreased numbers of collembolans and biomass of fungi in organic soil of uncut plots. In addition, N content of pine seedlings increased after trenching. Overall, the effects of trenching on the measured variables were similar in sod-cut and uncut plots. We conclude that the effects of mechanical site preparation on decomposers and decomposition processes can be explained partly by exclusion of mycorrhizal-root connections and partly by a decrease in unfavourable conditions created by the organic soil layer and ground vegetation.     

Water table is a relevant source for water uptake by a Scots pine (Pinus sylvestris L.) stand: Evidences from continuous evapotranspiration and water table monitoring

The objective of this study was to quantify the main terms of the water cycle in a Scots pine stand (Pinus sylvestris L.) growing on a sandy soil and to estimate the contribution of the shallow water table (0.80 m deep in spring) to the forest water use. Continuous monitoring was organized in 2005 to measure climate, throughfall, soil moisture, tree transpiration and water table variations at a half-hourly basis. Leaf area index seasonal dynamic was measured and roots were counted down to the bottom of the soil profile. Forest floor evapotranspiration was modelled with Granier et al. [Granier, A., Bréda, N., Biron, P., Villette, S., 1999. A lumped water balance model to evaluate duration and intensity of drought constraints in forest stands. Ecol. Model. 116, 269–283]. From May to November, pine transpiration never exceeded 1.85 mm d⁻¹ and reached a total of 176.4 mm, which corresponded to 25% of potential evapotranspiration, whereas the understorey evapotranspiration was 130 mm (i.e. 18–20% of the stand water use). The maximum soil water reserve measured over the soil rooted zone was 250 mm, in which 145 mm was extractable water. A 3.5-week period with no rain was observed in June, which induced a regulation of pine transpiration when the soil extractable water reached 0.25 of its maximum value.We applied the water table fluctuation (WTF) method [White, W., 1932. A method for estimating groundwater supplies based on discharge by plants and evaporation from soil. US Geol. Survey Water Supply Paper 659-A. United States Government Printing Office, Washington, DC] to estimate the water table daily loss of water. A relationship was established with potential evapotranspiration and the actual transpiration fluxes of the stand. Yet, it was not possible to extract from the WTF results the part that was effectively contributing to actual transpiration. We applied then the WTF methodology on longer time intervals, with a focus on periods with no rains. From May to November, the contribution of the water table to forest transpiration reached 61%. During the drought period in June, the water table contributed to 98.5% of the water uptake by vegetation, through its contribution to the capillary rise above the water table. The presence of a groundwater table with a floor down to 180–200 cm allowed this stand to rely upon water that otherwise would have drained deeper.     

Impact of N and P fertilizer application on nutrient cycling in jarrah (<Emphasis Type="Italic">Eucalyptus marginata</Emphasis>) forests of south western Australia

Jarrah (Eucalyptus marginata Donn ex Smith) forest grows on poor soils with low stores of plant-available nutrients. We evaluated the impact of fertilizers on nutrient cycling in soil under Jarrah forest using a field study with three rates of P (0, 50, 200 kg P ha^–1) and three rates of N (0, 100, 200 kg N ha^–1) in a full factorial design. Litterfall was significantly increased by N application (30% relative to controls) in the first 2 years after treatment and by P application in the second year. The amounts of N, P, K, Ca and Mg in litterfall were also increased significantly by both N and P fertilizer. Although fertilizer treatments did not affect the total amount of litter accumulated on the forest floor over 4–5 years after application, there were large treatment differences in the amounts of N and P stored in the forest floor. Microbial respiration in litter was significantly greater (19%) on P-treated plots relative to controls, but this increase did not translate into increased decomposition rates as measured in long-term (5-year) mesh-bag studies. The results indicate that factors other than nutrition are mainly responsible for controlling the rate of decomposition in this ecosystem. Application of P, in particular, resulted in substantial accumulation of P in forest floor litter over 5 years. This accumulation was partly a result of the deposition of P in litterfall, but was also probably a result of translocation of P from the mineral soil. During the 5-year decomposition study, there was no net release of P from leaf litter and, at the highest rate of P application, the amounts of P stored in forest floor litter were more than four-fold greater than in fresh litter. Regular fire, a common phenomenon in these ecosystems, may be an important P-mobilizing agent for enhancing plant P uptake in these forests.     

In situ net N transformations in pine,fir, and oak stands of different ages on acid sandy soil, 3 years after liming

Summary The effect of liming on in-situ N transformations was studied in two stands of different ages of each of Scots pine (Pinus sylvestris L.), Douglas fir [Pseudotsuga menziesii (Mirb.) Franco], and common oak (Quercus robur L.). The stands were located on acid sandy soils in an area with high atmospheric N input. The organic matter of the upper 10-cm layer of the soil, including the forest floor, had a relatively high N content (C: N ratio <25) in all stands. Using a sequential core technique, N transformations were measured in both control plots and plots that had been limed 3 years previously with 3 t ha^-1 of dolomitic lime. Limed plots had a higher net NO _inf3 ^sup- production and a higher potential for NO _inf3 ^sup- leaching than the controls in all stands except that of the younger oak. Net N mineralization did not differ significantly between limed and control plots in oak stands and younger coniferous stands but was significantly lower in the limed plots of the older coniferous stands. It is concluded that long-term measurements of net N mineralization in limed forest soils are needed to evaluate the effect of liming with respect to the risk of groundwater pollution.     

Effect of Chronic Nitrogen Additions on Soil Nitrogen Fractions in Red Spruce Stands

The responses of temperate and boreal forest ecosystems to increased nitrogen (N) inputs have been varied, and the responses of soil N pools have been difficult to measure. In this study, fractions and pool sizes of N were determined in the forest floor of red spruce stands at four sites in the northeastern U.S. to evaluate the effect of increased N inputs on forest floor N. Two of the stands received 100 kg N ha^-1 yr^-1 for three years, one stand received 34 kg N ha^-1 yr^-1 for six years, and the remaining stand received only ambient N inputs. No differences in total N content or N fractions were measured in samples of the Oie and Oa horizons between treated and control plots in the three sites that received N amendments. The predominant N fraction in these samples was amino acid N (31-45% of total N), followed by hydrolyzable unidentified N (16-31% of total N), acid-soluble N (18-22% of total N), and NH₄ ⁺ (9^-13% of total N). Rates of atmospheric deposition varied greatly among the four stands. Ammonium N and amino acid N concentrations in the Oie horizon were positively related to wet N deposition, with respective r2 values of 0.92 and 0.94 (n = 4, p < 0.05). These relationships were somewhat stronger than that observed between atmospheric wet N deposition and total N content of the forest floor, suggesting that these pools retain atmospherically deposited N. The NH₄ ⁺ pool may represent atmospherically deposited N that is incorporated into organic matter, whereas the amino acid N pool could result from microbial immobilization of atmospheric N inputs. The response of forest floor N pools to applications of N may be masked, possibly by the large soil N pool, which has been increased by the long-term input of N from atmospheric deposition, thereby overwhelming the short-term treatments.     

Spatial variability of O layer thickness and humus forms under different pine beech–forest transformation stages in NE Germany

Spatial variability of humus layer (O layer) thicknesses can have important impacts upon soil water dynamics, nutrient storage and availability, as well as plant growth. The purpose of the present study was to elucidate the impact of forest‐transformation practices on the spatial variability of O layer thicknesses. The study focused on the Kahlenberg forest area (NE Germany) with stands of Scots pine (Pinus sylvestris) and European beech (Fagus sylvatica) of different age structures that form a transformation chronosequence from pure Scots pine stands towards pure European beech stands. Topsoil profiles including both, the O layer and the uppermost humic mineral soil horizon were excavated at intervals of 0.4 m along 15–20 m long transects, and spatial variability of O layer thicknesses was quantified by variogram analysis. The correlation lengths of total O layer thickness increased in the sequence consisting of pure pine stand (3.1 m) → older mixed stand (3.7 m) → pure beech stand (4.5 m), with the exception of the younger mixed stand, for which no correlation lengths of total O layer thickness could be determined. The degree of spatial correlation, i.e., the percentage of the total variance which can be described by variograms, was highest for the two monospecies stands, whereas this percentage was distinctly lower for the two mixed stands. A similar minimum for the two mixed stands was observed for the correlation lengths of the Oh horizon. These results suggest that the spatial structures of forest‐transformation stands may be interpreted in terms of a disturbance (in the form of the underplanting of beech trees). After this disturbance, the forest ecosystem requires at least 100 y to again reach relative equilibrium. These findings are in line with the results of other soil‐related investigations at these sites.     

Long‐term development of nitrogen fluxes in a coniferous ecosystem: Does soil freezing trigger nitrate leaching?

In many forest ecosystems chronically large atmospheric deposition of N has caused considerable losses of inorganic N by seepage. Freezing and thawing of soil may alter the N turnover in soils and thereby the interannual variation of N seepage fluxes, which in turn makes it difficult to evaluate the N status of forest ecosystems. Here, we analyzed long‐term monitoring data of concentrations and fluxes of dissolved inorganic N (DIN) in throughfall and seepage from a Norway spruce stand at the Fichtelgebirge (SE Germany) between 1993 and 2004. Despite constant or even slightly increasing N inputs in throughfall, N losses with seepage at 90 cm declined from 15–32 kg N ha^–1 y^–1 in the first years of the study period (1993–1999) to 3–10 kg N ha^–1 y^–1 in 2000 to 2004. The large N losses in the first years coincided with extreme soil frost in the winter of 1995/96, ranging from –3.3°C to –1.0°C at 35 cm soil depth. Over the entire observation period, maximum fluxes of nitrate and ammonium were observed in the mineral soil following thawing of the soil. The elevated ammonium and nitrate fluxes resulted apparently from increased net ammonification and nitrification rates in the mineral soil, whereas mineral‐N fluxes in the O horizon were less affected by frost. Our data suggest that (1) extreme soil frost may cause substantial annual variations of nitrate losses with seepage and that (2) the assessment of the N status of forest ecosystems requires long periods of monitoring. Time series of biogeochemical data collected over the last 20–30 y include years with extreme cold winters and warm summers as well as unusual precipitation patterns. Analysis of such long‐term monitoring data should address climate extremes as a cause of variation in N outputs via leaching. The mean loss of 14.7 kg N with seepage water during 12 y of observation suggests that the forest ecosystem was saturated with N.     

Carbon Control on Nitrogen Dynamics in the Forest Floor of an N-Enriched Deciduous Forest Ecosystem

Recent evidence from nitrogen (N) saturation studies indicates that forest floors in moderately impacted forests are the primary sink for atmospheric N inputs. Some researchers have suggested that the sink capacity of organic horizons is dependent on the amount of available carbon (C), which can be used for microbial N assimilation. To test the hypothesis that C limitation in forest floors exposed to chronic N deposition leads to an enhanced N leaching, a field C input manipulation experiment is under way in a deciduous forest. Since September 1999 aboveground C input has been doubled (by doubling litter input or by amending glucose) or excluded in replicated plots. Here we report the short-term response of concentrations of dissolved inorganic N (DIN: NO₃ ^?-N and NH₄ ⁺-N) in forest floor percolate to the C input manipulation. In autumn following the C input manipulation, DIN concentrations in forest floor percolate decreased in all plots except the No Litter plots compared to the pre-treatment summer concentrations. In contrast, the concentrations of DIN in the No Litter plots remained high. A different seasonal pattern of DIN leaching among treatments, along with measurements of microbial biomass C and potential nitrification rates of forest floor samples, indicates that seasonal N dynamics in the forest floor are largely regulated by C availability changes assoicated with litterfall C input.     

Forest Litters as a Link in the Carbon Cycle in Coniferous–Broadleaved Forests of the Southern Far East of Russia

Forest litter as a component of the carbon cycle in pine–broadleaved forests of different ages was characterized. Field studies of the forest site of the Primorskaya State Agricultural Academy in the south of the Sikhote Alin Range continued for three years. Multiple sampling of forest litter and plant litter fall and measurements of the CO₂ emission from the litter and underlying soil horizons were performed on test plots. The maximum litter pool (14.44 ± 0.86 t/ha) was found in the mature stand of Pinus koraiensis; the minimum litter pool (11.52 ± 0.65 t/ha), in the 80-year-old stand. The carbon stock in the litters amounted to 3.7% of the phytomass carbon. The rate of carbon turnover in the forest litters was relatively low in comparison with that in other regions: the ratio of carbon pools in the litter horizons and annual plant falloff reached 3.5. The winter season provided about 10–25% of the annual plant litter fall. The data obtained in this study describe a part of the carbon cycle and contribute to our understanding of the ecosystem function of climate regulation by valuable forest massifs in the south of the Far East of Russia. In this region, the decomposition of forest litters generates the CO₂ flux amounting up to 16% of the total CO₂ emission from the soil.     

Nutrient cycling in adirondack conifer plantations: Is acidic deposition an influencing factor?

An evaluation of the influences of acidic deposition and forest development on nutrient cycling and conifer productivity at the Charles Lathrop Pack Demonstration Forest, near Warrensburg, New York, was made. This site has a known land use history and is the source of 60 years of soils and silviculture research. Soils were characterized by a nutritional imbalance and support conifer plantations that exhibited declining growth. Historical and contemporary evaluations of nutrient cycling in 47- to 57-yr-old red pine plantations provided no evidence that acidic deposition has had an adverse influence on nutrient cycling. Ap horizon pH decreased from 1949 to 1962 but remained the same from 1962 to 1985. In the B horizon, pH was stable from 1962 to 1985. Exchangeable potassium levels in the Ap horizon fluctuated but did not significantly change from 1949 to 1985: in the B horizon it increased during the period 1962 to 1985. Levels of potassium in the foliage of red pine in unfertilized plots increased from 1949 to 1985, paralleling increases in B horizon potassium levels during that period. There was no increase in cation leaching from the mineral soil that could be attributed to anthropogenic inputs of NO₃ ^? and SO₄ ^2? due to retention of N and S in this ecosystem. Soil solution K⁺ chemistry was similar between the 1960's and the 1980's. Mineral soil pH and base cation status were differentially influenced by tree species since 1930. In general, temporal and contemporary trends of mineral soil pH and base cation status of the soil and foliage indicated that forest development has been the dominant factor influencing nutrient cycling in these conifer plantations. While results of these studies do not conclusively preclude involvement of acidic deposition effects as part of a forest decline syndrome, they indicate the importance of recognizing and measuring natural variability in forest soil processes due to differential species effects and forest aggradation. Because these effects may have a greater impact on stand productivity than the effects of acidic deposition, they can confound interpretation of acidic deposition research if not clearly understood.     

Effects of root and litter exclusion on soil CO2 efflux and microbial biomass in wet tropical forests

We examined the effects of root and litter exclusion on the rate of soil CO₂ efflux and microbial biomass at a soil depth of 25 cm in a secondary forest (dominated by Tabebuia heterophylla) and a pine (Pinus caribaea) plantation in the Luquillo Experimental Forest in Puerto Rico. The experimental plots were initially established in 1990, when root, forest floor mass and new litterfall were excluded for 7 y since then. Soil respiration was significantly reduced in the litter and root exclusion plots in both the secondary forest and the pine plantation compared with the control. Root exclusion had a greater effect on soil CO₂ efflux than the litter exclusion in the plantation, whereas a reversed pattern was observed in the secondary forest. The reduction of microbial biomass in the root exclusion plot was greater in the secondary forest (59%) than in the plantation (31%), while there was no difference of the reduction in the litter exclusion plots between these forests. Our results suggest that above-ground input and roots (root litter and exudates) differentially affect soil CO₂ efflux under different vegetation types.