Forest Nutrition Research Articles

The scientific value of long-term field trials in forest soils and nutrition research: An opportunist's perspective

Prescott, C. E. 2014. The scientific value of long-term field trials in forest soils and nutrition research: An opportunist's perspective. Can. J. Soil Sci. 94: 255-262. Long-term field trials are essential in allowing accurate prediction of stand responses to silvicultural treatments. Less well appreciated is the added value that long-term field trials afford to science through a variety of means, often not included in the original experimental plan. Long-term field trials provide a platform upon which additional studies can be conducted; for example a suite of alternative silvicultural trials allowed assessment of influences of forest harvesting on rates of litter decomposition. Well-designed, long-term field trials can be re-purposed to address questions not related to the original research; for example, many of the common garden experiments used to discern influences of different tree species on soil were not originally intended for this purpose. Long-term trials may reveal effects on other ecosystem ...

Deposição de serapilheira e nutrientes em plantio de Eucalyptus urophylla × E. globulus

Objetivou-se com o presente estudo avaliar a deposição de serapilheira e nutrientes em plantio de Eucalyptus urophylla × Eucalyptus globulus, em Eldorado do Sul-RS. Foram alocadas sistematicamente quatro parcelas de 20 m × 20 m, cada uma com quatro coletores de serapilheira de 1 m². A serapilheira foi coletada quinzenalmente, entre janeiro/2007 e dezembro/2010. A produção de serapilheira foi crescente, com o aumento da idade do povoamento, sendo 6,9 Mg ha-1 aos seis e 8,5 Mg ha-1 aos nove anos. A fração folhas correspondeu, em média, a 66,9% da serapilheira total, seguida pelos galhos finos (14,7%), miscelânea (10,5%) e galhos grossos (7,9%). A deposição apresentou padrão sazonal, sendo maior no período de aumento da temperatura do ar. A fração folhas foi responsável por maior parte do retorno de nutrientes via serapilheira, variando de 58,2 a 81,8% da quantidade de Cu e N, respectivamente.

Effects of forest harvest on soil nutrients and labile ions in Podzols of southwestern Canada: Mean and dispersion effects

Forest harvest can disrupt biogeochemical cycles with consequences for regenerating forest nutrition and drainage water quality. Few studies have examined harvest impacts on soil chemistry in conifer forests which have not been significantly affected by acid deposition, as found on the Canadian West Coast. This study investigates the effects of conventional clear-cutting on soil chemistry in Podzols of Roberts Creek Study Forest (southwestern Canada). We measured forest floor composition, soil pH and salt-extractable ions concentrations in undisturbed forested stands (control plots), stands harvested 2 to 5years prior to sampling (cleared plots) and stands harvested 8 to 15years prior to sampling (regenerating plots). We focused on the effects of forest harvest both on mean (differences in average values) and dispersion parameters (differences in variance between treatments).We found that forest floors of harvested plots had lower phosphorus and potassium concentrations than control plots. In the mineral subsoil, exchangeable K was however higher in harvested than in control plots. This suggests that some of the K lost from the forest floor was preferentially retained in mineral horizons, possibly due to sorption to poorly crystalline and free aluminum and iron mineral phases. The subsoil of harvested plots was slightly more acidic than control plots. In contrast to classic studies of forest harvest impacts conducted in the U.S. Northwest, we did not measure pronounced acidification, a loss of base cations or an increase in exchangeable Al, most likely due to the much lower prior acid deposition load at our sites. The most notable harvest effect was a large increase in the variability of inorganic N concentration. This suggests an increase in micro-heterogeneity of post-harvest nutrient availability which has implications for the nutrition of regenerating vegetation, nutrient leaching potential as well as our ability to detect harvest-induced changes.

Ectomycorrhizal fungi and the nitrogen economy of conifers — implications for genecology and climate change mitigation

The nitrogen (N) economy of conifers is hypothesized to reflect three spatially defined and interacting sources of variability in forest nutrition. These include the physiological adaptations of the host tree (N uptake capacities among populations), matched to the particular amount and nature of soil N supply (organic N, NH4+, and NO3–), as mediated by communities of site-adapted ectomycorrhizal (EM) fungi. The spatial attributes of an N economy may vary considerably over the ranges of tree species because of wide gradients in climate and soil fertility, underpinning a potentially important aspect of conifer genecology with implications for climate change mitigation. The evidence for an intersection of N supply with host demand, as mediated by EM fungi, will be briefly reviewed and then evaluated in light of assisted migration studies involving provenance trials of coastal Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco var. menziesii) in southwestern British Columbia. The trials were established across a wide range of site types, and so they provide valuable data on host response to gradations in soil N supply and interactions with local EM fungal communities. Preliminary results and knowledge gaps will be discussed under the framework of an N economy and management of forest genetic resources.

Forest nutrition and fertilization in teak (Tectona grandis L.f.) plantations in Central America†

Soil fertility management and forest nutrition are key factors determining management and productivity of both natural and planted forests. Reference values for foliar and soil nutrient contents and assessment of nutrient balances to evaluate the sustainability of planted forest systems can guide forest managers in determining whether or not additional fertilisation is required. This review summarises the authors' research into the nutritional requirements for planted teak (Tectona grandis L.f.) forests in Central and South America. Teak is an important species for commercial forest plantations, usually in carefully selected productive sites, with rotations of 20-25 years and commercial volume anticipated to be around 10 m3 ha-1 year-1. Foliar nutrient concentration values can be used as a reference to evaluate the nutritional status of planted teak forests. In addition, there may be an association between the dynamics of the concentrations of K, Mg and N with tree age and the age-related declines in teak productivity. Timber extraction by felling constitutes a major nutrient output from the system and repeated nutrient exports during several rotations could be a cause of soil nutrients depletion, especially P and K which typically have low availability in these Central American systems. Multivariate analyses have been shown to be appropriate and helpful tools for grouping forest stands by fertility classes (i.e. soil management zones using the terminology of precision agriculture). The techniques developed can be used as tools for the design of efficient fertilisation programmes, taking into account the inherent heterogeneity of soil fertility across different stands. This is considered as a first step towards a precision forestry scheme. Whether age-related changes in nutrient concentrations are a cause or a consequence of age-related declines in productivity is an important issue for future research.

Nutrient concentration age dynamics of teak (Tectona grandis L.f.) plantations in Central America

Aim of study. Appropriate knowledge regarding teak (Tectona grandis L.f.) nutrition is required for a better management of the plantations to attain high productivity and sustainability. This study aims to answer the following questions: How can it be determined if a teak tree suffers a nutrient deficiency before it shows symptoms? Are nutrient concentration decreases in older trees associated with age-related declines in forest productivity?Area of study. Costa Rica and Panama.Material and Methods. Nutrient concentration in different tree tissues (bole, bark, branches and foliage) were measured at different ages using false-time-series in 28 teak plantationsResearch highlights. Foliar N concentration decreases from 2.28 in year 1 to 1.76% in year 19. Foliar Mg concentration increases from 0.23 in year 1 to 0.34% in year 19. The foliar concentrations of the other nutrients are assumed to be constant with tree age: 1.33% Ca, 0.88% K, 0.16% P, 0.12% S, 130 mg kg-1 Fe, 43 mg kg-1 Mn, 11 mg kg-1 Cu, 32 mg kg-1 Zn and 20 mg kg-1 B. The nutrient concentration values showed can be taken as a reference to evaluate the nutritional status of similar teak plantations in the region. The concentrations of K, Mg and N could be associated with declines in teak plantation productivity as the plantation becomes older. Whether age-related changes in nutrient concentrations are a cause or a consequence of age-related declines in productivity is an issue for future research with the aim of achieving higher growth rates throughout the rotation period.Key words: forest nutrition; age-related decline in productivity; nutrient foliar concentration; nutrient bole concentration; resorption.

Towards the Operational Use of Satellite Hyperspectral Image Data for Mapping Nutrient Status and Fertilizer Requirements in Australian Plantation Forests

EO-1/Hyperion data can potentially reduce the cost of nutrition assessments in plantation forests, supplementing standard point-based measurements with comprehensive and repeated broad-acre coverage. We present a synopsis of studies using EO-1/Hyperion data for foliar nutrition assessments in Australia. The earliest study compared modeling methods and calculated models in the order of <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</i> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> = 0.7 for Nitrogen, Phosphorus and Boron in Eucalyptus and Pinus species. Several recommendations of that work were adopted in a subsequent project which concluded that observing stand structure may improve nutrient prediction models calibrated from image data over those calibrated from laboratory spectra. The most recent study examined the range of age classes over which nutrients could be accurately predicted in P. radiata from Hyperion images. Canopy cover fraction, calculated using spectral mixture analysis, ranged from 69% in unthinned 5 year old stands to 43% and 41% in stands 10 to 20 years old that had been thinned once or twice respectively. The <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</i> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> value when predicting Nitrogen across all age classes was 0.45 increasing to 0.87 when calibrated on only the 5 year old trees. Collectively, these studies demonstrate that several important nutrients can be accurately mapped from Hyperion data at ages that are critical for the management of plantation forests. However, some of Hyperion's spatial and radiometric characteristics limit its practical operational application. This manuscript discusses potential improvements that might be provided by the HyspIRI mission, and the key challenges in developing hyperspectral image data as an operational tool for forest nutrition assessments in Australia.

Acidification and Nitrogen Eutrophication of Austrian Forest Soils

We evaluated the effect of acidic deposition and nitrogen on Austrian forests soils. Until thirty years ago air pollution had led to soil acidification, and concerns on the future productivity of forests were raised. Elevated rates of nitrogen deposition were believed to cause nitrate leaching and imbalanced forest nutrition. We used data from a soil monitoring network to evaluate the trends and current status of the pH and the C : N ratio of Austrian forest soils. Deposition measurements and nitrogen contents of Norway spruce needles and mosses were used to assess the nitrogen supply. The pH values of soils have increased because of decreasing proton depositions caused by reduction of emissions. The C : N ratio of Austrian forest soils is widening. Despite high nitrogen deposition rates the increase in forest stand density and productivity has increased the nitrogen demand. The Austrian Bioindicator Grid shows that forest ecosystems are still deficient in nitrogen. Soils retain nitrogen efficiently, and nitrate leaching into the groundwater is presently not a large-scale problem. The decline of soil acidity and the deposition of nitrogen together with climate change effects will further increase the productivity of the forests until a limiting factor such as water scarcity becomes effective.

Potassium for better crop production and quality

Increasing crop production while improving quality remains an important goal, particularly in the developing world. Significant increases in food prices and growing economic crises have a major impact on nutritional status of human populations and exacerbate global malnutrition. These developments make nutrient security together with food security a key global challenge. Among many factors, an adequate and well balanced nutrition with mineral nutrients is a fundamental issue in achieving a high crop production and a better quality in practical agriculture. Of the mineral nutrients, imbalanced nutrition with potassium (K) is well known and becoming an important constraint to crop production in the developing countries. Very low rates of potash fertilizer application in agricultural production in India and other developing countries lead to rapid depletion of K in the soil. Depletion of plant-available K in soils results in a variety of negative impacts, including preventing optimum utilization of applied nitrogen and phosphorus fertilizers, decreasing farmers’ income, threatens the yields of the cropping systems (e.g., wheat-rice cropping systems) and hence jeopardizes the future food and nutrient security. Indian growers and their advisors need to adopt advanced tools for potash fertilizer applications and updated K recommendations by considering nutrient management practices based on the latest scientific findings. Currently, there is increasing evidence for the diverse functions of K from the molecular level to field performance. The role of K in stress signaling is becoming an important topic (Amtmann et al. 2008; Wang and Wu 2010) that needs to be addressed increasingly in future research by molecular biologists, plant physiologists and agronomists. The stressmitigating role of K is another role in plants, particularly under drought, salinity, and upon pathogenic infection (Cakmak 2005; Amtmann et al. 2008). An adequate K nutrition is also of great importance for the composition of harvested products and the quality of diet. In addition, impaired nutrient management and related nutrient inputoutput imbalances, especially with K, may represent a serious issue in forest nutrition and wood production (Ache et al. 2010). The Potassium Symposium entitled “Potassium Role and Benefits in Improving Nutrient Management for Food Production, Quality and Reduced Environmental Damages” was organized in order to discuss and analyze the issues described above. The papers given in this Special Issue focus on the role of potassium and other mineral nutrients in cropping systems, nutrient-use efficiency, food production and quality, forest nutrition, and climatic changes. This Potassium Symposium provided an excellent opportunity Plant Soil (2010) 335:1–2 DOI 10.1007/s11104-010-0534-8

Variability of indices of macronutrient availability in soils at different spatial scales along an elevation transect in tropical moist forests (NE Ecuador)

The availability of key plant nutrients may change with elevation in tropical mountains due to altitudinal gradients in temperature and moisture which affect pedogenesis and nutrient cycling. In a transect from upper lowland to montane forests in NE Ecuador, we tested the hypotheses that (1) the availability of P is low in low-elevation forests but increases upslope, while the availability of N is relatively high at low elevations but decreases with elevation, and (2) increasing amounts of calcium, magnesium and potassium are stored on top of the soil with progressive humus accumulation toward higher elevations, likely to improve nutrient availability. In each 20 plots in undisturbed natural forest at 500, 1000, 1500 and 2000 m a.s.l., we measured in situ N net mineralization and nitrification rate (NNM and NNI, buried bag method), plant-available phosphorus (Pa, resin-bag method), and salt-exchangeable calcium, potassium and magnesium concentrations (Caex, Kex, Mgex) in the organic and mineral topsoils. NNM and NNI, and the Caex, Kex and Mgex concentrations were much more variable at the plot level than across the four elevations, while Pa varied equally at small and large spatial scales. Pa increased more than 10fold from 500 to 2000 m. The net release of nitrate dominated over ammonium at all elevations. While mass-related NNM and NNI rates and also organic matter C/N ratio in the topsoil remained invariant along the slope, NNM and NNI rates per ground area decreased by about 40% from 500 to 2000 m. Thus, the NNM/Pa ratio decreased markedly with elevation proving our first hypothesis. In support of the second hypothesis, the pools of Caex, Mgex and Kex in the organic layers increased with elevation, demonstrating the key role that organic topsoil horizons are playing for forest nutrition at high elevations. We suggest that the large difference in N versus P availability of tropical (upper) lowland and montane forests is likely to be a key factor influencing the species composition and productivity along tropical mountain slopes.

Soil organic phosphorus dynamics following perturbation of litter cycling in a tropical moist forest

The productivity of tropical lowland moist forests is often considered to be limited by the availability of phosphorus. Organic phosphorus is often abundant in tropical soils, but its role in forest nutrition is largely unknown. We addressed this by using a large‐scale litter manipulation experiment to investigate the stability of soil organic phosphorus in a tropical lowland forest in Central Panama. Three years of litter removal reduced the organic phosphorus concentration in the surface 2 cm of mineral soil by 23%, as determined by NaOH‐EDTA extraction and 31P‐NMR spectroscopy; this included decreases in phosphate monoesters (20%) and DNA (30%). Three years of litter addition (equivalent to adding 6 kg P ha–1 per year) increased soil organic phosphorus by 16%, which included a 31% increase in DNA. We did not detect higher‐order inositol phosphates, despite their abundance in mineral soils of temperate ecosystems. Our observed turnover rate suggests that even the 0–2‐cm layer of the mineral soil contributes a fifth of the total phosphorus needed to sustain above‐ground growth in this forest. Soil organic phosphorus is thus likely to make a more important contribution to the nutrition of semi‐evergreen forest plants than has hitherto been acknowledged.

Nutrient cycling and soil leaching in eighteen pure and mixed stands of beech ( Fagus sylvatica) and spruce ( Picea abies)

Studies on the combined effects of beech–spruce mixtures are very rare. Hence, forest nutrition (soil, foliage) and nutrient fluxes via throughfall and soil solution were measured in adjacent stands of pure spruce, mixed spruce–beech and pure beech on three nutrient rich sites (Flysch) and three nutrient poor sites (Molasse) over a 2-year period. At low deposition rates (highest throughfall fluxes: 17 kg N ha −1 year −1 and 5 kg S ha −1 year −1) there was hardly any linkage between nutrient inputs and outputs. Element outputs were rather driven by internal N (mineralization, nitrification) and S (net mineralization of organic S compounds, desorption of historically deposited S) sources. Nitrate and sulfate seepage losses of spruce–beech mixtures were higher than expected from the corresponding single-species stands due to an unfavorable combination of spruce-similar soil solution concentrations coupled with beech-similar water fluxes on Flysch, while most processes on Molasse showed linear responses. Our data show that nutrient leaching through the soil is not simply a “wash through” but is mediated by a complex set of reactions within the plant–soil system.

Intact amino acid uptake by northern hardwood and conifer trees

Empirical and modeling studies of the N cycle in temperate forests of eastern North America have focused on the mechanisms regulating the production of inorganic N, and assumed that only inorganic forms of N are available for plant growth. Recent isotope studies in field conditions suggest that amino acid capture is a widespread ecological phenomenon, although northern temperate forests have yet to be studied. We quantified fine root biomass and applied tracer-level quantities of U-(13)C(2)-(15)N-glycine, (15)NH(4) (+) and (15)NO(3) (-) in two stands, one dominated by sugar maple and white ash, the other dominated by red oak, beech, and hemlock, to assess the importance of amino acids to the N nutrition of northeastern US forests. Significant enrichment of (13)C in fine roots 2 and 5 h following tracer application indicated intact glycine uptake in both stands. Glycine accounted for up to 77% of total N uptake in the oak-beech-hemlock stand, a stand that produces recalcitrant litter, cycles N slowly and has a thick, amino acid-rich organic horizon. By contrast, glycine accounted for only 20% of total N uptake in the sugar maple and white ash stand, a stand characterized by labile litter and rapid rates of amino acid production and turnover resulting in high rates of mineralization and nitrification. This study shows that amino acid uptake is an important process occurring in two widespread, northeastern US temperate forest types with widely differing rates of N cycling.

Nutrient fluxes in pure and mixed stands of spruce (Picea abies) and beech (Fagus sylvatica)

Studies on the combined effects of beech-spruce mixtures are very rare. Hence, forest nutrition (soil, foliage) and nutrient fluxes via litterfall, throughfall (+ stemflow) and soil solution were measured in adjacent stands of pure spruce, mixed spruce-beech and pure beech on a nutrient rich site at Kreisbach, as well as in adjacent spruce and mixed stands on a nutrient poor site at Frauschereck to evaluate the impact of tree species composition (spruce versus beech) on these parameters. The highest recorded throughfall (+ stemflow) fluxes were 22.4 kg N ha−1 and 9.6 kg S ha−1 yr−1 and increased from beech over the mixed to the spruce stand at Kreisbach, but were similar for both stands at Frauschereck. At Frauschereck, atmospheric inputs were more or less reflected in element outputs, slightly modified by tree species composition. At Kreisbach, there was hardly any linkage between nutrient inputs and outputs. Our overall conclusion is that tree species composition affects forest nutrition, atmospheric input and consequently soil solution chemistry and input–output budgets of nutrients. However, these effects are site specific and dependent on the studied chemical element and process.

Seasonal soil and foliage nutrient dynamics of a juvenile loblolly pine plantation: Impacts of fertilizer formulation and vegetation suppression

Understanding soil and foliage nutrient dynamics can enhance effectiveness and sustainability of forest nutrition improvement practices. Monthly soil and foliage nutrient concentrations were measured in a juvenile loblolly pine ( Pinus taeda L.) plantation in southeastern Oklahoma, USA, in response to: untreated control, herbaceous vegetation suppression (VS), urea and diammonium phosphate (DAP), urea and DAP with VS, and coated urea fertilizer (CUF) with VS. Fertilization treatments persistently increased soil NO 3 − and foliage N concentrations. All fertilization treatments also reduced foliage P:N and K:N ratios below optimum levels, suggesting that the fertilizer treatments used in this study (which are conventionally applied to mid-rotation loblolly pine plantations of the region) did not adequately match the nutrient demands of this juvenile plantation. Herbaceous vegetation suppression prolonged soil and foliage N increases, prolonged declines in P:N ratios, and increased foliage B and P concentrations in the second year of the study. Fertilizer formulations yielded similar foliage and soil N and P concentrations.

A survey of forest pollution with heavy metals in the Natural Forest Region (NFR) Moravskoslezské Beskydy with particular attention to Jablunkov Pass

A survey of forest nutrition was carried out in Natural Forest Region (NFR) No. 40 Moravskoslezské Beskydy. The reason for this survey was the gradually worsening state of forest stands in this region and especially in a part of it – in the Jablunkov Pass. Air pollution was the suspected cause of the unfavourable development. According to methodology established for the survey of forest nutrition, the samples of soil and assimilatory organs were collected at 375 sampling sites. The spatial distinctness of Jablunkov Pass was expressed on the basis of selected soil characteristics (quantity of organic material, exchangeable pH, content of total nitrogen, zinc, lead, chromium, cadmium) and of the contents of chemical elements (total nitrogen, magnesium, zinc, lead, chromium, cadmium) in two-years-old Norway spruce needles. These analyses were done by the software Statistica. The medians of concentrations of elements in two-years-old Norway spruce needles in the area of NFR except Jablunkov Pass are: Zn – 34, Pb – 0.71, Cd – 0.15 and Cr – 0.38 (mg/kg). In the area of Jablunkov Pass: Zn – 43, Pb – 12.1, Cd – 0.25 and Cr – 0.41 (mg/kg). Particular attention was paid to the content of heavy metals both in the whole area of NFR and in the area of Jablunkov Pass particularly. The spatial homogeneity is disturbed by the influence of air pollution there. Markedly higher contents of zinc, lead and cadmium are found in the whole soil profile, in the case of chromium in the forest floor only. The distribution of heavy metal contents in the soil profile is influenced by the quantity and quality of organic matter and by the altitude of sampling sites. The higher values of medians of zinc, lead and cadmium contents are found in the area of the Pass. Chromium is an exception with the highest contents found in the southern part of NFR. The medians of concentrations of elements in the forest floor of Norway spruce stands in the area of NFR except Jablunkov Pass are: Zn – 70.6, Pb – 88.6, Cd – 6.4 and Cr – 0.69 (mg/kg). In the area of Jablunkov Pass: Zn – 103, Pb – 138, Cd – 8.8 and Cr – 1.02 (mg/kg). The spatial distinctness of the area around the Jablunkov Pass is confirmed by the evaluation of the data of forest nutrition survey. Particularly, it consists in the high contents of phytotoxic heavy metals. The exceptionally high pollution of this area can be a cause of the physiological weakness of trees with following attack of the honey fungus.

Geoadditive Bayesian models for forestry defoliation data: a case study

AbstractWe analyze forestry defoliation data from the Emission Impact and Forest Nutrition (IWE) survey, which was carried out in Baden‐Württemberg, Germany in the year 1988. The survey contains information on individual trees such as the degree of defoliation, age, species and measurements on nutrients in the needles, as well as information on tree locations such as soil and geographical characteristics. Our goal is to find suitable predictors for tree defoliation from the above information, and to find a set of models which can explain the underlying biological and environmental processes. To model the spatial correlation in the data and possible nonlinear effects of the covariates we use a geoadditive hierarchical Bayesian model. Posterior inference and model comparison are computationally assessed via Markov Chain Monte Carlo (MCMC) techniques and deviance information criterion (DIC) respectively. Copyright © 2008 John Wiley &amp; Sons, Ltd.

Current state of mineral nutrition and risk elements in a beech ecosystem situated near the aluminium smelter in Žiar nad Hronom, Central Slovakia

The current state in heavy metals contamination and mineral nutrition of beech forests near the aluminium plant Žiar nad Hronom (Central Slovakia) was evaluated based on soil analysis and on element analysis of potential fungal and plant indicator species. The research was conducted in two monitoring plots with high (PMP Žiar nad Hronom) and low (BEES Kremnické vrchy Mts.) immission loads, respectively. Supply of macronutrients (Ca 2+, Mg 2+, K +) was found sufficient to sustain forest growth at both sites. Differences in trace metal concentrations between these two localities were confirmed to be persistent. In the more polluted site, trace metal contents were found to be higher in the A horizon compared to the B horizon, indicating an essentially anthropogenic origin of the current metal levels and a strong binding of certain trace metals to soil organic matter. Different distribution patterns were found for calcium, magnesium, sodium, copper, cadmium, lead in plant and fungal biomass. In the herbal plant species Carex pilosa and Dentaria bulbifera, increased concentrations of potassium in aboveground biomass and a tendency to retain copper in the root biomass were observed. Tolerable cadmium concentrations were exceeded in plant samples from PMP Žiar nad Hronom. Both cadmium and lead concentrations were above the recommended limits in fruit bodies of many fungal species, which may hence constitute a health hazard if consumed. The highest concentrations of heavy metals were found in Agrocybe praecox for Pb (48.77 mg kg −1), in Gymnopus aquosus for Cd (4.75 mg kg −1), in Polyporus varius for Zn (364.97 mg kg −1) and in Clitocybe nebularis for Cu (34.10 mg kg −1).

Impact of harvesting and logging slash on nitrogen and carbon dynamics in soils from upland spruce forests in northeastern Ontario

The potential impact of timber harvesting in the boreal forest on aquatic ecosystem water quality and productivity depends in part on the production of nutrients within the soil of the harvested catchment. Nitrogen supplied by organic matter decomposition is of particular interest because of the important role that N plays in biotic processes in surface waters, and in forest nutrition in general. Logging slash quality and input to the forest floor has the potential to influence N availability after harvest on clearcut sites. Net production of organic and inorganic-N and microbial biomass C and N concentrations were determined during a 90-day laboratory incubation at constant temperature and moisture. Incubated soils included F horizon and shallow mineral soil horizons (0–5 cm) from unharvested and full-tree harvested (2 and 12 growing seasons since harvest) boreal forest sites at the Esker Lakes Research Area (ELRA), in northeastern Ontario, Canada. In an ancillary experiment, black spruce foliage was added to unharvested forest floor material after 30 days during a 90-day laboratory incubation to simulate the influence of logging slash from full-tree harvesting on C and N dynamics. Twelve-year old clearcut F horizon material released on average 75 and 5 times more NO 3 - -N and 3 and 2 times as much inorganic-N than soil collected from unharvested and 2-year-old clearcuts, respectively. This increase in NO 3 - -N accumulation during the incubation was accompanied by decreases in both exchangeable NH 4 + -N and microbial biomass C and N levels. Net daily changes in microbial biomass N were significantly related to organic and inorganic-N accumulation or loss within the F horizon. Mineral soil release of inorganic-N was lower than release from the forest floor. Nitrate-nitrogen accumulation was lower, and NH 4 + -N accumulation was higher in mineral soil from unharvested sites when compared to 12-year-old clearcuts. Calculated harvest response ratios indicated that incubated mineral soil from the 12-year-old clearcut sites released significantly greater amounts of NO 3 - -N than 2-year-old clearcuts. Incorporation of black spruce needles into F horizon material reduced the production of organic and inorganic-N and increased microbial biomass N. Laboratory incubations of F horizon and shallow mineral soil from 12-year-old clearcuts suggested that these boreal soils have the capacity for increased inorganic-N production compared to uncut stands several years after harvesting. This has the potential to increase N availability to growing boreal forest plantations and increase N leaching due to greater NO 3 - -N levels in the forest soil.

Nitrogen-fertilization impacts on carbon sequestration and flux in managed coastal Douglas-fir stands of the Pacific Northwest

We examined whether N-fertilization and soil origin of Douglas-fir [ Psuedotsuga menziesii (Mirb.) Franco] stands in western Washington state could affect C sequestration in both the tree biomass and in soils, as well as the flux of dissolved organic carbon (DOC) through the soil profile. This study utilized four forest sites that were initially established between 1972 and 1980 as part of Regional Forest Nutrition Research Project (RFNRP). Two of the soils were derived from coarse-textured glacial outwash and two from finer-textured volcanic-source material, primarily tephra, both common soil types for forestry in the region. Between 1972 and 1996 fertilized sites received either three or four additions of 224 kg N ha −1 as urea (672–896 kg N ha −1 total). Due to enhanced tree growth, the N-fertilized sites (161 Mg C ha −1) had an average of 20% more C in the tree biomass compared to unfertilized sites (135 Mg C ha −1). Overall, N-fertilized soils (260 Mg C ha −1) had 48% more soil C compared to unfertilized soils (175 Mg C ha −1). The finer-textured volcanic-origin soils (348 Mg C ha −1) had 299% more C than glacial outwash soils (87.2 Mg C ha −1), independent of N-fertilization. Soil-solution DOC collected by lysimeters also appeared to be higher in N-fertilized, upper soil horizons compared to unfertilized controls but it was unclear what fraction of the difference was lost from decomposition or contributed to deep-profile soil C by leaching and adsorption. When soil, understory vegetation and live-tree C compartments are pooled and compared by treatment, N-fertilized plots had an average of 110 Mg C ha −1 more than unfertilized controls. These results indicate these sites generally responded to N-fertilization with increased C sequestration, but differences in stand and soil response to N-fertilization might be partially explained by soil origin and texture.