Nutrient balance in Scots pine (Pinus sylvestris L.) forest. 5. Tree growth in a field plot experiment

A field plot experiment on fertilization with N, Mg and P in Scots pine forest was established. The experiment had a factorial design with three levels of N (0, 30 and 90 kg ha^?1), two levels of Mg (0 and 1.5 kg ha^?1) and two levels of P (0 and 5.3 kg ha^?1). The application was done annually. There was a significant growth increase for the two N treatments. During a period of 5-years the mean increase in volume increment was 2.3 and 4.5 m³ ha^?1 for the 30 N and 90 N kg ha^?1 yr^?1 treatments, respectively. This represents a percentage increase in volume increment of 53 and 102% compared to the untreated control plots. No significant growth effect of P and Mg application was detected, either alone or in combination with N. The needle nutrient concentrations have been followed along with the annual measurements. An increase in N-concentration was detected after the first growing season in the N treated trees. After five years the Mg concentrations in the needles are lower in these treatments. The one year old needles have concentrations as low as 0.05% Mg. No visible deficiency symptoms have been observed. The field experiment effects demonstrates that N is still the most limiting nutrient under these conditions and that there is a relative large potential for N accumulation in these forest types without negative effects.     

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.     

Nutrient balance in Scots pine (Pinus sylvestris L.) forest 4. Testing the nutrient cycling model (NuCM)

The Nutrient Cycling Model (NuCM), developed during the Integrated Forest Study in the USA, is one of the most detailed models simulating processes in the forest-soil-water system. In the present study NuCM simulations are compared to observed data from a lysimeter experiment. The use of NuCM requires input of a large number of parameters. Even though the lysimeter system is simple and relatively well known, some of the parameters necessary for model running are highly uncertain. To produce a better fit between simulated and observed data, adjustments of those highly uncertain parameters are necessary. The adjustments are discussed, and thereby also the question what might be regarded as good modelling-ethics. So is also the question; how to calibrate models with data which contain errors. In addition challenges related to the use of NuCM on this type of data are discussed. Model complexity (here number of parameters) is usually highly related to the amount of data available for the specific site the model was developed for. This study illustrates the uncertainty which appears when complex models are applied in studies with less extensive parameter collection     

Nutrient balance in Scots pine (Plnus sylvestris L.) forest. 3. Fluxes of N2O from lysimeter as influenced by nitrogen input

Forest soils may become an increasingly important source of N₂O, due to disturbances to the forest ecosystem (e.g. fertilization to increase growth, or atmospheric deposition of air-borre nitrogen compounds such as NH₃, NO₃ and NO_x). A lysimeter experiment was used to study the effects of different amounts of N input [0 (control), 30 kg (Medium) and 90 kg (High) N ha^?1 y^?1 as NH₄NO₃] on fluxes of N₂O, measured by the close chamber method. The estimated annual N₂O flux were about 0.4 kg N₂O-N ha^?1 for control, 0.9 kg N₂O-N ha^?1 for medium N and 1.8 kg N₂O-N ha^?1 for high N treatments. The relation between the estimated annual N₂O flux and fertilizer dose showed an almost perfect proportionality between fertilizer dose and the increase in N₂O flux. This is important, since one crucial question is wether we can extrapolate results from high N-doses to situations with low amounts of N inputs prevailing in forests exposed to moderate input of N. The increase in N₂O fluxes from the control to the fertilised treatments corresponds to 1.7% of the annual N input in the medium N treatments and 1.6% of the annual input in the high N treatment.     

Scots pine (Pinus sylvestris L.) roots and soil moisture did not affect soil thermal sensitivity

Through their effects on microbial metabolism, temperature and moisture affect the rate of decomposition of soil organic matter. Plant roots play an important role in SOM mineralization and nutrient cycling. There are reports that rhizosphere soil exhibits higher sensitivity to temperature than root-free soil, and this can have implications for how soil CO₂ efflux may be affected in a warmer world. We tested the effects of 1-week incubation under different combinations of temperature (5, 15, 30 ^°C) and moisture (15, 50, 100% WHC) on the respiration rate of soil planted with Scots pine and of unplanted soil. Soil respiration in both soils was the highest at moderate moisture (p < 0.0001) and, increased with temperature (p < 0.0001). There was also marginally significant effect of soil kind on respiration rate (p < 0.055), but the significant interaction of temperature effect with soil kind effect, indicated, that soil respiration of planted soil was higher than unplanted soil only at 5 ^°C (p < 0.05). The soil kind effect was compared also as Q₁₀ coefficients for respiration rate, showing the relative change in microbial activity with increased temperature. However, there was no difference in the thermal sensitivity of soil respiration between planted and unplanted soils (p = 0.99), irrespective of the level of soil moisture. These findings were similar to the latest studies and confirmed, that in various models, being useful tools in studying of soil carbon cycling, there is no need to distinguish between planted and unplanted soil as different soil carbon pools.     

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.     

Silvicultural use of wood ashes — Effects on the nutrient and heavy metal balance in a pine (Pinus sylvestris,L) forest soil

In a sustainable forestry recirculation of nutrients through the application of ashes from forest residues can be an essential way to guarantee healthy and vital forests. Wood ashes can also be regarded as a measure against soil acidification. Wood ashes were applied at various rates to the soil in a 35 years old pine (Pinus sylvestris, L) stand at Ringamåla in Blekinge, South Sweden. The experiments started in 1984. The different treatments gave a clear effect on soil chemistry with decreased acidity and aluminum ion concentrations. The base saturation increased in both mor and upper mineral soil layers. Generally no significant increases were found in soil concentrations of heavy metals, except for Cu which increased significantly in the mor layer. Also the extractable Mn concentration increased, in spite of the increased pH in the soil after application of ashes. In order to achieve a biological circulation of nutrients through ash application without polluting the environment, it is of ultimate importance that the wood chips used in power plants and other furnaces have a low concentration of heavy metals and other pollutants.     

Transpiration and hydraulic conductivity in three Scots pine (Pinus sylvestris L.) stands with different air pollution histories

As part of a project studying the effects of massive reductions in the output of air pollutants in eastern Germany we monitored stand transpiration rates and water stress and analyzed the hydraulic architecture of Scots pine in three stands with different air pollution histories. Sap flow densities were continuously measured in 15 trees per stand with a thermoelectric method. The sap flow densities were scaled up to the stand transpiration rate via the conductive xylem area, which was measured with computer-tomography in the same trees. Radiation (PAR), humidity and temperature were monitored at three levels in the stands, water stress is assessed by predawn water potentials. As a parameter of hydraulic architecture we studied leaf specific conductivity (LSC). The proportion of the heartwood area did not significantly vary along the gradient of air pollution. The variation of sap flow densities within the stands was large. The ratios of sap flow densities in the inner and outer xylem were site-specific and significantly different between the stands. In the stand with the highest rate of air pollution there was a sharp decline in the sap flow densities towards the heartwood. Stand transpiration in the site with the lowest pollution was significantly higher than in the two more polluted sites. LSC in 2 years old twigs was significantly higher in the low pollution stand. In the dry summer of 1994 predawn water potentials fell to extreme values of below 1.6 MPa. At that stage transpiration ceased until the next substantial rainfalls.     

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.     

Radial distribution patterns of Cd and Zn in stems of Scots pine (Pinus sylvestris L.) trees analyzed 12 years after a contamination event

Radial distribution patterns of Cd and Zn in stems of Scots pine trees (Pius sylvestris L.) were investigated 12 years after a soil pollution event. The trees were growing on experimental plots near Krakow, southern Poland, which had been contaminated with heavy-metal-containing dust in 1980/81. The element distributions were examined for visible signals of the pollution event. Distributions of Cd and Zn in trees on contaminated plots showed elevated concentrations but were not uniform in shape. Only 2 of the 12 examined trees on plots with elevated Cd levels had highest Cd concentrations in xylem rings produced at the time of the pollution event. None of the sampled trees from the Zn plots had highest Zn concentrations in xylem rings which corresponded to the time of the pollution event. In the majority of sampled trees, concentrations of Cd and Zn decreased markedly in rings produced after the application of Cd and Zn dusts. In trees on contaminated plots concentrations of Cd and Zn were generally higher in sapwood than in heartwood. A sharp decline of both elements across the sapwood-heartwood boundary was observed. The distribution patterns of Cd and Zn are discussed with respect to endogenous physiological processes in stem wood. The element patterns observed in the wood of individual trees did not correspond to the known timing of pollution inputs to respective forest stands.     

Cellulolytic and pectolytic activity of streptomycetes isolated from root-free soil,rhizosphere and mycorrhizosphere of pine (Pinus sylvestris L.)

Summary Our studies have revealed that streptomycetes inhabiting root-free soil and the root zone of pine trees differ in their capacity to produce cellulolytic and pectolytic enzymes. Most of the root-zone organisms but only a few of the root-free soil isolates exhibited cellulolytic activity. A few of the root-zone organisms but no soil isolate showed pectolytic activity. In general the cellulolytic activity was higher in cellulase producers from the root zone than in those derived from the root-free soil. The streptomycetes studied produced only endopolymethylgalacturonase. The mean total activity of this enzyme was higher in the rhizosphere isolates but the mean specific activity was higher in the mycorrhizosphere organisms.     

Chitinolytic and proteolytic activity of streptomycetes isolated from root-free soil,rhizosphere and mycorrhizosphere of pine (Pinus sylvestris L.)

Summary We tested 75 strains of Streptomyces spp. (25 taken from each environment of soil, rhizosphere, and mycorrhizosphere of pine, Pinus sylvestris L.) and all exhibited chitinolytic activity and hydrolysed gelatine and sodium caseinate in agar media. Enrichment of these media with glucose and NH₄NO₃ caused induction or stimulation of proteolytic Streptomyces spp. strains (80%) derived from root-free soil; inhibition of this activity was observed in most strains (92%) isolated from the root zone. The post-culture liquids of the rhizosphere strains cultured in the absence of glucose revealed a significantly higher proteolytic activity than those obtained from the root-free soil. The addition of glucose to the medium stimulated proteolytic activity in the post-culture broth of Streptomyces strains derived from soil and the mycorrhizosphere.     

Effects of sod-cutting on the nematode community of a secondary forest of Pinus sylvestris L.

Atmospheric S and N compounds accumulate in the surface layers of the forest soil environment, where they affect soil biota and nutrient availability for tree growth. In addition to measures to reduce the input of atmospheric deposition, removal of the ectorganic layers by sod-cutting may contribute to the recovery of the soil ecosystem. In this study, we examined the effects of sod-cutting on the nematode fauna of a Scots pine forest, 1 and 3 years after treatment. Sod-cutting reduced the total numbers of nematodes, nematode taxa, and Maturity Index. The first taxa that colonized the newly developing organic layers after sod-cutting had low colonizer-persister (c-p) values, and appeared to have originated from the tree canopy and mineral soil. Colonization, presumably from nearby untreated plots, was observed 3 years after the sod-cutting. The initial (after 1 year) nematode community of the new organic layer comprised hyphal-, bacterial-, and algal-feeding nematodes, whereas plant-feeders, predators, and omnivores were not detected. The composition of the nematode fauna in the ectorganic layers 15 and 39 months after sod-cutting was highly similar to that of the nematode fauna of the early stages of a primary succession of Scots pine forest in a reference area in the Netherlands. In the mineral soil only insect parasites were negatively affected by sod-cutting.     

Enchytraeid and nematode numbers in urban,polluted Scots pine (Pinus sylvestris) stands in relation to other soil biological parameters

Summary We examined the number of enchytraeids and nematodes in the mor humus layer of polluted Scots pine (Pinus sylvestris L.) stands, located on a sulphur gradient from 1.2 to 2.8 mg g^-1 in mor humus and up to a distance of 40 km from the centre of Oulu, an industrialized city in northern Finland, in autumn 1989 and spring 1990. The number of enchytraeids, dominated by one species, Cognettia sphagnetorum, showed a clear positive correlation with the soil respiration rate and the diversity and production of mycorrhizal fungi, and all these were negatively related with S and N concentrations in the soil, as measured in 1987 and 1988. This negative correlation may have been caused by an alteration in food supply of enchytraeids, owing to changes in litter quality and the amount and species composition of fungi and mycorrhizae. Nematode numbers showed a positive correlation with the activity of dehydrogenase enzymes mineral N, and soil pH. The feeding characteristics of nematodes as a group need further study. The numbers of both enchytraeids and nematodes were higher in the autumn than in the spring and in the case of nematodes this variation was related to soil moisture.The work was carried out in the Department of Botany, University of Oulu, Linnanmaa, SF-90570 Oulu, Finland, and in Forestry Canada, Petawawa National Forestry Institute, Chalk River, Ontario, K0J 1J0, Canada     

Some Effects of N on Ectomycorrhizal Diversity of Scots Pine (Pinus Sylvestris L.) in Northeastern Germany

In the last three decades high industrial nitrogen (N) emissions have led to eutrophication of a Scots pine stand (Pinus sylvestris [L.]) near Schwedt characterized by a broad cover of Calamagrostis epigejos [L.] Roth (Poaceae). In comparison to the relatively unimpacted control site (low N site), this high N site showed a remarkably low mycorrhizal frequency (percentage of mycorrhizas on total amount of root tips) with seasonal lows down to 27 %. At the low N site the highest number of mycorrhizal root tips was found in the organic layer. At the high N site the amount of mycorrhizas per soil volume was similar in both organic and mineral soil layers, and also significantly lower when compared to the amount at the low N site. The high N site revealed only nine mycorrhizal morphotypes instead of eighteen found at each sampling date at the control site. 80 % of the coenosis at the high N site were represented by only four morphotypes resulting in a low diversity. The seasonal decrease in the mycorrhizal frequency, the small amount of mycorrhizas and the low diversity suggest that the high N deposition at this site has reduced the ability of the pine trees to withstand natural stresses such as prolonged drought or frost periods. This corresponds well with the 42 % reduction in tree stocking density at the high N site compared to the low N site.     

Spatial heterogeneity of soil solution chemistry in a mature Norway spruce (Picea abies (L.) Karst.) stand

The determination of the average soil solution concentrations in forest soils is hindered by the spatial heterogeneity of the soil conditions and the stand structure on all scales. The aim of this paper is to investigate the spatial heterogeneity of the soil solution chemistry within a mature stand of Norway spruce and to evaluate the implication of this heterogeneity for the sampling design for soil solutions. The site is a 140 years old Norway spruce stand of 2.5 ha located in the German Fichtelgebirge at 800 m elevation on granitic, deeply weathered bedrock. At 35 cm soil depth, 59 ceramic suction lysimeters (5 cm length, 2 cm diameter) were installed in a systematic grid of 25 · 25 m and soil solution was sampled at 3 dates in June and July 1994. The solutions were analysed for major cations and anions. Semi-variance of the concentrations at a given date revealed no systematic spatial patterns. The coefficients of variance of the element concentrations were between 36 and 298% with highest values for NH₄ ⁺-N. The implications of the observed heterogeneity for the appropriate number of replicates was investigated by Monte Carlo simulations. As an example, the probability that the measured average concentration of SO₄ ^2?-S is outside a ±10% range (related to the ‘true’ 59 lysimeter average) is about 68% if only 3 replicates would have been used, 41% with 10 replicates and 25% with 20 replicates. Due to the generally large spatial heterogeneity of the soil solution chemistry in forest soils the number of lysimeters used must be carefully adjusted to site conditions and the specific question.     

Annual and long-term fluctuations of the nematode fauna in a Swedish Scots pine forest soil

Samples from an old Scots pine forest at Ivantjärnsheden in the middle of Sweden were used to study predictability and patterns of variation of soil nematode communities. There were two annual sampling series (1974–75 and 1977–78) and one long-term series sampled in September ten times over a period of 25 years. The abundance and the composition of the fauna fluctuated rather considerably in both the annual and long-term series. In the annual series abundance and species composition varied in a way which can partly be explained by changes in temperature and moisture. Total nematode abundance was influenced by soil water contents as indicated by co-variations with precipitation. Although the variations in abundance and fauna composition were large no systematic changes could be detected during 25 years. The differences in faunal structure between the two annual series were greater than between the annual and the long-term series.In all series there was a distinct vertical stratification of the fauna. In the superficial moss and litter layers species belonging to Adenophorea (Plectus) dominated. In deeper layers members of Rhabditida (Acrobeloides) contributed a greater proportion of the fauna. Variations of the annual series indicate that coexistence of different nematode species is facilitated by differences in response to temperature and moisture. The abundance of fungal and bacterial feeders changed in a regular way. During the summer the proportions of fungal and bacterial feeders were almost equal, but during the wet and cold winter the proportion of bacterial feeders increased. Rapidly growing bacterial feeding species belonging to Rhabditida were common in late summer and early autumn, whereas the more slowly growing bacterial feeders belonging to Adenophorea were most abundant during the winter. Although the community fluctuated rather much the average values indicated a rather high degree of predictability and also a high similarity with nematode faunas of other pine forest soils.     

Effects of liming and fertilization on soil solution chemistry in North German forest ecosystems

The effect of aboveground liming and fertilization as well as ploughing and liming of forest soils on soil solution chemistry was studied in various experimental plots of the German Solling area. Due to low solubility of limestone, aboveground liming had only moderate effects on soil pH and base saturation of CEC. Calcium and Mg concentration increased and Ca/Al and Mg/Al ratios of the soil solution improved. Despite extreme doses of lime, nitrate leaching did not increase in the case of a beech plot. Elevated nitrate leaching was found in the case of a spruce and a beech plot previously fertilized with N. Nitrate concentrations are far from drinking water thresholds in the case of beech. Nitrate levels of soil solution of the unfertilized spruce plot are in the range of 3 to 8 mg L⁻¹. Liming did increase these values slightly in the first years, and nitrate levels reached those of the untreated plot in the following years. Ploughing connected with high liming doses obviously led to inhomogeneous distribution of lime. No significant deacidification of seepage water at a depth of 100 cm occurred because of leaching of sulfate from the industrial lime used. This was followed by Al-leaching. Nitrate levels slightly exceeded drinking water standards throughout the first winter period after the measure. The development of young trees was significantly improved.     

Effects of ammonia,ammonium sulphate and sulphur dioxide on the frost sensitivity of scots pine (Pinus sylvestris L.).

The deterioration of forest vitality has been at least partly attributed to air pollution. Especially NH₃, originating from intensive livestock farming and locally deposited in high concentrations, may contribute to forest decline in The Netherlands. Therefore, the effect of NH₃ and SO₂ fumigations on cold stress and water stress of Pinus svlvestris were examined. P. sylvestris trees (3 yr old) were exposed to ambient air supplemented with several NH₃ concentrations, with SO₂ or a combination of NH₃ and SO₂.Tops of branches were then exposed to various subzero temperatures and the effect of air pollution on frost damage was examined. Neither ambient air, NH₃ or SO₂ significantly influenced from sensitivity at –4 or –7°C. Following freezing treatments of –10°C, the influence of NH₃ and SO₂ became apparent. The effect of the combination of these pollutants is synergistic. Exposure to NH₃ alone followed by freezing temperatures lower than –10°C resulted in more severe frost damage in early autumn and spring than in the winter. It also increased the susceptibility of P. sylvestris to water stress. A greater loss of water was observed in NH₃-fumigated needles following drought stress, suggesting increased cuticular transpiration. Bud burst and subsequent shoot growth was also strongly reduced by NH₃ fumigations.     

Effects of endogeic earthworms on soil processes and plant growth in coniferous forest soil

Summary The effects of the endogeic earthworm, Aporrectodea caliginosa tuberculata (Eisen) on decomposition processes in moist coniferous forest soil were studied in the laboratory. The pH preference of this species and its effects on microbial activity, N and P mineralization, and the growth of birch seedlings were determined in separate pot experiments. Homogenized humus from a spruce stand was shown to be too acid for A. c. tuberculata. After liming, the earthworms thrived in the humus and their biomass increased (at pH above 4.8). In later experiments in which the humus was limed, the earthworms positively influenced the biological activity in humus and also increased the rate of N mineralization. A. c. tuberculata increased the growth of birch seedlings, with increases observed in stems, leaves, and roots. Neither NH ₄ ⁺ -N fertilizer nor mechanical mixing with artificial worms affected seedling growth. No plant-growth-affecting compounds (e.g., hormone-like compounds) due to the earthworms were present in the humus. The shoot: root ratio in the birch seedlings was not affected by either the earthworms or the fertilizer. The experiments revealed the impact of earthworm activity on soil processes and plant growth.