Effects of previous N fertilizations on soil‐water pH and N concentrations after clear‐felling and soil scarification at a Pinus sylvestris site

The study describes effects of clear‐felling and soil scarification on the N concentration and pH of soil water in experimental plots previously supplied with different doses of N. The experiment is situated in central Sweden in a former Pinus sylvestris L. stand. Over a 20‐yr period, plots were fertilized three times with ammonium nitrate, resulting in total doses of 360, 720, 1080, 1440 and 1800 kg N ha^‐1. Soil water was sampled at a depth of 40–50 cm using suction lysimeters, and analysed for N and pH. The study covers one growing season before clear‐felling and six and four growing seasons after clear‐felling and soil scarification, respectively. Statistically significant (p < 0.05) elevations in total N and nitrate‐N concentrations were noted in the fourth to the sixth growing seasons after clear‐felling in the plots that had received 1800 kg N ha^‐1, and in the fifth and sixth seasons in the plots that had received 1440 kg N ha^‐1. Ammonium‐N concentrations were not significantly affected. After clear‐felling, total N and nitrate‐N increased with time at a higher rate in the plots that had received 1440 and 1800 kg N ha^‐1 doses compared with the control. In the sixth post‐cutting season, the nitrate‐N concentration was 0.26 mg l^‐1 in the control and between 0.51 and 4.0 mg l^‐1 in the various fertilized plots. Before clear‐felling, a linear relationship between pH and fertilizer dose was absent. After clear‐felling, negative relationships prevailed, but they differed significantly from the pre‐cutting relationship only during the fourth, fifth and sixth post‐cutting seasons. In the sixth post‐cutting season, the pH was 6.0 in the control, and 6.1, 5.7, 5.6, 5.2 and 4.3 in the plots supplied with 360, 720, 1080, 1440 and 1800 kg N ha^‐1 doses, respectively. The absolute difference in pH between the sixth growing season after clear‐felling and period before clear‐felling increased linearly with increasing fertilizer dose (p < 0.05, R ² = 0.79). Before clear‐felling, nitrate‐N was elevated only in the plots that had received 1800 kg N ha^‐1. After clear‐felling, nitrate‐N seemed to increase in all fertilized plots, but the increase began first in the plots receiving the highest fertilizer dose. It was not until the fifth and sixth growing seasons after clear‐felling that nitrate‐N concentrations appeared elevated in all fertilized plots compared with the control. It seems likely that nitrification caused the increases in nitrate‐N because nitrate‐N accounted for most of the variation in pH in the fourth to the sixth growing seasons. Disc trenching was simulated around some of the lysimeters so that 50% of the soil was disturbed. This did not significantly affect the N concentration or pH of the soil water during the first 4 yrs after scarification.     

Effects of nutrition and soil water availability on water use in a Norway spruce stand

We investigated effects of nutrition and soil water availability on sap flux density, transpiration per unit leaf area (EL), and canopy stomatal conductance (GS) of Norway spruce (Picea abies L. (Karst.)) in northern Sweden during the 1996 growing season. Our objectives were to determine (1) if artificially imposed drought (65% rain diversion) reduces soil water sufficiently to cause physiological limitations to whole-tree and plot-scale water transport, and (2) whether increased capacity for water transport resulting from fertilization-induced increases in leaf (> 3-fold) and sapwood areas (> 2.3-fold) deplete soil water sufficiently to cause a negative feedback on GS and EL. We monitored soil water content (theta) and soil water potential (PsiS) in control (C), drought (D), fertilized (F) and irrigated + fertilized (IL) treatment plots, along with site meteorological conditions. Ten trees per plot were monitored for sap flow. Although there were significant treatment differences in mean daily EL (C > D > F; P < 0.01) and GS (C > D > F; P < 0.05), variation in absolute magnitudes was small. Therefore, transpiration differences on a unit ground area basis (EC) were nearly proportional to leaf area differences. Precipitation was well distributed throughout the study period and so PsiS remained high, except during short dry periods in Plot F when it declined rapidly. Thus, although soil water was not limiting to GS, EL or EC when precipitation was uniformly distributed throughout the growing season, we cannot conclude that water availability would not limit GS in fertilized stands if the seasonal distribution of precipitation were altered.     

Water stress integral-a link between short-term stress and long-term growth

Water stress integral (S(Psi)), the cumulative integral of pre-dawn leaf water potential over any chosen period of time, was estimated from measurements of pre-dawn water potential made every two weeks in a Pinus radiata D. Don plantation near Canberra, Australia. Also measured were final length of current-season needles and annual stem basal area increment. Data were gathered over a 4-year period from a control plot, a fertilized plot, an irrigated plot, and two plots that were both fertilized and irrigated. Among years and treatments, annual basal area increment varied over a threefold range. Of this variation, 91% was accounted for by variation in S(Psi) for the entire year, during every month of which stem diameter growth occurred. Of variation in annual needle elongation, 90% was accounted for by variation in S(Psi) from late August to late February, which was the period of needle growth. In dry years, the annual value of S(Psi) in non-irrigated plots was mainly determined by soil water content, but in wet years in non-irrigated plots, and in all years in irrigated plots, it was closely correlated with tree nutrient status (r(2) = 0.81).     

Effect of increased rainfall on water dynamics of larch (<Emphasis Type="Italic">Larix cajanderi</Emphasis>) forest in permafrost regions,Russia: an irrigation experiment

Sap flow measurements, from July to August 2004, were coupled with micrometeorological, soil moisture, and soil temperature measurements to analyze forest water dynamics in irrigated and undisturbed (control) larch (Larix cajanderi) forest plots in eastern Siberia. Plots were irrigated with 120 mm (20 mm day⁻¹) of water from 17 to 22 July. Sap flow measurements of ten trees at each plot were scaled up to daily stand canopy transpiration (E _c ). Canopy transpiration at the irrigation and control plots was similar before irrigation. Forest evapotranspiration (E _a ) was obtained from Ohta et al. (Agric For Meteorol 148:1941–1953, 2008) while E _a in the irrigation plot was estimated based on the E _{c_irrig}/E _{c_cont} ratio. Rainfall during July–August was 63.4 mm but, after including water from thawing soil layers, the actual water input was 109.9 and 218.5 mm in the control and irrigation plots, respectively. Despite this large difference, a corresponding difference in E _c (and E _a ) was not observed [42.6 (61.5) mm and 46.4 (71.8) mm in control and irrigation plots, respectively]. Daily canopy conductance (g _c ) increased as long as moisture was well supplied in the upper soil layers and evaporative demand was high. Soil moisture and rainfall contribution to E _a was 36.9 and 24.6 mm in the control plot and 34.5 and 37.3 mm in the irrigation plot, respectively. Water supply from soil thawing layers in the control plot and high runoff (105.6 mm) rates in the irrigation plot accounted for the similarity in water dynamics. Under increased precipitation, the forest used less soil water stored from previous growing seasons.     

Root distribution ofDactyladenia (Acioa) barteri andSenna (Cassia) Siamea in alley cropping on Ultisol. II. Impact on water regime and consequences for experimental design

Tensiometer measurements were carried out on a typic Paleudult in the humid forest zone of south eastern Nigeria in an alley cropping trial using fertilized and unfertilizedDactyladenia (Acioa) barteri andSenna (Cassia) siamea as hedgerow trees and a no-tree control. The interrow space of alley cropped and no-tree control plots were planted to maize/cassava intercrop. Water withdrawal during short dry spells and the dry season occurred fastest in the no-tree control plot and resembled the pattern in the adjacentS. siamea alley cropping. Previous root investigations showed that the whole no-tree control plot was within the range of root propagation of the adjacent hedgerow trees. Installation of a 70 cm deep root barrier led to a retarded water withdrawal in unfertilized no-tree control plots to a depth of 150 cm. In fertilized no-tree control this retardation occurred to a depth of 110 cm, while at 130 and 150 cm water withdrawal with root barriers was faster than without barriers. Results indicate thatS. siamea depleted water resources in the no-tree control plot and shortened the growing season of cassava. Restricting roots to the assigned plot size can reduce competition for water in adjacent plots even in layers below the depth of the barrier but can also induce compensative water withdrawal from layers which were not necessarily affected by the barrier. It appears that currently no standard methodology is available to conduct agroforestry trials without the risk of invalidation through root interference. Methods to determine minimum plot size in order to reduce the risk of invalidation and misinterpretation of results are suggested.     

Effect of nitrogen fertilization on growth in a Salix viminalis stand using a response surface experimental design

In order to find a nitrogen fertilization regime that is economically feasible in commercial short‐rotation forest stands of basket willow (Salix viminalis L.), a field trial was established on a clay soil near Västerås, central Sweden, in early 1990. A response surface design was used in which three levels of treatment were chosen for each single year: year 1—0, 30, 60, kg N ha^?1; year 2—0, 60, 120, kg N ha^?1; year 3—0, 90, 180, kg N ha^?1; year 4—0, 60, 120, kg N ha^?1. Thirty‐two combinations of these levels, out of 81 possible, were chosen and divided into four blocks. Thus, eight unique treatments were randomized to the plots within each block, providing no replicates at the end of the experimental period. This gave us a more flexible and informative experiment than many of those used earlier with rather few treatments, although they were replicated. After 4 years the willow stand was harvested and the accumulated stem production of each treatment was assessed. The effect of nitrogen fertilization on accumulated stem growth over the experimental period was found to be significant only for nitrogen applied in years 2 and 3, with a somewhat (statistically significant) larger effect in year 2. Growth response to nitrogen fertilization was best approximated with a function including terms with applied amount of nitrogen in years 2 and 3 and, furthermore, a term of interaction with negative coefficient between these years. The interaction between these years was interpreted as the system's ability to recycle nitrogen from one year to another.     

Projected benefit-cost analysis of agri-silvicultural system: vegetable crops intercropping with <Emphasis Type="Italic">Salix alba</Emphasis> (Willow)

An experiment upon an agri-silvicultural system involving Willow (Salix alba) tree, Kale (Brassica oleracea var. acephala) and Knol khol (Brassica oleracea var. caularapa) was laid in randomized block designed at farmers’ willow field at Shalimar near Sher-e-Kashmir University of Agricultural Sciences and Technology of Kashmir, Srinagar India during 2005 and 2006. The main plot was divided into sub-spots with 8 m × 2 m in size each in which four two-year-old willow (Salix alba) trees were at a spacing of 2 m × 2 m in a sub-spot. The intercrops were maintained at recommended spacing and supplied with recommended doses of fertilizers. The benefit-cost ratio in willow plantation intercropped with vegetable crops of Kale and Knol Khol was analyzed and compared with the benefit-cost ratio of sole willow tree forestry. The results showed that every rupee invested in plantation of agri-silvicultural system generates benefit-cost ratio of 2.78 and 2.79 in case of Willow intercropping with Kale and Willow with Knol khol, respectively, while as for sole crop of willows benefit-cost ratio was calculated to be 2.66. These results provided circumstantial evidence in favour of adopting agroforestry involving willow instead of Sole tree forestry.     

Seasonal fluctuations of low‐molecular‐weight sugars,starch and nitrogen in sapwood of Pinus sylvestris L.

The content of water‐soluble substances and starch in the living tree stem at the time of felling influences wood durability during further utilization. The aim of the study was to describe the annual and seasonal fluctuations in the contents of stored carbohydrates and nitrogenous compounds. The contents of soluble sugars, starch, and nitrogen were measured in the outer sapwood (0–15 mm from cambium) of 65‐yr‐old Scots pine {Pinus sylvestris L.) trees during an annual cycle. To study the influence of growth conditions, samples were taken from different stands in Sweden, in one stand from a control and a fertilized block. The effect of the age of the trees on the content of stored substances was also considered by comparing young (10–15 yrs old) and older trees (40–65 yrs old). Determination of the carbohydrates was carried out using enzymatic analysis. The outer pine sapwood contained a higher content of low‐molecular weight sugars during autumn and winter than during spring and summer. Starch content rose at the beginning of the growth period and decreased in autumn. The content of soluble sugars increased towards the cambium on all sampling occasions. Fructose and glucose were dominant sugars in all the stands studied. Seasonal changes of sucrose were different from those of glucose and fructose, in that the sucrose content was already decreasing in February. The variations in the nitrogen content of the sapwood were far smaller than those of the soluble sugars. No significant differences were found between the stands with regard to glucose, fructose and the sum of all three sugars. The fertilized block showed low content of sucrose and nitrogen. It is concluded that seasonal fluctuations are more important with regard to the sugar content than the effect of growth conditions. Data indicate a lower content of soluble sugars and nitrogen in the outermost sapwood of young trees as compared with older trees.     

Effect of plantation design on stem‐infecting form of rust in willow biomass coppice

Planting of genotype mixtures is a major strategy for the non‐chemical control of willow rust in short‐rotation coppice willows grown for biomass. In 1997 and 1998, the relative severity and spatiotemporal distribution of stem canker damage by Melampsora spp. on Salix viminalis `Bowles Hybrid' in a field trial containing monocultures and two design mixtures (random or regular) of three or five genotypes were assessed. Sphaerellopsis filum, a hyperparasite of Melampsora spp. was detected in all plots during the summer (1998) between the time of the two canker assessments. The percentage of rust pustules with this hyperparasite was initially greater in monoculture plantings than in mixtures in June, but by July, more than 92% of pustules were parasitized, irrespective of plantation design. The stem rust assessments showed that, in general, there were fewer cankers per stool in plots containing mixtures of willow genotypes compared with monoculture plantings. The distribution of rust cankers was different between monocultures and willow mixture designs, with differences between years for monocultures.     

Seasonal changes of understorey herbage yield in relation to light intensity and soil moisture content in a Pinus pinaster plantation

The relationship of understorey herbage yield with light intensity and soil moisture content was investigated in a 20-year-old Pinus pinaster plantation in Kilkis of Macedonia, northern Greece, in three seasons (fall, winter and spring). The plantation was thinned at three density levels, high, medium and low (2500, 1750 and 1000 trees/ha respectively) and it was seeded with Dactylis glomerata. In addition, two fertilization levels (0 and 110 N+150 P₂O₅ kg/ha) and grazing intensity levels (0 and 0.8 sheep/ha/yr) were applied in a split-split plot experimental design. It was found that herbage yield was highest in the ungrazed and fertilized low tree density stands in all seasons. In the medium tree density stand, although light was lacking, fertilized plots produced higher herbage yield as compared to unfertilized low tree density stands while fertilization is of no use in close stands if herbage production is the goal. Animals seemed to prefer fertilized and medium density stands. Third degree polynomial equations were the best to explain herbage variation through the seasons both in fertilized and unfertilized plots.     

Comparison of organic matter dynamics in soil between Japanese cedar (Cryptomeria japonica) forest and adjacent Japanese red pine (Pinus densiflora) forest established on flatland

In order to clarify the effects of tree species on organic matter dynamics in soil, we investigated the amount of forest floor material, leaf litter decomposition rate, soil chemical characteristics, soil respiration rate and cellulose decomposition rate in a Japanese cedar forest (cedar plot) and an adjacent Japanese red pine forest (pine plot) established on a flatland. The amount of forest floor material in the cedar plot was 34.5 Mg ha⁻¹ which was greater than that in the pine plot. Because the leaf litter decomposition rate was higher in the pine plot than in the cedar plot, it is likely that the difference in the amount of forest floor material between the plots is caused by the difference in the leaf litter decomposition rate. The C concentrations of soil in the cedar plot were 1.2–2.1 times higher than those in the pine plot. Soil pH(H₂O)s in the cedar plot were significantly higher than those in the pine plot. The soil respiration rates and the rates of mineralized C in the cedar plot byin vitro incubation were higher than those in the pine plot. From this result, it is assumed that soil organic matter in the cedar plot was decomposed relatively faster compared with the pine plot. Furthermore, microbial activities, which were reflected as cellulose decomposition rates in the cedar plot, were higher than those in the pine plot. A part of this paper was presented at the 109th Annual Meeting of the Japanese Forestry Society (1998).     

Effects of mulching with multipurpose-tree prunings on soil and water run-off under semi-arid conditions in Kenya

The effect of adding leaf mulches ofGrevillea robusta, Cassia siamea andGliricidia sepium on the rate of soil and water run-off from a crop field were studied during two cropping seasons in an alfisol under semi-arid conditions at Machakos, Kenya. The experiment was conducted in a randomized complete block design with three replications; two rates of mulch of each species (2.24 t and 4.48 t, on dry matter basis, per ha) and a no-mulch control constituted the seven treatments. Soil and water run-off losses after each major rainfall event and the changes in ground and crop cover were measured. Rainfall erosivity and changes in soil bulk density and infiltration rate were also determined.Soil losses from the plots with mulches ofCassia siamea, Gliricidia sepium andGrevillea robusta were significantly lower than those from the control (p=0.10). Over the two seasons, the cumulative soil losses from plots mulched with cassia, gliricidia and grevillea were 11%, 57% and 81% lower than that of the control plot. Similarly, water run-off losses from cassia, gliricidia and grevillea mulch plots were 28%, 48% and 58%, respectively, lower than that of the control plot. Thus, cassia was found to be better than gliricidia and grevillea in reducing both soil and water run-off losses.Soil bulk density did not change while infiltration rate at the end of the experiment was significantly more than in the beginning; however, there were no significant differences in these soil physical properties among the treatments.     

Changes in the stand structure on permanent Picea abies plots managed with single‐tree selection

Eleven permanent plots, established in central and northern Sweden during the years 1913–59, were repeatedly treated with single‐tree selection for between 30 and 67 years. The plots were all dominated by Norway spruce (Picea abies (L.) Karst.), soil moisture was mesic, and the ground vegetation was dominated by Vaccinium myrtillus L. All trees higher than 1.3 m were numbered and cross‐calipered at the time of plot establishment, and at following treatments. In the study trees with DBH < 8.5 cm were excluded from the calculations. Stand densities generally decreased as a result of harvests and mortality together exceeding increment and ingrowth. The number of trees was generally declining over DBH at the time of plot establishment. Six plots maintained such distributions during the whole observation period. Changes in stand structure were mainly caused by the harvests being concentrated to trees with DBH less than 30 cm, and low levels of ingrowth. The low ingrowth was probably an effect of over cutting of saplings and small trees.     

Long-term effect of wood and peat ash on the growth of Pinus sylvestris on drained peatland

The effect of ash fertilization on height growth and volume production of Scots pine (Pinus sylvestris L.) was studied on oligotroph peatland in southeast Norway. In the year 1944, plots 15 m × 15 m size were fertilized with 0, 4, 7, and 10 tons ha^?1 of wood or peat ash. The area was treeless, but a satisfactory number of pine seedlings were present. All measurements were confined to the central inner plot, 10 m × 10 m area. Most plots were re-fertilized with 10 tons of wood ash ha^?1 in the year 1993. Wood ash had higher content of nutrients, and generally, it had greater growth enhancement effect than peat ash. When the amount of ash was increased, volume production significantly increased for the age period 38–50 years and the total production at age 50 years. The mean annual increment during the first 50 years was about 6 m³ ha^?1 for the plots applied with 10 tons of ash ha^?1. Trees on plots fertilized with 7 or 10 tons in 1944 and replenished with 10 tons ha^?1 at age 50 years (1993) had a mean annual increment of 14 m³ ha^?1 for the stand age period 51–68 years. Over time some tree roots from control plots and plots fertilized with 4 tons ha^?1 have captured nutrients from richer plots. Such effect is to a smaller extent relevant for treatment 7 tons. It is concluded that the content of mineral nutrients of wood and peat ash makes these ashes well suited as fertilizers on peatland.     

Silvicultural options to promote seedling establishment on Kalmia–Vaccinium-dominated sites

Seedling growth is often hampered on sites dominated by Kalmia angustifolia. In June 2000, a trial was established on a clear-cut site in Quebec, Canada, with a high cover of Kalmia and Vaccinium species. The objectives were to evaluate how soil scarification and fertilization at the time of planting influence early growth and establishment of black spruce [Picea mariana (Mill.) BSP] and jack pine (Pinus banksiana Lamb.) seedlings. During the first 2 years, scarification reduced Kalmia cover three-fold and doubled the distance from seedlings to the nearest Kalmia stem. Scarification did not increase soil-extractable NH₄-N concentration, and reduced soil potassium, calcium and magnesium. Scarification had no effect on seedling water stress. Seedling growth improved and foliar nutrient concentrations were generally higher in scarified plots than in unscarified control plots. No differences were observed between single- and double-pass scarification for any variables except for ground-level stem diameter of seedlings, which was greater with double-pass scarification (12.1 vs 13.1 mm). Spot fertilization increased seedling growth and foliar nitrogen concentrations. Jack pine growth was greater than black spruce growth, an effect enhanced when seedlings were fertilized.     

Distribution and yield of biomass from young Pinus sylvestris and Picea abies stands on drained and fertilized peatland

Above‐ground biomass has been measured on fertilized and control plots up to stand age 31 years. Each biomass fraction was estimated by two statistically coupled linear models with squared diameter at breast height as independent variable. All fractions except reproductive structures of pine and dead branches of spruce were estimated at high precision levels, R. between 0.93 and 0.99. The above‐ground biomass fractions per hectare could be precisely described by stem volume with bark. Application of the models for prognostic purposes is discussed. Annual above‐ground net biomass production in pine increased from 2.05 to 4.34 MT d.m./ha‐yr on control plots over 11 years, while plots given complete fertilizer mixture ranged from 6.75 to 9.09. Spruce stands with a nearly optimum water relationship and fertilizer programmes yielded from 9.50 to 11.86 MT d.m./ha‐yr. The combination of energy and timber production in highly productive peatland stands is discussed.     

Effect of simulated acid rain on the growth performance of the European pine sawfly [Neodiprion sertifer)

The effect of simulated acid rain on the performance of Neodiprion sertifer larvae fed on treated Scots pine needles was tested in a subarctic area with low ambient pollution level. Acid rain treatments (pH 4 and pH 3, both with H₂SO₄ and HNO₃) did not significantly affect the relative growth rates or cocoon weights of N. sertifer 2 or 3 years after the start of the treatments. The relative growth rate of N. sertifer larvae was slightly (nonsignifi‐cantly) higher on plots receiving only ambient rain than on irrigated control plots. The quality of foliage before the start of the treatments explained a significant proportion of the variation in the performance of N. sertifer larvae in the bioassay conducted 3 years later.     

广西大青山西南桦人工林土壤养分特征及其与立地生产力的关系

[目的]探讨西南桦人工林对土壤的适应性及土壤养分特征,揭示土壤养分状况与立地生产力的关系,为其造林地选择及人工林养分管理提供参考。[方法]在广西大青山林区西南桦人工林内设置47块600 m2的典型样地,调查常规测树因子,采集土壤样品,测定10项常规土壤化学性质指标;按照土壤养分分级标准评价土壤养分状况,基于立地指数将样地分为高产和低产组,进一步比较分析两组立地间各养分指标的差异性,探讨土壤养分对立地生产力的影响。[结果]表明:广西大青山西南桦人工林地土壤绝大部分为强酸性,有机质、有效N、全N含量中等偏上,有效P甚缺,其它养分含量中等偏下。高产和低产立地间土壤有机质和全K含量均呈极显著差异(P0.01),有效N含量差异显著(P0.05)。[结论]西南桦对于低pH值、低P含量的土壤具有较强的适应性;有机质、全K和有效N含量是影响广西大青山西南桦人工林立地指数的关键土壤养分因子。     

Effects of sulphuric acid and heavy-metal deposition on frequency of asymptomatic infections of Gremmeniella abietina in Scots-pine seedlings

The isolation frequency of Gremmeniella abietina was measured from asymptomatic 4-year-old Scots-pine seedlings. The seedlings had been subjected to simulated sulphuric deposition (pH 3.1 or 4.1) or control treatments (irrigation with spring water (pH 6), or no irrigation) during the three previous growing seasons. The seedlings were planted in soil originating from two localities with different backround levels of copper (Cu) and nickel (Ni), and the soil was further amended with Cu (63.3 mg/1 of soil) and Ni (20.5 mg/1 of soil), or a combination of the two. The seedlings were inoculated with conidia of G. abietina during their third growing season in the field. Asymptomatic infections of G. abietina were recovered frequently from seedlings that had received water irrigation. The addition of sulphuric acid to the irrigation water, and/or the lowered pH (pH 3.1 and 4.1) resulting from this addition, mitigated the effect of water application. The effect of Ni-treatment on the recovery of G. abietina depended on the irrigation treatment; with no irrigation, Ni-treatment increased isolation frequency, but, in irrigated seedlings the response was the opposite. Only 10.6% of the seedlings had symptoms caused by G. abietina; most of the seedlings had become infected before the application of the various treatments.     

The effect of nitrogen fertilization on fungistatic phenolic compounds in roots of beech (Fagus sylvatica) and Norway spruce (Picea abies)

The effect of nitrogen fertilization on fungistatic phenolic compounds in fine roots of beech and Norway spruce growing in afforestation plots was analysed. The plots were situated at two sites in Switzerland on acidic soil with low base saturation. For 9 years, the trees have been treated with dry ammonium nitrate to give 0, 10, 20, 40, 80, 160 kg N ha^?1 year^?1, respectively. The phenolic compounds responded differently to fertilization. Fine roots of beech showed a significant decrease of (?)‐epicatechin and piceatannol with increasing nitrogen fertilization. The concentration of protocatechuic acid was increased with fertilization. Roots of fertilized Norway spruce showed significantly decreased concentrations of 4‐hydroxyacetophenone and piceatannol. The mycelial growth of three isolates each of Heterobasidion annosum s.l. and Cylindrocarpon destructans was tested on agar media containing various phenolic compounds in concentrations found in fine roots of Norway spruce (Picea abies) and beech (Fagus sylvatica). All three H. annosum isolates were inhibited by p‐coumaric acid and (?)‐epicatechin. Two isolates were inhibited by another four phenolic compounds (p‐hydroxybenzoic acid, 4‐hydroxyacetophenone, piceatannol and protocatechuic acid), one by (+)‐catechin. Two of three C. destructans isolates were inhibited by all phenolic compounds except for (+)‐catechin which affected only one isolate, one isolate did not respond at all.