Effects of enhanced nitrogen deposition on foliar chemistry and physiological processes of forest trees at the Bear Brook Watershed in Maine

Effects of enhanced nitrogen deposition on nutrient foliar concentrations and net photosynthesis of sugar maple (Acer saccharum Marsh.), American beech (Fagus grandifolia Ehrh) and red spruce (Picea rubens Sarg.) were evaluated at the Bear Brook Watershed in Maine (BBWM). The BBWM is a paired-watershed forest ecosystem study with one watershed treated since 1989 with bimonthly dry ammonium sulfate ((NH₄)₂SO₄) additions at a rate of 25.2 kg N ha⁻¹ year⁻¹, while the other watershed serves as a reference. The (NH₄)₂SO₄ treatment resulted in significant increases in foliar N concentrations for all three species and significant reductions in foliar Ca, Mg and Zn concentrations for American beech and red spruce. Treatment effects on foliar concentrations of other nutrients were not significant in any species. Despite higher N concentrations in all species, only treated sugar maple showed significantly higher photosynthetic rates. The non-response in net photosynthesis to higher foliar N in American beech and red spruce might be attributed to their low foliar Ca and/or Mg concentrations. Higher net photosynthetic rates in sugar maple might be explained by the higher foliar N and by the ability of this species to maintain an adequate Ca and Mg supply. Results suggested that nutrient imbalances due to inadequate supply of Ca and Mg might have counteracted a potential increase in net photosynthesis induced by higher N concentrations in American beech and red spruce.     

Species mixing effect on Norway spruce response to elevated CO2 and climatic variables: root and radial growth response

A 7-year study was conducted to examine the growth (diameter and root) response of Norway spruce (Picea abies (L.) Karst.) seedlings to elevated CO₂ (CO_2ELV, 770 μmol (CO₂) mol^?1) in different mixture types (monospecific (M): a Norway spruce seedling surrounded by six spruce seedlings, group-admixture (G): a spruce seedling surrounded by three spruce and three European beech seedlings, single-admixture (S): a spruce seedling surrounded by six beech seedlings). After seven years of treatments, no significant effect from elevated CO₂ was found on the root dry mass (p?=?0.90) and radial growth (p?=?0.98) of Norway spruce. Neither did we find a significant interaction between [CO₂]?×?mixing treatments (p?=?0.56), i.e. there was not a significant effect of CO₂ concentrations [CO₂] in all the admixture types. On the contrary, spruce responses to admixture treatments were significant under CO_2AMB (p?=?0.05), which demonstrated that spruce mainly increased its growth (diameter and root) in M and neighbouring with beech was not favourable for spruce seedlings. In particular, spruce growth diminished when growing beside high proportions/numbers of European beech (S). Here, we also evaluated the association between tree-ring formation and climatic variables (precipitation and air temperature) in different admixture types under elevated and ambient CO₂ (CO_2AMB, 385 μmol (CO₂) mol^?1). Overall, our result suggests that spruce responses to climate factors can be affected by tree species mixing and CO₂ concentrations, i.e. the interaction between climatic variables?×?admixture types?×?[CO₂] could alter the response of spruce to climatic variables.

     

Cystein und Glutathion in gesunden und SO2-geschädigten Fichtennadeln

Cysteine and glutathione in healthy and SO₂ damaged spruce needles. SO₂ damaged and healthy spruce needles were analysed for water soluble SH groups. Total SH content was mainly due to glutathione with some cysteine. Increased cysteine content was found only in old needles. Total content of SH groups fluctuates seasonally in the same way in both healthy and damaged needles. SO₂ damaged needles, however, always contain more SH-groups than healthy needles except immediately after flushing.     

Histometrische Untersuchungen am Holz einer rauchgeschädigten Fichte

Histometrical investigations on the xylem of spruce after SO₂ pollution . The influence of SO₂ pollution on xylem differention in spruce was investigated. Besides such quantitative changes as reduced annual growth, qualitative changes also occur. With pollution, the percentage of latewood increases. Tracheids are shorter, possess more pits and are more frequent per unit area.     

S-Lokalisation in SO2-begasten Fichtennadeln

Localisation of sulphur in spruce needles treated with SO₂. After exposure to SO₂ the tips of spruce needles arc richer in sulphur compounds than the bases. The accumulation of sulphur compounds results mainly in an increased content of inorganic sulphur. The analytical results explain the local occurrence of injuries at the needle tips.     

Der Einfluß von kontinuierlichen,niedrigen SO2-Begasungen auf den Phenolgehalt und die Phenoloxidase-Aktivität in Blättern einiger Waldbaumarten

Influence of continuous fumigation by low levels of SO₂ on the phenolic contents and phenoloxidase activities in leaves of forest trees. Potted clonal trees of Norway spruce, black alder and English birch were continuously exposed to low levels of So₂ in fumigation chambers. The phenolic content of the Norway spruce needles was increased consiberably over the controls months before the trees showed any symptoms of damage to the naked eye. Fumigated black alder had a significant higher phenoloxidase activity in the leaves; but this increase only occurred two weeks before the development of necroses. In English birch neither the phenolic content nor the phenoloxidase activity was changed against the unfumigated controls during the course of the experiment.     

Nutrient contents and efficiencies of beech and spruce saplings as influenced by competition and O<Subscript>3</Subscript>/CO<Subscript>2</Subscript> regime

Saplings of Fagus sylvatica and Picea abies were grown under conditions of intra and interspecific competition in a 2-year phytotron study under combinations of ambient and elevated ozone (+O₃ which is 2 × O₃, but <150 nl l⁻¹) as well as carbon dioxide concentrations (+CO₂ which is amb. CO₂ + 300 μl CO₂ l⁻¹) in a full factorial design. Saplings were analysed for various mineral nutrients in different plant organs as well as biomass production and crown development. The study was based on the assumption that nutritional parameters important for growth and competitiveness are affected by stress defence under limiting nutrient supply. The hypotheses tested were (1) that nutrient uptake-related parameters (a) as well as efficiencies in nutrient use for above-ground competition (b) of beech rather than spruce are impaired by the exposure to elevated O₃ concentrations, (2) that the efficiency in nutrient uptake of spruce is enhanced by elevated CO₂ concentrations in mixed culture, and (3) that the ability to occupy above-ground space at low nutrient cost is co-determinant for the competitive success in mixed culture. Clear nitrogen deficiencies were indicated for both species during the 2-year phytotron study, although foliar nitrogen-biomass relationships were not so close for spruce than for beech. O₃ stress did not impair nutrient uptake-related parameters of beech; thus hypothesis (1a). was not supported. A negative effect of elevated O₃ (under amb. CO₂) on the N and P based efficiencies in above-ground space occupation (i.e. lower crown volume per unit of N or P invested in stems, limbs and foliage) of beech supported hypothesis (1b). It appeared that ozone stress triggered a nutrient demand for stress defence and tolerance at the expense of above-ground competition (trade-off). Crown volume of beech under O₃ stress was stabilized in monoculture by increased nutrient uptake. In general, the +CO₂-treatment was able to counteract the impacts of 2 × O₃. Elevated CO₂ caused lower N and S concentrations in current-year foliage of both tree species, slightly higher macronutrient amounts in the root biomass of spruce, but did not increase the efficiencies in nutrient uptake of spruce in mixed culture. Therefore hypothesis (2) was not supported. At the end of the experiment spruce turned out to be the stronger competitor in mixed culture as displayed by its higher total shoot biomass and crown volume. The amounts of macronutrients in the above-ground biomass of spruce individuals in mixed culture distinctly exceeded those of beech, which had been strongly reduced by interspecific competition. The superior competitiveness of spruce was related to higher N and P-based efficiencies in above-ground space occupation as suggested in hypothesis (3). This article belongs to the special issue “Growth and defence of Norway spruce and European beech in pure and mixed stands”.     

Ultrastructure of mesophyll cells of spruce needles exposed to O3 alone and together with SO2

Mesophyll cells of spruce [Picea abies (L.) Karst.] needles fumigated for two months with O₃ alone and together with SO₂ were studied with electron microscope. The observations showed the specific type of injuries for both pollutants, the dependency of severity of injuries both on the concentration of the pollutant and the duration of daily exposure as well as enhanced effects with combined O₃ and SO₂ in the older needles.     

Einfluß von SO2 und HF auf freie Aminosäuren der Fichte (Picea abies [L.] Karsten)

The influence of SO₂ and HF on free amino acids of spruce . The influence of the air pollutants SO₂ and HF on composition and amount of free amino acids was investigated. Distinct differences in the pattern of amino acids are caused, particularly in glutaminic acid and compounds based on it.     

Growth recovery of mature Norway spruce and European beech from chronic O<Subscript>3</Subscript> stress

Elevated O₃ levels can strongly impair the health and vitality of forest ecosystems. Free-air exposure systems reveal that forest tree and stand growth can be reduced strongly under chronic O₃ stress. Detailed knowledge of the effect of O₃ exposure on photosynthesis, carbon sequestration, allometry and growth during chronic stress is available. However, knowledge of growth response after O₃ reduction is scarce. Here, we analyse the growth of mature Norway spruce (Picea abies (L.) Karst.) and European beech (Fagus sylvatica L.) in the free-air O₃ fumigation experiment at Kranzberg Forest. We compare tree growth over a 9-year period (2008–2016) after exposure to O₃ (2000–2007). During 2?×?O₃ exposure, the annual basal area growth of Norway spruce and European beech decreased by 24 and 32%, respectively. After cessation of 2?×?O₃ exposure, the annual basal area growth of Norway spruce and European beech not only recovered but exceeded the growth of the trees in the control condition by 14 and 24%, respectively. The growth resilience and resistance of trees previously exposed to 2?×?O₃ towards drought stress and late frost was hardly lower than that of the trees in the control condition. The capacity for growth recovery even after long-term chronic O₃ stress emphasizes the strong beneficial effect of air pollution control on the health of forest ecosystems and on the global land carbon sink.     

Interspecific competition impacts on the morphology and distribution of fine roots in European beech (Fagus sylvatica L.) and Norway spruce (Picea abies (L.) Karst.)

Morphology and vertical distribution patterns of spruce and beech live fine roots (diameter ≤2 mm) were studied using a soil core method in three comparable mature stands in the Solling: (1) pure beech, (2) pure spruce and (3) mixed spruce–beech. This study was aimed at determining the effects of interspecific competition on fine root structure and spatial fine root distribution of both species. A vertical stratification of beech and spruce fine root systems was found in the mixed stand due to a shift in beech fine roots from upper to lower soil layers. Moreover, compared to pure beech, a significantly higher specific root length (SRL, P<0.05) and specific surface area (SSA, P<0.05) were found for beech admixed with spruce (pure beech/mixed beech SRL 16.1–23.4 m g⁻¹, SSA 286–367 cm² g⁻¹). Both indicate a flexible ‘foraging’ strategy of beech tending to increase soil exploitation and space sequestration efficiency in soil layers less occupied by competitors. Spruce, in contrast, followed a more conservative strategy keeping the shallow vertical rooting and the root morphology quite constant in both pure and mixed stands (pure spruce/mixed spruce SRL 9.6/7.7 m g⁻¹, P>0.10; SSA 225/212 cm² g⁻¹, P>0.10). Symmetric competition belowground between mixed beech and spruce was observed since live fine roots of both species were under-represented compared to pure stand. However, the higher space sequestration efficiency suggests a higher competitive ability of beech belowground.     

Effects of the extreme drought in 2003 on soil respiration in a mixed forest

We present a field study on the drought effects on total soil respiration (SR_t) and its components, i.e., “autotrophic” (SR_a: by roots/mycorrhizosphere) and “heterotrophic” respiration (SR_h: by microorganisms and soil fauna in bulk soil), in a mature European beech/Norway spruce forest. SR_a and SR_h were distinguished underneath groups of beech and spruce trees using the root exclusion method. Seasonal courses of SR_a and SR_h were studied from 2002 to 2004, with the summer of 2003 being extraordinarily warm and dry in Central Europe. We (1) analyzed the soil temperature (T _s) and moisture sensitivity of SR_a and SR_h underneath both tree species, and (2) examined whether drought caused differential decline of SR_a between spruce and beech. Throughout the study period, SR_a of beech accounted for 45–55% of SR_t, independent of the soil water regime; in contrast, SR_a was significantly reduced during drought in spruce, and amounted then to only 25% of SR_t. In parallel, fine-root production was decreased during 2003 by a factor of six in spruce (from 750 to 130 mg l⁻¹ a⁻¹), but remained at levels similar to those in 2002 in beech (about 470 mg l⁻¹ a⁻¹). This species-specific root response to drought was related to a stronger decline of SR_a in spruce (by about 70%) compared to beech (by about 50%). The sensitivity of SR_a and SR_h to changing T _s and available soil water was stronger in SR_a than SR_h in spruce, but not so in beech. It is concluded that SR_a determines the effect of prolonged drought on the C efflux from soil to a larger extent in spruce than beech, having potential implications for respective forest types. This article belongs to the special issue "Growth and defence of Norway spruce and European beech in pure and mixed stands."     

An assessment of rainfall modification in mountainous ecosystems dominated by Fagus sylvatica L. and Picea abies (L.) Karst. (Western Balkans,Bulgaria) by multivariate analyses

Bulk precipitation, throughfall, and stemflow samples were collected in Petrohan site (Western Balkan, Bulgaria), operating in the framework of the Long-Term Ecological Research network, during a 6-year period (1995–2000). This mountain area is characterized by the presence of beech and spruce forests (Fagus sylvatica L. and Picea abies (L.) Karst.) and is utilized for drinking water supply. All samples were analyzed for pH and major inorganic anions (Cl^?, NO₃ ^?, and SO₄ ^2?) and cations (Ca²⁺, K⁺, Mg²⁺, Na⁺, and NH₄ ⁺). Results show that bulk precipitation in this region is mainly acidic (pH = 5.1), and the dominant neutralization components in the rainwater are Ca²⁺ and NH₄ ⁺. As for Ca²⁺, K⁺, Mg²⁺, Cl^?, and SO₄ ^2?, they are not originated by marine source. Cluster analysis and principal component analysis were used for investigating the possible sources contributing to the chemical composition of the bulk precipitation and its possible modifications during the passing through beech and spruce stands. Results highlight that local and long-range transport-related anthropogenic sources and natural sources contribute to the anion and cation content of the bulk precipitation. The enrichment of the solution through the foliage made up of dry depositions is significant in both stands, but canopy leaching processes are much greater in the spruce forest, especially for Ca²⁺. As for the stemflow, it follows the same pattern as the throughfall, but N uptake and a strong K⁺ and Mg²⁺ leaching are observed mainly in the spruce stand.     

Thirteen-year monitoring of liming and PK fertilization effects on tree vitality in Norway spruce and European beech stands

The chemical fertility of the forest soils in the Belgian Ardenne is threatened by acidifying and eutrophying deposition and by the nutrient removal due to timber harvesting. Experiments were launched to evaluate the ability of liming and fertilization to improve foliar nutrition, maintain or restore crown condition and promote tree growth. In 1995, 10 liming and fertilization trials were installed in even-aged stands of European beech (5) and Norway spruce (5) distributed throughout the Ardenne. In each stand, two treatments were tested: liming with 3,000 kg ha⁻¹ of dolomitic limestone and liming plus fertilization with 0 to 800 kg ha⁻¹ of rock phosphate and 0 to 350 kg ha⁻¹ of K₂SO₄. Between 1995 and 2006, the foliar Ca and Mg status of spruce and beech trees improved in the limed stands, which limited significantly but did not prevent the decline in crown condition triggered by the summer drought in 2003. For spruce, liming also increased the increment in basal area. The additional fertilization increased the foliar nutrition in P but had no significant effects on soil chemistry and tree vitality.     

Über die Ursachen und Kriterien der Immissionsresistenz bei Fichte,Picea abies (L.) Karst.

Causes and critcria of resistance to air pollution in Norway spruce. II. Reflexive resistance . The different reactions of stomata of resistant and “normal” spruce grafts were investigated. Resistant grafts were shown to have a more sensitive reaction by measuring water potentials and by analyzing S content in SO₂ fumigated needles or F contents in grafts exposed to polluted air. Other tcsts involving gas permeability of stomata, clecrrical conductivity of needle cxtracts and watcr content of SO₂ fumigated needles were less effective.     

Der Einfluß einer praxisnahen SO2-Begasung auf das 14CO2-Fixierungsmuster von Buchen (Fagus sylvatica L.)

The influence of a SO₂-fumigation on the ¹⁴CO₂-fixation pattern of beeches (Fagus sylvatica L.) under field conditions. The influence of a fumigation with a low SO₂ concentration on the metabolism of beech leaves (Fagus sylvatica L.) was investigated. Changes due to SO₂ were observed in the sulfur content, the ¹⁴CO₂-uptake and the ¹⁴CO₂-fixation pattern. The use of these parameters for the indication of air pollution effects on plants is discussed.     

Die Leitfähigkeit von Fichtenborken-Extrakten als empfindlicher Indikator für Luftverunreinigungen

The Conductivity of Bark-Extracts from Spruce, a Sensitive Indicator for Air Poilution . Bark of spruce is a useful and sensitive indicator for air pollution. The latter may be determined more precisely by electrolytic conductivity of bark extracts than by pH-value or sulphate level of foliage. By an additional simple sulphate analysis of bark extracts the effects of SO₂ may be distinguished from those of certain components in dust.     

Physiologische Reaktionen der Fichte (Picea abies) auf komplexen SO2- und Trockenstreß

Physiological reactions of spruce (Picea abies) on complex SO₂- and drought-induced stress. Part 3. Responses of SO₂-stressed spruces to subsequent drought-induced stress. SO₂-stressed spruces under drought-stress showed less reduced water content, less increased osmotical potential and less restricted photosynthesis compared to spruces without preceding SO₂-stress and thus seemed to be in a better physiological situation. Their ability to retain water (in cut-off twigs) as well as their ability to withstand a quick and strong water-loss in the needle-tissue without cell-damage were reduced. Reasons for the temporarily favourable effect of a pre-going SO₂-stress in surviving a drought-stress are discussed.     

Eine einfache Methode zur SO2-Begasung von Fichtenpfropflingen im Labor1

A simple method for SO₂ fumigation of Norway spruce grafts in the laboratory. To investigate the resistance mechanism of Norway spruce to SO₂ a simple fumigation chamber was used. The conditions of fumigation gave the desired range of symptom expression.     

Peroxidase- und Superoxiddismutase-Aktivität sowie Prolingehalte von Fichtennadeln nach Belastung mit O3, SO2 und NO2

In long-term experiments the influence of various combinations of O₃, SO₂ and NO₂ on peroxidase activity, superoxide dismutase activity as well as on proline contents of spruce needles was studied. The reactions of these parameters varied depending on the type of pollution and the needle age. Peroxidase and superoxide dismutase activity were also influenced by Mg and Ca supply of the plants.