Pathogenicity of Phytophthora species and Pythium undulatum isolated from Abies procera Christmas trees in Ireland

Phytophthora cryptogea, Phytophthora cinnamomi, Phytophthora cambivora, Phytophthora megasperma and Pythium undulatum were isolated from diseased Noble fir (Abies procera) seedlings and soil associated with dead Noble fir in Ireland. Seedlings of four Christmas tree species (A. procera, Picea sitchensis, Picea abies and Pinus contorta) were inoculated with these oomycetes to test their pathogenicity and the susceptibility of the various tree species. Phytophthora spp. and Pythium undulatum caused root rot on all tree species. Disease symptoms included reddish brown cambial discoloration, crown symptoms, brown foliage, dark brown roots, root rot and seedling mortality. These symptoms were similar to those observed on Noble fir in naturally infested plantations. Pythium undulatum appeared as the most virulent pathogen followed by P. cinnamomi, P. cambivora, P. megasperma and P. cryptogea. Noble fir showed to be most susceptible and lodgepole pine most tolerant while Sitka spruce and Norway spruce were intermediate.     

Occurrence of Phytophthora species in oak stands in Italy and their association with declining oak trees

Soil‐borne species of Phytophthora were isolated from 19 of 30 examined oak forest areas in Italy. The frequency of isolated Phytophthora spp. (35.2%) was significantly correlated with soil pH and longitude of the sites. Eleven Phytophthora species were detected. Phytophthora cambivora, P. cinnamomi and P. cactorum were recovered from sites in central and southern Italy whereas P. quercina was isolated in the northern and central part of the country. Phytophthora citricola occurred all over Italy. Phytophthora quercina was the only species significantly associated with declining oak trees.     

Occurrence and diversity of Phytophthora species in declining broadleaf forests in western Ukraine

In western Ukraine, forest decline and dieback of several broadleaved tree species have become increasingly evident during recent years, and surveys in some areas have shown symptoms indicative of Phytophthora infections. In this study, we aimed to determine the occurrence and diversity of Phytophthora species associated with several broadleaved tree species (Alnus glutinosa, Betula pendula, Castanea sativa, Fagus sylvatica and Quercus robur) from forest stands where dieback has been observed. Rhizosphere soil samples were collected from 14 forest stands during 2017 and 2018 and tested for the presence of Phytophthora species using morphological and molecular methods. Seven Phytophthora species (P. bilorbang, P. cactorum, P. gallica, P. gonapodyides, P. lacustris, P. plurivora and P. polonica), and two other clade six taxa were detected from the various forest types, several of which are probable agents responsible for decline. Four of the Phytophthora species (P. bilorbang, P. gallica, P. plurivora and P. polonica) have previously never been reported from broadleaf forests in Ukraine.     

Deterioration of mycorrhizal short roots and occurrence of Mycelium radicis atrovirens on declining Norway spruce in Bavaria

From four locations in Bavaria, the only known pathogenic fungi identified from fine roots (< 2mm dia) of declining Norway spruce (Picea abics) were Cylindrocarpon destructans and Mycelium radicis atrovirens, the latter being much more common (25 vs. 95 isolations from 219 root segments). Norway spruce from six additional locations were sampled for mycorrhizae and fine roots. There were always more active mycorrhizal root tips (1.28 to 3.44 fold) on spruce which were less symptomatic of decline [P(T) = 0.0156]. However, the occurrence of inactive mycorrhizae and M. r. atrovirens were similar on all spruce that were sampled. In tins study, no evidence was found that a root pathogen is causing the deterioration in the fine root system of declining Norway spruce.     

A comparative study of above- and below-ground parameters of healthy and declining young Norway spruce trees in a mountain area affected by air pollution

The aim of this study was to characterize possible connections between above- and below-ground parameters and the decline of Norway spruce trees in the Jeseníky Mountains of the Czech Republic – an area affected both by long-term air pollution and subjected to liming. A part of this study was dedicated to soil analysis, which showed considerable changes in the soil environment and highlighted particularly high concentrations of magnesium and calcium, exceeding optimal limits by as much as 8 and 13 times, respectively. Our results suggest that the decline of evaluated trees is primarily connected to root system development, as we found no differences between evaluated above-ground parameters for either healthy or declining trees. Tree decline related directly to low numbers of skeletal roots, root origin and higher maximal angles between skeletal roots. Declining trees had on average five skeletal roots with maximal angles between them of 173^o, indicating poor mechanical stability. Regardless of tree vitality, 93% of all examined root systems were restricted to upper humus horizons with an average rooting depth of 10.2?cm. All evaluated trees showed severe root deformation into tangle, which suggests crucial influence of artificial planting on the architectural development of root systems.     

Nutrient limitation and site-related growth potential of Norway spruce (Picea abies [L.] Karst) in the Bavarian Alps

The hypothesis that soil chemistry is a main constraint for the vigour of Norway spruce trees on calcareous soils is scrutinised based on data from 60 existing and new intensive study sites in the Bavarian Alps, where comprehensive information on soils, climate, foliar nutrient concentration, ground vegetation, and tree growth is available. We characterised ecological gradients of the response variables site index (SI), foliar nutrient level and needle weight by constrained ordination, identified nutrient limitations based on regression trees and modelled SI based on vegetation-based mean Ellenberg indicator values. Our study confirms the assumption that soil development and concurrent acidification are key determinants for the vitality and growth of spruce in the Bavarian Alps, which surpass the importance of climate on nutrition and growth. Pools and availability of P and N are limiting nutrition and growth of spruce in this region. We hypothesize that N-limitation persists despite considerable deposition inputs because N tends to be locked up in organic horizons with low biological activity. K and trace elements, especially Fe, can also be deficient in some cases but do not appear as major limiting factors. High foliar Mn concentrations are a reliable indicator of mature soils and favourable site conditions in the Bavarian Alps, but Mn itself is usually not limiting. P must be regarded as the most critical macronutrient in the Bavarian Alps, particularly in the face of biomass harvesting. Consequently, at sites with shallow soils forest, management should focus on sustaining or restoring humus stocks. SI of spruce can be predicted from composition of ground vegetation and Ellenberg indicator values with remarkable precision (R ² = 0.75).     

Effects of experimental drought on the fine root system of mature Norway spruce

Norway spruce (Picea abies (L.) Karst.) is an economically important, but relatively drought-sensitive tree species that might suffer from increasing drought intensities and frequencies, which are predicted to occur in parts of central Europe under future climatic change. In a throughfall exclusion experiment using sub-canopy roofs, we tested the hypothesis that enhanced drought leads to an increase in fine root mortality, and also to a higher, subsequent fine root growth. Fine root production and mortality were assessed using two independent approaches, sequential soil coring (organic layer) and direct observations in minirhizotrons (organic layer plus upper mineral soil). Six weeks of throughfall exclusion resulted in mild drought stress, i.e. a reduction in average soil moisture from 20 to 12 vol.% during the treatment. Based on the sequential coring data, experimental drought did not result in significant changes in fine root biomass during the 6-week treatment period, but caused an increase in fine root mortality by 61% in the 6 weeks following the drought treatment. Remarkably, fine root production showed a synchronous increase in this period, which more than compensated for the loss due to increased mortality. The minirhizotron data confirmed that the drought treatment increased fine root loss in the organic layer. Based on this method, however, root loss occurred during the drought period and was not compensated by increased root production. The mild drought stress was mainly restricted to the organic layer and did not significantly influence fine root dynamics in the mineral soil. We calculated that the drought event resulted in an extra input of about 28 g C m⁻² and 1.1 g N m⁻² to the soil due to increased fine root mortality. We conclude that even periods of mild drought significantly increase fine root mortality and the associated input of root-derived C to the soil organic matter pool in temperate Norway spruce forests.     

Radial distribution of carbohydrate reserves in the trunk of declining European beech trees (Fagus sylvatica L.)

Context

European beech (Fagus sylvatica L.) is considered threatened by anticipated climate change, but the physiological causes of potential beech decline or mortality remains poorly understood.

Aims

The purpose of the present study was to fuel debate about the assumption that carbohydrate depletion is involved in the decline of mature European beech.

Methods

The health status of beech trees from a severely declining stand was visually assessed by examining their crown condition. Content and radial distribution of non-structural carbohydrates (starch and soluble carbohydrate) were analyzed in the trunks and compared to those reported earlier in trunks of healthy beech trees.

Results and discussion

The distribution of carbohydrate in the beech trunks recorded here seemed affected by decline. We found a stronger radial decrease of starch content than those reported earlier for healthy beech trees. Carbohydrate reserves appear partially maintained in the outermost rings while starch depletion occurred in older wood rings in declining trees that may be able to mobilize carbohydrate reserves from older wood rings in response to successive climatic constraints.     

The effect of nitrogen supply on root growth and development in sycamore and Sitka spruce trees

Sycamore (Acer pseudoplatanus L.) and Sitka spruce (Picea sitchensis(Bong.) Carr.) were grown in sand culture in glasshouses withtwo levels of N supplied with irrigation 1.0 (deficient) and6.0 (sufficient) molNm^–3, all as NH₄NO₃. Providing trees with a sufficient N supply increased both theirabove ground growth and N content compared with the N deficientplants. Provision of the generous N supply also altered thedistribution of growth between leaves and roots, with the N-deficientplants having a higher root:leaf or root:needle ratio than thewell fertilized trees. Provision of a generous N supply stimulatedroot growth, especially at the later harvests, which was reflectedmainly in growth of the tap root in sycamore. There was an increasein both root mass and root diameter with N supply. When thegrowth of white roots was monitored using a borescope, it wasshown that there were significantly more new roots producedby the well-fertilized trees. The borescope data also showeddetail of the bimodal seasonal pattern of root growth underhigh N in Sitka spruce which related to trends in nitrogen uptake.     

Investigations on viruses from declining beech trees (Fagus sylvatica L.) in Rhineland and Westfalia,Federal Republic of Germany

Viruses of the Poty-, Potex- and Tobamo-virus groups, and presumably Nepoviruses could be isolated from degenerating beech trees (Fagus sylvatica L.) in West-Germany. They are discussed as predisposing factors of tree decline.     

The effects of Douglas-fir on tree-specific arthropod communities in mixed species stands with European beech and Norway spruce

The ecological effects of planting exotic Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] in Central Europe are still poorly understood. The aim of this study was to answer the question of whether Douglas-fir affects tree specific arthropod communities in different mature forest types (Douglas-fir, spruce and beech dominated) in Southern Germany. Therefore, arthropod communities of stem and tree crown strata of Douglas-fir and spruce (Picea abies L.) were sampled in the years 1999–2001 using arboreal photo-eclectors and flight interception traps. Statistical analysis was conducted for all species and focused on conifer specialists at three levels: (1) species diversity, (2) guild structure and (3) community structure. Within the stem stratum, species diversity was significantly higher on spruce than on Douglas-fir independent of year and stand composition. This could not be explained by a single feeding guild, rather by species changing strata during the vegetation period. In contrast, species diversity in tree crowns was approximately the same for both conifer species. However, communities in Douglas-fir crowns were conspicuously different from those in spruce crowns, especially in the Douglas-fir dominated stand type. While zoophagous insects exhibited higher activity on Douglas-fir in 2000, xylophagous beetles were more abundant on spruce in 2001. In European beech stands with widely spaced Douglas-fir trees, the site specific and broad-leaved tree related fauna might be maintained. In addition, Douglas-fir with its resource of Adelges cooleyi and crowns that overtop the broad-leaved tree canopy, offer additional resources for several aphidophagous and thermophile species.     

Root and transpiration studies on young Norway spruce trees with die back symptoms in Sweden

In the spring of 1977, scattered trees in young plantations of Norway spruce showed discoloration and loss of 1976 needles on twigs just below the apex. The main roots of damaged trees were smaller than those of healthy trees, and the extension roots lacked short roots and mycorrhizae. The transpiration rate of the current shoots of damaged trees was also higher. The damage was assumed to be the result of drought during the two previous years; the trees were thought to differ genetically in their ability to withstand water stress.     

Comparing growth and fine root distribution in monocultures and mixed plantations of hybrid poplar and spruce

Disease prevention, biodiversity, productivity improvement and ecological considerations are all factors that contribute to increasing interest in mixed plantations. The objective of this study was to evaluate early growth and productivity of two hybrid poplar clones, P. balsamifera x trichocarpa (PBT) and P. maximowiczii x balsamifera (PMB), one improved family of Norway spruce (Picea glauca (PA)) and one improved family of white spruce (Picea abies (PG)) growing under different spacings in monocultures and mixed plots. The plantations were established in 2003 in Abitibi-Témiscamingue, Quebec, Canada, in a split plot design with spacing as the whole plot factor (1 × 1 m, 3 × 3 m and 5 × 5 m) and mixture treatments as subplot factor (pure: PBT, PMB, PA and PG, and 1:1 mixture PBT:PA, PBT:PG, PMB:PA and PMB:PG). Results showed a beneficial effect of the hybrid poplar-spruce mixture on diameter growth for hybrid poplar clones, but not for the 5 × 5 m spacing because of the relatively young age of the plantations. Diameter growth of the spruces decreased in mixed plantings in the 1 × 1 m, while their height growth increased, resulting in similar aboveground biomass per tree across treatments. Because of the large size differences between spruces and poplars, aboveground biomass in the mixed plantings was generally less than that in pure poplar plots. Leaf nitrogen concentration for the two spruce families and hybrid poplar clone PMB was greater in mixed plots than in monocultures, while leaf nitrogen concentration of clone PBT was similar among mixture treatments. Because of its faster growth rate and greater soil resources demands, clone PMB was the only one showing an increase in leaf N with increased spacing between trees. Fine roots density was greater for both hybrid poplars than spruces. The vertical distribution of fine roots was insensitive to mixture treatment.     

Atmospheric deposition and impact of forest thinning on the throughfall of mountain forest ecosystems in the Bavarian Alps

The input into two forested watersheds in the Bavarian Alps is characterised by 2000 mm mean annual precipitation. Evaporation from the tree crown surfaces varies between 25 and 30%. The input is influenced by multiple natural and man-made processes. In addition to the general climate, these are local weather conditions, the growing season, processes of combustion (traffic and domestic fuel), tourism, farming, and not least by processes in the canopy. The input of SO₄-S is comparatively low, while high amounts of acidity and nitrogen are deposited. The input occurs mainly as dissolved salts. A considerable amount of the acidity deposited is buffered in the canopy by cation exchange and by calcareous dusts, which are blown out from the limestone and dolomite mountains nearby, and redeposited on leaf surfaces. Forest thinning (removal of 40% of the stem volume) caused marked changes in the deposition pattern. Interception and deposition rates of individual ions were reduced by up to 45%. The amount and chemical composition of the throughfall occupied an intermediate position between bulk precipitation and the throughfall of the control watershed. Ions which are preferentially exchanged and leached from the leaves, e.g. potassium and organic compounds, were affected the most.     

Relationships between the mean trees by basal area and by volume: reconciling form factors in the classic Bavarian yield and volume tables for Norway spruce

The Norway spruce forests of southern Germany and Austria have been at the forefront of forestry research for well over 100 years. The 1960s were a particularly productive period that saw the development of the yield tables of Ernst Assmann and Friedrich Franz, and the form and volume tables of Reinhard Kennel. Both of these works (or the equations that underpin them) are still in common use today. Even though both sets of tables were developed concurrently in the Institute for Growth and Yield at the Munich Forest Research Institute, a cursory examination suggests they are mutually incompatible, as they appear to use different values of form factor. The discrepancy can be explained by examining the differences between the mean tree by basal area (the tree with the quadratic mean diameter) and the mean tree by volume. This difference is shown to be predictable from data contained in the yield tables, and a conversion equation is developed and tested. The results show that the two sets of tables can be considered fully compatible if we accept that the volumetric mean tree is not identical to the mean tree described in the yield tables.     

Seasonal patterns of radial root growth and starch dynamics in plantation-grown Sitka spruce trees of different ages

Seasonal patterns of radial root growth within 1 m of tree stems were examined in Scottish plantations of Sitka spruce trees aged 9, 15 and 20 years. Results were compared with parallel measurements of shoot extension, radial growth of stems and amounts of starch stored in tissues external to root wood. Youngest trees produced the largest annual increments in root cross-sectional area and numbers of new cells along radial files of tracheids. Irrespective of tree age, new cells were present in roots before bud burst and the onset of radial growth occurred progressively later with increasing distances from the stems. At ages 15 and 20, both stem cross-sectional area and radial root growth up to 0.5 m from the stem base had a minor peak of activity preceding and a major peak following shoot elongation. Further than 0.5 m from the stem, root growth was frequently restricted to the period following shoot extension. Starch storage in the roots reached a maximum in April and May, which was greatest for 9-year-old trees and least for 20-year-old trees. At all ages, radial root growth in early spring occurred concurrently with increased starch storage. Later in the season starch reserves declined rapidly during the period of shoot elongation and root growth occurred whilst reserves were low. At all ages for positions on the root at the base of the stem and 0.25 m from it, starch depletion, at its maximum rate during June, accounted for less than the measured increment of root wood growth at that point. This indicates a substantial translocation of substrates to these zones during growth. At the same time, the reduction in starch concentrations at more distal points from the stem far exceeded that required for local root thickening.     

Polyphenols in the woody roots of Norway spruce and European beech reduce TTC

A common method to determine the vitality of fine root tissue is the measurement of respiratory activity with triphenyltetrazolium chloride (TTC). The colorless TTC is reduced to the red-colored triphenyl formazan (TF) as a result of the dehydrogenase activity of the mitochondrial respiratory chain. However, measurements with woody fine roots of adult Norway spruce and European beech trees showed that dead control roots had a high potential to react with TTC. High reactivity was found in boiled fine roots and the bark of coarse roots, but not in the boiled wood of coarse roots. By sequential extraction of dried and ground adult Norway spruce fine roots, reactivity with TTC was reduced by about 75% (water extraction), 93% (water/methanol extraction) and 94% (water/acetone extraction). The water extract reacted with TTC in the same way as polyphenols such as lignin, catechin and epicatechin. Boiling did not affect the extent to which fine roots of adult trees reduced TTC, whereas it greatly reduced TTC reduction by seedling roots. Application of the TTC test to roots of spruce seedlings subjected to increasing drought showed a progressive decrease in TTC reduction. The decrease in TTC reduction was paralleled by a reduction in O(2) consumption, thus supporting the conclusion that for roots with a low polyphenol content the TTC test provides a valid assessment of tissue vitality. Our results suggest, however, that the TTC test should not be applied to the fine roots of adult trees because of their high content of polyphenolic compounds whose reaction with TTC masks changes in TTC reduction due to changes in the respiratory capacity of the tissue.     

Simultaneous analyses of chromosomes in root meristems and of the biochemical status of needle tissues of three different clones of Norway spruce trees challenged with moderate ozone levels

Biochemical effects of both low and high ozone impact in long-term and short-term experiments are well investigated and documented; however, short-term treatments with moderate ozone levels have revealed divergent information concerning the biochemistry of needle tissues. Damage to the meristems of spruce trees have been found for several ozone treatments, in the form of an enhanced number of chromosomal aberrations, which appeared to be persistent for up to 2 years after the ozone challenge. One of the main aims of the present study was to determine whether a moderate ozone concentration is able to induce damage in needle biochemistry and/or only in the genetic material of root meristems. In the experiment three different clones of Norway spruce trees (Picea abies) were challenged with moderate ozone concentrations (up to 80 nl/l) for 11 weeks in greenhouses. Simultaneous investigations of root tip meristematic cells and the biochemical status of needle tissues regarding antioxidants and pigments were performed at two different sampling times: directly after the ozone treatment and 1 year later. Ozone effects in needles were absent both at the end of the fumigation and also after 1 year, but different clonal behaviour was found. Effect of ozone on chromosomal aberration rates in root tip meristems were observed and also the types of persisting chromosomal aberrations changed within the time course and within the different clones.