A new species of Boletopsis Associated with Pinus sylvestris L. in Scotland

Summary

The identity of a recent Scottish collection thought to be Boletopsis leucomelaena was examined with the help of molecular techniques. This poroid fungus proved to be a new species of Boletopsis differing from the European species occurring with Pinus sylvestris, which should continue to be called B. grisea. The new name Boletopsis peplexa is introduced for all the Scottish collections with Pinus sylvestris.     

Ameliorating effect of UV-B radiation on the response of Norway spruce and Scots pine to ambient ozone concentrations

Elevated levels of both ozone and UV-B radiation are typical for high-altitude sites. Few studies have investigated their possible interaction on plants. This study reports interactive effects of O₃ and UV-B radiation in four-year-old Norway spruce and Scots pine trees. The trees were cultivated in controlled environmental facilities under simulated climatic conditions recorded on Mt Wank, an Alpine mountain in Bavaria, and were exposed for one growing season to simulated ambient or twice-ambient ozone regimes at either near ambient or near zero UV-B radiation levels. Chlorotic mottling and yellowing of current year needles became obvious under twice-ambient O₃ in both species at the onset of a high ozone episode in July. Development of chlorotic mottling in relation to accumulated ozone concentrations over a threshold of 40 nL L^–1 was more pronounced with near zero rather than ambient UV-B radiation levels. In Norway spruce, photosynthetic parameters at ambient CO₂ concentration, measured at the end of the experiment, were reduced in trees cultivated under twice-ambient O₃, irrespective of the UV-B treatment. Effects on photosynthetic capacity and carboxylation efficiency were restricted to trees exposed to near zero levels of UV-B radiation, and twice-ambient O₃. The data indicate that UV-B radiation, applied together with O₃, ameliorates the detrimental effects of O₃. The data also demonstrate that foliar symptoms develop more rapidly in Scots pine than in Norway spruce at higher accumulated ozone concentrations. Symbols and abbreviations: LSD, least significant difference; PAS300, UV-B irradiance weighted according to the plant action spectrum of Green et al. (1974) normalized at 300 (nm); AOT40, (AOT = accumulated over threshold) reflects the sum of hourly ozone concentrations above 40 nL L^–1 during daylight hours (> 50 Wm^–2) ( Kärenlampi & Skärby 1996 ); A₃₅₀, net photosynthesis at ambient CO₂; G₃₅₀, stomatal conductance for water vapour at ambient CO₂; A₂₅₀₀, net photosynthesis at saturating CO₂ (maximal potential photosynthetic activity); CE, carboxylation efficiency; ROS, reactive oxygen species; RuBP, ribulose 1,5-bisphosphate; Rubisco, ribulose 1,5-bisphosphate carboxylase/oxygenase; GLM, general linear model.     

Comparative analysis of leaf trichome structure and composition of epicuticular flavonoids in Finnish birch species

The morphology, ultrastructure, density and distribution of trichomes on leaves of Betula pendula, B. pubescens ssp. pubescens, B. pubescens ssp. czerepanovii and B. nana were examined by means of light, scanning and transmission electron microscopy. The composition of flavonoids in ethanolic leaf surface extracts was analysed by high pressure liquid chromatography. All taxa examined contained both glandular and non-glandular trichomes (short and/or long hairs) but differed from each other in trichome ultrastructure, density and location on the leaf. Leaves of B. pubescens were more hairy than those of B. pendula, but the latter species had a higher density of glandular trichomes. Of the two subspecies of B. pubescens, leaves of ssp. pubescens had more short hairs on the leaf surface and four times the density of glandular trichomes of leaves of ssp. czerepanovii, whereas, in the latter subspecies, short hairs occurred largely on leaf veins, as in B. nana. The glandular trichomes were peltate glands, consisting of medullar and cortical cells, which differed structurally. Cortical cells possessed numerous small, poorly developed plastids and small vacuoles, whereas medullar cells had several large plastids with well-developed thylakoid systems and fewer vacuoles. In B. pubescens subspecies, vacuoles of the glandular cells contained osmiophilic deposits, which were probably phenolic, whereas in B. pendula, vacuoles of glandular trichomes were characterized by the presence of numerous myelin-like membranes. The composition of epicuticular flavonoids also differed among species. The two subspecies of B. pubescens and B. nana shared the same 12 compounds, but five of these occurred only in trace amounts in B. nana. Leaf surface extracts of B. pendula contained just six flavonoids, three of which occurred only in this species. In summary, the structure, density and distribution of leaf trichomes and the composition of epicuticular flavonoids represent good taxonomic markers for Finnish birch species.     

Purification of plasma membranes from leaves of conifer and deciduous tree species by phase partitioning and free-flow electrophoresis

Purified plasma membrane fractions were obtained from leaves of Picea abies L., Pinus sylvestris L., Fagus sylvatica L. and Quercus robur L., whereas plasma membranes from Pinus halepensis Mill, proved to be more difficult to obtain, perhaps due to the higher content of volatile substances in this plant species. Plasma membranes were purified by both phase partitioning and free-flow electrophoresis from microsomal fractions and identified on the basis of biochemical and in some cases morphological and cytochemical markers. Electron micrographs revealed that membrane vesicles from Pinus sylvestris exhibited a very clear dark-light-dark pattern and measurements of membrane thickness showed that it ranged from 6 to 10 nm. Most membranes were 8 nm thick and stained with phosphotungstic acid at low pH, both typical characteristics of the plasma membrane. Enzymatic identification of plasma membranes consisted in the determination of the vanadate-sensitive ATPase (EC 3.6.1.3) activity. The specific activity in the upper phase (U₂) fraction was 10–25 times higher than those in the lower phase and microsomal fractions, depending on plant species. 1,3-β-glucan synthase II (EC 2.4.1.3), another putative plasma membrane marker, was not detected in the plasma membrane-enriched fractions of conifer needles and showed a very low specific activity in membranes of deciduous trees. Contamination by membranes of other origin was determined by analysis of membrane markers: cytochrome c oxidase (EC 1.9.3.1) for mitochondria, inosine diphosphatase (EC 3.6.1.6) for Golgi apparatus, cytochrome c reductase (EC 1.6.2.4) for endoplasmic reticulum, and pyrophosphatase (EC 3.6.1.1) for tonoplasts. The main, but relatively low contamination, was due to tonoplasts, as determined by the activity of pyrophosphatase. Plasma membrane characteristics were quite different depending on the season during which needles were taken. Membrane preparations of better quality were more easily obtained from samples taken during winter.     

Radial growth response of four dominant boreal tree species to climate along a latitudinal gradient in the eastern Canadian boreal forest

To address the central question of how climate change influences tree growth within the context of global warming, we used dendroclimatological analysis to understand the reactions of four major boreal tree species –Populus tremuloides, Betula papyrifera, Picea mariana, and Pinus banksiana– to climatic variations along a broad latitudinal gradient from 46 to 54°N in the eastern Canadian boreal forest. Tree‐ring chronologies from 34 forested stands distributed at a 1° interval were built, transformed into principal components (PCs), and analyzed through bootstrapped correlation analysis over the period 1950–2003 to identify climate factors limiting the radial growth and the detailed radial growth–climate association along the gradient. All species taken together, previous summer temperature (negative influences), and current January and March–April temperatures (positive influences) showed the most consistent relationships with radial growth across the gradient. Combined with the identified species/site‐specific climate factors, our study suggested that moisture conditions during the year before radial growth played a dominant role in positively regulating P. tremuloides growth, whereas January temperature and growing season moisture conditions positively impacted growth of B. papyrifera. Both P. mariana and P. banksiana were positively affected by the current‐year winter and spring or whole growing season temperatures over the entire range of our corridor. Owing to the impacts of different climate factors on growth, these boreal species showed inconsistent responsiveness to recent warming at the transition zone, where B. papyrifera, P. mariana, and P. banksiana would be the most responsive species, whereas P. tremuloides might be the least. Under continued warming, B. papyrifera stands located north of 49°N, P. tremuloides at northern latitudes, and P. mariana and P. banksiana stands located north of 47°N might benefit from warming winter and spring temperatures to enhance their radial growth in the coming decades, whereas other southern stands might be decreasing in radial growth.     

Chlorophyll content and the light response curve of shade-adapted conifer needles

Rates of photosynthesis were measured for shade-adapted conifer needles [ Picea abies (L.) Karst., Picea glauca (Moench) Voss, Picea mariana (Mill.) B. S. P., Picea sitchensis (Bong.) Carr., Pinus sylvestris L.] illuminated on i) their top surface, ii) their top and bottom surfaces simultaneously, or iii) uniformly in a light integrating sphere. The rate of bending of the light response curve of photosynthesis was strongly correlated with the amount of chlorophyll per unit of illuminated leaf area, when the amounts of chlorophyll were above 200 mg m⁻². Below 200 mg m⁻² only small differences in the rate of bending occurred and the light response curves took the form of a quasi-Blackman response. At chlorophyll contents below 200 mg m⁻² the rate of bending of the light response curves was insignificantly different from a mean published value for enzymatically isolated cells of angiosperm leaves (I. Terashima and T. Saeki. Ann. Bot. 56: 489–499, 1985). The apparent quantum yield of photosynthesis (based on incident light) also showed a response to chlorophyll content not different from the pattern reported for angiosperm leaves (E. K. Gabrielsen. Physiol. Plantarum 1: 5–37, 1948). Neither CO₂ nor O₂ concentration significantly affected the rate of bending of the light response curves. It is concluded that the light response curve of individual chlorenchyma cells is a quasi-Blackman response and that the rate of bending of the light response curve of intact leaves is a strong function of the development of gradients of light and thus the chlorophyll content of leaves.     

Recent cooling and recession of Norway spruce (Picea abies (L.) Karst.) in the forest—alpine tundra ecotone of the Swedish Scandes

Abstract. Repeated crown condition surveys, 1974–94, of subalpine clonal groups of Norway spruce ( Picea abies (L.) Karst.) were carried out in the Swedish Scandes. Complementary analyses concerned radial and vertical growth, sexual regeneration and range limit responses of other plant species. Significant defoliation of spruce progressed linearly over the period of study, reaching cumulative values of about 85%. It is inferred that defoliation was preconditioned by decreasing radial growth since the thermal climax in 1937 and was proximately initiated by the extremely cold winter of 1965/66 and paralleled by consistently declining radial growth and staggering vertical increase. It appears that severe and prolonged ground freezing invoked winter desiccation (xylem cavitation), extensive needle loss and reduced radial growth. Hypothetically, from circumstantial evidence, these processes are interrelated in a positive feedback system, implying increasing sensitivity to climatic stress and decreasing ability to take advantage of positive climatic anomalies. Thus, the total demise of the supranival stems is cautiously predicted, by linear regression of the 20-yr defoliation pattern, to be less than a decade ahead. The recession of P. abies , clearly relevant in a landscape perspective, conforms with analogous responses of Pinus sylvestris L. and Betula pubescens Ehrh. ssp. tortuosa (Ledeb.) Nyman and a significant altitudinal range-limit retraction of certain silvine field-layer species. The structural development examined in this study concurs with long-term climate cooling and cold events and strongly contrasts with simulations of the performance of this system in response to a putative enhanced'greenhouse'effect.     

Adhesion and development of the root rot fungus (Heterobasidion annosum) on conifer tissues: effects of spore and host surface constituents

The objective of this study was to correlate the occurrence of particular root and woody stump surface components with the ability of spores of the root rot fungus (Heterobasidion annosum) to adhere, germinate and establish on conifer tissues. With the aid of high performance liquid chromatography, several sugars (pinitol, xylitol, dulcitol, mannitol, D-glucose, mannose, fructose) were detected on both stump and fine root surfaces of Scots pine and Norway spruce. Of all the sugars observed, xylose and arabinose were poorly utilized for initiation of germ tube growth whereas spore germination was enhanced in the presence of D-glucose, mannose or fructose. Oxidation of these sugars by pretreatment of wood discs or roots with periodic acid abolished the ability of the spores to germinate. Non-sugar components such as long chain fatty acids on spores and root surfaces as detected with nuclear magnetic resonance were found to have a significant influence on adhesion and initiation of germ tube development. Removal of these aliphatic compounds from the root surface increased spore germination by 2-fold, whereas similar treatment on spores led to a 5-fold decrease in adhesiveness to root material. In vitro studies revealed that the di-ethyl ether extract from the roots had no long term adverse effect on spore germination which suggests that the fungus may possess the capability to detoxify this substance. Similarly, adhesion of spores was affected by low and freezing temperatures. The role of significant levels of mannitol and trehalose accumulated in spores and hyphae of the fungi on viability, survival and tolerance to adverse conditions such as oxidative stress, freezing and desiccation are discussed.     

Tree species dynamics and disturbance in three Swedish boreal forest stands during the last two thousand years

Abstract. Data from three forest stands for the past 2000 yr show how the shade-intolerant species Pinus sylvestris and Betula pubescens maintain significant populations in the Swedish boreal landscape. Age structure data from a northern stand close to the range limits of Picea abies and Pinus complement a local pollen diagram, and reveal cyclic population fluctuations which can be related to periods of climatic stress and fire. Pollen data from two southern stands show that high fire frequencies in the past prevented the expansion of Picea populations. Reduction of the fire frequency during the last 200 yr has favoured Picea. A long time perspective reveals the population dynamics of long-lived species and indicates the controlling factors. Such knowledge permits assessment of the current status and likely future of forest stands.     

不同木材结构树干液流对比研究

采用热扩散法,对东北东部山区代表主要木材解剖构造的水曲柳和樟子松树干液流密度动态特征进行研究,并同步测定光合有效辐射、气温、空气相对湿度、风速、土温、土壤容积含水量等因子。结果表明,水曲柳和樟子松在生长季不同时期晴天的树干液流密度日进程一般为单峰型,水曲柳日最高液流峰值为430.53 cm3.cm-2.h-1,明显高于樟子松(142.43 cm3.cm-2.h-1)。晚上及凌晨液流量占全天比例在生长季结束后,明显增加,其他时期低于20%,说明水曲柳和樟子松存在根压。水曲柳和樟子松树干液流密度变化呈单峰曲线,平均液流密度分别为12.26、6.49 cm3.cm-2.h-1。影响树干液流密度日变化的主导因子为光合有效辐射和水汽压亏缺,二者对主导因子敏感度相当。