Rolf Gref

Effects of nitrogen fertilization on pine needle chemistry and sawfly performance

SummaryChanges in needle nitrogen and resin acid concentrations in young Scots pine trees fertilized with ammonium nitrate were followed over 3 years. Sawfly larvae (Neodiprion sertifer) were reared on fertilized and control trees the year after fertilization. Both nitrogen and resin acid concentrations increased in fertilized trees. The fact that resin acid concentrations increased contradicts predictions of the carbon/nutrient balance hypothesis. We suggest that needle resin-acid concentrations are limited more by the size of the resin ducts than by the availability of substrate for resin acid synthesis, and that the formation of resin ducts is limited by the availability of nitrogen. A modification of the carbon/nutrient balance hypothesis, relating compartment formation to allelochemical synthesis, is discussed. Performance of sawfly larvae was not affected by fertilization treatment, probably because concentrations of nitrogen (positively affecting performance) and resin acids (adversely affecting performance) increased simultaneously in fertilized trees. Thus, the results of this study do not support the notion that fertilization increases the resistance of trees to needle-eating insects.

Responses of Neodiprion sertifer (Hym., Diprionidae) larvae to variation in needle resin acid concentration in Scots pine

SummaryWe have studied how differences in needle resin acid concentrations between two clones of Scots pine influenced larval survival, larval developmental time, and cocoon weight in Neodiprion sertifer. Larvae were reared under controlled conditions in the laboratory on needles showing a three-fold difference, in resin acid concentration. Larval developmental time was significantly longer for larvae fed needles high in resin acids. No significant differences were found in cocoon weight. Larvae fed needles high in resin acids suffered significantly higher mortality, most of which occurred, in the first two instars. Data on relative growth rate for last-instar larvae, based on a traditional growth efficiency experiment, did not show any negative effects of resin acids, indicating that a possible induction takes place during early instars. Observations on the feeding behaviour of last-instar larvae, the high consumption of bark tissue (with high concentrations of resin acids) by larvae fed needles low in resin acids and preference for needle tissues high in resin acids, indicate that these larvae might actively search for tissues rich in resin acids. We conclude that the physiology and behaviour of N. sertifer has been shaped, in part, by the conflict between the negative effects of resin acids, primarily in early instars (longer developmental time with a corresponding increase in exposure to natural enemies and an increase in direct mortality), and the positive effect of resin acids in later instars (a need for resin acids for use in its own predator defence secretion).

Toxic effects of some conifer resin acids and tea tree oil on human epithelial and fibroblast cells

The present study was undertaken to assess and compare the in vitro cytotoxic effects of three resin acid analogues: dehydrobietic acid, podocarpic acid, O-methylpodocarpic acid; an essential oil from Australia (tea tree oil); and tapped oleoresin from Thailand, on human epithelial and fibroblast cells, using a quantitative neutral red spectrophotometric assay. All of the investigated compounds except for tea tree oil exhibited a cytotoxic activity which was proportional to their concentrations and time of exposure up to 24 h, i.e. higher concentrations and longer time of exposure caused increased cell death. Dehydroabietic acid and the oleoresin were the most toxic compounds followed by O-methylpodocarpic acid, whereas podocarpic acid and tea tree oil showed a lower level of toxicity. On the basis on these findings it is concluded that an isopropyl group on the aromatic C-ring is of great importance for the cytotoxicity of the tested abietane resin acids, thus indicating that the cytotoxic activity of oleoresins most probably is caused by synergistic or additive effects of resin acids. The results from this work support the view that antibacterial activity parallels cytotoxic activity which suggests a similar mode of action, most probably exerted by membrane-associated reactions.

Plant-part specific and temporal variation in phenolic compounds of boreal bilberry (Vaccinium myrtillus) plants

Leaves and stems of bilberry were analysed for phenolic metabolites using a simple method of extraction and HPLC analysis. Hydroxycinnamic acid derivatives (HCAs) and flavonoids were identified on the basis of their UV-spectra. Temporal fluctuations in the levels of selected phenolic compounds were followed during the growth season of 2000. Qualitative and quantitative differences were detected in phenolic profiles between leaf and stem tissues. The most abundant peak in leaf samples was tentatively identified as chlorogenic acid (5-O-caffeoylquinic acid). In stems, this compound was found at much lower levels than in leaves and an unidentified p-coumaric acid derivative dominated the phenolic profile. The most abundant flavonols in leaves and stems were quercetin derivatives. The total sum of methanol-soluble phenolics was generally higher in leaves than in stems. The concentrations of some alkaline hydrolysis products were higher in stems than in leaves, indicating that a larger part of the phenolic pool was incorporated into lignified cell walls in the stems. Individual phenolic compounds differed in their seasonal fluctuation patterns. It is suggested that the observed plant-part specific and within-seasonal variation may influence the ecological interactions between bilberry and its natural enemies.

Isolation and characterization of a germination inhibitor from leaves of Empetrum hermaphroditum Hagerup

An extract of Empetrum hermaphroditum Hagerup leaves was examined for germination inhibitors using an assay based on germination of Populus tremula L. seeds. The substances were extracted in water and purified by solvent partitioning. The acidic ethyl acetate fraction, containing the major part of the inhibitory activity was purified by reversed‐phase high‐performance liquid chromatography. Two zones of inhibitory activity were detected, combined and further purified by normal‐phase HPLC. One major zone of inhibitory activity was thereafter detected and the substance in this fraction was crystallized and identified by nuclear magnetic resonance and gas chromatography‐mass spectrometry as 5‐methoxy‐3,3´‐dihydroxy‐dihydrostilbene or batatasin III. Ca. 100 mg of the substance was then, by sequential HPLC, isolated in crystalline form from E. hermaphroditum leaves. The inhibitory activity of the pure substance was compared with a crude water extract of E. hermaphroditum leaves. It was concluded that the pure ...

Emission of Volatile Aldehydes and Ketones from Wood Pellets under Controlled Conditions

Different qualities of biofuel pellets were made from pine and spruce sawdust according to an industrial experimental design. The fatty/resin acid compositions were determined by gas chromatography-mass spectrometry for both newly produced pellets and those after 2 and 4 weeks of storage. The aldehydes/ketones compositions were determined by high performance liquid chromatography at 0, 2, and 4 weeks. The designs were analyzed for the response variables: total fatty/resin acids and total aldehydes/ketones. The design showed a strong correlation between the pine fraction in the pellets and the fatty/resin acid content but the influence decreased over storage time. The amount of fatty/resin acids decreased approximately 40% during 4 weeks. The influence of drying temperature on the aldehyde/ketone emission of fresh pellets was also shown. The amounts of emitted aldehydes/ketones generally decreased by 45% during storage as a consequence of fatty/resin acid oxidation. The matrices of individual concentrations were subjected to multivariate data analysis. This showed clustering of the different experimental runs and demonstrated the important mechanism of fatty/resin acid conversion.

Effects of mono‐ and diterpenes in scots pine needles on moose browsing

We compared the degree of browsing by moose on 30 clones of Scots pine with the concentrations of mono‐ and diterpenes in their needles. The pine clones originated from 11 Swedish and one Norwegian locality within the latitudes 61–69° N. They were grown in a nursery in northern Sweden, close to 63° N, and were accidently exposed to moose during one winter. The relative amount of twig biomass removed differed significantly between clones. No statistically significant correlation was found between monoterpene concentrations in the needles and degree of moose browsing. For the diterpene pinifolic acid, however, there was a significant negative correlation.

Detection of pinosylvins in solid wood of Scots pine using Fourier transform Raman and infrared spectroscopy

Diffuse reflectance Fourier transform infrared (DRIFT) and near infrared (NIR) FT-Raman spectroscopy were used to detect pinosylvins in the wood of Pinus sylvestris L. trees. NIR FT-Raman spectroscopy offered the possibility of revealing pinosylvins simply by visual inspection of Raman spectra whereas DRIFT spectra needed a more complicated evaluation. Pinosylvin and resin acids from Scots pine were examined as to the possibility of their being the cause of observed spectral differences between sapwood and heartwood. Since pinosylvins are important compounds for the decay resistance of Scots pine wood, the detection of pinosylvins with Raman spectroscopy might be used to assess durability of wood products.

Weak responses of pine sawfly larvae to high needle flavonoid concentrations in scots pine.

Responses of sawfly larvae (Hymenoptera, Diprionidae) to the flavonoid taxifolin glucoside in their host plant were studied in a laboratory experiment. Larvae ofNeodiprion sertifer andDiprion pini were raised from egg hatch to cocoon spinning on two Scots pine (Pinus sylvestris) chemotypes, one without needle taxifolin glucoside (−) and the other containing 2–4% taxifolin glucoside (+). The (+) chemotype had somewhat lower concentrations of needle terpenoids (resin acids) than the (−) chemotype. Current-year needles had higher taxifolin glucoside concentrations than mature needles. There were no differences in survival or body size betweenN. sertifer larvae that fed on the (+) chemotype and those that fed on the (−) chemotype. FemaleD. pini larvae raised on (+) needles developed 6% more slowly than larvae fed (−) needles. The results from this study are contrary to earlier findings showing that flavonoid glucosides have strong negative effects on insect performance. Possible explanations for the different outcomes are discussed.

Seasonal changes of pinosylvin distribution in the sapwood/heartwood boundary of Pinus sylvestris

Abstract Changes in pinosylvin concentration and distribution across the sapwood/heartwood boundary were studied on Scots pine (Pinus sylvestris L.) tree stems to detect seasonal activity in heartwood formation. Pinosylvin concentrations were measured with FT-(NIR) Raman spectroscopy for a total of 96 trees equally distributed on 16 different sampling occasions. In another experiment, cores were sampled every month from six individual Scots pine trees from June to October and analysed for pinosylvin. There was a great between-tree variation in concentration and spatial distribution of pinosylvin. No seasonal trend in the distribution pattern or concentration of pinosylvin was found. Therefore, the results indicate that there is no specific period during the year when heartwood is formed.