Search

To test for the effects of far-red light on preventing budset in Picea abies, seedlings of six populations originating from latitudes between 67°N and 47°N were grown for 4-8 weeks in continuous incandescent (metal halogen) light at 300 μmol m -2 s -l and 20°C and then transferred, at the same temperature, to a daily regime of 8 h incandescent light (300 μmol m -2 s -1 ) followed by 16 h cool white fluorescent light (40 μmol m -2 s -1 ). (Cool white lamps are deficient in far-red light, with a R/FR ratio of 7.5 compared with 2.0 for the incandescent lamps.) All the seedlings from 67° and 80% of those from 64° stopped extension growth and set terminal buds within 28 days of the change of regime. The seedlings from 61° and further south continued growing, as did control seedlings from 67° grown as above but with incandescent light at 20 μmol m -2 s -1 replacing cool white illumination. To distinguish between a clinal and ecotypic pattern of variation, the interval between 64° and 59° was investigated by growing populations originating from that area in the same regimes as before. After 28 days in the cool white day-extension regime, the percentage budset was 86 for the population from 64°; 0 for the population from 59° and 25-50 for the intermediate populations; i.e. the populations showed a clinal variation in requirement for far-red light according to latitude. Thus northern populations of Picea abies appear to behave as 'light-dominant' plants for the photoperiodic control of extension growth and budset, whereas the more southern populations behave as 'dark-dominant' plants.

The aim of the thesis was to study the methane flux (CH4) from crack willow (Salix fragilis) and bay willow (Salix pentandra) at the ecosystem station Wet Meadow by Třeboň (49°01 N; 14°46 E). The research was carried out in May 2016. Methane is one of the important greenhouse gases, which plants can emit into the atmosphere. Neither the fluxes of methane from willows nor the factors influencing them were so far sufficiently monitored. The thesis became a part of the whole year's monitoring of these fluxes, carried out by the Global Change Research Institute of the Czech Academy of Sciences, under the lead of expert consultant Dr. rer. nat. Mgr. Macháčová. The fluxes of CH4 were measured with the help of manual static chamber systems located in three height-levels and online portable laser gas analyser. The fluxes were processed, statistically evaluated and coherent tables and charts were created from the results. Based on these results we can conclude, that all examined trees have released CH4 and CO2 from their trunks, however no significant statistical difference between morning and afternoon fluxes was measured. S. fragilis was emitting higher amounts of CH4 and CO2 than S. pentandra. At the same time emissions dramatically decreased along with decreasing trunk height. Therefore the highest emissions were detected directly at the ground level. Moreover, the emissions of CH4 and CO2 were measured from the soil as well.

Flavonoids, proanthocyanidins (PAs) and salicylic alcohol derivatives are the main groups of ingredients in Salix needed as defensive tools and signal molecules, but have also pharmaceutical importance. The present study investigated total PA content, complete PA pattern, the oligomeric/total PAs quotient and the contents of catechin and epicatechin during one growing-season for the leaves and this year's sprouts in ten willows (Salix pentandra L. ♂, S. alba L. ♂, S. fragilis L. ♀, S. caprea L. ♂ & ♀, S. cinerea L. ♂, S. caprea x cinerea ♂, S. daphnoides Vill. ♂ & ♀ and S. purpurea L. ♀; all Salicaceae). Comparison of the different species revealed distinct seasonal fluctuations of the oligomeric and polymeric PA fractions, but the contents of both groups always developed in the same direction. All willows prefer the synthesis of PAs with DP-2 - DP-4 within the oligomeric fraction (DP-2 – DP-10) and species with rather low PA contents like S. purpurea (0.1–2.6 mg/g) as well as species with rather high PA contents like S. alba (3.8–14.7 mg/g) were found. Only slight gender specific differences could be observed for both sexes of S. daphnoides and S. caprea. The PA pattern of the hybrid S. caprea x cinerea seems to be influenced by both parents. Thus, the accumulation of the oligomeric PAs accorded to S. caprea and the polymeric PAs matched S. cinerea resulting in an overall depression of PAs in the sprouts and a varying seasonal trend in the leaves. In contrast, the content of catechin remained high and seemed to be not influenced in the hybrid. Although only one individual of each Salix species could be considered in this screening study, the present results demonstrate the variability of the flavan-3-ol pattern within the genus Salix but also some preliminary correlations could be observed. Future studies with more Salix species will provide more insights into chemotaxonomic correlations.

One of the objectives of the Management Plan of Vitosha Nature Park is to protect the natural conditions and restore populations of species of conservation significance. Bay Willow (Salix pentandra L.) and Giant Snowdrop (Galanthus elwesii Hook.) are included in Annex 3 of the Bulgarian Biodiversity Act and are enlisted in the Bulgarian Red Data Book as Critically Endangered (CR) and Endangered (EN) species respectively. Bay Willow in Bulgaria occurs only in the territory of Vitosha Nature Park with lmited numbers and Giant Snowdrop is considered extinct from the park territory. Methods of vegetative propagation, suitable substrates and period of collection of vegetative propagules are established through an in vivo experiment. New individuals of the two species have been produced and they have been planted in their natural habitats in Vitosha. High degree of survival of new individuals has been found through subsequent monitoring.

Application experiments have suggested that short-day-induced cessation of elongation growth in trees is caused by photoperiodic regulation of the conversion of gibberellin GA 19 to GA 20 . In the present study we examined further the photoperiodic control of GA metabolism in trees with focus on the conversion of GA 19 in Salix pentandra, hybrid aspen (Populus tremula × tremuloides) and silver birch (Betula pendula) using [17,17- 2 H 2 ]-GA 19 or unlabelled GAs in application studies. GA 20 and GA 1 were able to restore growth also in hybrid aspen and silver birch under short days (SD), whereas GA 19 had no or only a very small activity. Contrary to hybrid aspen and S.pentandra, the activity of GAS in silver birch was significantly lower than that of GA 1 . Gas chromatography-mass spectrometry (GC-MS) analysis revealed a smaller turnover of [ 2 H 2 ]-GA 19 in SD than in long days (LD) in hybrid aspen. No such difference in turnover of [ 2 H 2 ]-GA 19 was observed in photoperiod-insensitive hybrid aspen overexpressing PHYA. Application of unlabelled GAs to seedlings of S. pentandra, hybrid aspen and silver birch under SD followed by quantification of metabolites by GC-MS analysis, showed that applied GA 19 was not readily converted to GAS and GA 1 Although the sensitivity to GAs is also known to decrease under SD, the present data are in favour of a photoperiodic regulation of the metabolism of GA 19 in vivo in the woody species S.pentandra, hybrid aspen and silver birch. The data might also suggest that silver birch differs from S.pentandra and hybrid aspen by exhibiting a possible photoperiodic control also of the conversion of GAS to GA 1 .

Most of the energy today is obtained from fossil fuels, which are becoming more expensive and less available. Energy from biomass produced on agricultural land is an alternative option. Energy crops should guarantee high yield and good quality parameters, associated with their use in energy production. This study analysed the thermophysical and chemical properties of biomass obtained from 15 new clones of willow selected in the Department of Plant Breeding and Seed Production of the University of Warmia and Mazury in Olsztyn. The plants were cultivated in one- and three-year rotation cycles, run in 2009-2011 at two research stations: in Baldy and in Łezany. The energy content as well as elemental and physical properties of biomass were analysed. The higher heating value was better in biomass from one-year shoots (on average 19.66 MJ kg -1 d.m.). The highest value of this parameter was recorded for the clone of Salix acutifolia UWM 093 (20.04 MJ kg-1 d.m.). The higher heating value in biomass of three-year old clones was on average lower by 0.06 MJ kg -1 d.m. The lower heating value in biomass increased in longer willow coppice harvest cycles. The highest lower heating value was recorded for the clone UWM 035 of Salix pentandra (9.27 MJ kg -1 ) harvested in a three-year cycle, whereas the lowest one was achieved by the clone of Salix dasyclados UWM 155 (7.55 MJ kg -1 ) harvested in a one-year cycle. The average moisture content in three-year shoots was 50.01% d.m., being higher by 2.31% in one-year shoots. The ash content was lower in biomass harvested in three-year rotation. In conclusion, willow biomass obtained in a three-year harvest cycle contains less of undesirable elements and proves to be better quality fuel than biomass obtained in a one-year harvest cycle.

In the leaves of 13 Finnish willow species, the content of a phenolic, chlorogenic acid, was found to vary from 0 up to 18 mg g−1 D.W. Effects of pure chlorogenic acid on insect feeding behaviour were tested using four common leaf beetle species which are in the field mainly found on willows with low-chlorogenic acid leaves. One species, Lochmaea capreae L., was invariably deterred by pure chlorogenic acid applied in naturally occurring concentrations on the willow leaves. Accordingly, in 2-choice laboratory feeding trials L. capreae was found to prefer low-chlorogenic acid leaves of four willow species over high-chlorogenic acid leaves of Salix pentandra L. and S. myrsinifolia Salisb. When presented on the leaves of S. phylicifolia L, pure chlorogenic acid inhibited also the feeding by Phratora polaris Sp.-Schn. Instead, chlorogenic acid had no significant effect on Ph. polaris when it was presented on the leaves of another willow S. cinerea L. In laboratory, Ph. polaris did not show general preference for willow species with low chlorogenic acid content in their leaves. Thus, the response of Ph. polaris to chlorogenic acid seems to depend on the plant species. Apparently variation in other traits such as leaf hairyness may easily override the potential effect of chlorogenic acid content on Ph. polaris. To two other leaf beetle species, Galerucella lineola F. and Plagiodera versicolora Laich., chlorogenic acid is an ineffective deterrent even at unnaturally high concentrations. In laboratory, G. lineola and P. versicolora did not prefer willows with low chlorogenic acid content in their leaves. Thus, among four studied leaf beetle species, only L. capreae seems to be clearly affected by this phenolic. Therefore, overall importance of chlorogenic acid as a defence against willow-feeding leaf beetles appears to be very limited.

The food selection, growth, and fecundity of insect herbivores are largely dictated by the chemical composition and nutritive values of plant foliage. We studied the host-use efficiency of larvae of the generalist moth, Operophtera brumata (Lepidoptera: Geometridae) on three chemically divergent but nutritively similar willows (Salix spp.). The 4th instars were able to use the salicylate-free leaves of S. phylicifolia efficiently. Growth was slightly reduced on S. pentandra, which contained a moderate level of acetylated salicylates. The high concentration of salicylates found in the leaves of S. myrsinifolia seemed to provide efficient protection against non-specialized O. brumata. We also studied assimilation of nutrients and degradation of salicylates and other secondary compounds in the digestive tract of O. brumata larvae. Neither the assimilation of nitrogen nor of carbon were affected by secondary chemicals of ingested food. Salicylates were shown to be degraded to salicin and catechol, while further degradation of salicin to saligenin was rather slow. In an artificial diet experiment, we showed that two degradation products of salicylates, catechol and saligenin markedly reduced the growth of the larvae. Neither salicin nor chlorogenic acid affected larval growth. We conclude that salicylates reduced the growth of the generalist winter moth mainly by feeding deterrence caused by 6-hydroxy-2-cyclohexenone and catechol. Compared to the deleterious effects of salicylates the effects of other secondary compounds were minor.

In young plants of Salix pentandra, a temperate zone deciduous woody species, elongation growth ceases and a terminal bud is formed at day lengths shorter than a critical length. This is the first step in dormancy development, making survival under harsh winter conditions possible. Early studies strongly indicate that gibberellin is involved in the photoperiodic control of bud set and bud break. GA(1) action was studied by application under short days to plants where cessation of shoot elongation had occurred, followed by subsequent anatomic investigations of shoot tips. Under short days the frequency of cell division decreased rapidly along with the earlier observed decrease in GA(1) levels. Application of GA(1) to short-day-induced terminal buds rapidly stimulated cell division in apices several days before visible shoot elongation in response to this treatment was observed. One day after GA(1) application a fourfold increase in cell division frequency in apices was observed, increasing to a maximum of sevenfold 2 days after application. Long-day treatment leading to induction of bud break after about 4-6 days was followed by slowly increasing frequency of cell divisions. In earlier studies of this species, short days and gibberellins had no effect on cell elongation. These data show that increased GA(1) content, by application or long-day treatment, results in increased frequency of mitosis. This strongly indicates that GA(1) affects stem elongation in connection with bud set and bud break primarily by affecting cell divisions in subapical tissues.

Larvae of Phratora vitellinae (Coleoptera: Chrysomelidae) convert salicyl glucosides from the host plant into a larval defensive secretion with salicylaldehyde. This secretion repels generalist predators. Willows vary greatly in the concentrations of salicyl glucosides in their leaves. One may predict that P. vitellinae prefers and survives better on plants that contain more salicyl glucosides. We determined the amount of larval secretion, host preference, larval growth, and larval survival of P. vitellinae on Salix myrsinifolia, S. pentandra, and S. phylicifolia. We also measured feeding rates of three natural predators on P. vitellinae larvae feeding on different hosts. Salix pentandra and S. myrsinifolia contained substantial amounts of salicyl glucosides, but S. phylicifolia contained very little of them. Phratora vitellinae larvae produced more secretion on S. pentandra than on S. myrsinifolia. They produced little secretion on S. phylicifolia. Adult beetles preferred S. myrsinifolia over S. pentandra and S. pentandra over S. phylicifolia. Larvae grew most rapidly on S. myrsinifolia and S. pentandra. Their growth was slowest on S. phylicifolia. The larval survival was similar on S. myrsinifolia and S. phylicifolia, but it was significantly lower on S. pentandra. The natural predators fed equally well on P. vitellinae feeding on S. myrsinifolia and S. phylicifolia. Thus, the host preference of P. vitellinae did not cor- respond to larval survival on these hosts, but rather to larval growth. Larval survival of P. vitellinae was not related to the amount of defensive secretion. Natural predators were not repelled by the host-derived defensive secretion. We discuss the implications of these findings for the evolution of host plant use in this herbivore.

Differences in the ability of salivary proteins from Scandinavian and North American moose (Alces alces) to bind tannins from various preferred food plant sources were studied. Both Scandinavian and North American moose produce a salivary tannin-binding protein which binds only condensed tannins common in their diet. The tannins of winter-browsed stems of Pinus sylvestris and Salix pentandra were more effectively bound by salivary tannin-binding protein from North American moose than by those from Scandinavian moose. Tannins of P. sylvestris and S. pentandra stems were also more effective binding agents than tannins from S. caprea and Betula species. The interactions between salivary tannin-binding protein and plant tannins may be one factor affecting food plant choice of moose. The chemical and biochemical characteristics of plant tannins and the ability of salivary tannin-binding proteins to react with tannins should be taken into account in diet selection.

The effects of individual phenolic glucosides and total glucoside fractions on the feeding behaviour of three willow-feeding leaf beetles (Coleoptera: Chrysomelidae) were tested in the laboratory. Feeding preferences of the tested leaf beetles were strongly influenced by certain phenolic glucosides which are typical secondary compounds of willows (Salicaceae: Salix). Two of the tested leaf beetles, Galerucella lineola and Lochmaea capreae showed rather similar responses to glucoside treatments. Both of them were strongly stimulated by total glucoside fractions from Salix triandra and by its major glucoside salidroside. The third species, Phatora vitellinae, was attracted most by the fractions from S. myrsinifolia and S. pentandra, and by two related salicylate glucosides, tremulacin and salicortin. Food selection pattern of the tested beetles in the laboratory concords fairly well with their distributions in the field and with the occurrence of phenolic glucosides in their host willows. Phenolic glucoside extracts stimulated more feeding than individual pure glucosides. This indicates that different compounds have synergistic effects in the feeding behaviour of leaf beetles. Our results clearly show that willow leaf beetles select their food based on phenolic glucosides of their host plants.

Gibberellin A4 (GA4) is biologically active in Salix pentandra and is able to induce stem elongation in seedlings grown under short day (SD) conditions, as well as in seedlings grown under long day (LD) conditions and treated with a growth retardant BX-112. [3H2]GA4 and [2H2]GA4 were applied to seedlings and leaf and stem explants of S. pentandra, and metabolites were studied using HPLC and GC-MS. After application of [3H2]GA4 to seedlings of S. pentandra, one of the three main radioactive metabolites in the free acid fraction had retention properties similar to GA1. Using [2H2]GA4, this compound was identified by GC-MS with SIM as [2H2]GA1 both from short day-grown and BX-112-treated seedlings, as well as in leaf and stem explants. After injection of GA4 into a mature leaf, GA1 was mainly found in the elongating stem tissue. Thus, the possibility that the biological activity of GA4 in Salix is due to its conversion to GA1 cannot be excluded.

To evaluate the general extent to which sex-related differences in palatability occur in boreal dioecious woody plants, males and females of five dioecious woody plant species were presented to free-ranging mountain hares (Lepus timidus) during winter. Hares strongly preferred branches from male plants when feeding on Populus tremula and Salix caprea and weakly preferred male S. pentandra. However, they did not show any sex-related preference when feeding on the other two species studied (Myrica gale and Juniperus communis). Nitrogen concentration and, to some degree, digestibility showed strong relationships with hare food preferences. By contrast, the concentration of phenolics was only weakly related to feeding preference. Phenolics could, nevertheless, still be important if only one or a few specific compounds deter hare feeding. These results indicate that sex-related differences in plant palatability in the boreal forest might be more widespread than previously believed, particularly for species of the family Salicaceae. Thus, herbivores might be responsible for the female-biased sex ratios found in willow populations in northern Scandinavia (e.g. Elmqvist et al. 1988).

Effects of gibberellins A1, A4/7, A9, A19 and A20 and growth retardants were studied on shoot elongation in seedlings of Salix pentandra L. The growth-retarding effects of CCC and ancymidol were antagonized by all the gibberellins tested. The novel plant growth regulator prohexadione (free acid of BX-112), which is suggested to block 3β-hydroxylation of gibberellins, effectively prevented shoot elongation in seedlings grown under long photoperiod. Initiation of new leaves was only slightly reduced. GA1, but not GA19 and GA20, was active in overcoming the inhibition of stem elongation of seedlings, treated with prohexadione, GA19, GA20 and GA1 are native in S. pentandra, and the results are compatible with the hypothesis that GA1 is active per se in shoot elongation, and that the effect of GA19 and GA20 is dependent on their conversion to GA1. A mixture of GA4 and GA7 was as active as GA1 in promoting shoot elongation in seedlings treated with prohexadione, while GA9 showed slight activity only when applied at high doses.

Acclimation in seedlings and young plants of various ecotypes and crosses between ecotypes of Salix pentandra L. were studied under natural climatic conditions at 69°39’ N lat. and in a phytotron. Rapid cold acclimation was initiated after cessation of apical growth and outdoors it occurred about four weeks earlier in a northern (from 69°39’ N lat.) than in a southern (from 59°40'N lat.) ecotype. F1‐populations from crosses between a northern and a southern ecotype gave an intermediate response. Experiments with different morphogenetic light treatments indicated that these treatments affected cold acclimation mainly through their effects on cessation of growth. There was, however, an indication that blue light, given during a daylength extension period, slightly prevented acclimation in seedlings of a northern ecotype. After budset cold hardening was effectively triggered by low temperatures (3°, ‐3°C), but also seedlings that were kept in short day conditions at a high temperature (12, 15°C) developed a ...

Salix pentandra Linnaeus, Species Plantarum 2: 1016. 1753. "Habitat in Europae paludibus montosis duris." RCN: 7359. Lectotype (Jonsell & Jarvis in Nordic J. Bot. 14: 152. 1994): Amman 8, Herb. Linn. No. 1158.5 (LINN). Current name: Salix pentandra L. (Salicaceae)., Published as part of Jarvis, Charlie, 2007, Chapter 7: Linnaean Plant Names and their Types (part S), pp. 806-877 in Order out of Chaos. Linnaean Plant Types and their Types, London :Linnaean Society of London in association with the Natural History Museum on page 809, DOI: 10.5281/zenodo.291971

Tree species growing at northern latitudes are characterised by significant annual variation in their cold hardiness. Due to their height, trees are not protected by insulating snow cover and, in order to survive, they must be able to develop high level of cold hardiness. Lack of capacity for sufficient cold hardiness is, however, often not a limiting factor for winter survival of deciduous and evergreen tree species growing in boreal and subarctic regions. Their survival is primarily dependent on a proper timing of cold hardening and dehardening. This is a well-known fact and has been demonstrated in numerous studies, and the basic aspects of the environmental regulation of these processes have been studied comprehensively. These studies have provided strong evidence for the central role of photoperiod as a cue for timing of hardening in northern tree species, and for interaction between photoperiod and temperature. Due to the decisive effect of photoperiod on cold hardening, adaptation to photoperiodic conditions appears to be a prominent feature in these tree species.

We studied the effects of natural wounding by insects and artificial wounding by clipping with scissors on the phenolic chemistry of two willows, Salix myrsinifolia and Salix pentandra. Half of the blade of a mature leaf was removed from each experimental plant either by allowing insects (chrysomellid beetles) to feed on the leaf or by clipping off half the blade of a leaf with scissors. We also examined the ability of wounded plants to warn neighboring plants of imminent wounding by an airborne signal by maintainign one set of control plants in the room containing the wounded plants and another set of control plants in a room hermetically sealed from the room containing the wounded plants. After 48 h, the experimental leaf and the fourth leaf and eighth leaf upwards in the leaf sequence from the experimental leaf were analyzed for phenols by high-pressure liquid chromatography. The same leaves in the leaf sequence from each control plant were similarly analyzed for phenols. Only one phenol, salicortin in leaves of S. myrsinifolia, increased in concentration in response to defoliation, and the observed response was small. The type of wounding affected this increase in salicortin, with natural wounding by insects causing a greater response than artificial wounding in one S. myrsinifolia clone, and artificial wounding causing a greater response than insect wounding in the other clone. This result indicates that S. myrsinifolia cannot control the effects of diffeeent types of wounding on its leaf secondary chemistry. We also found no indication of airborne warning signals between wounded and unwounded plants that trigger an elevation of leaf defenses in unwounded plants in anticipation of herbivore attack.

Strong bottom-up effects dominated the trophic system of the host plant, Salix pentandra, the specialist galling sawfly ; Euura amerinae, inquilines in the genus Eurytoma and the most common parasitoid attacking both genera of herbivores, Pteromalus. capreae. A young willow population provided the basic resources for the second and third trophic levels, and the inquilines and parasitoid species showed strong positive, but density-independent, responses to food supply. Colonized trees ranged from 3 to 7 years old in 1989, and the Euura population had increased by 1991, declined significantly by 1992, and went almost extinct in 1994. The sex ratio declined steadily from 1989 to 1992. Populations of Eurytoma and Pteromalus tracked their resources closely, without influencing the major aspects of Euura population change dictated by availability of young trees and the rapid development of host resistance correlated with tree age. Trees continuously colonized by Euura from before 1989 to 1992 were much more favorable to both higher trophic levels than trees colonized for the first time between 1989 and 1992, indicating the importance of host heterogeneity in the system. Overall, effects from the host plant up the trophic system were very much stronger than the effects of carnivores down the food web.

The shoot-galling sawfly, Euura amerinae, usually attacks only young trees of Salix pentadra. Similar patterns of attack by other herbivores on plants have generated four alternative hypotheses to account for these patterns: The hypotheses on induced defenses in attacked plants, plant age, plant vigor, and regulation by carnivores. This long-term study followed all individual trees in a population from establishment of sawflies to their local extinction. Trees colonized the site in 1978, they were first attacked by sawflies in 1983 and the population of sawflies became extinct in 1990, after a brief flush to peak densities of galls in 1988. Mean productivity of adults declined steadily from 1983, at two per gall, to zero in 1990, while willows grew very rapidly

The daily course of evapotranspiration (E) in a willow carr (stand of Salix cinerea L. and Salix pentandra L.) was calculated from meteorological data for 3 months (July–September 1983) by the Bowen-ratio method, and compared with evapotranspiration of the surrounding sedge-grass marsh (Carex gracilis Curt., Calamagrostis canescens (Weber) Roth and Glyceria maxima (Hartm.) Holmberg evaluated in the previous years by the same method. A considerable difference was found only for July, which was extremely hot in 1983. The daily average E was 4.8, 3.2 and 2.4 mm day−1, in July, August and September, respectively. The enhancement or reduction of E under non-neutral air stability conditions were less than 10% of E under air stability conditions. Calculation of E for non-neutral air stratification is discussed in the paper.

Fifteen different gibberellins (GA's) were tested for their ability to induce elongation growth under short day conditions in seedlings of Salix pentandra L. GA's were applied either to the apex or they were injected into a mature leaf. GA3 was highly active and also GA4+7 and GA4 showed high activity. GA1, GA2, GA5, GA9, GA13, GA20, GA36 and GA47 showed moderate activity. GA16, GA17, GA27 and GA41 exhibited low or no activity in doses up to 10 μg per plant. In general, a better growth response was obtained with an application to the apex than with an injection into the leaf.

Activities of acidic gibberellin(GA)-like substances in shoots of Salix pentandra trees growing under natural conditions (69°39′ N, 18°37′ E) were studied in relation to shoot elongation and tip abscission. Bioassay after separation on SiO2 partition columns was accomplished with the lettuce hypocotyl and dwarf rice 'Tan-ginbozu' assays. The GA-like activity in the apical part of the shoot greatly decreased before cessation of growth and shoot tip abscission. In the basal part of the shoot the marked reduction of GA-like substances occurred well before shoot tip abscission and even before shoot elongation had ceased. Low GA-like activity in the shoot may be a prerequisite for apical growth cessation and for the development of lateral flower buds.

Apical growth cessation as affected by photoperiod and temperature has been studied in seedlings of two latitudinal ecotypes of Salix and Betula. The critical photoperiod for apical growth cessation at constant temperatures of 15 and 21°C was about 22 h for a northern (69°C39′N) and about 15–16 h for a southern (59°C40′N) ecotype of Salix pentandra. Fluctuating day/night temperatures (21°C/9°C, 15°C/6°C) induced apical growth cessation in northern ecotypes even at 24–h photoperiod. Disagreements in critical photoperiods found in various studies are discussed.

Samples of 17 plant species (one herb, dwarf shrubs and trees) were collected monthly throughout the winter 1976/77. Samples were frozen down to selected temperatures and hardiness was estimated by visual observations of oxidative browning and bud break. In most species hardiness rapidly increased from September to November and dehardening started in February–March. In six species (Betula pubescens Ehrh., Picea abies (L.) Karst., Salix caprea L., Sorbus aucuparia L., Vaccinium myrtillus L., V. vitis-idaea L.) hardening developed faster at the continental than at the coastal location. Differences in maximum hardiness between sampling locations were generally small and there were no real differences in dehardening of the plants between the locations. Both twigs and buds of Salix pentandra L. and Populus tremula L. survived liquid nitrogen in January–February.

Time course of apical shoot growth and shoot tip abortion in northern ecotypes (lat. 69°39′N, long. 18°37′E) of Salix pentandra and S. caprea have been investigated. In trees more than 15 years old growing under natural climatic conditions apical growth cessation and shoot tip abortion normally occurred in June-July when the day length still was 24 h. Application of GA3, in spring to the apex effectively delayed growth cessation and shoot tip abortion. Application of kinetin was without effect. First-year seedlings of both species grew continuously at temperatue of 9 to 24°C in 24 h photoperiod. Short days induced apical growth cessation, but two to four (S. pentandra) or three to five (S. caprea) weeks of 12 h photoperiod were required to stop the elongation growth. The results indicated that the critical photoperiod for apical growth cessation in the used ecotype of S. pentandra was 16 to 18 h at 18°C. Short days had a minor effect only on the formation of apical leaf primordia in small seedlings. Development of axillary buds and radial growth were stimulated by short days when compared with long days. Small seedlings of both species (3 to 8 cm high at the start) formed terminal buds in short days, but in large seedlings (more than about 15 cm high) apical growth cessation was accompanied by shoot tip abortion. Abscisic acid applied to the apex or through a leaf did not induce growth cessation in S. pentandra seedlings grown in continuous light. The growth retardants CCC, B-9 and Phosphon D reduced growth rate under continuous light and induced shoot tip abortion in some plants. The effect of CCC was counteracted by GA3. Apical growth cessation in short days was significantly delayed by a single GA1 application.

Gibberellins A 1 , A 19 , A 20 , and A 29 have been identified by sequential high-performance liquid chromatography retention time (Rt) and combined gas chromatography-mass spectrometry (Rt and characteristic mass spectra) from elongating shoots of Salix pentandra L. Gibberellins A 1 and A 19 were also detected in purified extracts from male and female flowers (catkins) of S. pentandra.

The timing and amount of stem damage and bud kill, along with the Cl content of twigs, were observed over one or two winters in Fraxinus pennsylvanica Marsh, Cornus stolonifera Michx, Malus sp. cv. Hopa, Salix pentandra L., and Syringa vulgaris L. growing along Minnesota highways. Depending on species and the year, damage occurred between January and May.Cold hardiness was compared for highway- and garden-grown Syringa vulgaris L. and Fraxinus pennsylvanica Marsh. Hardiness was assessed as percentage of xylem and cambial browning and percentage of bud kill after exposure to test temperatures between −45 and +4 °C. In November, hardiness was the same, but from mid-December into March, highway twigs showed more damage than garden twigs at the same test temperatures. The differences between highway and garden twigs coincided in time with differences in twig Cl.

Indolyl-3-acetic acid from vegetative shoots of Salix pentandra L. has been isolated and identified by high performance liquid chromatography and combined gas chromatography-mass spectrometry.

Both dark and red light germination of lettuce seeds (cv. “Maikonig”) as well as their root and hypocotol elongation were inhibited when the seeds were sown in petri dishes together with a few seeds of Heracleum laciniatum Horn. This inhibition was not significantly counteracted by the presence of gibberellic acid (GA3) or/and 6-benzylaminopurine (BA). However, a large proportion of the lettuce seeds germinated abnormally (only cotyledons emerged) when treated with BA in the presence of Heracleum seeds. GA3 had alone no significant effect on abnormal germination, but it counteracted the effect of BA to some extent. The inhibitory effect of Heracleum seeds gradually disappeared during a moist incubation period of one to seven days in darkness at 25°C. When lettuce seeds were pre-incubated together with Heracleum seeds for one to five days the remaining, non-germinated lettuce seeds had lost their ability for subsequent germination in darkness in distilled water. This induced dark dormancy was to a great extent broken by red light, but not by GA3 or/and BA. H. laciniatum seeds inhibited the germination of Salix pentandra seeds and to some extent also the germination of radish but had no effect on the germination of spruce.

Summary Effects of plant hormones and defoliation on shoot tip abortion in vegetatively propagated plants of Salix pentandra have been studied under controlled conditions. Both gibberellic acid and cytokinins effectively prevented shoot tip abscission under inductive short day conditions. Auxins, even when applied repeatedly, had a minor effect only. Shoot tip abortion could not be induced by abscisic acid at 18 °C under continuous illumination. Shoot tip abortion was delayed but not prevented completely by defoliation.

Granular simazine (2-chloro-4,6-bis(ethylamino)-s-triazine), at 3.36, 6.72, and 10.08 kg/ha, was applied to new transplants of Caragana arborescens Lam., Cotoneaster acutifolia Turcz., Crataegus sp., Fraxinus pennsylvanica Marsh. var. subintegerrima (Vahl.) Fern., Hippophae rhamnoides L., Lonicera tatarica L., Malus baccata (L.) Borkh., Picea glauca (Moench) Voss, Picea pungens Engelm., Pinus sylvestris L., Populus deltoides Marsh., Populus × Northwest (Hort.), Prunus padus L. var. commutata Dipp., Prunus virginiana L. var. melanocarpa (A. Nels.) Sarg., Rosa rugosa Thunb. cult Hansa, Salix acutifolia Willd., Salix pentandra L., Shepherdia argentea Nutt., Sorbus americana Marsh., Syringa villosa Vahl., Ulmus americana L., and Ulmus pumila L. Simazine at 6.72 kg/ha gave 68% control of annual weeds and this was sufficient for the adequate growth of most of the tree and shrub species in this test. None of the species showed visible injury symptoms at any of the simazine rates tested, but the growth of some was reduced at the high simazine rate.