Non-freeze survival of spruce budworm larvae,Choristoneura fumiferana, at sub-zero temperatures during diapause

Spruce budworm larvae,Choristoneura fumiferana (Clem.) (Lepidoptera: Tortricidae), in early-, mid- and latediapause (maintained at 2°C), were exposed to various sub-zero temperatures, above the supercooling point, for different periods to determine the insect’s cold-hardiness in terms of non-freeze survival. Larvae which were in the middle of diapause showed the highest survival (percentage of larvae emerging from hibernacula after diapause), followed by larvae in late- and early-diapause respectively. When exposed to −23°C, larvae which were acclimatized to outside air temperatures had a much higher survival than the larvae maintained at 2°C. This survival was correlated with a glycerol content that was ten times higher and a depressed supercooling point in acclimatized larvae compared to lab-maintained larve. Experiments also demonstrated that mortality of the larvae maintained in an extended supercooled state at −23°C was due to cold injury rather than freezing. The present study supports the hypothesis that glycerol may have a cryoprotective role other than depressing the supercooling point in freeze-intolerant insects and highlights the importance of investigating non-freeze mortality during insect diapause.

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Résumé Des larves de tordeuse des bourgeons de l’épinette,Choristoneura fumiferana (Clem.), en début, milieu et fin de diapause (maintenue à 2°C) furent soumises à divers régimes de températures supérieures au point de congélation cellulaire, de fa?on à déterminer la capacité de l’insecte à survivre à ces températures. Les larves en milieu de diapause furent celles ayant le mieux survécu (proportion des larves émergeant de leur hibernacula après la diapause). Elles furent suivies respectivement par celles en fin et en début de diapause. La suivie larvaire, suite à une exposition à −23°C, fut plus élevée dans le cas des larves préalablement acclimatées aux températures de terrain que dans le cas des larves maintenues à 2°C. Comparativement aux larves non acclimatées sur le terrain, le point de congélation cellulaire des larves acclimatées était inférieur et leur contenu en glycérol était dix fois plus élevé. Cette étude a aussi montré que la mortalité des larves maintenues durant une longue période à −23°C ne fut pas causée par un phénomène de congélation cellulaire mais plut?t par d’autres effets létaux du froid. Les résultats de cette étude sont en accord avec l’hypothèse selon laquelle le glycérol jouerait, en tant que cryoprotectant, un r?le autre que celui d’abaisser les points de congélation cellulaire des insectes du type intolérant au gel. De plus, ces résultats montrent l’importance d’étudier la mortalité induite par les températures situées au-dessus du point de congélation cellulaire durant la diapause de l’insecte.

     

Effect of P supply upon seasonal growth and internal cycling of P in Sitka spruce (Picea sitchensis(Bong.)Carr.) seedlings

The availability of phosphorus in many UK forest soils limits growth of Sitka spruce (Picea sitchensis (Bong.) Carr.). Efficient cycling of P within such systems is therefore necessary for sustained tree growth. Internal cycling of P is an important component of the overall P cycle in forests and the current work aims to quantify the impact of P nutrition on internal cycling and seasonal growth of Sitka spruce.Two-year old seedlings of Sitka spruce were grown in sand culture in the glasshouse for one year. Two treatments were imposed in which trees received either a complete nutrient solution from which P was excluded (-P) or one in which P was applied as labelled ³²P (+P). Internal cycling of P was measured directly in plants which had received no P and by difference in those which received ³²P.The contrasting P treatments produced an eight-fold difference in P content and a three-fold difference in tree growth between May and October. Root:shoot ratios increased during the growing season from 0.29 to 0.38 and from 0.29 to 0.52 in +P and-P treatments, respectively. In both treatments P was translocated from old shoots to support new shoot growth. P supply did not affect the amount of P remobilised but there was evidence that the rate of remobilisation may have been affected. The partition of remobilised P was affected by current P supply and differed from the partition of current P uptake.Results are compared to those from studies of growth and internal cycling of nitrogen in Sitka spruce.     

Decomposition and nitrogen dynamics of fine roots of Norway spruce (Picea abies (L.) Karst.) at different sites

Long-term decomposition and nitrogen dynamics of Norway spruce finest (<1 mm in diameter) and fine (<2 mm in diameter) roots were estimated using the root litter-bag techniques. The seasonal decomposition of the finest roots was investigated in a 40-year-old high site quality stand grown on brown lessive soil at different depths as part of productivity studies. The fine root decomposition studies were conducted on 8 permanent plots in the Estonia with the aim to describe the site variation. The initial material was collected from one of stands (high quality site) and incubated at the depth of 10 cm in 1989 (at one site 1990). The bags were collected once or twice a year except for one site, where the seasonal dynamics was investigated. In all initial and decomposing root samples oven-dry weight, ash and energy content and nitrogen concentration was determined. After five years the finest roots had lost 40% of their initial dry weight, half of it during the first year. The initial concentration of nitrogen was 1.29%, the mean concentrations varied during the incubation from 1.47 to 1.78%. After the first year fine roots had lost 21.0 to 32.7% of their initial dry weight, after two years the weight loss was 22.5 to 43.2%. The initial N concentration in fine roots was 0.73% and in the first years it varied from 0.97 to 1.40% at different sites.     

Biological activity, identification and quantification of gibberellins in seedlings of Norway spruce (Picea abies) grown under different photoperiods

Short photoperiod induces growth cessation in seedlings of Norway spruce ( Picea abies (L.] Karst.). Application of different gibberellins (GAS) to seedlings growing under a short photoperiod show that GA₉ and GA₂₀ can not induce growth. In contrast application of GA, and GA₄ induced shoot elongation. The results indicate that 3β-hydroxylation of GA₉ to GA₄ and of GA₂₀ to GA₁ is under photoperiodic control. To confirm that conclusion, both qualitative and quantitative analyses of endogenous GAs were performed. GA₁, GA₃, GA₄, GA₇, GA₉, GA₁₂, GA₁₅, GA₁₅, GA₂₀, GA₂₉, GA₃₄ and GA₅₁ were identified by combined gas chromatography-mass spectrometry in shoots of Norway spruce seedlings. The effect of photoperiod on GA levels was determined by using deuterated and ¹⁴C-labelled GAs as intermal standards. In short days, the amounts of GA₉, GA₄ and GA₁ are less than in plants grown in continuous light. There is no significant difference in the amounts of GA₃, GA₁₂, and GA₂₀ between the different photoperiods. The lack of accumulation of GA₉ and GA₂₀ under short days is discussed.     

Growth response to different types of NPK-fertilizer in Norway spruce plantations in Western Denmark

In Norway spruce planted on former heathland and fertilized to increase production, a series of experiments (72 sample plots) was established throughout Central and Western Jutland (Denmark) during the springs of 1978 and 79. The sample plots were all fertilized with 120 kg nitrogen in each of two five-year periods. Different types of mixed nitrogen/potassim/phosphorus fertilizer were applied. According to results from fertilization trials in the 1950s and 60s a gain of 3–4 m³ · ha^-1 · year^-1 was expected. In contrast to these earlier findings, only 0, 76 m³ · ha^-1 · year^-1 was gained over the two periods as an average of all sample plots. The initial assumption that nitrogen is the main limiting factor for tree growth in Western Denmark no longer seems valid. The results might indicate that due to increasing nitrogen deposition during the 1970s and 80s, potassium and maybe phosphorus are developing into new minimum factors, limiting tree growth and devitalizing the forest ecosystem. Hence, fertilization on these soils should mainly be considered as a way to compensate such nutrient imbalances.     

Conifer somatic embryogenesis for studies of plant cell biology

Summary Embryogenic cultures have been produced for a wide range of conifers and current methods developed for spruce permit the maturation of high quality embryos that can be desiccated and then germinated to form plantlets. Embryogenic suspensions consisting of immature embryos are an excellent source of regenerable protoplasts. This review considers examples of applications of embryogenic suspension cultures for basic studies in three areas of plant cell biology. a) Immunofluorescence studies of microtubules in mitotic spruce cells reveal focused spindle poles at prophase and anphase, suggesting the presence of microtubule organizing centers (MTOCs). Antibodies known to recognize animal MTOCs do not stain the polar regions but do stain developing kinetochores. b) Embryo-derived protoplasts regenerate directly to somatic embryos. Fluorescence studies of the cytoskeleton in freshly derived protoplasts reveal random cortical microtubules and a fine network of actin filaments. During culture, protoplasts change shape and develop transverse cortical microtubule arrays. Embryonal cells of newly formed embryos possess distinctive arrays of cortical microtubules and networks of fine actin filaments while suspensor cells are characterized by transverse cortical microtubules and longitudinal actin cables. c) Transmission electron microscope studies of endocytosis in spruce protoplasts reveal an endocytotic pathway similar to that described previously for soybean. Uptake results are confirmed using high pressure freeze fixation instead of conventional chemical fixation. Presented in the Session-in-Depth Morphogenesis: Plant Cell and Tissue Differentiation at the 1994 Congress on Cell and Tissue Culture, Research Triangle Park, NC, June 4&#x2013;7, 1994.     

Carbon isotope variations in a plantation of Sitka spruce,and the effect of acid mist

Intra- and inter-tree variations in ¹³C/¹²C ratios were studied within a single clone plantation of 20-year-old Sitka spruce, some of which were treated with mist simulating acidic cloud water. For groups of trees of similar height and the same treatment, sampled at the same whorl height, ¹³C values for current year needles showed variations (1 SD) of between 0.2 and 0.7. The variations reflect the seasonally averaged influences, on intercellular CO₂ concentrations, of slight variations in the microhabitat within a group. For a typical intra-group variation of 0.4 one may be able to distinguish between groups whose mean intercellular CO₂ concentrations differ by only 8 ppm. Acid misting resulted in a lowering of ¹³C values by c. 0.7 (significant at the P0.05 level). This reflects higher intercellular CO₂ concentrations for acid misted trees, which can be interpreted in terms of their having assimilation rates c. 10% lower than those of control trees, and might explain the observed reduction in stem growth for acid-misted trees. Without careful attention to sampling strategy, however, these small inter-tree ¹³C variations can be easily masked by the much larger intra-tree variations with height. Large gradients of increasing needle ¹³C with height, of c. 0.5 m^-1, were observed in two untreated trees of different total height. The gradient was similar for both trees so, though ¹³C values of both trees were identical close to their leaders (–27), the taller tree displayed much lower values close to the ground (–31). The gradients are believed to reflect lower light levels close to the ground, rather than the accumulation of respired CO₂ in the atmosphere. The different height response of stems versus needles, reflected by an increase in ¹³C_stems–¹³C_needles with height (for cellulose), is discussed in terms of stem photosynthetic recapture of internally respired CO₂.     

High level histone H2A gene expression during early stages of adventitious bud formation in Norway spruce (Picea abies)

We have demonstrated the correlation between cell division and the expression of a histone H2A-encoding gene, His2A , in Norway spruce. Picea abies (L.) Karst and used a cDNA clone in in situ hybridization experiments to monitor the cytokinin-induced cell division during early stages of adventitious bud development. A general stimulation of division of epidermal and cortical cells followed upon the cytokinin treatment. After two weeks in culture a high mitotic activity was detected only in single cells or small groups of cells in the epidermis and subepidermal cell layers. These cells presumably constitute the early stages of meristem primordia. The small clusters of dividing cells enlarge and subsequently form adventitious buds. Cells of the meristem and needle primordia of adventitious buds divide frequently as do the corresponding cells in vegetative buds. A quiescent center is distinguished within the apical meristem of vegetative buds. These cells, in the summit of the domed meristem, divide with a considerably lower frequency than cells in the flanking region. Differences in the temporal expression pattern of the histone H2A gene in cells of the vascular tissue, detected between embryos germinating in vitro and bud-induced embryos, suggest that the cytokinin treatment affects the timing of cell divisions in the differentiating procambium.     

The effects of SO2 and O3 fumigation on acid deposition and foliar leaching in the Liphook forest fumigation experiment

The ambient pollution climate at the Liphook forest fumigation site, where coniferous trees were fumigated with SO₂ and O₃, for 4 years under field conditions, was characteristic of the fringes of the areas where pollutant effects are a problem. Experimental treatments increased SO₂ concentrations to levels more characteristic of Eastern Europe, and summer O₃ concentrations by 30%. Deposition of SO₂ to the soil between the trees (inferred from shallow lysimeters) was significant, the deposition velocity being 2–1 mms^?1. Deposition to Scots pine and Sitka spruce canopies was greater, deposition velocities being 8.5 and 9.4 mm s^?1, respectively. These high values may perhaps be explained by co-deposition with NH₃. Calculations assume that dry deposition was the sole source of SO₄^2? gain in throughfall, and that there was no significant retention by the trees. There was a trend for O₃ to enhance SO₂ deposition to both soil and trees. Fumigation with SO₂ led to a significant increase in leaching of cations from foliage. Each species neutralized about 63% of the dry-deposited SO₂, predominantly by ion exchange for Ca and K. Equations are provided which allow calculation of foliar leaching given SO₂ concentrations or SO₄^2? deposition. Fumigation increased the rate of nutrient cycling considerably, without affecting foliar concentrations or damaging the trees. Ozone treatments did not enhance foliar leaching, calling into question some suggested mechanisms for the causes of forest decline.