Leaf Water Potential and Control of Water Loss in Droughted Sitka Spruce Seedlings

Sitka spruce seedlings were subjected to drought in experimentsin a growthroom, a greenhouse, and out of doors. The plantswere grown in a double chamber with the bulk of the roots inthe upper part where they dried out the soil when water waswithheld. A few new roots penetrated into the lower part inwhich the soil remained moist. The double chamber system enabledthe plant to attain a high water psotential by night and theshoot was only periodically under mild water stress. Measurementswere made on soil water potential (_solt), leaf water potential(₁), transpiration (E), and stomatal conductance (k_s). As soildecreased over a period of 4.5 d, E and k_s decreased progressively.The decline in E and k_s which indicated stomatal closure, occurredat a higher ₁ than has been reported for Sitka spruce. The behaviourof the stomata appeared to be modified by conditions at theroot, and it is proposed that differences in the response to₁,depend on Whether the latter is reduced by resistances in thexylem between root and leaf, as is known to occur in large treesin moist soil, or by stresses at the root itself.     

Water Relations of Sitka Spruce Seedlings After Root Damage

Sitka spruce[Picea sitchensis(Bong.) Carr] seedlings were subjectedto varying degrees of root damage in a growth room, rangingfrom careful transplanting to exposure of the root system toair for up to 3 h. After replanting, transpiration (E), leafwater potential (₁) and growth of the shoot and root were measuredand observations made on plant survival. Some plants in the root exposure treatments died 20–85days after planting. In plants which eventually died, E wasdepressed directly after treatment, but ₁ showed a variableresponse. In some plants ₁ decreased from —8·0x 10⁵ to —30 x 10⁵ Pa after only 10 days but in othersthere was little change in ₁ for 50 days. In spite of the maintenanceof a high water potential in some of the latter plants for longperiods, no root or shoot growth occurred. In plants which lived, the root damage reduced root and shootgrowth relative to untreated controls, and most treatments stronglydepressed E but had little or no effect on ₁. The changes of E and ₁ in treated plants suggest that the suppressionof E was often independent of ₁ although water stress eventuallydeveloped in some of the severely treated plants. Sitka spruce, Picea sitchensis (Bong.)Carr, water relations, root damage, transpiration, leaf water potential     

Effects of Waterlogging on Water Relations of Actively-growing and Dormant Sitka Spruce Seedlings

Two-year-old Sitka spruce [Picea sitchensis (Bong.) Carr.] seedlings,either actively growing or dormant, were waterlogged in a growthroom at 15 °C. Shoot and root growth, transpiration andleaf water potential were observed. In actively-growing plants shoot extension continued after waterlogging,though at a reduced rate, and shoots of dormant plants brokebud and extended during the waterlogging period. Root growthwas suppressed by waterlogging in both types of plant. The 22day waterlogging treatment eventually killed the actively-growingplants but plants which were dormant at the time of waterloggingwere more tolerant. Changes in plant water relations after waterloggingwere entirely different depending on the condition of the plantswhen the soil was flooded. Dormant plants showed a gradual reductionin transpiration and increased water stress over the waterloggingperiod; after the soil was drained leaf water potential increasedto equal the value of control plants which had been maintainedin a freely drained condition, but transpiration did not increaseuntil root growth began. Actively-growing plants exhibited amore complex behaviour, characterized by a very rapid reductionin transpiration after waterlogging, accompanied by a briefperiod of water stress, followed by a period of increasing transpirationrate in the absence of water stress. Finally a second reductionin transpiration occurred and water stress increased as theseedlings died. The importance of the stage of activity of theroot system to the response of plants to waterlogging is discussed. Picea sitchensis (Bong.) Carr., Sitka spruce, waterlogging, water relations, dormancy, transpiration, water potential     

Critical Water Potential for Stomatal Closure in Sitka Spruce

Steady state rates of net photosynthesis and stomatal conductance at high water potentials were measured under controlled conditions in a leaf chamber on Sitka spruce [Picea sitchensis (Bong.) Carr.] shoots detached from the forest canopy or on seedlings. The water supply to the seedlings was terminated by excision and the shoot water potential (or critical water potential) and osmotic potential at the onset of stomatal closure measured. The turgor potential was calculated. The initial osmotic potential before insertion of the shoot into the chamber was also measured. Shoot water potential and osmotic potential at stomatal closure, and initial osmotic potential were significantly higher (less negative) in foliage from the lowest level in the canopy compared with foliage in the upper canopy, and higher in shoots of seedlings transferred to low light than in those at high light. Critical water potential also varied with season, being higher in July than in October and November. In all except one instance, turgor potential at the onset of stomatal closure was negative, possibly because of dilution of the cell sap by the extracellular water during the estimate of osmotic potential. Over all the experiments variation in critical water potential was correlated with variation in critical osmotic potential and, to a lesser extent, the initial osmotic potential. However, turgor potential at the critical potential varied from +0.6 to -4.6 bar. This suggests that difference in turgor between the guard cells and subsidiary cells, which controls stomatal aperture, is only loosely coupled with the bulk leaf turgor and hence that bulk leaf turgor is not a good index of the turbor relations of the guard cells.     

The Effects of Shoot Water Status on Some Photosynthetic Partial Processes in Sitka Spruce

Clonal cuttings of Picea sitchensis (Bong.) Carr. were grown in a controlled environment and, after completion of shoot extension and maturation, subjected to a drying cycle. Photosynthesis and stomatal conductance were measured in situ using ¹⁴CO₂ and a porometer, respectively. Shoot water potential was measured with the pressure chamber. Photosystem and carboxylase activities of chloroplast preparations were measured in vitro. A considerable fall in photosynthetic rate occurred at low water potential. This was associated with stomatal closure and a decrease in CO₂ transfer or fixation processes in the mesophyll. Little change in activity of photosystem I, photosystem II, and ribulose 1,5-diphosphate carboxylase was detected during the drying cycle. Any decline in activity of the photosynthetic partial processes in vivo under severe water stress (Ψ < – 30 bar) was probably masked in vitro as a result of rehydration prior to assay.     

Leaf Conductance as Related to Xylem Water Potential and Carbon Dioxide Concentration in Sitka Spruce

Current year shoots of Sitka spruce [Picea sitchensis Bong. (Carr.)] from the forest canopy were equilibrated in a leaf chamber. The shoots were excised in air, and removed at differing times in order to establish a relationship between stomatal conductance and xylem water potential. The experiment was repeated at five ambient CO₂ concentrations. A second set of excised forest shoots, and shoots excised from 2-year- old nursery seedlings were allowed to evaporate freely in a controlled environment wind tunnel until a constant rate of transpiration was measured, to establish a relationship between cuticular conductance and xylem water potential. Cuticular conductance was estimated to be 0.012 cm s^-1 at high water potential and declined linearly to 0.007 cm s^-1 at ?3.5 MPa. The implication of this decline in the subsequent calculation of stomatal and mesophyll conductance is considered. Stomatal conductance remained constant at water potentials above ?1.4 MPa and was not affected by ambient carbon dioxide concentrations between 20 and 600 cm^-3. At lower water potentials, stomatal conductance declined and approached zero at ?2.5 to ?2.6 MPa. The results suggest that stomatal aperture is not controlled by either ambient or intercellular space carbon dioxide concentration, and that stomatal closure at low water potential is unlikely to be mediated by carbon dioxide.     

The Effect of Scion Water Potential on Graft Success in Sitka Spruce (Picea sitchensis)

The effect of scion storage on graft success in Sitka sprucehas been examined. Scions kept in cold store for up to 7 d werefound to graft successfully to active rootstocks in about 95%of cases. From 7 d, however, there was a marked decline in successuntil, after 14 d of storage prior to grafting less than 40%of grafts survived. Scion leaf-water potential decreased continuouslyduring storage and fell dramatically during the first 3 d aftergrafting. In successful grafts, scion water potential then recovered,reaching a stable level after 3 weeks. No recovery occurredin grafts, which eventually failed. The relationship betweenscion leaf water potential and graft success rate is discussedwith reference to the role of callus development in graft formation. Picea sitchensis, water potential, graft success     

Damage caused by the Green Spruce Aphid to Norway and Sitka spruce needles

Three-month-old needles of Sitka spruce were less susceptible to Elatobium abietinutn than 15-month-old needles. Symptoms appeared after longer aphid feeding times but only a proportion of damaged needles fell. After short feeding periods symptoms appeared in more Norway spruce needles than in Sitka spruce, whereas longer feeding periods resulted in more needles producing symptoms in the Sitka spruce. The symptoms took 4—6 days longer to appear in Norway spruce, and needle fall followed a longer feeding period than on Sitka spruce. Following 72 h feeding, needle fall occurred more quickly on Sitka spruce than on Norway spruce. The time taken for needle fall to occur was inversely related to the feeding time in Sitka spruce but such a response was not evident in Norway spruce. The results are discussed in relation to the differences exhibited in the probing behaviour of the aphid on the two spruces.     

The Influence of Pine on the Form of Sitka Spruce Fine Roots

The form of fine roots of Sitka spruce (Picea sitchensis Bong.Carr.) when grown in immediate proximity to roots of Scots pine(Pinus sylvestris L.) and when grown separately was comparedusing split-root systems. When spruce roots were intimatelymixed with pine roots the mean length of individual spruce lateralswas significantly greater, while the length: weight ratio andnumber of root tips: weight ratio were smaller than when grownalone. A similar alteration in growth strategy was achievedby direct addition of mineral nitrogen. Key words: Fine root form, pine-spruce interactions     

Photoactivation of Oxygen-evolving System in Dark-grown Spruce Seedlings

Plastids prepared from dark-grown spruce seedlings showed a negligible activity of photosystem II, and no fluorescence variation was observed during actinic illumination. The photosystem II reaction centre, however, was present in primary thylakoids. Exposure of such seedlings to continuous light induced the development of photosystem II activity via three stages (rapid, lagged and gradual), and the variable fluorescence appeared. The rapid development of photosystem II may be attributed to the activation of the oxygen-evolving system, possibly the manganese-catalyzing site, and the lagged and gradual developments may be closely related to the formation of thylakoid membranes and their assembly to grana.     

Synthesis of Polygalacturonate Trans-eliminase and Polygalacturonase by a Strain of Enterobacter cloacae Isolated from Ponded Sitka Spruce

During the ponding of Sitka spruce in lake water there was a change from a diverse, aerobic flora (16 species) to a restricted, facultatively anaerobic flora (1 or 2 species). This change corresponded with a marked increase in the degradation of pectin and a concomitant increase in the permeability of the wood to preservatives. A strain of Enterobacter cloacae (NCPPB 2909) isolated during ponding, synthesized an extracellular and intracellular polygalacturonase (PG) and an intracellular polygalacturonate trans-eliminase (PGTE). Both PG and PGTE were growth–linked; extracellular PG was produced initially and then replaced by intracellular PG and PGTE. A change in the pH value of the medium did not alter the relative synthesis of enzyme. Reduced oxygen tension retarded growth but had no effect on enzyme activities. PG and PGTE of E. cloacae were shown to have specific ion requirements and when tap-water was used in the preparation of a medium growth did not occur. The results are discussed in relation to an artificial system of sprinkling water, seeded with known species of bacteria, on to spruce wood in order to control the rate of pectin degradation and thus the permeability of the wood to preservatives.     

Quantum Requirements of Photosynthetic Electron Transport In Sitka Spruce from Different Light Environments

Quantum requirements of photosynthetic electron transport have been measured in shoots of Picea sitchensis (Bong.) Carr. (Sitka spruce) from different levels in a forest canopy and in shoots from plants grown in contrasting light environments in controlled environment chambers. Neutral density filters were used to obtain very low photon flux densities. The light absorbed by the chloroplast suspensions was calculated from measurements of the transmittance of the suspensions. The shoots from the top of the forest canopy (“sun” shoots) had lower quantum requirements for photosystems I and II than the shoots from the bottom of the forest canopy (“shade” shoots). High light grown plants and “sun” shoots had higher rates of electron transport at light saturation than low light grown plants and “shade” shoots. Thus a higher potential for electron transport was found to exist in “sun” shoots than in “shade” shoots at both high and low photon flux densities.     

Genetic diversity in a seed production population vs. natural populations of Sitka Spruce

Isozyme analysis was applied to estimate the level of variation and the genetic structure of a seed-production population (i.e., seed orchard) and 10 range-wide natural populations of Sitka spruce (Picea sitchensis (Bong.) Carr.). Gene diversity and heterozygosity estimates were comparatively high in both the seed orchard and the natural populations studied. The seed orchard population showed a significantly higher number of alleles per locus and percentage of polymorphic loci. Though not significant, mean heterozygosity of the seed orchard was higher than that observed for all natural populations. Genetic distance analysis indicated that the seed-orchard population was genetically similar to three natural populations from which the parent trees were selected. Parent trees sampling breadth has been identified as the major cause for the observed increased level. The impact of recurrent selection and seed orchard biology and management on maintaining the genetic diversity is discussed.     

Water Flow in Wheat Seedlings after Small Water Deficits

Cultures of Scenedesmus obliquus when grown heterotrophically for 10 or 30 days without addition of fresh medium showed 85 and 98% loss of their photosynthetic capacity respectively. This loss in photosynthetic capacity was accompanied by an increase in quantum requirement. No major changes in the pigment amounts or types were detected which would explain the decay in photosynthetic capacity. Partial reactions mediated by photosystem II or I showed a more or less constant decay over a period of 30 days. Photosystem II reactions appeared less stable than those of photosystem I, decaying by 95% as compared with 70%, over this time period. The results of comparative studies on aged cells for their potential of cytochrome f photooxidation, fluorescence kinetics, 520 nm absorbance change and the variable influence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea and 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone on the photosynthetic capacity of such cells, suggest that it is the inherent ability of the cells to photooxidize plastohydroquinone which is affected primarily. In addition, secondary changes were noted in the activity of reactions on the water-splitting side of photosystem II and in the P700 — plastocyanin — cytochrome f complex.     

Circadian Timekeeping for the Photoperiodic Control of Budset in Picea abies (Norway Spruce) Seedlings

Romanian populations of Norway spruce are induced to set terminal buds by four inductive cycles of 8 h light/16 h darkness. To distinguish between circadian and hourglass timekeeping for the photoperiodic control of budset, seedlings were raised in continuous light at 300 µmol m^-2s^-1 at 20°C for 10 weeks. They were then exposed to an extended night regime consisting of three cycles of 8 h light/40 h dark with 4-h or 1-h nightbreaks (120 µmol m^-2s^-1) applied to groups of plants at intervals during the extended night. Following a final cycle of 8 h light/16 h dark to maximize budset, the plants were transferred to continuous light. Budset was delayed when the night-break was applied close to the critical nightlength (CNL) of 6–7 h or about 22–23 h later in the extended night, consistent with circadian rather than hourglass timekeeping. Confidence intervals were calculated for the times to maximum effect of the night-breaks.     

Circadian Timekeeping for the Photoperiodic Control of Budset in Picea abies (Norway Spruce) Seedlings

Romanian populations of Norway spruce are induced to set terminal buds by four inductive cycles of 8 h light/16 h darkness. To distinguish between circadian and hourglass timekeeping for the photoperiodic control of budset, seedlings were raised in continuous light at 300 µmol m^-2s^-1 at 20°C for 10 weeks. They were then exposed to an extended night regime consisting of three cycles of 8 h light/40 h dark with 4-h or 1-h nightbreaks (120 µmol m^-2s^-1) applied to groups of plants at intervals during the extended night. Following a final cycle of 8 h light/16 h dark to maximize budset, the plants were transferred to continuous light. Budset was delayed when the night-break was applied close to the critical nightlength (CNL) of 6-7 h or about 22-23 h later in the extended night, consistent with circadian rather than hourglass timekeeping. Confidence intervals were calculated for the times to maximum effect of the night-breaks.     

Fine Structure of Acid Mist Treated Sitka Spruce Needles: Open-top Chamber and Field Experiments

Sitka spruce grafts (clones DF and 141) grown in open-top chambers(OTC) and ‘mature ’, 6 –8m tall Sitka spruce(clone DF) grown in the field were exposed to acid mist containingan equimolar ion mixture of H₂SO₄and NH₄NO₃at pH2.5. Mist wasapplied 4 times a week (4 x1mm) in the OTC experiment and twicea week (2 x2mm) on average in the field experiment, betweenMay and Oct. 1991. Samples for light and electron microscopywere collected in Nov. and Jan. following acid mist treatment.Acid mist significantly decreased the amount of calcium depositedin the outer epidermal cell walls, the reduction being mostpronounced in the OTCs. Ultrastructurally, acid mist causeda significant increase in chloroplast and grana width. Othersymptoms associated with acid mist included swelling of chloroplastthylakoids, chloroplast protrusions, cytoplasm vacuolization,increase in large lipid accumulations and sickle-shaped chloroplastthylakoids. In the OTCs, acid mist hastened the acquisitionof frost hardening in both clones. In the field, the controltrees exhibited more frost injury than the acid mist treatedtrees suggesting, again, that acid mist had either hastenedor enhanced the stage of frost hardiness of treated trees. Ingeneral, acid mist induced changes were more pronounced in theOTCs than in the field. Picea sitchensis; Sitka spruce; acid mist; fine structure; calcium oxalate; frost hardening     

Apical Structure of Actively Growing Fern Rhizoids Examined by DIC and Confocal Microscopy

The development and cytology of gametophyte primary rhizoidsof the fern Dryopteris affinis was examined using actively growingmaterial. During development an apical cytoplasmic ‘ accumulation’forms and is associated with active tip growth. This accumulationdeteriorates as terminal differentiation and cessation of growthapproaches. During early development the nucleus moves fromthe rhizoid cell base into the newly extending rhizoid. Later,during the active elongation phase, the nucleus takes up a relativelystable location approx. 100 µm behind the extending apex.Towards terminal differentiation the nucleus lags further behindthe tip. In actively growing rhizoids four distinct zones weredistinguished: a richly cytoplasmic ‘cap’; an apicalregion with tubular vacuolar intrusions; a region distinguishedby a peripheral sheath of cytoplasm and fine irregular cytoplasmicstrands connecting to the nucleus; and the main subapical vacuole.Confocal microscopy of gametophytes stained with fluorescentvital dyes, not previously used to examine fern rhizoid structure,confirmed that the tubular vacuolar system extends well intothe apical cytoplasm, and that the network of fine cytoplasmicstrands leads back from the apical cytoplasm to the nucleus.It also revealed that mitochondria are distributed throughoutthe rhizoid and are not excluded from the extreme apex. Membranestaining by FM 4-64 suggested a high density of membrane vesicleswithin the cytoplasm of the extreme apex. Uptake of this endocytosismarker into endomembranes also suggested rapid plasma membraneturnover in the rhizoid. This study highlights the similarityin the developmental stages and appearance of D. affinis rhizoidsto angiosperm root hairs and their much less distinct apicalzonation compared to pollen tubes. Copyright 2000 Annals ofBotany Company Rhizoid, root hair, confocal imaging, vital stains.     

Photosynthetic Electron Transport in Shoots of Sitka Spruce from Different Levels in a Forest Canopy

Shoots from the lower levels of a Sitka forest canopy [Picea sitchensis (Bong.) Carr.] have much lower photosynthetic capacities per unit leaf area than do those from the top of the canopy. Chloroplast fragments have been isolated from the needles at three levels in the canopy and Photosystem I and Photosystem II activities measured. Measurements were made at eight photon flux densities giving light response curves for photosystem activity in the three canopy levels. Expressed per unit leaf area, light-saturated activities of Photosystem I and II were lower at the bottom of the canopy than at the top suggesting that photosystem activity might be limiting photosynthesis in the shoots from the bottom of the canopy. Chlorophyll concentration per unit fresh weight did not vary amongst the three levels, but specific leaf area increased and dry weight fraction decreased with increasing depth in the canopy, leading to a large reduction with depth in chlorophyll content per unit leaf area.