Coarse and fine root respiration in aspen (Populus tremuloides)

Coarse and fine root respiration rates of aspen (Populus tremuloides Michx.) were measured at 5, 15 and 25 degrees C. Coarse roots ranged from 0.65 to 4.45 cm in diameter, whereas fine roots were less than 5 mm in diameter. To discriminate between maintenance and growth respiration, root respiration rates were measured during aboveground growing periods and dormant periods. An additional measurement of coarse root respiration was made during spring leaf flush, to evaluate the effect of mobilization of resources for leaf expansion on root respiration. Fine roots respired at much higher rates than coarse roots, with a mean rate at 15 degrees C of 1290 micromol CO2 m-3 s-1 during the growing period, and 660 micromol CO2 m-3 s-1 during the dormant period. The temperature response of fine root respiration rate was nonlinear: mean Q10 was 3.90 for measurements made at 5-15 degrees C and 2.19 for measurements made at 15-25 degrees C. Coarse root respiration rates measured at 15 degrees C in late fall (dormant season) were higher (370 micromol CO2 m-3 s-1) than rates from roots collected at leaf flush and early summer (200 micromol CO2 m-3 s-1). The higher respiration rates in late fall, which were accompanied by decreased total nonstructural carbohydrate (TNC) concentrations, suggest that respiration rates in late fall included growth expenditures, reflecting recent radial growth. Neither bud flush nor shoot growth of the trees caused an increase in coarse root respiration or a decrease in TNC concentrations, suggesting a limited role of coarse roots as reserve storage organs for spring shoot growth, and a lack of synchronization between above- and belowground growth. Pooling the data from the coarse and fine roots showed a positive correlation between nitrogen concentration and respiration rate.     

Root water flow and growth of aspen (Populus tremuloides) at low root temperatures

Effects of root zone temperature on growth, shoot water relations, and root water flow were studied in 1-year-old aspen (Populus tremuloides Michx.) seedlings. Seedlings were grown in solution culture and exposed to day/night air temperatures of 22/16 degrees C and solution culture temperatures of 5, 10, or 20 degrees C for 28 days after bud flush. Compared with root growth at 20 degrees C, root growth was completely inhibited at 5 degrees C and inhibited by 97% at 10 degrees C. The 5 and 10 degrees C treatments severely reduced shoot growth, leaf size, and total leaf area. Root water flow was inhibited by the 5 and 10 degrees C treatments. However, when seedlings were grown for 28 days at 5 degrees C and root water flow was measured at 20 degrees C, there was an increase in flow rate. This increase in root water flow was similar in magnitude to the decrease in root water flow observed when seedlings were grown for 28 days at 20 degrees C and root water flow was measured at 5 degrees C. Reduced root water flow of seedlings grown at 5 and 10 degrees C resulted in decreased stomatal conductance, net assimilation, and shoot water potentials. Root water flow was positively correlated with leaf size, total leaf area, shoot length, and new root growth. Transferring seedlings from 5 to 20 degrees C for 24 h significantly increased root water flow, shoot water potential, and net photosynthesis, whereas transferring seedlings from 10 to 20 degrees C resulted in only a slightly increased shoot water potential. Transferring seedlings from 20 to 5 degrees C greatly reduced root water flow, stomatal conductance, and net photosynthesis, whereas shoot water potential decreased only slightly.     

Naphthenic acids inhibit root water transport,gas exchange and leaf growth in aspen (Populus tremuloides) seedlings

Effects of sodium naphthenates (NAs) on root hydraulic conductivity (Lp) and gas exchange processes were examined in aspen (Populus tremuloides Michx.) seedlings grown in solution culture. Exposure of roots to NAs for 3-5 weeks significantly decreased Lp and stomatal conductance. Root-absorbed NAs also decreased leaf chlorophyll concentration, net photosynthesis and leaf growth. Short-term (< or = 2 h) exposure of excised roots to NAs significantly decreased root water flow (Qv) with a concomitant decline in root respiration. We conclude that NAs metabolically inhibited Lp, likely by affecting water channel activity, and that this inhibition could be responsible for the observed reductions in gas exchange and leaf growth.     

Hebeloma crustuliniforme facilitates ammonium and nitrate assimilation in trembling aspen (Populus tremuloides) seedlings

This study examined the role of ectomycorrhizal associations in nitrogen assimilation of Populus tremuloides seedlings. Seedlings were inoculated with Hebeloma crustuliniforme and compared with non-inoculated plants. Nitrogen-metabolizing enzymatic properties were also determined in H. crustuliniforme grown in sterile culture. The seedlings and fungal cultures were subjected to nitrogen treatments (including NO??, NH?? and a combination of NO???+?NH??) for 2 months to examine the effects on growth, nitrogen-assimilating enzyme activities and xylem sap concentrations of NH?? and NO??. Seedlings were also provided for 3 days with 1?N-labeled NH?? and NO??, and leaf and root 1?N content relative to total nitrogen was measured. Both NO?? and NH?? were effective in supporting seedling growth when either form was provided separately. When NO?? and NH?? were provided together, seedling growth decreased while enzymatic assimilation of NH?? increased. Additionally, nitrogen assimilation in inoculated seedlings was less affected by the form of nitrogen compared with non-inoculated plants. Fungal ability to enzymatically respond to and assimilate NH?? combined with aspen's enzymatic responsiveness to NO?? was likely the reason for efficient assimilation of both nitrogen forms by mycorrhizal plants.     

Profiling of phenylpropanoid monomers in developing xylem tissue of transgenic aspen (Populus tremuloides)

Here we describe alterations in the cinnamate/monolignol pathway in three transgenic aspen lines: one with downregulated expression of 4-coumarate:CoA ligase (4CL), one with upregulated expression of coniferaldehyde 5-hydroxylase (CAld5H), and a 4CL downregulated/CAld5H upregulated line. Compared with the wild type, the 4CL downregulated line showed significantly increased levels of p-hydroxycinnamic acids such as p-coumaric, ferulic, and sinapic acids. In contrast, the CAld5H upregulated line had increased content of p-coumaryl and 5-hydroxyconiferyl alcohols. In the 4CL downregulated line, it was likely that most hydroxycinnamic acids were glycosylated. These results strongly suggest that the downregulation of 4CL and upregulation of CAld5H disrupt the metabolic flow through the cinnamate/monolignol pathway and thus alter the amount and structure of its final product, lignin.     

Predicting decay and round-wood end use volume in trembling aspen (Populus tremuloides Michx.)

? In Quebec (Canada), predicting net merchantable volume of standing trees is essential to adjust stumpage fees. Furthermore, round-wood end use is important in the provincial forest management context because it is used to split the allowable annual cut among the different mill types.

? A method relying on linear, binomial and cumulative logit regressions is proposed to predict both decay volume and round-wood end use volume. Tree age, height and quality, as well as ecological region, stand origin and presence of Phellinus tremulae (Bond.) Bond. & Boriss. and Ceratocystis fimbriata (Ellis & Halst.) fungi are the main factors that contribute to the presence and the proportion of decayed merchantable volume. Once the net merchantable volume is estimated, its division into round-wood end use is estimated through a series of steps involving the presence of Phellinus tremulae, saw log height, stem quality and size as explanatory variables. The first step is a multinomial regression which predicts the number of end uses (pulp wood, low-grade saw logs, saw logs, low-grade veneer, and veneer) that are present in the stem. A series of logistic regressions then determines the presence of each end use, with linear regressions predicting the round-wood volume of each end use.

     

On the reproduction of aspen (Populus tremula L.) with emphasis on its suckering ability

Numerical data are presented that support the proposal mentioned as early as the mid‐19th century that aspen roots may remain alive for a long period after the disappearance of parent trees. The mechanism that makes this possible is the ability of this species to form suckers continuously. In stands the bulk of the suckers live a few years and are then replaced by new ones. If conditions allow some suckers may develop into big trees even in old stands. The conclusions are based on material obtained in experiments comprising chemical control of aspen, including different application methods, herbicides, doses and in some cases control treatment (cleaning).     

Seedling response of two trembling aspen (Populus tremuloides) families to infection by Hypoxylon mammatum

Open-pollinated progenies from two trembling aspen (Populus tremuloides) families with a 30-year field history of 91% (putatively susceptible, PS) and 45% (putatively resistant, PR) mortality, respectively, caused by Hypoxylon mammatum, were grown in a greenhouse for 3 and 9 months. Seedlings were inoculated with two isolates of H. mammatum, representing high and low aggressiveness, through a stem wound. Beginning 4 days after inoculation, host responses were examined on 312 seedlings per family for a period of 5 weeks on 3- and 9-month-old seedlings. Significant differences in host responses were observed between the two isolates, with the more aggressive isolate allowing less callus formation, causing more tissue necrosis and producing longer cankers than the less aggressive isolate on both aspen families. Between-family difference was much greater than within-family difference for tissue necrosis, callus formation and canker length for both seedling ages. When the 3-month-old seedlings were challenged with H. mammatum, the PR family showed greater tissue necrosis, longer cankers, and less callus formation than the PS family. However, when the more lignifìed 9-month-old seedlings of the same families were inoculated, the PR seedlings had much less tissue necrosis, shorter cankers, more callus formation and less seedling mortality than the PS family. The results indicate that artificial inoculation of seedlings in a greenhouse can differentiate two aspen families at the seedling stage, but their correlation to field performance is highly dependent upon the seedling age. Host responses of older seedlings may be a better indicator of field performance.     

Developmental factors responsible for heterosis in aspen hybrids (Populus tremuloides x P. tremula

Juvenile growth and bud set phenology were analyzed to study the biological basis of heterosis (hybrid vigor) in interspecific hybrids of Populus tremuloides Michx. (T) and P. tremula L. (Ta). Growth, measured as seedling volume index, was significantly higher for each of the two reciprocal interspecific crosses, T x Ta and Ta x T, than for the T x T intraspecific cross. Broad-sense heritabilities were 2-6 times larger than narrow-sense heritabilities for growth and shoot components in the T x T intraspecific cross, suggesting an important role for dominance or overdominance in aspen growth. Previous genetic analyses have indicated that hybrid vigor may be the result of overdominance at several key loci each with an allele inherited from each of parental species. Internode length and leaf number contributed substantially to the heterosis of stem volume, but their effects on heterosis differed between the T x Ta and Ta x T hybrids. In T x Ta seedlings, heterosis of stem volume was attributed to a high diameter growth rate, whereas in Ta x T seedlings heterosis of stem volume was probably the result of delayed bud set resulting in a longer duration of height growth. In addition to internode number and length and leaf number, other morphological or physiological components might affect heterosis, for example, extended leaf retention.     

Regional differences in aspen (Populus tremuloides Michx.) seedling response to an established nursery protocol

New Forests - In seedling-based reforestation operations, seed source is known to be an influential variable affecting outplanting success. Adaptive variation among seed sources may also be an...     

Understanding the role of the cytoskeleton in wood formation in angiosperm trees: hybrid aspen (Populus tremula x P. tremuloides) as the model species

The involvement of microfilaments and microtubules in the development of the radial and axial components of secondary xylem (wood) in hybrid aspen (Populus tremula L. x P. tremuloides Michx.) was studied by indirect immunofluorescent localization techniques. In addition to cambial cells, the differentiated cell types considered were early- and late-wood vessel elements, axial parenchyma, normal-wood fibers and gelatinous fibers, and contact and isolation ray cells. Microfilaments were rare in ray cambial cells, but were abundant and axially arranged in their derivatives once cell elongation had begun, and persisted in that orientation in mature ray cells. Microfilaments were axially arranged in fusiform cambial cells and persisted in that orientation in all xylem derivatives of those cells. Microtubules were randomly oriented in ray and fusiform cells of the cambial zone. Dense arrays of parallel-aligned microtubules were oriented near axially in the developing gelatinous fibers, but at a wide range of angles in normal-wood fibers. Ellipses of microfilaments were associated with pit development in fiber cells and isolation ray cells. Rings of co-localized microtubules and microfilaments were associated with developing inter-vessel bordered pits and vessel-contact ray cell contact pits, and, in the case of bordered pits, these rings decreased in diameter as the over-arching pit border increased in size. Although only microtubules were seen at the periphery of the perforation plate of vessel elements, a prominent meshwork of microfilaments overlaid the perforation plate itself. A consensus view of the roles of the cytoskeleton during wood formation in angiosperm trees is presented.     

Surface quality sensing of trembling aspen (Populus tremuloides Michx.) veneer products by near infrared spectroscopy

Abstract

The potential of near infrared spectroscopy (NIRS) to estimate wood moisture content (MC), surface energy characteristics and adhesive bond strength were evaluated on aspen (Populus tremuloides Michx.) veneer subjected to different drying times. For samples dried progressively at 103°C, the best MC prediction model was for the total MC range (0–100%) with an R² value of 0.68. However, exposure at 180°C produced surface colour changes, and the CIE L*a*b* colour parameters measuring colour changes were better estimated using the 400–900 nm spectral data than the 1100–2400 nm spectral data. Increased exposure time at 180°C resulted in lower wettability and, hence, larger contact angles, especially when ethylene glycol was used as probe solvent. Lap shear strength tests on veneers showed that adhesion by phenol formaldehyde resins was impaired by the high temperature exposure; however, the lap shear strength test had high variability so there was not always a clear relationship between contact angle and lap shear strength test.     

Seasonal photosynthetic responses to light and temperature in white spruce (Picea glauca) seedlings planted under an aspen (Populus tremuloides) canopy and in the open

Photosynthetic light and temperature response curves were measured seasonally in seedlings of white spruce (Picea glauca (Moench.) Voss) grown for two years in the understory of aspen (Populus tremuloides Michx.) or in the open in central Alberta. Light-saturated rate of net photosynthesis, the optimum temperature for net photosynthesis, transpiration rate, photochemical efficiency, and stomatal and mesophyll conductances increased from spring to summer and declined thereafter, whereas dark respiration rate and compensation and saturation points were highest in spring. Depression of photosynthetic parameters was greater in open-grown seedlings than in understory seedlings during the periods in spring and autumn when night frosts were common. Net photosynthetic rates were similar in understory and open-grown seedlings in summer, but they were significantly lower in open-grown seedlings in spring and autumn. Significantly lower transpiration rates and stomatal conductances in open-grown seedlings than in understory seedlings were also observed at 15 and 25 degrees C in the autumn. Shoot and needle growth were less in open-grown seedlings than in understory seedlings. In summer, when irradiances were low in the aspen understory, understory white spruce seedlings maintained a positive carbon balance by decreasing their compensation and saturation points and increasing their photochemical efficiency compared to spring and autumn.     

Genotypic variation in growth and physiological responses of Finnish hybrid aspen (Populus tremuloides x P. tremula) to elevated tropospheric ozone concentration

Saplings of six Finnish hybrid aspen (Populus tremuloides Michx. x P. tremula L.) clones were exposed to 0, 50, 100 and 150 ppb ozone (O3) for 32 days in a chamber experiment to determine differences in O3 sensitivity among genotypes. Based on the chamber experiment, three clones with intermediate sensitivity to O3 were selected for a free-air O3 enrichment experiment in which plants were exposed for 2 months to either ambient air (control) or air containing 1.3 x the ambient O3 concentration. We measured stem height and radial growth, number of leaves, dry mass and relative growth rate of leaves, stem and roots, visible leaf injuries, net photosynthesis and stomatal conductance of the clones. There was high clonal variation in susceptibility to O3 in the chamber experiment, indicated by foliar injuries and differential reductions in growth and net photosynthesis. In the free-air O3 enrichment experiment, ozone caused a shift in resource allocation toward stem height growth, thereby altering the shoot to root balance. In both experiments, low O3 concentrations tended to stimulate growth of most clones, whereas 100 and 150 ppb O3 in the chamber experiment impaired growth of most clones. However, growth of the most O3-tolerant clone was not significantly affected by any O3 treatment.     

Productivity and thinning effects in hybrid aspen (Populus tremula L. x P. tremuloides Michx.) stands in southern Sweden

The productivity of hybrid aspen stands in southern Sweden,originating from clone selections performed during the 1980s,was investigated. Thirteen former research and demonstrationsites were included. Repeated measurements of tree diametersand heights were taken, from which yields were estimated. Theresults indicate that the mean annual increment, obtained withoutany artificial addition of fertilizers or irrigation, will exceed20 m³ of stem wood ha^–1 a^–1 during a 20–25-yearrotation period. This corresponds to a total average woody biomassproduction, including branches, of over 8 tonnes dry matterha^–1 a^–1. These production levels show that hybridaspen is a competitive alternative for short rotation forestryin Sweden, and that the clone selection programme has greatlyenhanced productivity, compared with published growth ratesof the material previously used. For comparison, two standsthat regenerated via root suckers from material used in thebreeding programme up to the 1960s were included. They showedhigher growth than the 13 planted stands, mainly due to higherstem density and faster height development. This indicates thateven further increases in hybrid aspen yield are possible instands derived from suckers of the most recently selected clones.Thinning studies, including three different weights of thinning,were carried out on five of the sites. Five years after thestart of the treatments, stands given no thinning showed significantlyhigher current annual increment, but significantly smaller meanstem diameter than stands in which thinning was applied. However,the faster diameter development (and thus higher volumes ofvaluable wood assortments) associated with heavier thinningsmay compensate economically under current market conditionsfor the loss in total volume production.     

The effects of mechanical site preparation and subsequent wildfire on trembling aspen (Populus tremuloides Michx.) regeneration in central Alberta,Canada

The objective of this study was to assess the regeneration response oftrembling aspen (Populus tremuloides Michx.) to differentmechanical site preparation (MSP) techniques commonly used in operationalforestry (disc trenching, drag scarifying and blading) and the specificmicrosites created by each treatment. This study was designed to measureregeneration after at least the first two growing seasons, however a largewildfire burned 80% of the study sites at the beginning of the second growingseason. Consequently, only limited second year data were presented, butregeneration from the first growing season following the fire was alsoassessed.Results indicated that microsites where the forest floor was disturbed and theparent root system was only lightly injured were more conducive to suckeringthan undisturbed microsites or where the root system was severely injured.Also,the fire disturbance after the first growing season resulted in increasedsuckering relative to the untreated controls in the first year. These resultssuggest that aspen sites with thick organic layers or vigorous competition fromother species can benefit from MSP when applied before the first growingseason.In addition, if first year suckering is inadequate, subsequent disturbancessuchas prescribed fire have the potential to improve suckering provided the parentroot system remains intact.     

Cultural factors influencing adventitious shoot and plantlet formation from slash pine cotyledons

Cultural factors affecting in vitro shoot and subsequent plantlet formation of slash pine (Pinus elliotti Engelm.) cotyledons were investigated. Basal media composition, N⁶-benzylaminopurine (BAP) concentration and exposure time significantly influenced bud induction in cotyledons cultured under a continuous photoperiod of 35–40 mol m^–2 s^–1 at 24 ± 1 °C. The largest number of adventitious shoots was obtained after 28 days exposure to 66 M BAP-supplemented modified Gresshoff and Doy 1 (GD1) medium. Relatively high frequencies of large shoots were obtained after a 14-day exposure to 22 M BAP-supplemented Brown and Lawrence (BL) or 66 M BAP-supplemented GD1. Adventitious shoots derived from 21- or 28-day exposures to BAP developed more slowly and were smaller in size than those derived from a 14-day exposure to the cytokinin. Shoot differentiation and subsequent growth were also influenced by basal media, media concentration, and presence of activated charcoal in the medium. The percentage of cotyledons forming shoots was highest on half-strength GD1 medium containing activated charcoal. Rooting was achieved in vitro under a continuous photoperiod of 60–70 mol M^–2 S^–1. Roots were formed when excised shoots were planted on GD 1/2 medium supplemented with 2.68 M 1^–1 a-napthaleneacetic acid (NAA) with or without BAP for 14 days. The proposed technique of slash pine propagation using cotyledon explants can produce up to 100 seedlings per embryo.     

Hormone level analysis on adventitious root formation in Eucalyptus globulus

Eucalyptus globulus is the one of the most economically important trees for pulp and paper industries due to its fast growth and short harvesting cycle. However, E. globulus is well known as a woody plant that is hard to propagate vegetatively. In this study, we found wide distribution of rooting ability among seven independent genotypes we tested. Analysis of the mechanism of adventitious rooting by using the auxin transport inhibitor, N-naphthylphthalamic acid, revealed that polar auxin transport is crucial in root formation. The gravitropism of the stem was highly correlated to the percentage of adventitious root formation. Hormonal analysis showed that the levels of indole-3-acetic acid (IAA) were the same between difficult-to-root and easy-to-root genotypes, whereas levels of IAAsp (indole-3-acetyl aspartic acid) were higher in the difficult-to-root genotype, indicating that IAA metabolism might play an important role in adventitious root formation in this species. Levels of several cytokinins exhibited differences between genotypes that varied in their cutting performance and rooting ability. Furthermore, higher level of cytokinin in elongating shoots were correlated with rooting percentage. Taken together, our results indicate that both auxins and cytokinins play a role in adventitious root formation in E. globulus, and that a complex interplay between the levels of auxins and cytokinins and their metabolism might result in root formation in this commercially important plant.     

Effect of stock type characteristics and time of planting on field performance of aspen (Populus tremuloides Michx.) seedlings on boreal reclamation sites

Aspen (Populus tremuloides Michx) has great potential as a reclamation species for mining sites in the boreal forest, but planting stock has shown poor field performance after outplanting. In this study we tested how different aspen seedling characteristics and planting times affect field outplanting performance on reclamation sites. We produced three different types of aspen planting stock, which varied significantly in seedling size, root-to-shoot ratio (RSR), and total non-structural carbohydrate (TNC) reserves in roots, by artificially manipulating shoot growth during seedling production. All three stock types were then field-planted either in late summer, late fall, or early spring after frozen storage. Seedlings were outplanted onto two reclaimed open-pit mining areas in the boreal forest region of central and east-central Alberta, Canada, which varied significantly in latitude, reclamation history, and soil conditions. Overall, height growth was better in aspen stock types with high RSR and TNC reserves. Differences in field performance among aspen stock types appeared to be more strongly expressed when seedlings were exposed to more stressful environmental site conditions, such as low soil nutrients and moisture. Generally, aspen seedlings planted with leaves in the summer showed the poorest performance, and summer- or fall-planted seedlings with no shoot growth manipulation had much greater stem dieback after the first winter. This indicates that the dormancy and hardening of the stem, as a result of premature bud set treatments, could improve the outplanting performance of aspen seedlings, particularly those planted during summer and fall.     

毛白杨叶片愈伤组织的诱导、芽的分化及不定根的再生

以毛白杨叶片为外植体进行组织培养研究。结果表明:培养基MS 6-BA 1.0 mg/L NAA 1.0 mg/L有利于愈伤组织的诱导;培养基MS 6-BA 0.5 mg/L NAA 0.5 mg/L诱导愈伤组织并且有大量不定芽发生;培养基MS ZT 0.1 mg/L NAA 0.3 mg/L可使叶片生根率达100%。