Nitrogen budgeting and quality of exponentially fertilized <Emphasis Type="Italic">Quercus robur</Emphasis> seedlings in Ireland

Current policy in Ireland calls for increased quality and quantity of broadleaved seedling plantings. Simultaneously, concerns regarding environmental contamination necessitate development of nursery production methods that minimize impacts. Exponential (E) fertilization has potential for producing high-quality seedlings through nutrient loading, while simultaneously minimizing nitrogen (N) losses during culture. We investigated the effects of a wide range (0.10–1.0 g N seedling⁻¹ year⁻¹) of E fertilization rates on seedling morphology and nutrition of Quercus robur L., as well as soil N status and N budget during one growing season in a bareroot nursery in County Carlow, Ireland. The N budget showed significant N losses, especially in the highest fertilizer treatments, due to high precipitation. Seedlings receiving the 0.5 E rate were morphologically and nutritionally superior to all other treatments. Results indicate that it may be possible to produce 1-0 bareroot seedlings meeting target specifications in Ireland and other countries of similar climate and soils if further manipulations to seedling culture are implemented; however, potential environmental degradation via N leaching must be considered when N loading in wet years.     

Performance and nutrient dynamics of holm oak (<Emphasis Type="Italic">Quercus ilex</Emphasis> L.) seedlings in relation to nursery nutrient loading and post-transplant fertility

Holm oak (Quercus ilex L.) seedlings were exponentially (E) nutrient loaded using incremental increases in fertilizer addition or conventionally (C) fertilized using a constant fertilizer rate during nursery culture. The fertility treatments (mg N plant⁻¹) were control (0), 25E, 100E, and 100C. Subsequently, 1-year-old plants were transplanted under simulated soil fertility gradients in a greenhouse to evaluate effects of nutrient loading and post-transplant fertility on seedling performance. Post-transplant fertility consisted of fertilizing plants at two rates (0 vs. 200 mg N plant⁻¹). A water-soluble fertilizer 20-20-20 was supplied in both nursery and post-transplant experiments. Nutrient loading increased plant N content by 73% in 100E and by 75% in 100C relative to controls, although no significant differences were detected between constant and exponential fertilization regimes at the 100 mg N plant⁻¹ rate. When transplanted, nutrient loading promoted post-transplant root growth relative to shoot, implicating potential to confer competitive advantage to loaded holm oak seedlings after trans-planting. In contrast, post-transplant fertility increased new shoot dry mass by 140% as well as N, P and K content relative to controls. Results suggest that holm oak seedlings can be successfully nutrient loaded in the nursery at higher fertility rates, improving its potential to extend new roots, but alternative fertilization regimes and schedules that better fit nutrient availability to the growth rhythm and conservative strategy of this species must be tested.     

Thidiazuron-induced somatic embryos,their multiplication,maturation, and conversion in <Emphasis Type="Italic">Cinnamomum pauciflorum</Emphasis> Nees (Lauraceae)

Thidiazuron (TDZ) induced somatic embryogenesis from immature zygotic embryos in Cinnamomum pauciflorum Nees while 2,4-dichlorophenoxyacetic acid (2,4-D), 6-benzylaminopurine (BA) or picloram only induced callus and/or adventitious buds. The highest induction frequency for somatic embryogenesis was achieved with MS medium (Murashige and Skoog in Physiol Plant 15:473–497 1962) supplemented with 2.5 μM TDZ using torpedo-shaped embryos (3–5 mm in length) as explants. In addition, induction medium was supplemented with 0.8 g l⁻¹ casein, 0.4 g l⁻¹ glutamine, and 10 g l⁻¹ sucrose. Somatic embryos (SEs) initiated from root tips or hypocotyls without callus formation. SEs were maintained and multiplied via secondary somatic embryogenesis. Embryo maintenance medium was similar to induction medium except that TDZ was reduced to 0.5 μM. Secondary embryogenesis was enhanced by supplementation of 5 g l⁻¹ activated charcoal in the culture. The best medium for embryo maturation was MS medium containing 30 g l⁻¹ sucrose and 5 g l⁻¹ Phytagel without plant growth regulators. A typical mature SE consisted of two large cotyledons and a short embryo proper. Approximately 82% of selected mature SEs were able to germinate and 63% could convert into plantlets on germination medium that was composed of half strength MS medium salts, 10 g l⁻¹ sucrose, 3 g l⁻¹ Phytagel, and 5 g l⁻¹ activated charcoal.     

Effect of animal browse protection and fertilizer application on the establishment of planted Nuttall oak seedlings

For establishment to be successful, planted oak must emerge above vegetative competition and browse level. A 3 year study was established in 2000 in a cutover bottomland hardwood forest in west Alabama to examine the influences of seedling browse protection and fertilizer use on growth of Nuttall oak (Quercus nuttallii Palm.) seedlings. The treatments included: control, 1.2 m tall wire tree shelter, and 1.2 m tall plastic tree shelter. Fertilizer (20–10–5) was applied to one-half of all seedlings at planting. Competing vegetation was controlled around all seedlings with mulch mats and herbicide. Fertilization did not affect height growth or successful establishment after 3 years. Four percent of protected seedlings (plastic and wire tree shelters combined) were browsed compared to 95% of control seedlings. After 3 years, plastic tree shelters were the most effective treatment for promoting height growth and successful seedling establishment of Nuttal oak seedlings (193 cm, 92.71% compared to 120 cm, 68.75% and 52 cm, 8.33% for wire tree shelter, and control seedlings, respectively). Animal browse protection is deemed essential for successful seedling establishment in southern bottomland forests where deer density is high (density estimated at 27 km⁻² in vicinity of study area).     

Half-sib seed source and nursery sowing density affect black walnut (<Emphasis Type="Italic">Juglans nigra</Emphasis>) growth after 5 years

The effect of seed source (half-sib family) and nursery bed density on the nursery stock quality and subsequent growth of black walnut (Juglans nigra L.) was investigated. Nine black walnut female genitors were selected to represent a range of phenotypes. Seeds were collected, cleaned, cold-treated, and pre-sprouted to ensure that germination was uniform and complete. The pre-sprouted seeds were planted in a randomized complete block design into standard nursery beds in Indiana, USA at three sowing densities, (11.2 plants m⁻²; 24.2 plants m⁻²; 29.4 plants m⁻²). After lifting, the trees were measured for height, ground-line diameter and root volume and then planted into a plantation in a randomized complete block design and re-measured after 1 and 5 years of growth. One year after planting, the effects of family (half-sib seed source) and density were significant or very highly significant for seedling height, and ground-line diameter, although family effects were greater than those for density, especially at moderate and high nursery bed density. After 5 years of growth, the same effects contributed significantly to ground-line diameter and dbh, but only family significantly influenced height. Family was more important than nursery bed density in determining the size of the trees after 5 years. Although there were no significant family × density interactions after 5 years, family variance for all the traits was considerably higher among seedlings grown at moderate and high density in the nursery. Phenotypic correlations among traits within and among years were generally very high (0.65 < r < 0.90) and insensitive to planting density in the nursery.     

Influences of seedling size,container type and mammal browsing on the establishment of <Emphasis Type="Italic">Eucalyptus globulus</Emphasis> in plantation forestry

Rapid early growth of tree seedlings is critical to the success of plantation establishment. We investigated the effects of seedling size (small and large) and container types (small [Lannen 121], medium [Lannen 81] and large [Forestry Tube]) in the nursery and the effects of mammal browsing after planting on growth of Eucalyptus globulus in Tasmania’s Southern Forests. After planting, seedlings were either exposed to browsing or protected from browsing by wire-mesh cages until age 6 months. Low browsing pressure resulted in around 20% and 5–10% of foliage being browsed in the large and small size categories, respectively, between 1 and 3 months after planting the uncaged treatment. 6 months after planting, height growth increment was lower, and 4 years after planting, mortality was higher in uncaged large than caged large seedling treatments. Six and twelve months after planting, seedlings raised in Forestry Tube containers had significantly greater height increment and root collar diameter relative to other treatments. By 4 years after planting, trees of the small seedling treatment had significantly greater diameter than those of the large seedling treatment, but there was no effect of container type treatment. Four years after planting there was no effect on diameter growth by browsing of <30% of foliage up to 3 months after planting, although there was greater incidence of double leaders in trees that had been browsed as seedlings. Small seedlings produced more growth 4 years after planting than large seedlings of E. globulus.     

Organic amendment and inorganic fertilization affect soil properties and quality of Larix olgensis bareroot stock

Bareroot Changbai larch (Larix olgensis Henry.) seedlings were reared with inorganic fertilizer (nitrogen (N):phosphorus (P) = 1:1, W/W) applied at a rate of 100 (F100) or 200 kg N ha⁻¹ (F200) with (+) or without (−) chicken manure as a soil amendment (O) in north-eastern China. An unfertilized control treatment was included. Inorganic and organic fertilizer treatments tended to increase soil ammonium, nitrate, available P, total P, organic carbon content and electrical conductivity, and biomass and N concentration in seedlings. Organic amendment improved first order lateral root number, tap root length, fine root morphology (length, surface area, volume) in seedlings, while the F100 treatment increased N accumulation in needles and stems compared to the F200 treatment, on average. Most fertilizer treatments tended to increase P content in combined stems and roots, but F200 − O and F100 + O treatments diluted P in needles. Organic amendment combined with inorganic fertilizer at a rate of 100 kg N and P ha⁻¹ is recommended to improve seedling growth and N reserves in woody tissues.     

Seedling quality and field performance of commercial stocklots of containerized holm oak (Quercus ilex) in Mediterranean Spain: an approach for establishing a quality standard

Holm oak is the hardwood most used for reforestation in Mediterranean Spain, which makes the development of stock quality standards in order to improve establishment success, a priority. However, its nursery culture is characterized by a wide range of practices resulting in stock heterogeneity and a potentially varied outplanting performance. Previous research has focused on specific seedling quality attributes, obviating the integral effect of nursery culture on overall quality. We studied growing regime, seedling quality, and field performance in nine holm oak stocklots produced in commercial nurseries during two consecutive growing years. Results proved variations in field performance were related to stocklot quality and, hence, to the growing regime practised. This dependence on stock quality may vary with planting site weather: in the drier year, survival was related to attributes like height, water status and K concentration, while, in the second, milder year, only growth performance was related to nutrient concentrations, plant size and water status. Results indicated the following quality standards for height: 12–17 cm, diameter: 3.5–4.8 mm, shoot and root weights: 1.3–1.6 and 2.8–4.7 g, respectively, N–P–K foliar concentrations: over 10–0.9–3.7 mg g⁻¹, respectively and in water status parameters: E_MX < 5 MPa and SWD_TL > 15%. These attributes can be adjusted using nursery cultural practices in order to meet seedling quality standards for holm oak for planting across similar sites.     

Effects of calcium, boron and nitrogen fertilization on the growth of teak (Tectona grandis) seedlings and chemical property of acidic soil substrate

Many teak plantations are established on acidic soils with low nutrient availability. There is also poor documentation of nutrient budgets for teak, therefore, a pot experiment with optimal hybrid regression design (Roquemore R311A) was implemented with calcium, boron and nitrogen treatments with teak seedlings (Tectona grandis L.f.) planted in acidic lateritic red soil substrate. Seedling growth, biomass production and root development, and soil pH, and exchangeable Ca and Al concentration were measured. Plant height, root collar diameter, biomass of leaves, stems and roots, root volume, taproot length, number of lateral roots of teak seedlings were significantly and positively correlated with soil exchangeable Ca, pH and Ca/Al molar ratio, and negatively correlated with exchangeable Al. All growth traits were significantly affected by calcium, nitrogen and their interaction, but B fertilizer and other interactions had insignificant effects. To effectively cultivate teak seedlings in acidic soil substrates, 1.68 g kg⁻¹ quicklime (CaO) and 0.65 g kg⁻¹ urea was suggested to be added to neutralize soil acidity, and enhance soil exchangeable Ca content and Ca/Al molar ratio. Urea should not be added without quicklime.     

Production and establishment techniques for the restoration of Nothofagus alessandrii,an endangered keystone species in a Mediterranean forest

Ruil (Nothofagus alessandrii) is an endangered keystone species from the Mediterranean climate zone of Chile. Ruil’s fragile state of conservation urges development of restoration programs, but specific protocols for nursery production and field establishment that ensure plant survival are largely unknown. Therefore, we examined the effect on nitrogen (N) fertilization and container size during nursery production in combination with the use of mesh shelters after outplanting on survival and growth during the first growing season in the field. First year outplanting survival of nursery-grown container seedlings was enhanced when seedlings were given nitrogen (N) during nursery production and deployed with mesh tree shelters in the field. The volume of the container had no effect on outplanting survival and growth. Increasing N from zero to 200 mg N L^?1 provided sufficient N levels, resulting in increased seedling height, root-collar diameter, shoot biomass, and total seedling N and phosphorous concentrations. Additional N provided by the 400 and 600 mg N L^?1 treatments underwent luxury consumption by the seedlings with no further benefits in field performance. Improved growth in the nursery, along with the use of mesh tree shelters after outplanting, especially during the typical summer drought, may be responsible for increased survival during the first growing season. Increasing the performance of nursery-grown ruil seedlings is essential to restoring this endangered, vulnerable, and foundation species within the highly biodiverse, yet seriously threatened endemic Maulino Costero Forest of the Mediterranean climate of central Chile.

     

Influence of growth hormones on adventitious root formation in semi-hardwood cuttings of <Emphasis Type="Italic">Celasturs paniculatus</Emphasis> Willd.: a contribution for rapid multiplication and conservation management

Celastrus paniculatus Willd. (Celastraceae) is an important medicinal tree valued for its seeds. Indiscriminate collection of this plant from the habitat zones has posed a serious threat to its existence in the wild, results in globally a threatened plant species. Ex situ conservation is a prioritized agenda of research for redlisted plant species. Semi-hardwood stem cuttings collected from 10 to 15 year old trees were treated with different concentrations (0, 0.5, 1.0, 2.0, 3.0, 4.0 and 5.0 g l⁻¹) of growth hormones; indole-3-acetic acid (IAA), indole-3-butyric acid (IBA) and 1-naphthalene acetic acid (NAA) for positive effect on root induction. After 90 days of treatment, results were analyzed for percentage of rooting, root number and average root length per rooted cuttings. The highest rooting (57%) response with highest number of roots (~77.2) was obtained in indole-3-acetic acid at 3.0 g l⁻¹. Overall, high significant (P ≤ 0.05) rooting response was noticed in IAA treatment comparative to hormones IBA and NAA. Rooted cuttings exhibited 100% survival in the experimental field. This study reveals the propagation of semi-hardwood cuttings derived from partially matured branches is possible and it provides a basis for conservation of this threatened plant species by reducing pressure on its natural populations.     

Impacts of nursery cultural treatments on stress tolerance in 1 + 0 container white spruce (<Emphasis Type="Italic">Picea glauca</Emphasis> [Moench] Voss) seedlings for summer-planting

Impacts of nursery cultural treatments (T) on stress tolerance of greenhouse-grown 1 + 0 container white spruce (Picea glauca [Moench] Voss) seedlings (mean height 24 cm, root collar diameter 3.1 mm) for summer planting were studied. Seedlings were subjected to 12-h short-day treatments of 0 (T0), 3 (T3), 7 (T7), 10 (T10), or 15 (T15) days, followed by 0, 7, 17, 40, or 46 days of reduced N supply, respectively. Relevant physiological and morphological factors were examined concurrently. Foliar N concentrations exceeded optimal levels and differed little among treatments, suggesting a minor confounding role for N reduction. Both frost and drought tolerance increased incrementally from T0 through T15. Electrolyte leakage index decreased steadily from T0 (25% for roots, 17% for needles) to T15 (1% for roots, 2% for needles) after 2-h exposure of fine roots to − 2°C and of needles to − 8°C. Withholding soil watering for 19 days caused 80% mortality among seedlings in T0, 50% in T3, and < 10% in T7–T15. The transpiration decline curve suggested that enhanced drought tolerance was largely attributable to quicker stomatal closure during water stress and lower cuticular transpiration rate. The treatments increased root growth capacity on a per-seedling, but not per-root-mass, basis. Needle primordia were developed in all T7-T15 seedlings but not in T0 and T3 treatments, suggesting that nurseries may need no more than 7 days of blackout application for conditioning spruce seedlings for summer planting. Shoot dry weight fraction increased gradually from T0 through T15 and was linearly correlated with needle specific weight and frost tolerance, and may thus be useful in monitoring progress of conditioning treatments.     

Regeneration of <Emphasis Type="Italic">Melia volkensii</Emphasis> Gürke (Meliaceae) through direct somatic embryogenesis

Experiments were conducted to study plant regeneration through direct somatic embryogenesis using mature zygotic embryo and cotyledonary explants from seeds of Melia volkensii stored for <3 and >12 months. Explants were cultured on Murashige and Skoog (MS) medium supplemented with BAP, NAA and 2,4-D (0.5, 1.0 and 2.0 mg l⁻¹) alone, and BAP (0.5, 1.0, 2.0 and 4.0 mg l⁻¹) in combination with 2,4-D or NAA (0.2 and 0.5 mg l⁻¹). After 4 weeks in culture, up to 60% of cotyledonary explants from the seeds stored for <3 months produced direct somatic embryos on BAP (0.5–4.0 mg l⁻¹) in combination with 2,4-D (0.2 mg l⁻¹). The number of somatic embryos ranged from 5 to 14 per explant in BAP (0.5 mg l⁻¹) and 2,4-D (0.2 mg l⁻¹) combination. Only 20% of cotyledonary explants from seeds stored for >12 months produced somatic embryos. Mature zygotic embryos failed to produce any somatic embryos. Subcultures of somatic embryos from cotyledonary explants of seeds stored for <3 months formed clusters of shootlets on semi solid MS and 1/2 MS media. After 6 weeks of subculture on multiplication MS media augmented with BAP (0.5 mg l⁻¹) and IAA (0.2 mg l⁻¹), 70% of the shoot tips formed 4–7 shoots per explant. Up to 33% of the multiplied shoots were rooted in MS medium supplemented with 2.0 mg l⁻¹ IBA. Plantlets developed normally into seedlings in the greenhouse.     

Plant water relations and edaphoclimatic conditions affecting acorn production in a holm oak (<Emphasis Type="Italic">Quercus ilex</Emphasis> L. ssp. <Emphasis Type="Italic">ballota</Emphasis>) open woodland

Acorn production patterns and the annual evolution of water relations parameters of Quercus ilex ssp. ballota (Desf.) Samp. in a dehesa (an open woodland forest) subject to various soil treatments (ploughing, ploughing + sowing, control) were studied in southwest Spain from June 2006 to December 2008. The effects of soil water holding capacity and effective soil depth on soil and plant water status and acorn production were also investigated. Water parameters showed significant differences between the ploughing treatment and the control, and there were also significant temporal differences. Xylem water potential ranged from −3.4 ± 0.1 to −0.7 ± 0.2 MPa, and cuticular transpiration was 62.4–192.9 mmol H₂O kg⁻¹ s⁻¹. Acorn production did not differ significantly according to soil treatment, and showed large intra-specific variability. Individual values ranged from 0 to 1,220 g m⁻² (fresh weight). Positive relationships were found between xylem water potential, cuticular transpiration and relative water content measured at midsummer, and acorn production during the three studied years. These results suggest that climatic conditions and soil water availability have a strong influence on plant water status, and therefore on acorn development during summer. The results also reflect the ability of this species to adapt to the Mediterranean climate by preserving water during dry periods, which to a large extent can be attributed to stomatal closure at high relative water content levels, and low cuticular transpiration during these periods.     

Effects of nursery shading on seedling quality and post-planting performance in two Mediterranean species with contrasting shade tolerance

In Mediterranean climates, seedlings are frequently shaded in the nursery to avoid heat damage and save water. However, the impact of this shading on the seedling quality and transplanting performance of Mediterranean species is not well known. We studied the effect of nursery shading on pre-planting features and post-planting performance of two Mediterranean tree species: the shade-intolerant pioneer Pinus halepensis and the shade-tolerant late-successional Quercus ilex. We grew one-year-old seedlings of both species under 100, 40 and 5% full sunlight. Shade had a low impact on the morphology and physiology of Q. ilex seedlings. In pines, only the deep shade treatment produced low quality seedlings with poor root development. In both species, transference to high light at planting in autumn did not impose any additional stress than that caused by frosts, but initial root growth was impaired in the two shaded treatments in pine. Post-planting growth and survival of oak seedlings showed no difference between treatments. Pine seedlings grown in deep shade showed higher mortality and lower growth after planting than those grown in full sun and intermediate light treatments, while intermediate light only reduced growth. For the nursery culture of Q. ilex seedlings, we advise using low light levels during summer to save water without impairing field performance. In P. halepensis, seedlings should be cultured under full sunlight conditions to maximize post-planting growth, but they can be cultured under intermediate light without impairing survival.     

Responses of fine root mass,length, production and turnover to soil nitrogen fertilization in <Emphasis Type="Italic">Larix gmelinii</Emphasis> and <Emphasis Type="Italic">Fraxinus mandshurica</Emphasis> forests in Northeastern China

The responses of fine root mass, length, production and turnover to the increase in soil N availability are not well understood in forest ecosystems. In this study, sequential soil core and ingrowth core methods were employed to examine the responses of fine root (≤1 mm) standing biomass, root length density (RLD), specific root length (SRL), biomass production and turnover rate to soil N fertilization (10 g N m⁻² year⁻¹) in Larix gmelinii (larch) and Fraxinus mandshurica (ash) plantations. N fertilization significantly reduced fine root standing biomass from 130.7 to 103.4 g m⁻² in ash, but had no significant influence in larch (81.5 g m⁻² in the control and 81.9 g m⁻² in the fertilized plots). Similarly, N fertilization reduced mean RLD from 6,857 to 5,822 m m⁻² in ash, but did not influence RLD in larch (1,875 m m⁻² in the control and 1,858 m m⁻² in the fertilized plots). In both species, N fertilization did not alter SRL. Additionally, N fertilization did not significantly alter root production and turnover rate estimated from sequential soil cores, but did reduce root production and turnover rate estimated from the ingrowth core method. These results suggested that N fertilization had a substantial influence on fine root standing biomass, RLD, biomass production and turnover rate, but the direction and magnitude of the influence depended on species and methods.     

Chlorophyll fluorescence,root growth potential,and stomatal conductance as estimates of field performance potential in conifer seedlings

After cold storage, conifer seedlings in British Columbia are tested for field growth potential before planting. We compared three tests of performance potential using container-grown seedlings of Douglas-fir, interior spruce, lodgepole pine, and western larch (14 seedlots total). On several autumn dates, seedlings were lifted and stored at −2°C. The following spring we tested stored seedlings for root growth potential (RGP), chlorophyll fluorescence (CF), and stomatal conductance (Gs), and then planted seedlings in nursery beds. We assessed survival and shoot dry weight (SDW) after one growing season. Performance test results were significantly correlated with each other (r ≥ 0.47) but showed different relationships with field performance, which varied with lift date. The best performance predictor was the sum of CF and RGP (R ² = 0.79 for 78 seedlot by lift-date combinations), which minimized the risk of planting poor seedlings and not planting good seedlings. A sum of 83 for CF (Fv/Fm %) and RGP (new roots >1 cm) provided a threshold above which survival and growth were good. For evergreen conifers, Gs was a good performance predictor, but required extra time to measure leaf area. We recommend a combination of CF and RGP to assess vigor of shoot and root systems before planting. Wolfgang D. Binder––Scientist Emeritus.     

Nitrogen retranslocation, allocation, and utilization in bare root Larix olgensis seedlings

We quantified biomass accumulation and nitrogen (N) retranslocation, allocation, and utilization of Changbai larch (Larix olgensis) seedlings subjected to four fertilization treatments (24, 59, 81, 117 kg·ha-1 N) with an unfertilized control during summer and autumn 2009. Ammonium phosphate (18-46-0) was the fertilizer used in all treatments. On both sampling dates, the needles had greater biomass and N content than new (2009) stems and old (2008) stems, and coarse, medium and fine roots (diameters of >5, 2-5 mm, and 0-2 mm, respectively). Higher N concentration was observed in old stems and coarse roots than that in new stems and medium roots. In mid-summer, fine roots had higher N concentration than coarse roots. The treatment with 24 kg·ha-1 N had the greatest biomass and N content in needles and old stems, and highest net N retranslocation (NRA) and amount of N derived from soil. On September 21, no N translocation was observed, while the treatment with 24 kg·ha-1 N had the highest N utilization efficiency and fertilizer efficiency. Vector analysis revealed that all four fertilization treatments induced N excess relative to the control. The treatments with 59, 81, 117 kg·ha-1 N induce N excess compared with treatments at 24 kg·ha-1 N. We conclude that the traditional local fertilizer application rates exceeded N requirements and N uptake ability for Changbai larch seedlings. The application rate of 24 kg·ha-1 N is recommended.     

Induction of somatic embryogenesis and analysis of genetic fidelity of in vitro<Emphasis Type="Italic">-</Emphasis>derived plantlets of <Emphasis Type="Italic">Bambusa nutans</Emphasis> Wall., using AFLP markers

Bambusa nutans Wall., is an evergreen, perennial, and multipurpose bamboo having strong culms, which are largely used for construction, scaffolding, craft purposes, pulp, and paper industry. Multiple shoots from nodal segments (3–4 cm) of young branches of mature culms were established in Murashige and Skoog (1962) (MS) medium supplemented with various concentrations of 6-benzylaminopurine (BAP) (1.0–6.0 mg l⁻¹) or in combination with α-naphthaleneacetic acid (NAA) (0.5–1.0 mg l⁻¹) or kinetin (Kn) (1.0–2.0 mg l⁻¹). February–March and December were found to be the best seasons for culture establishments. Maximum shoots were achieved on MS medium fortified with BAP (2.0 mg l⁻¹). Embryogenic callus (slightly greenish compact, globular, and slow growing) was initiated from the base of severed sprouted buds in 2–3 subsequent subcultures on MS medium supplemented with 2,4-dichlorophenoxy acetic acid (2,4-D) (5.0 mg l⁻¹) under dark incubations. Maturation and germination of well-organized somatic embryos was achieved on MS medium containing BAP and 2,4-D (1.0 mg l⁻¹ each) with 20.0 mg l⁻¹ ascorbic acid. Full-strength MS medium supplemented with 2% glucose favored further development of proliferated somatic embryos into plantlets. Genetic variations of field-established B. nutans plants regenerated through tissue cultures were assessed by amplified fragment length polymorphism (AFLP) analysis using 6 primer combinations. Four hundred and seven scorable fragments were amplified, of which 402 (98.8%) have recorded conservation at various morphogenetic stages leading to plantlets regeneration, therefore, revealed a high level of genetic stability.     

Fine-root dynamics in a young hinoki cypress (<Emphasis Type="Italic">Chamaecyparis obtusa</Emphasis>) stand for 3 years following thinning

Fine roots play a key role in carbon and nutrient dynamics in forested ecosystems. Fine-root dynamics can be significantly affected by forest management practices such as thinning, but research on this topic is limited. This study examined dynamics of fine roots <1 mm in diameter in a 10-year-old stand of hinoki cypress (Chamaecyparis obtusa) for 3 years following thinning (65% in basal area). Fine-root production and mortality rates were estimated using a minirhizotron technique in combination with soil coring. In both thinned and un-thinned control plots, fine-root elongation occurred from early spring to winter (March to December) and fluctuated seasonally. In the thinned and the control plots, the annual fine-root production rates were estimated to be 101 and 120 g m⁻² year⁻¹, respectively, whereas the estimated annual fine-root mortality rates were 77 and 69 g m⁻² year⁻¹, respectively. At 3 years after thinning, live fine-root biomass was significantly smaller in the thinned plot (143 g m⁻²) than in the control plot (218 g m⁻²), whereas dead fine-root biomass was not (147 and 103 g m⁻², respectively). Morphological and physiological indices of fine roots such as diameter, specific root length, and root tissue density of the live fine roots was similar in both plots. These results suggested that thinning tended to decrease biomass and production of fine roots, but the effects on characteristics of fine roots would be less evident.