Organogenic responses of Pinus pinea cotyledons to hormonal treatments: BA metabolism and cytokinin content

Isolated cotyledons from mature Pinus pinea L. embryos were cultured in vitro in a factorial combination of 4.4, 10 and 44.4 microM N6-benzyladenine (BA) for 2, 4, 8, 16 and 35 days to optimize shoot regeneration. Incubation of explants in 44.4 microM BA for 4 days, in place of the standard incubation in 4.4 microM BA for 35 days, reduced the entire culture period to 4 weeks. Shortening the culture period had no significant effect on the caulogenic response or the number of buds formed per cotyledon. To establish the relationship between key moments in the caulogenic process induced by 4.4 microM BA and the endogenous concentrations of the active forms of BA and other isoprenoid-type cytokinins (CKs), we examined uptake, metabolism and amount of BA, as well as the amounts of zeatin, dihydrozeatin and their ribosides in P. pinea cotyledons after 1, 2, 6, 12 and 24 h, and 2, 4, 8, 16 and 35 days of exposure to 8-[14C]BA. Uptake and release of BA were associated with water movement between explants and the medium during the first 8 days of culture. The interconvertible forms of BA were the main metabolites formed in the tissues. Inactivation of BA as a result of conjugation or oxidation was insignificant. The endogenous concentration of BA + N6-benzyladenosine was 20-fold higher than the exogenously applied BA during the competence acquisition phase (Days 0-3). The concentration of isoprenoid-type CKs also increased 16-fold and then decreased during this time. Induction of shoot buds (Days 4-8) was characterized by a second peak of BA uptake by explants that triggered the synthesis of N6-benzyladenosine-5 -monophosphate and by the maintenance of isoprenoid-type CKs. Reestablishment of CK homeostasis marked the shift from the induction phase to the shoot development phase in this organogenic process (Days 8-12).     

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A new multistage dynamic model for biological control exemplified by the host–parasitoid system <Emphasis Type="Italic">Spodoptera exigua</Emphasis>–<Emphasis Type="Italic">Chelonus oculator</Emphasis>

Over the last few decades, important advances have been made in understanding of host–parasitoid relations and their applications to biological pest control. Not only has the number of agent species increased, but new manipulation techniques for natural enemies have also been empirically introduced, particularly in greenhouse crops. This makes biocontrol more complex, requiring a new mathematical modeling approach appropriate for the optimization of the release of agents. The present paper aimed at filling this gap by the development of a temperature- and stage-dependent dynamic mathematical model of the host–parasitoid system with an improved functional response. The model is appropriate not only for simulation analysis of the efficiency of biocontrol agents, but also for the application of optimal control methodology for the optimal timing of agent releases, and for the consideration of economic implications. Based on both laboratory and greenhouse trials, the model was validated and fitted to the data of Chelonus oculator (F.) (Hym.: Braconidae) as a biological control agent against the beet armyworm, Spodoptera exigua Hübner (Lep.: Noctuidae). We emphasize that this model can be easily adapted to other interacting species involved in biological or integrated pest control with either parasitoid or predator agents.     

Technological properties and fire performance of medium density fibreboard (MDF) treated with selected polyphosphate-based fire retardants

ABSTRACT

The objective of the work was to evaluate the efficacy of two new polyphosphate-based fire retardants (FRs) and one commercial product named Siriono^® on the fire performance and physical–mechanical properties of medium density fibreboard (MDF) fabricated in the laboratory from Scots pine (Pinus sylvestris L.) wood. The fibres were treated with aqueous solutions of fire retardants, at 12% loading (dry salt on dry wood), and bonded with a melamine urea formaldehyde (MUF) adhesive. The physical and mechanical properties of panels were assessed using the European standards, whereas their fire performance was evaluated using an in-house method and the Cone calorimeter. In overall, the chemicals added enhanced the fire and smoke properties of the panels to varying degrees. Critical FR parameters such as peak heat release rate (peak HRR), total heat release (THR) and total smoke production (TSP) were significantly improved in the FR-treated panels, as exhibited in cone calorimeter tests. However, the internal bond strength of treated panels largely decreased by the addition of fire retardants, while thickness swell and water absorption negatively affected to a significant extent. In contrast, the formaldehyde release of the panels was considerably decreased at the E1 class level, with the incorporation of the polyphosphate-based additives.     

Effects of various densities of Ophiostoma ips inoculations on Pinus sylvestris in north‐western Spain

The aim was to determine the inoculation density above which Scots pine (Pinus sylvestris) is overcome by the blue‐stain fungus Ophiostoma ips that is associated with the bark beetle Ips sexdentatus. In north‐western Spain, stems of 16 Scots pines were inoculated at various densities (0, 400, 800 or 1600 inoculi/m²) along circumferential 100 or 150 cm wide inoculation belts. Each inoculum consisted of a 5 mm diameter cylinder of malt extract agar colonized by the fungus. Three months later, all trees were harvested and trunk resinosis and foliage colour were visually assessed. The percentage of healthy, desiccated, resin soaked, and blue‐stained sapwood, as well as growth productivity indices, were calculated from stem disks cut from within the inoculated zone of each tree. Sapwood‐specific hydraulic conductivity (Ks) of each tree was measured in the middle of the inoculated zone. All parameters of tree vigour changed dramatically to the worse when inoculation densities were above 400 inoculi/m², and foliage changed from green to yellow‐green or yellow when an inoculation density of 800 instead of 400 was used. The percentage loss of sapwood‐specific conductivity (PLC) increased from 30 to 90% and the percentage of healthy, conductive sapwood dropped from 85 to 35% at 800 inoculi/m². No effect of the width of the inoculation belt was observed, and there was no relationship between tree productivity indices and the level of resistance. A non‐linear negative relationship was found between PLC and the percentage of healthy sapwood. It is concluded that tree resistance was overcome and that trees were going to die when the inoculation density was ≥800 inoculi/m².     

环境因子对浙江省重点公益林生物量的影响研究

利用在浙江省200万hm2重点公益林范围内取得的854个典型样地的调查资料,分析比较了不同地貌、坡度、坡向、坡位、土层厚度等条件下样地的生物量及其组成,结合林龄、立木数等指标,研究了环境因子对浙江省重点公益林生物量的影响,结果表明,(1)重点公益林现存生物量与地貌、坡向、坡位、坡度等地理特征密切相关,往往与平均生长量呈负相关。现存生物量随着地势的下降而下降,即中山>低山>丘陵;从坡向分析,西北向的平均生物量最大,南坡、东南和西南次之;从坡度看,以陡坡最高,急坡、斜坡次之,缓坡和险坡最低;从坡位分析,以上坡最高,中坡和山脊次之,下坡最低。(2)土层厚度是影响林地生物量的重要因素,随着土层厚度的加深,林地生物量迅速增加。年均生物量生长也与立地状况密切相关。年均生物量以丘陵最高,低山次之,中山最低;各坡向年均生物量由高到低依次为南、西南、东南、西北、东北、西、东、北;从下坡、中坡、上坡至山脊也呈逐渐下降趋势。     

Predicting stand damage and tree survival in burned forests in Catalonia (North-East Spain)

The study developed models for predicting the post-fire tree survival in Catalonia. The models are appropriate for forest planning purposes. Two types of models were developed: a stand-level model to predict the degree of damage caused by a forest fire, and tree-level models to predict the probability of a tree to survive a forest fire. The models were based on forest inventory and fire data. The inventory data on forest stands were obtained from the second (1989–1990) and third (2000–2001) Spanish national forest inventories, and the fire data consisted of the perimeters of forest fires larger than 20 ha that occurred in Catalonia between the 2nd and 3rd measurement of the inventory plots. The models were based on easily measurable forest characteristics, and they permit the forest manager to predict the effect of stand structure and species composition on the expected damage. According to the stand level fire damage model, the relative damage decreases when the stand basal area or mean tree diameter increases. Conversely, the relative stand damage increases when there is a large variation in tree size, when the stand is located on a steep slope, and when it is dominated by pine. According to the tree level survival models, trees in stands with a high basal area, a large mean tree size and a small variability in tree diameters have a high survival probability. Large trees in dominant positions have the highest probability of surviving a fire. Another result of the study is the exceptionally good post-fire survival ability of Pinus pinea and Quercus suber.     

Modelling agroforestry systems of cacao (Theobroma cacao) with laurel (Cordia alliodora) and poro (Erythrina poeppigiana) in Costa Rica

The agroforestry systems of cacao (Theobroma cacao) under laurel (Cordia alliodora) and cacao under poro (Erythrina poeppigiana) were studied at CATIE, Turrialba, Costa Rica. An inventory was taken of the organic matter and nutrients (N, P, K, Ca, and Mg) separating the species into their compartments (leaves, branches, trunks and roots). Studies of the litter and of the mineral soil (0–45 cm) yielded these results: Patterns of nutrient accumulation are discussed in relation to the characteristics of these agroforestry systems.     

Optimising the management of even-aged Pinus sylvestris L. stands in Galicia, north-western Spain

The study developed management instructions for even-aged Pinus sylvestris stands in Galicia (north-western Spain). Although these stands are highly productive, no silvicultural management schedules have been proposed so far for them on the basis of systematic analyses. This study used data from 2160 optimisation runs to develop the management instructions. Land expectation value was used as the objective function. Different prices of timber assortments were considered and the discounting rate was varied from 0.5 to 5%. The method employed to find the optimal management schedules of stands was the combination of a stand simulator and an optimisation algorithm. The simulator uses an earlier growth and yield model for Pinus sylvestris in Galicia to predict the future development of the stand with a given management schedule while the optimisation algorithm seeks the best management schedule among all the possible alternatives. The results show that optimal rotation lengths vary widely between 42 and 170 years, high discounting rates and good site quality resulting in the shortest rotations. Four thinnings were found to be suitable for all sites and discounting rates. With discounting rates higher than 1% the commercial thinnings should gradually decrease the stand basal area towards the end of the rotation.     

A comparison of decomposition dynamics among green tree leaves,partially decomposed tree leaf litter and their mixture in a warm temperate forest ecosystem

Decomposition dynamics were compared among green tree leaves, partially decomposed tree leaf litter (i.e., decayed tree leaf litter on forest floor) and a mixture of the two in a warm temperate forest ecosystem in central China to test the influence of litter chemical quality on the degree of decomposition. The study was conducted in situ at two contrasting forest sites, an oak forest dominated by Quercus aliena var. acuteserrata Maxim., and a mixed pine and oak forest dominated by Pinus armandii Franch. and Q. aliena var. acuteserrata. We found marked differences in the rate of decomposition among litter types at both forest sites; the litter decomposition constant, k, was about 39 % greater at the oak forest site and more than 70 % greater at the pine-oak forest site, for green leaves than for partially decomposed leaf litter. The decomposition dynamics and temporal changes in litter chemistry of the three litter types also greatly differed between the two forest sites. At both forest sites, the higher rate of decomposition for the green leaves was associated with a higher nitrogen (N) content and lower carbon to N ratio (C/N) and acid-unhydrolyzable residue to N ratio (AUR/N). We did not find any non-additive effects when mixing green leaves and partially decomposed leaf litter. Our findings support the contention that litter chemical quality is one of the most important determinants of litter decomposition in forest ecosystems at the local or regional scale, but the effect of litter chemical quality on decomposition differs between the contrasting forest types and may vary with the stage of decomposition.