Tracheid diameter is the key trait determining the extent of freezing-induced embolism in conifers

We tested the hypotheses that freezing-induced embolism is related to conduit diameter, and that conifers and angiosperms with conduits of equivalent diameter will exhibit similar losses of hydraulic conductivity in response to freezing. We surveyed the freeze-thaw response of conifers with a broad range of tracheid diameters by subjecting wood segments (root, stem and trunk wood) to a freeze-thaw cycle at -0.5 MPa in a centrifuge. Embolism increased as mean tracheid diameter exceeded 30 microm. Tracheids with a critical diameter greater than 43 microm were calculated to embolize in response to freezing and thawing at a xylem pressure of -0.5 MPa. To confirm that freezing-induced embolism is a function of conduit air content, we air-saturated stems of Abies lasiocarpa (Hook.) Nutt. (mean conduit diameter 13.7 +/- 0.7 microm) by pressurizing them 1 to 60 times above atmospheric pressure, prior to freezing and thawing. The air saturation method simulated the effect of increased tracheid size because the degree of super-saturation is proportional to a tracheid volume holding an equivalent amount of dissolved air at ambient pressure. Embolism increased when the dissolved air content was equivalent to a mean tracheid diameter of 30 microm at ambient air pressure. Our centrifuge and air-saturation data show that conifers are as vulnerable to freeze-thaw embolism as angiosperms with equal conduit diameter. We suggest that the hydraulic conductivity of conifer wood is maximized by increasing tracheid diameters in locations where freezing is rare. Conversely, the narrowing of tracheid diameters protects against freezing-induced embolism in cold climates.     

Investigation and utilization of intron length polymorphisms in conifers

Intron length polymorphisms (ILPs) are a new kind of molecular markers, which can be detected by PCR with specific primers designed on exons flanking the target introns. In this study, we identified 2300 putative introns and successfully designed primers for them in loblolly pine by comparing the cDNAs of loblolly pine with the homologous genes of Arabidopsis and rice, and experimentally examined 400 of them using 9 conifer species of two families (7 of Pinaceae and 2 of Cupressaceae) as materials. We found that about 88% of the predicted introns appeared to be correct, suggesting that the exon–intron structures are highly conservative in plants, even between Magnoliophyta and Coniferophyta. Therefore, prediction of introns in the species of Coniferophyta by referring to the model species of Magnoliophyta is feasible. Based on 39 ILP markers, a reasonable dendrogram of the 9 conifer species was constructed, demonstrating that ILP markers are quite suitable for phylogenetic studies involving distant species or higher taxonomic ranks.     

Family differences in height growth and photosynthetic traits in three conifers

We investigated variation in height growth, gas exchange, chlorophyll fluorescence and leaf stable carbon isotope ratio among wind-pollinated progenies of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco var. glauca), ponderosa pine (Pinus ponderosa Dougl. ex Laws.) and western white pine (Pinus monticola Dougl. ex D. Don) from a small group of contiguous stands on the Priest River Experimental Forest in northern Idaho. Photosynthetic variables differed between height classes in the pines, but not in Douglas-fir. Among species and families, tall families of ponderosa pine regained photosynthetic capacity earliest in the spring and maintained it latest in the growing season. Tall families of western white pine had higher instantaneous water-use efficiencies and lower photosynthetic rates than short families on warm days in August.     

Ungulate herbivory of regenerating conifers in relation to foliar nutrition and terpenoid production

Ungulate browsing greatly influences regeneration dynamics of some forest ecosystems, yet the relationship between browse susceptibility and foliar chemistry of forest tree seedlings is not well understood. We applied field fertilization (15N-9P-10K controlled-release fertilizer at 0, 20, 40, and 60 g per seedling) and investigated how subsequent changes in terpenoid production and foliar nutrition influence ungulate browse preference for Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco), western hemlock (Tsuga heterophylla Raf. Sarg.), and western redcedar (Thujaplicata Donn ex D. Don) seedlings across four sites in northwestern Oregon, USA. Fertilization increased foliar N concentration of all three species, but above-ground growth of only Douglas-fir and western hemlock. Foliar monoterpene concentrations for western hemlock and western redcedar also increased at higher fertilization rates, while Douglas-fir monoterpene production was not affected by fertilization. Regardless of monoterpene levels, ungulate browse preference was greater for fertilized western hemlock seedlings. The opposite response, however, was observed for western redcedar at two of the four study sites where the likelihood of browse was greater for non-fertilized than fertilized seedlings. Differences in browse preference among species may depend on the type and amount of individual monoterpenes manufactured in response to fertilization. Western redcedar produce α- and β-thujone, oxygenated monoterpenes known to promote gastroenteritis and possibly inhibit microbial rumen activity, which were absent from Douglas-fir or western hemlock. Higher concentrations of α- and β-thujone associated with increasing fertilizer rate provide a plausible explanation as to why ungulates preferred non-fertilized western redcedar. Our results illustrate species-specific adaptation in browse avoidance and selective ungulate browsing behavior of individual trees as linked to foliar chemistry.     

Tracheid Dimensions in Relation to Shoot Vigour in Picea

Radial tracheid diameter is shown to be correlated with rateof shoot growth in Picea sitchensis and Picea abies; this relationshippresumably accounts for the negative correlation between rateof shoot growth and calculated wall material per unit area,since wall thickness does not vary with shoot vigour. Tracheiddiameter is also correlated with ring width and rate of xylemincrement in P. abies. It is suggested that it may be possibleto predict wood density from the rate of shoot elongation, asdistinct from its duration.     

Tracheid differentiation in Pinus radiata

Summary Differentiating tracheids in Pinus radiata D. Don have been examined with the electron microscope. Despite the fact that one of the major differentiation processes is cellulose formation, little ultrastructural evidence has been found to indicate how this occurs. On the other hand, there is ample evidence of the incorporation of non-cellulosic material into both the expanding primary wall and the developing secondary wall. The only structure which could possibly be related to cellulose formation is a system of osmiophilic particles which have been found in the space between the plasmalemma and the developing wall, or attached to the most recently formed wall layer. The absence of microtubules during the main phase of secondary wall formation supports the view that these structures are not involved directly in the biosynthesis of cellulose.The author wishes to thank Mrs B. A. Hodgkiss for technical assistance.     

Development of height curves for Japanese larch in relation to GIS-derived site index

The objectives of this study were: (1) to relate the height growth pattern to the GIS-derived site index, (2) to construct various types of polymorphic height curves, and (3) to select the most accurate height curve for Japanese larch (Larix kaempferi). A total of 14 dominant trees were felled for stem analysis. Richards' function was first fitted to the height/age dataset recorded from stem analyses of 14 trees, and its parameters (i.e., A, k, and m) were then estimated for each sample tree. The relationship between parameter A and the GIS-derived site index was significant, while that of parameters k and m were not significant. The 12 height curve equation forms developed from the Richards' function were then fitted to the dataset consisting of 563 observations of height, age, and GIS-derived site index derived from 14 trees. All height curves were unbiased and provided an equally good fit. The shape of the height curves differed among sites of different site indices. These results indicated that Richards' function was sufficiently flexible to represent the polymorphic height growth pattern of Japanese larch. Finally, the best-fit height curve was selected so that accurate height growth predictions would be possible at any given age and site.     

Movement of Injected Dyes in Gymnosperm Stems in Relation to Tracheid Alignment

The path of upward movement of acid fuchsin dye was traced inpole-size stems of Japanese larch (Larix leptolepis Murr.),European larch (Larix decidua Mill.), Lawson cypress (Chamaecyparislawsoniana (A. Murr. Parl.)), Sitka spruce (Picea sitchensis(Bong. Carr.)), Norway spruce (Picea abies (L.) Karst.), andScots pine (Pinus sylvestris L.). In all of these species amarked, preponderantly clockwise spiral pattern of dye ascentwas observed. In general the upward movement of the dye followedtracheid alignment, except at the sapwood-heartwood boundary.The characteristic patterns of dye movement indicated that spiralgrain was much commoner than was straight grain among the pole-sizegymnosperms investigated. Large differences in spiral grainwere found among species, among trees within species, in differentannual rings within trees, and at different stem heights. Patternsof dye uptake were influenced somewhat by the method of injection.Dye injections through tubes driven into the stem were foundmore suitable for determining tracheid arrangement than wereinjections through individual roots immersed in dye. Factorsinfluencing spiral grain development and applications of thedye injection technique to spiral grain determination are discussed.     

Canadian conifers as hosts of the pinewood nematode (Bursaphelenchus xylophilus): Results of seedling inoculations

Seedlings of 22 species of conifers from across Canada were inoculated with m and r form isolates of the pinewood nematode (Bursaphelenchus xylophilus). In an experiment made under ambient (summer‐fall) temperatures in a shadehouse at Victoria, British Columbia, Canada, 8 of the 22 conifer species were killed by the nematodes, but mortality was low, i.e. 4–30%. Pines (eastern white, Jack and red) were more susceptible than other conifers. Yellow cypress, eastern white cedar, western red cedar and western hemlock were not killed by the nematodes. In a second experiment made at elevated temperatures (30°C‐16h long days, 25°C‐8 h long nights) in a greenhouse, 18 of the 22 conifer species died following nematode inoculation. Again, pines (lodgepole, eastern white, western white and red) were among the most susceptible tree species and the four conifers that were unaffected in the first experiment were not killed. Tamarack and western larch, both immune at ambient temperatures, were the two most susceptible conifers at elevated temperatures. Compared to ambient temperatures, seedlings at elevated temperatures died quicker and contained more nematodes. M and r form nematodes were equally pathogenic in both experiments.     

Vulnerability of several conifers to air embolism

Hydraulic properties of xylem in seven species of conifer were studied during late winter and early spring 1991. Vulnerability to cavitation and air embolism was investigated using hydraulic conductivity and acoustic techniques. Embolisms were induced in branches excised from mature trees by air-drying them in the laboratory. Both techniques gave comparable results indicating that they both assess the same phenomenon. Within a tree, vulnerability was related to the permeability of the xylem, the largest stems tended to cavitate before the smallest ones when water deficits developed in a branch. Interspecific comparisons showed large differences in the xylem water potential needed to induce significant embolism, values ranged from -2.5 MPa in Pinus sylvestris to -4 MPa in Cedrus atlantica, but these differences did not correlate with differences in the xylem permeability of the species. The vulnerability of a species to air embolism was found to be consistent with its ecophysiological behavior in the presence of water stress, drought-tolerant species being less vulnerable than drought-avoiding species.     

Assessment of hedgerow species for seed size,stand establishment and seedling height

The relationships between seed size, emergence, stand establishment and seedling height were examined in a trial comparing tree and shrub species as hedgerows for alley cropping in four environments in Haiti. Logarithmic functions relating % emergence, % stand establishment and seedling height to seed weight were positive and significant. These relationships were stronger when species weighing > 10 g 100⁻¹ seed were excluded from the analysis. Higher R² values were obtained regressing % stand than regressing % emergence on seed weight. Although exceptions were noted, a majority of species having seed weights between 2.5 g and 10 g 100⁻¹ had good stands. Establishment was poor or inconsistent for species with seed < 2.5 g 100⁻¹. The effect of seed size on height was more important for seed weights < 5 or 8.8 g 100⁻¹, depending upon the site, than for larger seed. Species with < 2.5 g 100⁻¹ seed are unsuitable for direct seeding where the chance of drought is high.     

Tracheid anatomy changes as responses to changing structural requirements of the tree

Summary After determining growth stresses at 10 positions around the periphery of the stem of a bent, 22 years old conifer (Pinus radiata), morphological details, density, increment rate, and strength were recorded for wood from each position. The trend of average microfibril angle exhibited a strong inverse relationship to the gravitationally induced strains at each position on the periphery, and correspondingly influenced the strength properties of the tissues there.The intensity of growth-stress generation was closely related to variations in microfibril angle, but not to lignin content. Together with changes in rate of differentiation, each was related to externally induced strains. It was concluded that the strains stimulated corresponding morphological controls of the differentiating tissue. Thus they modulated structural responses of the bent tree at all positions around its periphery, and so developed efficiently integrated action to reorient the stem to a stabilized vertical position.Similar conclusions resulted from a less comprehensive study on a straight tree of the same age and species. Further, somewhat compatible published data on growth stresses and property relationships in a large number of eucalypts indicated that the conclusions drawn from the detailed study of the bent Pinus radiata tree were generally applicable to other trees and species.The authors wish to acknowledge the valuable assistance of the Division of Mathematical Statistics, CSIRO, and particularly Miss N. Ditchburne for advice on sampling for the morphological studies, and for extensive calculations of results. In addition they are most grateful to colleagues J. E. Nicholson and G. Waugh for the field measurements of growth stresses, and to D. E. Bland for the lignin analyses.     

Ungulate herbivory of boreal and temperate forest regeneration in relation to seedling mineral nutrition and secondary metabolites

Fertilization at planting may improve reforestation productivity on sites frequented by ungulates by stimulating rapid growth above the browse line, allowing seedlings to escape animal damage. Additionally, stored nutrients may aid seedlings in recovery from browse damage. High plant nutrient content may, however, deem seedlings more susceptible to ungulate browsing because of increased foliar protein content and, thus, nutritional value. Research examining the relationship between fertilization of forest trees and ungulate herbivory has been conducted almost exclusively in boreal and temperate zones of North America and Europe, and has produced two common themes. The first is that nearly all trials used broadcast application of fertilizer. This method supplies nutrients to both the target species and competing vegetation, resulting in significant increases in nutritional value for all potential forage. The second common theme is that there is a higher likelihood of browse for fertilized plants. Exceptions to this thread exist, however, because browse preference of fertilized seedlings is apparently species-specific due to differences among species in resource allocation. Palatability appears to interact with the production of plant chemical defenses (i.e., alkaloids, phenylpropanoids, terpenoids). Variations in plant mineral nutrition and secondary metabolite production can play a significant role determining forage preference; however, ungulates under starvation or stress will browse plants of high toxicity or low nutritional value to maintain fitness.     

Susceptibility to low-temperature photoinhibition in three conifers differing in successional status

Susceptibility to photoinhibition of the evergreen conifers Abies alba Mill., Picea abies (L.) Karst. and Pinus mugo Turra was investigated in an unheated greenhouse during winter and spring 2003. Photosynthetic performance of the seedlings was assessed by chlorophyll a fluorescence and analyses of chlorophyll and total carotenoid concentrations in needles. During winter months, maximum quantum yield of PSII photochemistry (ratio of variable to maximum fluorescence, Fv/Fm) was significantly greater in A. alba than in P. abies and P. mugo. Abies alba also sustained higher maximum apparent electron transport rate (ETRmax) than P. abies and P. mugo. Total concentrations of chlorophyll and carotenoids in needles decreased during the winter in P. mugo and P. abies, but remained stable in A. alba. For all species, Fv/Fm decreased from December until February and then increased to a maximum in April. Photoinhibition was greatest (Fv/Fm < 0.80) in all seedlings in February, the month with the lowest mean temperature. Saturating photosynthetic photon flux (PPFsat) and ETRmax were positively related to air temperature. All species had lower values of ETRmax and PPFsat in winter than in spring. Non-photochemical quenching of chlorophyll fluorescence (NPQ) was highest at low air temperatures. Differences among species in susceptibility to winter photoinhibition resulted from their specific light preferences and led to different mechanisms to cope with photoinhibitory stress. The more shade-tolerant A. alba sustained a higher photosynthetic capacity in winter than P. abies and P. mugo. Winter photoinhibition in P. abies, P. mugo and, to a lesser extent, in A. alba may reflect adaptive photoprotection of the photosynthetic apparatus in winter.     

福建柏苗高生长期划分的有序样本聚类分析

以福建柏苗高15 d净生长量为样本,采用有序样本聚类分析方法,将福建柏苗高生长过程划分为5个时期:出苗期为3月1~30日,幼苗期为4月1日~5月30日,速生前期为6月1~15日,速生期为6月16日~9月30日,生长后期为10月1日~12月30日。速生前期和速生期的净生长量只占全年总生长量的28.5%,而幼苗期、生长后期的净生长量分别占全年总生长量的30.0%、34.9%。因此结合福建柏的生理特性提出幼苗期、生长后期的管理措施,为培育福建柏优质壮苗提供依据。     

Morphological and water-stress characteristics of three Douglas-fir stocktypes in relation to seedling performance under different soil moisture conditions

This one-time greenhouse study examined the phenology, morphology, frost hardiness and response to moisture stress of three Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) stocktypes from the same seed lot. The types were mini-plug^TM transplants (MPT), 1+1 bareroot transplants (1+1), and 2+0 bareroot seedlings (2+0). In late summer and fall before lifting, 2+0 seedling set bud before 1+1 seedlings, 1+1 seedlings before MPT seedlings. The 2+0 seedlings appeared slowest to acquire frost hardiness in fall and seemed to deharden most rapidly in spring. Although the 2+0 seedlings were taller than the MPT stocktype, MPT and 2+0 seedlings were relatively similar in other morphological respects, but 1+1 seedlings were much larger. All stocktypes were potted on January 20, 1989, placed in a greenhouse, and subjected to 39%, 18%, 16%, or 6% soil water content (% dry weight) until the end of the experiment in mid-July 1990. The largest decrease in pre-dawn xylem water potential occurred with 16% and 6% soil water content; pre-dawn xylem water potential averaged over the three stocktypes generally declined 219% from low to high soil moisture stress. The 1+1 seedlings used more water than the other two stocktypes, and at maximum soil moisture stress, plant moisture stress increased in the order: MPT <2+0<1+1. During the 6-month greenhouse experiment, the larger 1+1 stocktype showed the most absolute growth, but the smaller stocktypes grew more on a relative scale. Growth of the stocktypes appeared to be related to differences in morphology and water-use patterns as the seedlings competed for available water within each pot. The results show that MPT seedlings, a new stocktype, performed as well as the more traditionally used 2+0 and 1+1 seedlings and that stocktype selection is important in reforestation efforts.     

Factors affecting somatic embryogenesis in conifers

This review seeks to examine the extreme response of isolated somatic plant cells of apical meristematic tissues of mature conifer trees towards specific stress conditions in vitro resulting in somatic embryogenesis.Signal molecules regulating embryo development have been described in angiosperms,but very little is known about somatic rejuvenation in conifers.Recent studies on cloning of mature conifers provide new perspectives on signal molecules on cellular dedifferentiation into the embryogenic pathway.Our recent studies show that signal molecules such as butenolide,calcium ions,salicylic acid,antioxidants,amino acids,triacontanol and 24-epibrassinolide all play an important role in the conversion of somatic cells into an embryogenic pathway in many recalcitrant pines.This constitutes a major breakthrough in forest biotechnology with many practical applications in clonal forestry.     

Harvest index in northern temperate cultivated conifers

Harvest index is defined and its relationship with primary production, biomass partitioning and yield components in forest trees examined. As stand density has been found to have a major effect on harvest index, it is concluded that further development of the harvest index concept in forest trees will need to take account of density-yield relationships.     

Stump infection by Armillaria in first-rotation conifers

Information about the entry of Armillaria into first-rotation pine and spruce stands was obtained by searching for infected stumps, rhizomorph systems or trees that had been killed. In pines Armillaria foci were very rare. In pure Norway spruce Armillaria lutea and A. mellea were detected in stumps but rhizomorphs did not extend into the soil; in Norway spruce mixed with oak, by contrast, A. lutea sometimes produced extensive rhizomorph systems. In Sitka spruce small groups of trees had been killed by A. ostoyae. All foci investigated in conifers contained different genotypes of Armillaria and probably originated from spore infection of stumps created by thinning. Some implications of these findings are discussed.