Trade-offs among establishment success,stem morphology and productivity of underplanted Toona ciliata: Effects of nurse-species and thinning density

Toona ciliata (Australian red cedar), a valuable hardwood species, requires a nurse-tree overstorey to prevent damage from frost and drought in some regions of north-eastern Argentina. Different nurse-species offer different degrees of protection, resource competition, and thinning revenues. In addition, choice of nurse-species will influence trade-offs between T. ciliata establishment success, stem quality and productivity as well as revenue from intermediate and final harvests. We tested the effects of overstorey species and planting density on underplanted T. ciliata survival, stem morphology and growth. Initial stand densities of nurse-species Pinus taeda (625 stems/ha), P. elliottii × P. caribaea (625 stems/ha), and Grevillea robusta (833 stems/ha) were thinned by 0%, 25%, 50%, and 75% in three experiments, each using a randomized block design. Initial mortality, light availability and growth of T. ciliata, as well as growth of its nurse-trees, were measured before and two years after thinning. In the third year, we characterized T. ciliata stem morphology (straightness and height-to-diameter-ratio) and destructively harvested a subsample of T. ciliata in order to investigate T. ciliata biomass production and allocation patterns in response to overstorey species, thinning density and light availability. T. ciliata mortality was lower when planted under G. robusta than the pines, and increased in plots with greater exposure to solar radiation. T. ciliata productivity was also greater under G. robusta than under the pines, and was generally greatest where any of the nurse-species were thinned by 75%. Stem form was best when growing under P. taeda and in stands thinned by 50%, regardless of nurse-species. With the exception of early mortality, light levels appeared to have limited effects on T. ciliata growth dynamics. Neither growth rate nor stem morphology was strongly correlated with light availability. Total overstorey basal-area was highest in P. taeda stands and individual overstorey tree growth generally increased with decreasing stand densities, except for slower height growth of G. robusta in more open stands. Thinning operations resulted in sawn-wood revenue for the pine species only. Because stand productivity and stem quality were optimized under different nurse-species and thinning treatments, we conclude that the choice of nurse-species and thinning intensity will depend on management objectives and will change with market preferences and conditions.     

Formation of Ligno-Suberized Tissues in Jack Pine Resistant to the European Race of Gremmeniella abietina

ABSTRACT A histological study was conducted to provide insights into the defense mechanisms of Pinus banksiana resistant to the European (EU) race of Gremmeniella abietina in naturally infected sites. At the time of sampling, the only apparent symptom was a blight induced at the tip of the shoots. The identity of G. abietina during microscopic examinations was confirmed by an immunogold labeling method. Once the fungus had succeeded in penetrating the bracts through stomata, it invaded the stem cortex and the phloem cells and attained the vascular cambium. The progression of the pathogen to the pith was possible principally through intense colonization of needle traces but also by the invasion of the rays. Ligno-suberized tissues confining the pathogen within the necrotic area were revealed by histochemical tests. Well-defined boundaries were initiated at the base of healthy needles and at the vascular cambium level. They regularly formed one continuous suberized barrier completely crossing the shoot from one needle to the other. A nonlamellar form of suberin was observed in transmission electron microscopy. Restoration of cambial activities and tissue regeneration following necrophylactic periderm formation were suggested as essential factors in the defense system of P. banksiana against the EU race of G. abietina. To our knowledge, this is the first demonstration of an anatomical defense mechanism of a conifer against Scleroderris canker.     

Immunocytochemical Evidence that Secretion of Pectin Occurs During Gel (Gum) and Tylosis Formation in Trees

ABSTRACT During gel (gum) formation in angiosperm trees, fibrillar material accumulated in protective layers of xylem parenchyma cells before being secreted across half-bordered pit membranes into vessel elements. Immunogold labeling demonstrated that this fibrillar material was mainly composed of partially esterified pectic polysaccharides. The primary wall of expanding tyloses, an extension of the parenchyma protective layer, secreted similar pectic substances to completely block vessel elements. In most studies, these occluding structures were reported to be formed in response to causative factors such as aging processes, injuries, or infections. Current observations support the view that partial to complete embolism, which almost always accompanies these factors, might be the main cause triggering the formation of vessel occlusions. Whereas pectin seems to be the basic component of gels (gums) and of the external layer of tyloses, other substances, such as phenols, were also detected either as a part of these plugs or as accumulations beside them in vessels. Finally, it is proposed that the term 'gel' instead of 'gum' be used in future studies to describe the occluding material secreted by ray and paratracheal parenchyma cells.     

Disentangling the effect of topography and microtopography on near-ground growing-season frosts at the boreal-temperate forest ecotone (Québec,Canada)

New Forests - Permanent landscape attributes such as topography (elevation [m]) and microtopography (local variation in elevation [cm]) can increase the risk of cold air drainage down-slopes and in...     

Bovine Immunodeficiency Virus in Relation to Embryos Fertilized In Vitro

The association of bovine immunodeficiency virus (BIV) with embryos derived by in vitro fertilization from oocytes of experimentally infected heifers or oocytes/embryos exposed to the virus in vitro was investigated. Using a nested-PCR assay, proviral DNA of BIV was not detected in follicular fluid or in embryos derived from BIV-infected donors. In vitro exposure of oocytes to BIV during maturation or insemination with BIV-infected semen resulted in zona pellucida-intact embryos testing negative for BIV provirus. However, exposure of zona pellucida-free day-7 embryos to the virus resulted in a positive BIV assay for 28% of the batches of embryos, suggesting that the zona pellucida has a role in protecting against BIV infection. The presence of BIV in the IVF system had no apparent effect on the development of bovine embryos to the blastocyst stage.     

Endomycorrhizae in a newly cultivated acidic meadow: Effects of three years of barley cropping,tillage, lime,and phosphorus on root colonization and soil infectivity

The dynamics of mycorrhizae under disturbance created by crop production is not well understood. A 3-year experiment was undertaken on a nutrient-poor and acidic land that had last been cultivated in the early 1970s. We observed the effects of cropping spring barley (Hordeum vulgare L.) under four P-fertilizer levels and four levels of lime, in a minimum (rototillage), a reduced (chisel), or a conventional tillage system, on the mycorrhizal receptiveness of the host (maximum level of mycorrhizal colonization, as measured at harvest) and soil infectivity most probable number method. The host receptiveness decreased with time, while crop yields and soil infectivity increased simultaneously with time. Liming increased mycorrhizal colonization of barley roots and soil infectivity. P additions decreased root colonization but did not significantly affect the most probable number valuse. Slightly higher soil infectivity estimates were found under reduced tillage.     

Comparing the intra-annual wood formation of three European species (Fagus sylvatica, Quercus petraea and Pinus sylvestris) as related to leaf phenology and non-structural carbohydrate dynamics

Monitoring cambial phenology and intra-annual growth dynamics is a useful approach for characterizing the tree growth response to climate change. However, there have been few reports concerning intra-annual wood formation in lowland temperate forests with high time resolution, especially for the comparison between deciduous and coniferous species. The main objective of this study was to determine how the timing, duration and rate of radial growth change between species as related to leaf phenology and the dynamics of non-structural carbohydrates (NSC) under the same climatic conditions. We studied two deciduous species, Fagus sylvatica L. and Quercus petraea (Matt.) Liebl., and an evergreen conifer, Pinus sylvestris L. During the 2009 growing season, we weekly monitored (i) the stem radial increment using dendrometers, (ii) the xylem growth using microcoring and (iii) the leaf phenology from direct observations of the tree crowns. The NSC content was also measured in the eight last rings of the stem cores in April, June and August 2009. The leaf phenology, NSC storage and intra-annual growth were clearly different between species, highlighting their contrasting carbon allocation. Beech growth began just after budburst, with a maximal growth rate when the leaves were mature and variations in the NSC content were low. Thus, beech radial growth seemed highly dependent on leaf photosynthesis. For oak, earlywood quickly developed before budburst, which probably led to the starch decrease quantified in the stem from April to June. For pine, growth began before the needles unfolding and the lack of NSC decrease during the growing season suggested that the substrates for radial growth were new assimilates of the needles from the previous year. Only for oak, the pattern determined from the intra-annual growth measured using microcoring differed from the pattern determined from dendrometer data. For all species, the ring width was significantly influenced by growth duration and not by growth rate, which differs from previous studies. The observed between-species difference at the intra-annual scale is key information for anticipating suitability of future species in temperate forests.     

Growing American ginseng in maple forests as an alternative land-use system in Québec, Canada

American ginseng (Panax quinquefolium) is a medicinal crop which provides tens of millions of dollars in income every year for Canadian farmers. Most of the ginseng roots are produced in open fields under expensive shade structures. Farmers need to plant ginseng at a very high density to achieve profitability. Since high planting densities are related to high disease levels, field-cultivated ginseng requires frequent applications of pesticide. Growing ginseng in forests eliminates the need of a shade structure and may reduce the need for pesticides. Thus, an experiment was performed in a maple (Acer rubrum) forest in Québec to evaluate the effects of nutrient inputs such as lime or compost on ginseng development. Ginseng emergence and survival rates, leaf area and foliar and root weight were evaluated for each treatment. Soil samples were taken in each plot to determine the concentration of various soil nutrients. During the first two years of the experiment, it was noted that the application of lime had a significative positive effect on ginseng growth. This effect could be related to higher calcium concentration and/or lower aluminium toxicity. Liming would be an efficient way to improve the early development of ginseng in maple forests. This practice is also known to improve the health of maple stands. This revised version was published online in June 2006 with corrections to the Cover Date.     

Phenotypic biodiversity of an endemic wild pear, Pyrus mamorensis Trab., in North-Western Morocco using morphological descriptors

In this paper, we report on morphological diversity, ecology and flowering phenological records of an endangered and an endemic species of Morocco Pyrus mamorensis Trab. For this study, a survey was undertaken in North-Western Morocco (Mamora forest and Zaër region) whereby 67 accessions of P. mamorensis were sampled. A set of 33 genotypes of Pyrus spp. from the international collection INRA-Angers (France) of the genus Pyrus were also analyzed. The variability of the total of 100 accessions was assessed by twenty-six characters including fourteen qualitative and twelve quantitative traits. The results demonstrated high levels of morphological variation in the sampled accessions of P. mamorensis and established the relationships among the local germplasm using the UPGMA cluster analysis and the factorial discriminant analysis. Furthermore, we were able to distinguish three types of flowering in the Mamora forest: early, intermediate and late flowering type. Otherwise, the UPGMA classification comparing local accessions of P. mamorensis to the international collection led to the formation of four major groups showing the closest correspondence to their geographical origins: (1) The North African species represented by P. mamorensis, (2) The East Asian pea species, (3) The West Asian species and (4) The European species. These findings suggest the importance of implementing a conservation strategy preserving the genetic resources of wild pear in North-Western Morocco.