Variability of Bark Structure in Plantation-Grown Eucalyptus Globulus

The bark structure of Eucalyptus globulus Labill. grown in plantations in Central Portugal is described, based on specimens extracted at six height levels from ten 15-year-old trees. No significant variation of qualitative features between trees was observed. The non-collapsed phloem is characterised by multiseriate tangential rows of phloem parenchyma alternating with rows of phloem fibres, interspersed with large sieve tubes and their respective companion cells, and uniseriate rays . With the onset of sieve tube collapse (collapsed phloem ), some parenchyma cells expand and sclerify, the course of rays becomes irregular, and ray dilatation is initiated. The periderm is composed of a phellem of lignified cells with horseshoe thickening (phelloids), followed by a layer of cells with suberised tangential walls, and a phelloderm with a variable number of layers of thin-walled cells. Age-related secondary changes give rise to a specific within-tree pattern of axial variation. Both the intensity of sclerification of phloem parenchyma cells and the degree of ray dilatation increase with tree age.

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WITHIN–TREE VARIATION IN PHLOEM CELL DIMENSIONS AND PROPORTIONS IN EUCALYPTUS GLOBULUS

IAWA Journal ◽

10.1163/22941932-90000234 ◽

2000 ◽

Vol 21 (1) ◽

pp. 31-40 ◽

Cited By ~ 27

Author(s):

Teresa Quilhó ◽

Helena Pereira ◽

Hans Georg Richter

Keyword(s):

Wall Thickness ◽

Eucalyptus Globulus ◽

Tree Height ◽

Sieve Tube ◽

Bark Thickness ◽

Cell Type ◽

Fibre Width ◽

Axial Variation ◽

Sieve Tubes ◽

Old Trees

The axial variation of bark thickness and quantitative anatomical features of Eucalyptus globulus bark were analysed for one site based on individual measurements of ten 15-year-old trees at six height levels (DBH, 5%, 15%, 35%, 55% and 75% of total tree height). The parameters studied were: length, tangential diameter and percentage of sieve tubes; length, width, cell wall thickness and percentage of fibres; height and percentage of rays; percentage of sclereids in the secondary phloem. Bark thickness decreases from base to top of the tree. Fibre width and wall thickness decrease from base upwards. No distinct axial patterns of variation were observed for the other biometric variables studied. Parenchyma is the main cell type of the bark (50%) followed by fibres (27.9%), rays (12.1%), sieve tubes (2.7%), and sclereids (7.3%). The cell type proportions vary significantly within the tree, i.e., parenchyma, ray and sclereid proportions decrease, fibre and sieve tube proportions increase towards the top of the tree.

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Climate Warming Alters Age-Dependent Growth Sensitivity to Temperature in Eurasian Alpine Treelines

Forests ◽

10.3390/f9110688 ◽

2018 ◽

Vol 9 (11) ◽

pp. 688 ◽

Cited By ~ 2

Author(s):

Raúl Sanchez-Salguero ◽

J. Camarero ◽

Emilia Gutiérrez ◽

Antonio Gazol ◽

Gabriel Sangüesa-Barreda ◽

...

Keyword(s):

Climate Warming ◽

Tree Growth ◽

Radial Growth ◽

Terrestrial Ecosystems ◽

Tree Age ◽

Growth Responses ◽

Polar Urals ◽

Cold Environments ◽

Age Related ◽

Old Trees

Treeline ecotones are considered early-warning monitors of the effects of climate warming on terrestrial ecosystems, but it is still unclear how tree growth at treeline will track the forecasted temperature rise in these cold environments. Here, we address this issue by analysing and projecting growth responses to climate on two different cold-limited alpine treelines: Pinus uncinata Ram. in the Spanish Pyrenees and Larix sibirica Ledeb. in the Russian Polar Urals. We assess radial-growth changes as a function of tree age and long-term climate variability using dendrochronology and a process-based model of tree growth. Climate‒growth relationships were compared considering young (age < 50 years) and old trees (age > 75 years) separately. Warm summer conditions enhanced radial growth, particularly after the 1980s, in the Polar Urals sites, whereas growth was positively related to warm spring and winter conditions in the Pyrenees sites. These associations were stronger in young than in old trees for both tree species and regions. Forecasted warm conditions are expected to enhance growth rates in both regions, while the growing season is forecasted to lengthen in the Pyrenees treelines, mostly in young trees. The observed age-related responses to temperature also depend on the forecasted warming rates. Although the temperature sensitivity is overall increasing for young trees, those responses seem more divergent, or even reversed, throughout the contrasting emission scenarios. The RCP 8.5 emission scenario corresponding to the most pronounced warming and drier conditions (+4.8 °C) could also amplify drought stress in young trees from the Pyrenees treelines. Our modelling approach provides accessible tools to evaluate functional thresholds for tree growth in treeline ecotones under warmer conditions.

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Vascularization of the scutellum of wheat

Australian Journal of Botany ◽

10.1071/bt9700045 ◽

1970 ◽

Vol 18 (1) ◽

pp. 45 ◽

Cited By ~ 15

Author(s):

JG Swift ◽

TP O'Brien

Keyword(s):

Vascular System ◽

Sieve Tube ◽

Serial Sections ◽

Phloem Tissue ◽

Phloem Parenchyma ◽

Parenchyma Cells ◽

Single Ring

The pattern of vascularization of the wheat scutellum shortly after germination is reconstructed from serial sections of plastic-embedded specimens. Nearly half of the phloem in the scutellum is unaccompanied by xylem. Most of the phloem tissue consists of distinct strands, composed of a central sieve tube encircled by a single ring of phloem parenchyma cells. The possible functions of this unusual vascular system are discussed in detail.

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Structure of Wood and Cambial Variant in the Stem of Dalbergia Paniculata Roxb.

IAWA Journal ◽

10.1163/22941932-90000526 ◽

1990 ◽

Vol 11 (4) ◽

pp. 379-391 ◽

Cited By ~ 14

Author(s):

M. N. B. Nair ◽

H. Y. Mohan Ram

Keyword(s):

Succinate Dehydrogenase ◽

Dehydrogenase Activity ◽

Sieve Tube ◽

Secondary Phloem ◽

Succinate Dehydrogenase Activity ◽

Successive Cambia ◽

Phloem Parenchyma ◽

Companion Cells ◽

Parenchyma Cells ◽

Cambial Variant

The wood of Dalbergia paniculata is unique as it consists of concentric layers of broad xylem, alternating with bands of narrow phloem. This anomaly results from the periodic formation of successive cambia in the secondary phloem. Some phloem parenchyma cells dedifferentiate to form a discontinuous ring of cambium. Such parenchyma cells have higher succinate dehydrogenase activity than the neighbouring cells of secondary phloem. The newly differentiated cambial layer functions bidirectionally, and its products give rise to xylem internally and phloem externally. The phloem along with cambium present internal to the newly formed xylem becomes included.The wood is diffuse-porous and the intervessel pits are vestured. The phloem has welldifferentiated sieve tube members and companion cells.

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Structure of Stem and Cambial Variant in Spatholobus Roxburgii (Leguminosae)

IAWA Journal ◽

10.1163/22941932-90001317 ◽

1993 ◽

Vol 14 (2) ◽

pp. 191-204 ◽

Cited By ~ 4

Author(s):

M.N.B. Nair

Keyword(s):

Vascular Tissue ◽

Secondary Growth ◽

Sieve Tube ◽

Secretory Cells ◽

Secondary Phloem ◽

Phloem Parenchyma ◽

Companion Cells ◽

Parenchyma Cells ◽

Ray Cells ◽

Cambial Variant

The stern of Spatholobus roxburghii, a tropicalliana, has alternating layers of xylem and phloem as a result of formation and activity of successive cambia. Successive cambial rings are developed by dedifferentiation of groups of parenchyma cells outside the discontinuous band of sclereid-fibres. The sclereid- fibre band is formed by the development of sclereids between the primary bark fibres. Each successive cambium first produces a layer of sclereid-fibres which separates the vascular tissue produced by one cambial ring from the other. After secondary growth, the epidermis is replaced by periderm. In the older stern phelloderm contributes to the formation of new cambiallayers. Secondary phloem has sieve tube members; companion cells, phloem parenchyma, phloem fibres and secretory cells. The wood shows a tendency towards ring-porosity only in the first xylem layer. The subsequent layers are diffuseporous. The vessels are wide and narrow. Perforated ray cells or radial vessels are frequent in the wood and probably help in vertical conduction by interconnecting vessel endings. In this scandent species parenchyma cells are abundant. It is inferred that they help the vessel segments to remain undamaged when the woody stern twists around supports.

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Elemental Analysis of Phloem Tissue in Lemna Minor Root Tips

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s1431927600003470 ◽

1980 ◽

Vol 38 ◽

pp. 798-799

Author(s):

Patrick Echlin ◽

Thomas Hayes ◽

Clifford Lai ◽

Greg Hook

Keyword(s):

Vascular Tissue ◽

Lemna Minor ◽

Atomic Weight ◽

Companion Cell ◽

Root Tips ◽

Phloem Tissue ◽

Cell Stage ◽

Phloem Parenchyma ◽

Parenchyma Cells ◽

Xylem Element

Studies (1—4) have shown that it is possible to distinguish different stages of phloem tissue differentiation in the developing roots of Lemna minor by examination in the transmission, scanning, and optical microscopes. A disorganized meristem, immediately behind the root-cap, gives rise to the vascular tissue, which consists of single central xylem element surrounded by a ring of phloem parenchyma cells. This ring of cells is first seen at the 4-5 cell stage, but increases to as many as 11 cells by repeated radial anticlinal divisions. At some point, usually at or shortly after the 8 cell stage, two phloem parenchyma cells located opposite each other on the ring of cells, undergo an unsynchronized, periclinal division to give rise to the sieve element and companion cell. Because of the limited number of cells involved, this developmental sequence offers a relatively simple system in which some of the factors underlying cell division and differentiation may be investigated, including the distribution of diffusible low atomic weight elements within individual cells of the phloem tissue.

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Potential of Alnus acuminata based agroforestry for carbon sequestration and other ecosystem services in Rwanda

Agroforestry Systems ◽

10.1007/s10457-021-00619-5 ◽

2021 ◽

Author(s):

Athanase R. Cyamweshi ◽

Shem Kuyah ◽

Athanase Mukuralinda ◽

Catherine W. Muthuri

Keyword(s):

Ecosystem Services ◽

Carbon Sequestration ◽

Soil Fertility ◽

Tree Age ◽

Average Height ◽

Total Biomass ◽

Biomass Carbon ◽

Alnus Acuminata ◽

Sequestration Potential ◽

Old Trees

AbstractAlnus acuminata Kunth. (alnus) is widely used in agroforestry systems across the globe and is believed to provide multiple ecosystem services; however, evidence is lacking in agroforestry literature to support the perceived benefits, particularly in Rwanda. To understand carbon sequestration potential and other benefits of alnus, a household survey, tree inventory and destructive sampling were conducted in north-western Rwanda. Over 75% of the respondents had alnus trees in their farms. The trees provide stakes for climbing beans, firewood and timber. They also improve soil fertility and control soil erosion. Farmers had between 130 and 161 alnus trees per hectare with an average height of 7.7 ± 0.59 m and diameter at breast height of 16.3 ± 1.39 cm. The largest biomass proportion was found in stems (70.5%) while branches and leaves stock about 16.5 and 13% of the total biomass, respectively. At farm level, aboveground biomass of alnus trees was estimated to be 27.2 ± 0.7 Mg ha−1 representing 13.6 Mg of carbon (C) per hectare. Biomass carbon increased with tree size, from 7.1 ± 0.2 Mg C ha−1 in 3 years old trees to 34.4 ± 2.2 Mg C ha−1 in 10 years old trees. The converse was observed with elevation; biomass carbon decreased with increasing elevation from 21.4 ± 1.29 Mg C ha−1 at low (2011–2110 m) to 9.6 ± 0.75 Mg C ha−1 in the high elevation (> 2510 m). In conclusion, alnus agroforestry significantly contributes to carbon sequestration, although the magnitude of these benefits varies with tree age and elevation. Planting alnus trees on farms can meet local needs for stakes for climbing beans, wood and soil fertility improvement, as well as the global need for regulation of climate change.

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Anatomy and Chemical Composition of Pinus Pinaster Bark

IAWA Journal ◽

10.1163/22941932-90001444 ◽

1996 ◽

Vol 17 (2) ◽

pp. 141-150 ◽

Cited By ~ 18

Author(s):

Elsa Nunes ◽

Teresa Quilhó ◽

Helena Pereira

Keyword(s):

Chemical Composition ◽

Pinus Pinaster ◽

Variable Number ◽

Starch Granules ◽

Secondary Phloem ◽

Scale Type ◽

Resin Ducts ◽

Sieve Cells ◽

Parenchyma Cells

The secondary phloem of Pinus pinaster Aiton bark has sieve cells and axial and radial parenchyma, but no fibres. Resin ducts are present in fusiform rays . Stiloid crystals, starch granules and tannins occur inside sieve and parenchyma cells. The rhytidome of P. pinaster bark has a variable number of periderms forming scale-type discontinuous layers over expanded parenchyma cells. Phellem comprises 4-6 layers of thickwaIled and little suberized cells and phelloderm a layer of 2 or 3 thickened lignified ceIls and a layer of expanded cells.

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