On 2nd Ocotber 2017 I gave a presentation for students and employees at Département des sciences fondamentales at the Université du Québec à Chicoutimi in Canada, with the title Xylem and phloem formation in European beech (Fagus sylvatica). The goal of the presentation was to make the attendees familiar with the processes of wood formation, to present the impact of environmental factors on radial growth of trees and the relationships between growth conditions and wood quality. Namely, we are monitoring the dynamics of cambial activity and xylem and phloem formation in European beech (Fagus sylvatica L.) continuously at two different sites in Slovenia since 2008. We discussed about the relevance of such studies but also about the methodology. Specifically, cambium phenology and dynamics of xylem and phloem growth-ring formation are analysed with light microscope and image analysis system. However, transmission electron microscope and UV-microspectrophotometry are also used, for observations at cellular and ultrastructural level, to get a detailed understanding of wood and phloem formation processes (e.g cell divisions in cambium, cell enlargement, cell wall formation and lignification). Within the lectures I also presented research topics and the laboratory capacities at the Slovenian Forestry Institute.
B.04 Guest lecture
COBISS.SI-ID: 4966822Between 11. and 12. May 2017 I attended to the 2nd Slovene Microscopy Symposium, organised by Slovenian Society for Microscopy in Piran. My main goal was to present: (I) the recent methodological advances at the field of ultrastructural observation of cambium cells in deciduous and coniferous tree species and (II) to present the results of cambium and xylem formation phenology observations by means of light microscopy and transmission electron microscopy. Observations with LM and TEM helped us to get detailed information on the fine structure of cambial cells, dynamics of cambial activity and production of new xylem cells in beech. TEM observations of beech revelled that the ultrastructure of cambium cells differs significantly in its active and dormant state and can be seen in the different organisation, distribution, number and shape of the organelles. Most obvious are the differences in shape and size of the vacuoles, which are small, round, numerous and within a dense cytoplasm in dormant cells. Active cambial cells contain, among other elements, large vacuoles which occupy most of the lumen, rough ER (endoplasmic reticulum), numerous dictyosomes, which produce vesicles and lack storage products such as lipid droplets. When studying wood formation on samples fixed with FEA under LM, the reactivation of the cambium is histologically defined by an increased number of cambial cells and the presence of newly formed xylem and phloem cells in early developmental stages. Observations with TEM have been particularly important in the phase of transition of cambial cells to activity and dormancy, when the number of cell layers in the cambial zone did not change but ultrastructural changes already occurred in the cambial cells. The studies clearly helped us to differentiate between active cambium (ultrastructural changes in cell organelle size and distribution during transition from dormant to active state) and productive cambium which can be observed also with LM, due to presence of cambium derivatives (xylem and phloem cells).
B.06 Other
COBISS.SI-ID: 4353871Between 16th and 21st May 2017 I attended to the conference TRACE 2017 (Trees rings in archaeology and ecology) organised in Svetlogorsk Kaliningrad region, Russia. The main goal was to present our latest results on adaptation strategies to local environment assessed on ultrastructural observations of cambial rhythm in Pinus halepensis and Pinus sylvestris. To understand the adaptation strategies of intra-annual radial growth in Pinus halepensis and Pinus sylvestris to local environmental conditions, seasonal rhythm of cambial activity and cell differentiation at tissue and cellular levels was examined. Two contrasting sites differing in temperature and amount of precipitation were selected for each species, one typical for their growth and the other represented border climatic conditions, where the two species coexisted. Mature P. halepensis trees were selected at Mediterranean (Spain) and sub-Mediterranean (Slovenia) sites, and P. sylvestris trees at sub-Mediterranean (Slovenia) and temperate (Slovenia) sites. We hypothesized that cambial rhythm in trees growing at the sub-Mediterranean site where the two species co-exist will be similar as at typical sites for their growth. Repeated sampling was performed throughout the year and samples were prepared for examination with light (LM) and transmission electron microscopes (TEM). Seasonal changes in the cytoplasm of cambial cells were examined by TEM. Number of cell layers in the cambium, as well as the number of developing xylem cells in the stage of expansion, and secondary cell-wall formation along the same radial file was assessed by LM. Cambium in P. halepensis at the Mediterranean site was active throughout the year and was never truly dormant, whereas at the sub-Mediterranean site it appeared to be dormant during the winter months. In contrast, cambium in P. sylvestris was clearly dormant at both sub-Mediterranean and temperate sites, although the dormant period seemed to be significantly longer at the temperate site. Thus, the hypothesis was only partly confirmed. Different cambial and cell differentiation rhythms of the two species at the site where both species co-exist and typical sites for their growth indicate their high but different adaptation strategies in terms of adjustment of radial growth to environmental heterogeneity, crucial for long-term tree performance and survival.
B.06 Other
COBISS.SI-ID: 4842406Between 11th and 15th May 2016 I attended to the conference TRACE 2016 (Trees rings in archaeology and ecology), organised in Bialowieza Poland. The main goal was to present our studies on intra-specific plasticity of xylem formation and xylem structure in common beech from different sites in Slovenia. High intra-specific plasticity in common beech (Fagus sylvatica L.) trees growing in favourable, yet different climatic conditions in Slovenia were observed in our previous studies (e.g. Prislan et al. 2013). It is suggested that temperature before the occurrence of most of the observed phenological phases significantly differed in trees from different locations. To evaluate how beech trees adjust xylem structure to changing environmental regimes the dynamics of xylem differentiation processes as well as vascular characteristics were investigated in the current study. Analyses were performed on micro-cores collected at weekly intervals at Menina planina (ME – 1200 m a.s.l.) and Panska reka (PA – 400 m a.s.l.) between 2008–2011 growth seasons. Time intervals between major cell differentiation steps were investigated in the initial and terminal parts of the xylem increments; i.e., onset / end of (i) cell expansion (PC), (ii) wall thickening and lignification (SW), and (iii) fully matured cells (MT). In addition, vessel characteristics (density, diameter, mean area, and total conductivity area) were analysed in the first and last quarters of the growth rings. Results showed that although duration of the growing seasons was much longer at PA than at ME time differences between first observed PC and SW cells as well as between first SW and MT cells were similar at both sites. At the end of the growing seasons the time intervals between the cessation of PC and MT phases significantly differed between sites. We observed differences in xylem differentiation dynamics in the initial and terminal part of the growth rings which are partly reflected in differences of vessel features in beech. Vessel density was the only vessel characteristics that significantly differed between sites. Vessel density was thus found to be a promising climatic proxy, whereas other vessel features seemed to be predominantly intrinsically controlled.
B.06 Other
COBISS.SI-ID: 4404390Samples of beech bark samples (received from the Department for Forest Protection of the Slovenian Forestry Institute) with unusual lumpy growth (hyperplasia) were analysed. We prepared permanent transverse sections for observation under light and UV-fluorescence microscope to verify their anatomical structure. The samples of beech bark showed extremely anomalous anatomical structure at the site of the burls in comparison with normal bark structure. The anomalous anatomical structure was characteristic just for limited region/location in periderm (secondary protective tissue) and the outer collapsed phloem. In both tissues the number of cells was significantly higher, and their distribution was different at the affected parts. We concluded that the reason may be unusual reaction (in terms of increased cell number – hyperplasia) of phellogen (cork cambium) and the living parenchyma cells in the surrounding tissue. Bark burls are described as growth anomaly’s or tumorous tissue, since they are often associated with the pathological development of tissue.
D.11 Other
COBISS.SI-ID: 4888486