The effect of slope on root architecture and anatomy of Rumex scutatus L. was analysed in plants growing on slopes and on flat ground, on the flanks of Mt. Vesuvius. Roots of plants on steep slopes developed asymmetrically, with lateral roots growing upslope acting as tie-rods. In roots growing on flat ground, lignified xylem was limited to thin radial strips, surrounded by unlignified parenchyma cells filled with starch. A trend towards a larger lignified area was evident from plants growing on flat ground to those on steep slopes, as well as from taproots to tie-rod roots. The latter also showed larger vessels and a lower incidence of narrow vessels than taproots. Roots developing on steep slopes were characterised by high frequency of very-thick-walled, lignified fibres with long tips which accumulated both starch and phenolic compounds. Such fibres did not show lignified cell walls in roots growing on flat ground. Overall analysis showed that slope influences root architecture and anatomical traits, not only affecting mechanical properties but also water transport capacity.
Characterisation of anatomical properties and analysis of lignin content and monomer composition were performed on twigs of the shrub Rhamnus californica L. in order to highlight their role in the adaptive strategies of this species in Mediterranean-type ecosystems. Our results showed that R. californica twigs develop a thick cuticle accompanied by several layers of subepidermal cells with suberised walls aiming to save water. The xylem is characterised by anatomical and chemical traits ensuring safety of water transport and preventing permanent damage through the enhancement of mechanical strength, also favoured by the lignification of pith cell walls. Moreover, the accumulation of phenolic compounds in the cortical cylinder is a strategy to protect against herbivory and to screen against high levels of radiation. Our overall analysis suggests that R. californica has evolved a strategy of shoot development that allows it to cope with the multiple environmental stresses found in Mediterraneantype ecosystems, among which summer drought and grazing play a major role especially for the survival of seedlings and young plants.
Mediterranean trees and shrubs form intra-annual density fluctuations (IADFs) in tree rings as a sign of their plasticity in wood formation in response to intraseasonal variations of environmental conditions. Different species show a different aptitude to form IADFs, due to their diverse ability to cope with climate stressors, since the occurrence of IADFs may affect plant hydraulics. Dendroecology and quantitative wood anatomy were used to characterise IADFs in Pinus pinea and Arbutus unedo co-occurring at a Mediterranean site in Italy. The relations between climate parameters (i.e. temperature and precipitation) and intra-annual tree-ring traits (i. e. IADF frequency and conduit size) were analysed to highlight the main triggers for IADF formation and their functional role.
Data showed that both species are characterised by a high plastic response to climate and formed a high frequency of L-IADFs (occurrence of earlywoodlike conduits in latewood). The two species, although forming the same type of IADFs, showed different sensitivity to environmental factors. Pinus pinea showed a high dependence of tracheid size on temperature, while Arbutus unedo was more sensitive to precipitation in spring and autumn. Arbutus unedo promptly developed more than one IADF per year in response to rainfall events following drought periods.
The overall results were useful to compare the aptitude of the two species in forming IADFs and to highlight the factors priming their formation. This is useful to understand wood growth reactions to environmental drivers and to evaluate the adaptive capabilities in these two species, and thus to predict forest reactions after climate changes.
Peatland ecosystems are an important archive of paleoclimatic information. Within this context, tree-ring data from trees growing in such ecosystems are extremely valuable resources, and subfossil trees from peat bogs have been widely employed in dendroclimatological studies. However, there are still gaps in our understanding of the relationships among tree growth, peatland hydrology and climate factors. Here, we summarize the principal studies on living peatland trees, with a particular focus on their use as a source of information on past climatic conditions. We discuss the main factors influencing tree growth in this environment, whether it is the local hydrological cycle or climate. We put a particular focus on the reliability of the climate signal recorded by living peatland trees, comparing it with that found in subfossil trees. Finally, we discuss the relevance of quantitative wood anatomy in the context of peatland ecosystems research.
Tree rings provide information about environmental change through recording stress events, such as fires, that can affect their growth. The aim of this study was to investigate wood growth reactions in Pinus halepensis Mill. trees subjected to wildfires, by analysing anatomical traits and carbon and oxygen isotope composition. The study area was Southern France where two sites were selected: one subjected to fires in the last 50 years, the other characterised by comparable environmental conditions although not affected by fire events (control site). We analysed whether wood growth depends on the tangential distance between developing xylem cells and the limit where the cambium was directly damaged by fire. In the burnt site, thick wood sections, including fire-scar, were taken from surviving plants. Digital photo-micrographs were analysed to measure early- and latewood width, wood density, and tracheid size. Anatomical and isotopic traits were analysed in two series of tree rings (5 rings before and 5 after the fire) selected at different positions along the circumference (close or far from the scar). Anatomical and isotopic traits were quantified also on tree rings of the same years from cored trees growing at the control site. Results showed different wood reaction tendencies depending on the distance from the scar. The comparison between plants from the two sites allowed to exclude possible climate interference.
Our results are discussed in terms of two kinds of growth reactions: the local need to promptly compartmentalise the scarred cambial zone and sapwood after fire, and the general growth perturbations due to tree reaction to crown scorch during fire. Anatomical results, combined with dendrochronological and isotopic analysis, could provide an efficient way to distinguish between direct growth reactions due to heat-related damage on cambium and indirect outcomes related to defoliation.
The transcriptional activator EgMYB2, which belongs to the large R2R3 MYB transcription factor family, plays a major role in the coordinated control of genes in the lignin biosynthetic pathway. Given that lignin genetic modification can lead to xylem alterations compromising vascular functionality, we characterised wood anatomical properties of two transgenic tobacco lines over-expressing EgMYB2, using light, fluorescence, confocal, transmission electron microscopy, immunocytochemical labelling and digital image analysis. Transgenic wood, compared with wild type, was characterised by both reduced frequency of larger vessels and lower vessel grouping; these traits are known to have physiological implications in terms of water transport efficiency and safety against embolism. Transgenic wood also appeared denser due to the occurrence of thicker cell walls and higher incidence of fibres than wild type. Increased lignin content was accompanied by a concomitant increase in cellulose and xylan, but no alterations in the usual distribution of guaiacyl and syringyl units in secondary cell walls were observed. Altogether, these results show that EgMYB2 is a master regulator controlling the synthesis of the three major polymers of the secondary cell wall and that its overexpression has significant influence on quantitative anatomical traits of wood which affect its functional properties.
We investigated the variation of wood anatomical characteristics and carbon isotopic composition of tree rings showing intra-annual density fluctuations (IADFs) in plants of Pinus pinaster Ait. growing at a coastal plantation in Tuscany (Italy). IADFs are regions of the tree ring where wood density changes abruptly due to a sudden change of environmental conditions, particularly of water availability. Dendrochronological analyses allowed dating of the rings and four regions were considered in each tree ring: earlywood, IADF, late-earlywood and latewood. Although IADF commonly has been classified as latewood-like tissue in the literature, we found differences in anatomical characteristics and carbon isotopic composition between tracheids of the two regions. The lumen area of tracheids in IADF was significantly larger than in latewood, while still smaller than in earlywood and late-earlywood. Latewood and IADF had a greater proportion of narrow tracheids than both earlywood and late-earlywood. Although latewood and IADF were characterized by tracheids with lumina lengthened in the tangential direction, while earlywood tracheids were elongated in the radial direction, some differences were found also between latewood and IADF. Moreover, IADF tracheids had a higher 13C/12C ratio than any other region and showed isotopic values significantly different from the latewood. The quantification of anatomical features of tracheids within rings was useful to discriminate between latewood and IADFs, as well as helpful for the identification of tree-ring boundaries. The overall interpretation of dendrochronological, wood anatomical and carbon isotopic data seems to be a promising approach for the dating and the ecological interpretation of tree rings in Mediterranean ecosystems and for gaining climatic information with intra-annual resolution.