Afforestation success is measured by the tree establishment and growth capacity which contribute to a range of ecosystem services. In the Mongolian steppe, Populus sibirica and Ulmus pumila have been ...tested as candidate species for large afforestation programs, by analyzing their response to a combination of irrigation and fertilization treatments. While in temperate and Mediterranean forest ecosystems, xylogenetic studies provide insight into the trees’ plasticity and adaptability, this type of knowledge is non-existent in semi-arid regions, whose climatic features are expected to become a global issue. Furthermore, in general, a comparison between the stem and root response is scarce or absent. In the present study, we show that the anatomical traits of the vascular cambium and the xylem, from stem and root microcores, reflect the previously noted dependence of P. sibirica from irrigation – as they proportionally increase and the higher adaptability of U. pumila to drought – due to the reduced impact across all five characteristics. As the first wood anatomy study of these species in semiarid areas, future research is urgently needed, as it could be a tool for quicker understanding of species’ suitability under expected to be exacerbated semi-arid conditions.
Why trees grow at night Zweifel, Roman; Sterck, Frank; Braun, Sabine ...
The New phytologist,
September 2021, Letnik:
231, Številka:
6
Journal Article
Recenzirano
Odprti dostop
Summary
The timing of diel stem growth of mature forest trees is still largely unknown, as empirical data with high temporal resolution have not been available so far. Consequently, the effects of ...day–night conditions on tree growth remained uncertain.
Here we present the first comprehensive field study of hourly‐resolved radial stem growth of seven temperate tree species, based on 57 million underlying data points over a period of up to 8 yr.
We show that trees grow mainly at night, with a peak after midnight, when the vapour pressure deficit (VPD) is among the lowest. A high VPD strictly limits radial stem growth and allows little growth during daylight hours, except in the early morning. Surprisingly, trees also grow in moderately dry soil when the VPD is low. Species‐specific differences in diel growth dynamics show that species able to grow earlier during the night are associated with the highest number of hours with growth per year and the largest annual growth increment.
We conclude that species with the ability to overcome daily water deficits faster have greater growth potential. Furthermore, we conclude that growth is more sensitive than carbon uptake to dry air, as growth stops before stomata are known to close.
Wood formation consumes around 15% of the anthropogenic CO₂ emissions per year and plays a critical role in long-term sequestration of carbon on Earth. However, the exogenous factors driving wood ...formation onset and the underlying cellular mechanisms are still poorly understood and quantified, and this hampers an effective assessment of terrestrial forest productivity and carbon budget under global warming. Here, we used an extensive collection of unique datasets of weekly xylem tissue formation (wood formation) from 21 coniferous species across the Northern Hemisphere (latitudes 23 to 67°N) to present a quantitative demonstration that the onset of wood formation in Northern Hemisphere conifers is primarily driven by photoperiod and mean annual temperature (MAT), and only secondarily by spring forcing, winter chilling, and moisture availability. Photoperiod interacts with MAT and plays the dominant role in regulating the onset of secondary meristem growth, contrary to its as-yet-unquantified role in affecting the springtime phenology of primary meristems. The unique relationships between exogenous factors and wood formation could help to predict how forest ecosystems respond and adapt to climate warming and could provide a better understanding of the feedback occurring between vegetation and climate that is mediated by phenology. Our study quantifies the role of major environmental drivers for incorporation into state-of-the-art Earth system models (ESMs), thereby providing an improved assessment of long-term and high-resolution observations of biogeochemical cycles across terrestrial biomes.
•Intra-annual growth patterns differ between cold and dry sites.•Growth bimodality is typical for the dry continental site.•Growth bimodality is the response to autumn soil moisture ...availability.•Growth at the cold site exhibits a right-skewed unimodal distribution.•High spring growth rates can compensate for growth cessation during dry summers.
Mediterranean trees and shrubs adjust physiological processes to ensure their functioning under shifting dry conditions. However, little is known about spatial and between-species differences in cambial dynamics and how their temporal variability determines climatic adaptability. We used the Vaganov‒Shashkin process-based model to simulate five decades of daily cambial dynamics of coexisting junipers (shrubs/short-stature trees) and pines (tall trees) at two climatically contrasting continental sites in northeastern Spain. We hypothesized that different sites and growth forms may shift from unimodal to bimodal growth patterns, which in turn determines their ability to cope with climate stress. The model produced simulations coherent with ring-width chronologies, xylogenesis data and field monitoring of soil moisture. The model successfully captured differences in growth patterns between sites, but it was unable to highlight differences between coexisting species. The cambial dynamics of all the species were controlled by soil moisture in summer, resulting in bimodal or right-skewed unimodal growth patterns. Simulated cambial dynamics were strongly bimodal, with two distinct peaks in spring and autumn and frequent growth cessation during summer at the dry site with Juniperus thurifera and Pinus halepensis. The growth dynamics of both species at the cold site (Juniperus communis, Pinus uncinata) were rather right-skewed unimodal, suggesting reduced but continuous summer cambial activity. Species at the cold site responded to increasing moisture limitation over the last decades by earlier onset of cambial activity and increased spring cambial kinetics. The shifting of spring growth phenology and kinetics was less effective at the dry site, where both species reduced their growth during summer significantly. Our results suggest that growth adaptability on intra-annual scale determines the performance of woody plants under ongoing climate change in drought-prone regions. High responsiveness of cambial activity corroborates other physiological adaptations which jointly determine the climate-change resistance of junipers and pines.
Auxin is a crucial phytohormone regulating multiple aspects of plant growth and differentiation, including regulation of vascular cambium activity, xylogenesis and its responsiveness towards ...gravitropic stress. Although the regulation of these biological processes greatly depends on auxin and regulators of the auxin signalling pathway, many of their specific functions remain unclear. Therefore, the present study aims to functionally characterise Eucalyptus grandis AUX/INDOLE-3-ACETIC ACID 13 (EgrIAA13), a member of the auxin signalling pathway. In Eucalyptus and Populus, EgrIAA13 and its orthologs are preferentially expressed in the xylogenic tissues and downregulated in tension wood. Therefore, to further investigate EgrIAA13 and its function during xylogenesis, we conducted subcellular localisation and Induced Somatic Sector Analysis experiments using overexpression and RNAi knockdown constructs of EgrIAA13 to create transgenic tissue sectors on growing stems of Eucalyptus and Populus. Since Aux/IAAs interact with Auxin Responsive Factors (ARFs), in silico predictions of IAA13-ARF interactions were explored and experimentally validated via yeast-2-hybrid experiments. Our results demonstrate that EgrIAA13 localises to the nucleus and that downregulation of EgrIAA13 impedes Eucalyptus xylem fibre and vessel development. We also observed that EgrIAA13 interacts with Eucalyptus ARF2, ARF5, ARF6 and ARF19A. Based on these results, we conclude that EgrIAA13 is a regulator of Eucalyptus xylogenesis and postulate that the observed phenotypes are likely to result from alterations in the auxin-responsive transcriptome via IAA13-ARF modules such as EgrIAA13-EgrARF5. Our results provide the first insights into the regulatory role of EgrIAA13 during xylogenesis.
•Cambial phenology and xylogenesis of trees were monitored over six years.•Warming advanced and lengthened the growing season.•Growth onset advanced 3.1 days decade−1 while growth end advanced ...1.8 days decade−1.•A longer growing season did not result in a greater wood production.•Early summer drought reduced growth rate and wood production.
Studies of xylogenesis can provide mechanistic understandings of the influence of climate on wood production and carbon sequestration at the cellular level. It is not yet clear how trees will respond to increasing temperature and precipitation variability and other extreme meteorological events that are expected to occur as climate continues to change. Here, we analyzed cambial phenology and xylogenesis of Juniperus przewalskii Kom. weekly (2011–2014) or biweekly (2015–2016) over six years on the northeastern Tibetan Plateau. We found that temperature plays a decisive role in the onset of xylogenesis and a daily mean temperature of 6.1 °C appears to be the threshold that determines growth onset. Additionally, we observed the end of xylogenesis is related to summer drought conditions. During the course of our observations, the onset of xylogenesis advanced nearly twice as much as the end of xylogenesis (3.1 vs 1.8 days decade−1, respectively), indicating a slight lengthening of the growing season. However, an increase in the duration of the growing season did not necessarily result in a greater level of wood production. In fact, we found that water availability affects the growth rate and early summer precipitation appears to be a key factor of wood production over the northeastern Tibetan Plateau. Our study provides new evidence of the malleable nature of tree growth and reveals potential mechanisms of how tree growth adjusts to climatic variations in cold and arid region.
European beech Fagus sylvatica and Sessile oak Quercus petraea are reaching the north-eastern limits of their natural ranges in northern Poland. According to the projected changes in potential ranges ...in this region, climatic conditions for both species until 2080 will remain stable. On the other hand, a decrease in the vitality of mature trees and a reduction in their radial growth are currently observed. To understand these contradictory findings, we monitored the cambial activity in both species during two vegetation seasons. 2015 was characterized by a negative water balance, while 2017 was wet. This provided an opportunity to compare how the xylogenesis proceeds in diffuse-porous beech and ring-porous oak during contrasting in the summer precipitation seasons. The forming annual increments were sampled with Presler borer at variable time intervals depending on the leaf phenological phases. The cores were prepared using a sledge microtome and double-stained with safranin and astra blue. Observations of the phases of wood formation and measurements of the width of the forming increments were analysed on the microslide digital images. Differences in the dates of the phenological phases were analysed using Two-Way ANOVA, while the dynamics of the formation of annual increments were fitted to the Single and Double Gompertz function for beech and oak, respectively. The beginning of vessel formation started earlier in both seasons compared to previous studies. Inter-seasonal differences in the duration of spring phenological phases were insignificant for both species, while inter-species differences were significant due to physiological diversity between diffuse-porous beech and ring-porous oak. In dry 2015, cambial activity ceased sooner in both species than in 2017. Differences between oak and beech were insignificant in both years, but statistically significant disparities existed within each species due to varying in precipitation seasons. Rainfall significantly elongated the duration of cambial activity and caused wider tree-rings. According to our study, despite predicted maintaining their climatic niche, both species, situated at the north-eastern cooler range boundary, are expected to produce wood at a lower rate due to the projected warmer central European climate with increased heatwaves and summer droughts.
•Moisture availability influenced positively xylem growth besides thermal conditions.•Trees with earlier onsets and longer durations of vessel enlargement exhibited larger hydraulic diameters.•Larger ...diameters caused by warming-induced earlier resumption are more vulnerable to drought-induced cavitation.•The continuous warming and drying climatic may menace the survival of high-altitude Himalayan birch forests.
The Himalayas are experiencing dramatic warming and drought events, which occur at a faster rate than the global average. How will the high-elevation ecosystems cope with such changing conditions? This study aims to combine cambial phenology with quantitative wood anatomy to understand how the growth dynamics affect the trade-off between safety and efficiency of water transport in the Himalayan forests. We investigated the timing of xylogenesis and its relationship with hydraulic wood anatomical traits in Himalayan birch (Betula utilis D. Don) at two altitudes in the central Himalayas. Xylogenesis was monitored weekly from April to September 2014 by collecting microcores. We measured vessel area on histological sections, calculated the hydraulic diameter, and assessed the effects of climate on xylem production rate. Xylogenesis occurred from June to September in both study sites. Moisture availability influenced positively xylem growth besides thermal conditions. The onset and duration of vessel enlargement were correlated with the hydraulic diameter. Trees with earlier onsets and longer durations of vessel enlargement exhibited larger hydraulic diameters. The close relationship between cambial phenology and hydraulic diameter suggests that earlier growth resumption induced by climate changes may result in larger vessels, which are more efficient in water transport, but vulnerable to drought-induced cavitation. The ongoing warming and drying climate conditions may menace the survival of birch forest in the central Himalayas.
In extratropical ecosystems, the growth of trees is cyclic, producing tree rings composed of large-lumen and thin-walled cells (earlywood) alternating with narrow-lumen and thick-walled cells ...(latewood). So far, the physiology behind wood formation processes and the associated kinetics has rarely been considered to explain this pattern. We developed a process-based mechanistic model that simulates the development of conifer tracheids, explicitly considering the processes of cell enlargement and the deposition and lignification of cell walls. The model assumes that (1) wall deposition gradually slows down cell enlargement and (2) the deposition of cellulose and lignin is regulated by the availability of soluble sugars. The model reliably reproduces the anatomical traits and kinetics of the tracheids of four conifer species. At the beginning of the growing season, low sugar availability in the cambium results in slow wall deposition that allows for a longer enlargement time; thus, large cells with thin walls (i.e., earlywood) are produced. In late summer and early autumn, high sugar availability produces narrower cells having thick cell walls (i.e., latewood). This modeling framework provides a mechanistic link between plant ecophysiology and wood phenology and significantly contributes to understanding the role of sugar availability during xylogenesis.
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