Key message: Although the radial diameter and wall thickness of conifer tracheids from dry environments are 10 climatic-sensitive across the full ring area, each cell parameter has a specific zone in a ring where its climatic response 11 reaches the maximum. 12Abstract Seasonal dynamics of the timing and rate in cell production and differentiation imprint climate signals 13 into intra-ring variations of anatomical wood structure (e.g. intra-annual density fluctuations). Despite recent 14 methodological advances in quantitative wood anatomy, our understanding of xylem response to climate at the finest scale 15 of intra-ring resolution is incomplete. The goal of this study is to investigate intra-ring changes of tracheid dimensions (cell 16 radial diameter and wall thickness) controlled by moisture stress. Anatomical wood parameters of Pinus sylvestris and 17 Larix sibirica from two drought-susceptible locations in Khakassia, South Siberia, were analysed. We found that inter-18 annual variation of tracheid parameters regularly exceeds the variation between radial tracheid files. This suggests that the 19 climatic signal is recording throughout the entire ring. However, each cell parameter has a specific zone in the ring where 20 its climatic response reaches the maximum. The climatic response of the radial cell diameter has a temporal shift across the 21 ring, which is particularly apparent in pine rings. The climatic response of cell-wall thickness at the intra-ring scale has a 22 more complex pattern. Our results facilitate investigation of the climate impact on tree rings at the finest intra-ring scale by 23 quantifying the timing of climatic impact on ring structure and identifying specifically when climate impacts the formation 24 of a particular cell. 25Acknowledgements This study was supported by the Russian Foundation for Basic Research (project no. 17-04-30 00315). Collaborative activities of I. Panyushkina were sponsored by the CRDF-Global project #FSCX-18-63880-0. We would like to thank Prof. S. W. Leavitt (University of Arizona) for proofreading of the manuscript. We are grateful to 32 editor and reviewers for their helpful comments. 33Conflict of interest The authors declare that they have no conflict of interest. 34climate variations at the time of their formation, and furthermore xylem formation may be responding to climatic stress 65 with various strategies (Castagneri et al. 2017). 66The main goal of this research was to evaluate the intra-ring dynamics of climatic signals in xylem anatomical 67 parameters of conifer trees growing in a moisture-stressed environment in order to understand the climatic sensitivity of 68 xylem at very fine intra-seasonal resolution. For this, we aim to 1) develop site chronologies of xylem anatomical 69 parameters and evaluate their statistical characteristics, 2) determine the relationship between tree-ring width, cell number 70 and mean cell size, 3) compare the intra-seasonal and inter-annual variability of xylem anatomical parameters, and 71 4) identify main clima...
In mountain ecosystems, plants are sensitive to climate changes, and an entire range of species distribution can be observed in a small area. Therefore, mountains are of great interest for climate-growth relationship analysis. In this study, the Siberian spruce"s (Picea obovata Ledeb.) radial growth and its climatic response were investigated in the Western Sayan Mountains, near the Sayano-Shushenskoe Reservoir. Sampling was performed at three sites along an elevational gradient: at the lower border of the species range, in the middle, and at the treeline. Divergence of growth trends between individual trees was observed at each site, with microsite landscape-soil conditions as the most probable driver of this phenomenon. Cluster analysis of individual treering width series based on inter-serial correlation was carried out, resulting in two subset chronologies being developed for each site. These chronologies appear to have substantial differences in their climatic responses, mainly during the cold season. This response was not constant due to regional climatic change and the local influence of the nearby Sayano-Shushenskoe Reservoir. The main response of spruce to growing season conditions has a typical elevational pattern expected in mountains: impact of temperature shifts with elevation from positive to negative, and impact of precipitation shifts in the opposite direction. Chronologies of trees, growing under more severe micro-conditions, are very sensitive to temperature during September-April and to precipitation during October-December, and they record both inter-annual and long-term climatic variation. Consequently, it would be interesting to test if they indicate the Siberian High anticyclone, which is the main driver of these climatic factors.
Due to its advantages in terms of much longer cover period and less demanding measurements, wood anatomy of Picea obovata Ledeb. was offered as spatiotemporal proxy record for tracheid differentiation kinetics. In this study, external and internal regulation of earlywood-to-latewood transition and properties of latewood were considered. The values and interrelations between cell number, tree ring width, maximal and mean radial cell diameter, maximal cell wall thickness and position of the transition to thick-walled tracheids were investigated within site and along the altitudinal gradient. Correlations with moving 21-day climatic series were used to estimate high-resolutional external influences. Relationships between tree ring traits are spatially stable and close within one stage of differentiation and between cells production and expansion. Relationships between sites differ in upper and lower parts of the gradient. Most of traits respond to the primary limiting factors near summer solstice; however, maximal cell wall thickness responds positively to the temperatures at the +10°C threshold. Altitudinal anatomical patterns revealed interaction of intrinsic and external factors in the regulation of tracheid differentiation. Timing of climatic response highlighted role of photoperiod as a trigger in the earlywood-to-latewood transition, and crucial role of the growth season ending for latewood development.
The response of vegetation to climate change is of special interest in regions where rapid warming is coupled with moisture deficit. This raises the question of the limits in plants' acclimation ability and the consequent shifts of the vegetation cover. Radial growth dynamics and climatic response were studied in Scots pine (Pinus sylvestris L.), Siberian larch (Larix sibirica Ledeb.), and silver birch (Betula pendula Roth.) in the forest-steppe, and for Siberian elm (Ulmus pumila L.) in the steppe of South Siberia, as indicators of vegetation state and dynamics. Climate-growth relationships were analyzed by the following two approaches: (1) correlations between tree-ring width chronologies and short-term moving climatic series, and (2) optimization of the parameters of the Vaganov-Shashkin tree growth simulation model to assess the ecophysiological characteristics of species. Regional warming was accompanied by a slower increase of the average moisture deficit, but not in the severity of droughts. In the forest-steppe, the trees demonstrated stable growth and responded to the May-July climate. In the steppe, elm was limited by moisture deficit in May-beginning of June, during the peak water deficit. The forest-steppe stands were apparently acclimated successfully to the current climatic trends. It seems that elm was able to counter the water deficit, likely through its capacity to regulate transpiration by the stomatal morphology and xylem structure, using most of the stem as a water reservoir; earlier onset; and high growth rate, and these physiological traits may provide advantages to this species, leading to its expansion in steppes.
Tree-ring formation studies are important for assessing the impact of environmental factors on tree growth at intra-seasonal resolution. This information is necessary for understanding plant acclimatization to current and expected climate changes. Little is still known about how tree age may affect the duration and rate of annual ring formation. In this study, we investigated tree-ring formation in Scots pine (Pinus sylvestris L.) trees of different ages (30- and 95-year-old trees) from the foreststeppe zone in Southern Siberia. The main objectives were 1) to estimate the timing of cambial activity by distinguishing the phases of division, enlargement, wall thickening, and maturation of tracheids and 2) to compare the anatomical structure of the tracheids forming the annual rings of the differently aged trees. Stem tissue was sampled weekly from April to September 2014. The results showed a 1-2 week difference in duration of the phases of xylem formation between the groups; in addition, the ring width of the young trees was slightly narrower. The size of the tracheids of the entirely formed ring (i.e. the results of the enlargement phase) did not differ between the groups whereas the dynamics of the cell-wall thickness showed significant differences. The data obtained in the present study can provide references to calibrate process-based models linking environment to wood formation. These data can be used to benchmark time-explicit simulated measurements of annual ring increment and cell anatomical structure against the corresponding parameters of mature trees growing under natural conditions
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