Abstract
In the conifer tree rings, each tracheid goes through three phases of differentiation before becoming an element of the stem water-conducting structure: division, extension, and cell wall thickening. These phases are long-lasting and separated temporally, especially cell wall thickening. Despite the numerous lines of evidence that external conditions affect the rate of growth processes and the final anatomical dimensions during the respective phases of tracheid differentiation, the influence of the environment on anatomical dimensions during the cell division phase (cambial activity) has not yet been experimentally confirmed. In this communication, we provide indirect evidence of such an effect through observations of the small fluctuations in the latewood cell wall thickness of rapidly growing tree rings, which exhibit a high cell production rate (more than 0.4 cells per day on average). Such small fluctuations in the cell wall thickness cannot be driven by variations in external factors during the secondary wall deposition phase, since this phase overlaps for several tens of latewood cells in the rings of fast-growing trees due to its long duration.
Highlights
The relative simplicity of the anatomical structure of conifer xylem, which consists of more than 90% the radial files of tracheids [1, 2, 3], has attracted the attention of wood anatomists, and other scientists: ecophysiologists, biophysicists, biomathematicians, information technology specialists, technical engineers, etc. [4, 5, 6, 7, 8, 9, 10, 11]
In several of our works, it was clearly shown that morphometric parameters of tracheids perceive growth-limiting effects of climatic factors for short intervals during the growing season [28, 29, 30]. It is still unresolved which of the three phases of tracheid differentiation is the most sensitive to external influence [12, 31, 32, 33]. We considered this question based on tracheidograms of tree rings producing various numbers of cells per ring
The comparison of the seasonal kinetics of conifer xylogenesis in the study region during several seasons ([10, 40], unpublished data) with the corresponding temperature series showed that the threshold temperatures coinciding with the onset of cambial activity are approximately 8 ̊C for both species
Summary
The relative simplicity of the anatomical structure of conifer xylem, which consists of more than 90% the radial files of tracheids [1, 2, 3], has attracted the attention of wood anatomists, and other scientists: ecophysiologists, biophysicists, biomathematicians, information technology specialists, technical engineers, etc. [4, 5, 6, 7, 8, 9, 10, 11]. Together with the total number of cells in a tree ring (N), these characteristics can be integrated into other characteristics frequently used in dendroclimatology, e.g., tree-ring width and maximum wood density [15] It is well known that each tracheid, before becoming a functional element of the conifer xylem, passes through three stages of differentiation: 1) cell production by xylem mother cells in the cambial zone, 2) cell expansion, and 3) cell wall thickening, i.e., synthesis and lignification of the secondary cell wall [12, 16, 17, 18, 19].
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