Abstract
1. The terminal shoot (or current-year shoot), as one of the most active parts on a woody plant, is a basic unit determining plant height and is potentially influenced by a variety of environmental factors. It has been predicted that tissues amount and their allocation in plant stems may play a critical role in determining plant size in alpine regions. The primary structure in terminal shoots is a key to our understanding treeline formation. The existing theories on treeline formation, however, are still largely lacking of evidence at the species level, much less from anatomy for the terminal shoot.2. The primary structures within terminal shoot were measured quantitatively for 100 species from four elevation zones along the eastern slope of Gongga Mountain, southwestern China; one group was sampled from above the treeline. An allometric approach was employed to examine scaling relationships interspecifically, and a principal components analysis (PCA) was performed to test the relation among primary xylem, ground tissue, species growth form and altitude.3. The results showed that xylem tissue size was closely correlated with ground tissue size isometrically across species, while undergoing significant y- or/and x-intercept shift in response to altitudinal belts. Further, a conspicuous characteristic of terminal shoot was its allocation of contrasting tissues between primary xylem and ground tissues with increasing elevation. The result of the PCA showed correlations between anatomical variation, species growth form/height classes and environment.4. The current study presents a comparative assessment of the allocation of tissue in terminal shoot across phylogenically and ecologically diverse species, and analyzes tissue, function and climate associations with plant growth forms and height classes among species. The interspecific connection between primary xylem ratio and plant size along an elevation gradient suggests the importance of primary xylem in explaining the treeline formation.
Highlights
The tree growth form has long been viewed as an integrated ecological strategy for species [1] responding to geographic and ecological mechanisms and biotic and abiotic limits [2,3,4,5,6]
The current study presents a comparative assessment of the allocation of tissue in terminal shoot across phylogenically and ecologically diverse species, and analyzes tissue, function and climate associations with plant growth forms and height classes among species
Of the three tissue systems, the primary xylem is a key component of the stem, and its developmental process is prone to be influenced by the environmental conditions that the latter imprint on its primary structure [18,19]
Summary
The tree growth form has long been viewed as an integrated ecological strategy for species [1] responding to geographic and ecological mechanisms and biotic and abiotic limits [2,3,4,5,6]. Increasing tree height is associated with shoot architecture, stem anatomy, and xylem production or allocation [20,21,22,23] Based on these observations, the terminal shoots, as basic active modules [24], determine the terminal shoots’ vertical growth at the very top of a woody plant and eventually determine the height of the entire plant, considering the modular structure of vertical growth [17] and the integration among functional modules in the body of woody species [25]
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