Scientists Reveal Niche Differentiation between Diploid and Polyploid Betula Species in NE China
Compared to diploid plant, polyploid plants generally dominate in drought, high latitude or high altitude environment.
In Changbai Mountain of NE China, white birch (Betula plalyphylla) and yellow birch (Betula costata)are diploids, fast-growingcompanion trees in Broadleaved Korean pine forest.
White birch distributes in low elevations and is a dominant species in secondary forest after forest fire or forest felling. Betula dahurica and Betula ermanii are polyploids. B. dahurica is drought tolerant and a companion tree species in broad leaved Korean pine forest, and grows on dry sunny slopes or in dry mixed forest. B.ermanii absolutely dominates on high elevations. The habitat differentiation of the four species may be related to the enhanced stress resistance, especially the changes in water transport efficiency and cavitation resistance after chromosome doubling.
To illustrate the physiological mechanism of the habitat differentiation in four Betula tree species, the research group of Plant Physilogical Ecology of Institute of Applied Ecology (IAE) of the Chinese Academy of Sciences compared the xylem hydraulic architecture of these four species in relation to their ability of maintaining water balance and competitive advantage.
The results show that B. ermanii and B. dahurica have significantly larger hydraulic weighted mean vessel diameters than the two diploids B. platyphylla and B. costata(45.1 and 45.5 vs 25.9 and 24.5 μm).
The two polyploids exhibited significantly higher resistance to drought-induced embolism than the two diploids (-5.23 and -5.05 vs -3.86 and -3.13 MPa) despite their larger vessel diameters.
The higher resistance may be related to the smaller pits. The increase in stress resistance co-occurs with the decrease in growth rate, implicating a trade off relations between stress resistance and growth rate.
This research revealed the effect of changes in chromosome ploidy to the hydraulics and mechanism, provided a base for better use of polyploidy plant.
The results were published in Tree Physiology entitled "Divergences in Hydraulic Architecture form an Important Basis for Niche Differentiation between Diploid and Polyploid Betula Species in NE China".
The work was supported by NNSFC, Key Research and Development Program of Ministry of Science and Technology, Frontier Key Research Program of CAS and One hundred Talent Program of CAS.
Abstract: Habitat differentiation between polyploid and diploid plants are frequently observed, with polyploids usually occupying more stressed environments. In woody plants, polyploidization can greatly affect wood characteristics but knowledge of its influences on xylem hydraulics is scarce. The four Betula species in NE China, representing two diploids and two polyploids with obvious habitat differentiation, provide an exceptional study system for investigating the impact of polyploidization on environmental adaptation of trees from the point view of xylem hydraulics. To test the hypothesis that changes in hydraulic architecture play an important role in determining their niche differentiation, we measured wood structural traits at both the tissue and pit levels and quantified xylem water transport efficiency and safety in these species. The two polyploids had significantly larger hydraulic weighted mean vessel diameters than the two diploids (45.1 and 45.5 vs 25.9 and 24.5 μm) although the polyploids are occupying more stressed environments. As indicated by more negative water potentials corresponding to 50% loss of stem hydraulic conductivities, the two polyploids exhibited significantly higher resistance to drought-induced embolism than the two diploids (-5.23 and -5.05 vs -3.86 and -3.13 MPa) despite their larger vessel diameters. This seeming discrepancy is reconciled by distinct characteristics favoring greater embolism resistance at the pit level in the two polyploid species. Our results showed clearly that the two polyploid species have remarkably different pit-level anatomical traits favoring greater hydraulic safety than their congeneric diploid species, which have likely contributed to the abundance of polyploid birches in more stressed habitats; however, less porous inter-conduit pits together with a reduced leaf to sapwood area may have compromised their competitiveness under more favorable conditions. Contrasts in hydraulic architecture between diploid and polyploid Betula species suggest an important functional basis for their clear habitat differentiation along environmental gradients in Changbai Mountain of NE China.
Publication Name: ZHANG Weiwei; SONG Jia; WANG Miao; LIU Yanyan; LI Na; ZHANG Yongjiang; N Michele Holbrook; HAO Guangyou.
Email:zwwno_1@163.com.
