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Palaeo-adaptive properties of the xylem of metasequoia: mechanical/hydraulic compromises

Author:
Jagels, R., Visscher, G.E., Lucas, J., Goodell, B.
Source:
Annals of botany 2003 v.92 no.1 pp. 79-88
ISSN:
0305-7364
Subject:
water content, Metasequoia glyptostroboides, boreal forests, temperate forests, tropical forests, forest trees, conifers, xylem, wood anatomy, paleobotany, tracheids, plant-water relations, Quercus, heartwood, wood physical properties, wood strength, tensile strength, durability, mechanical stress, decay fungi, decay resistance, tree growth, wet environmental conditions, plant adaptation, climatic zones, latitude, evolutionarily stable strategy, China, North America, New Jersey
Abstract:
The xylem of Metasequoia glyptostroboides Hu et Cheng is characterized by very low density (average specific gravity = 0.27) and tracheids with relatively large dimensions (length and diameter). The microfibril angle in the S2 layer of tracheid walls is large, even in outer rings, suggesting a cambial response to compressive rather than tensile stresses. In some cases, this compressive stress is converted to irreversible strain (plastic deformation), as evidenced by cell wall corrugations. The heartwood is moderately decay resistant, helping to prevent Brazier buckling. These xylem properties are referenced to the measured bending properties of modulus of rupture and modulus of elasticity, and compared with other low-to-moderate density conifers. The design strategy for Metasequoia is to produce a mechanically weak but hydraulically efficient xylem that permits rapid height growth and crown development to capture and dominate a wet site environment. The adaptability of these features to a high-latitude Eocene palaeoenvironment is discussed.
Agid:
1423348