Palaeo-adaptive Properties of the Xylem of Metasequoia: Mechanical/Hydraulic Compromises

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.

Adaptive anatomy of Pinus halepensis trees from different Mediterranean environments in Spain

“…These results concur with earlier studies in which high values for the double cell wall (t) in relation to the tangential width (b) are associated with resistance to collapse due to bending stress (e.g., Young 1989) and implosion stress in the conduit (e.g., Sperry et al 2006). However, the greater mechanical requirements of the trees from the Inland Catalonia region did not result in longer tracheids, in contrast to what has been suggested in other studies (Mencuccini et al 1997;Ezquerra and Gil 2001;Jagels et al 2003;Jagels and Visscher 2006).…”

Lignin in Woody Plants under Water Stress: A Review

“…Within terrestrial plants, lignin content can vary greatly in different tissues. Lignin provides a hydrophobic surface allowing plants to transport water to heights of several meters (Carder, 1995;Koch et al, 2004) as well as contributes to the organism mechanical strength that make trees to support large amounts of biomass (Jagels et al, 2003).…”

Carbon and hydrogen isotope fractionation under continuous light: implications for paleoenvironmental interpretations of the High Arctic during Paleogene warming

“…However, more water is required to meet the demand of higher growth rates under CL conditions. While water supply is not limited and an efficient hydraulic system exists in Metasequoia (Jagels et al 2003), a prolonged transpiration with more water loss during the 24-h cycle is a viable strategy to sustain carbon uptake and rapid redistribution during periods of high productivity. This may explain the large offset of hydrogen fractionation factors in Metasequoia between CL and DL conditions.…”

“…Implications for the interpretation of precipitation in the Paleogene High Arctic Celebrated as ''living fossils,'' Metasequoia and Larix are well known for their slow evolutionary rates and morphological stasis since the Paleogene (LePage and Basinger LePage et al 2005;Yang and Jin 2000), and it is likely that their physiological characteristics were conserved through time (Jagels and Day 2004;Jagels et al 2003). Therefore, genus-specific e lipid-water determined under controlled conditions offers the best hydrogen fractionation factors for reconstructing the dD values of ancient source waters.…”