Abstract
Investigating space allocation patterns of plant secondary xylem along a latitudinal gradient is useful to evaluate structure-function tradeoffs in woody angiosperm xylem. An anatomical dataset including 700 woody angiosperm species across China was compiled together with latitudinal and climate data for each species. The relative tissue fractions of vessels, fibers, and parenchyma (including ray and axial parenchyma) in xylem were analyzed to determine the effect of latitudinal differences and phylogeny on anatomical variation. The analyses revealed a trade-off between vessel and non-vessel fraction across latitude, with tissue fraction trade-offs mainly occurring between vessels and fibers, and between fibers and total parenchyma. Among 13 climate variables, thermal indices generally had greater explanatory power than moisture indices in bi-variate models for all cell types, while mean annual temperature, mean temperature of the coldest month, and annual actual evapotranspiration were included in the top multi-variate models explaining variance of different tissue fractions. Phylogeny and climate together explained 57–73% of the total variation in xylem space occupancy, with phylogeny alone accounting for over 50% of the variation. These results contribute to our knowledge of wood structure-function and are relevant to better understand forest response to climate change.
Highlights
The structure of wood xylem is closely related to its functions
Among the five tissue fractions, axial parenchyma had the highest value of lambda (0.895) followed by vessels (0.852), total parenchyma (0.760), fibers (0.732), and ray parenchyma (0.673)
Since hydraulic conductivity scales to the fourth power of the vessel diameter, but linearly with vessel density according to the Hagen–Poiseuille law, it is possible that increased vessel density alone is not enough to compensate the effect of narrow vessel diameters
Summary
Angiosperm wood carries out three key functions simultaneously: water transport, mechanical support, and water and nutrient storage. These functions correspond largely to three principal cell types, namely vessels, fibers, and parenchyma. Xylem Tissue Fractions Along Latitude increased mechanical support often decreases water conduction efficiency but may contribute to embolism resistance (Hacke et al, 2001; Pratt and Jacobsen, 2016). Despite various recent studies on functional trade-offs in wood (e.g., Gleason et al, 2016b; Pratt and Jacobsen, 2016), xylem space allocation represents a rather new view on this topic that deserves due attention because xylem volume is limited and space must be shared by different cell types (Bittencourt et al, 2016; Brodersen, 2016; Gleason et al, 2016a). Previous papers have confirmed the existence of trade-offs between tissue fractions in xylem (Zheng and Martínez-Cabrera, 2013; Zieminska et al, 2015; Morris et al, 2016b), none of them attempted to explore trends of those trade-offs along a large latitudinal gradient and the role climate and phylogeny played in it as this paper aimes to do
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