Variation in Tracheid Dimensions of Conifer Xylem Reveals Evidence of Adaptation to Environmental Conditions.

Jingming Zheng,Yajin Li,Hugh Morris,Filip Vandelook,Steven Jansen

doi:10.3389/fpls.2022.774241

Abstract

Globally distributed extant conifer species must adapt to various environmental conditions, which would be reflected in their xylem structure, especially in the tracheid characteristics of earlywood and latewood. With an anatomical trait dataset of 78 conifer species growing throughout China, an interspecific study within a phylogenetic context was conducted to quantify variance of tracheid dimensions and their response to climatic and soil conditions. There was a significant difference in tracheid diameter between earlywood and latewood while no significant difference was detected in tracheid wall thickness through a phylogenetically paired t-test. Through a phylogenetic principle component analysis, Pinaceae species were found to be strongly divergent in their tracheid structure in contrast to a conservative tracheid structure in species of Cupressaceae, Taxaceae, and Podocarpaceae. Tracheid wall thickness decreased from high to low latitudes in both earlywood and latewood, with tracheid diameter decreasing for latewood only. According to the most parsimonious phylogenetic general least square models, environment and phylogeny together could explain about 21∼56% of tracheid structure variance. Our results provide insights into the effects of climate and soil on the xylem structure of conifer species thus furthering our understanding of the trees’ response to global change.

Highlights

Understanding how trees respond to environmental conditions is crucial for an accurate prediction of future changes to forest dynamics caused by global warming, especially in the Northern boreal ecosystems (Vaganov et al, 2006; Zhang et al, 2020)
A study on Juniperus przewalskii provides additional evidence that soil moisture is more important than temperature at initiating xylem growth under cold and dry conditions (Ren et al, 2018). These results suggest that wood formation and xylem structure of various conifers could be controlled by genetic and multiple environmental factors such as temperature, soil moisture content and other soil properties, an interspecific study in a phylogenetic context and along a wide latitudinal gradient could shed light on this important research topic
We address the following questions: (1) do tracheid dimensions always differ between earlywood and latewood? (2) What is the role of phylogeny in associations among tracheid dimensions? (3) Are there clear trends of xylem structure along a latitudinal gradient? (4) How much of the xylem structure variance can be explained by environment and phylogeny, respectively? To the best of our knowledge, there is currently no cross-species anatomical study of conifers along such a wide gradient, making our study an important contribution to plant science

Summary

Introduction

Understanding how trees respond to environmental conditions (e.g., climate, soil, etc.) is crucial for an accurate prediction of future changes to forest dynamics caused by global warming, especially in the Northern boreal ecosystems (Vaganov et al, 2006; Zhang et al, 2020). A latitudinal gradient is associated with consistent temperature differences that can act as a natural laboratory, helping us to understand forest responses to global warming (De Frenne et al, 2013). Tracheid Variance Reveals Environment Adaptation environmental conditions. Tracheid dimensions can provide us with valuable information about how conifer species adapt to various environments and their possible responses to climate change (Vaganov et al, 2006). The latitudinal patterns of tracheid traits have been surprisingly understudied compared to vessel traits (Brodribb et al, 2012)

Methods

Discussion

Conclusion