Tree ring phototropism and implications for the rotation of the North China Block

Zikun Jiang,Yuanzheng Lu,Yong Cao,Benpei Liu,Min Huang,Tom Kapitany,Shenghui Deng,Ning Tian,Yongdong Wang

doi:10.1038/s41598-019-41339-2

Abstract

Trees grow towards the sunlight via a process of phototropism. The trunk phototropism processes are frequently observed in Northern Hemisphere from high latitude to at least the Tropic of Cancer region, and also occur in some in situ preserved vertical petrified woods in various geological ages. However, such evidence is still very limited and poorly known in fossil record; and the relationship between tree ring phototropism and rotation of tectonic blocks is unclear. Here we report the eccentricities of living and fossil trees as a proxy to determine geological block rotation at the same latitudes within the North China Block. The dominant eccentricity of living trees is southwest 219° ± 5°. By contrast, standing in situ fossil trunks in the Mid-Late Jurassic Tiaojishan Formation and the Late Jurassic Tuchengzi Formation had average eccentricities of 237° and 233.5°, respectively. These differences shed light on the palaeogeographical changes, indicating that the North China Block rotated clockwise from the Late Jurassic to the present day. This result is largely coincident with the palaeomagnetic results, indicating that the North China Block rotated clockwise by 26.5° ± 5.5° since the Middle to Late Jurassic transition.

Highlights

Light is a key environmental factor that drives many aspects of plant growth and development[1]
The shape, dominant eccentricities and other directions from the pith to the largest growing part of living tree trunks were observed within the latitude ranges from 39°59.6′N to 43°15′N in northern China region
In the Northern Hemisphere, trunk phototropism is observed at high latitudes and extends south to at least the Tropic of Cancer (N23°26′)[34]

Summary

Introduction

Light is a key environmental factor that drives many aspects of plant growth and development[1]. In recent years, increased data have been accumulated for such eccentricity phototropism in both living and fossil tree ring observations, especially in some well-preserved individual fossil trunks[34,35]. Such evidence is still very limited and poorly known in fossil record and the relationship between ring phototropism and rotation of block is undetermined. We report our recent systematic field surveys and investigation results on both living trees and in situ fossil wood from the North China Block, including 253 living trees from Beijing and Jilin Provinces, and 7 fossil in situ trunks from the Jurassic Tiaojishan and Tuchengzi formations in Liaoning and Beijing regions (Supplementary Information S1). Our palaeomagnatic data from the Tiaojishan Formation in Beipiao of Liaoning Province provide support for the fossil data interpretation, indicating that the North China Block had rotated clockwise since the Middle to Late Jurassic transition (Supplementary Information S1)

Methods

Results

Conclusion