Comparison of Intra-Annual Xylem and Phloem Formation of Picea crassifolia Stands at Two Latitudes in Northwest China

Biyun Yu,Ping Zhao,Jianguo Huang,Xuebin Li

doi:10.3390/f12111445

Biyun Yu, Ping Zhao + Show 2 more

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https://doi.org/10.3390/f12111445

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Abstract

Understanding the changes in xylem and phloem formation of trees and their relationship along latitudes are important for evaluating and predicting how fragile forests may respond to climate change; however, corresponding studies are still relatively scarce. This study investigated the intra-annual dynamics of xylem and phloem formation of Picea crassifolia and their relationship at two latitudes of arid and semi-arid forests in China. The results showed that both xylem and phloem formation varied at different latitudes. Xylem formation at the low-latitude site (Luoshan) started two weeks earlier than that at the high-latitude site (Helanshan) but ended one week later, resulting in an extended growing season at the low-latitude site. Phloem formation preceded cambium activity and xylogenesis at both sites by 24.6 days in Luoshan, which had warmer conditions, and by 17.3 days in Helanshan. In Luoshan, compared to Helanshan, there occurred significantly more enlarging and wall thickening cells, during (relatively wet) June–August, but significantly fewer enlarging and wall thickening cells as well as total xylem cells, during (relatively dry) April–May. Sample trees produced significantly fewer early phloem cells during the early growing season (April–May) in Luoshan, but generated significantly more late phloem cells during the late growing season in Helanshan. Additionally, different trade-offs between xylem and phloem formation were observed at different sites. The longer duration of early phloem formation might have shortened the duration of xylem lignification in Helanshan; in Luoshan, the date that late phloem reached its maximum growth rate was significantly positively correlated with the date when xylem lignification ended. The results revealed the plasticity of xylem and phloem formation under changing environmental conditions and a complex and site-specific relationship between xylem and phloem formation. These findings could help us better understand and predict the future growth of arid and semi-arid forests in China in response to climate change.

Highlights

Our study found that in warmer Luoshan, early phloem formation began and culminated earlier (Figure 5) and the number of late phloem cells rapidly increased to a maximum and was higher than in Helanshan (Figure 4)
We compared the dynamics of xylem and phloem formation and their relationship for P. crassifolia at two latitudes of arid and semi-arid forests in China
We found that both xylem and phloem formation of P. crassifolia were responsive to environmental changes

Summary

Introduction

In the context of global climate change, uneven temperatures and precipitation patterns have resulted in increased frequency of extreme climatic events, such as droughts, sandstorms, and floods, which profoundly affect the forest ecosystems that human beings rely on [1,2,3,4]. As the main component of forest ecosystems, trees play a key role as windbreaks and in sand fixation, water conservation, and climate regulation [5,6,7]. Tree growth depends on the division and differentiation of cambial cells [10,11]. Cambial cells outwardly divide into phloem cells and inwardly give rise to xylem cells [12] In the face of the challenges posed by climate change, understanding how trees grow and respond to climate change is of great significance for predicting and scientifically managing forests in the future, especially fragile forests [8,9]. 4.0/).

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