Leaf anatomy and ultrastructure in senescing ancient tree, Platycladus orientalis L. (Cupressaceae)

Abstract

Platycladus orientalis L. (Cupressaceae) has a lifespan of thousands of years. Ancient trees have very high scientific, economic and cultural values. The senescence of ancient trees is a new research area but is poorly understood. Leaves are the primary and the most sensitive organ of a tree. To understand leaf structural response to tree senescence in ancient trees, experiments investigating the morphology, anatomy and ultrastructure were conducted with one-year leaves of ancient P. orientalis (ancient tree >2,000 years) at three different tree senescent levels (healthy, sub-healthy and senescent) at the world’s largest planted pure forest in the Mausoleum of Yellow Emperor, Shaanxi Province, China. Observations showed that leaf structure significantly changed with the senescence of trees. The chloroplast, mitochondria, vacuole and cell wall of mesophyll cells were the most significant markers of cellular ultrastructure during tree senescence. Leaf ultrastructure clearly reflected the senescence degree of ancient trees, confirming the visual evaluation from above-ground parts of trees. Understanding the relationships between leaf structure and tree senescence can support decision makers in planning the protection of ancient trees more promptly and effectively by adopting the timely rejuvenation techniques before the whole tree irreversibly recesses.

Tree age did not affect the leaf anatomical structure or ultrastructure of Platycladus orientalis L. (Cupressaceae)

“…Here, we investigated the following information for all P. orientalis trees in the three plots: tree age, tree height, diameter at breast height, site condition (altitude, slope, longitude and latitude) and health condition (Zhou et al, 2019). According to the investigation results, the basic information of the nine sampled trees and their site situations are shown in Table 1.…”

“…This area has between 1,100 and 1,300 annual hours of sunshine, a frost-free period of 170 d, an altitude range of 1,100 to 1,200 m, and a typical temperate continental climate with distinct seasonal features. The average annual temperature is 9.4 °C, and the average annual precipitation is 596.3 mm, while the average annual evaporation capacity is 487.3 mm (Zhou et al, 2019). The history of the artificial pure P. orientalis forest exceeds 4,000 years according to historical records and scientific research (Chang et al, 2012a; Zhang et al, 2015).…”

“…In each plot, we conducted an investigation of every single P. orientalis tree (tree age was determined using government records The Local County Records of Huangling County ). Tree vitality degree was assessed using the method of The senescent degree evaluation of trees according to above-ground parts (Zhou et al, 2019). The distance from the trunk to the sampling site were measured following the branching of the tree.…”

“…Aging is the last stage of plant development. However, aging has been a familiar but poorly understood issue in biology for a long time (Kirkwood, 2005; Zhou et al, 2019). Thousands of studies have been conducted to research the characteristics and causes of aging in human, animals and herbaceous plants (Guarente, 2014; Jones et al, 2014).…”

“…However, the senescence of leaves is not equal to the senescence of trees. Unlike deciduous trees, conifers do not renew their crowns every year, and the leaves themselves are metabolized (Zhou et al, 2019). As the most important cell organelles of plant photosynthesis, chloroplasts greatly influence the senescence of trees (Doorn & Yoshimoto, 2010).…”