Intra-Annual Wood Formation of Cryptomeria fortunei and Cunninghamia lanceolata in Humid Subtropical China

Abstract

Monitoring cambial activity is important for a better understanding of the mechanisms governing xylem growth responses to climate change, providing a scientific basis for tree-ring-based climate reconstructions and projections about tree growth under future climate scenarios. It plays an even more important role in investigating evergreen tree growth in regions with less distinct seasonal cycles. Subtropical evergreen forests have been studied in recent years for their sensitivity to climate change, but it remains unclear how xylem growth is driven by subtropical climates. To further understand the climate-growth response strategies of subtropical conifers, we micro-cored Cryptomeria fortunei and Cunninghamia lanceolata weekly in 2016 and 2017 at the humid subtropical Gushan Mountain in southeastern China. Our weekly growth monitoring showed that the vegetation periods of these two species were both approximately 2–3 months longer than trees in temperate and boreal forests. The growth of C. fortunei in 2016 and 2017 and C. lanceolata in 2017 showed a bimodal pattern of xylogenesis, which was induced by summer drought. The results also indicated that the earlier end of the xylem formation was related to the yearly drought stress. These findings provide more specific information about tree growth and evidence of how climate influences wood production at the cellular level in subtropical regions.

Intra-annual dynamic of opposite and compression wood formation of Pinus massoniana Lamb. in humid subtropical China

“…began in March and ceased in November. The growth duration was prolonged by 3-4 months compared to coniferous species in cold environments (Rossi et al, 2016) but was consistent with the findings of Huang et al (2018) and Zheng et al (2021) who reported that the regional climate plays a significant role in wood formation processes of subtropical conifers. A humid and warm climate is optimal for leaf photosynthesis, which will further promote the radial growth of trees (Ding et al, 2021).…”

“…Microcores were collected from both the CW (the widest tree rings) and the OW (the narrowest tree rings) (as seen in Supplementary Figure 2). Each core had a diameter of 2 mm and a length of 2-3 cm that contained at least two intact xylem and lamellar bands with adjacent phloem ( Zheng et al, 2021). To maximize the use of limited sampling locations and minimize influences between adjacent sample areas, samples were taken in a zigzag pattern around the trunk, with a minimum distance of 5 cm between each sample (Supplementary Figure 3).…”

“…where nc i is the standardized number of xylem cells, ncm i is the measured number of xylem cells, rw m is the mean width of the previous tree rings for all samples, and rw s is the width of the previous tree rings for each sample (Zheng et al, 2021). Different from the simple unimodal growth characteristics in the alpine region, the radial growth in the humid subtropical region has a complex growth pattern (Huang et al, 2018;Liu et al, 2019;Zheng et al, 2021). Given that generalized additive models (GAMs) are data-driven, they are better able to describe complex intra-annual wood formation dynamics than traditional Gompertz functions (Cuny et al, 2013).…”

The intra-annual intrinsic water use efficiency dynamics based on an improved model

“…The field tree growth monitoring research conducted at the GM study site shows that the cambium cells of Cryptomeria fortunei begin to expand around April, and the entire lignification process ends around November (Zheng et al 2021). Combined with dendrometer data, we determined that the entire growing season of Cryptomeria fortunei in the study site is approximately from April 6th to November 5th each year, of which June 15th is the dividing line between earlywood and latewood.…”

“…2 and Fig. 7c), the stomata of Cryptomeria fortunei trees would close (Gan et al 2017;Guo et al 2018;Zheng et al 2021), resulting in the decrease of Ci, and finally leading to the increase of iWUE (Tei et al 2014) (Eq. 5).…”