Purpose

It has been well reported in many studies globally that the increased atmospheric carbon dioxide (CO₂) concentration has positively influenced plant growth in the past century. However, it is crucial to understand how long the tree growth trend will remain alongside the rising CO₂ concentration before it is tipped over.

Methods

In this study, we focused on studying the long-term tree growth responses to the rising CO₂ concentration, in combination with other environmental factors, and its feedback to the changing climate. This study has reported two tree species, Pseudolarix amabilis (P. amabilis) and Cryptomeria japonica (C. japonica), sampled from a subtropical monsoon forest located in eastern China, and established the long-term tree ring chronologies by applying tree ring width measurement and cross dating, and then, basal area increment (BAI) was calculated. Meanwhile, intrinsic water-use efficiency (iWUE) was calculated through the measurement of carbon isotope composition (δ¹³C) in tree ring samples, and its relationships with BAI and atmospheric CO₂ concentration were also quantified.

Results

BAI values continuously increased in both P. amabilis and C. japonica with the rising of CO₂ concentration until the atmospheric CO₂ concentration tipping points were reached, after which tree growth started to decline with the rising CO₂, while iWUE exerted a continuous increase trend with the increasing CO₂ concentration.

Conclusions

Tree growth of both species was more photosynthesis driven before reaching the maximum BAI points, once the tipping points of atmospheric CO₂ were passed, leading to the positive feed of forest carbon cycling to climate change and global warming. Therefore, tree growth was more water limitation driven in the last 20 years.