Asynchronous and correlations of radial growth between different lateral meristems in Abies forrestii var. smithii.

Understanding radial growth phenology is crucial in the comprehension of tree physiology and its susceptibility to climate change. Numerous studies have investigated the impacts of radial growth activity in stem meristems and environmental factors on wood formation and tree growth in treeline trees. Nevertheless, studies on the radial growth dynamics of lateral meristems across different tree parts and the variations in their responses to environmental factors are scarce. To test the hypothesis that the radial growth phenology of diverse tree organs is synchronized, three sample strips were set up along an elevational gradient in the Jiaozi Mountain National Nature Reserve, Yunnan Province, China. To clarify the differences in radial growth dynamics between shoots and stems at the cellular level, weekly microcore samples were collected from shoots and stems from 2019-2021. The results indicated that: (1) Radial growth between shoots and stems was asynchronous, with the onset of radial growth of shoots preceding that of stems. (2) The temperature threshold for the onset of radial growth in Abies forrestii var. smithii converges within the range of 3.67-6.61°C, with a mean value of 4.99 ± 0.16°C. (3) The cell development of shoots and stems was more closely related to photoperiod and temperature than to other environmental factors. Our study offers novel insights into the dynamics of the cambium in treeline trees and the results support the apical growth limitation hypothesis.