Intra-annual radial growth of Quercus acutissma and its response to hydrometeorological factors in the Nandadish experimental catchment, eastern China

Abstract

Investigating the relationship between tree growth within a year and environmental factors is crucial for understanding how climate change affects seasonal tree growth patterns. In this study, high-resolution point dendrometers were used to monitor the stem radial changes of Oak trees (Quercus acutissma) over two years (2020 and 2021) in the eastern subtropical monsoon region of China. We find that the main growth period of Oak trees spans from March to September, and air temperature significantly affects the growth onset of Oak trees but with no clear impact on their growth cessation. The observations show that precipitation substantially affects daily stem radial increment (SRI), but the frequency of precipitation days plays a more crucial role in enhancing seasonal growth than the total precipitation amount. In the growing season, the stem radius of the Oak trees shows obvious diurnal cycles with shrinkage during the day and expansion at night, reflecting a delicate balance between canopy water loss and soil water absorption. The diurnal variations of the stem radius during the cold period (January and December) show an opposite pattern to that of the growing season, due to the sap's freezing under the condition of low air temperature at night as well as no or weak transpiration in the daytime. Because the temporal dynamics and intensity of tree activities significantly affect the timing and mechanisms of carbon assimilation in terrestrial ecosystems, our results are helpful to evaluate the carbon sequestration capacity of subtropical forests under the global climate change.