Environmental Factors’ Effects on Stem Radial Variations of Populus euphratica in the Lower Reaches of the Tarim River in Northwestern China

Abstract

Microscopic understanding of tree xylogenesis processes and their relationships with environmental factors is important for tree conservation. To assess the relationship between Euphrates poplar (Populus euphratica) radial growth and environmental factors on short time scales, micro-core samples were collected in the lower Tarim River in northwest China in 2020. We analyzed the intra-annual radial variation in P. euphratica and its relationship with the environment. Our results showed that P. euphratica started to manifest stem radial variations in late April (around DOY (day of year) 114) and stopped displaying stem radial variations in early to mid-September (around DOY255), with an annual stem radial increment of 2620.89 μm and a maximum stem radial variation rate of 22.42 μm/d. The stem radial variation rate was positively correlated with the mean temperature (R2 = 0.55, p < 0.01), the maximum temperature (R2 = 0.45, p < 0.01), the minimum temperature (R2 = 0.49, p < 0.01), the surface temperature (R2 = 0.64, p < 0.01), and the vapor pressure deficit (R2 = 0.49, p < 0.01), and negatively correlated with the mean atmospheric pressure (R2 = 0.41, p < 0.01) and the groundwater depth (R2 = 0.45, p < 0.01). The stem radial variations of P. euphratica are mainly influenced by groundwater during the main growing period, and its stem radial variation rate was positive when the fluctuation range of the groundwater depth was 4.17~5.38 m. Therefore, the stem radial variations of P. euphratica in the lower reaches of the Tarim River are mainly influenced by groundwater, which has a reasonable range of 4.17~5.38 m.