Abstract: As the single dominant tree species in the Tarim River Basin, Populus euphratica plays a significant role in the regional carbon cycle. We employed in situ observation methods to measure the emission rates of greenhouse gases (CH₄, CO₂, and N₂O) in the trunk (at breast height, 130 cm from the base of the tree) in a natural Populus euphratica forest in the middle reaches of the Tarim River. The aim is to investigate the characteristics of CH₄, CO₂, and N₂O emission fluxes from the tree trunk at different distances from the riverbank and to identify the potential influencing factors. The results showed that CH₄ and CO₂ emission fluxes from the trunks were significantly influenced by sampling site and temperature period (P<0.05). CH₄ and CO₂ emissions during the low-temperature period (05:00-08:00) were greater than those during the high-temperature period (16:00-19:00). In contrast, N₂O flux was relatively stable. The fluxes of CH₄, CO₂, and N₂O during the low-temperature period were within the ranges of 0.0583-0.6042, 35.944-127.521, and 0.020-0.058 μg·m^-2·h^-1, respectively. During the high-temperature period, the emission fluxes for CH₄, CO₂, and N₂O were 0.0542-0.6085, 33.968-101.344, and 0.019-0.102 μg·m^-2·h^-1, respectively. CO₂ fluxes showed a statistically significant positive correlation with air temperature during the high-temperature period. CO₂ and CH₄ emission fluxes were mainly positively regulated by core moisture content and core density, particularly more significant during high-temperature periods (AM: P<0.01; PM: P<0.001). Wind speed exerted a significant and negative impact on CO₂ emissions (P<0.001), while N₂O emissions were not affected by growth and meteorological factors. The emissions of CH₄, CO₂, and N₂O from trunk showed nonlinear relationships with soil moisture. CH₄ and CO₂ fluxes initially decreased and then increased with increasing soil moisture, whereas the N₂O emission fluxes displayed an opposite trend. In general, greenhouse gas emissions from Populus euphratica trunks varied significantly among individual trees. CH₄ and CO₂ fluxes showed large fluctuations that were closely associated with soil moisture and plant growth indicators. In contrast, N₂O fluxes exhibited minimal variation and were insensitive to environmental factors.

Key words: Populus euphratica, emission flux, tree trunk, Tarim River, greenhouse gas