Variation in carbon flux and its response to environmental factors in schrenk spruce forests on the northern slopes of the central Tianshan Mountains

The Tianshan Mountains serve as a crucial ecological security barrier and carbon sequestration reservoir in western China. The forests in this area are dominated by Picea schrenkiana, which plays a key role in regional carbon storage and cycling and is thus a significant factor for the carbon balance in this region. To elucidate the variation in carbon flux in the Tianshan forest ecosystem as well as the influencing factors, we conducted continuous carbon flux measurements from 2023 to 2024 at the national positioning observation and research station of the Xinjiang Tianshan forest ecosystem using the eddy covariance technique. The key findings are as follows: (1) the P. schrenkiana forests on the northern slopes of the central Tianshan Mountains functioned as a net carbon sink, with an annual carbon sequestration rate of 635.633 μmol·m-2. The diurnal variation in CO2 flux exhibited a U-shaped pattern, ranging from -36.82 to 13.02 μmol·m-2·s-1. (2) The flux footprint was predominantly concentrated between the northwestern and southwestern sectors, aligning with the prevailing wind direction and vegetation-covered area, indicating that the spatial flux distribution is co-regulated by both biological and meteorological factors. (3) Temperature was the key environmental factor regulating the carbon source/sink dynamics of this system. At the monthly scale, net ecosystem exchange (NEE) was primarily controlled by air temperature and photosynthetically active radiation. In contrast, at the diurnal scale, soil temperature governed NEE dynamics by regulating the diurnal rhythm of ecosystem respiration. This study provides critical information for accurately assessing the carbon sink capacity of the P. schrenkiana-dominated forest ecosystem in the Tianshan Mountains.