Net ecosystem exchange of Pinus sylvestris var. mongolica plantation in the western Liaoning Province, China

Abstract

Pinus sylvestris var. mongolica is one of the important tree species for afforestation in Three-North Regions of China. Investigating net ecosystem exchange (NEE) and its influencing factors is of significance in understanding carbon balance of P. sylvestris var. mongolica plantation . We used the eddy covariance system and its supporting instruments to measure NEE and environmental factors of P. sylvestris var. mongolica plantation in the western Liaoning Province in 2020. The results showed that, at the half-hour scale, plantation emitted carbon during nighttime and sequestrated carbon over daytime. Carbon sequestration was inhibited by drought stress in the afternoon from May to August. At the daily scale, seasonal dynamics of nighttime NEE were mainly controlled by soil temperature and moisture, while that of daytime NEE were mainly controlled by soil moisture and vapor pressure deficit due to drought stress. When soil was dry, precipitation promoted nighttime and daytime NEE and improved photosynthetic and respiration parameters. At the month scale, there was significant negative linear relationship of daytime NEE with ecosystem apparent quantum yield and ecosystem maximum photosynthetic capacity. When air temperature was lower than 5 ℃, ecosystem respiration rate at 10 ℃ and temperature sensitivity of ecosystem respiration increased linearly with decreasing air temperature. The cumulative NEE of P. sylvestris var. mongolica plantation was -145.17 g C·m-2, indicating a weak carbon sink in 2020.