Environmental and biotic controls on the interannual variations in CO2 fluxes of a continental monsoon temperate forest

Abstract

The interannual variability (IAV) of CO2 fluxes of temperate forests in continental East Asia was rarely explored via direct measurements. To explore the IAV of net ecosystem exchange of CO2 (NEE) and its driving factors, we continuously measured the CO2 fluxes of a temperate deciduous broadleaved forest at the Maoershan site, northeast China with a continental monsoon climate, by eddy covariance over 11 years (2008 – 2018). The means of NEE, gross primary production (GPP), and ecosystem respiration (Re) were −157 ± 64 (mean ± standard deviation), 1356 ± 148, and 1200 ± 138 g C m−2 yr−1, respectively. For annual fluxes, the IAV of NEE was jointly controlled by the length of net CO2 uptake period and the summer peak of net CO2 uptake, whereas those of GPP and Re were predominated by the summer peaks (GPPmax and Remax). Meanwhile, the dominant role of GPPmax on the IAV of GPP was attributed to the leaf-level photosynthetic capacity rather than the maximum leaf area index. However, the environmental factors showed weak impacts on NEE, largely because of the offset between the positive responses of GPP and Re to the spring and autumn soil water content, respectively. For particular seasons, phenology was the dominant biotic driver of the spring and autumn NEE, whereas spring precipitation and autumn photosynthetically active radiation were the main environmental drivers of the spring and autumn NEE, respectively. Overall, this work filled the gap of the relatively long-term CO2 fluxes measured in the temperate forests of continental East Asia. Taking the influences of ecosystem- and leaf-level physiology, canopy structure, and phenology, together with their environmental interactions, on the CO2 fluxes into account will improve the understanding and prediction of the forest carbon dynanics.