Dynamics of water-carbon fluxes and water use efficiency in jujube orchards in arid regions

[Objective] Understanding the dynamics of water and carbon fluxes, as well as water use efficiency (WUE) in ecosystems is crucial for optimizing crop yield and improving resource management. This paper experimentally investigated the seasonal dynamics of these processes in jujube orchards located in arid regions in Northwestern China. [Method] Water and carbon fluxes in a jujube orchard were continuously measured during 2018 and 2019 using the eddy covariance technique. The net ecosystem carbon flux (NEE) measured in the experiment was partitioned into ecosystem respiration (Reco) and gross primary productivity (GPP) using the REddyProc package in R. Seasonal variations in water and carbon fluxes, along with WUE, were analysed based on these data. [Result] ① Evapotranspiration showed minimal variation during the dormant period but fluctuated significantly during the reproductive period, with annual total being 657.64 mm/a in 2018 and 677.40 mm/a in 2019. ② Seasonal trends were evident in half-hourly and daily variations in carbon flux components (NEE, GPP, and Reco), remaining stable during dormancy but changing markedly during the growing season. Annually, the orchard acted as a carbon sink, with total NEE being -582.4 and -494.96 g/(m2·a) in 2018 and 2019, respectively. ③ The annual WUE was 2.08 and 1.92 g/kg in 2018 and 2019, respectively, fluctuating during the growing season. It was comparable to the WUE of the forest ecosystems in warm temperate and semi-arid regions but exceeded the WUE of wheat farmland ecosystems. [Conclusion] The seasonal variation in carbon flux in jujube orchards in arid regions is influenced by air temperature, solar radiation, precipitation, irrigation, and crop growth. Annually, the orchard acted as a carbon sink, although it emitted more carbon than it sequestered during non-growing seasons. These findings underscore the importance of managing water and carbon fluxes to improve water use efficiency and productivity of jujube orchards in arid regions.