Variability of turbulent carbon dioxide flux netto at different time scales in an apple orchard ecosystem in Central Poland

The impact of increasing CO₂ on global temperature and strengthening of the greenhouse effect makes the measurements of gas exchange between the Earth’s surface and the atmosphere particularly important. Observational data on greenhouse gases exchange between different types of ecosystem and the atmosphere are crucial in thorough understanding the global climate mechanisms. Fruit tree ecosystems constitute an important kind of land use in Central Europe and apple is very extensively cultivated fruit tree crop in the world. Because intensively used apple orchards have a potential for carbon (C) sequestration and to be an important sink of atmospheric CO₂ the continuous measurements of processes of ecosystem-atmosphere exchange are necessary for properly determining of global carbon (C) budget.

This work presents the results of continuous closed-path EC measurements of carbon dioxide (CO₂) fluxes in the apple orchard located near Grójec in the Masovian voivodeship on the largest orchard area in Poland. These are the results of the first and the only measurements of the net CO₂ fluxes (started in February 2023) carried out in the apple orchard ecosystem in Poland. The main goal of the work is to present variations of CO₂ flux at different time scales at different stages of fruit tree growth and during different climatic conditions. The turbulent fluxes of CO₂ were calculated on a 30-min basis. The raw data were computed using the EddyPro -7.0.9 software taking into account the necessary corrections and procedures to correct the obtained results. CO₂ fluxes were characterized by clear daily variability with negative values during the day (CO₂ uptake in the photosynthesis process) and positive at night (CO₂ release in plants respiration processes). The most intensive CO₂ absorption took place between May and September (phases of flowering and fruit development and ripening) the with a maximum in June. Negative 30 min mean CO₂ flux value reached for this month was around 12 µmol ּ m^-2 ּ s^-1 around noon. In the remaining months the CO₂ absorption processes were lower and ranged around a few µmol ּ m^-2 ּ s^-1.