Technical note: A low-cost, automatic soil-plant-atmosphere enclosure system to investigate CO₂ and ET flux dynamics

Abstract. Investigating greenhouse gases (GHG) and water flux dynamics within the soil-plant-atmosphere-interphase is a key for understanding ecosystem functioning, as these dynamics reflect the ecosystem's responses to environmental changes. Understanding these responses is hence essential for developing sustainable agriculture systems that can help to adapt to global challenges such as inter-alia increased drought. Typically, an initial understanding of GHG and water flux dynamics is gained through laboratory or greenhouse pot experiments, where gas exchange is often measured using commercially available, manual closed (leaf) chamber systems. However, these systems are usually rather expensive and often labor-intensive, thus limiting the number of different treatments that can be studied and their repetitions. Here, we present a fully automatic, low cost (<1.000 Euro), multi-chamber system based on Arduino, termed “greenhouse coffins”. It is designed to continuously measure canopy CO₂ and evapotranspiration (ET) fluxes. And it can operate in two modes: an independent and a dependent measurement mode. The independent measurement mode utilizes low cost NDIR CO₂ (K30 FR) and relative humidity (SHT31) sensors, thus making each “greenhouse coffin” a fully independent measurement device. The dependent measurement mode connects multiple “greenhouse coffins” via a low cost multiplexer (< 250 Euro) to a single infrared gas analyzer (LI-850, LI-COR Inc., Lincoln, USA), allowing for measurements in series, achieving cost efficiency, while also gaining more flexibility in terms of target GHG fluxes (potential extension to N₂O, CH₄, stable isotopes). In both modes, CO₂ and ET fluxes are determined through the respective concentration increase during closure time. We tested both modes and demonstrated that the presented system is able to deliver precise and accurate CO₂ and ET flux measurements using low cost sensors, with an emphasis on calibrating the sensors to improve measurement precision. Through connecting multiple greenhouse coffins via our low cost Multiplexer to a single infrared gas analyzer in the dependent mode, we could show moreover that the system can efficiently measure CO₂ and ET fluxes in a high temporal resolution across various treatments with both labor and cost efficiency. Therefore, the developed system offers a valuable tool for conducting greenhouse experiments, enabling comprehensive testing of plant-soil dynamic responses to various treatments and conditions.