Modelling Higher Plants Gas Exchange in Reduced Gravity Environment
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Long-duration human space missions and the establishment of permanent off-Earth bases (e.g. on the Moon or Mars) is one of the main focuses of today’s space exploration. This poses many severe challenges at the life-support level, which needs to recycle atmosphere, water and waste for crew survival. The European Space Agency (ESA) project Micro-Ecological Life Support System Alternative (MELiSSA) can ensure these functions. It is a closed-loop bio-regenerative life-support system functioning with microorganisms and higher plants and providing a circular cycling of mass, including O2 production, CO2 capture, water recycling and food production. The growth and development of higher plants are strongly influenced by environmental conditions (e.g. gravity, pressure, temperature, relative humidity, partial pressure of O2 or CO2) so bio-regenerative life support systems require a high level of control and management. The goal is to develop a mechanistic physical model of plant growth to predict the effects of microgravity or of a reduced gravity environment (like on Mars or on the Moon) on plant growth at its morphological, physicochemical and biochemical levels. Current existing plant growth models are developed for agronomy and are therefore not adapted for modeling plant growth for applications in life-support systems, which require being able to extrapolate plants behavior for a wide range of environmental conditions. The first mechanistic plant growth model developed in the framework of the MELiSSA project has attempted to address these limitations. Based on this work, a preliminary structure of the model was defined. In this presentation, the addition of gravity as a parameter is addressed, taking into account the altered gas exchanges due to the low or lack of free convection in reduced gravity environments. The influences of forced and free convection are studied according to the levels of gravity and the interdependence of low gravity and ventilation are addressed.