Is elevated CO₂ in space really harmful to growth and development? A case study of Chufa (Cyperus esculentus L.) in Lunar Palace-1

CO₂ concentration [CO₂] level in artificial ecosystems such as greenhouse agriculture and space farming can easily exceed 1000 μmol mol⁻¹ (or ppm). In order to understand how the growth and development in crop plants may respond to elevated CO₂, it is necessary to determine if crop leaves in the closed artificial ecosystem have a fully developed photosynthetic apparatus, and whether or not photosynthesis in these leaves is more responsive to elevated CO₂ concentration. To address this issue, we evaluated the response of photosynthetic characteristics, leaf water status and antioxidant capacity of Chufa (Cyperus esculentus L.), which is a sedge-like plant with 1–2 cm small sweet tubers in length, under elevated CO₂ concentrations in an artificial closed ecosystem. The results showed that Chufa plants cultivated in the elevated CO₂ environment from the seedling stage to the maturity stage were characterized by more appropriate chlorophyll content and photosynthetic rate. The photosynthetic rate of Chufa plants in the 1000 and 3000 ppm treatments was no significant difference with that in 500 ppm CO₂ condition both at seedling stage and rapid growth stage. All the treatments had a high relative water content (RWC) about 60% at the maturity stage. However, there was no significant difference in membrane stability index (MSI) at the rapid growth stage. The antioxidase enzymes activities experienced a rise and a drop and reached the peak at the rapid growth stage. Elevated CO₂, especially more than 1000 ppm conditions, may accelerant Chufa plants aging process.