Physiological processes in Phalaenopsis pulcherrima cultivated in hermetically sealed vessels

The hermetic condition is the least studied factor associated with the spaceflights. Phalaenopsis pulcherrima is promising for space farming as it can be cultivated in small substrate blocks, and its photosynthetic apparatus is well adapted to elevated CO2 concentrations and temperatures. Three-year-old meristematic P. pulcherrima plants were planted into plastic (acrylic) vessels filled with fibrous substrate. In control, vessels had an open top. The hermetic conditions were reached by sealing the vessels’ covers with a parafilm. Both control and hermetic vessels were placed in a plant growth chamber where test plants were cultivated under controlled conditions of air temperature, illumination, air humidity, and soil moisture. After 6 and 24 months of cultivation, the CO2 concentration in the hermetic and control vessels was measured, and the physiological characteristics of each test plant, such as the content of macro- and micronutrients, photosynthetic pigments, free amino acids, and content of labile carbohydrates (%) in the leaves of the test-plants were determined. It was revealed that cultivation of P. pulcherrima in hermetic conditions affected its basic physiological processes such as photosynthesis, mineral nutrition, carbohydrates, and amino acid metabolisms. The effect size of this stress factor depended on the duration of exposition period. Long-term cultivation of P. pulcherrima under hermetic conditions promoted the accumulation of nonenzymatic antioxidants (viz. chlorophyll b, carotenoids, and amino acids), which contributed to the adaptation of this orchid species to oxidative stress caused by hermetic environment.