Exploring nitrogen regulation of plant transpiration in preparation for future space missions

MSc-thesis abstract (submitted 28 August 2017): Increased understanding of how plants respond to fertilization might be utilized in plant space research to overcome reduced transpiration imposed by reduced gravity. It has been suggested that plant fertilization with low or restricted nitrogen, causing nitrogen limitation but not deficiency, may induce increased stomatal conductance and transpiration.

In this research, the effect of nitrogen availability, in particular nitrate, on the regulation of plant water uptake, transpiration and stomatal conductance in hydroponically grown lettuce plants (Lactuca sativa, cv. Cecilia RZ butterhead) was studied.
Nutrient solutions containing nitrate levels of: 0, 1.25, 5, 10, 20 and 30 mM were supplied to the plants and stomatal conductance and transpiration were measured during light and dark conditions. Plant biomass accumulation and morphology were measured after harvest.

In light, no effect of nitrogen concentration on stomatal conductance and transpiration was observed. In dark, increased nitrate level reduced both stomatal conductance and transpiration. No effect of nitrate was observed on plant growth except for root length, root fresh weight and the 0 mM nitrate treatment.
Thus, in water culture with roots directly submerged in the nutrient solution, plants seem to be able to grow vigorously for one week even at very low N concentrations.

Key-words: stomatal conductance, transpiration, nitrate, NO3, hydroponics, space missions, plants, fertilization