Gioia D. Massa

Temperature affects long-term productivity and quality attributes of day-neutral strawberry for a space life-support system

Strawberry (Fragaria x ananassa L.) is a promising candidate crop for space life-support systems with desirable sensory quality and health attributes. Day-neutral cultivars such as Seascape are adaptable to a range of photoperiods, including short days that would save considerable energy for crop lighting without reductions in productivity or yield. Since photoperiod and temperature interact to affect strawberry growth and development, several diurnal temperature regimes were tested under a short photoperiod of 10 h per day for effects on yield and quality attributes of Seascape strawberry during production cycles longer than 270 days. The coolest day/night temperature regime, 16°/8u2009°C, tended to produce smaller numbers of larger fruit than did the intermediate temperature range of 18°/10u2009°C or the warmest regime, 20°/12u2009°C, both of which produced similar larger numbers of smaller fruit. The intermediate temperature regime produced the highest total fresh mass of berries over an entire production cycle. Independent experiments examined either organoleptic or physicochemical quality attributes. Organoleptic evaluation indicated that fruit grown under the coolest temperature regime tended to score the highest for both hedonic preference and descriptive evaluation of sensory attributes related to sweetness, texture, aftertaste, and overall approval. The physicochemical quality attributes Brix, pH, and sugar/acid ratio were highest for fruits harvested from the coolest temperature regime and lower for those from the warmer temperature regimes. The cool-regime fruits also were lowest in titratable acidity. The yield parameters fruit number and size oscillated over the course of a production cycle, with a gradual decline in fruit size under all three temperature regimes. Brix and titratable acidity both decreased over time for all three temperature treatments, but sugar/acid ratio remained highest for the cool temperature regime over the entire production period. Periodic rejuvenation or replacement of strawberry propagules may be needed to maintain both quality and quantity of strawberry yield in space.

A strategic approach for investigating light recipes for ‘Outredgeous’ red romaine lettuce using white and monochromatic LEDs

To optimize crop production/quality in space, we studied various light recipes that could be used in the Advanced Plant Habitat currently aboard the International Space Station (ISS). Lettuce (Lactuca sativa cv. Outredgeous) plants were grown for 28 days under seven treatments of white (W) LEDs (control), red (635u202fnm) and blue (460u202fnm) (RB) LEDs, Wu202f+u202fblue (B) LEDs, Wu202f+u202fgreen (520u202fnm) (G) LEDs, Wu202f+u202fred (R) LEDs, Wu202f+u202ffar red (745u202fnm) (FR) LEDs, and RGBu202f+u202fFR LEDs with ratios similar to natural sunlight. Total PAR was maintained near 180u202fµmolu202fm-2u202fs-1 with an 18u202fh photoperiod. Lettuce grown under RGBu202f+u202fFR produced the greatest leaf expansion and overall shoot biomass, while leaves from WB and RB showed the highest levels of pigmentation, secondary metabolites, and elemental nutrients. All other supplemental treatments had varying impacts on morphology that were dependent on crop age. The WG treatment increased fresh mass early in the cycle, while WR increased biomass later in the cycle. The plants grown under WFR exhibited elongation of petioles, lower nutrient content, and similar shoot biomass to the W control. The findings suggest that supplementing a broad spectrum, white light background with discrete wavelengths can be used to manipulate total yield, morphology, and levels of phytonutrients in lettuce at various times during the crop cycle.

Modeling and Control of the pH Neutralization Process for a Recirculating Hydroponic Growth Chamber

In this paper, a pH control system for an experimental recirculating hydroponic growth chamber for the NASA Mars exploration program has been modeled and implemented. The resulting model has a bilinear Weiner type structure. A novel approximation approach is presented to obtain a simplified plant model controller design. Perturbation analysis validates the applicability of the approximation for the specific pH control of a closed-loop hydroponic growth chamber. A modified PI controller that takes into account on-off nature of the solenoid valve actuator was designed to control the pH level. The closed-loop system is shown to be BIBO stable with respect to the original bilinear plant model. Experimental results for reference tracking and disturbance rejection in an operational hydroponic chamber with growing plants have demonstrated the effectiveness of the proposed approach.Copyright