BLT in a Bottle A BioBottle Exploration. Chloe Robitaille, Elli Wollenweber PLS 321X, University of Rhode Island. INTRODUCTION. RESEARCH QUESTIONS. RESULTS. DISCUSSION.
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A BioBottle Exploration
Chloe Robitaille, Elli Wollenweber
PLS 321X, University of Rhode Island
Our group decided to explore how hydroponic growing methods could be used in the closed ecosystem of a BioBottle, or on a larger scale in a Biosphere II situation. We chose to use common food crops like lettuce and tomato because these would be the types of plants grown for human consumption in Biosphere II. In closed ecosystems, proper nutrient levels, specifically N, P, and K are crucial to plant health. We designed our experiment to explore how excess levels of nutrients, specifically N, would affect the growth of lettuce and tomato seedlings. We took a “minimalist” approach to bottle design in order to mitigate the effects of confounding variables, such as soil organisms or plant pests. This approach could be used in a classroom setting to model the scientific method to students. In addition, this experimental design aligns with the Rhode Island Grade Span Expectation for Life Science “LS2 (9-11)-3 Students demonstrate an understanding of equilibrium in an ecosystem by describing ways in which humans can modify ecosystems and describe and predict the potential impact (e.g. human population growth; technology; destruction of habitats; agriculture; pollution; and atmospheric changes).”
-Based on the seedling deaths and overall decline in plant health that occurred after the addition of excess nutrients to the experimental bottles, we have concluded that high levels of N, P, and K would kill food crops in a closed ecosystem. These conclusions are supported by the fact that seedling deaths were more pronounced in bottle D. It is likely that N levels in the experimental bottles were so high that they became toxic to the seedlings. The cloudiness in bottle D may have resulted from a microbial bloom due to all of the available nutrients. This bloom may have also negatively impacted seedling health.
-Due to the success of the seedlings in bottle A, it is feasible that lettuce and tomato crops could be grown hydroponically under Biosphere II conditions (i.e. in a closed ecosystem).
-While lettuce seeds germinated more readily inside the closed bottles, the tomato seedlings lasted longer after the addition of the excess nutrients. Because of their longer persistence against toxic levels of nutrients, we would consider tomatoes “heartier” for growth at adverse nutrient levels.
-What is the effect of over-fertilization on common vegetables?
-Would hydroponically grown vegetables be feasible to cultivate in Biosphere II?
-Will lettuce or tomatoes prove to be heartier in a closed ecosystem?
Chart 1. Average Lettuce Height Over Time (in cm).
METHODS AND MATERIALS
-All bottles (A,B,C, and D) follow the construction and planting scheme pictured in Figure 1. Bottle parts come from rinsed 2L soda bottles.
-each bottle contains: one 5.7cm straw vent (sealed with tape), 1 ¾ cups play sand (saturated with baseline nutrient solution then allowed to drain), one 65cm cotton wick buried in the sand and reaching the nutrient water chamber (threaded through a hole in the bottle cap), 600mL of nutrient solution (0.5g of Miracle Gro per liter of de-ionized water), and 3 seeds of each type of plant
-straw hole is sealed with hot glue and bottle junctures are sealed with tape
-4 bottles used: A (control) and B, C, D with various amounts of excess Miracle Gro added after germination
-on 4/2/13 0.3g of Miracle Gro was added to water chamber of B, 0.6g to C and 1.2g to D
-kept in the same room under constant light and temperature (~25C) conditions between bottles
-rotated every few days to negate + phototropism
-Bottles were observed prior to the addition of excess nutrients to ensure germination occurred. After the addition, plants were assessed for overall health and approximate measurements of their growth were taken.
Chart 2. Average Tomato Height Over Time (in cm).
Figure 4. Bottles at the Conclusion of the Experiment.
-In the above graphs, “average height” refers to the mean height of the seeds that showed germination prior to the addition of excess nutrients on 4/2/13
-Prior to the addition of excess nutrients the following number of seeds germinated in each bottle: 3 lettuce and 3 tomato in A, 3 lettuce and 2 tomato in B, 4 lettuce and 2 tomato in C, and 3 lettuce and 2 tomato in D.
-by 4/5/13 all plants were “leggy” so we opened the straw vents to allow in CO₂ and reduce condensation
-by 3 days after the addition of excess nutrients, lettuce seedlings in all experimental bottles were suffering, with one specimen in bottle D completely disintegrated
-by 7 days after the addition, lettuce in all experimental bottles is dead and tomato plants begin to suffer, with one in D already dead and the others in C and D beginning to die
-on 4/9/13 a cloudiness in the nutrient water chamber of D is observed
-by 4/15/13 the tomatoes in B are falling over and slightly pale, the tomatoes in C appear to be rotting, and one tomato in D is still alive and very pale
-by 4/15/13 all germinated seeds in A remain alive and appear to be growing
Based on the findings of this experiment, we would recommend hydroponically cultivating lettuce and tomatoes within closed ecosystems at concentrations of 100mg each of N, P and K per liter of water. At higher levels of nutrients, we would recommend growing tomatoes over lettuce, due to their better performance under adverse conditions. For more information on our experimental design process, materials and methods and more detailed observations of our results, see our experimental log.
Figure 1. Building and Planting Methods.
Figure 3. Bottles Prior to Excess Nutrient Addition.
Figure 2. Lettuce and Tomato Seeds Used.