Having assembled our hydroponics system, it needed to be tested to quantify performance. This involved measuring the light intensity that the LEDs output to determine the lux ranges possible. We also investigated whether it was possible to germinate seeds and grow seedlings in our system.

Introduction

In order to understand the performance of the NH-1, two experiments were conducted. The first experiment was to compare germination rates of seeds placed to germinate in the NH-1 compared to an environment with natural light. This would inform us whether or not the environmental settings within the system were suitable for seed germination. The second experiment was to explore the range of conditions that the system can generate and to assess how these influence plant growth. This was a proof of principle experiment, to determine if different light conditions would generate different phenotypic responses in the plants.

Experiment 1: Germination in the NH-1 vs. natural light

The first experiment was performed to compare germination rate in the NH-1, under controlled and artificial light conditions, to germination rate in natural light conditions (laboratory windowsill). Arabidopsis thaliana seeds were planted at each position in an agar-filled 96-position pipette-tip rack. Two identical racks were prepared, one to be placed in the NH-1, and one to be placed in natural light. Germination percentage was quantified by counting the number of seeds that had germinated after 4-day and 8-day intervals.

The results showed that the percentage germination in the NH-1 after 4 days was over 50 % compared to approximately 25 % in natural light conditions. After 8 days, over 90 % of the seeds had germinated in the NH-1 compared to only 60 % in natural light conditions (Figure 6).

Figure 6. The percentage germination of Arabidopsis thaliana seeds after 4 and 8 days in either the NH-1 or in natural light.

Experiment 2: The effect of light intensity on plant phenotype

For the second experiment, a simple barrier was created by recycling plywood off-cuts from the architecture workshop which had been wrapped in aluminium foil. This provided a reflective divide that could be placed inside the NH-1 allowing us to expose different areas of the hydroponics to varying wavelengths of light by addressing individual LEDs. Figure 3 shows the dividers in use.

Utilising the Arduino's easy-to-adapt design we were able to manipulate this device to display the desired wavelengths at each individual LED. The first four LEDs emitted green light and the remainder emitted purple (separated by a divider), the intensities were measured to be 200, 1700 lux respectively (code can be found here). Eruca sativa seeds were then planted in two agar-filled 96-position pipette-tip racks, one placed in green light (A) and one placed in purple light conditions (B). These were left to germinate for one week before germination success was analysed.

After one week, the seeds were checked for germination (Figure 4) and the height of each seedling was measured (Figure 5). From this, we made several observations: firstly, the results showed that a higher percentage of seeds had germinated from the batch kept in purple light (23 %) compared to those kept in green light (4 %). Secondly, the seedlings that germinated and grew in green light were were much taller than those grown in purple light. Finally, the purple light conditions resulted in more uniform growth amongst seedlings. This demonstrated the ability of the NH-1 to elicit a range of phenotypic responses as a result of different programmed light provision, thus fulfilling its design purpose.

Figure 4. The percentage germination of Eruca sativa seedlings after 1 week in green or purple light.

Figure 5. The mean height of Eruca sativa seedlings after one week in either green or purple light. n=22 and 4 replicates for purple and green light respectively (number of seeds that germinated). Error bars show the standard error of the mean.