After assembling our hydroponics system we needed to measure the light intensity that the LEDs output. This gave us a bearing on the probability of successful germination. For example, an overcast day in lux is between 1,000 - 30,000 [1]. Therefore a lux sensor will give us a starting point. From this, we can then begin to experiment with different colours of light. Through our Human Practices we expected that purple light would give us the most lux since this is the most commonly used in the industry.

Introduction

In order to understand the performance of the NH-1, two experiments were conducted. The first experiment was conducted to determine the range of conditions that the system can generate. This was a proof of principle experiment, which is meant to outline that different conditions can generate different phenotypic responses in the plants. The second experiment measured the percentage germination from the optimal purple light conditions of the NH-1 against natural light conditions.

Method

For the first experiment we had to make a simple barrier to place inside the NH-1 in order to block light effectively. We did this by taking off-cuts of plywood and wrapping them in tinfoil to create a reflective surface, sourced from the architecture workshop. Figure 3 shows the dividers used. This allowed us to expose different areas of the hydroponics to varying wavelengths of light by addressing individual LEDs.

Utilising the Arduino's easy-to-adapt design we can 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 pipette-tip racks (96 in each), one green (A), one purple (B). They were then left to germinate for a week.

Figure 3. Demonstration of divider being used within the hydroponic system.

Results

After 1 week the seedlings were checked for germination (Figure 4) and had their height measured (Figure 5). The results show that a greater percentage germination was obtained from purple light (22/96) than green light (4/96). Out of the 4 seedlings that germinated in green light, the seedlings were much taller than those in the purple light, though those grown in purple light were more uniform in their growth, showing the ability of the NH-1 to elicit a range of phenotypic responses and 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 1 week in either green or purple light. Error bars show the standard error of the mean.

Figure 6. The percentage germination of Arabidopsis thaliana seedlings after 1 week in the NH-1 or on the laboratory windowsill.

The second experiment concerned comparing the NH-1 to laboratory conditions. The results show the percentage germination in NH-1 after conditions after 4 days was over 50 % compared to approximately 25 % in laboratory conditions. After 8 days over 90% of the seedlings had germinated in the NH-1 compared to approximately 60 % in laboratory conditions (Figure 6).

Conclusions

Both of the experiments provided data that suggests our system is effective at creating a high throughput growth and germination environment for plant research, not only did Arabidopsis thaliana seeds germinate in the NH-1, but the rate of germination is greater than that of laboratory conditions with the added advantages of being programmable and a controlled environment allowing greater standardisation. Within the system we were able to create a range of growing environments that elicited different phenotypic responses in Eruca sativa seedlings showing the range of possibilities the NH-1 provides for researchers interested in high-throughput plant research.

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