1. Seeds need water to germinate, since absorption of water is involved in the activation of different biological mechanisms that promote germination.
1.1. Water stress and drought do have a role to play in the percent germination of seeds. Although some seeds are more resistant to water stress, many are not. Under conditions of water stress across the seeds types here, there was a reduction in germination percentage as water stress increased. Some seed species were still able to have some seeds germinate under lots of water stress, other plant species were unable to at all. (Sevik, Cetin 2014).
1.2. "Water is a prerequisite for seed germination since seeds must absorb a certain amount of water to germinate. A seed germination bed, as a place to obtain water, definitively affects seed germination by controlling the water content; if there is too little water, the seeds will not germinate without reaching the minimum water requirement; however, when there is too much water, factors such as hypoxia will reduce the germination rate" (Jiang, Su 2018).
1.2.1. Prediction: We predict that too little water (0mL) and too much water (3mL) will decrease the percent germination, and that 1 mL of water will promote the highest percent germination.
1.2.1.1. Experiment: With all other factors kept constant, seeds will be given either 0 mL, 1 mL, 2mL, or 3mL of tap water at the start of the experiment. Measure the percent of germination after 48 hours.
1.3. Sesame seeds are a drought tolerant crop but very sensitive to drought during seed germination. 5 sesame cultivars and 4 levels of drought were experimented. They measured percent germination and shoot length and they all decreased as water stress increased. (Bahrami, Jafari, Razmjoo 2008).
1.4. Effects of water potential wereon germination were studied in six provenances of Pinus brutia from different bioclimatic zones in Turkey. As water levels decreased, so did germination percentage and rate of germination. (BOYDAK, DIRIK 2002(.
2. Why do Different Volumes (mL) of H2O effect Seed Germination?
3. Why do Different Concentrations of Salt effect Seed Germination?
3.1. Seeds have a high water capacity and due to basic laws of biology and chemistry, the interior environment of the seed can be easily affected through the osmosis of water.
3.1.1. Prediction: We predict that adding 0.1 M NaCl, 0.5 M NaCl, and 1.0 NaCl solutions to our seeds will show a decreased germination percentage compared to using regular tap water for our seeds.
3.1.1.1. Experiment: With all other factors kept constant, seeds will be given 1 mL of either 0.1 M NaCl, 0.5 M NaCl, 1.0 M NaCl, or tap water (control treatment) at the start of the experiment. Measure percent germination after 48 hours.
3.1.2. Salt stress affects the seed germination and seedling establishment through osmotic stress, ion toxicity, and oxidative stress. Salinity may adversely influence seed germination by decreasing the amounts of seed germination stimulants such as GAs, enhancing ABA amounts, and altering membrane permeability and water behavior in the seed.(Uçarlı 2020)
3.1.3. In general, high soil salinity inhibits seed germination due to the low osmotic potential created around the seed, which prevents water uptake (Welbaum et al., 1990).
3.1.4. The effects of salinity on crops are multiple, such as the reduction of growth due to high osmotic potential and ion toxicity, photosynthesis inhibition by decreased CO2 availability and pigment content, diminished nutrient and water uptake, and root damage; all of these phenomena eventually result in yield reduction. One of the crop growth stages most affected by salinity is seed germination, a phase in which plants are generally quite sensitive to salt stress. Moderate levels of salinity cause an increase of abscisic acid (ABA) production, which is known to induce or maintain seed dormancy, which results in a reduction in the germination level and a delay in germination time, especially inhalophyte species. High rates of salinity are also responsible for stronger hormonal alterations and other effects, such as the reduction in water uptake and cell damage that reduce the embryo viability and hamper the germination in sensitive species, or postpone the start of germination in tolerant species. (Fogliatto et al. 2019)
3.1.5. Salt stress decreases growth in most plants, including halophytes (Kaymakanova 2014)
4. Why do Different Intensities of light effect Seed Germination?
4.1. Seeds respond to external factors to determine the optimal time for growth. Too much light or too little light may indicate an unideal seasonal period for growth as it may reflect nutrient availability/water supply in the environment.
4.1.1. It has been found that for the Shorea wantianshuea seed, under no shading (100% light exposure), as well as complete shading, germination was delayed. Germination was accelerated under medium amounts of shade (55.4% natural light) (Bao, 2007).
4.1.2. Positive photoblastic seeds germinate after minimal exposure to light, negative photoblastic seeds germinate in the dark only, and light-neutral seeds germinate under both dark/light conditions (Merai, 2019).
4.1.3. Light is detected by phytochrome's, a type of photoreceptor that regulates hormonal levels like that of Gibberellic acid and abscisic acid. Gibberellic acid induces germination, and abscisic acid promotes seed dormancy, so the levels of these hormones in relation to one another determines the fate of the seed (Merai, 2019)
4.1.4. Light plays a key role in regulating seed germination as it gives vital information such as how deep the seed is in the soil, the presence of competition, and the seasonal period. The amount of light that is optimal for growth of a plant changes based on the habitat, so there is not a specific amount of light that is ideal for germination across all seeds (Merai, 2019).
4.1.5. It has been found that for seeds of C. odorata, 150 lux promoted the greatest success of seed germination (68 %), and light intensity higher than 1500 lux had an inhibitory effect on germination (Ambika, 2006)
4.1.5.1. Prediction: We predict that light intensity of 150-200 lux will promote the highest percent germination, and too much light (>1500 lux) or too little light (<50 lux) will lower the percent germination.
4.1.5.1.1. Experiment: With all other factors kept constant, grow seeds under light intensities of 50 lux, 150 lux, 1500 lux, or 2500 lux. Measure percent germination after 48 hours.
5. Why do Different Wavelengths of light effect Seed Germination?
5.1. Plants do not absorb green light-> green light is poorly absorbed by chlorophyll (it reflects it) -> chlorophyll is involved in photosynthesis -> basis of plants source of energy
5.1.1. Cowpea seeds show maximum germination rate under red light (98%) followed by natural light (95%), then blue light (71%) then yellow light (56%) , after 84 hour period. No germination found under green light (Lal, 2017.)
5.2. EM spectrum of visible light has a predicted and tested effect, as well as UV light:
5.2.1. Stem growth of B. rapa has been found to be longest under green LED, followed by UV, then blue LED, white LED, then least with infrared light. (Maiza, 2019).
5.2.2. A. thaliana has been found to have more germination growth in black light, then clear (unknown wavelength), then green (520 nm), and least by blue (420 nm). (Clipsham, 2014).
5.2.2.1. Prediction: We predict that under red light (wavelength= 700 nm) we will have the highest percent germination while under green light (wavelength= 550 nm) we will have the lowest percent germination.
5.2.2.1.1. Experiment: With all other factors kept constant, grow seeds under either red light, green light, blue light, or white light (control treatment). Measure percent germination after 48 hours.
5.3. duration of exposure to different wavelengths effects germination rate
5.3.1. rate of germination of cowpea seeds under natural light is much FASTER than other wavelengths (Lal, 2017).