Michael French Alex Visconti and Michelle Mendez

Comparison of percent germination, size, and CO2 production in arugula plants affected and unaffected by fire, as well as with and without mycorrhizae assisted growth

Michael French Alex Visconti and Michelle Mendez

Department of Biological Science

Saddleback College

Mission Viejo, CA 92692

Introduction

Around the world, and especially in southern California, forest fires are a near constant concern for any species growing in the wild. The rate of secondary succession for a plant species is an important factor for the species’ overall survival chances in areas with a high fire risk because if the plants are unable to grow back effectively, they will be swiftly replaced by a species that can. One of the most prevalent methods of gaining a proverbial leg up in terms of growth rate, is the formation of mutualistic relationships with mycorrhizae, a type of fungus that ineracts with plant roots, present in the surrounding soil (Callaway 1995). These relationships between plants and mycorrhizal fungi form commonly in plant roots as a way of more effectively providing both with a greater amount of nutrients. The mycorrhizae are supplied with a constant supply of carbohydrates to be ingested, while the plant roots use the comparatively greater surface area of the fungi’s mycelia to increase their water and mineral absorption from the soil (Harrison 2005).

Fire has been shown to increase the amount of certain raw nutrient factors present in soil such as nitrogen and phosphorous (Ahlgren 1974). If the soil was sterilized by a fire and the microorganisms living within it were eliminated, simply having a greater amount of the nutrient factors may not

increase their availability, since mycorrhizae facilitate the absorption of

nitrogen and phosphate ions, and the burnt soil has a tendency to not be able

to retain as much water as its unburnt counterpart (Alghren 1974) (Ortas 2003). There has not been much research done on the effect mycorrhizae may have on the growth of plants in fire-damaged soil compared to plant growth in regular soil. This experiment is meant to find out whether mycorrhizal relationships in burnt soil will facilitate the growth of arugula plants more effectively compared with burnt soil without mycorrhizae. This experiment will also determine if there is a significant difference in the effect mycorrhizae has on plants grown in regular soil compared to those grown in burnt soil. It is expected that there will be a significant difference in the growth of plants with mycorrhizae in burnt soil compared to those without mycorrhizae.

Materials and Methods

A pack of wild arugula seeds (Eruca sativa) weighing one gram and containing about 150 seeds was purchased at Green Thumb Nursery in Lake Forest, California. Also purchased were a bag of Miracle Gro potting mix (28.3l) and a pack of Mykos arbuscular mycorrhizae. The experiment consisted of four different groups: unburned soil with no mycorrizae, unburned soil with mycorrizae, burned soil with no mycorrizae, and burned soil with mycorrizae. In order to simulate a fire, roughly 14.15 liters of potting soil was placed in the oven at 550 ̊F for one hour and fifteen minutes. For the groups containing mycorrhizae, one half of a teaspoon of arbuscular mycorrizae was added and mixed into the soil.

Three days prior to preparing the variables for each group, 105 arugula seeds were placed in between a moist paper towel and put aside to germinate. Out of the 105 germinating seeds, the healthiest looking 60 seeds were transferred to containers containing about 355mL of soil. All 60 plants were grown and maintained outside. Each plant was given 150mL of water twice a day, once in the morning and once at night.

After twenty five days of growing, various tests were conducted on the arugula plants. The total number of plants that grew in each group was counted and documented. Individually, each plant was placed into an 8L airtight plastic container. Using a PASPORT carbon dioxide gas sensor, carbon dioxide production was measured for each plant for four minutes.

Results among the four groups were compared using a Chi2 analysis followed by a one way analysis of variance (ANOVA).

Differences were considered significant at P<0.05.

Results

A Chi2 analysis was run on each of the distinctions in the groups. In the comparison of plants grown in burnt and unburned soils, regardless of mycorrhizae content there was a significant difference in plant growth (p=.0042 Chi2). In the comparison of mycorrhizae presence’s effect on plant growth, regardless of soil condition, no significant difference was found (Chi2 P=.0698). In The comparison of mycorrhizal presence in unburned soil only, a significant difference was found (P=.0142 Chi2). In the comparison of mycorrhizal presence in burnt soil only, no significant difference in the growth of plants was found. (Chi2 p=.1.000)

The rate of cell respiration based on CO2 production was also measured. No significant difference (ANOVA) was present between any of the groups.

Figure 1: Number of plants grown in burnt and unburned soils. There is a significant difference in plants grown in burnt vs. unburned soil (P=.0042 Chi2 two-tailed)

Figure 2: Number of plants grown in any soil with mycorrhizae present or absent. There is no significant difference in cumulative plant growth with or without mycorrhizae present (P=.0698 Chi2 two tailed)

. Figure 3: Number of plants grown in unburned soil with and with mycorrhizae. There is a significant difference in plants grown in unburned soil with or without mycorrhizae (P=.0142 Chi2 two-tailed)

Figure 4: Number of plants grown in burnt soil with and without mycorrhizae. There is no significant difference in plants grown in burnt soil with or without mycorrhizae present (P=1.000 Chi2 two-tailed)

Figure 5: Comparison of rate of CO2 production in all groups. No significant difference rate of CO2 production was found (ANOVA)

Discussion

In the observation of how many plants grew in each group, there was a significant difference between unburned soil and burnt soil. There was also a significant difference between the groups unburned with mycorrhizae and burnt with mycorrhizae. The data indicates that both plants and mycorrhizae had a difficult time growing in sterilized soil. The burnt soil was a much more difficult environment, and therefore the mycorrhizae may have been unable to survive effectively enough to form effective symbioses with the arugula roots. This may be a reason why there was a significant difference in the unburned soil in terms of mycorrhizal acitivity but not the burnt soil. On the contrary there was no significant difference between the presence of mycorrhizae compared to no mycorrhizae present. Lastly there was no significant difference between the burnt soil containing mycorrhizae and burnt soil without mycorrhizae present. The rate of CO2 production was not significant between all four groups. The experiment indicates that cellular metabolism is unaffected by the presence of mycorrhizae.

References Cited

Ahlgren, I. F. (1974). The Effect of Fire on Soil Organisms.Fire and Ecosystems.

Amaranthus, M. P., & Trappe, J. M. (1993). Effects of erosion on ecto- and VA-mycorrhizal inoculum potential of soil following forest fire in southwest Oregon.Plant Soil,150(1), 41-49.

Callaway, R. M. (1995). Positive interactions among plants.The Botanical Review,61(4), 306-349.

Ortas, I. (2003). Effect of selected mycorrihzal inoculation on Phosphorus sustainability in sterile and non-sterile soils in the harran plain in south anatolia. Journal of Plant Nutrition, 26(01), 1-17. Retrieved March 3, 2014

Harrison MJ (2005). "Signaling in the arbuscular mycorrhizal symbiosis".

Annu Rev Microbiol. 59: 19–42.