Results! Effects of Salinity on Stressed Common Roadside Plants

By: Natalie Fry and Meghan Kelley

__________________________________________________

 

 

Eariler this semester of Fall 2013, in the blog entitled "Trade-off of Salting Winter Roads: Human Safety vs. Plant Survival," our Plant Ecology class at John Carroll University set up a laboratory experiment in order to test different concentrations of salt on common roadside plants to determine how tolerant certain species (Purple Coneflowers, Black-Eyed Susans, Shasta Daisies, and Mexican Asters) are to man-made stressors, such as salted winter roads. During this last week of November 4, 2013, we were able to begin assessing the results on our study plants.
 

The first step before harvesting dead and alive plants is to record the observations of how plant individuals of each species look, by examining characteristics such as leaf senescence or dropped leaves, leaf coloration abnormalities like tip yellowing, and morphological drying, wilting, or withered plant leaves and stems, as can be seen in the picture below. For more information about how plants cope with salt, visit the page for the Society of Experimental Biology.

 

Qualitatively, of the four species, it appeared that the Purple Coneflower (ECPU) did not do quite as well with the salt stress as some of the other plant species.  For example, the Shasta Daisy (CHMA) in this photo is clearly green and growing better at the highest salt concentration than the Purple Coneflower grew at the intermediate salt concentration. Observations such as these were recorded in addition to the counting of plants that lived and died for each species, for each salt concentration.  Overall, as stated in the previous blog, five experimental blocks were created with replicates of each species for the salt treatments- however, as an example, only one block will be used to indicate some preliminary observational results.  Of the twelve original plants in this block, only five survived, and three of those five were from controls that were not salt stressed.  Therefore, we can say that these four common roadside plants are not all amenable to winter salinity treatments of roads that can accumulate toxic salt levels over time. However, more tests were also performed in this lab to further strengthen this claim or to add additional information about physiological tolerance in these species.

For more definitive quantitative measurements, our class used a LICOR machine, which includes a clamp for leaves in a 2x3 centimeter frame in order to measure the amount of light captured for photosynthesis as well as other functions linked to photosynthesis. The LICOR machine used in this study is pictured below, showing its easy to read digital monitor for assessing measurements.

 

Next, a Scholander Pressure Bomb was used to measure the water potential of different leaves of the species that lived, which were only the Shasta Daisy, the Black-Eyed Susan, and the Mexican Aster for one block, not the Purple Coneflower.  The leaf is placed in the pressure bomb upside down and sealed, in order to allow the pressurized nitrogen gas to force water to the center of the leaf petiole. This water movement has to be monitored by someone to determine the correct point of pressure of the plant's water potential, as seen in lower right photo.

Finally, the aboveground (stems and leaves) and the belowground (roots) biomass were harvested along with a soil sample for the purpose of drying the organic materials to weigh for our final results.  Aboveground biomass was clipped with shears at the soil surface, and roots were collected by filtering soil through a metal sieve into a bucket. These will be weighed at a later date. Following the analysis of all data collected in this lab, statistics will be run to make conclusions about this study.  Some discussionary points to help examine the results could include the use of fluorescent lights in the greenhouse in place of sunlight, which was not available during the measurements of this study. Seen in the picture below, plants were harvested under these conditions indoors. Also, possible sources of error along with relevant plant biology could be discussed for drawing further conclusions as to which of the four plant species is the most salt tolerant and would therefore be more likely to survive along midwest and northern roads.

 

 

 

Additional Links:

 

University of California: "Salt Injury in Strawberries" (2012)

 

North Carolina State University: "Got Salt? Winter Weather May Be Toxic to Plants" (2013)