A Day in the Lab: Plant Data Collection

Jered Korfhage and Katie Sagarin

After harvesting biomass and collecting data last week, the next step was to process the samples. This was also the last step we needed to take before we could analyze our data and draw conclusions about our results. Hopefully we'll see that salt has had a significant detrimental effect on our plants.

Dr. Drenovsky struggles to open
a tin can with a hammer.

The soil collected in tins in last week’s lab had been dried completely. Some lids had even cemented closed, to the point where a hammer was required to dislodge them. After struggling to remove some of the lids, we carefully measured 40 grams of soil from each tin, and placed each sample into a labeled plastic bottle. We added 200 ml of distilled water to each bottle to create a 1:5 mixture. All of the samples were put in a shaker for fifteen minutes to mix the soil and dissolve any salts into the water. These then sat for an hour to make sure everything dissolved, and then were shaken again to make the liquid uniform in composition.

Soil in the shaker

This mixture of soil and water was then vacuum-filtered (Watch how to vacuum filter here). This involved hooking a flask up to a vacuum to separate the soil from the liquid, a small portion of which was poured into a small, labelled vial. Electrical conductivity (EC) was measured for each vial by inserting the probe of an electrical conductivity meter into the liquid (Watch how to use an EC meter here). Electrical conductivity can be used to estimate the amount of dissolved salt in the mixture (more information here).

Vacuum filtration

The EC measures we observed matched our expectations. We saw a trend of increasing EC with increasing salt treatment. In other words, the 0 mM-treated soil had a lower EC than the 50 mM which had a lower EC than the 100 mM-treated soil.

The aboveground plant material and roots collected last week had also been dried. Each sample was weighed to the nearest 0.1 gram, unless it was lighter than 0.1 gram in which case it was measured to the nearest 0.001 gram. All samples were gently brushed to remove soil and sand before weighing. The biomass observed also matched our expectations. The 100 mM-treated plants were either dead or small, whereas the 0 mM-treated plants were alive and sometimes thriving.

Measuring electrical conductivity

At the end of the lab, each group entered their EC, aboveground, and below-ground biomass data into the same Excel spreadsheet, for later analysis. Based on our observations, we feel optimistic that our data will support our hypotheses.