I ended the last post with as much of a cliffhanger as I could muster. I had students in my lab stain Wolffia to make their stomata (the tiny lines on the photograph; they are actually easier to see with a regular microscope) more visible for the purpose of counting and identifying the species. The results were interesting but hard to quantify with the equipment on hand so the project never got much further.
The stain we used was specific for the cuticle (the waxy coating) of the plant. We had two species we were trying to distinguish, partly by stomata count and so we stained both. The species with the fewest stomata stained poorly while the species with the large number of stomata stained well. The explanation I came up with I think is the most simple (I’m always interested in better explanations if there any out there).
Photosynthesis is all about gas exchange. Plants need carbon dioxide to turn into glucose and they need to get rid of oxygen as the waste product of that process. They also need to retain water which is largely the role of the cuticle (wax and water don’t get along; wax, a lipid, is hydrophobic). So, the species with many stomata had many sites for gas exchange and had little need for gas exchange across the rest of the surface of the plant. The other species, with few stomata, had a much thinner cuticle because there is a need for gas exchange across the rest of the surface of the plant.
I’m not sure how I would have quantified the difference in staining intensity. I am sure that there are spectrometers somewhere that could have done the job but they weren’t available.
The moral of the story? I return to my theme of interesting stories from the smallest of vernal pool life. What we found was hardly a major breakthrough in science. But it re-enforces the importance of observation of even the smallest details. I know most people involved with vernal pools are after the largest species (amphibians) but the vernal pool ceases to be much of a home when there is no supporting ecosystem. Try raising salamanders in distilled water or even filtered pond water and it is unlikely they will survive for long. They need something to eat which needs something else to eat. Think about the relationship between yourself and the size of the bites of food you consume. Even with hands to manipulate our food, we take in only a small amount with each bite. A salamander has similar constraints (and no hands) so their food must be that much smaller, the size of Daphnia and other similar food items. And the food of Daphnia has to be that much smaller again.
I started this story with observations about “duckweed” but I think there are lessons here about more than these tiny plants. My admonition, again, is to keep your eyes open and appreciate all that is going on in these tiny worlds.
