Hi again! After a ton of work, during which we collected kelp meristems,
Tethered them into their individual flumes (shallow flow tanks),
Incubated them lovingly for two weeks (four times! In July, August, October, and December!),
Harvested and measured them (look how much they grew!),
And dried them and ground them to a fine powder for analysis…
…the experiment didn’t work. Or, the experiment did work, and my hypotheses were disproved.
We analyzed kelp tissue samples from before they went into FLAVI, and after they were incubated in FLAVI for 2 weeks. We analyzed them to determine their stable isotope signature of carbon (∂13C). As I explained in an earlier post, I hypothesized that kelp growing under high light (high carbon demand) or low water flow (low carbon supply) environments would have enriched values of ∂13C (relatively more bicarbonate uptake, and more of the stable isotope 13C). On the other hand, I hypothesized that low light levels and/or fast water flow would result in depleted ∂13C values (using only dissolved CO2, and much less of the stable isotope 13C).
My data says, “Sorry, kid. Neither light level or flow speed has a consistent effect on the ∂13C of kelp tissue. It’s just one big variable mess.”
Given all that work, this is pretty disappointing. If I did everything correctly, and chose light levels that were high enough (bright sunlight) and low enough (dark, weak, forest floor light), and flow levels that were high enough (to deliver nutrients quickly and freely) and low enough (to slow down or stop the delivery of nutrients), then this data means something: It means we still don’t understand stable isotope signature variability in Giant Kelp, and that it isn’t determined by bicarbonate use.
If, however, there is too much variability (after all, light intensity changes pretty seriously from July to December, no matter how sunny it is in California), and I failed to control important environmental features, this data might just be one thing–an inconsistent set of unrelated conditions. In that case, there still might be a story for bicarbonate and Giant Kelp–I just have to try to measure it in a different way.
Stay tuned…and cry for me.
Plant Eco-Phys 