CAM experiments at UGA

I am excited to report the results of our ongoing study taking place in UGa's (Marc van Iersel's) specialized experimental chambers for measuring CO2 exchange. We are studying two commonly used greenroof plant species, Sedum album, and Sedum kamtschaticum. These species are CAM cyclers which means they carry out C3 (CO2 exchange positive during the day, negative at night) photosynthesis when well watered and switch to CAM (CO2 exchange neutral during the day, positive at night)photosynthesis in response to drought

In our experiment, we began with well watered plants and monitored CO2 exchange as substrate moisture content declined. In the enclosed graphs, you can see how the two species (Sedum album in red above and Sedum kamtschaticum in green below) gradually reduce CO2 exchange during the day and increase exchange at night over the course of the experiment. We think this is pretty exciting because the patterns observed fit some classic predictions found in the literature. It's also interesting that the two different species seem to have different photosynthetic responses to drought.Future work will involve analyzing the photosynthetic response in more detail (calculating other parameters such as daily carbon gain, correcting for differences in initial plant biomass, etc) and combining this information with detailed data we are collecting on substrate moisture content. 

urban swamp

Had a great chance the other day to visit the US tax court building and see these huge bald cypress trees growing on a bridge:

Post conference touring

After the conference, we took special guest, Manfred Koehler, around to see some sights.  Shown here are the Dansko greenwall (thanks for arranging this Michale Furbish and Dansko host Daria) and the greenroof at the National Botanic Gardens in DC

UMD greenroof conference

Also, in August, we were able to host a bunch of greenroof researchers and professionals here in MD at our first Greenroof Science and Technology Symposium:

Data! and ESA in Portland

So, it's about time I've posted some data from my experiment.  These are some results I have so far that I presented at the Ecological Society of America meeting in Portland in August.  The graph shows my different experimental treatments on the x axis (whether the greenroofs were unplanted or planted with one of the Sedum species) and the y axis shows the field capacity, or the mositure content of the greenroofs after a rain.  This shows that the plants were able to increase the ability of the greenroofs to capture water.  Albeit this increase was only a 3% (or roughly 3mm) difference, 3mm is a decent proportion of an average rain depth.  Also, these results are only after 2 years of plant growth, so we would expect the difference to increase over time.  Sedum sexangulare may have the biggest increase due to its fine root structure.

Seattle

After Pullman, it was off to Seattle for some personal time and some meeting with some stormwater professionals. I also got to hang out with our lab tech, Bruk, at the market.
The best part was the tour of the underground city! You can see the old water conveyance system made of wood.  I'm also including a view of the glass sidewalk tiles from below.

Decagon and Pullman

Getting caught up after a summer of meetings and travel.
First, back in July, I attended an SCRI project meeting in Pullman, WA and got to tour around the Decagon Devices facility.  Hopefully, there will be more pics of this, but for now, here's a pic of the building: