Gas exchange

I’m nearing the end of ten day stretch of gas exchange measurements.  I’ve been using a pair of LI-COR 6400s to measure photosynthetic parameters on some of the common species on the BEO. The aim is to measure key species that represent the different plant functional types found on the tundra. 

Following a lesson in Arctic botany from Victoria Sloan (ORNL) I set to work.  The first four species on my list were Carex aquatilis, Petasites frigidus, Eriophorum angustifolium and Dupontia fisheri.  One of the targets this trip was to determine the maximum rate of carboxylation by the enzyme rubisco (v_c,max), a critical input for modeling CO₂ uptake, and for Chonggang Xu’s nitrogen optimization model (LANL).  Back at the lab I can use measurements of leaf N content and determine the fraction of leaf N invested in rubisco (F_LNR). Sensitivity analysis of CLM4.0 has revealed that F_LNR is a critical parameter to constrain and these data will help do that for the Arctic.

I was impressed with the high rates.  Preliminary analysis suggests that the winner was P. frigidus.  When normalized to 25⁰C this little forb stands toe-to-toe with many crops.  This makes sense because Arctic plants have to operate at low temperatures where a large investment in rubisco would be required to gain carbon. I also made two important gas exchange discoveries; (1) mosquitos can quickly fill the head of the Leaf Chamber Fluorometer, stuffing the fan and air space with their mangled carcasses, causing instrument failure and (2) If you leave a 6400 unattended and it tips over into a trough full of water, all is not lost.  A night in the oven, a few new fuses and some fresh chemicals and you’re back in business.