Light respiration (R_L) is an important component of plant carbon balance and a key parameter in photosynthesis models. R_L is often measured using the Laisk method, a gas exchange technique that is traditionally employed under steady-state conditions. However, a non-steady-state dynamic assimilation technique (DAT) may allow for more rapid Laisk measurements. In two studies, we examined the efficacy of DAT for estimating R_L and the parameter C_i* (the intercellular CO₂ concentration where rubisco’s oxygenation velocity is twice its carboxylation velocity), which is also derived from the Laisk technique. In the first study, we compared DAT and steady-state R_L and C_i* estimates in paper birch (Betula papyrifera) growing under control and elevated temperature and CO₂ concentrations. In the second, we compared DAT-estimated R_L and C_i* in hybrid poplar (Populus nigra L. x P. maximowiczii A. Henry ‘NM6’) exposed to high or low CO₂ concentration pre-treatments. The DAT and steady-state methods provided similar R_L estimates in B. papyrifera, and we found little acclimation of R_L to temperature or CO₂; however, C_i* was higher when measured with DAT compared to steady-state methods.  These C_i* differences were amplified by the high or low CO₂ pre-treatments. We propose that changes in the export of glycine from photorespiration may explain these apparent differences in C_i*.

These data come from two experiments in which foliar gas exchange via the Laisk method was used to collect estimates of light respiration and C_i* (the intercellular CO₂ concentration where rubisco's oxygenation velocity is twice its carboxylation velocity). All gas exchange data were collected using the LI-6800.  The Laisk method involves collecting photosynthetic CO₂ response curves at multiple light intensities. Traditionally the Laisk method has been employed under steady-state conditions, but more recently a non-steady-state technique, called the dynamic assimilation technique (DAT), has become available in gas exchange systems such as the LI-6800. 

In experiment 1, Laisk curves were collected using both the steady-state and DAT methods on paper birch grown under six treatments reflecting possible climate change scenarios for boreal forests.

In experiment 2, Laisk curves were collected with DAT. Light respiration was also measured using the Yin method. In this method, a photosynthetic light response curve is run to collect gas exchange data simultaneously with chlorophyll fluorescence. These measurements were taken on hybrid poplar that were first pre-treated with either high CO2 and high light for 45 minutes or low CO₂ and high light for 45 minutes. Full methods can be found in the Plant Physiology publication.

The datafile is a .csv file that can be opened in most programs and/or software including Microsoft Excel, R and Python.