While the fundamental biophysics of C3 photosynthesis is highly conserved across plants, substantial variation in leaf structure and enzymatic activity translates into variability in rates of photosynthesis. Although this variation is well-documented, it remains poorly understood how photosynthetic rates evolve over short and long time scales, and whether these macroevolutionary changes are related to the evolution of key morphological and biochemical leaf traits. Large-scale comparative studies have been hampered by the substantial logistical and statistical challenges in disentangling evolutionary adaptation from environmental acclimation. Here we get around this limitation with a ‘macroevolutionary common garden’ approach in which we measured the metabolic traits Jmax and Vcmax from 111 phylogenetically diverse species in a shared environment. Using several phylogenetic comparative methods, we find substantial phylogenetic signal in these traits at shallow phylogenetic scales, but this signal dissipates quickly at deeper time scales. Leaf morphological traits exhibit phylogenetic signal over much deeper time scales, suggesting that these traits are less evolutionarily constrained than metabolic traits. Furthermore, we find that while morphological and biochemical traits (LMA, Narea and Carea) are weakly predictive of Jmax and Vcmax, evolutionary changes in these traits are mostly decoupled from changes in metabolic traits. This lack of tight evolutionary coupling implies that it may not be possible to use changes in these functional traits in response to global change to infer that photosynthetic strategy is also evolving.
There are 3 sets of data files, corresponding to measurements taken for 138 individuals growing at the UBC and Van Dusen Botanical Gardens in Vancouver, BC, Canada. All of these data have been measured on the same set of leaves, between May and September of 2019.
n.b. Following data processing and quality checks, only data for 111 species were used in the final analysis.
1. Rapid A/Ci Response (RACiR) data
Find these data in neto-bradley_et_al_2021_physiological_data.zip
Files are named in the following format yyyy-mm-dd-hhmm_genus_species
Provided in .txt format, as output by the LiCor6800 machine.
Blurb: RACiR curves (as described in Stinziano et al. 2017) characterize the change in Net photosynthesis A relative to changes in CO2. Functionally this describes the physiological constraints of how quickly and efficiently a plant can take up CO2. During our RACiR curve measurements, CO2 is ramped from 10 ppm to 1010 ppm at a rate of + 100 ppm per minute. While this is ongoing, CO2 accumulates in the chamber such that the true CO2 contents of the chamber are slightly out of sync with the concentration of CO2 measured by the machine. In order to correct for this lag, two curves are measured - a data curve and an empty curve for callibrating the data curve.
Data Specifics: The RACiR data is comprised of 2 data files: an "empty curve" and a "data curve" (see above.) The empty curve characterizes how CO2 accumulates in an empty chamber throughout the course of the A/Ci measurement, and the data curve characterizes a leaf's photosynthetic rates change in response to increasing CO2. Empty curves were collected every hour to two hours - for every empty curve multiple that were collected in close temporal proximity can be corrected (for the lag in CO2 measured - as described above.) Every measurement has its own txt file that was generated by the LiCor6800 machine when the measurement was finalized.
Time & Place: RACiR curves were measured on the youngest fully expanded leaves of each of the 138 species studied here. These measurements were taken between May 5th and July 18th 2019 at the UBC and VanDusen Botanical Garden.
2. Morphological data
Find these data in neto-bradley_et_al_2021_morphological_data.csv
Blurb: After each RACiR curve was measured, the leaf (or several leaves in the case of small leaves/needles) on which this was taken were harvested and put in a sealed bag, which was stored in a cooler overnight. The next morning, the leaves were measured for fresh mass and leaf area. The leaves were then dried for 48 hours in an oven at 60 degrees Celsius. After this the leaves were weighed for dry mass.
Time & Place: These measurements were taken the day of, or the following day at the Beaty Biodiversity Research Centre at the UBC Vancouver Campus.
3. Biochemical data
Find these data in neto-bradley_et_al_2021_biochemical_data.csv
Blurb: Once the leaf tissues were dried, these were sent off for chemical analysis for the Nitrogen and Carbon contents by combustion.
Time & Place: These measurements were done at the Analytical Chemical Services Laboratory (at the BC Ministry of Environment and Climate Change Strategy), during September 2019.