Fig. 3: The capacity for CO2 assimilation is downregulated in winter and reactivated with warm temperature in Scots pine.
From: Two dominant boreal conifers use contrasting mechanisms to reactivate photosynthesis in the spring
a Seasonal photosynthetic CO2 assimilation (AN) was measured under saturated conditions (light intensity, 1200 μmol photons m−2 s−1 and CO2 concentration, 800 μmol mol−1, 23 °C). Needles of Scots pine (open circle) and Norway spruce (closed triangle) were collected from March 2017 through January 2018. The dates of budburst in Scots Pine and Norway spruce are indicated with open and closed arrows, respectively. b Response of assimilation (AN) to the internal CO2 concentration (Ci) in a controlled recovery experiment. Samples of Scots pine (closed circle) and Norway spruce (closed triangle) were collected from the field in April. After the initial measurements, the Scots pine (open circle) and Norway spruce (open triangle) samples were recovered in room temperature for 24 h, and measured again. c Response of assimilation (AN) to the internal CO2 concentration (Ci) in seedlings grown in climate chambers. The A/Ci curves were measured in 1-year-old cold-acclimated Scots pine (open circle) and Norway spruce (open triangle) seedlings. Seedlings were transferred either to warm (22 °C, indicated in black) or cold (5 °C, indicated in gray) chambers for 4 weeks, and A/Ci curves were determined again. d rbcL expression during the spring recovery phase in Scots pine (open circle) and Norway spruce (closed triangle). Relative expression values were normalized against the reference gene PP2A and related to the amount present in the February samples. Each data point represents the mean (± SE) of at least three replicates. The daily mean of air temperature (gray line) for the period February to May 2017 is shown in light gray. e Photosynthetic parameters calculated from the A/Ci curve are shown in b and c. AN rate of CO2 assimilation, Vcmax maximum rate of carboxylation, Jmax maximum rate of electron transport, gs stomatal conductance. Units are μmol m−2 s−1. Asterisks indicate the significant difference between values calculated from treatments and control (one-way ANOVA, P < 0.01). Each data represent mean of 4–6 replicates (mean ± SE, n = 4–6).
