Abstract
Background and AimsKnowledge of thermal acclimation of physiological processes of boreal tree species is necessary to determine their ability to adapt to predicted global warming and reduce the uncertainty around the anticipated feedbacks of forest ecosystems and global carbon cycle to climate change. The objective of this work was to examine the extent of thermal acclimation of net photosynthesis (An) and dark respiration (Rd) of two distant white spruce (Picea glauca) seed sources (from south and north of the commerial forest zone in Québec) in response to latitudinal and seasonal variations in growing conditions.MethodsThe temperature responses of An, its biochemical and biophysical limitations, and Rd were measured in 1-year-old needles of seedlings from the seed sources growing in eight forest plantations along a regional thermal gradient of 5.5 °C in Québec, Canada.Key ResultsThe average optimum temperature (Topt) for An was 19 ± 1.2 °C and was similar among seed sources and plantation sites along the thermal gradient. Net photosynthesis at Topt (Aopt) varied significantly among plantation sites and was quadratically related to the mean July temperature (MJT) of plantation sites. Topt for mesophyll conductance, maximum electron transport rate and maximum rate of carboxylation were 28, 22 and 30 °C, respectively. Basal respiration rate (Rd at 10 °C) was linearly and negatively associated with MJT. Q10 of Rd (the rate of change in Rd with a 10 °C increase in temperature) did not show any significant relationship with MJT and averaged 1.5 ± 0.1. The two seed sources were similar in their thermal responses to latitudinal and seasonal variations in growing conditions.ConclusionsThe results showed moderate thermal acclimation of respiration and no evidence for thermal acclimation of photosynthesis or local genetic adaptation for traits related to thermal acclimation. Therefore, growth of local white spruces may decline in future climates.
Highlights
In the large boreal forest of Canada, global warming should be leading to an increase in average daily temperature of at least 2 °C by 2050 (IPCC, 2014) and to rises in the frequency and duration of summertime episodes of extreme heat waves and drought (Romero-Lankao et al, 2014)
The present study provides an exhaustive assessment of thermal acclimation of photosynthesis and dark respiration for a conifer under natural conditions, with valuable insights into the temperature responses of photosynthetic capacity attributes (Vcmax and Jmax) and mesophyll conductance under natural conditions
Our results indicate that the photosynthesis of seedlings of two white spruce seed sources from southern and northern origins had a lower thermal optimum of photosynthesis and no ability to acclimate to warmer temperature
Summary
In the large boreal forest of Canada, global warming should be leading to an increase in average daily temperature of at least 2 °C (scenario B1) by 2050 (IPCC, 2014) and to rises in the frequency and duration of summertime episodes of extreme heat waves and drought (Romero-Lankao et al, 2014). It is important to understand how physiological processes involved in photosynthetic and respiration rates will respond to future climatic regimes in order to (1) accurately predict climate change effect on carbon uptake at different scales (Way and Yamori, 2014), (2) reduce the uncertainty around the anticipated feedbacks of forest ecosystems, and global carbon cycle to climate change (Niu et al, 2012; Girardin et al, 2016) and (3) determine the intrinsic acclimation and genetic abilities of tree species to adapt to climate change in the short and longer terms (Bigras, 2000; Way and Sage, 2008b; Gunderson et al, 2010) Thermal acclimation of both dark respiration (Rd) and net photosynthetic rate (An) through biochemical, biophysical and structural adjustments may help plants to maintain a positive carbon balance in warming conditions (Medlyn et al, 2002; Atkin et al, 2005; Sage et al, 2008; Way and Yamori, 2014).
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