Hot drought reduces the effects of elevated CO2 on tree water‐use efficiency and carbon metabolism. Issue 6 (17th March 2020)

• Record Type: Journal Article
• Authors: Birami, Benjamin; Nägele, Thomas; Gattmann, Marielle; Preisler, Yakir; Gast, Andreas; Arneth, Almut; Ruehr, Nadine K.
• Is Part Of: New phytologist. Volume 226:Issue 6(2020)
• Page Start: 1607
• Page End: 1621
• Publication Date: 2020-03-17
• Subjects: carbon balance -- drought -- elevated CO2 -- heat -- photosynthesis -- primary metabolites -- protein -- respiration; Botany -- Periodicals; 580
• DOI: 10.1111/nph.16471
• Languages: English
• ISSNs: 0028-646X

Abstract

Summary: Trees are increasingly exposed to hot droughts due to CO2 ‐induced climate change. However, the direct role of [CO2 ] in altering tree physiological responses to drought and heat stress remains ambiguous. Pinus halepensis (Aleppo pine) trees were grown from seed under ambient (421 ppm) or elevated (867 ppm) [CO2 ]. The 1.5‐yr‐old trees, either well watered or drought treated for 1 month, were transferred to separate gas‐exchange chambers and the temperature gradually increased from 25°C to 40°C over a 10 d period. Continuous whole‐tree shoot and root gas‐exchange measurements were supplemented by primary metabolite analysis. Elevated [CO2 ] reduced tree water loss, reflected in lower stomatal conductance, resulting in a higher water‐use efficiency throughout amplifying heat stress. Net carbon uptake declined strongly, driven by increases in respiration peaking earlier in the well‐watered (31–32°C) than drought (33–34°C) treatments unaffected by growth [CO2 ]. Further, drought altered the primary metabolome, whereas the metabolic response to [CO2 ] was subtle and mainly reflected in enhanced root protein stability. The impact of elevated [CO2 ] on tree stress responses was modest and largely vanished with progressing heat and drought. We therefore conclude that increases in atmospheric [CO2 ] cannot counterbalance the impacts of hot drought extremes in Aleppo pine.