Pinus sylvestris switches respiration substrates under shading but not during drought

• Published in: The New phytologist 2015-08, Vol.207 (3), p.542-550
• Main Authors: Fischer, Sarah, Hanf, Stefan, Frosch, Torsten, Gleixner, Gerd, Popp, Jürgen, Trumbore, Susan, Hartmann, Henrik
• Format: Article
• Language: English
• Subjects: Amino acids; Body organs; Carbohydrates; Carbon dioxide; Carbon Dioxide - metabolism; Carbon Isotopes; carbon starvation; Cell Respiration; Depletion; Drought; Droughts; Humidity; hydration; Lipids; Organs; Photosynthesis; Pine trees; Pinus sylvestris - cytology; Pinus sylvestris - physiology; Quotients; Rapid reports; Respiration; Respiratory quotient; respiratory substrates; Shading; Soil - chemistry; Storage; stress physiology; Substrates; Switches; tree ecophysiology; tree mortality; Trees; Water - chemistry
• ISSN: 0028-646X; 1469-8137
• DOI: 10.1111/nph.13452

Reduced carbon (C) assimilation during prolonged drought forces trees to rely on stored C to maintain vital processes like respiration. It has been shown, however, that the use of carbohydrates, a major C storage pool and apparently the main respiratory substrate in plants, strongly declines with decreasing plant hydration. Yet no empirical evidence has been produced to what degree other C storage compounds like lipids and proteins may fuel respiration during drought. We exposed young scots pine trees to C limitation using either drought or shading and assessed respiratory substrate use by monitoring the respiratory quotient, δ13C of respired CO2 and concentrations of the major storage compounds, that is, carbohydrates, lipids and amino acids. Only shaded trees shifted from carbohydrate-dominated to lipid-dominated respiration and showed progressive carbohydrate depletion. In drought trees, the fraction of carbohydrates used in respiration did not decline but respiration rates were strongly reduced. The lower consumption and potentially allocation from other organs may have caused initial carbohydrate content to remain constant during the experiment. Our results suggest that respiratory substrates other than carbohydrates are used under carbohydrate limitation but not during drought. Thus, respiratory substrate shift cannot provide an efficient means to counterbalance C limitation under natural drought.