Elevated CO₂ and temperature alter net ecosystem C exchange in a young Douglas fir mesocosm experiment

• Published in: Plant, cell and environment cell and environment, 2007-11, Vol.30 (11), p.1400-1410
• Main Authors: TINGEY, DAVID T, LEE, E. HENRY, PHILLIPS, DONALD L, RYGIEWICZ, PAUL T, WASCHMANN, RONALD S, JOHNSON, MARK G, OLSZYK, DAVID M
• Format: Article
• Language: English
• Subjects: Agricultural and forest climatology and meteorology. Irrigation. Drainage; Agricultural and forest meteorology; Agronomy. Soil science and plant productions; Biological and medical sciences; Climatic adaptation. Acclimatization; Fundamental and applied biological sciences. Psychology; General agronomy. Plant production; global change; photosynthesis; respiration
• ISSN: 0140-7791; 1365-3040
• DOI: 10.1111/j.1365-3040.2007.01713.x

We investigated the effects of elevated CO₂ (EC) [ambient CO₂ (AC) + 190 ppm] and elevated temperature (ET) [ambient temperature (AT) + 3.6 °C] on net ecosystem exchange (NEE) of seedling Douglas fir (Pseudotsuga menziesii) mesocosms. As the study utilized seedlings in reconstructed soil-litter-plant systems, we anticipated greater C losses through ecosystem respiration (Re) than gains through gross photosynthesis (GPP), i.e. negative NEE. We hypothesized that: (1) EC would increase GPP more than Re, resulting in NEE being less negative; and (2) ET would increase Re more than GPP, resulting in NEE being more negative. We also evaluated effects of CO₂ and temperature on light inhibition of dark respiration. Consistent with our hypothesis, NEE was a smaller C source in EC, not because EC increased photosynthesis but rather because of decreased respiration resulting in less C loss. Consistent with our hypothesis, NEE was more negative in ET because Re increased more than GPP. The light level that inhibited respiration varied seasonally with little difference among CO₂ and temperature treatments. In contrast, the degree of light inhibition of respiration was greater in AC than EC. In our system, respiration was the primary control on NEE, as EC and ET caused greater changes in respiration than photosynthesis.