The dependence of respiration on photosynthetic substrate supply and temperature: integrating leaf, soil and ecosystem measurements

Abstract

Interactions between photosynthetic substrate supply and temperature in determining the rate of three respiration components (leaf, belowground and ecosystem respiration) were investigated within three environmentally controlled, Populus deltoides forest bays at Biosphere 2, Arizona. Over 2 months, the atmospheric CO 2 concentration and air temperature were manipulated to test the following hypotheses: (1) the responses of the three respiration components to changes in the rate of photosynthesis would differ both in speed and magnitude; (2) the temperature sensitivity of leaf and belowground respiration would increase in response to a rise in substrate availability; and, (3) at the ecosystem level, the ratio of respiration to photosynthesis would be conserved despite week-to-week changes in temperature. All three respiration rates responded to the CO 2 concentration-induced changes in photosynthesis. However, the proportional change in the rate of leaf respiration was more than twice that of belowground respiration and, when photosynthesis was reduced, was also more rapid. The results suggest that aboveground respiration plays a key role in the overall response of ecosystem respiration to short-term changes in canopy photosynthesis. The short-term temperature sensitivity of leaf respiration, measured within a single night, was found to be affected more by developmental conditions than photosynthetic substrate availability, as the Q 10 was lower in leaves that developed at high CO 2, irrespective of substrate availability. However, the temperature sensitivity of belowground respiration, calculated between periods of differing air temperature, appeared to be positively correlated with photosynthetic substrate availability. At the ecosystem level, respiration and photosynthesis were positively correlated but the relationship was affected by temperature; for a given rate of daytime photosynthesis, the rate of respiration the following night was greater at 25 than 20 1C. This result suggests that net ecosystem exchange did not acclimate to temperature changes lasting up to 3 weeks. Overall, the results of this study demonstrate that the three respiration terms differ in their dependence on photosynthesis and that, short-and medium-term changes in temperature may affect net carbon storage in terrestrial ecosystems.

Temperature sensitivity of drought-induced tree mortality portends increased regional die-off under global-change-type drought

“…An analysis of time-integrated respiration revealed that trees in the elevated-temperature drought treatment consumed C reserves faster than trees in the ambient drought treatment (Fig. 2C), reflecting the increased C cost for maintenance of tissue under warmer temperatures (34). Mean time-integrated cumulative respiration just before mortality for drought trees did not differ significantly between temperature treatments (P ϭ 0.57).…”

Variability of annual CO<sub>2</sub> exchange from Dutch grasslands

“…However, R e originates from the soil and the vegetation, representing a complex interplay between various aboveground and belowground processes. Photosynthesis and some of the processes contributing to ecosystem respiration may be intimately linked at various time and spatial scales (Hartley et al, 2006). Because photosynthesis is driven by aboveground temperatures, it need not be surprising that the fraction of variance in R e explained by (3) using either T a or T s does usually not differ much.…”

Maize and Prairie Root Contributions to Soil CO2 Emissions in the Field

“…Studies have shown photosynthesis is a significant driver of soil CO 2 emissions in forests (Curiel Yuste et al, 2007;Davidson et al, 1998;Hartley et al, 2006;Vargas et al, 2011), un-managed grasslands (Bahn et al, 2006;GomezCasanovas et al, 2012;Norman et al, 1992) and winter barley (Moyano et al, 2007); our study demonstrates the linkage exists in both summer annual and perennial cropping systems as well.…”