A Comparison of Dark Respiration between C₃ and C₄ Plants

Abstract

Lower respiratory costs were hypothesized as providing an additional benefit in C4 plants compared to C3 plants due to less investment in proteins in C4 leaves. Therefore, photosynthesis and dark respiration of mature leaves were compared between a number of C4 and C3 species. Although photosynthetic rates were generally greater in C4 when compared to C3 species, no differences were found in dark respiration rates of individual leaves at either the beginning or after 16 h of the dark period. The effects of nitrogen on photosynthesis and respiration of individual leaves and whole plants were also investigated in two species that occupy similar habitats, Amaranthus retroflexus (C4) and Chenopodium album (C3). For mature leaves of both species, there was no relationship between leaf nitrogen and leaf respiration, with leaves of both species exhibiting a similar rate of decline after 16 h of darkness. In contrast, leaf photosynthesis increased with increasing leaf nitrogen in both species, with the C4 species displaying a greater photosynthetic response to leaf nitrogen. For whole plants of both species grown at different nitrogen levels, there was a clear linear relationship between net CO2 uptake and CO2 efflux in the dark. The dependence of nightly CO2 efflux on CO2 uptake was similar for both species, although the response of CO2 uptake to leaf nitrogen was much steeper in the C4 species, Amaranthus retroflexus. Rates of growth and maintenance respiration by whole plants of both species were similar, with both species displaying higher rates at higher leaf nitrogen. There were no significant differences in leaf or whole plant maintenance respiration between species at any temperature between 18 and 42TC. The data suggest no obvious differences in respiratory costs in C4 and C3 plants.The unique biochemical and structural differences found in leaves of C4 species allow for more efficient use of N when compared to C3 species, primarily due to increased catalytic efficiency of Rubisco, the major soluble protein in mesophyll cells of C3 plants (7,26). In general, C4 plants also invest proportionally less N in leaves than C3 plants (7,27 Rn2 in plants has been examined in terms of two conceptual components, growth and maintenance (10,13,18,19,29). Growth respiration is considered the energy source for the synthesis of new phytomass. Maintenance respiration supplies energy to maintain current phytomass, is independent of substrate concentration, and includes processes such as protein tumover, ion balance, and tissue acclimation to environmental change (1). Because C4 plants synthesize and maintain less photosynthetic protein in leaves (26), it is possible that both growth and maintenance respiration would be lower than in C3 species.Differences in respiration exist among species (18, 25) and among plant parts (10, 15), yet few comparisons have been made between C3 and C4 species. In the few respiratory studies including different photosynthetic types, the question of whether C3 and C4 differed in their mainten...

Direct Inhibition of Plant Mitochondrial Respiration by Elevated CO2

“…Elevated C, did not inhibit the alternative oxidase. The levels of inhibition obtained in soybean cotyledon mitochondria matched those reported for soybean leaves and whole plants by doubling ambient levels of C, (Bunce, 1990;Byrd et al, 1992;Thomas and Griffin, 1994).…”

“…A reversible inhibition of CO, evolution by Rumex crispus leaves was observed when C, was increased stepwise through the range of O to 1000 pL L-' (Amthor et al, 1992). Inhibition of respiration by increasing C, has also been reported in whole plants (Bunce, 1990;Ryle et al, 1992), leaves (Reuveni and Gale, 1985;Bunce, 1990;El Kohen et al, 1991;Amthor et al, 1992;Byrd et al, 1992;Thomas and Griffin, 1994;Ziska and Bunce, 1994), roots (Reuveni and Gale, 1985;Palta and Nobel, 1989;Qi et al, 1994), microorganisms (Koizumi et al, 1991), and animal tissues (Palet et al, 1991). Respiration can also be unaffected or even increased when C, increases (Palet et al, 1991;Ryle et al, 1992).…”

Photosynthate costs associated with the utilization of different nitrogen–forms: influence on the carbon balance of plants and shoot–root biomass partitioning

“…Based on these, the calculated respiration for protein turnover from the present work equates to 3n5-8n2 % and 6n3-14n5 % of total maintenance respiration, respectively, for 1 and 8 mol m −$ N-supplied plants. Similar calculations based on the data of Byrd et al (1992) for C $ and C % species with leaf N content comparable to that of the 8 mol m −$ N-supplied plants from the present work, also show respiration for protein turnover to be c. 3-20 % of total maintenance respiration. These results generally agree with those reported by Byrd et al (1992) and Amthor (1994), in that respiration due to protein turnover is not a major component of maintenance respiration.…”

“…Similar calculations based on the data of Byrd et al (1992) for C $ and C % species with leaf N content comparable to that of the 8 mol m −$ N-supplied plants from the present work, also show respiration for protein turnover to be c. 3-20 % of total maintenance respiration. These results generally agree with those reported by Byrd et al (1992) and Amthor (1994), in that respiration due to protein turnover is not a major component of maintenance respiration. Similarly, van der Werf et al (1992) found that, in the roots of Dactylis glomerata, a mere 4-7 % of the total energy production was used by protein turnover.…”

“…The data of Li & Jones (1992) add further evidence, generally indicating a positive relationship between any two of the following : N supply (or plant N concentration), S : R DM and specific dark respiration rates. Byrd, Sage & Brown (1992), however, found no consistent responses : in mature leaves, respiration rates were independent of leaf N content whereas at a wholeplant level, both growth and maintenance respiration rates increased with increased leaf N content. In general, however, it appears that the photosynthate consumed by the N-assimilation processes (as Cskeleton, reductant and energy sources) affects the C available for plant growth and, perhaps, shoot-root DM partitioning.…”