Effects of elevated atmospheric CO ₂ concentration on leaf dark respiration of Xanthium strumarium in light and in darkness

Abstract

Leaf dark respiration (R) is an important component of plant carbon balance, but the effects of rising atmospheric CO2 on leaf R during illumination are largely unknown. We studied the effects of elevated CO 2 on leaf R in light (RL) and in darkness (RD) in Xanthium strumarium at different developmental stages. Leaf RL was estimated by using the Kok method, whereas leaf RD was measured as the rate of CO 2 efflux at zero light. Leaf RL and RD were significantly higher at elevated than at ambient CO2 throughout the growing period. Elevated CO2 increased the ratio of leaf RL to net photosynthesis at saturated light (Amax) when plants were young and also after flowering, but the ratio of leaf R D to Amax was unaffected by CO2 levels. Leaf RN was significantly higher at the beginning but significantly lower at the end of the growing period in elevated CO 2-grown plants. The ratio of leaf RL to RD was used to estimate the effect of light on leaf R during the day. We found that light inhibited leaf R at both CO2 concentrations but to a lesser degree for elevated (17-24%) than for ambient (29 -35%) CO2-grown plants, presumably because elevated CO 2-grown plants had a higher demand for energy and carbon skeletons than ambient CO2-grown plants in light. Our results suggest that using the CO2 efflux rate, determined by shading leaves during the day, as a measure for leaf R is likely to underestimate carbon loss from elevated CO 2-grown plants.P hotosynthesis and mitochondrial respiration (also referred to as dark respiration, as opposed to photorespiration) are metabolic pathways that produce ATP and reductants to meet energy demands for plant growth and maintenance. Although the light reaction in photosynthesis provides ATP and reductants for biosynthesis in a leaf cell during illumination, mitochondrial respiration in light is necessary for biosynthetic reactions in the cytosol, such as sucrose synthesis (1, 2). Respiratory activity in light can even be considered part of the photosynthetic process, because it is needed to regulate the state of stromal redox during photosynthesis (3) and to maintain the cytosolic ATP pool (1). Mitochondrial respiration might also be a source for biosynthetic precursors, such as acetyl-CoA or acetate for chloroplastic fatty acid synthesis in light (1). The required magnitude of mitochondrial respiration in light is therefore determined by the potential need for this process to provide energy and carbon skeletons in the light (2).Mitochondrial respiratory activity during illumination varies between 25 and 100% of the respiratory activity in darkness (1). The lower rate of nonphotorespiratory mitochondrial CO 2 release during illumination has been interpreted as evidence for partial inhibition of leaf respiration by light (4-6). The magnitude of light inhibition of respiration seems to depend on the photosynthetic capacity (1), but the mechanism of light regulation of mitochondrial respiration is not clearly understood (2, 3). Although there has been much study of, albeit little agreement o...

Long-term acclimation of mesophyll conductance, carbon isotope discrimination and growth in two contrasting Picea asperata populations exposed to drought and enhanced UV-B radiation for three years

“…The measurements were performed for one randomly selected seedling per block, a total of five plants per each population/watering/UV-B. Respiration in the light (R L ) was estimated using the Kok method by extending the linear portion of the light curve between 45 and 80 mol photons m −2 s −1 the y intercept (Wang et al, 2001). Measurements of the respiration in the dark (R D ) was obtained through gas exchange measurements after covering the leaf chamber for 15 min.…”

Responses of Arabidopsis and Wheat to Rising CO2 Depend on Nitrogen Source and Nighttime CO2 Levels

“…Nighttime elevated CO 2 may inhibit, have a negligible effect on, or stimulate dark respiration, depending on the plant species (Bunce, 2001(Bunce, , 2003Wang and Curtis, 2002), plant development stage (Wang et al, 2001;Li et al, 2013), experimental approach (Griffin et al, 1999;Baker et al, 2000;Hamilton et al, 2001;Bruhn et al, 2002;Jahnke and Krewitt, 2002;Bunce, 2004), and total N supply (Markelz et al, 2014). The current study is, to our knowledge, the first to examine the influence of N source, NO 3 2 versus ammonium (NH 4 + ), on plant dark respiration at elevated CO 2 during the night.…”

Photosynthetic and Respiratory Acclimation to Experimental Warming for Four Species in a Tallgrass Prairie Ecosystem

“…Each measurement of photosynthesis and respiration was the average of three values logged at 30 s intervals. Although the respiration rate in darkness (R d ) is generally 20%-30% higher than night dark respiration rate (Wang et al 2001), this measurement is more practical in the field and these numbers reflect CO 2 release of leaf respiration in the daytime. …”