Changes in source–sink relations during development influence photosynthetic acclimation of rice to free air CO2 enrichment (FACE)

Abstract

Relationships between photosynthetic acclimation and changes in the balance between source-sink supply and demand of carbon (C) and nitrogen (N) were tested using rice (Oryza sativa L. cv. Akitakomachi). Plants were field-grown in northern Japan at ambient CO2 partial pressure [p(CO2)] or free air CO2 enrichment (FACE; p(CO2) ~ 26-32 Pa above ambient) with low, medium or high N supplies. Leaf CO2 assimilation rates (A) and biochemical parameters were measured at 32-36 (eighth leaf) and 76-80 (flag leaf) d after transplanting, representing stages with a contrasting balance between C and N supply and demand in sources and sinks. Acclimation due to FACE was pronounced in flag leaves at each N supply. This was not fully accounted for by reductions in leaf N concentrations, because A/N and Vcmax/N were lower in FACE-grown flag leaves. Acclimation did not occur in the eighth leaf, and A/N and Vcmax/N was not significantly increased in FACE-grown leaves. Soluble protein / sucrose and amino acid / sucrose concentrations decreased under FACE, whereas sucrose phosphate synthase protein levels increased. At flag leaf stage, there was a discrepancy between the demand and supply of N, which was resolved by enhanced leaf N remobilization, associated with the lower Rubisco concentrations under FACE. In contrast to the early growth stage, enhanced growth of rice plants was accompanied by increased plant N uptake in FACE. We conclude that photosynthetic acclimation in flag leaves occurs under FACE because there is a large demand for N for reproductive development, relative to supply of N from root uptake and remobilization from leaves.

Effect of panicle removal on photosynthetic acclimation under elevated CO₂ in rice

“…Acclimation to elevated [CO 2 ] has been reported for many C 3 plant species, including rice , Seneweera et al 2002, Shimono and Bunce 2009), wheat (Farage et al 1998, Wall et al 2000, soybean (Xu et al 1994, Sawada et al 2001, Ainsworth et al 2004), barley (Fangmeier et al 2000, cotton (Delucia et al 1985) and other plant species (Moore et al 1998).…”

“…Considering a sink-source balance, plants with a relatively limited sink strength can therefore suffer from more severe photosynthetic down-regulation than those with stronger sinks (Arp 1991, Ainsworth et al 2004. However, N levels in leaves can also affect the magnitude of photosynthetic down-regulation under elevated [CO 2 ] , Farage et al 1998, Fangmeier et al 2000, Seneweera et al 2002. With increasing sink strength as growth progresses, the N demand by the large ---reproductive organs such as panicles and pods increases N translocation out of leaves and can therefore lead to photosynthetic down-regulation under elevated [CO 2 ] as a result of N limitations (Farage et al 1998).…”

Genetic Adjustment to Changing Climates: Rice

“…The validity of the conclusions from such studies has been questioned recently , stating that yield increase under elevated [CO 2 ] was significantly higher in enclosures than in FACE systems and that conditions inside enclosures did not reflect the real environment. The potential of the FACE rings is, however, limited since their actual size (octagonal plot of about 20 m of diameter) enables studies with contrasted genotypes (Kim et al 2001;Seneweera et al 2002;Hasegawa et al 2007;Shimono et al 2010) but should be significantly increased to characterize the genotype variability and conduct phenotyping activities. Larger rings should then be designed, established in tropical conditions where global warming is a strong issue , and equipped with smaller rings of infra-red heaters or heating cables placed inside the water (as in the case of the FACE system in Japan) to modify the temperature locally and evaluate in situ the interaction between temperature and [CO 2 ].…”

“…According to canopy-scale gas exchange measurements taken under closed chamber systems, downregulation of photosynthesis was identified as the major reason for the decreasing trend in canopy carbon gains within the ontogenetic development of rice ). At process level, the downregulation of photosynthesis appears to be caused by declining trends in both maximum carboxylation rate (Vc max ) and maximum rate of electron transport (J max ) (Seneweera et al 2002;Chen et al 2005). Because of lower carboxylation and electron transport rates, the plant cannot take full advantage of elevated [CO 2 ] at more mature stages.…”

“…Different authors have tried to untangle this apparent discrepancy. As initial studies pointed toward different patterns of downregulation of photosynthetic rates, two FACE experiments conducted in Japan and China (Seneweera et al 2002;Chen et al 2005) indicated that the downregulation of photosynthetic rates is independent from the experimental setup. An important indirect consequence of the decrease in stomatal conductance is the reduction in water use.…”