Do the Rich Always Become Richer? Characterizing the Leaf Physiological Response of the High-Yielding Rice Cultivar Takanari to Free-Air CO2 Enrichment

Abstract

The development of crops which are well suited to growth under future environmental conditions such as higher atmospheric CO2 concentrations ([CO2]) is essential to meeting the challenge of ensuring food security in the face of the growing human population and changing climate. A high-yielding indica rice variety (Oryza sativa L. cv. Takanari) has been recently identified as a potential candidate for such breeding, due to its high productivity in present [CO2]. To test if it could further increase its productivity under elevated [CO2] (eCO2), Takanari was grown in the paddy field under season-long free-air CO2 enrichment (FACE, approximately 200 µmol mol−1 above ambient [CO2]) and its leaf physiology was compared with the representative japonica variety ‘Koshihikari’. Takanari showed consistently higher midday photosynthesis and stomatal conductance than Koshihikari under both ambient and FACE growth conditions over 2 years. Maximum ribulose-1,5-bisphosphate carboxylation and electron transport rates were higher for Takanari at the mid-grain filling stage in both years. Mesophyll conductance was higher in Takanari than in Koshihikari at the late grain-filling stage. In contrast to Koshihikari, Takanari grown under FACE conditions showed no decrease in total leaf nitrogen on an area basis relative to ambient-grown plants. Chl content was higher in Takanari than in Koshihikari at the same leaf nitrogen level. These results indicate that Takanari maintains its superiority over Koshihikari in regards to its leaf-level productivity when grown in elevated [CO2] and it may be a valuable resource for rice breeding programs which seek to increase crop productivity under current and future [CO2].

Nitrogen Distribution in Leaf Canopies of High‐Yielding Rice Cultivar Takanari

“…However, compared with the difference in root size, the difference in N plant between the two cultivars was rather small (5-20%, Fig. Rather, the large root size in Takanari may contribute to water uptake; it is known that Takanari has higher transpiration rate in canopy top leaves via higher hydraulic conductance (Taylaran et al, 2011;Chen et al, 2014). This result indicates that N uptake in Takanari is not necessarily as large as that expected from its large root size, and the benefit of large root size is limited compared with the cost.…”

“…It has been shown that top leaves of Takanari have a higher photosynthetic capacity with higher leaf N content and stomatal conductance, suggesting that higher yield in Takanari is partly attributable to its higher leaf N content (Taylaran et al, 2011;Chen et al, 2014). It has been shown that top leaves of Takanari have a higher photosynthetic capacity with higher leaf N content and stomatal conductance, suggesting that higher yield in Takanari is partly attributable to its higher leaf N content (Taylaran et al, 2011;Chen et al, 2014).…”

“…Koshihikari has been used as a reference cultivar in previous studies (Hiraoka et al, 1992;Xu et al, 1997;Saitoh et al, 2002;Taylaran et al, 2009;Chen et al, 2014). Koshihikari has been used as a reference cultivar in previous studies (Hiraoka et al, 1992;Xu et al, 1997;Saitoh et al, 2002;Taylaran et al, 2009;Chen et al, 2014).…”

Grain growth of different rice cultivars under elevated CO2 concentrations affects yield and quality

“…The opposite was true in Akita 63, and Koshihikari was located between the two cultivars. The greater response in GM to E-[CO 2 ] in Takanari could contribute to larger sink strength (Marcelis, 1996) and a greater yield response in this than other cultivars, the leaf-level productivity of Takanari was also tested to be larger than Koshihikari under elevated [CO 2 ] (Chen et al, 2014). This has indeed been observed when Hasegawa et al (2013) reported varietal difference in grain yield response to E-[CO 2 ] (their Table 3), although, in this study, the effect of CO 2 x cultivar interaction on single grain weight did not reach the significance level (Table 2).…”

Increasing canopy photosynthesis in rice can be achieved without a large increase in water use—A model based on free‐air CO2 enrichment

“…Takanari maintains high photosynthesis rate mainly because of its high hydroconductivity and better nitrogen utilization (Hirasawa, Ozawa, Taylaran, & Ookawa, ; Muryono et al., ; Ohsumi, Kanemura, Homma, Horie, & Shiraiwa, ; Takai et al., ; Taylaran, Adachi, Ookawa, Usuda, & Hirasawa, ). Under free‐air CO 2 enrichment (FACE) conditions, Takanari had 30% greater brown rice yield than Koshihikari (a common japonica variety) (Hasegawa et al., ) and achieved its higher productivity over Koshihikari in elevated [CO 2 ] due to its high‐source capacity (i.e., photosynthesis rate) (Chen et al., ) and high‐sink capacity, as determined by spikelet density and grain mass (Hasegawa et al., ; Zhang et al., ). Koshihikari has been the most commonly planted rice cultivar in Japan for the past 30 years, and identifying superior traits in other cultivars compared to Koshihikari provides a useful strategy for its improvement in the future.…”