The effects of free-air CO2 enrichment (FACE) on carbon and nitrogen accumulation in grains of rice (Oryza sativa L.)

Abstract

Rising atmospheric CO2 concentrations will probably increase rice (Oryza sativa L.) yield but decrease grain nitrogen (GN) concentration. Grains attached to different positions in the panicles differ greatly in weight and quality, but their responses to elevated CO2 (e[CO2]) are poorly understood, which limits our understanding of the mechanisms of yield enhancement and quality degradation. Thus a free-air CO2 enrichment experiment was conducted to examine the effects of e[CO2] on grain mass (GM), grain carbon (GC), and GN accumulation in the spikelets attached to the upper primary rachis branch (superior spikelets; SS) and those attached to the lower secondary rachis (inferior spikelets; IS). e[CO2] stimulated the rice yield by 13% but decreased the N concentration in the panicle by 7% when averaged over two levels of N fertilizations (P < 0.01). The responses of SS and IS to e[CO2] were different particularly under higher N supply. For SS, e[CO2] decreased GN by 24% (P < 0.01) but did not affect GM. For IS, e[CO2] increased GM by 13% (P < 0.05) but GN was not affected. The reduction of GN due to e[CO2] started to appear at the beginning of grain filling. These results suggest that future [CO2] levels probably stimulate the grain growth of IS, most of which are not marketable due to limited size, at the expense of GN reduction in SS. Translocation of N from SS to IS may be a possible mechanism for reduction in GN of SS. This may degrade the grain quality of marketable rice under e[CO2].

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

“…The seasonal mean air temperature was 25.0 • C in 2010 and 24.1 • C in 2011, higher than the long-term average of about 23 • C ( Table 1). The 2011 season had fewer sunny days than the 2010 season (Zhang et al, 2013).…”

“…Crop cultivation practices in 2010 and 2011 were reported by Zhang et al (2013). Briefly, equal amounts of phosphorus (P) and potassium (K) were given to all the plots in early April, before plowing; compound P-K fertilizer was applied at a rate of 4.36 g P m −2 and 8.30 g K m −2 .…”

“…If E-[CO 2 ] preferentially supports grain mass and N accumulation of IS, reduction in grain protein could be more pronounced in SS than in IS, as shown in Koshihikari (Zhang et al, 2013). If the proportion of IS is larger in a cultivar with a larger number of secondary rachis branches, as typically seen in Takanari, the increment of grain yield maybe larger due to the stimulated grain growth of IS and the grain N reduction in SS may be more than that seen in ].…”

“…In experiments using the standard japonica-type rice cultivar Koshihikari, Zhang et al (2013) indicated that E-[CO 2 ] stimulates the growth of inferior grains at the expense of reductions in the protein content of superior grains. The results suggested that, rather than a dilution effect caused by the stimulated accumulation of carbohydrates by E-[CO 2 ], the differential allocation of N and assimilates between superior and inferior grains is responsible for the reduction in grain protein content and the resultant change in grain quality due to E-[CO 2 ].…”

Regional disparities in the beneficial effects of rising CO2 concentrations on crop water productivity

“…Figure S4 includes data at additional sites reporting only on either yield or water use, for which we could not derive data on CWP. These include one additional site for rice at Ibaraki, Japan (Zhang et al, 2013) and two additional sites for wheat at Jiangsu and Beijing, China (Liu et al, 2008, Yang et al, 2006, 2009. We also collected additional data for soybean (Morgan et al, 2005), rice (Kim et al, 2003, Shimono et al, 2008 and wheat (Cai et al, 2015, Han et al, 2015 at the sites reported in Table S1.…”