Effect of N and CO₂ supply on source size per grain at anthesis and its relationship with grain growth in wheat

Abstract

Rising atmospheric CO 2 concentration ([eCO 2 ]) increases the yield of wheat mainly by increasing grain number, but effects on single grain weight are variable. It is discussed whether single grain growth is limited by the sink or the source size under a non-stress environment. This study explores the effect of e[CO 2 ] combined with varying N supply on the source and sink size during grain filling. Source size was defined as the amount of stem reserves per grain (SRG) and the proportion of incident radiation intercepted by the green canopy per grain (f IR G) at anthesis. Data from a 2-year free-air CO 2 enrichment experiment with wheat with three N levels (on average 38 [Nd], 190 [Nad] and 320 kg N ha −1 [Nex]) and two CO 2 levels (393 and 600 ppm) on SRG, f IR G and grain filling rate (GFR) and duration (GFD) were evaluated. SRG ranged from 2.5 to 12.9 mg and f IR G from 4.0 × 0.001% to 6.8 x 0.001%. Rising N supply or e[CO 2 ] decreased SRG and f IR G via their increases in grain number. Accordingly, there was a negative linear relationship between grain number and SRG (r 2 ≥ 0.84) or f IR G (r 2 ≥ 0.97). Increasing N supply decreased GFR, but increased GFD, and GFR was increased by e[CO 2 ] under Nad and Nex. For GFR and final grain weight, there was a strong positive (r 2 ≥ 0.85), and for GFD, a strong negative linear relationship (r 2 ≥ 0.76) with f IR G under Nad and Nex. Under these N levels, f IR G supplied the largest share (>86%) for grain growth and thus single grain growth was possibly source limited under Nad and Nex. Under high grain number such as under Nex and e[CO 2 ], there might be a risk for low final grain weight due to the low SRG that is insufficient for buffering assimilate shortage under unfavourable environmental conditions in early grain filling.

Dilemma between yield and quality: Multigenerational effect of elevated CO2 and nitrogen supply on wheat cultivars

“…enrichment increases GY of wheat mainly by increasing SN, GN and GNPS(Manderscheid & Dier, 2022;Mulholland et al, 1997), which were all observed in the present study, especially for 325Jimai that had the greatest enhancement in GY, GN and SN at both N levels. Irrespective of cultivar and N treatment, the increase of GY, GN, SN and GNPS by CO 2 elevation was larger in G3 than in G1, suggesting a multigenerational 'cumulative effect' of e[CO 2 ] on yield components in wheat plants.…”

“…While in the present study, the same results was found in the first two generations but the opposite was true in the third generation (Table S1). As Manderscheid and Dier (2022) reported, the larger GN under e [CO 2 ] and excess N supply led to lower single grain weight because of the limited source size per grain including the assimilates shortage at early grain filling and the reduced stem reserves of water‐soluble carbohydrates per grain. This could explain the results obtained here, that is despite the increasing enhancement in GN with generation, the single grain weight under e [CO 2 ] is reduced, thus resulting in a lower TGW where the increases of average grain weight could not keep pace with the much higher increase in GN.…”