Can additional N fertiliser ameliorate the elevated CO₂‐induced depression in grain and tissue N concentrations of wheat on a high soil N background?

Abstract

Elevated CO2 stimulates crop yields but leads to lower tissue and grain nitrogen concentrations [N], raising concerns about grain quality in cereals. To test whether N fertiliser application above optimum growth requirements can alleviate the decline in tissue [N], wheat was grown in a Free Air CO2 Enrichment facility in a low‐rainfall cropping system on high soil N. Crops were grown with and without addition of 50–60 kg N/ha in 12 growing environments created by supplemental irrigation and two sowing dates over 3 years. Elevated CO2 increased yield and biomass (on average by 25%) and decreased biomass [N] (3%–9%) and grain [N] (5%). Nitrogen uptake was greater (20%) in crops grown under elevated CO2. Additional N supply had no effect on yield and biomass, confirming high soil N. Small increases in [N] with N addition were insufficient to offset declines in grain [N] under elevated CO2. Instead, N application increased the [N] in straw and decreased N harvest index. The results suggest that conventional addition of N does not mitigate grain [N] depression under elevated CO2, and lend support to hypotheses that link decreases in crop [N] with biochemical limitations rather than N supply.

Nitrogen application is required to realize wheat yield stimulation by elevated CO2 but will not remove the CO2‐induced reduction in grain protein concentration

“…In agreement with this, results from chamber‐based experiments (open‐top chambers [OTC]) suggest that the eCO 2 ‐induced reductions in GPC cannot be compensated by higher N fertilization rates, since this may simply result in additional biomass and yield production rather than GPC enhancement (Fangmeier et al, ; Weigel & Manderscheid, ). Similar results were obtained in recent experiments with wheat, explicitly designed to test this effect (Tausz et al, ; Walker, Armstrong, Panozzo, Partington, & Fitzgerald, ).…”

Cisgenic overexpression of cytosolic glutamine synthetase improves nitrogen utilization efficiency in barley and prevents grain protein decline under elevated CO2

“…Elevated CO 2 has been shown to impede NO 3 − reduction (Bloom, ; Bloom et al ., ), thus negatively affecting the generation of NH 4 + for subsequent incorporation in amino acids. In support of this biochemical bottleneck it was observed that NO 3 − constituted a higher proportion of total N in plants exposed to elevated CO 2 (Bahrami et al ., ) and that additional N fertilizer was not able to counteract the decline in grain and tissue N concentrations in wheat (Tausz et al ., ). A possible way to sustain tissue N concentrations and growth responses under elevated CO 2 might be to supply plants with NH 4 + instead of NO 3 − (Rubio‐Asensio and Bloom, ).…”

“…The results for the cisgenic lines corroborate the importance of GS1 in maintaining grain protein concentration, as has also been highlighted through identification of QTLs in barley (Fan et al ., ) and via a positive correlation between GS activity and grain protein content in wheat cultivars (Nigro et al ., ; Zhang et al ., ). Considering the fact that extra N supply cannot offset the decline in grain protein concentration of wheat plants growing in an elevated CO 2 environment (Tausz et al ., ; Walker et al ., ), overexpression of HvGS1‐1 may thus provide a means to prevent declining grain protein concentration under elevated atmospheric CO 2 .…”

“…Despite this interconnection, grain protein concentrations have in several cases been shown to decline under elevated CO 2 (Ainsworth and Long, ; Fernando et al ., ; Högy and Fangmeier, ; Ingvordsen et al ., ; Wroblewitz et al ., ). Application of additional N fertilizer to wheat plants growing in a free air CO 2 enrichment facility was not able to counteract the decline in grain protein (Tausz et al ., ), thus emphasizing the associated biochemical limitations. Overexpression of GS1 might be a way to bypass this limitation.…”

Water availability moderates N2 fixation benefit from elevated [CO2]: A 2‐year free‐air CO2 enrichment study on lentil (Lens culinaris MEDIK.) in a water limited agroecosystem

“…The amount of N remobilized from vegetative tissues was calculated as the difference between N in vegetative organs (leaves and stems) at flowering and N in those same organs plus chaff (inflorescence minus grains) at maturity, assuming the difference has been translocated into the grains (Tausz et al, ). …”