Will rising atmosphericCO₂concentration inhibit nitrate assimilation in shoots but enhance it in roots ofC₃plants?

Abstract

Bloom et al. proposed that rising atmospheric CO 2 concentrations 'inhibit malate production in chloroplasts and thus impede assimilation of nitrate into protein of C 3 plants, a phenomenon that will strongly influence primary productivity and food security under the environmental conditions anticipated during the next few decades'. Previously we argued that the weight of evidence in the literature indicated that elevated atmospheric [CO 2 ] does not inhibit NO 3 − assimilation in C 3 plants. New data for common bean (Phaseolus vulgaris) and wheat (Triticum aestivum) were presented that supported this view and indicated that the effects of elevated atmospheric [CO 2 ] on nitrogen (N) assimilation and growth of C 3 vascular plants were similar regardless of the form of N assimilated. Bloom et al. strongly criticised the arguments presented in Andrews et al. Here we respond to these criticisms and again conclude that the available data indicate that elevated atmospheric [CO 2 ] does not inhibit NO 3 − assimilation of C 3 plants. Measurement of the partitioning of NO 3 − assimilation between root and shoot of C 3 species under different NO 3 − supply, at ambient and elevated CO 2 would determine if their NO 3 − assimilation is inhibited in shoots but enhanced in roots at elevated atmospheric CO 2 .

Revisiting Why Plants Become N Deficient Under Elevated CO2: Importance to Meet N Demand Regardless of the Fed-Form

“…To eliminate the effect of biomass increase, we used the percentage of nitrate-N in total N (nitrate-N content per total N content) as an index of nitrate accumulation. As a result, in most species, we found that eCO 2 decreased (i.e., wheat, potato, and guinea grass) or did not change (i.e., Amaranthus ) nitrate accumulation at the whole-plant level under the nitrate-fed condition ( Figure 1E ; Table 2 ), which likely supports the view of Andrews et al ( 2019 , 2020 ).…”

“…Currently, there are different views on whether eCO 2 inhibits nitrate assimilation in C 3 plants (Bloom et al, 2020 ) or not (Andrews et al, 2020 ). Inhibition of nitrate assimilation under eCO 2 results in nitrate accumulation.…”

Photorespiration: The Futile Cycle?

“…Accordingly, NO3 − assimilation significantly declined on with mutations that nearly eliminated enzyme activities [104,117,118], and 50% higher NO3 − reductase activities did not assimilate more NO3 − [119]. St confused rates of enzyme activities with those of NO3 − assimilation as a wh false conclusions [120,121]. One physiological mechanism that may be responsible for the inter photorespiration and shoot NO3assimilation involves the reduction of complex during oxidation of RuBP.…”

Potential metabolic mechanisms for inhibited chloroplast nitrogen assimilation under high CO2

“…On a whole plant basis, elevated CO 2 can increase nitrogen assimilation ( Andrews et al, 2019 ). To date, the mechanisms underlying the effects of elevated CO 2 on chloroplastic nitrogen assimilation in C 3 plants are still unresolved ( Andrews et al, 2020 ; Bloom et al, 2020 ). These different responses might be related to the diversity of plant primary metabolism in C 3 species, reflected in different enzymatic activities and metabolite levels ( Arrivault et al, 2019 ).…”