Nitrate supply and plant development influence nitrogen uptake and allocation under elevated CO2 in durum wheat grown hydroponically

Abstract

Growth in elevated CO 2 often leads to decreased plant nitrogen contents and down-regulation of photosynthetic capacity. Here, we investigated whether elevated CO 2 limits nitrogen uptake when nutrient movement to roots is unrestricted, and the dependence of this limitation on nitrogen supply and plant development in durum wheat (Triticum durum Desf.). Plants were grown hydroponically at two N supplies and ambient and elevated CO 2 concentrations. Elevated CO 2 decreased nitrate uptake per unit root mass with low N supply at early grain filling, but not at anthesis. This decrease was not associated with higher nitrate or amino acid, or lower non-structural carbohydrate contents in roots. At anthesis, elevated CO 2 decreased the nitrogen content of roots with both levels of N and that of aboveground organs with high N. With low N, elevated CO 2 increased N allocation to aboveground plant organs and nitrogen concentration per unit flag leaf area at anthesis, and per unit aboveground dry mass at both growth stages. The results from the hydroponic experiment suggest that elevated CO 2 restricts nitrate uptake late in development, high N supply overriding this restriction. Increased nitrogen allocation to young leaves at low N supply could alleviate photosynthetic acclimation to elevated CO 2 .

Interactive Effects of Elevated [CO2] and Water Stress on Physiological Traits and Gene Expression during Vegetative Growth in Four Durum Wheat Genotypes

“…Elevated [CO 2 ] generally decreased N content in the present study (Tables 3, 4), which has been observed in C 3 plants through shifts in N uptake and/or assimilation (which agrees with the changes in transcript levels of N-metabolism enzymes; see below) together with other uncertain mechanisms, e.g., the biomass dilution effect, increased N loss, and sink limitation (Stitt and Krapp, 1999; Aranjuelo et al, 2011; Vicente et al, 2015a,b). N content was also diminished by severe water stress in Regallo, in agreement with previous studies in durum wheat (Yousfi et al, 2012, 2016).…”

“…On the other hand, elevated [CO 2 ] did not alter g s at this growth stage, except for an increase in g s under moderate water stress in Regallo, which could favor CO 2 assimilation and consequently biomass accumulation under this water regime (Tables 1, 3). Earlier studies have shown a decrease in g s under water stress (Peremarti et al, 2014; Pazzagli et al, 2016), while negligible changes have been reported under elevated [CO 2 ] in tomato and durum wheat, and increases have even been recorded for Regallo (Vicente et al, 2015a; Pazzagli et al, 2016). Therefore, the growth stage and the severity of the water stress influenced stomatal closure, while elevated [CO 2 ] had minor effects on g s during vegetative growth.…”

“…This down-regulation was associated with lower N content and higher δ 15 N in a genotype-dependent manner. The former could be explained by non-selective decreases in N or reallocation of N within the plant under elevated [CO 2 ] (Aranjuelo et al, 2011; Vicente et al, 2015a). The latter was probably associated with changes in N uptake, assimilation or redistribution within the plant (Araus et al, 2013).…”

“…However, growth over the long-term under elevated [CO 2 ] leads to a down-regulation of photosynthetic capacity, which has been related to a decline in Rubisco protein content and activity, together with a higher carbohydrate accumulation and a decline in N concentration and protein content in wheat (Aranjuelo et al, 2011, 2013; Vicente et al, 2015a,b). This phenomenon suggests that regulatory mechanisms may occur in the plant, e.g., end-product inhibition, carbon sink limitation, biomass dilution effects, or a decline in nutrient uptake and/or assimilation (Stitt and Krapp, 1999; Vicente et al, 2015a). Moreover, elevated [CO 2 ] leads to an altered expression pattern of genes involved in the photosynthetic apparatus, the distribution of C, respiration, and N metabolism in durum wheat (Vicente et al, 2015b).…”

“…Studies carried out with different durum wheat genotypes demonstrated that the responsiveness to elevated [CO 2 ] (Aranjuelo et al, 2013), water stress (De Leonardis et al, 2007; Aprile et al, 2013; Habash et al, 2014), and the combination of both (Erice et al, 2014) is genotype specific. Moreover, the growth stage greatly influences the response of durum wheat to elevated [CO 2 ] (Aranjuelo et al, 2011; Vicente et al, 2015a) and drought (Liu et al, 2016). In addition, the interactive effects of environmental conditions and genotypic variability cannot be anticipated from the individual effects of these treatments (Ceccarelli et al, 1991).…”