The impact of elevated CO2 on acid-soil tolerance of hexaploid wheat (Triticum aestivum L.) genotypes varying in organic anion efflux

Abstract

It is unclear how elevated CO2 (eCO2) affects the response of crops to soil acidity. This study examined the effect of eCO2 on acid-soil tolerance of hexaploid wheat genotypes that vary in Al3+ resistance due to differences in root efflux of citrate and malate. Three pairs of near-isogenic lines were grown for 24–25 days under ambient CO2 (400 µmol mol-1) and eCO2 (800 µmol mol-1) in acid soils and hydroponics with various Al3+ concentrations. The lines consisted of pairs that differed in alleles of the TaALMT1 and TaMATE1B genes. Plant growth parameters and rhizosphere soil properties were measured. Elevated CO2 increased the slope of negative correlations between root and shoot biomass and Al3+ concentration in the rhizosphere of a line that has an Al3+-sensitive allele of the TaALMT1 gene conditioning malate efflux (ES8), but did not change that of a near-isogenic sister line with an Al3+-resistant TaALMT1 allele (ET8). Elevated CO2 decreased the relative root length and biomass (% of limed soil) of a line that lacked both malate and citrate efflux (Egret), but did not affect lines that possessed either malate or citrate efflux. Elevated CO2 had no effect on either malate or citrate efflux from root tips of Al3+-resistant lines. Elevated CO2 also increased Al3+ concentration and decreased NH4+ concentration in rhizosphere soil, but decreased concentrations of Al and Zn in shoots. Elevated CO2 decreased acid-soil tolerance of Al3+sensitive genotypes but not of Al3+ resistant genotypes. Malate efflux played a dominant role in conferring acid-soil tolerance to hexaploid wheat.