The effect of elevated CO2 on nitrogen allocation between components of the photosynthetic machinery in Spring wheat

Theobald, Julian C. (2001). The effect of elevated CO2 on nitrogen allocation between components of the photosynthetic machinery in Spring wheat. PhD thesis The Open University.

Abstract

Wheat (Triticum aestivum L. cv Minaret) was grown long-term under CO2 partial pressures of 36 and 70 or 100 Pa with various N applications (4 to 23 g m-2 N), to test hypotheses of N re-allocation: 1) a decrease in N from leaves to other organs, 2) a relative decrease in N from Rubisco to other photosynthetic components.

Elevated CO2 did not affect phenology, main stem leaf appearance, the pattern of N allocation throughout the plant, or the fraction of crop N in grain at harvest, but 1) stimulated biomass and yield by 5 to 20% over the N range used, and 2) caused a faster loss of N and components from flag leaves during grain-fill.

Responses of photosynthesis to varying pCi were fitted, and rates of maximal carboxylation and non-photorespiratory respiration estimated. The former, was proportional to Rubisco content, and light-saturated photosynthetic rate at 70 Pa CO2 was proportional to A TP-synthase. Potential photosynthetic rates at 70 Pa CO2 were calculated, compared with observed, and used to estimate excess investment in Rubisco. The excess was greater in high N treatments than low, declining as leaves senesced. The fraction of Rubisco estimated to be in excess, was strongly dependent on leaf N content, increasing from - 5% in leaves with 1 g N m-2 to -40% in leaves with 2 g N m-2. Growth at elevated CO2 usually decreased the excess somewhat, but only as a consequence of a general decrease in leaf N, given that relationships of components to leaf N content were independent of CO2 and N treatment, demonstrating that no direct CO2 effect on N allocation within leaves had occurred. It is concluded that there is scope for improving the N-use efficiency of C3 crop plants in elevated CO2 conditions, by genetic manipulation to decrease the amount of Rubisco.

Viewing alternatives

Download history

Item Actions

Export

About

Recommendations