Radiation and nitrogen use in wheat and oilseed rape crops

Raising yield potential of crops with an efficient use of nutrients is imperative, given the prospects of increase in world population and the need to reduce environmental problems. Yield potential is proportional to the total biomass of a crop, which is highly responsive to nitrogen supply. In this thesis, the response of biomass formation to nitrogen availability and the possibilities to manipulate it to increase yield potential were investigated.The study was focused on wheat ( Triticum aestivum L.) and oilseed rape ( Brassica napus L.), the most important winter-spring components of cereal-oilseed rotations of temperate regions. Experiments were combined with models of explanatory nature. It was demonstrated that in oilseed rape there is scope for raising biomass and yields by prolonging the duration of leaf area during reproductive stages. In wheat, the improvement in the capacity to produce biomass will have to rely on future breakthroughs of photosynthesis at the leaf level. In both crops, selecting genotypes with high capacity to form reproductive organs is essential for the expression of potential production in a high CO 2 -world. The chances of application of these findings by crop breeding and nitrogen management are discussed.</p

Nitrogen use at the leaf and canopy level: A framework to improve crop N use efficiency

This chapter reviews how N affects biomass production in a canopy by looking at its effects on radiation interception and radiation use efficiency, and the main processes behind them, i.e., leaf expansion, senescence and photosynthesis. Examples have been mostly drawn from extensive grain crops, but most of them extend to pastures or horticultural crops. Understanding the magnitude and dynamics of N demand and availability during critical periods for yield definition was identified as crucial to improve the efficiency of N use at the crop canopy level. Genetic variability in processes that could influence N use efficiency, and the complexity involved in scaling from cellular to crop level are discussed

Comparative response of wheat and oilseed rape to nitrogen supply: absorption and utilisation efficiency of radiation and nitrogen during the reproductive stages determining yield

We investigated the response of spring wheat and oilseed rape to nitrogen (N) supply, focusing on the critical period for grain number definition and grain filling. Crops were grown in containers under a shelter and treated with five combinations of applied N. Wheat and oilseed rape produced comparable amounts of biomass and yield when corrected for the costs of biomass synthesis (SC). From the responses of biomass and yield to late N applications and the apparent contribution of mobilised biomass to yield, it seems that the yield of oilseed rape was more source-limited during grain filling than that of wheat, particularly at the medium and high N levels. Both species recovered equal amounts of N from the total available N in the soil and had similar N use efficiencies, expressed as yield per unit of N absorbed. However, oilseed rape had higher efficiency to convert absorbed N in biomass, but lower harvest index of N than wheat. Oilseed rape had similar or lower root biomass than wheat, depending on N level, but higher root length per unit soil volume and specific root length. The specific uptake rate of N per unit root dry weight during the critical period for grain number determination was higher in oilseed rape than in wheat. In wheat, N limitation affected growth through a similar or lower reduction in radiation use efficiency corrected for synthesis costs (RUESC) than in the cumulative amount of intercepted photosynthetically active radiation (IPARc). In oilseed rape, lower growth due to N shortage was associated more with RUESC than IPARc, during flowering while during grain filling both components contributed similarly to decreased growth. RUESC and the concentration of N in leaves and inflorescence (LIN€decreased from flowering to maturity and were curvilinearly related. Oilseed rape tended to have higher RUESC than wheat at high N supply during the critical period for grain number determination, and generally lower during grain filling. The reasons for these differences and possibilities to increase yield potential are discussed in terms of the photosynthetic efficiency of the different organs and changes in source–sink ratio during reproductive stages

Radiation and nitrogen use at the leaf and canopy level by wheat and oilseed rape during the critical period for grain number definition

During the critical period for grain number definition, the amount of biomass produced per unit absorbed radiation is more sensitive to nitrogen (N) supply in oilseed rape than in wheat, and reaches a higher value at high N. This response was investigated by combining experimental and modelling work. Oilseed rape and wheat were grown at three levels of N supply, combined with two levels of plant density at high N supply. Canopy photosynthesis and daytime radiation use efficiency (RUEA) were calculated with a model based on observed N-dependent leaf photosynthesis and observed canopy vertical distribution of light and leaf N. In oilseed rape, RUEA was higher than in wheat and, in contrast to wheat, the sensitivity to canopy leaf N content increased from the start to the end of the critical period. These results were partly explained by the higher leaf photosynthesis in oilseed rape vs wheat. In addition, oilseed rape leaves were increasingly shaded by the inflorescence. Thus, RUEA increased because more leaves were operating at non-saturating light levels. In both species, the vertical distribution of leaf N was close to that optimising canopy photosynthesis. The results are discussed in relation to possibilities for improvement of N productivity in these crops

Dynamics of vertical leaf nitrogen distribution in a vegetative wheat canopy Impact on canopy photosynthesis

The development of vertical canopy gradients of leaf N has been regarded as an adaptation to the light gradient that helps to maximize canopy photosynthesis. In this study we report the dynamics of vertical leaf N distribution during vegetative growth of wheat in response to changes in N availability and sowing density. The question of to what extent the observed vertical leaf N distribution maximized canopy photosynthesis was addressed with a leaf layer model of canopy photosynthesis that integrates N-dependent leaf photosynthesis according to the canopy light and leaf N distribution. Plants were grown hydroponically at two amounts of N, supplied in proportion to calculated growth rates. Photosynthesis at light saturation correlated with leaf N. The vertical leaf N distribution was associated with the gradient of absorbed light. The leaf N profile changed during crop development and was responsive to N availability. At high N supply, the leaf N profiles were constant during crop development. At low N supply, the leaf N profiles fluctuated between more uniform and steep distributions. These changes were associated with reduced leaf area expansion and increasing N remobilization from lower leaf layers. The distribution of leaf N with respect to the gradient of absorbed irradiance was close to the theoretical optimum maximizing canopy photosynthesis. Sensitivity analysis of the photosynthesis model suggested that plants maintain an optimal vertical leaf N distribution by balancing the capacity for photosynthesis at high and low ligh

Dynamics of vertical leaf nitrogen distribution in a vegetative wheat canopy Impact on canopy photosynthesis

The development of vertical canopy gradients of leaf N has been regarded as an adaptation to the light gradient that helps to maximize canopy photosynthesis. In this study we report the dynamics of vertical leaf N distribution during vegetative growth of wheat in response to changes in N availability and sowing density. The question of to what extent the observed vertical leaf N distribution maximized canopy photosynthesis was addressed with a leaf layer model of canopy photosynthesis that integrates N-dependent leaf photosynthesis according to the canopy light and leaf N distribution. Plants were grown hydroponically at two amounts of N, supplied in proportion to calculated growth rates. Photosynthesis at light saturation correlated with leaf N. The vertical leaf N distribution was associated with the gradient of absorbed light. The leaf N profile changed during crop development and was responsive to N availability. At high N supply, the leaf N profiles were constant during crop development. At low N supply, the leaf N profiles fluctuated between more uniform and steep distributions. These changes were associated with reduced leaf area expansion and increasing N remobilization from lower leaf layers. The distribution of leaf N with respect to the gradient of absorbed irradiance was close to the theoretical optimum maximizing canopy photosynthesis. Sensitivity analysis of the photosynthesis model suggested that plants maintain an optimal vertical leaf N distribution by balancing the capacity for photosynthesis at high and low ligh