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How much nitrogen does rice need to produce high yields?

Researchers use 3D modelling of rice canopies to determine how nitrogen availability affects photosynthetic productivity.

Increased crop yield will be needed to sustain the growing global population.

Additional application of nitrogen (N), which is a primary constituent of essential proteins and enzymes involved in important plant metabolic processes, may boost yields. However, it is important to determine how much N is necessary to improve yield – high N levels do not necessarily improve yield (Kropff et al., 1993; Murchie et al., 2009; Peng et al., 2010). Additionally, fertilizer is expensive for farmers and excessive use can result in environmentally damaging runoff.

Not only does N availability affect leaf-level photosynthesis, it also affects plant architecture such as leaf angle, number of tillers, and leaf area index (LAI; leaf area per unit ground area). On a canopy level, these changes can impact light distribution and therefore affect productivity.

In a new paper published in in silico Plants, University of Nottingham Professor Erik Murchie, and his coauthors used computer modelling to better understand nitrogen’s influence of architecture on productivity of rice.

Plant canopy reconstruction at different growth stages.

“The architecture of the canopy affects the light environment that plants are exposed to.  To explore the effect of nitrogen on plant structure and estimate crop productivity at the whole canopy scale, we took a new approach using 3D modelling. It is not feasible to collect some of the more complex parameters, such as leaf angle, using manual measurements,” says Murchie.

First, the researchers established trials where three rice lines (two Malaysian and one high-yielding indica cultivar) were either N deficient or received surplus N. They manually measured leaf-level photosynthesis, leaf nitrogen content, greenness (an indicator of chlorophyll content), tiller number, leaf area, and plant height throughout development. Every 2 weeks select plants were imaged and reconstructed in 3D. From this data, they were able to calculate.

The individual plant reconstructions were then used to reconstruct an entire crop canopy. From the reconstructed canopies, the researchers were able to model light distribution through the canopy, canopy photosynthesis, and canopy carbon gain.

The authors found that while N did not affect leaf photosynthetic rate in this case, changes in canopy architecture caused by high N, such as enhanced biomass and altered architecture, resulted in higher seed yield in the Malaysian cultivars. The indica cultivar did not responded to N in terms of biomass or yield.

This work indicates that there is potential for increasing rice yield through manipulation of canopy architecture to improve light distribution throughout the canopy.

Rachel Shekar

Rachel (she/her) is a Founding and Managing Editor of in silico Plants. She has a Master’s Degree in Plant Biology from the University of Illinois. She has over 15 years of academic journal editorial experience, including the founding of GCB Bioenergy and the management of Global Change Biology. Rachel has overseen the social media development that has been a major part of promotion of both journals.

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