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Has agricultural intensification impacted maize root traits?

How have the roots of maize changed since the introduction of synthetic nitrogen fertiliser in the 1940s?

Synthetic nitrogen (N) fertilizers have fundamentally changed the availability of this critically important plant nutrient in agricultural systems, replacing organic sources such as compost and cover crops. Application of inorganic N has increased more than 40-fold since the introduction of synthetic fertilizers, from 2 kg ha−1 in 1940 to 90 kg ha−1 in 2015. Decades of plant breeding have created maize varieties that are highly productive under synthetic nitrogen fertilization, but potential trade-offs for uptake of organic nitrogen remain unclear. It is thought that this targeted breeding may have altered root functional traits of maize and the beneficial interactions between plants and soil microorganisms, hampering their ability to acquire organic N.

A maize seedling growing in a rhizobox
A maize seedling growing in a rhizobox, with tracings to show roots, an organic-nitrogen-containing treatment patch, and a control patch. Root proliferation, rhizosphere interactions regulating nitrogen transformations, and uptake of organic nitrogen were measured in a panel of maize genotypes spanning the introduction of synthetic nitrogen fertilizers. Image credit: J.E. Schmidt.

In their new study published in AoBP, Schmidt et al. investigate how adaptation to inorganic N may have impacted rhizosphere transformations and plant uptake of organic N. They grew three maize varieties released pre-1942 and three varieties released post-1942 in rhizoboxes and measured root morphological plasticity, extracellular enzyme activity, microbial genes related to inorganic N cycling and organic N uptake (from an isotopically labelled source). They found minimal impacts of modern breeding on maize root traits, interactions between roots and associated microorganisms that regulate organic matter breakdown and transformations, and uptake of organic nitrogen from cover crops. This suggests that agricultural intensification does not appear to have impaired N cycling and acquisition from organic sources by modern maize and its rhizobiome. The authors conclude that an improved understanding of rhizosphere processes and their response to selective pressures will contribute greatly to rhizosphere engineering for sustainable agriculture.

Researcher highlight

Jennifer Schmidt recently completed her PhD at the University of California, Davis, where she worked with Dr. Amélie Gaudin. She currently works as a postdoctoral scientist with Mars, Inc., studying the cacao rhizosphere microbiome. Her interest in agroecology was sparked by gardening at a young age and strengthened through her experience at the Pomona College Organic Farm, an REU internship at Kellogg Biological Station, and a Fulbright Fellowship at the Research Institute of Organic Agriculture (FiBL). 

As a rhizosphere ecologist, Jennifer has studied plant-soil-microbe interactions in corn, soybean, tomato, and cacao. She is interested in how understanding rhizosphere processes can guide the design of biologically-based agroecosystems that feed a growing population without sacrificing environmental quality.

William Salter

William (Tam) Salter is a Postdoctoral Research Fellow in the School of Life and Environmental Sciences and Sydney Institute of Agriculture at the University of Sydney. He has a bachelor degree in Ecological Science (Hons) from the University of Edinburgh and a PhD in plant ecophysiology from the University of Sydney. Tam is interested in the identification and elucidation of plant traits that could be useful for ecosystem resilience and future food security under global environmental change. He is also very interested in effective scientific communication.

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