Can nitrogen availability impact plant performance under water stress? A review of traits, mechanisms, and whole plant effects

Identifying mechanisms with potential to increase crop performance under limited water availability is critical to the future of agriculture. Many plant traits (stomatal behavior, specific leaf area, xylem architecture, ROS scavenging, root allocation, and increased osmotic potential) may enable crops to avoid or tolerate water limitation. Additionally, there is evidence that increased nitrogen (N) availability can ameliorate the negative effects of water limitation, although the mechanisms driving this effect are unclear. Here we seek to identify and synthesize the diverse plant physiological mechanisms by which increased N availability may improve plant performance under water limitation. We present four primary plant functional areas in which increased N availability has the potential to offset the negative impacts of water limitation: 1. Belowground resource acquisition, 2. Osmotic adjustment, 3. Photoprotective mechanisms, and 4. Regulation of water and light utilization.

We synthesized the diverse literature with variable N and water treatments for three important grain crop species: Zea mays, Triticum aestivum, and Oryza sativa. N treatments were standardized to ppm and normalized by soil water holding capacity, background soil N concentrations and number of fertilizer applications.

Ultimately, we conclude that moderate N availability may improve plant yield under water limitation via mechanisms from all four plant functional areas, but high levels of N availability can also be detrimental to plant responses to water limitations.

We provide recommendations for specific traits to measure in future field studies, as well as caveats to consider N species, N levels, and timing of N application in such studies.