Republished from the Australian Plant Phenomics Facility blog.

A study featuring research by Adelaide-Nottingham PhD student Olivia Cousins, has found cycling water availability from wet to dry reduced plant growth in wheat more than maintaining a constant level of drought, suggesting plants, like people, struggle with change.

“Our aim was to identify how changes in soil moisture and N concentration affect shoot-root biomass, N acquisition in wheat, and soil N cycling”, said senior author, Associate Professor Tim Cavagnaro.

“We conducted a 3 × 3 factorial experiment subjecting wheat plants to three rates of N application and three soil moisture regimes (well-watered, variable and reduced).

“Both uniform soil water treatments resulted in similar plant biomass, while the variable water treatment resulted in less biomass overall, suggesting wheat prefers consistency whether at a well-watered or reduced water level.

“We expected the greatest reduced biomass to come from the reduced water regime so this was a really interesting result”.

Current climate models project that water availability will become more erratic in the future. With soil nitrogen (N) supply coupled to water availability, it is important to understand the combined effects of variable water and N supply on food crop plants (above- and below-ground).

“That the plants did not respond well to variable soil moisture, highlights the need to understand plant adaptation and biomass allocation with resource limitation”, said Olivia.

“This is particularly relevant to developing irrigation practices, but also in the design of water availability experiments”, she said.

Olivia and her co-authors from the University of Adelaide, University of Nottingham and the Australian Plant Phenomics Facility (APPF) achieved precise soil moisture and wetting-drying cycles using the APPF’s fully automated, gravimetric, lysimeter-based, plant growth platform, the DroughtSpotter. Here, plants are placed on individual lysimeters and automated watering occurs when soil moisture (as determined by pot weight) falls below a pre-determined level. In addition, this platform makes it possible to establish pre-determined patterns of water supply, including wetting-drying cycles, along with recording water-use throughout the entire plant growth cycle.

“Our findings suggest that quantities of water available at the start of a cropping season or at later growth stages can have important consequences on plant health and yield”, said Olivia.

“Our plants did not respond well to the variable water treatment (cycling between well-watered and reduced water), regardless of N treatment, consistently producing smaller plants and affecting N mineralisation and uptake. Therefore, to maximise grain yields, it is important to find the right application of N in relation to variable rainfall or irrigation patterns”, she continued.

“This knowledge can inform breeding programs targeting adaptable crops and cultivars, with root systems optimised for N and water acquisition”, added Tim.

“Understanding trade-offs between water and N uptake efficiency, as a result of variable water regimes, can also lead to the development of crop management strategies to help improve crop productivity and improve the environmental and economic sustainability of food production”, said Tim.

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