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- Background: In the UK, climate change increases in temperature are predicted to reduce relative humidity. In addition over shorter time frames, extreme rainfall events will impact local humidity levels. Since both photosynthesis and transpiration are affected by relative humidity, crop growth and development is likely to be impacted. In order to sustainably enhance agriculture production, a BBSRC priority, we need to understand how changing environmental conditions will affect whole plant physiology. This research project will address how whole plant physiology responds to changing humidity with a focus on below ground physiology. Plants change their leaf structure and arrangement depending on the atmospheric humidity which impacts on leaf photosynthetic and transpiration rates. In turn this affects the quantity of available resources for root growth but exactly how roots respond and change their functional behaviour is currently unknown. Understanding how humidity affects nutrient and water uptake patterns, and in turn affects resource availability, is crucial for predicting how crops will respond to abiotic stresses. Cereal crops including wheat and maize depend on stem-formed root types (Figure 1) with seminal roots often dying early in development. Despite this, much crop root research has focussed on seminal root physiology or at best crown root numbers at harvest times. As a result, little is known about how the functions of each root type differ, or how their functional behaviour (physiology) changes in response to environmental conditions. In this project photosynthesis, transpiration and leaf area will be measured over time and linked to below ground traits including growth rates, root angles, nutrient uptake and soil water availability. Two important cereal crop species - wheat and maize - will be compared to determine whether identified traits are species-specific. These two species also differ in their photosynthetic strategy with wheat using C3 photosynthesis and maize being C4. Determining the functional importance of each root type across these two species will allow us to better predict responses of other monocot crop species (such as rice and sorghum).