Frequency vs Quantity: Root Adaptation to Variability of Water and Nitrogen

Plants have evolved traits which optimise water and nitrogen (N) uptake, however, the current climate is changing faster than plants’ ability to adapt. Therefore, genotypic variation is becoming an increasingly important measure for improving food security. However, tackling the issue of food security means understanding plant-soil-water interactions. Plant growth is affected not just by the quantity of water, but the frequency of rainfall will also impact root plasticity; thus this understanding is challenging current agricultural practices. Additionally, water variability directly affects N availability, therefore as climate change models predict rainfall to become more erratic in the near future, it is important to understand how the timing of rainfall will affect crop N supply.

We examined responses of wheat to changes in water and N availability. The experiment was carried out using a gravimetric platform, which permits fine-scale control of soil moisture by precisely measuring pot weight in real-time and irrigating according to a pre-programmed water treatment. Two wheat genotypes were subjected to five soil moisture regimes (wet, dry, variable, wet after 48 hours, dry after 48 hours) and three N fertilisation rates (low, medium, high N). The experiment addressed how soil moisture variability affects biomass accumulation, allocation and N acquisition. Results showed plant growth was adversely affected by 48-hour variability, with more biomass under long-term variable water supply combined with low or high N, suggesting that plants prefer consistency whether adequate or deficient water or N level, to a variable and infrequent application.

Identifying root system adaptations to short-term and long-term changes in watering and N will provide better insight into how crops interact with the environment. Understanding trade-offs between water and N uptake efficiency will guide crop variety development and new management strategies to improve the environmental and economic sustainability of food production.