The ROLLBAR project has investigated the interaction of roots of wetland plants with the surrounding soil. Emphasis has been on radial oxygen loss (ROL) from the roots to the soil and the root trait that several wetland plants have evolved to reduced ROL, called barrier to ROL. This root trait confers flood tolerance to wetland plants and it is widely studied in rice. The barrier to ROL is a deposition of chemical compounds in the outer cell layers of roots physically restricting the loss of oxygen from the roots to the anoxic soil. High internal oxygen status enables plants to thrive in flooded soils, where oxygen is low, and to possibly restrict the intrusion of volatile phytotoxins (e.g. sulfides). In the absence of a ROL barrier, oxygen escapes from the roots and oxidizes the rhizosphere resulting in precipitation of iron at the root surfaces, with the formation of the so-called iron plaques consisting of rust. Plaques can potentially reduce gas exchanges and phytotoxin intrusion acting as a physical shield, an armour.
The objective of the ROLLBAR project was to investigate the role of the ROL barrier and of iron plaques in restricting the diffusion of gases, allowing plants to grow in flooded anoxic soils. In addition, ROLLBAR aimed at elucidating the potential role of iron plaques to assist oxygen retention in roots by restricting oxygen diffusion to the soil. This restriction potentially affects any other gas, including organic volatile molecules or sulfide that are commonly produced in anoxic soils.
The society will benefit from the project via inclusion of this root trait in future climate-smart crops that possess genes involved in ROL barrier formation but also from possible new approaches in phytoremediation with plants showing large ROL resulting in high amount of iron plaques. The ROL barrier as well as iron plaques are key features enabling growth in flooded soils and plaques could have an important role in flooded and salt-affected soils, since salt affects the formation of iron crusts. Therefore, these two traits will receive large attention in the future, considering that agricultural fields and natural areas will be more exposed to flooding due to increase of the mean sea level and climate change resulting in extreme weather events.
