Roots in armour - a barrier induced to protect against intrusion of soil phytotoxins?

Project Information

ROLLBAR

Grant agreement ID: 839542

DOI

10.3030/839542

Project closed

EC signature date 15 April 2019

Start date 2 September 2019

End date 1 September 2021

Funded under

• EXCELLENT SCIENCE - Marie Skłodowska-Curie Actions

Total cost

€ 207 312,00

EU contribution

€ 207 312,00

Coordinated by

KOBENHAVNS UNIVERSITET
Denmark

Periodic Reporting for period 1 - ROLLBAR (Roots in armour - a barrier induced to protect against intrusion of soil phytotoxins?)

Reporting period: 2019-09-02 to 2021-09-01

Summary of the context and overall objectives of the project

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.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

The 2-years ROLLBAR project allowed to i) determine the presence and tightness of the barrier to ROL in wild species and in rice using qualitative and quantitative methods; ii) highlight novel functions of the barrier, e.g. in restricting water vapour losses; iii) quantify the possible reduction of ROL mediated by plaques formed on roots with or without a barrier.

The project advanced methodologies to measure ROL beyond the state-of-art, which were summarised in a review recently submitted in the journal Plants, including protocols for new users, thanks to a fruitful collaboration with Nagoya University (Japan).

The restricted water vapour loss in roots with a barrier to ROL suggests a potential involvement of the barrier in drought tolerance, which is another major social challenge cause by climate change. The study was recently published in the highly ranked journal New Phytologist (IF 10.15). A video showing the striking differences in water loss between a root with and without a barrier to ROL is available at the link https://www.youtube.com/watch?v=6H5zSml-QKU.

In the presence of oxygen, iron plaques are spontaneously formed on root surfaces exposed to reduced iron and the formation increases with higher pH and salt concentrations (see e.g. https://flooding.dk/blog/iron-plaque-formation-on-roots-of-wetland-plants). Iron plaques seem capable to restrict oxygen loss but only when the iron depositions are thick and homogenous; this results in better internal oxygen status of plants and potentially prevents intrusion of toxins (data not published yet).

During the 2-years project, several new collaborations were established including University of Aarhus (DK), Wien (AT) and Ljubljana (SLO). In addition to peer-review papers, main results were also exploited and disseminated trough teaching activities, student supervision, social media and websites (e.g. ResearchGate or https://plant-and-soil.com/research).

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

The ROLLBAR project allowed to progress beyond the state-of-the-art of the debated role of the barrier to ROL highlighting new functions of the barrier and alternative strategies that plants can adopt to cope with flooding stress (Figure).

The role of the ROL barrier to restrict the diffusion of other gases, like hydrogen and water vapour, had not previously been report. Moreover, the restricted water loss in roots with a barrier to ROL, demonstrated in rice roots, suggests a possible involvement of this trait in drought tolerance of species subjected to fluctuation between flooding and soil desiccation (for instance, due to the tide).

Iron plaques are largely formed at high salt concentrations, suggesting a key role of the barrier to ROL in the future, where flooding and salinity are expected to increase due to climate change. The involvement of iron plaques in protecting plants from ROL and phytotoxin intrusion is also a novel result of the project. Plaques could improve the tolerance of some species to flooding, especially of those species that are not capable to form a barrier to ROL.

The project results are important for the society benefitting from the project via a potential for future climate-smart crops possessing genes involved in ROL barrier formation or from possible new approaches in phytoremediation involving plants showing large ROL so that large iron crusts are formed. Both ROL barrier and iron plaques help plants to thrive in flooded soils and iron plaques could have an important role in salt-affected soils.

ROLLBAR achievements: ROL barrier and plaques reduce gas exchanges from roots to soil and viceversa