ROOT BIOLOGY: FROM CURIOSITY TO SAVING THE PLANET OVER 100 YEARS

By Larry York

Charles Darwin was fascinated by plants and, in 1880, wrote a book The Power of Movement in Plants based on experiments he conducted with his son, Francis. On the topic of roots, they concluded: It is hardly an exaggeration to say that the tip of the radicle thus endowed, and having the power of directing the movements of the adjoining parts, acts like the brain of one of the lower animals; the brain being seated within the anterior end of the body, receiving impressions from the sense-organs, and directing the several movements.

Were the esteemed father and son correct? Indeed, research since that time has shown how the root cap, and especially the quiescent centre, respond to several stimuli to cause differential bending and even lateral root branching. This type of plant behaviour even gave rise to the controversial field of plant neurobiology. Beyond semantics and mechanisms, nobody can dispute that plants are able to sense the environment and rely on complex embodied cognition to optimise their architecture. Modular growth is needed, because, as plant biologists are simultaneously happy and woe to say, “Plants are sessile organisms”.

Another common trope is that roots are the “hidden half” of the plant, which leads to the common misconception that roots are too difficult to study. However, many tools exist to study roots as a normal activity for plant biologists, so the challenge should not deter the exercise. Free and open-source software like RhizoVision Explorer are lowering barriers to quantify important root traits such as length. In fact, now is the time for more biologists than ever to study roots, because root biology is central to both food security and climate change mitigation. Crop domestication and breeding have selected primarily on yield in agroecosystems that have tended to increase inputs over the years, which may have acted with some level of neutral selection on roots. An important area of research over the past 50 years has been on which specific root traits influence crop water use and nutrient use efficiency, and subsequent identification of specific genes and alleles that are involved.

Ecosystem ecologists have long understood that roots and root exudation are the primary avenues through which carbon arrives in stable, long-term soil pools. As atmospheric carbon dioxide increased and the Earth responded with increased average temperatures (global warming), these potential soil sinks have been highlighted as part of carbon dioxide reduction strategies. Agricultural systems offer the opportunity to modify millions of hectares around the world with practices and seed that increase root inputs of recalcitrant molecules. However, at the same time researchers need to understand that soil carbon ecology is nuanced, and that poking and prodding carbon pools and fluxes can have unintended consequences. For example, rhizosphere priming can actually lead to the “burning off” of previously stored carbon when new carbon enters the system. Only interdisciplinary teams of crop scientists, geneticists, soil scientists and ecologists can overcome these challenges.

Over the next century, hopefully all types of root biologists, from development researchers to forest ecologists, will come together. Luckily, organisations like the International Society of Root Research and the SEB are well positioned to achieve a more diverse and inclusive root biology community.