Growth & Development

Two plants in a pot, intraspecific root competition in soybean and sunflower

Can a split pot design provide insights into belowground competition between neighbouring plants?

Competition for soil resources among plants is critical in determining the structure and dynamics of terrestrial ecosystems. The impact of belowground competition on the growth and productivity of plants has long been an important topic in plant ecology and agriculture. Game theoretical models predict that plants should overinvest in root growth in competition for soil resources and commit less to aboveground biomass production and reproductive tissues.

To test this hypothesis, in their new study published in AoBP, Chen et al. conducted two greenhouse experiments on intraspecific root competition in two common crop species, soybean (Glycine max) and sunflower (Helianthus annuus). The authors realised that to adequately estimate the extent of root growth of plants in response to neighbours independen of nutrient availability, they needed use a set-up allowing them to simultaneously control both the nutrient concentration and soil volume of individual plants.

Illustration of the experimental design for (A) neighbour treatment, i.e. two plants in one pot divided by a food-grade nylon mesh; and (B) solitary treatment,  i.e. two plants in one pot divided by a plastic film.

In their experiments they devised a set up in which two plants were grown in the same pot, with either a plastic film or a nylon mesh dividing their roots. The mesh allowed soil water, together with nutrient ions, to move between the two compartments, whilst the plastic film prevented any form of exchange. Each experiment was terminated, and plants harvested when the seeds were ripe, and most leaves had turned yellow. Plants were separated into root, vegetative shoot, and reproductive organs, then dried and weighed.

In contrast to their hypothesis, Chen et al. found that in their experiments, soybean plants grew roots regardless of belowground competition, whilst sunflower plants actually tended to under-invest in root growth when a neighbour plant was present. From their results they concluded that neighbour-induced root over-proliferation is not a ubiquitous feature in plants. They highlight that the mesh-divider design is probably not an ideal set-up for testing such responses, since the sensitivity of plants to neighbour-induced nutrient depletion can be largely reduced. However, they state that, “this ‘disadvantage’ appears to make this design a promising set-up for testing interplant chemical communication in the studies of below-ground neighbour detection, results of which are often confounded by the effect of nutrient competition.”