Plants establish symbioses with soil microbes that are important for nutrient extraction from soils and plant development. One such symbiosis is the rhizophagy cycle, where bacteria alternate between a free-living phase in soil where they acquire nutrients, and a plant-dependent protoplast phase inside plant root cells where root cells oxidatively extract nutrients from bacteria. In the rhizophagy cycle roots attract bacteria to root tips by secretion of exudates (sugars, organic acids, etc.). Experiments using plants free of bacteria, and plants where the rhizophagy cycle is inhibited through application of elevated CO2 to suppress reactive oxygen nutrient extraction from microbes, has shown that plant growth and development are inhibited without rhizophagy cycle activity. Invasive Phragmites australis is a plant that is notoriously difficult to control. We hypothesize that rhizophagy cycle activity in Phragmites australis may be inhibited through applications of organic acids and sugars to soils to interfere with or confuse exudate signaling between plant and soil microbes, and that this will reduce growth and invasiveness of plants. We conducted in vitro (Petri dish) and greenhouse experiments where plants were treated with organic salts (calcium propionate, calcium butyrate) and sugars (sucrose and mannose).
Results/Conclusions
In Petri dish experiments we found that organic salts and sugars suppressed entry of bacteria into Poa annua roots, resulting in failure of roots to form root hairs and root length suppression. In six-week greenhouse experiments using Phragmites australis plants, organic salt treatments at 50 mM in combination with sugars (50 mM) was particularly effective at inhibiting root and shoot development. Plants treated with organic salts and sugars showed high levels (> 2000 ppm) of soil CO2 that also may contribute to rhizophagy cycle suppression in roots through inhibition of root cell produced superoxide. In future experiments the plant to bacterium signal confusion strategy will be further evaluated to determine whether the strategy may be practically employed as a way to reduce growth and persistence of invasive plant species like Phragmites australis. Reduced rhizophagy cycle activity is expected to result in plants with reduced stress tolerance. Reduced stress tolerance may leave plants more susceptible to biotic stresses such as mowing, reducing the time for effective control of Phragmites australis.