Neighbor sensing through rhizodeposits in sorghum affects plant physiology and productivity

Plant-plant interactions play a crucial role in shaping the growth environment for crops, impacting their productivity and stress response. The interaction between plants aboveground has been studied and incorporated into breeding programs that select for plants that reduce aboveground competition between plants. However, few studies have focused on belowground interactions, and these looked at combined interactions and root partitioning in the soil. This study focuses on the developmental and physiological responses of sorghum (Sorghum bicolor L.) genotypes to neighboring sorghum plants. In this study, we used two growing methods: i) a focal plant surrounded by neighboring plants in the same pot but without shading, and ii) a focal plant grown either alone or surrounded by neighbors, irrigated with nutrient solution passed through pots (leachates) with or without plants. Our results showed that the presence of neighbors in the same pot led to reduced size-dry weight height, and leaf area of the focal plant. In addition, the presence of neighbors reduced stomatal conductance and PSII quantum yield. While the response direction was similar across tested genotypes, the magnitude varied. The results were repeated when neighboring plants were not grown in the same pot, but the nutrient solution passed through the root system of plants of the neighboring genotype. Furthermore, we saw a reduction in assimilation rate and stomatal conductance when plants were exposed to either the physical presence of neighbors or leachate. We did not find differences in root architecture in either treatment. These results show plants change their growth in response to neighbors and that the signal is carried through the liquid phase of the soil. Our findings provide insights into sorghum plants responses to below-ground signaling from neighboring plants and lay the foundation for future studies enabling increased crop performance under high-density planting conditions.