Modification of Root Associated Bacteria, Root Architecture and Ph as Response to the Nitrogen Source Applied in Tomato

Crops often show plasticity in their root morphology and physiology to environmental changes that can influence the soil nutrient availability. Likewise, the application of mineral or organic fertilizers can lead to chemical changes in the soil that may affect the biological properties like the abundance of ammonia-oxidizing bacteria and nitrite oxidizing bacteria that are the most important organisms responsible for critical steps in the soil nitrogen cycle. Our objective was to measure the dynamic response of plants and root-associated bacteria to the nitrogen source applied, via invasive and non-invasive quantification of the rhizosphere processes. We compared the effect of organic source of nitrogen (amino acids) with an inorganic source (struvite, a recovered product from manure) on root architecture of tomato (Solanum licopersicum). The experiment was conducted in rhizotrons (allowing visualization of roots), including planar optodes for non-invasive in situ measurements of pH dynamics in the rhizosphere. Further, the effect of the fertilizers on the bacterial communities in the rhizosphere and the bulk soil was analyzed by high throughput sequencing analysis. Fertilizer type had a significant effect on total root length and the ratio of primary to secondary, increasing the secondary root growth in tomato with the organic nitrogen. The pH monitoring in the rhizosphere zone via optodes revealed that the organic fertilizer increased rhizosphere pH for short time duration. It is hypothesized that the increase of pH was due to co-uptake of protons from the substrate when tomato uptake the nitrate, which is consistent with low nitrate concentration measured in the substrate at harvest. The diversity measurements of microbial community were significantly different between fertilizers and between rhizosphere and rhizosheath (substrate directly attached to the root). Those results might explain the higher nitrification activity and the highest relative AOB abundance found in combination with the organic fertilizer compared to struvite