Synthetic fertilizer production is associated with a high environmental footprint, as compounds typically dissolve rapidly leaching emissions to the atmosphere or surface waters. We tested two recovered nutrients with slower release patterns, as promising alternatives for synthetic fertilizers: struvite and a commercially available organic fertilizer. Using these fertilizers as nitrogen source, we conducted a rhizotron experiment to test their effect on plant performance and nutrient recovery in juvenile tomato plants. Plant performance was significantly improved when organic fertilizer was provided, promoting higher shoot biomass. Since the microbial community influences plant nitrogen availability, we characterized the root-associated microbial community structure and functionality. Analyses revealed distinct root microbial community structure when different fertilizers were supplied. However, plant presence significantly increased the similarity of the microbial community over time, regardless of fertilization. Additionally, the presence of the plant significantly reduced the potential ammonia oxidation rates, implying a possible role of the rhizosheath microbiome or nitrification inhibition by the plant. Our results indicate that nitrifying community members are impacted by the type of fertilizer used, while tomato plants influenced the potential ammonia-oxidizing activity of nitrogen-related rhizospheric microbial communities. These novel insights on interactions between recovered fertilizers, plant and associated microbes can contribute to develop sustainable crop production systems.
Aims Phosphorus (P) recovery from specific waste streams is necessary to develop environmentally sustainable and efficient fertilizers, achieving maximum productivity with minimum losses. A promising example of a Precovery product is struvite (MgNH 4 PO 4 ⋅6H 2 O). Phosphorus availability from struvite is profoundly influenced by soil pH and/or processes in the rhizosphere. Root exudates (e.g., organic anions) and root morphology affect fertilizer bioavailability. The overall objective of our study was to identify root morphological and physiological traits of the narrow-leaf lupine (Lupinus angustifolius L. subsp. angustifolius, cultivar: blau "Boregine") involved in the acquisition of P from struvite, compared with KH 2 PO 4 as a soluble P source. The study included different pH conditions, as soil pH is one of the main factors affecting P availability. Methods Narrow-leaf lupine plants were grown in river sand under three pH conditions (4.5, 6.5 and 7.5). Three different P treatment conditions were used: 1) KH 2 PO 4 (KP); 2) MgNH 4 PO 4 ⋅6H 2 O (Struvite), both supplied at 15 μg P g −1 dry sand; and 3) no P addition (Nil-P), as control. Organic acids in the rhizosheath were collected. Root morphological parameters such as specific root length and root diameter were analyzed. Results There was no significant difference in total plant biomass detected under any pH condition between struvite and KP treatments. In both acidic and alkaline conditions, the P-uptake efficiency (PUE: mg P plant −1 /cm 2 root surface area) with struvite was significantly greater than with KP. At neutral pH, there was no difference in PUE between plants supplied with KP or struvite. Plants growing at neutral pH showed greater root exudation of carboxylates (mainly citrate) when struvite was added compared with KP. At alkaline pH, the exudation per unit root surface area was greater than that at acidic or neutral pH. Plants growing in acidic pH had a higher specific root length (SRL) compared with those grown at alkaline or neutral pH. Conclusions Similar P-uptake efficiency from struvite and KH 2 PO 4 at neutral pH in conjunction with the higher total biomass compared to the Nil-P treatment (70% higher) suggests very effective mobilization of P from struvite by carboxylate exudation. Application of struvite, while taking into account the different
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