The heightened awareness concerning environmental preservation, resource scarcity, food safety, and nutrition has engendered the need for a more sustainable and resource-efficient agricultural production system. In this context, microalgae offer the potential to recover nutrients from waste streams and subsequently use the microalgal biomass as a sustainable slow-release fertilizer. The aim of this study was to assess microalgal bacterial flocs treating aquaculture wastewater and marine microalgae as organic slow-release fertilizers for tomato cultivation. Comparable plant growth was observed using microalgal and commercial organic fertilizer treatments. Furthermore, the microalgal fertilizers improved the fruit quality through an increase in sugar and carotenoid content, although a lower tomato yield was obtained. An economic evaluation indicates the economic feasibility of the microalgae-based fertilizers. Further research is required to optimize the microalgae-based fertilizer composition

The choice of soilless growing medium for plant nutrition, growth and support is crucial for improving the eco-sustainability of the production in horticultural systems. As our current understanding of the functional microbial communities inhabiting this ecosystem is still limited, we examined the microbial community development of the two most important growing media (organic and mineral) used in open soilless horticultural systems. We aimed to identify factors that influence community composition over time, and to compare the distribution of individual taxa across growing media, and their potential functionality. High throughput sequencing analysis revealed a distinctive and stable microbial community in the organic growing medium. Humidity, pH, nitrate-N, ammonium-N and conductivity were uncovered as the main factors associated with the resident bacterial communities. Ammonium-N was correlated with Rhizobiaceae abundance, while potential competitive interactions among both Methylophilaceae and Actinobacteridae with Rhizobiaceae were suggested. Our results revealed that soilless growing media are unique niches for diverse bacterial communities with temporal functional stability, which may possibly impact the resistance to external forces. These differences in communities can be used to develop strategies to move towards a sustainable horticulture with increased productivity and quality.

Purple non-sulphur bacteria (PNSB) are phototrophic microorganisms, which increasingly gain attention in plant production due to their ability to produce and accumulate high-value compounds that are beneficial for plant growth. Remarkable features of PNSB include the accumulation of polyphosphate, the production of pigments and vitamins and the production of plant growth-promoting substances (PGPSs). Scattered case studies on the application of PNSB for plant cultivation have been reported for decades, yet a comprehensive overview is lacking. This review highlights the potential of using PNSB in plant production, with emphasis on three key performance indicators (KPIs): fertilization, resistance to stress (biotic and abiotic) and environmental benefits. PNSB have the potential to enhance plant growth performance, increase the yield and quality of edible plant biomass, boost the resistance to environmental stresses, bioremediate heavy metals and mitigate greenhouse gas emissions. Here, the mechanisms responsible for these attributes are discussed. A distinction is made between the use of living and dead PNSB cells, where critical interpretation of existing literature revealed the better performance of living cells. Finally, this review presents research gaps that remain yet to be elucidated and proposes a roadmap for future research and implementation paving the way for a more sustainable crop production. Funding Information The authors would like to acknowledge: (i) the MIP i-Cleantech Flanders (Milieu-innovatieplatform; Environment innovation platform) project Microbial Nutrients on Demand (MicroNOD) for financial support; (ii) the China Scholarship Council for financially supporting Y. Sui (File No. 201507650015); (iii) the DOCPRO4 project 'Pur-pleTech', funded by the BOF (Bijzonder onderzoeksfonds); Special research fund from the University of Antwerp for financially supporting J. Spanoghe, and (iv) E. Koutsoukou for constructing components of Figs 5 and 6.

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.

Ombrotrophic peatlands are a recognized global carbon reservoir. Without restoration and peat regrowth, harvested peatlands are dramatically altered, impairing their carbon sink function, with consequences for methane turnover. Previous studies determined the impact of commercial mining on the physicochemical properties of peat and the effects on methane turnover. However, the response of the underlying microbial communities catalyzing methane production and oxidation have so far received little attention. We hypothesize that with the return of Sphagnum spp. postharvest, methane turnover potential and the corresponding microbial communities will converge in a natural and restored peatland. To address our hypothesis, we determined the potential methane production and oxidation rates in natural (as a reference), actively mined, abandoned, and restored peatlands over two consecutive years. In all sites, the methanogenic and methanotrophic population sizes were enumerated using quantitative PCR (qPCR) assays targeting the mcrA and pmoA genes, respectively. Shifts in the community composition were determined using Illumina MiSeq sequencing of the mcrA gene and a pmoA-based terminal restriction fragment length polymorphism (t-RFLP) analysis, complemented by cloning and sequence analysis of the mmoX gene. Peat mining adversely affected methane turnover potential, but the rates recovered in the restored site. The recovery in potential activity was reflected in the methanogenic and methanotrophic abundances. However, the microbial community composition was altered, being more pronounced for the methanotrophs. Overall, we observed a lag between the recovery of the methanogenic/methanotrophic activity and the return of the corresponding microbial communities, suggesting that a longer duration (Ͼ15 years) is needed to reverse mining-induced effects on the methane-cycling microbial communities.IMPORTANCE Ombrotrophic peatlands are a crucial carbon sink, but this environment is also a source of methane, an important greenhouse gas. Methane emission in peatlands is regulated by methane production and oxidation catalyzed by methanogens and methanotrophs, respectively. Methane-cycling microbial communities have been documented in natural peatlands. However, less is known of their response to peat mining and of the recovery of the community after restoration. Mining exerts an adverse impact on potential methane production and oxidation rates and on methanogenic and methanotrophic population abundances. Peat mining also induced a shift in the methane-cycling microbial community composition. Nev-

SummaryVegetables and fruits are an important part of a healthy food diet, however, the eco‐sustainability of the production of these can still be significantly improved. European farmers and consumers spend an estimated €15.5 billion per year on inorganic fertilizers and the production of N‐fertilizers results in a high carbon footprint. We investigated if fertilizer type and medium constituents determine microbial nitrogen conversions in organic growing media and can be used as a next step towards a more sustainable horticulture. We demonstrated that growing media constituents showed differences in urea hydrolysis, ammonia and nitrite oxidation and in carbon dioxide respiration rate. Interestingly, mixing of the growing media constituents resulted in a stimulation of the function of the microorganisms. The use of organic fertilizer resulted in an increase in amoA gene copy number by factor 100 compared to inorganic fertilizers. Our results support our hypothesis that the activity of the functional microbial community with respect to nitrogen turnover in an organic growing medium can be improved by selecting and mixing the appropriate growing media components with each other. These findings contribute to the understanding of the functional microbial community in growing media and its potential role towards a more responsible horticulture.

Funding InformationThe authors would like to kindly acknowledge (i) the MIP i-Cleantech Flanders (Milieu-innovatieplatform; Environment innovation platform) project Microbial Nutrients on Demand (MicroNOD) for financial support, (ii) the DOCPRO4 project 'PurpleTech', funded by the BOF (Bijzonder onderzoeksfonds; Special research fund) from the University of Antwerp for financially supporting J.S., (iii) all MicroNOD partners, including the University of Antwerp, Ghent University, AgrAqua, Greenyard Horticulture and Avecom; and (iv) all steering committee members, including Greenyard Frozen, Agristo, AVBS,

Microbial Diversity in Tomato Cultures soils supplemented with animal and plant by-products. Long-term fertilizer regimes significantly changed the PLFA fingerprints in both the soilless culture and soil based culture system. The use of these by-products in the soil was positively associated with arbuscular mycorrhizal fungi (AMF), which may influence rhizosphere communities through root exudates and C translocation. Community structure was distinct and consistently different over time, despite the fertilizer supplementation. The fungal microbial community composition was less affected by pH, while the composition of the bacterial communities (Actinomycetes, Gram-negative bacteria, and Gram-positive bacteria) was closely defined by soil pH, demonstrating the significance of pH as driver of bacterial community composition. Fertilizer application may be responsible for variations over time in the ecosystem. Knowledge about the microbial interactions in tomato cultivating systems opens a window of opportunity for designing targeted fertilizers supporting sustainable crop production.