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Dissolved organic matter (DOM) plays vital roles in carbon and other nutrient transformation at soil-water interfaces (SWI) in paddy fields. It is associated with the growth and withering of periphytic biofilms. However, the interactions between DOM and periphytic biofilms remain largely unknown. In this study, a microcosm experiment with different initial DOM contents elucidated that the biomass, and biomass nitrogen and phosphorus contents were greatly influenced by humic-like substances (C2 and C3), while the growth of periphytic biofilms increased the contents of humic-like (C1 and C2) and tryptophan-like substances (C5) in soil. Moreover, the decomposition of periphytic biofilms significantly increased soil pH, DOM, C2, C3 and C5 contents, but caused decrease in Eh, with consequent reduce in water soluble phosphorus (WSP) and release of algal available phosphorus (AAP). Results from this study revealed how DOM interacts with periphytic biofilms and the consequent effects on changes of bioactive phosphorus fractions, and provide practical information for designing periphytic biofilm based biofertilizer from the perspective of soil DOM., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Phototrophic biofilms are distributed widely at the sediment/soil-water interfaces (SWI) in paddy fields, where they immobilize phosphorus, thereby reducing its runoff loss. However, how soil carbon, nutrient availability and nutrient ratios drive the phototrophic biofilm community and its contribution to phosphorus cycling is largely unknown. A large scale field investigation in Chinese paddy fields reported here shows that soil organic carbon (SOC) and soil total nitrogen (STN) contents rather than soil total phosphorus (STP) triggered phosphorus immobilization of paddy biofilms, as they changed algal diversity and EPS production. High C: P and N: P ratios favored phosphorus immobilization in biofilm biomass via increasing the abundance of green algae. The C: N ratio on the other hand had only a weak effect on phosphorus immobilization, being counteracted by SOC or STN. Results from this study reveal how the in-situ interception of phosphorus in paddy fields is driven by soil carbon, nutrient availability and nutrient ratios and provide practical information on how to reduce runoff losses of phosphorus by regulating SOC and STN contents., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Upconversion phosphors (UCPs) can convert visible light into luminescence, such as UV, which can regulate the growth of microbes. Based on these fundamentals, the community composition of periphytic biofilms stimulated by UCPs doped with Pr 3+ -Li + was proposed to augment the removal of phosphorus (P) and copper (Cu). Results showed that the biofilms with community composition optimized by UCPs doped with Pr 3+ -Li + had high P and Cu 2+ removal rates. This was partly due to overall bacterial and algal abundance and biomass increases. The synergistic actions of algal, bacterial biomass and carbon metabolic capacity in the Pr-Li stimulated biofilms facilitated the removal of P and Cu 2+ . The results show that the stimulation of periphytic biofilms by lanthanide-doped UCPs is a promising approach for augmenting P and Cu 2+ removal., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Interactions among microbes determine the prevalence of harmful algal blooms that threaten water quality. These interactions can be indirectly mediated by shared resources or consumers, or through interference by the production of allelochemicals. Allelopathic interactions and resource competition have been shown to occur among algae and associated microbes. However, little work has considered seasonal influences on ecosystem structure and function. Here, we report results of our investigations on seasonal changes in the interactions between benthic microbial assemblies and the bloom forming cyanobacterium Microcystis aeruginosa. We show that phosphorus (P) competition and allelopathy by the microbial assembly vary seasonally and inhibit growth of M. aeruginosa. The interactions per unit biomass of the microbial assembly are stronger under winter than summer conditions and inhibit the recruitment of the cyanobacteria, thereby preventing the reoccurrence of cyanobacterial blooms in the following summer. The seasonality of these interactions correlates with changes in composition, metabolic activity and functional diversity of the microbial assembly. Our findings highlight the importance of competitive and allelopathic interactions in regulating the occurrence of harmful algal blooms. Our results also imply that seasonal variation of competition and allelopathy of the microbial assembly might be beneficial to adjust aquatic ecosystem structure and function., (© 2017 Society for Applied Microbiology and John Wiley & Sons Ltd.)

Periphyton is ubiquitous in paddy field, but its importance in influencing the bioavailability of phosphorus (P) in paddy soil has been rarely recognized. A paddy field was simulated in a greenhouse to investigate how periphyton influences P bioavailability in paddy soil. Results showed that periphyton colonizing on paddy soil greatly reduced P content in paddy floodwater but increased P bioavailability of paddy soil. Specifically, all the contents of water-soluble P (WSP), readily desorbable P (RDP), algal-available P (AAP), and NaHCO 3 -extractable P (Olsen-P) in paddy soil increased to an extent compared to the control (without periphyton) after fertilization. In particular, Olsen-P was the most increased P species, up to 216 mg kg -1 after fertilization, accounting for nearly 60 % of total phosphorus (TP) in soil. The paddy periphyton captured P up to 1.4 mg g -1 with Ca-P as the dominant P fraction and can be a potential crop fertilizer. These findings indicated that the presence of periphyton in paddy field benefited in improving P bioavailability for crops. This study provides valuable insights into the roles of periphyton in P bioavailability and migration in a paddy ecosystem and technical support for P regulation.

Phosphorus stored in lake sediments is an inner nutrient source and can be released into overlying water to exacerbate algal blooms. A simulated microcosm of Dianchi Lake was built to investigate phosphorus release from sediments to overlying water and its effect on the growth of Microcystis aeruginosa. The sediments of Dianchi Lake had a total phosphorus (TP) content of 1.7-1.8 mg g(-1) with Ca bound phosphorus (Ca-P, 50-54 %) and organic phosphorus (Org-P, 28-32 %) as the main fractions. The sediments released 8 % of TP into the overlying water with Fe/Al bound phosphorus (Fe/Al-P, 26 %) and Org-P (65 %) being the main fractions released. The phosphorus concentration of the overlying water increased from 0.14-0.16 to 0.28-0.33 mg L(-1). The biomass density of M. aeruginosa was positively correlated (R (2) = 0.825) with the concentration of orthophosphate, which was the predominant bioavailable phosphorus fraction for algal growth. Org-P can be partly utilized by M. aeruginosa but will not cause a bloom. A good understanding of the geochemical cycles of phosphorus is needed for regulating phosphorus release from sediments and thereby reducing the risk of cyanobacterial blooms.

Planted floating treatment bed (FTB) is an innovative technique of removing nutrients from polluted water but limited in deep water and cold seasons. Periphyton was integrated into FTB for a hybrid floating treatment bed (HFTB) to improve its nutrient removal capacity. To assess its potential for treating nutrient-polluted rivers, HFTB was up-scaled from 5L laboratory tanks to 350L outdoor tanks and then to a commercial-scale 900m section of polluted river. Plants and periphyton interacted in HFTB with periphyton limiting plant root growth and plants having shading effects on periphyton. Non-overlapping distribution of plants and periphyton can minimize the negative interactions in HFTB. HFTB successfully kept TN and TP of the river at less than 2.0 and 0.02mgL(-1), respectively. This study indicates that HFTB can be easily up-scaled for nutrients removal from polluted rivers in different seasons providing a long-term, environmentally-friendly method to remediate polluted ecosystems., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Benthic filamentous algae have evident advantages in wastewater treatment over unicellular microalgae, including the ease in harvesting and resistance to predation. To assess the potentials of benthic filamentous algae in treating horticultural wastewater under natural conditions in Belgium, three strains and their mixture with naturally wastewater-borne microalgae were cultivated in 250 ml Erlenmeyer flasks in laboratory as well as in 1 m(2) scale outdoor Algal Turf Scrubber (ATS) with different flow rates. Stigeoclonium competed well with the natural wastewater-borne microalgae and contributed to most of the biomass production both in Erlenmeyer flasks and outdoor ATS at flow rates of 2-6 L min(-1) (water velocity 3-9 cm s(-1)), while Klebsormidium was not suitable for growing in horticultural wastewater under the tested conditions. Flow rate had great effects on biomass production and nitrogen removal, while phosphorus removal was less influenced by flow rate due to other mechanisms than assimilation by algae., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

The N/P ratio of wastewater can vary greatly and directly affect algal growth and nutrient removal process. Three benthic filamentous algae species Cladophora sp., Klebsormidium sp. and Pseudanabaena sp. were isolated from a periphyton bioreactor and cultured under laboratory conditions on varying N/P ratios to determine their ability to remove nitrate and phosphorus. The N/P ratio significantly influenced the algal growth and phosphorus uptake process. Appropriate N/P ratios for nitrogen and phosphorus removal were 5-15, 7-10 and 7-20 for Cladophora sp., Klebsormidium sp. and Pseudanabaena sp., respectively. Within these respective ranges, Cladophora sp. had the highest biomass production, while Pseudanabaena sp. had the highest nitrogen and phosphorus contents. This study indicated that Cladophora sp. had a high capacity of removing phosphorus from wastewaters of low N/P ratio, and Pseudanabaena sp. was highly suitable for removing nitrogen from wastewaters with high N/P ratio., (Copyright © 2014 Elsevier Ltd. All rights reserved.)