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Biofilter systems coupling with microbial electrochemical technology can enhance the removal performance of pollutants. In this study, two types of coke (PK-A and PK-LSN) were used as electroconductive substrates in biofilter systems with silicone tubings. The results showed that the silicone tubings were beneficial for removing NH4+-N. The PK-A systems reached removal efficiencies up to 83.5–85.3% for NH4+-N without aeration. Compared to gravel systems, significantly higher removal efficiencies of NO3−-N (84.8–95.4%) were obtained in coke systems, and better removal of PO43--P (91.9–95.7%) was also simultaneously achieved in PK-A systems. Redundancy analysis (RDA) indicated that the better performances of coke systems rely on the functions of both electroactive (Trichococcus and Sulfurovum) and non-electroactive bacteria (Clostridium_sensu_stricto_1, Propionicicella, and Acinetobacter). These findings highlight the important contribution of silicone tubings to oxygen supply and provide useful guidance for the application of coke in composite matrix systems.

Background and results from a pot trial testing different fertilizer and compost combinations on soil fertility and parsley growth

Waterlogged soils contain monocarboxylic acids produced by anaerobic microorganisms. These “organic acids” can accumulate to phytotoxic levels and promote development of a barrier to radial O2 loss (ROL) in roots of some wetland species. Environmental cues triggering root ROL barrier induction, a feature that together with tissue gas-filled porosity facilitates internal aeration, are important to elucidate for knowledge of plant stress physiology. We tested the hypothesis that comparatively low, non-toxic, concentrations of acetic, propionic, butyric, and/or hexanoic acids might induce root ROL barrier formation in rice. Each organic acid, individually, triggered the ROL barrier in roots but with no effect (acetic or butyric acids) or with only slight effects (propionic or hexanoic acids) on root extension. Transcripts of four genes related to suberin biosynthesis were increased by some of the organic acid treatments. Respiration in root tissues was not, or moderately, inhibited. Beyond a narrow concentration range, however, respiration declined exponentially and the order (least to greatest) for EC50 (effective concentration for 50% inhibition) was butyric, propionic, acetic, then hexanoic acid. An understanding of the environmental cue for root ROL barrier induction should enhance future work to elucidate the molecular regulation of this root trait contributing to plant flooding tolerance.

(1) Phosphorus (P) is an essential plant nutrient, and P deficiency negatively affects plant growth and development. Furthermore, P is a finite and nonrenewable resource, and there is an urgent need to recover P from some of the important waste streams in society. Newly engineered calcareous materials (sol–gel coated cat litter (CATSAN®)) can bind P from wastewater in decentralized treatment systems and potentially enable P recycling into agricultural production by direct addition of the P saturated material. (2) The effects of the addition of two P-enriched calcareous materials as fertilizers for maize (Zea mays L.) growth were investigated in a mesocosm experiment. We compared fertilization with the P-enriched materials at rates of 6, 12, 25, 50, 100 kg P ha−1 yr−1 with fertilization with commercial NPK fertilizer. (3) The P fertilization by the P-enriched materials had a significant positive effect on plant height, biomass, maximum light-saturated photosynthetic rate, respiration rate, and total P content in biomass. However, plants fertilized by the commercial NPK fertilizer performed significantly better in the majority of measured parameters at identical fertilization rates. (4) The bioavailability of the P bound to the calcareous material was very low. However, the studied material has the potential to be used as part of a decentralized treatment solution to remove and subsequently recover and recycle P from wastewater.

During soil waterlogging, plants experience O2 deficits, elevated ethylene, and high CO2 in the root-zone. The effects on chickpea (Cicer arietinum L.) and faba bean (Vicia faba L.) of ethylene (2 μL L-1 ), CO2 (2-20% v/v) or deoxygenated stagnant solution were evaluated. Ethylene and high CO2 reduced root growth of both species, but O2 deficiency had the most damaging effect and especially so for chickpea. Chickpea suffered root tip death when in deoxygenated stagnant solution. High CO2 inhibited root respiration and reduced growth, whereas sugars accumulated in root tips, of both species. Gas-filled porosity of the basal portion of the primary root of faba bean (23%, v/v) was greater than for chickpea (10%), and internal O2 movement was more prominent in faba bean when in an O2 -free medium. Ethylene treatment increased the porosity of roots. The damaging effects of low O2 , such as death of root tips, resulted in poor recovery of root growth upon reaeration. In conclusion, ethylene and high CO2 partially inhibited root extension in both species, but low O2 in deoxygenated stagnant solution had the most damaging effect, even causing death of root tips in chickpea, which was more sensitive to the low O2 condition than faba bean.

Responses of wheat (Triticum aestivum) to complete submergence are not well understood as research has focused on waterlogging (soil flooding). The aim of this study was to characterize the responses of 2 wheat cultivars differing vastly in submergence tolerance to test if submergence tolerance was linked to shoot carbohydrate consumption as seen in rice. Eighteen-day-old wheat cultivars Frument (intolerant) and Jackson (tolerant) grown in soil were completely submerged for up to 19 days while assessing responses in physiology, gene expression, and shoot metabolome. Results revealed 50% mortality after 9.3 and 15.9 days of submergence in intolerant Frument and tolerant Jackson, respectively, and significantly higher growth in Jackson during recovery. Frument displayed faster leaf degradation as evident from leaf tissue porosity, chlorophylla , and metabolomic fingerprinting. Surprisingly, shoot soluble carbohydrates, starch, and individual sugars declined to similarly low levels in both cultivars by day 5, showing that cultivar Jackson tolerated longer periods of low shoot carbohydrate levels than Frument. Moreover, intolerant Frument showed higher levels of phytol and the lipid peroxidation marker malondialdehyde relative to tolerant Jackson. Consequently, we propose to further investigate the role of ethylene sensitivity and deprivation of reactive O2 species in submerged wheat.

Background and aims Floating sweet-grass ( Glyceria fluitans ) can form aerial as well as floating leaves, and these both possess superhydrophobic cuticles, so that gas films are retained when submerged. However, only the adaxial side of the floating leaves is superhydrophobic, so the abaxial side is directly in contact with the water. The aim of this study was to assess the effect of these different gas films on underwater net photosynthesis ( P N ) and dark respiration ( R D ). Methods Evolution of O 2 was used to measure underwater P N in relation to dissolved CO 2 on leaf segments with or without gas films, and O 2 microelectrodes were used to assess cuticle resistance of floating leaves to O 2 uptake in the dark. Key results The adaxial side of aerial leaves was more hydrophobic than the abaxial side and also initially retained a thicker gas film when submerged. Underwater P N vs. dissolved CO 2 of aerial leaf segments with gas films had a K m of 172 mmol CO 2 m -3 and a P max of 7·1 μmol O 2 m -2 s -1 , and the leaf gas films reduced the apparent resistance to CO 2 uptake 12-fold. Underwater P N of floating leaves measured at 700 mmol CO 2 m -3 was 1·5-fold higher than P N of aerial leaves. The floating leaves had significantly lower cuticle resistance to dark O 2 uptake on the wettable abaxial side compared with the superhydrophobic adaxial side. Conclusions Glyceria fluitans showed high rates of underwater P N and these were obtained at environmentally relevant CO 2 concentrations. It appears that the floating leaves possess both aquatic and terrestrial properties and thus have 'the best of both worlds' so that floating leaves are particularly adapted to situations where the plant is partially submerged and occasionally experiences complete submergence.

Concern regarding the potential negative impacts of released engineered nanoparticles (ENPs) on pollutant removal performance of wastewater treatment systems has received booming attention in recent years. However, the conclusions drawn from different studies often lead to fragmented overall knowledge, some of which are even contradictory. This scenario shows the necessity for a comprehensive review of the interactions of ENPs in wastewater treatment systems, particularly on the impacts of ENPs on microbial processes of carbon (C), nitrogen (N), and phosphorus (P) removal in water treatment systems. This review introduced the impact of 6 often reported ENPs in 5 types of treatment systems. We found that exposure to most of the investigated ENPs at low concentrations doesn't adversely influence the growth of the heterotrophic microbes, which are responsible for organic matter removal. The impacts of ENPs on various microbial nitrogen transformation processes have been investigated. Dosing of ENPs often causes acute microbial nitrogen removal inhibition at various concentrations, but does not influence long-term operation due to microbial adaption. No significant negative effects on biological phosphorus removal in different wastewater treatment processes have been reported after both short-term and long-term exposure (except copper nanoparticles). Environmentally relevant concentrations of ENPs have been reported to enhance the photosynthetic capacity of wetland plants, whereas chronic inhibition to photosynthesis was found in exposure to high concentrations of ENPs. Inhibition effects are often overestimated in pure cultivated toxicity test assays compared to testing with artificially prepared wastewater containing various ingredients or with real wastewater. Potential ligands in real wastewater can bind with ENPs and lower their dissolution. Some challenges exist regarding detection and quantification techniques of ENPs at environmental concentrations, modeling of engineered nanomaterial release on a worldwide scale, and inhibitory mechanisms to microbial transformations.

The review aims to report the state-of-the-art constructed wetlands (CW) in the Latin America and Caribbean (LAC) region not limited to national and local conditions. The aim is with a broader view, to bring updated and sufficient information, to facilitate the use of the CW technology in the different countries of LAC. Thus, 520 experiences extracted from the 169 reviewed documents in 20 countries were analyzed. According to the data, horizontal subsurface flow wetlands are the most reported CW in the region (62%), the second most common CW technology in the region is free water surface CW (17%), then vertical flow systems (9%), followed by intensified constructed wetlands (8%), and finally French systems (4%). The performance for nutrient removal is analyzed, finding that the mean of Chemical Oxygen Demand (COD), Total Nitrogen (TN), and Total Phosphorous (TP) removal efficiencies varies from 65% to 83%, 55% to 72%, and 30% to 84%, respectively. The results suggest a generally good performance for COD and TN removal, but a low performance for TP removal. Regarding plant species used for CWs, 114 different plant species were reported, being until now the most extensive report about plant species used in CWs in the LAC region.

BACKGROUND AND AIMS: Soil waterlogging adversely impacts most plants. Melilotus siculus is a waterlogging-tolerant annual forage legume, but data were lacking for the effects of root-zone hypoxia on nodulated plants reliant on N(2) fixation. The aim was to compare the waterlogging tolerance and physiology of M. siculus reliant on N(2) fixation or with access to NO(3)(−). METHODS: A factorial experiment imposed treatments of water level (drained or waterlogged), rhizobia (nil or inoculated) and mineral N supply (nil or 11 mm NO(3)(−)) for 21 d on plants in pots of vermiculite in a glasshouse. Nodulation, shoot and root growth and tissue N were determined. Porosity (gas volume per unit tissue volume) and respiration rates of root tissues and nodules, and O(2) microelectrode profiling across nodules, were measured in a second experiment. KEY RESULTS: Plants inoculated with the appropriate rhizobia, Ensifer (syn. Sinorhizobium) medicae, formed nodules. Nodulated plants grew as well as plants fed NO(3)(−), both in drained and waterlogged conditions. The growth and total N content of nodulated plants (without any NO(3)(−) supplied) indicated N(2) fixation. Respiration rates (mass basis) were highest in nodules and root tips and lowest in basal root tissues. Secondary aerenchyma (phellem) formed along basal root parts and a thin layer of this porous tissue also covered nodules, which together enhanced gas-phase diffusion of O(2) to the nodules; O(2) was below detection within the infected zone of the nodule interior. CONCLUSIONS: Melilotus siculus reliant on N(2) fixation grew well both in drained and waterlogged conditions, and had similar tissue N concentrations. In waterlogged conditions the relatively high respiration rates of nodules must rely on O(2) movement via the aerenchymatous phellem in hypocotyl, roots and the outer tissue layers of nodules.

Using constructed wetlands (CWs) for aquaculture wastewater treatment is a quite new technique in the Mekong Delta, Vietnam, where untreated aquaculture wastewater has been conventionally discharged into the rivers. The problem of poor water quality which causes illness in shrimp that has been recognized recently by local farmers. The aim of this study was to find an environmental friendly alternative method for sustainable shrimp production. A pilotscaleset-up consisting of a surface flow constructed wetlands planted Typha orientalis and Scirpus littoralis which was used as biofilter to purify recirculated wastewater from an intensive white leg shrimp (Litopenaeus vannamei) tank culture (Figure 1). The system was operated at a recirculation rate of 0.17 L/min (equivalent to 200% volume shrimp tank per day). Water quality in the shrimp tanks was monitored every two weeks. Mass balance method was used to quantify system performance, nitrogen and phosphorus storage in plant and water and nutrient removal mechanisms in each system. Water quality was stable over three months of feeding application. The system appeared to be a promising purification technique for sustainable shrimp production with zero-discharge. Using constructed wetlands (CWs) for aquaculture wastewater treatment is a quite new technique in the Mekong Delta, Vietnam, where untreated aquaculture wastewater has been conventionally discharged into the rivers. The problem of poor water quality which causes illness in shrimp that has been recognized recently by local farmers. The aim of this study was to find an environmental friendly alternative method for sustainable shrimp production. A pilotscaleset-up consisting of a surface flow constructed wetlands planted Typha orientalis and Scirpus littoralis which was used as biofilter to purify recirculated wastewater from an intensive white leg shrimp (Litopenaeus vannamei) tank culture (Figure 1). The system was operated at a recirculation rate of 0.17 L/min (equivalent to 200% volume shrimp tank per day). Water quality in the shrimp tanks was monitored every two weeks. Mass balance method was used to quantify system performance, nitrogen and phosphorus storage in plant and water and nutrient removal mechanisms in each system. Water quality was stable over three months of feeding application. The system appeared to be a promising purification technique for sustainable shrimp production with zero-discharge.

During soil waterlogging, plants experience O

Background and Aims: Plants regulate cellular oxygen partial pressures (pO2), together with reduction/ oxidation (redox) state to manage rapid developmental transitions such as bud burst after a period of quiescence. However, our understanding of pO2 regulation in complex meristematic organs such as buds is incomplete, and particularly lacks spatial resolution. Methods: The gradients in pO2 from the outer scales to the primary meristem complex were measured in grapevine (Vitis vinifera L.) buds, together with respiratory CO2 production rates and the accumulation of superoxide and hydrogen peroxide, from ecodormancy through the first 72 h preceding bud burst, triggered by the transition from low to ambient temperatures. Key Results: Steep internal pO2 gradients were measured in dormant buds with values as low as 2.5 kPa found in the core of the bud prior to bud burst. Respiratory CO2 production rates increased soon after the transition from low to ambient temperatures and the bud tissues gradually became oxygenated in a patterned process. Within 3 h of the transition to ambient temperatures, superoxide accumulation was observed in the cambial meristem, co-localising with lignified cellulose associated with pro-vascular tissues. Thereafter, superoxide accumulated in other areas subtending the apical meristem complex, in the absence of significant hydrogen peroxide accumulation, except in the cambial meristem. By 72 h, the internal pO2 gradient showed a biphasic profile, where the minimum pO2 was external to the core of the bud complex. Conclusions: Spatial and temporal control of the tissue oxygen environment occurs within quiescent buds, and the transition from quiescence to bud burst is accompanied by a regulated relaxation of the hypoxic state and accumulation of reactive oxygen species (ROS) within the developing cambium and vascular tissues of the heterotrophic grapevine buds.

Background and Aims Many stem-succulent halophytes experience regular or episodic flooding events, which may compromise gas exchange and reduce survival rates. This study assesses submergence tolerance, gas exchange and tissue oxygen (O2) status of two stem-succulent halophytes with different stem diameters and from different elevations of an inland marsh. Methods Responses to complete submergence in terms of stem internal O2 dynamics, photosynthesis and respiration were studied for the two halophytic stem-succulents Tecticornia auriculata and T. medusa. Plants were submerged in a glasshouse experiment for 3, 6 and 12 d and O2 levels within stems were measured with microelectrodes. Photosynthesis by stems in air after de-submergence was also measured. Key Results Tecticornia medusa showed 100 % survival in all submergence durations whereas T. auriculata did not survive longer than 6 d of submergence. O2 profiles and time traces showed that when submerged in water at air-equilibrium, the thicker stems of T. medusa were severely hypoxic (close to anoxic) when in darkness, whereas the smaller diameter stems of T. auriculata were moderately hypoxic. During light periods, underwater photosynthesis increased the internal O2 concentrations in the succulent stems of both species. Stems of T. auriculata temporally retained a gas film when first submerged, whereas T. medusa did not. The lower O2 in T. medusa than in T. auriculata when submerged in darkness was largely attributed to a less permeable epidermis. The submergence sensitivity of T. auriculata was associated with swelling and rupturing of the succulent stem tissues, which did not occur in T. medusa. Conclusions The higher submergence tolerance of T. medusa was not associated with better internal aeration of stems. Rather, this species has poor internal aeration of the succulent stems due to its less permeable epidermis; the low epidermal permeability might be related to resistance to swelling of succulent stem tissues when submerged.

Responses of wheat (Triticum aestivum) to complete submergence are not well understood as research has focused on waterlogging (soil flooding). The aim of this study was to characterize the responses of 2 wheat cultivars differing vastly in submergence tolerance to test if submergence tolerance was linked to shoot carbohydrate consumption as seen in rice. Eighteen-day-old wheat cultivars Frument (intolerant) and Jackson (tolerant) grown in soil were completely submerged for up to 19 days while assessing responses in physiology, gene expression, and shoot metabolome. Results revealed 50% mortality after 9.3 and 15.9 days of submergence in intolerant Frument and tolerant Jackson, respectively, and significantly higher growth in Jackson during recovery. Frument displayed faster leaf degradation as evident from leaf tissue porosity, chlorophyll

The present study examined the effects of three recirculation rates (50%, 200% and 400%) on water quality and biomass growth at low and high fish stocking densities (122 and 220 fish/m 3 ) in aquaponic systems. The system consisted of a Tilapia tank connected to a gravel filter and three hydroponic trenches in series with Ipomoea aquatica , Lactuca sativa and Canna glauca . The RRs influenced most water quality parameters with best water quality at the high RR. At the low RR of 50% mass mortality of fish occurred due to lack of oxygen. The fish growth and survival was excellent in the high RR of 400% at the low fish density of 122 fish/m 3 . The plant trenches were found to be effective in removing potential harmful concentrations of NH 4 -N and NO 2 -N from the recirculating water. For each kg of fish produced in this system approximately 1.0 m 3 water was needed. During a 25-day period about 1 kg of marketable fresh biomass of I. aquatica and 270 g dry weight aboveground biomass of C. glauca was produced. It is concluded that high recirculation rate of the water of 200–400% per day is needed to secure a good growth and a low FCR of Tilapia in aquaponic systems. High recirculation rates also secure a good water quality. The aquaponic system has a very low effluent discharge compared to traditional aquaculture techniques, and it recycles nutrients for plant growth. Hence, aquaponic system is a promising sustainable solution that can be applied on commercial fish pond scale.

The submerged aquatic freshwater macrophyte Isoetes australis S. Williams grows in rock pools situated in south-western Australia, an environment where dissolved inorganic phosphorus (Pi) availability possibly limits growth. In contrast to the two coexisting aquatic species, Glossostigma drummundii and Crassula natans, I. australis did not form relationships with mycorrhiza. Pi uptake kinetics were determined for I. australis in experiments using radioactive 33Pi. Roots had a higher Pi affinity (lower Km) than leaves, but roots also had a lower Vmax, which is discussed in relation to the low ambient Pi concentrations. I. australis showed morphological adaptation which could relate to the low Pi environment by having approximately twice as much root tissue as leaf tissue (by dry mass), facilitating access to the higher P pools in the sediment compared with the shallow water column. A short-term translocation experiment revealed high amounts of Pi translocation internally in the plant which seemed to go from roots and oldest leaves to younger leaves. As a result of the high root to shoot ratio, high surface area, root uptake kinetics, and sediment Pi availability, roots accounted for 87% of plant Pi uptake and the green parts of the leaves for about the remaining 13%. As a result the estimated P budget for the rock pools showed that the surface water had a Pi turnover of about 1.5 days, whereas the porewater Pi pool was renewed about 10 times per day to satisfy the P requirements of I. australis.

Most studies on emission of the greenhouse gases nitrous oxide (N2O) and methane (CH4) have been carried out in temperate areas so there is generally a lack of data from subtropical and tropical climates. A large part of the subtropical and tropical coastal wetlands consists of mangrove ecosystems, which have potential to act as sources of N2O and CH4. We measured N2O and CH4 emissions during 11 months in the brackish lagoon system Cienaga Grande de Santa Marta (CGSM) on the Caribbean coast of Colombia. The area has been seriously influenced by human disturbance which resulted in approximately 60% mangrove mortality but the ecosystem is now being rehabilitated. In addition to N2O and CH4 emissions at four sampling sites, we also measured temperature, salinity, pH, dissolved oxygen (DO), redox potential, nitrite ( NO 2 − ) , nitrate ( NO 3 − ) , ammonium ( NH 4 + ) and organic material in the water and/or the sediment. We found the mangrove sediments of CGSM to be a source of N2O and CH4 but there was large variability of the emissions on both temporal and spatial scale with N2O and CH4 fluxes in the range 35–1180 μg m−2 h−1 and 0–31570 μg m−2 h−1, respectively. Correlations between N2O fluxes and the water variables showed that salinity significantly contributed towards decreased emission of N2O (r = −0.38). By contrast, water concentrations of NO 3 − were correlated with increased emission of N2O (r = 0.54). Emission of CH4 was negatively correlated with DO in the water (r = −0.34) and there was a positive correlation between organic matter and CH4 emission (r = 0.75). It was found that untreated wastewater discharged into the Magdalena River and in turn, the lagoon system may have resulted in a substantially higher emission of both N2O and CH4 as the wastewater contributes substrate to the processes in the form of N and organic matter. With better treatment of wastewater, it is possible that emission of both gases would be lower, especially at the sites closest to Magdalena River.

Flooding of fields after sudden rainfall events can result in crops being completely submerged. Some terrestrial plants, including wheat (Triticum aestivum L.), possess superhydrophobic leaf surfaces that retain a thin gas film when submerged, and the gas films enhance gas exchange with the floodwater. However, the leaves lose their hydrophobicity during submergence, and the gas films subsequently disappear. We tested gas film retention time of 14 different wheat cultivars and found that wheat could retain the gas films for a minimum of 2 days, whereas the wild wetland grass Glyceria fluitans (L.) R.Br. had thicker gas films and could retain its gas films for a minimum of 4 days. Scanning electron microscopy showed that the wheat cultivars and G. fluitans possessed high densities of epicuticular wax platelets, which could explain their superhydrophobicity. However, G. fluitans also had papillae that contributed to higher hydrophobicity during the initial submergence and could explain why G. fluitans retained gas films for a longer period of time. The loss of gas films was associated with the leaves being covered by an unidentified substance. We suggest that leaf gas film is a relevant trait to use as a selection criterion to improve the flood tolerance of crops that become temporarily submerged.

The effects of N-form and pH on growth, morphology, nitrogen uptake and nutrients allocation in Job's Tears ( Coix lacryma-jobi L.) were determined. The plants were grown on a growth medium with either ammonium (NH 4 + ) or nitrate (NO 3 − ) at the same concentration (500 μM) and at four levels of pH: 3.5, 5.0, 6.5 and 8.5 under greenhouse conditions for forty days. C. lacryma-jobi prefers NO 3 − nutrition, as plants supplied with NO 3 − had higher relative growth rates than plants supplied with NH 4 + , particularly at neutral and alkaline pH. At low pH (3.5, 5.0) both NH 4 + and NO 3 − fed plants had brighter roots and more lateral roots than at higher pH. The NH 4 + uptake rates were highest at pH 6.5 and 8.5 whereas the NO 3 − uptake rates were highest at pH 5.0. The uptake rates of both NH 4 + and NO 3 − were very low at pH 3.5. The pH of the growth medium significantly affected plant mineral uptake. The calcium (Ca) concentrations in leaves were highest at pH 6.5 and 8.5. The tissue concentrations of potassium (K) were only affected for NO 3 − -fed plants where K concentrations were higher at pH 3.5 and 5.0 than at higher pH. It is concluded that C. lacryma-jobi has a preference for NO 3 − which makes it suitable for wastewater treatment in constructed wetland system where a substantial fraction of the N is on NO 3 − form such as in vertical flow constructed wetlands.

Floods and salinization of agricultural land adversely impact global rice production. We investigated whether gas films on leaves of submerged rice delay salt entry during saline submergence. Two-week-old plants with leaf gas films (+GF) or with gas films experimentally removed (-GF) were submerged in artificial floodwater with 0 or 50 mm NaCl for up to 16 d. Gas films were present9 d on GF plants after which gas films were diminished. Tissue ion analysis (Na

Common practice of aquaculture in Vietnam and other countries in South East Asia involves frequent discharge of polluted water into rivers which results in eutrophication and degradation of receiving water bodies. There is therefore a need to develop improved aquaculture systems which have a more efficient use of water and less environmental impact. The aim of this study was to assess the suitability of using constructed wetlands (CWs) for the treatment of fishpond water in a recirculating aquaculture system in the Mekong Delta of Vietnam. Water from a fishpond stocked with Nile tilapia (Oreochromis niloticus) and common carp (Cyprinus carpio) was recirculated through horizontal and vertical flow CWs. The CWs were able to keep a good water quality with DO (>1mg/l-1), BOD (

Constructed wetlands have a good potential for wastewater treatment in developing countries due to the simple operation and low implementation costs. Ornamental plants like Canna and Heliconia are used in the wetlands to increase their aesthetic value and these two species were compared in this study. Six pilot scale horizontal subsurface flow constructed wetland units were constructed at the Asian Institute of Technology (AIT) campus in Bangkok, Thailand, of which three were planted with Heliconia psittacorum L.f. × H. Spathocircinata (Aristeguieta) and three with Canna × generalis L. Bailey. The beds were loaded with domestic wastewater in four trials with hydraulic loading rates ranging from 55 to 440 mm d−1 corresponding to nominal detention times between 12 h and 4 days. Both plant species grew well in the systems and especially Canna had high growth rates (3100 ± 470 g DW m−2 yr−1) compared to Heliconia (550 ± 90 g DW m−2 yr−1). TSS mass removal rates were very high with efficiencies >88% even at hydraulic loading rates of 440 mm d−1. COD mass removal rates varied between 42 and 83% depending on the loading rates. The removal rate constants for COD as fitted by the first-order k–C* model were estimated to be 0.283 and 0.271 m d−1 for Canna and Heliconia beds, respectively (C* = 28.1 and 26.7 mg l−1). Removals of nitrogen (N) and phosphorus (P) were low compared to the loading rates, but removal of total-N was higher in the beds planted with Canna than in beds with Heliconia because of the higher growth rate of Canna. It is concluded that ornamental species like Canna and Heliconia can be used to enhance the aesthetic appearance and hence the public acceptance of wastewater treatment systems in tropical climates. Canna is the preferred species from a treatment perspective because of its more vigorous growth, but since Heliconia has an economic potential as cut flowers may be preferred in many cases.

Bud dormancy in winter is a crucial developmental stage in perennial plants. The densestructure of the bud protects the shoot apical meristem bearing next seasons’ inflorescencebut also creates hypoxic conditions. Currently, there is very little understanding of themolecular mechanisms in signalling the transitions of bud dormancy despite the importancefor reproductive fate. We have investigated temporal and spatial transitions of local oxygenpartial pressure (pO2) during the acute stages in buds burst in grapevine (Vitis viniferaL.).Wefound hypoxic condition at the core of dormant buds with a pO2 less than 5 kPa proximal tothe primary shoot apical meristem. Although removal of the outer scales relieved hypoxiaimmediately within a depth of 0 - 1800 μm from the outer scale, the primary bud meristemremained hypoxic (1800 - 2100 յm). Oxygenation of the internal tissue increased gradually 3,24 and 72 h after release of dormancy and was more pronounced under a 12/12 h light/darkphotoperiod when compared to complete darkness. A specific clade of ethylene responsivetranscription factors, the ERF VII class, is controlled through this pathway to timely regulatetheir protein stability during hypoxia. Database searches for homologs of class VII ERFs,combined with RNA-seq data from grape buds, identified three members of ERF withthe conserved MCGGA/L motif at the N-terminus as putative substrates of N-end proteindegradation pathway. These three ERFs are targets for future research in their possiblefunction to regulate hypoxia responsive and cell development genes.

Hordeum marinum Huds. is a waterlogging-tolerant wild relative of wheat (Triticum aestivum L.). Greater root porosity (gas volume per root volume) and formation of a barrier to reduce root radial O2 loss (ROL) contribute to the waterlogging tolerance of H. marinum and these traits are evident in some H. marinum–wheat amphiploids. We evaluated root porosity, ROL patterns and tolerance to hypoxic stagnant conditions for 10 various H. marinum (two accessions) disomic chromosome addition (DA) lines in wheat (two varieties), produced from two H. marinum–wheat amphiploids and their recurrent wheat parents. None of the DA lines had a barrier to ROL or higher root porosity than the wheat parents. Lack of a root ROL barrier in the six DA lines for H. marinum accession H21 in Chinese Spring (CS) wheat indicates that the gene(s) for this trait do not reside on one of these six chromosomes; unfortunately, chromosome 3 of H. marinum has not been isolated in CS. Unlike the H21–CS amphiploid, which formed a partial ROL barrier in roots, the H90–Westonia amphiploid and the four derived DA lines available did not. The unaltered root aeration traits in the available DA lines challenge the strategy of using H. marinum as a donor of these traits to wheat.

Submergence invokes a range of stressors to plants with impeded gas exchange between tissues and floodwater being the greatest challenge. Many terrestrial plants including wheat (Triticum aestivum L.), possess superhydrophobic leaf cuticles that retain a thin gas film when submerged, and the gas films enhance gas exchange with the floodwater. However, leaf hydrophobicity is lost during submergence and the gas films disappear accordingly. Here, we completely submerged wheat (with or without gas films) for up to 14 days and found that plants with gas films survived significantly longer (13 days) than plants without (10 days). Plants with gas films also had less dead tissue following a period of recovery. However, this study also revealed that reflections by gas films resulted in a higher light compensation point for underwater net photosynthesis for leaves with gas films compared with leaves without (IC = 52 vs 35 µmol photons m–2 s–1 with or without gas films, respectively). Still, already at ~5% of full sunlight the beneficial effect of gas films overcame the negative under ecologically relevant CO2 concentrations. Our study showed that dryland crops also benefit from leaf gas films during submergence and that this trait should be incorporated to improve flood tolerance of wheat.

Terrestrial saltmarsh plants inhabiting flood-prone habitats undergo recurrent and prolonged flooding driven by tidal regimes. In this study, the role of internal plant aeration in contrasting hypoxic/anoxic conditions during submergence was investigated in the two halophytes Limonium narbonense Mill. and Sarcocornia fruticosa (L.) A.J. Scott. Monitoring of tissue O2 dynamics was performed in shoots and roots using microelectrodes under drained conditions, waterlogging, partial and complete submergence, in light or darkness. For both species, submergence in darkness resulted in significant declines in tissue O2 status and when in light, in rapid O2 increases first in shoot tissues and subsequently in roots. During partial submergence, S. fruticosa benefitted from snorkelling and efficiently transported O2 to roots, whereas the O2 concentration in roots of L. narbonense declined by more than 90%. Significantly thinner leaves and articles were recorded under high degree of flooding stress and both species showed considerably high tissue porosity. The presence of aerenchyma seemed to support internal aeration in S. fruticosa whereas O2 diffusion in L. narbonense seemed impeded, despite the higher porosity (up to 50%). Thus, the results obtained for L. narbonense, being well adapted to flooding, suggests that processes other than internal aeration could be involved in better flooding tolerance e.g. fermentative processes, and that traits resulting in flooding tolerance in plants are not yet fully understood.

Roots in waterlogged soils experience low O2 and often high CO2.Comparative responses of waterlogging-sensitive chickpea and-tolerant faba bean to high root-zone CO2 concentrations were studiedin hydroponics. Plants were raised in aerated nutrient solution for 13days and then continued with aeration without additional CO2 or with2, 4, and 8% CO2 for 10 days. Some plants were also transferred todeoxygenated stagnant 0.1% agar nutrient solution. After 10 days oftreatments some plants were shifted back to aerated solution to assessrecovery for 7 days. Both genotypes showed sensitivity to CO2. Primaryroot growth, lateral root elongation and relative growth rate of rootsall decreased progressively as the CO2 concentration was increased.In both genotypes, primary root porosity was only increased when instagnant conditions and not when under high CO2 in aerated solution.There was a significant reduction in root respiration at 8% CO2 in bothgenotypes (not tested at the lower CO2 concentrations); respiration wasin chickpea 61% of control and in faba bean 72% of control. In bothgenotypes there was an increase in root sugars at 8% CO2, so substratewas presumably not limiting respiration. Upon recovery, both genotypesshowed only partial and delayed recovery of root growth from both highCO2 and from the stagnant treatment. This study on these two grainlegumes adds to data in the literature on soybean, and shows thateven if roots can access some O2, the high CO2 accumulation underwaterlogging might also contribute to growth reductions.

Oxygen deprivation is a key determinant of root growth and functioning under waterlogging. In this work, changes in net K+ flux and membrane potential (MP) of root cells were measured from elongation and mature zones of two barley varieties under hypoxia and anoxia conditions in the medium, and as influenced by ability to transport O2 from the shoot. We show that O2 deprivation results in an immediate K+ loss from roots, in a tissue- and time-specific manner, affecting root K+ homeostasis. Both anoxia and hypoxia induced transient membrane depolarization; the extent of this depolarization varied depending on severity of O2 stress and was less pronounced in a waterlogging-tolerant variety. Intact roots of barley were capable of maintaining H+-pumping activity under hypoxic conditions while disrupting O2 transport from shoot to root resulted in more pronounced membrane depolarization under O2-limited conditions and in anoxia a rapid loss of the cell viability. It is concluded that the ability of root cells to maintain MP and cytosolic K+ homeostasis is central to plant performance under waterlogging, and efficient O2 transport from the shoot may enable operation of the plasma membrane H+-ATPase in roots even under conditions of severe O2 limitation in the soil solution.

Oxygen deprivation is a key determinant of root growth and functioning under waterlogging. In this work, changes in net K(+) flux and membrane potential (MP) of root cells were measured from elongation and mature zones of two barley varieties under hypoxia and anoxia conditions in the medium, and as influenced by ability to transport O2 from the shoot. We show that O2 deprivation results in an immediate K(+) loss from roots, in a tissue- and time-specific manner, affecting root K(+) homeostasis. Both anoxia and hypoxia induced transient membrane depolarization; the extent of this depolarization varied depending on severity of O2 stress and was less pronounced in a waterlogging-tolerant variety. Intact roots of barley were capable of maintaining H(+) -pumping activity under hypoxic conditions while disrupting O2 transport from shoot to root resulted in more pronounced membrane depolarization under O2 -limited conditions and in anoxia a rapid loss of the cell viability. It is concluded that the ability of root cells to maintain MP and cytosolic K(+) homeostasis is central to plant performance under waterlogging, and efficient O2 transport from the shoot may enable operation of the plasma membrane H(+) -ATPase in roots even under conditions of severe O2 limitation in the soil solution.

Lowland rice (Oryza sativa L.) encounters flooded soils that are anaerobic and chemically reduced. Exposure of the roots to high soil Fe2+ concentrations can result in toxicity. Internal aeration delivering O2 to submerged roots via the aerenchyma is well understood, but the effect of Fe2+ on O2 transport in roots is less studied. We aimed to evaluate the effects of Fe2+ on growth and root aeration. O. sativa var. Amaroo was grown in aerobic and deoxygenated solutions with 0 mM, 0.18 mM, 0.36 mM, 0.54 mM or 0.72 mM Fe2+ using FeSO4.7H2O and a control with 0.05 mM Fe-EDTA. The treatments were imposed on 14-day-old plants (28–30 days old when harvested). Dry mass, shoot Fe concentration, root porosity and patterns of radial O2 loss (ROL) along roots were determined. In the aerobic solution, where Fe2+ was oxidised in the bulk medium, root dry mass increased with higher Fe2+; this was not the case in stagnant solutions, which had no significant root growth response, although Fe oxidation near the root surface was visible as a precipitate. In the highest Fe2+ treatment, shoot Fe concentrations in aerobic (667 mg kg–1) and stagnant (433 mg kg–1) solutions were below the level for toxicity (700 mg kg–1). Rice responded to high Fe2+ in aerobic conditions by increasing root porosity and inducing strong barriers to ROL. In stagnant conditions, root porosity was already high and the ROL barrier induced, so these root aeration traits were not further influenced by the Fe2+ concentrations applied.

Lowland rice (Oryza sativa L.) encounters flooded soils that are anaerobic and chemically reduced. Exposure of the roots to high soil Fe2+ concentrations can result in toxicity. Internal aeration delivering O2 to submerged roots via the aerenchyma is well understood, but the effect of Fe2+ on O2 transport in roots is less studied. We aimed to evaluate the effects of Fe2+ on growth and root aeration. O. sativa var. Amaroo was grown in aerobic and deoxygenated solutions with 0mM, 0.18mM, 0.36mM, 0.54mM or 0.72mM Fe2+ using FeSO4.7H2O and a control with 0.05mM Fe-EDTA. The treatments were imposed on 14-day-old plants (28-30 days old when harvested). Dry mass, shoot Fe concentration, root porosity and patterns of radial O2 loss (ROL) along roots were determined. In the aerobic solution, where Fe2+ was oxidised in the bulk medium, root dry mass increased with higher Fe2+; this was not the case in stagnant solutions, which had no significant root growth response, although Fe oxidation near the root surface was visible as a precipitate. In the highest Fe2+ treatment, shoot Fe concentrations in aerobic (667mgkg-1) and stagnant (433mgkg-1) solutions were below the level for toxicity (700mgkg-1). Rice responded to high Fe2+ in aerobic conditions by increasing root porosity and inducing strong barriers to ROL. In stagnant conditions, root porosity was already high and the ROL barrier induced, so these root aeration traits were not further influenced by the Fe2+ concentrations applied.

Bud dormancy is an important strategy in the phenology of temperate perennial trees, including important crops such as grapevine. Temperature and photoperiod play key roles in regulating dormancy, particularly accumulation of chilling hours. However, dormancy is a quantitative state and in many cases facultative. Where chilling is insufficient, bud burst is poorly coordinated; industry commonly apply chemicals such as hydrogen cyanamide to enforce a more even bud burst. Descriptive studies of transcriptional regulation during grapevine bud burst suggest an hypoxic state during the early stages of this transition, coincident with fermentation and an oxidative burst. To date there has been no physiological data to justify these conclusions. We investigated the internal oxygen status and respiration during a 72 h time course of bud burst. Buds were stored at 4EC to ensure complete satisfaction of endodormancy, before growing single bud explants in the dark or a 12/12 h photoperiod (150 μmol @m!1 @ s!1, 22EC). Transects of internal oxygen concentration showed a hypoxic state at the core of the bud (< 20 mM O2 at c. 2000 μm depth) at 3 h and 24 h in dark or dark/light (n $3). The influence of light, however was pronounced after 72 h; darkexposed buds had 80-100 mM O2, while dark/light-exposed buds were near oxygen saturation (200-260 mM O2). Hypotheses were further explored via respiratory, fermentation and qRT-PCR data.

Salt lakes of inland Australia are harsh environments, characterized by high soil salinity in combinationwith extreme changes in water availability, where both flooding and drought may occur. Stem succulenthalophytic shrubs of the genus Tecticornia (Chenopodiaceae) inhabit lake margins at the FortesqueMarshes and the communities exhibit patterns of species zonation. The species distributions might beinfluenced by gradients in elevation, depth to groundwater, flooding frequency and salinity.In the present study, physiological responses to submergence were evaluated in two species (T.medusaand T. auriculata) which may sometimes be completely submerged in freshwater as occurs after cyclonicrainfall events in the field. Plants were submerged for 3, 6 and 12 days and T. medusa showed highesttolerance with 100% survival in all treatments whereas T. auriculata could not survive longer than 6 dayssubmergence.The submergence sensitivity in T. auriculata was associated with swelling and rupturing of tissueeventually leading to necrosis. Underwater photosynthesis rates were compared between the speciesand the submergence tolerant T. medusa actually had the lowest rate. Oxygen profiles and time traces instems showed that T. medusa becomes anoxic in darkness although submerged in aerated water while T.auriculata still had aerobic tissue. However, measurements of tissue elasticity and strengthdemonstrated that T. medusa had higher tissue strength which was concluded to be the important traitfor survival in the inundated marshes although the exchange of gases may be slower in T. medusabecause of the less permeable tissue. This is the first study showing which mechanisms determinesubmergence tolerance in Tecticornia species and more studies are needed to find other possibledifferences between Tecticornia species.

Internal pressurization and convective gas flow, which can aerate wetland plants more efficiently than diffusion, are common in temperate species. Here, we present the first survey of convective flow in a range of tropical plants. The occurrence of pressurization and convective flow was determined in 20 common wetland plants from the Mekong Delta in Vietnam. The diel variation in pressurization in culms and the convective flow and gas composition from stubbles were examined for Eleocharis dulcis, Phragmites vallatoria and Hymenachne acutigluma, and related to light, humidity and air temperature. Nine of the 20 species studied were able to build up a static pressure of >50Pa, and eight species had convective flow rates higher than 1mlmin-1. There was a clear diel variation, with higher pressures and flows during the day than during the night, when pressures and flows were close to zero. It is concluded that convective flow through shoots and rhizomes is a common mechanism for below-ground aeration of tropical wetland plants and that plants with convective flow might have a competitive advantage for growth in deep water. © 2010 The Authors. New Phytologist © 2010 New Phytologist Trust.

The effects of inorganic nitrogen (N) source (NH4+, NO3- or both) on growth, biomass allocation, photosynthesis, N uptake rate, nitrate reductase activity and mineral composition of Canna indica were studied in hydroponic culture. The relative growth rates (0.05-0.06 g g-1 d-1), biomass allocation and plant morphology of C. indica were indifferent to N nutrition. However, NH4+ fed plants had higher concentrations of N in the tissues, lower concentrations of mineral cations and higher contents of chlorophylls in the leaves compared to NO3- fed plants suggesting a slight advantage of NH4+ nutrition. The NO3- fed plants had lower light-saturated rates of photosynthesis (22.5 μmol m-2 s-1) than NH4+ and NH4+/NO3- fed plants (24.4-25.6 μmol m-2 s-1) when expressed per unit leaf area, but similar rates when expressed on a chlorophyll basis. Maximum uptake rates (Vmax) of NO3- did not differ between treatments (24-35 μmol N g-1 root DW h-1), but Vmax for NH4+ was highest in NH4+ fed plants (81 μmol N g-1 root DW h-1), intermediate in the NH4NO3 fed plants (52 μmol N g-1 root DW h-1), and lowest in the NO3- fed plants (28 μmol N g-1 root DW h-1). Nitrate reductase activity (NRA) was highest in leaves and was induced by NO3- in the culture solutions corresponding to the pattern seen in fast growing terrestrial species. Plants fed with only NO3- had high NRA (22 and 8 μmol NO2- g-1 DW h-1 in leaves and roots, respectively) whereas NRA in NH4+ fed plants was close to zero. Plants supplied with both forms of N had intermediate NRA suggesting that C. indica takes up and assimilate NO3- in the presence of NH4+. Our results show that C. indica is relatively indifferent to inorganic N source, which together with its high growth rate contributes to explain the occurrence of this species in flooded wetland soils as well as on terrestrial soils. Furthermore, it is concluded that C. indica is suitable for use in different types of constructed wetlands.

Aquatic plants are never short of water but instead they are challenged with low light and slow movement of oxygen (O₂) and carbon dioxide (CO₂). In the present paper, we focus on CO₂ limitation of underwater photosynthesisand the various strategies to overcome the limitation resulting from evolutionary adaptation to growth under water. Knowledge of such strategies helps you toselect the right CO₂ environment and thereby maximize the chances that your favorite plants flourish.

Limonium narbonense Mill. and Sarcocornia fruticosa (L.) A.J. Scott are two perennial saltmarsh species sharing distribution in the Mediterranean coastal region. L. narbonense has basal leaves in rosettes and a deep root system connected to a vertical rhizome. S. fruticosa is instead a semi-woody plant with modified photosynthetic stems and superficial roots. The distribution of these two species, ranging from elevated saltmarsh sites to low and daily inundated areas, arose the interest around the flooding tolerance mechanisms involved and the possible adaptation to different levels of flooding stress. Field collected plants were conditioned in a controlled tidal system in a greenhouse, imposing two treatments: (1) changing from drained to waterlogged conditions and (2) changing from waterlogged to complete submergence. Internal tissue aeration was monitored using O2 microelectrodes during waterlogging, partial and complete submergence in darkness as well as in light. Underwater photosynthesis and dark respiration were measured by measuring the O2 balance from excised green stems and leaves while porosity measurements were performed in different epigeous and hypogeal plant tissues. O2 dynamics in soil showed a clear and rapid increase of O2 during drainage condition (1) and steady anoxic conditions in the submerged treatment (2), which adversely affected L. narbonense leaf production but stimulated the development of new articles in S. fruticosa. In both species, internal O2 declined upon partial and complete submergence in darkness: L. narbonense showed values closed to zero already during partial submergence, both in petioles (9.1 μmol∙l-1 in average) and in roots (5.6 μmol∙l-1), while S. fruticosa displayed better root aeration during partial submergence (44.4 μmol∙l-1). In light, internal O2 concentrations of the articles of S. fruticosa and the petioles of L. narbonense increased, entailing also a gradual increase in O2 in roots, especially during the re-establishment of waterlogging conditions (over 50 μmol∙l-1 in both species). At air equilibrium of CO2, rates of underwater photosynthesis and dark respiration differ significantly between treatments only when based on dry mass, highlighting a morphological acclimation in leaf thickness of the plants during submergence (higher SLA). Despite the low photosynthetic rates, intact plants were able to cover the O2 requirement during inundation under light conditions (up to 179.7 and 73.0 μmol∙l-1 in S. fruticosa and L. narbonense, respectively). High tissue porosity is a common trait providing a low-resistance internal pathway for O2 diffusion to roots. S. fruticosa displayed high tissue porosity both in lignified stems (up to 25%) and in roots (up to 27%) but for L. nabonense tissues had even higher porosity (in petioles and leaves up to 63%). These findings suggest that the low internal O2 recorded during submergence of L. nabonense must be due to unidentified bottlenecks for O2 diffusion in e.g. root-rhizome junctions or rhizome-petiole junctions, restricting internal aeration. Our findings demonstrate the importance of waterlogging and submergence tolerance in these two species inhabiting saltmarshes, providing additional knowledge to flooding tolerance of halophytes.