Wetland Paddy Field Research Articles

Theoretical analysis and design of inter cum intra-row wetland paddy field weeder

Most of the paddy field weeders developed belongs to inter-row types and the use of inter cum intra-row weeding in wetland paddy fields is obscure. This study aims to design and develop inter cum intra-row weeders so that weeds in both inter and intra-row zone can be eradicated in one go. From the design point of view, the power source (engine), cutting blades, rotor shaft, inter and intra-row weeding units, rectangular link, trapezoidal and lateral plates, and support frames were the important components for the functioning of the machine. The power requirement of the machine and finite element analysis (FEA) of the major components have been analyzed. The numerical values obtained from the available theoretical equations were plugged into the SolidWorks software to analyze the strength of each component. The magnitudes of every result showed superb agreement with the values obtained through analysis in the SolidWorks software. To eliminate weeds in the intra-row zone, a sinusoidal curve path was devised for the intra-row unit to move around the paddy plant. Thus, a 3-D (3-Dimensional) CAD model paddy field weeder suitable for inter cum intra-row weeding has been created and the path to be followed by the intra-row weeding unit has been traced using SolidWorks simulation.

Diversity and Abundance of Ichthyofaunal Species in Karingali Wetland of Central Kerala, India

Background: Karingali wetland is a collection of wetlands in Alappuzha and Pathanmthitta district. It is one of the major wetland paddy fields of central Travancore and had been considered as the rice bank of Mavelikara kingdom. This wetland has not yet been the subject of study. The present study is an inventorization of fish species in this wetland.This will eventually be utilised as a database. Methods: The study areas were divided into five sites; fish samples were collected monthly for a period of June 2020 – May 2022. The collected fish samples were stored in 10% formalin solution and identified with the help of standard literature. Result: During the course of the current study, a total of 35 species from 11 orders were discovered from the Karingali wetland. Cypriniformes, Siluriformes, Perciformes, Anabantiformes, Cichliformes, Beloniformes, Elopiformes, Synbranchiformes, Gobiiformes, Clupeiformes and Mugiliformes were the principal orders. The diversity value ranges high during march and low in July. Even though Karingali wetland are not as much polluted but at the verge of contamination.

Assessment of Macro and Micro Nutrients of Soil in Rice (Oryza sativa L.) Fields in Onattukara Wetlands Regions, Kerala

Background: The purpose of this study is to determine various topographic features as well as the characteristics of micro and macro nutrients in soil samples in the Onattukara wetland paddy fields’ special agricultural zone. Using the Global Positioning System, the particular locations of several soils sampling areas located in different Onattukara blocks were found (GPS). The macro (N, P, K) and micro (zinc, iron, copper, manganese) nutrients in soil samples taken from various places in the paddy fields region were studied. Methods: The Onattukara special agricultural wetland zone in this field investigation during 2017-2018, GPS technique method was used to locating 16 soil samples were collected. Laboratory methods used for chemical analysis of soil. Result: Nitrogen and phosphorus availability were found to be poor in almost all soil samples, whereas potassium availability was found to be medium. In almost all soil samples, the presence of micronutrients (zinc, copper and iron) was found to be critical. The data shows that soils are lacking in N, P and K, necessitating the addition of additional fertilizer and manures to make them acceptable for cultivation and promote healthy growth.

Emission of Methane From Wetland Paddy Fields: A Review

Cultivation of rice is widely practiced throughout the world as rice is a staple food for half of the world’s population. However, the emission of methane (CH4) is an issue associated with the cultivation of rice. Many reports on the level of CH4 emission after treatment of different kinds of organic materials in paddy fields were reported. It was observed that the application of a combination of tested locally available compost along with inorganic NPK fertilisers effectively reduced the rate of emission of CH4. Intermittent wetting and drying in addition to the combined application of compost and NPK fertilisers will help in reducing the emission of CH4 up to 40 to 45%. To undertake an intermittent drainage system is a difficult step for the farmers to implement as it has extra cost and labour. Therefore, lawmakers should initiate steps to help farmers in order to reduce the emission of CH4 from paddy fields.

Allelopathic effect of common weeds on germination and seedling growth of rice in wetland paddy fields of Mizoram, India

Weed invasion of crops contested for environmental resources alongside releasing a certain chemical into the soil and thereby lowering yield potential. The possible allelopathic influence of aqueous extract from leaves and shoots of Alternanthera philoxeroides (Mart.) Griseb., Ludwigia octovalvis (Jacq.) P.H. Raven and Persicaria hydropiper (L.) Delarbe on germination and seedling growth of rice (Oryza sativa L.) was investigated in this study. To prepare the extract, powdered air-dried leaves and shoots of certain weeds were soaked in distilled water (1 : 10) for 24 h at room temperature, and a different dilution was made from the stock. Aqueous extracts from various plant parts were found to suppress seed germination and the development of rice seedlings. As the extract concentration increases, the intensity of inhibition on germination, shoot length, root length and dry matter reduction increases. The average percent inhibition (API) of leaf extract treatments, namely 8% and 10% A. philoxeroides, 8% and 10% L. octovalvis, and 10% P. hydropiper, was found to be greater than 45%. Shoot extracts containing 2% A. philoxeroides, 2% and 4% L. octovalvis, and 2% P. hydropiper have less than 15% average percent inhibition. According to the findings, different weeds contain allelochemicals of variable types and quantities, and different portions of the same weed have distinct effects on germination and rice seedling development.

Environmental changes and human activities over the last about 220 years revealed by the pollen record of Lake Lianhuan in Heilongjiang Province

通过²¹⁰Pb测年建立年代标尺，利用黑龙江省连环湖阿木塔泡高分辨率的孢粉记录，探讨了研究区约220年的环境变化与人类活动.研究表明，1790—1820 AD期间，植被类型可能是以禾本科为主的草甸草原植被，沙地类型以固定沙地为主，气候相对较凉湿或环境几乎不受人类活动的破坏，湖泊营养较丰富.1820—1930 AD期间，草甸草原植被中禾本科和菊科植物比例下降，藜科和蒿属植物比例增加，固定沙地减少、半固定沙地逐渐增加，气候逐渐变干或可能伴随人类破坏环境的活动增强，湿地面积减少.1930—1980 AD期间，针叶乔木松树比例有所增加，草甸草原植被中菊科植物比例是220年来最高的，藜科植物也略有增加，而禾本科和蒿属植物比例下降，推测此阶段固定沙地持续减少，半固定沙地扩张到220年以来面积最大，指示气候进一步变干且伴随着人类活动对自然环境的破坏强度增加，湖泊湿地面积进一步减少.1980—2000 AD期间，草原植被中藜科植物的比例是220年以来最高的，流动沙地面积明显增加，湖泊湿地面积锐减，结合气象数据，得出此期的植被变化是由人类大范围围湖造田以及湿地水田化等活动导致的.2000—2010 AD期间，研究区周围以桦木/鹅耳枥属和栎属为主的落叶阔叶乔木比例增加，草原植被中藜科和菊科植物比例是220年以来最低的，揭示流动沙地和半固定沙地面积明显减少，结合气象数据，认为此期孢粉组合揭示的植被变化主要受人类退耕还草还林，种植桦木/鹅耳枥属、榆属等阔叶植物以及在八支干渠建闸引水至连环湖等活动的影响.;Based on the chronology established through the ²¹⁰Pb dating and the high-resolution pollen record of Amutapao in Lake Lianhuan, Heilongjiang Province, the environmental changes and human activities over the last about 220 years in the study area were discussed. The results showed that during 1790-1820 AD, the vegetation type was probably meadow steppe dominated by Poaceae, and the sandy type was mainly fixed sand. The climate was relatively cool and wet or the environment was hardly damaged by human activities, and lake was of relatively high nutrition. During 1820-1930 AD, the proportion of Poaceae and Compositae plants in the meadow steppe decreased, while that of Chenopodiaceae and Artemisia plants increased. The area of the fixed sand decreased, and the area of the semi-fixed sand gradually increased. The climate gradually became dry or it may be accompanied by the increased human activities, and the wetland area decreased. During 1930-1980 AD, the proportion of coniferous tree Pinus increased, and the proportion of Compositae plants in the meadow steppe was the highest in the past 220 years, and the proportion of Chenopodiaceae plants also increased slightly, while the proportion of Poaceae and Artemisia plants decreased. It is speculated that the fixed sand continued to shrink during this period, and the semi-fixed sand expanded to the largest area for the last about 220 years. It indicates that the climate became further dry and with the increased human activities, and the area of the wetland further decreased. During 1980-2000 AD, the proportion of the Chenopodiaceae plants in the steppe was the highest for the last about 220 years, the area of the mobile sand increased significantly, and the area of the wetland decreased sharply. Combined with the meteorological data, it was concluded that the vegetation changes in this period were caused by human activities such as large-scale lake reclamation and wetland paddy field. During 2000-2010 AD, the proportion of deciduous broad-leaved trees dominated by Betula/Carpinus and Quercus around the study area, and the proportion of Chenopodiaceae and Compositae plants in the steppe was the lowest in the last about 220 years, revealing a significant decrease in the areas of mobile sand and semi-fixed sand. Combined with the meteorological data, it is considered that the vegetation changes during this period revealed by the pollen assemblage were mainly influenced by humans returning farmland to grassland and forest, planting broad-leaved trees such as Betula/Carpinus and Ulmus et al., and building sluices in eight main canals to divert water to Lake Lianhuan.

Isolation and Genetic Diversity Studies of Nitrogen-Fixing Cyanobacteria from Wetland Paddy Field of Mizoram, India

Cyanobacteria are promising candidates for biofertilizer which is environmentally and economically friendly. Herein, we, for the first time reported the cyanobacterial population study in the wetland paddy field of North Vanlaiphai, Mizoram. Ten cyanobacterial strains from our study sites belonging to six genera (Fischerella, Scytonema, Calothrix, Nostoc, Anabaena and Westiellopsis) were isolated and characterized by morphological and molecular analyses. The morphological observation was congruent with their phylogenetic analyses based on 16SrRNA gene sequences and RAPD.

Application of Symmetric Ploughs for Tillage on Wetland Paddy Fields

Application of Symmetric Ploughs for Tillage on Wetland Paddy Fields

Factors Affecting Rice Production and Land Usages in Banten Province, Indonesia

Banten Province has a harvested area of paddy fields on the 2017 year of 415,687 ha and production of 2,369,731 tons of unhusked rice. The objectives of this study are: 1) Knowing the priority of resources and agricultural inputs use for food production, 2) Knowing the factors that influence the productivity of rice in irrigated land in Banten Province, 3) Knowing the efficiency of the use of production inputs. The sampling method used purposive sampling with 90 respondents. The analytical method used the Analytical Hierarchy Process (AHP) and multiple linear regression of Cobb Douglas production functions. The results of the study are: 1) The priority strategy in increasing food production is to increase the use of irrigated rice fields, so that the goal is achieved by increasing the crop index, this can be done by prioritizing the optimization of agricultural machinery 2) Significant factors that affecting the production of paddy rice in the irrigated wetland paddy field in Rainy Season 2017/2018 are the use of urea fertilizer, the amount of use of solid organic fertilizer, the amount of use of human labor rent, and the arable land area, 3). The cumulative elasticity is 1.45, which is elastic, meaning that the addition of 1% of the production factor will increase production by 1.45% or increasing return to scale. So rice farming in irrigated land is relatively efficient. To increase production, it is necessary to increase rice productivity and crop index in irrigated paddy fields.
 
 Keywords: Factors production, efficiency, priority analysis, rice, land usage.

Isolation and Characterization of Rhizospheric Phosphate Solubilizing Bacteria from Wetland Paddy Field of Mizoram, India

A significant amount of bacterial species have a beneficial effect upon plant growth. The ability of phosphate solubilizing bacteria (PSB) to convert insoluble form of phosphorous to an available form is an important trait in plant growth promoting bacteria for increasing crop yield. Mostly they are associated with the plant rhizosphere, hence are called as rhizobacteria. A study was undertaken to isolate and characterize rhizospheric PSB population from wetland paddy field of North Vanlaiphai, Mizoram, India. The study of beneficial microorganisms especially from wetland paddy field in Mizoram, India is still in infancy and the present study is the initial phase of exploration of PSB in this region. For screening of the potential PSB, qualitative and quantitative P solubilizing efficiency was estimated using Pikovskaya medium containing tricalcium phosphate as the phosphorous source. Molecular and biochemical characterizations of the isolates were carried out. Upon Screening and molecular identification using 16SrRNA gene, 15 best p-solubilizers were selected for further studies. Since the main mechanism of P-solubilization seemed to be mediated by organic acid production, HPLC analysis revealed production of multiple organic acids such as gluconic oxalic, citric, tartaric, succinic, formic and acetic acid in the culture supernatant. The isolated strains were also capable of producing Indole Acetic Acid (IAA) and estimation of enzyme acid phosphatase was done. Based on partial sequence analysis of 16S rRNA genes, the 15 isolates were found to belong to the genera Bacillus, Burkholderia, Paenibacillus sp.

Nitrogen transformation and carbon sequestration in wetland paddy field of Bangladesh

Rice-based cropping systems in Bangladesh have received little consideration of changing nitrogen (N) and carbon (C) in soil. Therefore, this study was conducted at the Research Field of Bangabandhu Sheikh Mujibur Rahman Agricultural University, Bangladesh, in monsoon to determine release patterns of ammonium–N (NH4+–N) and nitrate–N (NO3−–N), C contents of different sized soil fractions and to quantify the rates of C sequestration as influenced by organic amendments and N fertilizer in wetland paddy fields. Rice straw, vermicompost, rice husk biochar, cow dung and poultry manure were applied using 2 t C ha−1 with 0, 100 and 150 N kg ha−1 in a factorial randomized complete block design. Application of different organic materials attributed maximum amount of NH4+–N and NO3−–N in soils at 45–60 days after transplanting, while N fertilizer application considering 150 kg N ha−1 provided the maximum amounts of available N. Rice grain yield was found statistically similar between 100 and 150 kg N ha−1. Carbon contents in soils of different sized fractions inconsistently varied with organic and inorganic fertilization and time elapsed. The highest amount of organic C was sequestered in cow dung-treated plots followed by rice straw, rice husk biochar, poultry manure and vermicompost. Nitrogen fertilizer enhanced decomposition of organic materials, and therefore, C sequestration was significantly lower with higher N rates. The study recommends continuous application of organic fertilizers and optimization of N in the tropical and subtropical regions which ultimately either contribute to maintain or increase C sequestration in crop fields.

Impact of flucetosulfuron on weed seed bank in wet seeded rice

An experiment was conducted to assess the impact of flucetosulfuron, a new generation sulfonylurea herbicide, on weed seed bank dynamics of wet land paddy field. Field experiments were carried out during two consecutive seasons (Kharif 2016 and Rabi 2016-’17), to assess the bio-efficacy of flucetosulfuron in wet seeded rice which was accompanied by weed seed bank assay. Weed seed bank assay of the soil was carried out before and after the field experiments in both the seasons by the seedling emergence method. The experiment on weed seed bank was laid out in Completely Randomised Block Design (CRD) with 12 treatments replicated thrice. Flucetosulfuron @ 20, 25, and 30 g ha-1applied at 2-3, 10-12, and 18-20 days after sowing (DAS) along with two control treatments viz., hand weeding at 20 and 40 DAS and unweeded control comprised the treatments. The emerging weeds were uprooted at 14 days interval up to a period of two months; categorized as grasses, broad leaved weeds, and sedges and counted. Results revealed that non-herbicidal plots recorded significantly higher count of total emerged weeds compared to herbicide applied plots. In all the herbicide applied plots, effective reduction in weed seed bank could be obtained irrespective of the dose of the herbicide. Regarding the time of application, flucetosulfuron applied at 10-12 and 18-20 DAS recorded significantly lower weed seed bank during both the seasons, compared to its application at 2-3 DAS.

Toxicity of biocides to native cyanobacteria at different rice crop stages in wetland paddy field

Biocides (herbicides and insecticides) are intensively being used in rice cultivation, despite several adverse non-target effects on native cyanobacteria. Comparative effects of three herbicides (benthiocarb, butachlor, and 2,4-D) and four insecticides (furadon, phorate, methyl parathion, and ekalux) were studied at field-recommended doses. Field experiments of rice were carried out for three consecutive seasons in completely randomized block designs in both rainy and winter croppings at the Central Rice Research Institute, Cuttack, India. Toxicities of seven biocides individually to native cyanobacteria growing with rice crops in wetland fields were assessed for growth and acetylene reduction activity (ARA); several crop parameters of paddy were estimated concomitantly. It was observed that applications of butachlor and benthiocarb individually significantly decreased growth (15.86 and 17.50%), ARA (0.16 and 0.68%), and N-yield (0.26 and 0.85%) of the native cyanobacteria, whereas these parameters increased (24.04% in growth, 0.25% in ARA, and 0.40% in N-yield) due to the application of 2,4-D. Of the tested insecticides, furadon, phorate, and methyl parathion enhanced the growth (17.8, 10.7, and 11.7%), N2-fixation (0.10, 0.097, and 0.074%), and N-yield (0.16, 0.18, and 0.20%) of cyanobacteria, whereas ekalux had no significant effect on cyanobacteria. On the basis of cyanobacterial parameters, biocides could be recommended for rice crops in the order furadon < phorate < methyl parathion < ekalux. Applications of 2,4-D and furadon individually in comparison to the rest other biocides enhanced rice yield. These finding could help to revise integrated strategies of weed and pest management in wetland rice agriculture to save non-target soil microorganisms, particularly cyanobacteria.

Nitrogen discharge pathways in vegetable production as non-point sources of pollution and measures to control it

Discharge of nitrogen (N) from fertilizers applied to vegetables is becoming a serious environmental problem. In a field experiment involving a celery-tomato-fallow-lettuce rotation, leaching was the primary pathway of N loss (56.1±0.4% of the total), followed, in descending order, by runoff (11.7±0.3%), N2O emissions (1.6±0.1%), and volatilization of ammonia (0.5±0.1%). Decreasing the traditional dose of N by 40% in each growth season decreased N leaching by 22.3±4.5, 39.8±6.7, 40.3±2.9 and 27.4±3.6% in celery, tomato, fallow and lettuce seasons, respectively, without any yield loss, and modifying the rotation to include a leguminous crop reduced the N leaching by 72±2, 40±3, 24±2 and 13±1% in each season, respectively, without any economic impact. These measures decreased annual N leaching by 36±4%. A combination of the eco-ditches and wetland paddy fields adjacent to the vegetable plot led to annual N removal efficiency of 73±6% in runoff.

Draftbility of Power Tiller with Different Lug Angle of Cage Wheels in Puddle Soils for Paddy

The experiment was conducted on IGKV research farm in wet puddle condition in April month of 2015. The wet tillage practice was carried out by power tiller cage wheel attached with five tines cultivator. Paddy production increases by puddling of soil before transplanting. Cage wheel is an important traction device for any prime mower. The lug is wing provided in cage wheels which interact with the wet soil to churn the soil. The cage wheel 730 mm diameter with 30°, 45°, and 60° lug angle and three different diameter of 73 mm, 680 mm and 780 mm of 30° was tested at 0 to 50 mm, 50 to 100 mm, 100 to 150 mm and 150 to 200 mm, depth of water level in wet land field. The result was found that cage wheel C1 of 30° lug angle with 730 mm diameter give better performance than other cage wheel. The cage wheel showed the best result in 50–100 mm water level in respect to maximum tractive efficiency was found in the range of 73−78% at 996 N to 1009 N draft and drawbar power was in the range of 478.08 W to 484.32 W. While maximum drawbar power was (523.16 to 555.28 W) was observed at 0 to 50 mm water level. Therefore cage wheel of 30° lug angle with 730 mm diameter was found suitable for wet land paddy field condition.

An account of the ‘useful weeds’ associated with wetland paddy fields (Vayals) of wayanad, Kerala

This study conducted in Wayanad District of Kerala has documented the usefulness of the vascular flora associated with wetland paddy fields (Vayals). The plants were recorded from the paddy fields and paddy levees (bunds) and associated habitats. 65 farmer participants of the study, through a total of 945 sightings, have identified 95 useful plants species each from Paddy Fields/Levees (dominated by the members of Cyperaceae, Asteraceae, Poaceae, Amaranthaceae) and Paddy Associated habitats (dominated by the members of Solanaceae, Asteraceae, Fabaceae, Moraceae). 33 species were common to these habitats. The study reveals the importance of the plant diversity associated with paddy fields, in meeting the multiple requirements of the rural and tribal people of Wayanad.

Nitrogen removal from the surface runoff of a field scale greenhouse vegetable production system

Nutrient losses from greenhouse vegetable production systems may impair water quality in the Taihu Lake Region of China. We studied the characteristics of nitrogen (N) lost via runoff from greenhouse vegetable systems and strategies for minimizing N entering water bodies. A two-year experiment at a field scale was conducted to monitor N surface runoff. An eco-ditch (148 m2) and a low N input paddy field (135 kg N ha−1, 550 m2) were designed to remove N from the surface runoff of a 25 × 50 m greenhouse vegetable field. The greenhouse was not covered from late June to mid-October each year, and runoff occurred multiple times during this period. Annual total N loss in runoff from the greenhouse vegetable site was 25.3 and 33.5 kg ha−1 in 2010 and 2011, respectively. Nitrate-N was the major form of N lost in the runoff. The average runoff volume was 289 mm (varied from 221 to 357 mm), which contained 15.7 (varied from 3.3 to 39.2 mg L−1) mg L−1 total N. The eco-ditch system and the wetland paddy field (WPF) effectively reduced total N discharge; the removal rates reached 49.9% and 58.7% and the average removal capacities were 12.4 g N m−2 and 4.1 g N m−2 in 2010 and 2011, respectively. The combined system of the ecological ditch–WPF removed almost 79% total N in the runoff. Ecological ditch or paddy wetland can be a water management option available to growers in this region to economically reduce pollutants in agricultural runoff.

Physiological and anatomical variations in three rice (Oryza sativaL.) genotypes for transport and emission of methane

Plant-mediated transport is the major pathway of methane (CH4) emission from wetland paddy fields. The present experiment was conducted to understand the mechanism of CH4 transport through rice paddies. A field measurement of CH4 emission was done with three rice genotypes Ranjit, Piolee and Swarna Mahsuri to identify plant physiological and anatomical characteristics influencing gas emission, which could provide insight to the mechanism of CH4 transport. CH4 emission estimation by a closed chamber technique revealed significant variations in emission of CH4 among the varieties. Variety Ranjit was identified as a low emitting variety compared to the others. The leaf area index, tiller number, leaf and root dry weight were closely associated with CH4 emission. The rate of leaf transpiration, stomatal conductance, leaf stomatal frequency and size of the xylem vessels were identified to be strong determinants of CH4 emission suggesting a transport pathway of CH4 along with the transpirational xylem water flow and subsequently through open stomata of leaf blade. Low emitting variety Ranjit exhibited superior yield and yield attributing characteristics in terms of panicle dry weight and high density grain (%) highlighting the role of source–sink carbohydrate partitioning in regulating CH4 emissions. Cultivation of low emitting varieties with higher grain productivity can be an effective environmentally-friendly biological mitigation strategy for CH4 emission from rice paddies.

Isolation and characterization of methane utilizing bacteria from wetland paddy ecosystem

Methylotrophic bacteria which are known to utilize C1 compounds including methane. Research during past few decades increased the interest in finding out novel genera of methane degrading bacteria to efficiently utilize methane to decrease global warming effect. Moreover, evaluation of certain known plant growth promoting strains for their methane degrading potential may open up a new direction for multiple utility of such cultures. In this study, efficient methylotrophic cultures were isolated from wetland paddy fields of Gujarat. From the overall morphological, biochemical and molecular characterization studies, the isolates were identified and designated as Bacillus aerius AAU M 8; Rhizobium sp. AAU M 10; B. subtilis AAU M 14; Paenibacillus illinoisensis AAU M 17 and B. megaterium AAU M 29. Gene specific PCR analysis of the isolates, P. illinoisensis, B. aerius, Rhizobium sp. and B. subtilis showed presence of pmoA gene encoding α subunit particulate methane monooxygenase cluster. B. megaterium, P. illinoisensis, Rhizobium sp. and Methylobacterium extrorquens showed presence of mmoX gene encoding α subunit of the hydroxylase component of the soluble methane monooxygenase cluster. P. illinoisensis and Rhizobium sp. showed presence mxaF gene encoding α subunit region of methanol dehydrogenase gene cluster showing that both isolates are efficient utilizers of methane. To the best of our knowledge, this is the first time report showing presence of methane degradation enzymes and genes within the known PGPB group of organisms from wet land paddy agro-ecosystem, which is considered as one of the leading methane producer.

Cyanobacteria-Mediated Arsenic Redox Dynamics Is Regulated by Phosphate in Aquatic Environments

Studies of cyanobacteria in environments where arsenic (As) and phosphate (P) both occur in significant concentrations have so far only focused on the effect of P on As(V) toxicity and bioaccumulation, with little attention to the influence of P on As redox transformations. Our study revealed that As(III) oxidation by Synechocystis appeared to be more effective with increased P levels. We demonstrated that the higher As(III) percentage in the medium under P-limited conditions was due to enhanced As(V) uptake and the subsequent efflux of intracellularly reduced As(III) which in turn contributed to higher As(III) concentrations in the medium. Arsenic redox changes by Synechocystis under P-limited conditions is a dynamic cyclic process that includes the following: surface As(III) oxidation (either in the periplasm or near the outer membrane), As(V) uptake, intracellular As(V) reduction, and As(III) efflux. These observations not only expand our understanding of how P influences microbial As redox metabolisms but also provide insights into the biogeochemical coupling between As and P in As contaminated eutrophic aquatic environments and artificial wetland-paddy fields.