Tropical Rice Fields Research Articles

Influence of herbicide on rhizospheric microbial communities and soil properties in irrigated tropical rice field

Microbial diversity is an essential biological indicator of soil health as well as crop productivity and helps in maintaining the ecosystem dynamics. In land management, Nature based Solutions (NbS) are not mainstream management, however, for sustaining the balanced ecosystem, integrity in the structural and functional diversity of microbes via NbS is imperative. Direct seeded rice (DSR) cultivation is a promising technique for efficient rice production, but weed infestation can lead to yield loss, requiring extensive herbicide use like pendimethalin (PND) and pretilachlor (PRT). The results revealed that with a reduction in PND and PRT residues (0.93–0.01 µg g−1 soil), values of soil microbial biomass C (132.3–112.6 mg kg−1 soil) and MBN (12.6–8.5 mg kg−1 soil), and enzyme activities increased. Negative correlations were observed between herbicide residues and microbial parameters. In control soils, higher population sizes of archaea, bacteria, and fungi were obtained compared to herbicide-treated soils. High-throughput amplicon sequencing (16S rRNA, ITS genes) detected dominant archaea, atronorbrum_4312, MethanothrixX_B, and Methanosarcina_2619 in herbicide treated whereas Nitrosocosmicus, Methanoregula, in control. Bacillus, Methyloceanibacter, Azospira, and Nitrospira bacterial genera were present in both groups. Control soil showed the dominance of Humicola, Nigrospora, and Paramyrothecium fungi, while treated one exhibited Mariannaea, Ceratobasidium, Funneliformis (PND), Aspergillus, Pseudorhypophila, and Lecythophora (PRT). Overall, herbicides had a detrimental impact on microbial dynamics, and their residues correlated negatively with soil variables and microbial diversity. The research outcomes revealed the dramatic variations in microbial communities under the influence of herbicides. This will further aid in a better understanding of the development of NbS solutions for effectively managing herbicide application in direct-seeded rice for enhancing soil health and ecosystem services while supporting sustained productivity.

Deciphering insights into rhizospheric microbial community and soil parameters under the influence of herbicides in zero-tillage tropical rice-agroecosystem

Extensive use of chemicals like herbicides in rice and other fields to manage weeds is expected to have a lasting influence on the soil environment. Considering this rationale, we aimed to decipher the effects of herbicides, Pendimethalin and Pretilachlor, applied at 0.5 and 0.6 kg ha−1, respectively on the rhizosphere microbial community and soil characteristics in the tropical rice field, managed under zero tillage cultivation. The quantity of herbicide residues declined gradually since application up to 60 days thereafter it reached the non-detectable level. Most of the soil variables viz., microbial biomass, soil enzymes etc., exhibited slight reduction in the treated soils compared to the control. A gradual decline was observed in Mineral-N, MBC, MBN and enzyme activities. Quantitative polymerase chain reaction results showed maximal microbial abundance of bacteria, fungi and archaea at mid-flowering stage of rice crop. The 16 rRNA and ITS region targeted amplicons high throughput sequencing microbial metagenomic approach revealed total of 94, 1353, and 510 species for archaea, bacteria and fungi, respectively. The metabarcoding of core microbiota revealed that the archaea comprised of Nitrososphaera, Nitrosocosmicus, and Methanosarcina. In the bacterial core microbiome, Neobacillus, Nitrospira, Thaurea, and Microvigra were found as the predominant taxa. Fusarium, Clonostachys, Nigrospora, Mortierella, Chaetomium, etc., were found in core fungal microbiome. Overall, the study exhibited that the recommended dose of herbicides found to be detrimental to the microbial dynamics, though a negative relation between residues and soil variables was observed that might alter the microbial diversity. The outcomes offer a comprehensive understanding of how herbicides affect the microbial community in zero tillage rice soil, thus has a critical imputation for eco-friendly and sustainable rice agriculture. Further, the long-term studies will be helpful in elucidating the role of identified microbial groups in sustaining the soil fertility and crop productivity.

A trait-based perspective toward the mechanistic understanding of benthic macroinvertebrate assemblage in a tropical rice field

A trait-based perspective toward the mechanistic understanding of benthic macroinvertebrate assemblage in a tropical rice field

Biodiversity and community structure of Arthropod in tropical rice fields under organic and conventional ecosystems

The practice of conventional rice cultivation using inorganic fertilizers and synthetic chemical pesticides can affect the stability of ecosystems. This study aimed to compare the diversity and community structure of arthropods in tropical rice field under organic and conventional ecosystems. This research was conducted at Oloboju, located at an altitude of 120 m above sea level. The soil type was inceptisol. The research used observation and exploration methods. The sampling of arthropods in the field used a sweep net, a pitfall trap, a yellow pan trap and by hand. The variables measured were the taxonomic composition and relative morpho-species abundance, family and order composition. Relative morpho-species abundance was assessed based on functional roles, number of species, and the total number of individuals. The results show that the Shannon diversity index value (H') and Margalef richness index (Dmg) were higher in organic rice ecosystems than conventional. On the other hand, the organic rice ecosystem had a Simpson dominance index value (C) and an evenness index (E) lower than the values of C and E in conventional rice ecosystems. The organic ecosystem had a community structure of arthropod of 9 orders, 24 families, and 28 morpho-species, with an abundance of 4,002 individuals, while the conventional ecosystem had a community structure of arthropod of 7 orders, 17 families, and 20 morpho-species with an abundance of 1,789 individuals. The practice of organic rice cultivation would increase the biodiversity index towards ecosystem balance so that it could be used as an alternative to pest control

Death in the paddy field: Carcass decomposition and associated arthropods in subunits of a rice field landscape

Although rice production landscapes are often the scene of homicides, vertebrate decomposition and associated arthropods have never been described from rice paddies. Tropical rice landscapes are typically composed of irrigated/non-irrigated rice fields, fallow land (i.e., uncultivated fields), and low earthen levees (bunds) used as access pathways. The specific microclimatic and environmental conditions associated with each subunit of rice field landscapes are likely to impact carcass decomposition as well as the arthropod species associated with carrion. Here, we tested the hypothesis that the combined effects of constraints on arthropod colonization and survival, scarcity of necromass, limited habitat architecture, and recurrent disturbance limit the ability of carrion-related arthropods to colonize corpses and large carcasses in tropical rice-fields. Our results from monitoring pig carcasses in Philippine rice fields indicated that vertebrate decomposition in irrigated fields was slower and incomplete when compared to non-irrigated fields and bunds. Carcasses were colonized by a small complex of carrion-related arthropods that differed in composition and relative species abundance between dry bunds and relatively humid rice paddies. Fire ants (Solenopsis germinata) were observed frequently on carcasses exposed on bunds, rarely in non-irrigated fields, and almost never in irrigated fields. The presence of fire ants was associated with reduced blow fly (Chrysomya megacephala) abundance. Taken together, this indicates that the arthropod fauna associated with carcasses in tropical rice fields is relatively simple in contrast to the generally high arthropod diversity reported for other ecosystems at tropical latitudes. The limited richness of the community also means that an understanding of the development of one abundant calliphorid blow fly, C. megacephala, may be sufficient to investigate deaths and homicides under conditions similar to the ones described in this study.

Assessment of phytoplankton composition and physicochemical parameters of Omasi rice field, Anambra State, Nigeria

The microalgae and physicochemical parameters of floodwater of Omasi rice field in Anambra State, Nigeria were studied. Samples for the studies were collected at monthly intervals. The microalgae were studied using light microscopy and identified with taxonomic keys, text books and photograph materials from the internet. The physicochemical parameters and coliform content of the floodwater were analysed using the methods described by the American Public Health Association. Simple means of the parameters and percentages of the algal populations were calculated, while Pearson correlation (p ≤ 0.05) was used to check for significance of the relationships between the investigated parameters. A total of 12 algal taxa belonging to Chlorophyta (48.99%), Cyanophyta (32.89%), Euglenophyta (10.07%), and Bacillariophyceae (8.05%) were recorded in decreasing order of abundance. Water temperature ranged from 26-38 °C with mean of 33.3 ± 2.56 °C; colour ranged from 15-175 Hazen units with mean of 86.25 ± 33.19 Hazen units; depth of water ranged from 7-10.5 cm with mean of 9.38 ± 0.8 cm. Ranges of nitrates and phosphates with their respective means were 0.5-1.8 mg/l (0.86±0.31 mg/l) and 0.79-1.96 mg/l (1.18±0.28 mg/l). Omasi rice field supported the growth of diverse algal groups and species; this may be as a result of available nutrients and good climate as can be deduced from the correlation analyses. Omasi rice field is typical of tropical freshwaters and some tropical rice fields that have been studied in terms of microalgal diversities and some physicochemistry

Asp-376-Glu substitution endows target-site resistance to AHAS inhibitors in Limnocharis flava, an invasive weed in tropical rice fields.

Limnocharis flava (L.) Buchenau is a problematic weed in rice fields and water canals of Southeast Asia, and in Malaysia this invasive aquatic weed species has evolved multiple resistance to synthetic auxin herbicide and acetohydroxyacid synthase (AHAS) inhibitors. In this study, it was revealed that, a single nucleotide polymorphism (SNP) at amino acid position 376, where C was substituted to G at the third base of the same codon (GAC to GAG), resulting in Aspartate (Asp) substitution by Glutamate (Glu) was the contributing resistance mechanism in the L. flava population to AHAS inhibitors. In vitro assay further proved that, all the L. flava individuals carrying AHAS resistance mutation exhibited decreased-sensitivity to AHAS inhibitors at the enzyme level. In the bensulfuron-methyl whole-plant bioassay, high resistance indices (RI) of 328- and 437-fold were recorded in the absence and presence of malathion (the P450 inhibitor), respectively. Similarly, translocation and absorption of bensulfuron-methyl in both resistant and susceptible L. flava populations showed no remarkable differences, hence eliminated the possible co-existence of non-target-site resistance mechanism in the resistant L. flava. This study has confirmed another new case of a target-site resistant weed species to AHAS-inhibitors.

Spatiotemporal Patterns of Latrine-Site Use by Small-Clawed Otters in a Heterogeneous Rice Field Landscape

Tropical rice fields with asynchronous growth stages provide a good model to investigate the effects of landscape heterogeneity on the use of agricultural landscapes by wildlife. The small-clawed otter (Aonyx cinereus) uses rice fields as latrine sites in Southeast Asia. Through a 53-week survey of latrine sites, we analyzed the spatiotemporal patterns of latrine-site use by small-clawed otters in an asynchronous rice field in West Sumatra, Indonesia. Based on a generalized linear mixed model incorporating local environmental factors, otter latrine-site visitation was positively associated with the vegetative stage of rice cultivation and the biomass of a major prey item, the golden apple snail (Pomacea canaliculata). The vegetative stage of rice cultivation and golden apple snail biomass were closely associated with deep water in rice fields; therefore, water availability in rice fields is likely important in determining the spatiotemporal patterns of small-clawed otter latrine-site use in the asynchronous rice field landscape. To consistently provide latrine sites for small-clawed otters, we recommend that asynchronous rice cultivation be maintained, or zoning of synchronous and asynchronous rice cultivation areas be planned in the region.

Evaluating differential effect of deltamethrin and carbofuran on growth characteristics of Westiellopsis prolifica Janet, a dominant nitrogen fixing cyanobacterium of tropical rice field ecosystem

Recent trends of indiscriminate use of synthetic pesticides in different tropical rice fields has been affecting the soil flora and fauna including the most beneficial nitrogen fixing cyanobacteria . As nitrogen fixing cyanobacteria play an important role in soil fertility and acts as a natural bio fertilizer, the present study was carried out to investigate the differential effects of deltamethrin and carbofuran on Westiellopsis prolifica , an abundantly grown nitrogen fixing cyanobacterium in the rice fields of tropics. The study was conducted considering its dry biomass, protein, carbohydrate along with chlorophyll-a, and carotenoid content in a time- and dose-dependent exposure for 16 days. The resultant effect of both the pesticides was found to be pleiotropic for different concentrations of deltamethrin (25–75ppm) and carbofuran (20–60ppm). Results revealed that the growth parameters were more affected with carbofuran treatment than that of deltamethrin at their highest treated concentrations. Carbohydrate showed a gradual increase with carbofuran in a time and dose dependent manner whereas deltamethrin enhanced carbohydrate content up to 16th day from the day of inoculation only at 25ppm. Carotenoid showed a little but insignificant increase at the initial concentrations of both the pesticides whereas protein showed positive enhancement up to 4th day of inoculation when treated with deltamethrin. Though low concentrations stimulated some of the growth characteristics of the test organism, higher concentrations of both the pesticides were observed to be detrimental.

Description of 'Ca. Methylobacter oryzae' KRF1, a novel species from the environmentally important Methylobacter clade 2.

Members of the genus Methylobacter (Mtb) have been identified to be the most dominant methanotrophs in aquatic as well as terrestrial habitats. Methylobacter shows four species with validly published names and these are grouped in two clades based on phylogenetic and genomic comparisons. Mtb luteus and Mtb marinus (synonym: Mtb whittenburyi) belong to clade 1 Methylobacter. Clade 2 Methylobacter comprises of two species: Mtb tundripaludum and Mtb psychrophilus (type strain, no longer available). We isolated a yellow pigmented, rod-shaped methanotroph, strain (KRF1), from a tropical rice field in India, which might represent a putative novel species within Methylobacter clade 2. The cells are long, thick and motile rods. The strain grows under variable oxygen concentration (5-80% air) and also in nitrogen free media (5-50% air). The morphological, chemotaxonomic and genomic features of KRF1 were investigated in details. The digital DNA-DNA hybridization values and average nucleotide identity (ANI) comparisons with the members of its closest species, Mtb tundripaludum, were in the range of 20-26% and ~ 73-81%, respectively. The fatty acid methyl esters profile of KRF1 was different from the profile of Mtb tundripaludum SV96T. The major cell wall fatty acids of strain KRF1 are 16:1 ω7c/16:1 ω6c summed feature (55.4%) and 16:1 ω5c (28.6%). The draft genome of KRF1 is of 5.04 Mbp in size with a GC content of 49.3% and the whole genome shotgun sequencing project has the accession number RYFG00000000 (version: RYFG02000000). Due to the difficulties in the maintenance and cryopreservation of this culture, it could not be deposited in two international culture collections. We thereby propose KRF1 to be member of a Candidatus species, 'Candidatus Methylobacter oryzae' KRF1. The culture is maintained live in our laboratory and also in our institutional WDCM approved culture collection (MACS Collection of Microorganisms) as MCMB-1471.

A putative novel Methylobacter member (KRF1) from the globally important Methylobacter clade 2: cultivation and salient draft genome features.

Methane oxidation by methanotrophs is a very important environmental process in the mitigation of methane. Methylobacter (Mtb.) clade 2 members have been reported as dominant methane oxidisers in soils and sediments worldwide. We enriched and purified a methanotroph from a tropical rice field soil sample from India. The highly enriched culture showed the presence of motile, long and thick rods (3-5µm × 0.9-1.2µm) and minor presence of short, thin rods. The culture was purified on agarose medium and formed yellow colonies which showed the presence of only thick and long rods, henceforth termed as strain KRF1. Based on 16S rRNA gene sequence analysis, strain KRF1 shows close phylogenetic affiliation to Methylobacter tundripaludum SV96T (98.6% similarity). Due to the taxonomic novelty, and being the first member of Mtb. related to Mtb. tundripaludum from the tropics, the draft genome was sequenced. From the blastx analysis of the contigs, it was clear that the culture still had contamination of another organism, a Methylophilus species. The data binned in two clear bins: Mtb. related contigs and Methylophilus-related contigs. The binned draft genome of KRF1 shows features including the typical pathways for methane metabolism, denitrification and the presence of molybdenum iron and vanadium-iron nitrogenase genes. KRF1 is phylogenetically distinct from the five strains of Mtb. tundripaludum including SV96T, Lake Washington strains and OWC strains, showing ~ 26% DDH and ~ 81% ANIb values and a unique position in a phylogenomic tree. Subsequently, KRF1 has been completely purified from its methylotrophic partner and a pure culture has been established and maintained in a WDCM approved culture collection, the MACS Collection of Microorganisms (as MCM 1471). KRF1 is thus the first cultured member of a putative novel species of Methylobacter clade 2 isolated from the tropics.

Effects of bund crops and insecticide treatments on arthropod diversity and herbivore regulation in tropical rice fields

AbstractEcological engineering using vegetable or flower strips is promoted as a potential pest management strategy in irrigated rice. Farmers in the Philippines often plant rice levees (bunds) with vegetables, particularly string beans (Vigna unguiculata [L.] Walpers) to supplement income, but without considering the potential for pest management. This study examines the effects of planted bunds on rice herbivores and their natural enemies. We compared arthropods in (a) rice fields that had string beans planted on bunds, (b) fields without string beans and without any insecticide applications and (c) fields without string beans but with insecticide treatments (standard practice). Rice yield was similar across all treatments; however, the vegetation strips produced an extra 3.6 kg of fresh string bean pods per metre of bund. There were no apparent increases in major natural enemy groups in fields with string beans compared to fields with conventional bunds. Fields with insecticide treatments had higher damage from leaffolders (Lepidoptera: Pyralidae). The sprayed fields also had lower parasitism of planthopper eggs and fewer predatory dragonflies and damselflies (Odonata). Furthermore, the mortality of planthopper (Delphacidae: Hemiptera) and stemborer (Pyralidae) eggs by parasitoids and predators was density dependent only in the unsprayed fields (with and without string beans). Our results demonstrate that planting string beans on rice bunds improves the productivity of rice farms, but our ecological engineering system did not appreciably affect natural enemy or herbivore abundance; however, chemical insecticides adversely affected pest regulatory ecosystem functions leading to higher pest damage.

Ecological engineering with high diversity vegetation patches enhances bird activity and ecosystem services in Philippine rice fields

This study examines the potential for ecological engineering to enhance the beneficial ecosystem services provided by birds in tropical rice fields. Bird activities were monitored at six sites in the Philippines with high-diversity vegetation patches (HDVPs) established as an ecological engineering approach to restore ecosystem services. Adjacent plots of conventional rice were monitored as controls. Predatory birds (shrikes, Lanius spp., grassbirds, Megalurus palustris, and kingfishers, Halcyon spp.) were more active in the ecological engineering fields where they foraged for arthropods and snails among the rice plants. Pied trillers, Lalage nigra, and yellow vented bulbuls, Pycnonotus goiavier, foraged more in the HDVPs than in rice. These birds mainly responded to the availability of bamboo for perching in the HDVPs, although patch vegetation beneath the bamboo was also used for perching by some species. Aerial hunters such as swallows, Hirundo spp., avoided HDVPs likely because the tall vegetation and bamboo stakes represented an obstacle for their flight. Small changes in the design of HDVPs could avoid any negative effects on foraging by swallows and swifts. The results indicate that ecological engineering of rice paddies can have multiple benefits for farmers and the environment, including improved nutrition for farming communities, the creation of habitat for wildlife, and the enhancement of regulatory ecosystem services provided by insectivorous and snail-eating birds.

Compensatory mechanisms of litter decomposition under alternating moisture regimes in tropical rice fields

A conversion from permanently flooded rice cropping systems to crop rotations that include non-flooded upland crops is heavily promoted in tropical regions to meet the challenges of sustainable food production while reducing water consumption and trace gas emissions. Shorter periods of flooding and manipulation of fertilizer inputs affect belowground community composition, biomass and functioning. However, there have been no previous studies of how such shifts in rice field management might affect soil biota and decomposition. Our objective was to examine how crop diversification, which demands different moisture regimes and nitrogen inputs, influences belowground invertebrate assemblages and their contribution to the decomposition of crop residues.We conducted a litterbag experiment in lowland paddy fields at the experimental field sites of the DFG-ICON project (Laguna, the Philippines) that were either continuously flooded, had seasonally alternating wet and dry periods, or were continuously dry. Additionally, subplot treatments within these crop rotations included different N fertilizer management practices. At a total of 36 plots we used litterbags with two different mesh sizes to assess decomposition with and without fauna over a period of 72days. Furthermore, we sampled soil microfauna and mesofauna in both the wet (rainy) and dry seasons.Although we found no correlation between faunal abundance and the contribution by invertebrates to rice straw decomposition, we found that soil water content was the decisive factor determining the activity of decomposer invertebrates as well as the composition and abundance of the soil fauna in fields with alternating cropping regimes. The impact of invertebrates on rice straw decomposition was higher under anaerobic than aerobic soil conditions which compensated for reduced microbial decay rates during periods of flooding. In contrast, microbial decomposition rates were higher under aerobic conditions, whereas invertebrates had no apparent effects on the mass loss of rice straw despite their higher abundance in dry fields. Our results demonstrate that invertebrates are essential for the effective decay of rice straw residues under flooded soil conditions, and therefore play an important role in supplying nutrients to flooded rice.

Effect of rice variety and fertilizer type on the active microbial community structure in tropical paddy fields in Sri Lanka

Tropical rice fields are a special class of wetlands, which are vital for world food production. Microbial communities that drive biogeochemical processes and nutrient availability for rice growth rely on rhizodeposited C as a source of energy. The current study revealed information on the structure of the active microbial community in tropical paddy fields in Sri Lanka by employing in situ Phospholipid Fatty Acids based Stable Isotope Probing (PLFA-SIP) with 13CO2 pulse labeling. The study was conducted in selected rice fields cultivated long-term with two rice varieties (traditional, KH vs. improved, BG) in combination with two types of fertilizers (inorganic, ING vs. organic, ORG).Multivariate analysis on relative 13C concentration (13CCr) of the 0–10cm soil layer revealed that the active microbial community structure varied significantly between rice varieties and fertilizers, whereas the effect of variety×fertilizer was significant as well (p<0.05). Microbial community at the lower soil depth (10–20cm) was less abundant compared with the surface layer and indicated negligible reliance on rhizodeposit 13C.Factorial ANOVA on 13CCr revealed significant effects of variety, type of fertilizer and variety×fertilizer type on active C uptake by actinomycetes. Rice variety significantly influenced the active fungal and Gram-negative bacterial groups, while none of the factors affected Gram-positive bacteria. Active Gram-negative bacteria were higher with BG variety, whereas fungi and actinomycetes were higher with KH variety in both inorganic and organic fertilizer applied fields. Gram-negative and Gram-positive bacteria were the most active functional groups in the paddy soil microbial community, whereas actinomycetes only relied to a minor extent on rhizodeposit C to meet their energy requirement. It is concluded that rice microbial communities differ significantly as a function of cultivation practices, potentially showing a large impact on ecosystem processes such as greenhouse gas emissions and plant nutrient availability.

Small-scale variability in the contribution of invertebrates to litter decomposition in tropical rice fields

Sustainable management of agricultural systems includes promoting nutrient cycles, which can reduce the need for application of fertilizer. As rice is one of the most important food resources in the world, sustainable management of rice paddies is increasingly in demand. However, little is known about the influence of invertebrates on decomposition processes in these ecosystems. We hypothesized that invertebrates contribute significantly to the decomposition of rice straw in paddies and that their relative contribution is affected by the distance to other landscape structures within fields. We placed rice straw in litterbags of two different mesh sizes which prevent (20μm×20μm) or allow (5mm×5mm) access of invertebrates in six irrigated rice fields for 84 days. In each field, bags were set on three transects running from the bund to the center of the field. Invertebrates significantly increased total rice straw litter mass loss by up to 45% (total decomposition: fine-meshed bags 64%; coarse-meshed bags 83%). Litter mass loss in bags accessed by invertebrates decreased with increasing distance from the bund. Such a spatial trend in litter mass loss was not observed in bags accessed only by microbes. Our results indicated that invertebrates can contribute to soil fertility in irrigated rice fields by decomposing rice straw, and that the efficiency of decomposition may be promoted by landscape structures around rice fields.

Effect of inorganic fertilizers (N, P, K) on methane emission from tropical rice field of India

In the tropical experimental rice field of Central Rice Research Institute, Odisha, India, an experiment was conducted during the dry season (January–April) and wet season (July–November) of rice cultivation to study the effect of nitrogen (N), phosphorus (P) and potassium (K) fertilizer application on grain yield and methane (CH4) emission. The experiment was carried out with five treatments (No fertilizer (control), N-fertilizer, P-fertilizer, K-fertilizer and N + P + K fertilizer) with three replicates of each under a completely randomized block design. Significantly higher CH4 emission was recorded from all plots during wet season. Among fertilizer applied plots, significantly higher CH4 emission was recorded from N-fertilizer applied plots (dry season: 80.27 kg ha−1; wet season: 451.27 kg ha−1), while significantly lower CH4 emission was recorded from N + P + K applied plots (dry season: 34.60 kg ha−1; wet season: 233.66 kg ha−1). Low cumulative CH4 emission to grain yield ratio was recorded from N + P + K applied plots during both seasons (83.57 kg Mg−1 grain yield during dry season and 77.14 kg Mg−1 grain yield during wet season). CH4 emission from different treatment was positively correlated with microbial biomass carbon (r = 0.516), readily mineralizable carbon (r = 0.621) and sugar (r = 0.340) content of the soil. Negative CH4 emission was recorded during the fallow period which may be attributed to higher methanotrophic bacterial population. Study suggests that the effects of P and K-fertilizer on CH4 emission from rice field along with the CH4 emission during the fallow period need to be considered to reduce the uncertainty in upscaling process.

Marker Based Estimation of Gene Flow in Tropical Rice Fields and Its Ecological Consequences

Pollen mediated gene flow is the most widely debated biosafety issue in case of genetically modified crop plants and is a primary determining factor for permitting their field release, particularly major food crops like rice. The alleged consequences of gene escape into wild/weedy relatives that coexist together with cultivated forms in rice fields in several countries is perceived to be a major concern. In an effort to estimate the gene flow in rice in a tropical environment, rice varieties stacked with three bacterial blight (BB) resistance alleles and a cytoplasmic male sterile (CMS) line were used as donors and receiver of pollen respectively and the pollen flow was tracked with molecular markers that are closely linked to BB resistance genes. The study could detect gene flow up to 20 m distance with environmental factors like temperature and humidity influencing it. The gene flow observed at longer distances than the 10 m distance suggested earlier advocate caution and suggests that all the relevant biosafety issues need to be addressed prior to release of GM rice in tropical countries where sympatric association of wild relatives with cultivated rice with frequent crop-weedy gene flow both ways is quite common.

Changes in methanogenic population size and CH4 production potential in response to crop phenology in tropical rice field

In order to understand the microbial ecology of CH4 production in rice field, population size of methanogens and pattern of CH4 production potential was determined during rice cultivation for two years (2009 and 2010). Population size varied between 4.88 × 105 and 13.98 × 105 copies g−1 dws during the entire study period and followed the trend: flowering > ripening > tillering > post-harvest > pre-plantation. Pattern of CH4 production potential was similar to the population size for different stages of the crop and followed the pseudo-first order kinetics, indicating a positive relationship between the population size of methanogens and CH4 production potential. An exponential relationship between the cumulative methane production potential and methanogenic population size was established.

Community structure of methanogenic archaea and methane production associated with compost-treated tropical rice-field soil

The diversity and density of methanogenic archaea and methane production were investigated ex situ at different growth stages of rice plant cultivated in compost-treated tropical rice fields. The qPCR analysis revealed variation in methanogens population from 3.40×10(6) to 1.11×10(7) copiesg(-1) dws, in the year 2009 and 4.37×10(6) to 1.36×10(7) copiesg(-1) dws in the year 2010. Apart from methanogens, a large number of bacterial (9.60×10(9) -1.44×10(10) copiesg(-1) dws) and archaeal (7.13×10(7) -3.02×10(8) copiesg(-1) dws) communities were also associated with methanogenesis. Methanogen population size varied in the order: flowering > ripening > tillering > postharvest > preplantation stage. The RFLP-based 16S rRNA gene-targeted phylogenetic analysis showed that clones were closely related to diverse group of methanogens comprising members of Methanomicrobiaceae, Methanosarcinaceae, Methanosaetaceae and RC I. Laboratory incubation studies revealed higher amount of cumulative CH(4) at the flowering stage. The integration of methanogenic community structure and CH(4) production potential of soil resulted in a better understanding of the dynamics of CH(4) production in organically treated rice-field soil. The hypothesis that the stages of plant development influence the methanogenic community structure leading to temporal variation in the CH(4) production has been successfully tested.