Japanese Rice Paddy Research Articles

Diurnal variation in methane emission from a rice paddy due to ebullition.

Diurnal fluctuations in methane (CH4 ) emission are frequently observed in rice paddy fields, yet the driving mechanisms behind these variations are not fully understood. We posited that the observed diurnal patterns are predominantly due to temperature-dependent bubbling emissions (ebullition). To investigate this hypothesis, we conducted measurements of CH4 emission in a Japanese rice paddy using static chambers coupled with a high-time-resolution CH4 analyzer that allowed us to partition the total flux into its two principal components: plant-mediated transport and ebullition. Diurnal variation in the total flux was minimal during the early parts of reproductive growth (panicle formation and booting stages), when plant-mediated emission was dominant. At a later stage (heading period), ebullition accounted for 43%-70% of the total emission, and CH4 emission via both pathways varied diurnally; however, the diurnal range was much greater for bubbling emission (ratio of maximum to minimum=3.5) than for plant-mediated emission (ratio of maximum to minimum=1.4). The magnitude of emissions due to ebullition depended on the temperature, but was greater during the flux-increasing phase in the morning than the flux-decreasing phase in the afternoon even at the same temperature, forming a hysteresis in the flux versus temperature relationship. These findings support our hypothesis and indicate that abiotic processes, such as a change in the solubility of gases and the temperature dependence of the gas-phase volume (Charles's law), may play a central role in shaping the diurnal pattern of the CH4 ebullition.

Eclipta thermalis, a previously common weed, threatened by the expansion of the exotic congener E. alba in Japanese rice paddies

AbstractRice paddies are wetland ecosystems recognized as important habitats for many organisms; however, the hybridization‐related extinction risk of native plant species has not been investigated in this system so far. Eclipta L. (Compositae) is a common paddy weed in Japan; however, its genetic composition might be altered due to the hybridization between the native E. thermalis and the closely related exotic E. alba. We examined Eclipta's genetic composition using 12 microsatellite markers (612 samples collected from 109 populations) and found (i) widespread geographical distribution of E. alba in Japan, (ii) hybridization with E. thermalis, and a large number of later‐generation hybrids, and (iii) widely varying situations among regions and populations. Eclipta alba appears to have invaded an open niche in northern Japan but has not yet reached southern Japan. Both E. alba and E. thermalis were found in central Japan; however, the latter had become rare due to hybridization‐mediated processes such as competition, and demographic and genetic swamping. Notably, endogenous and exogenous selection plays an important role in the invasion of E. alba, but to varying degrees among different areas. In summary, considering the genetic variability in E. thermalis, the genetic cluster of mainland Japan is in a highly critical situation due to the invasion of E. alba.

Inheritance and stacking effect of mutant ALS genes in Schoenoplectiella juncoides (Roxb.) Lye (Cyperaceae)

Schoenoplectiella juncoides, a noxious sedge weed in Japanese rice paddy, has two ALS genes, and ALS-inhibitor-resistant plants have a mutation in one of the ALS genes. The authors aimed (a) to quantitate the effect of the number of mutant alleles of ALS genes on whole-plant resistance of S. juncoides and (b) to clarify a mode of inheritance of the resistance by investigating resistance levels of the progenies of a hybrid between two S. juncoides plants with Trp574Leu substitution in different ALS. A dose-response analysis on the parental lines and the F1 population suggested that the two ALS genes contribute equally to whole-plant resistant levels. A dose-response study on the F2 population indicated that it could be classified into five groups based on the sensitivities to metsulfuron-methyl. The five groups (in ascending order of resistance levels) were considered to have zero, one, two, three, and four mutant alleles. The stacking effect of mutant alleles on resistance enhancement was more significant when the number of mutant alleles was low than when it was high; in other words, each additional mutant allele stacking increases plant resistance, but the effect saturates as the number of mutant alleles increases. A chi-square test supported that the segregation ratio of the five groups corresponds to 1:4:6:4:1 of Mendelian independence for the two ALS loci.

Mitigation of Paddy Field Soil Methane Emissions by Betaproteobacterium <i>Azoarcus</i> Inoculation of Rice Seeds

Paddy fields are a major source of atmospheric methane, a greenhouse gas produced by methanogens and consumed by methanotrophs in flooded soil. The inoculation of rice seeds with the bacterium Azoarcus sp. KH32C alters the rice root-associated soil bacterial community composition. The present study investigated the effects of KH32C-inoculated rice cultivation on soil methanogens and methanotrophs involved in methane emissions from a rice paddy field. KH32C-inoculated and non-inoculated rice (cv. Nipponbare) were cultivated in a Japanese rice paddy with and without nitrogen fertilizer. Measurements of methane emissions and soil solution chemical properties revealed increases in methane flux over the waterlogged period with elevations in the concentrations of dissolved methane, dissolved organic carbon, and ferrous iron, which is an indicator of soil reduction levels. Reverse transcription quantitative PCR and amplicon sequencing were used to assess the transcription of the methyl-coenzyme M reductase gene (mcrA) from methanogens and the particulate methane monooxygenase gene (pmoA) from methanotrophs in paddy soil. The results obtained showed not only the transcript copy numbers, but also the compositions of mcrA and pmoA transcripts were related to methane flux. KH32C-inoculated rice cultivation recruited soil methanogens and methanotrophs that suppressed high methane synthesis, increased methane consumption, and decreased methane emissions by 23.5 and 17.2% under non-fertilized and nitrogen-fertilized conditions, respectively, while maintaining rice grain yield. The present study demonstrated the mitigation of paddy field methane emissions arising from the use of KH32C in rice cultivation due to its influence on the compositions of soil methanogen and methanotroph populations.

Animal abundance and soil properties affected by long-term organic farming in rice paddies in a typical Japanese yatsuda landscape.

Organic farming was developed to reduce agriculture's negative impacts on the environment and enhance biodiversity for sustainable productivity in agricultural ecosystems, but the long-term effectiveness of its application in Japanese rice paddies is unclear. We sought to understand how long-term organic farming affects the abundance of animals in both the rice growth and fallow seasons, and how soil properties change. We investigated the abundance of fishes, frogs, beetles, and shellfish in the floodwater in summer, and the abundance of earthworms (mainly Enchytraeidae), arthropods (spiders and springtails), and soil properties in aerobic soils in autumn. We examined fields which had been farmed organically for 10 and 18 years in Tochigi, Japan. Fields farmed with conventional management, located close to the selected organic fields, were used as a control. All selected fields were located in a valley, which is the typical landscape of a traditional Japanese farming village, called a yatsuda in Japanese. The results showed an increase in soil organic carbon, total nitrogen, and available phosphorus in plowed soils that had been converted from conventional to organic farming both 10 and 18 years earlier. However, the abundance of various animals were not affected significantly by long-term organic rice farming, other than arthropods in the aerobic soils that had been farmed organically for 18 years. The quantity of most animals in floodwater and fallow season soil was unaffected by long-term organic rice farming in the yatsuda paddy fields, probably due to the circumstances and similar irrigation systems for both conventional and organic rice farming, as well as lighter doses of agrochemical application for conventional rice cultivation.

Working conditions and labor flexibility in non-family farms: weather-based labor management by Japanese paddy rice corporations

Improving working conditions in agriculture is of great concern throughout the world. Just as in other industries, many young farm workers prefer to work as salaried employees, which has brought attention to non-family farms as providers of employment opportunities. However, in the presence of a strong need to flexibly respond to weather, there is still difficulty regarding whether workplaces without overworking can exist. This study is based on in-depth surveys of non-family rice farms in Fukui Prefecture, Japan. Our findings suggest that even in non-family farms, holiday-setting is done flexibly to account for weather, and systems that allow for harvesting at appropriate times are in place. During the busy farming period, in joint-stock farms, where multiple farmers invest together, full-time employees work overtime. In contrast, in community farms, many community residents take turns for working, which allows work to be done on time. A closer analysis of work records shows that, in either organizational structure, specific members need to overwork. Reasons behind this include issues with sunk costs in the form of monthly wages, lack of skills among part-time employees, and the communication costs of coordinating with many part-time employees.

Acute and chronic toxicity tests of systemic insecticides, four neonicotinoids and fipronil, using the tadpoles of the western clawed frog Silurana tropicalis

Extensive use of neonicotinoids and fipronil, which are popular systemic insecticides used in Japanese rice paddies, has raised concerns about their impacts on nontarget aquatic organisms such as amphibians. This study employed premetamorphic tadpoles of Silurana tropicalis and addressed the toxicity of four neonicotinoids (acetamiprid, clothianidin, dinotefuran, and imidacloprid) and fipronil. Acute toxicity tests were conducted under a 96-h semistatic exposure regime and median lethal concentration (LC50) values were calculated at 24-h intervals. All LC50 values of the four neonicotinoids exceeded 100 mg/L, suggesting their low acute toxicity to amphibians. Fipronil yielded much lower LC50 values (3.00–1.34 mg/L) and was highly toxic compared to the four neonicotinoids. Additionally, exposure to fipronil at >1 mg/L induced axial malformations, suggesting its teratogenicity. However, the LC50 values of fipronil were three orders of magnitude higher than the realistic concentrations in paddy water. Chronic toxicity tests were conducted with morphometric, gravimetric, and thyroid-histological endpoints. Premetamorphic tadpoles were exposed to each insecticide at two test concentrations: 0.1 and 1.0 mg/L for the four neonicotinoids; and 1/100 and 1/10 of the 96-h LC50 value for fipronil. Exposure to each insecticide continued until all tadpoles in the control reached late prometamorphic stages or the initial stage of metamorphic climax. At test termination, all insecticides showed no significant differences in any of the endpoints between the respective controls and chemical exposure groups. Overall, our results suggest that these insecticides alone do not directly affect amphibians through their larval stages at concentrations that likely occur in paddy water.

Spatial and temporal associations between fallow fields and Greater Painted Snipe density in Japanese rice paddy landscapes

Fallow fields provide suitable habitats for many farmland species in agricultural landscapes. Although the loss of fallow fields in the last few decades may be one of the major causes of the decline in farmland biodiversity, quantitative studies investigating the spatial and temporal associations between fallow fields and abundance of rice paddy organisms are few. This study focused on the Greater Painted Snipe (Rostratula benghalensis), a widespread wetland bird species in Asian rice paddies. We conducted replicated playback surveys in three regions of central Japan during the breeding seasons of 1997, 2006, 2007, 2018, and 2019. N-mixture models and model-selection approaches revealed positive associations between the immigration rate of Greater Painted Snipes and the area of wet fallow fields in 1997, when the species was still relatively common. Both observed and estimated densities showed (1) a severe decline in the population of Greater Painted Snipes in the Tsuchiura and Kasumigaura regions over a recent 22-year period in accordance with the reduction of fallow fields and (2) persistence of both wet fallow fields and Greater Painted Snipes in the Abiko region in 2018 and 2019. These results indicate that the loss of wet fallow fields since the late 1990s was associated with the decline of the Greater Panted Snipe population in Japanese agricultural landscapes. Our study highlights the potential importance of fallow fields for population trends of farmland birds and the necessity for their maintenance through, for example, agri-environmental schemes, in rice-producing countries.

Dissimilatory Nitrate Reduction to Ammonium and Responsible Microbes in Japanese Rice Paddy Soil.

Nitrification–denitrification processes in the nitrogen cycle have been extensively examined in rice paddy soils. Nitrate is generally depleted in the reduced soil layer below the thin oxidized layer at the surface, and this may be attributed to high denitrification activity. In the present study, we investigated dissimilatory nitrate reduction to ammonium (DNRA), which competes with denitrification for nitrate, in order to challenge the conventional view of nitrogen cycling in paddy soils. We performed paddy soil microcosm experiments using 15N tracer analyses to assess DNRA and denitrification rates and conducted clone library analyses of transcripts of nitrite reductase genes (nrfA, nirS, and nirK) in order to identify the microbial populations carrying out these processes. The results obtained showed that DNRA occurred to a similar extent to denitrification and appeared to be enhanced by a nitrate limitation relative to organic carbon. We also demonstrated that different microbial taxa were responsible for these distinct processes. Based on these results and previous field observations, nitrate produced by nitrification within the surface oxidized layer may be reduced not only to gaseous N2 via denitrification, but also to NH4+ via DNRA, within the reduced layer. The present results also indicate that DNRA reduces N loss through denitrification and nitrate leaching and provides ammonium to rice roots in rice paddy fields.

Water extractable organic carbon and nitrogen and their stable isotopes from long-term experiment in a Japanese rice paddy

Hot water- and water-extracted organic matter was extracted from soil samples collected after a 31-year long-term experiment which aimed to assess the effect of different fertilization strategies (inorganic fertilizers and organic matters) commonly used for paddy rice cultivation in Yamagata, northeastern Japan. The ratio of soil to extracted water was 2:3. The amounts of hot water-extracted organic carbon and nitrogen (HWEOC and HWEN) at 80 o C and 16 hours, water-extracted organic carbon and nitrogen (WEOC and WEN) at room temperature, and their δ 13 C and δ 15 N were measured from the five fertilizer treatment plots as [1) PK, 2) NPK, 3) NPK + 6 Mg ha -1 rice straw (RS), 4) NPK + 10 Mg ha -1 rice straw compost (CM1), and 5) NPK + 30 Mg ha -1 rice straw compost (CM3)], for surface (0-15 cm) and subsurface (15-25 cm) layers. HWEOC and WEOC accounted for an average of about 1.5 1 and 0.66% of SOC, while HWEN and WEN accounted for an average of about 1.09 and 0.40% of soil TN, respectively. About 90% of the extracted N was organic form among all treatments . The values of δ 13 C for HWEOC and WEOC ranged from -28.2 to -26. 5 ‰ and from -28.3 to -27.0‰, similar to the original rice straw and rice straw compost , and lower than the value of original soil at -22.5 ‰. The values of δ 15 N of HWEN, WEN and bulk soil ranged from 0. 8 to 3. 8 ‰, from 1.0 to 4.0‰, and from 0. 8 to 2. 8 ‰, respectively. It was clear that δ 15 N decreased in RS but increased in CM3 treatments. Our results indicated that the amounts of h ot water- and water-extracted organic matter were affected by long-term application of inorganic fertilizers and organic matter s remarkably. However, the values of δ 13 C for HWEOC and WEOC were not different among 5 treatments, but values of δ 15 N of HWEN and WEN were affected by RS and CM3 applications clearly .

Regional analyses of water use in Japanese paddy rice cultivation using modified water footprint indexes

Water use in paddy rice cultivation was evaluated from the perspective of the environmental impact of water resource consumption for seven regions in Japan. Water resources can be appropriately discussed on a flow basis, and the impact of water consumption depends on the available water flow, which varies largely by time and location, in addition to the amount of water consumption itself. In this study, differential and integral water footprints were used as the indexes for the analyses. These indexes were previously developed and can help draw conclusions regarding the continuous impact of consumption on the water resources on a flow basis, taking into account the regional and temporal conditions of water supply. The results showed that the impact of water consumption was higher in regions with less amount of river flow. In particular, a large variation of impact, with temporally high values, was observed in such regions. These results suggest the necessity of water management on the basis of not only total or average water flow, but also temporal variation.

Forms of trace arsenic, cesium, cadmium, and lead transported into river water for the irrigation of Japanese paddy rice fields

In this study, we focus on the behavior of geogenic, toxic trace elements, particularly As, Cs, Cd, and Pb, during their transportation in two rivers for irrigation commonly used in monsoon Asia; one river originates from an active volcano, Mt. Asama, and the other originates from a currently inactive volcano, Yatsugatake Mountains in Nagano, Japan. These rivers were investigated to understand the role of river water as a pollutant of rice and other aquatic plants (via irrigation) and aquatic animals. The results indicated that the behavior of toxic trace elements in river water are likely controlled by their interactions with particulate Fe, Al, and Ti compounds. The majority of Pb and Cd is transported as particulate matter with Fe, Al, and Ti, while the majority of As is transported in the dissolved form, predominantly as arsenate, with low abundance of particulate matter. Cs is transported either as the dissolved form or as particulate matter in both rivers. The investigated elements are transported in the rivers as particulate and dissolved forms, and the ratio of these forms is controlled by the pH and presence of particulate Fe, Al, and Ti phases in the river water. With respect to Cs in both rivers, the parameter governing the concentration and transportation of Cs, in the bimodal form (i.e., particulate and dissolved forms), through the river possibly shifts from sorption to pH by particulate Fe–Al–Ti, according to the abrupt increase in the concentration of Cs in the river. The chemical attraction of particulate Fe–Al–Ti for Cs is weaker than that for Pb and Cd, indicating that the lower electronegativity of Cs weakens the chemical attraction on a colloid for the competitive sorption with the other trace elements. The different relationships between As and Fe in the river and in the irrigation water and soil water, as well as those in paddy rice, suggested that As in paddy rice is not directly derived from As in the irrigation water from the river under flooding.

Effects of agricultural practices and fine-scale landscape factors on spiders and a pest insect in Japanese rice paddy ecosystems

We examined the effects of environmentally friendly (EF) farming and landscape factors on the abundances of major spider guilds and a rice pest, the small brown planthopper (SBPH), Laodelphax striatellus (Fallen), in a Japanese rice paddy ecosystem. The abundances of all spider guilds increased by EF farming, whereas different spider guilds showed contrasting responses to the size of the forest within 200 m of the fields. The abundances of ground spiders and horizontal web weavers increased with increasing forest area, unlike small ground spiders, whose abundance decreased. The abundances of SBPH nymphs and adults decreased by EF farming but responded differently to landscape: nymphs decreased with increasing forest area, but adults did not. Further analysis indicated a potential negative relationship between web-weaving spiders and SBPH nymphs. Our findings suggest that the size of the forest adjacent to fields is an important determinant of spider guild composition and pest abundance.

Estimation of total CH4 emission from Japanese rice paddies using a new estimation method based on the DNDC-Rice simulation model

Methane (CH4) is a greenhouse gas, and paddy fields are one of its main anthropogenic sources. In Japan, country-specific emission factors (EFs) have been applied since 2003 to estimate national-scale CH4 emission from paddy field. However, these EFs did not consider the effects of factors that influence CH4 emission (e.g., amount of organic C inputs, field drainage rate, climate) and can therefore produce estimates with high uncertainty. To improve the reliability of national-scale estimates, we revised the EFs based on simulations by the DeNitrification-DeComposition-Rice (DNDC-Rice) model in a previous study. Here, we estimated total CH4 emission from paddy fields in Japan from 1990 to 2010 using these revised EFs and databases on independent variables that influence emission (organic C application rate, paddy area, proportions of paddy area for each drainage rate class and water management regime). CH4 emission ranged from 323 to 455ktCyr−1 (1.1 to 2.2 times the range of 206 to 285ktCyr−1 calculated using previous EFs). Although our method may have overestimated CH4 emissions, most of the abovementioned differences were presumably caused by underestimation by the previous method due to a lack of emission data from slow-drainage fields, lower organic C inputs than recent levels, neglect of regional climatic differences, and underestimation of the area of continuously flooded paddies. Our estimate (406ktC in 2000) was higher than that by the IPCC Tier 1 method (305ktC in 2000), presumably because regional variations in CH4 emission rates are not accounted for by the Tier 1 method.

Analysis of Dual- and Full-Circular Polarimetric SAR Modes for Rice Phenology Monitoring: An Experimental Investigation through Ground-Based Measurements

Circularly polarized synthetic aperture radar (CP-SAR) is known to be insensitive to polarization mismatch losses caused by the Faraday rotation effect and antenna misalignment. Additionally, the dual-circular polarimetric (DCP) mode has proven to have more polarimetric information than that of the corresponding mode of linear polarization, i.e., the dual-linear polarimetric (DLP) mode. Owing to these benefits, this paper investigates the feasibility of CP-SAR for rice monitoring. A ground-based CP-radar system was exploited, and C-band anechoic chamber data of a self-cultivated Japanese rice paddy were acquired from germination to ripening stages. Temporal variations of polarimetric observables derived from full-circular polarimetric (FCP) and DCP as well as synthetically generated DLP data are analyzed and assessed with regard to their effectiveness in phenology retrieval. Among different observations, the H / α ¯ plane and triangle plots obtained by three scattering components (surface, double-bounce, and volume scattering) for both the FCP and DCP modes are confirmed to have reasonable capability in discriminating the relevant intervals of rice growth.

A New Morphological Type of Volvox from Japanese Large Lakes and Recent Divergence of this Type and V. ferrisii in Two Different Freshwater Habitats.

Volvox sect. Volvox is characterized by having unique morphological characteristics, such as thick cytoplasmic bridges between adult somatic cells in the spheroids and spiny zygote walls. Species of this section are found from various freshwater habitats. Recently, three species of Volvox sect. Volvox originating from rice paddies and a marsh were studied taxonomically based on molecular and morphological data of cultured materials. However, taxonomic studies have not been performed on cultured materials of this section originating from large lake water bodies. We studied a new morphological type of Volvox sect. Volvox (“Volvox sp. Sagami”), using cultured materials originating from two large lakes and a pond in Japan. Volvox sp. Sagami produced monoecious sexual spheroids and may represent a new morphological species; it could be clearly distinguished from all previously described monoecious species of Volvox sect. Volvox by its small number of eggs or zygotes (5–25) in sexual spheroids, with short acute spines (up to 3 μm long) on the zygote walls and elongated anterior somatic cells in asexual spheroids. Based on sequences of internal transcribed spacer (ITS) regions of nuclear ribosomal DNA (rDNA; ITS-1, 5.8S rDNA and ITS-2) and plastid genes, however, the Volvox sp. Sagami lineage and its sister lineage (the monoecious species V. ferrisii) showed very small genetic differences, which correspond to the variation within a single biological species in other volvocalean algae. Since V. ferrisii was different from Volvox sp. Sagami, by having approximately 100–200 zygotes in the sexual spheroids and long spines (6–8.5 μm long) on the zygote walls, as well as growing in Japanese rice paddies, these two morphologically distinct lineages might have diverged rapidly in the two different freshwater habitats. In addition, the swimming velocity during phototaxis of Volvox sp. Sagami spheroids originating from large lakes was significantly higher than that of V. ferrisii originating from rice paddies, suggesting adaptation of Volvox sp. Sagami to large water bodies.

Draft Genome Sequence of Bacteroidales Strain 6E, Isolated from a Rice Paddy Field in Japan.

We generated a high-quality draft genome sequence of Bacteroidales strain 6E, a strict anaerobe newly isolated from Japanese rice paddy field soil. The genome consists of 61 contigs, with a total size of 4,436,542 bp and mean G+C content of 45.4%. Annotation predicted 3,620 protein-coding and 54 RNA genes.

Potassium fertilizer and other materials as countermeasures to reduce radiocesium levels in rice: Results of urgent experiments in 2011 responding to the Fukushima Daiichi Nuclear Power Plant accident

Huge amounts of radionuclides, particularly radiocesium, were discharged from the Fukushima Daiichi Nuclear Power Plant (FDNPP), and widespread of contamination of the land, including paddy fields, was observed. Because rice is a staple food in Japan, contamination of paddy fields is a serious problem, and practical countermeasures to reduce radiocesium contamination of rice are urgently required. Potassium (K) fertilization was previously shown to be an effective countermeasure in fields contaminated by the Chernobyl accident, but researchers did not study the effects on rice (Oryza sativa L.). In the present study, we performed urgent field experiments to test the use of K fertilization, as well as other soil amendments, to reduce radiocesium contamination of rice. We found that K fertilization was an effective and practical countermeasure to reduce radiocesium uptake by rice from several soil types in Japanese paddy rice culture. Other treatments, including the application of expanded vermiculite or manure, were effective, and the effect appears to be explained by their K content. Based on these results, the recommended level of exchangeable soil potassium to lower the radiocesium content of rice to acceptable levels is about 200 mg K kg–1 soil before the usual fertilization. This K fertilizer application criterion was applied in a wide, low-contaminated area from the 2012 cropping season, and satisfactory results have been obtained generally.

Resistance levels of sulfonylurea‐resistant Schoenoplectus juncoides (Roxb.) Palla with various Pro197 mutations in acetolactate synthase to imazosulfuron, bensulfuron‐methyl, metsulfuron‐methyl and imazaquin‐ammonium

An investigation, using herbicidal pot tests in a greenhouse condition, was conducted to determine the whole‐plant dose–response relationships to several acetolactate synthase (ALS)‐inhibiting herbicides of sulfonylurea (SU)‐resistant Schoenoplectus juncoides with various Pro197 mutations in ALS that was collected from Japanese rice paddy fields. All the tested SU‐resistant accessions with a Pro197 mutation were highly resistant to two commonly used SU herbicides (imazosulfuron and bensulfuron‐methyl), but were much less resistant to another SU herbicide, metsulfuron‐methyl, and were substantially not resistant to imazaquin‐ammonium. These cross‐resistance patterns have been known previously in fragments of S. juncoides and other weed species and were comprehensively confirmed in this study with a whole set of Pro197 mutations. The analyses of resistance levels, based on ED90 values, newly showed that different accessions with a common amino acid substitution in ALS1 showed similar responses to these herbicides (confirmed with four amino acid substitutions), that the rankings of resistance levels that were conferred by various Pro197 mutations in ALS1 differed among the SU herbicides and that the resistance levels of the ALS2‐mutated accessions were higher than, lower than or similar to those of the corresponding ALS1‐mutated accessions, depending on the compared pair, but the deviation patterns were generally similar among the SU herbicides in each compared pair. The final finding might suggest that the abundance of ALS2 is not as stable as that of ALS1. In addition, as a result of these new findings, together with expected further research, a suggested possibility is that substituting amino acids at Pro197 generally could be estimated by plotting each accession's ED90 values of imazosulfuron and bensulfuron‐methyl in a two‐dimensional graph.

Insect natural enemies as bioindicators in rice paddies

In Asia, including Japan and Korea, rice paddies occupy the largest cultivated area in agricultural land. Rice paddies provide the habitats for many organisms including endemic species, sustaining high biodiversity. Insect natural enemies inhabiting rice paddies have an important function for rice production as agents of ‘ecosystem services’ because they play a major role in suppressing rice pests. The diversity and abundance of natural enemies can be a good index reflecting the ‘healthiness’ of agro-ecosystem services in rice paddies. The present study investigates whether insect natural enemies could be good biological indicators for general arthropod biodiversity and agricultural practice. First, the concept of ideal bio-indicators was summarized. The strategy to explore and select such bio-indicators was then proposed. Lastly, field survey was made to evaluate the abundance and biodiversity of natural enemies in Japanese rice paddies where chemical inputs, i.e., insecticide use, were different. The results showed that reduction of chemical inputs led to an increase in species richness or diversity of natural enemies including parasitoids and predators. Then, the data were analyzed to examine suitable indicator species to assess environmental soundness of agricultural practice and biodiversity in rice paddies. The density of several species of natural enemies did respond both to pesticide use and to general arthropod biodiversity. The analyses thus have indicated that natural enemies can be suitable as bio-indicators. Usefulness of indicator species in rice paddies is discussed in the context of ecologically sound agriculture.