Azolla Imbricata Research Articles

The responses of weed communities to field nutrients and their ecological benefits in rice fields: A review

AbstractWhile traditionally perceived as yield‐reducing elements in rice (Oryza sativa L.) cultivation, weed communities in paddy fields play a crucial role in the ecosystem. These communities, when selectively retained, can significantly enhance ecosystem services. This review examines the impact of various weed communities on rice in different paddy fields, their response to field nutrients, and the ecological benefits they offer. These benefits include nitrogen retention, promotion of microbial diversity, and reduction of diseases, pests, and weed proliferation. Examples of such benefits are seen in weeds like Lemna minor L. and Azolla imbricata (Roxb.) Nakai, which help in nitrogen fixation and act as biocontrol agents against harmful pests. However, current research in this area faces challenges, including the lack of intelligent and precise weed control technologies, comprehensive green control strategies, and expertise in weed management. Our findings suggest a strategic approach to weed control in paddy fields, emphasizing the importance of preserving weed species that have minimal impact on rice yields but offer significant ecological advantages. These practices can lead to grass‐mediated weed control and enhanced nutrient absorption, thereby reducing fertilizer loss. Ultimately, this approach could reduce the reliance on chemical fertilizers and herbicides in paddy fields, laying the groundwork for greener rice cultivation and sustainable agricultural practices.

Cadmium accumulation in rice grains is mitigated by duckweed-like hydrophyte through adsorption and increased ammonia nitrogen

Although increasing attention has been paid to agronomic measures for reducing the heavy metal load in rice grain, the effects of duckweed-paddy co-cropping technology on the accumulation of cadmium (Cd) in rice grains remain unclear. To investigate its specific effects on Cd accumulation in paddy fields, three types of duckweed-like hydrophyte (DH), Azolla imbricata, Spirodela polyrrhiza, and Lemna minor were chosen for study. Their use resulted in a reduction of Cd content in rice grains from 0.40 mg/kg to <0.20 mg/kg, with A. imbricata yielding the best results (0.15 mg/kg). The three types of DH reduced the available Cd content in the soil by 10 % to 35 % after the paddy tillering stage. The reduction of available Cd content was attributed to the absorption, high pH, and increase of relative abundance of special bacteria of immobilizing Cd. In addition, DH could regulate soil nitrogen leading to ammonium nitrogen increased from 75 mg/kg to 100 mg/kg, while nitrate nitrogen decreased from 0.55 to 0.1–0.3 mg/kg. The increase of ammonium nitrogen content might induce the low Cd transfer ability in rice plant and then low Cd content in rice grain. This study demonstrated that DH has a good effect on the reduction of the Cd concentration in rice grains. Consequently, duckweed-paddy co-cropping technology offers a potential solution to heavy metal pollution and agricultural non-point source pollution, as it not only reduces Cd levels in rice plants, but also fixes nitrogen, reducing the need for nitrogen application.

Biochemical responses and phytoremediation potential of Azolla imbricata (Roxb.) Nakai in water and nutrient media exposed to waste metal cutting fluid along with temperature and humidity stress

Phytoremediation of metals from water (WM) and nutrient (NM) media exposed to waste metal cutting fluid (WMCF) along with temperature (T) and humidity (H) stress was tested using Azolla imbricata (Roxb.) Nakai. In the absence of WMCF, biomass was higher in NM than in WM during all tests. Surprisingly, opposite results were noted in the presence of WMCF, with growth failing at exposure to > 0.1% and > 0.5% in NM and WM, respectively. Further, correlation analysis of the growth data following WM exposure revealed that biomass was affected positively by T and negatively by H and metal accumulation. Simultaneously, metal accumulation was affected negatively by T and positively by H. The average accumulations of Al, Cd, Cr, Fe, Pb, and Zn across all T/H tests were 540, 282, 71, 1645, 2494 and 1110 mg·kg−1, respectively. The observed bioconcentration factor indicated that A. imbricata acts as a hyperaccumulator or accumulator of Zn (>10) and as either accumulator (>1) or excluder (<1) of the other metals. Overall, the phytoremediation performance of A. imbricata in multi-metal-contaminated WMCF was high in WM under all environmental conditions. Therefore, the use of WM is an economically feasible approach for the removal of metals from WMCF.

Comparative analysis of the endophytic bacteria inhabiting the phyllosphere of aquatic fern Azolla species by high-throughput sequencing

BackgroundAzolla is a small floating fern living in symbiosis with nitrogen-fixing cyanobacteria and provides a variety of important ecosystem benefits. Previous studies have presented that Azolla harbors diverse bacteria that may play a key role in host fitness and productivity. However, the characteristics of endophytic bacteria inhabiting the phyllosphere of different species of Azolla have not yet been fully understood.ResultsIn this study, the 16S ribosomal DNA (rDNA) V5-V7 region of bacteria was determined by Illumina high-throughput sequencing platform to study the diversity and richness of endophytic bacterial communities in the phyllosphere of five Azolla species collected from different countries. A total of 1150 operational taxonomic units (OTUs) were detected for the endophytic bacteria community. According to the α diversity indices, the diversity of bacteria was ordered as Azolla imbricata > A. pinnata > A. filiculoides > A. mexicana > A. caroliniana. The PCoA results displayed that the bacterial communities of A. mexicana and A. caroliniana shared the highest similarity, followed by the similarity between A. pinnata and A. imbricata, and they were significantly distinct from the community of A. filiculoides. The dominant bacteria of Azolla mainly belonged to the phylum of Proteobacteria, followed by Actinobacteria, Chlorobillobacteria, and Firmicutes. In detail, the relative abundance of Proteobacteria in A. imbricata was 52.23%, whereas it was more than 80.00% in the other four species of Azolla. Notably, Herbaspirillum (45.91%, 44.08%) and Methylophilus (29.97%, 37.96%) were the main genera inhabiting A. mexicana and A. caroliniana respectively. Ferrovibrio (18.54%) and Rhizobium (16.68%) were the dominant genera inhabiting A. filiculoides. The group of unidentified genera (41.63%, 44.92%) consisted most of the bacteria in A. imbricata and A. pinnata respectively. Further analysis suggested that the significant different bacteria identified in LDA Effect Size analysis existed Azolla species-specific patterns.ConclusionsIn summary, all results suggested that the diversity and composition of the endophytic bacterial communities were different in Azolla species.

3,4,5-O-tricaffeoylquinic acid with anti-radiation activity suppresses LPS-induced NLRP3 inflammasome activation via autophagy in THP-1 macrophages

Damage to normal tissues caused by excessive ionizing radiation (IR) exposure is the major side effect of radiotherapy. Several recent studies have shown that IR-induced damage to tissues leads to a systemic immune response and NLRP3 inflammasome activation in immune cells. 3,4,5-O-tricaffeoylquinic acid (tCQA), extracted from the natural plant Azolla imbricata, relieves inflammation and has radioprotective function. Here, we aimed to investigate the inhibitory effect and molecular mechanism of tCQA on IR-induced NLRP3 inflammasome activation. First, the results of ELISA and qPCR assays showed that tCQA has anti-inflammatory effects in THP-1 cell line and healthy human peripheral blood mononuclear cells. Western blotting and ELISA suggested tCQA could inhibit NF-κB/MAPK signaling pathway, NLRP3 expression and the secretion of IL-1β in lipopolysaccharide (LPS)-stimulated THP-1 macrophages. Then, flow cytometry, LDH assay and western blotting demonstrated that tCQA could inhibit LPS- and nigericin-induced Caspase-1 activation and gasdermin D cleavage, thereby suppressing inflammatory cell death. Furthermore, we found that the autophagy inhibitor chloroquine, not the proteasome inhibitor MG132, could counteract the promoting effect of tCQA on NLRP3 degradation and the inhibitory effect on cell death. Western blotting and autophagosome staining results suggested tCQA could significantly enhance LPS-induced autophagic flux in macrophages and ATG5/ATG7 knockdown reverses the inhibitory effect of tCQA on NLRP3 expression and Caspase-1 activation, indicating that tCQA induces NLRP3 degradation via autophagy. Finally, THP-1 macrophages and BALB/c mice were irradiated with 137Cs γ-rays and tCQA could inhibit IR-induced NLRP3 inflammasome activation both in vitro and in vivo. To conclude, tCQA controls inflammation and NLRP3 inflammasome activation in vitro via NF-κB/MAPK signaling pathway and autophagy, meanwhile inhibits IR-induced NLRP3 inflammasome activation in vivo. Overall, our study provides an experimental and theoretical basis for the application of tCQA as a radioprotectant in clinical radiotherapy.

3,4,5-O-tricaffeoylquinic acid alleviates ionizing radiation-induced injury in vitro and in vivo through regulating ROS/JNK/p38 signaling.

Ionizing radiation (IR) brings many health problems to humans, causing damage to the digestive system, hematopoietic system, and immune system. Natural compounds derived from plants have attracted widespread attention due to their low toxicity. Here, we found that 3,4,5-O-tricaffeoylquinic acid (tCQA) extracted from natural plant Azolla imbricata could significantly alleviate the systemic damage in mice caused by IR. In order to further explore the molecular mechanism of the radioprotective effect of tCQA, in vitro experiments confirmed that tCQA could attenuate the cytotoxic effect of IR on the colonic epithelial cell line NCM460 and alleviate the IR-induced mitochondrial dysfunction characterized by the decrease of mitochondrial transmembrane potential, ROS production, and caspase-dependent apoptosis. In addition, the generation of ROS induced by H2 O2 could also be reversed by tCQA. Then, Western blot demonstrated that tCQA could reverse the MAPK signaling pathway activated by IR. However, the inhibitory effect of tCQA on JNK and P38 levels activated by the JNK agonist anisomycin is not obvious; meanwhile, tCQA could inhibit the activation of JNK/P38 induced by H2 O2 , which suggests that tCQA might inhibit the JNK/P38 signaling pathway by reducing ROS. In short, tCQA inhibits the generation of ROS caused by IR, and then regulates the activity of caspase in the mitochondrial pathway by inhibiting the JNK/P38 signaling pathway, thereby alleviating the apoptosis of NCM460. This research provides an experimental basis for the development of new types of radioprotective agents for medical diagnosis and radiotherapy.

Effect of Azolla Imbricata and Spirodela Polyrrhiza on Chromium(VI) Removal and Power Generation in a Plant Microbial Fuel Cell

Effect of Azolla Imbricata and Spirodela Polyrrhiza on Chromium(VI) Removal and Power Generation in a Plant Microbial Fuel Cell

Nutrient effects on aquatic litter decomposition of free-floating plants are species dependent

Among the most important ecosystem processes in wetlands is plant litter decomposition, which provides the detrital food chains with matter and energy and consequently could affect ecosystem health and integrity. Varying degrees of anthropogenic eutrophication mostly due to urbanization, are prevalent problems in many wetlands and aquatic ecosystems. Free-floating plants are widely distributed in (particularly, tropical and subtropical) still water bodies in wetlands and sensitive to water nutrient enrichment. However, little is known about how water nutrient affect litter decomposition of free-floating plants. In a subtropical wetland, we conducted an in-situ experiment in which litters of free-floating ferns (Azolla imbricata and Salvinia natans) and an angiosperm (Lemna minor) were incubated beneath water in 13 ponds with broadly similar size and shape but different levels of eutrophication. Litters of L. minor decomposed faster than those of the two fern species while its decomposition rate did not have a relationship to water nutrient content. However, we did find the decomposition rate of two ferns decreased significantly with water total phosphate content, which might be attributed to decline of microbial decomposers. Such interspecific variation in decomposition response to eutrophication could be explained by the functional traits of the species, e.g., SLA, leaf phosphorus content. These findings suggest water eutrophication would generally decrease plant litter decomposition rate but such effect is species- and/or trait-dependent. Thus, community composition and plant functional traits should be considered in analyses of ecosystem processes under water eutrophication.

Comprehensive identification of minor components and bioassay-guided isolation of an unusual antioxidant from Azolla imbricata using ultra-high performance liquid chromatography—quadrupole time-of-flight mass spectrometry combined with multicomponent knockout and bioactivity evaluation

Azolla imbricata (Roxb.) Nakai is used as a traditional Chinese medicine. However, very limited information is available on its effective components. Traditional procedures for discovering natural bioactive compounds, especially for minor ones, are usually time-consuming and labor-intensive. Therefore, an efficient approach using ultra-high performance liquid chromatography–quadrupole time-of-flight tandem mass spectrometry (UHPLC–QTOF–MS/MS) combined with multicomponent knockout and bioactivity evaluation was developed to obtain more information about the bioactive constituents in A. imbricata. A total of 93 compounds were identified or tentatively identified, including five major components knocked out by semi-preparative HPLC and 88 minor components in the extract with the major components’ knockout. These compounds involved chlorogenic acid derivatives, flavonoids, cinnamoyltyrosine derivatives, cinnamic acid derivatives, fatty acids and their derivatives, coumarins, lignans, and chromones. Eighty-two compounds have not been previously reported in the literature for this species, including a new flavanol derivative named brainin D. Among them, 64 compounds, including brainin D, exhibited antioxidant activities using 1,1-diphenyl-2-picrylhydrazyl radical (DPPH)–UHPLC–MS as guidance. The new antioxidant, brainin D, was concomitantly isolated and unequivocally identified by spectroscopic methods, and it showed good DPPH radical activity with an IC50 value of 9.3 ± 0.6 μg/mL. In conclusion, the proposed combination approach can be used for systematic identification of minor constituents and guided isolation of new compounds from natural sources with high efficiency. The comprehensive understanding of the minor constituents and antioxidants in A. imbricata lays the foundation for further rational utilization of this medicinal herb.

Distribution of antibiotic resistance genes in soil amended using Azolla imbricata and its driving mechanisms.

The floating aquatic plant of Azolla imbricata has an outstanding purification capability for polluted river water, and it is also employed to improve soil fertility. However, the occurrence and distribution of antibiotic resistance genes (ARGs) in soil amended using A.imbricata remain unclear. In the soil amendment with A. imbricata, heavy metals, antibiotics, transposase genes, ARGs, and bacterial communities in the soil were determined in this study. The results indicated that the diversity of bacteria and ARGs increased, while the diversity of ARGs decreased under the amendment using an appropriate amount of A. imbricata. The Firmicutes, Chloroflexi, Actinobacteria, and Cyanobacteria were the main host bacteria of ARGs. The vertical gene transfer of ARGs was weak, and the horizontal gene transfer became the dominant transfer pathway of ARGs. The amendment with A. imbricata altered the distribution of heavy metals, antibiotics, transposase genes, ARGs, and dominant bacteria. The amendment using A. imbricata promoted the degradation of antibiotics, decreased the concentrations of available heavy metals, and eliminated the abundance of ARGs and transposase genes. Our findings suggested a comprehensive effect of multiple stresses on the fate of ARGs in soil amended with A. imbricata, providing an insight into the distribution and propagation of ARGs in soil amended using plant residues.

Effects of physical space and nutrients on the growth and intraspecific competition of a floating fern

Physical space, defined by its volume and shape, is considered a resource for plant growth, as a plant can be limited by physical space even when other resources (e.g., light, water and nutrients) are unlimited. However, the effect of physical space limitation on intraspecific competition of plants, especially floating plants, is not well understood. Here we tested the hypothesis that physical space affects the growth and intraspecific competition of floating plants, which is further influenced by the volume and surface area of the containers in which these plants are grown. We grew either one or four clonal fragments of a floating clonal fern, Azolla imbricata, in cylindrical containers differing in diameter and height (and thus surface area and volume) and filled with solutions containing the same or different nutrient concentrations. Biomass and number of clonal fragments of A. imbricata were higher in the container with the larger diameter and thus water surface area, but were not significantly affected by the height/volume of the container. Biomass and number of clonal fragments were reduced by intraspecific competition and tended to increase first and then decreased with increasing nutrient concentration. Increasing nutrient concentration inhibited the growth and then reduced intraspecific competition of A. imbricata, but the diameter or height/volume of the container had no effect. Our findings suggest that nutrient levels can alter intraspecific competition of plants, but physical space may not.

Determination of caffeoylquinic acid derivatives in Azolla imbricata by chitosan-based matrix solid-phase dispersion coupled with HPLC–PDA

Five main components of Azolla imbricata were isolated and identified as caffeoylquinic acid derivatives, four of which were isolated from this species for the first time. The five compounds exhibited strong antioxidant activities and were used as chemical markers for quantitative analysis. A chitosan-based matrix solid-phase dispersion (MSPD) extraction coupled with high-performance liquid chromatography (HPLC) was developed for the determination of the five analytes in A. imbricata. The optimal conditions for the chitosan-based MSPD extraction were as follows: low viscosity chitosan HL-1 as the dispersant, sample-to-dispersant mass ratio of 1:1, 10 mL of a methanol-sulfuric acid aqueous solution (0.2 M) (7:3, v/v) as the elution solvent, and a grinding time of 1 min. Compared with ultrasonic assisted extraction (UAE), the chitosan-based MSPD extraction exhibited higher extraction efficiency, consumed less solvent and time, and provided a cleaner extract. Compared with C18-based MSPD, the developed method was less expensive and more environmentally-friendly. The validated MSPD–HPLC method was efficient, reliable, and applicable to the quantification of caffeoylquinic acids in A. imbricata.

Response of microbial communities to pesticide residues in soil restored with Azolla imbricata.

Under conditions of Azolla imbricata restoration, the high-throughput sequencing technology was employed to determine change trends of microbial community structures in the soil that had undergone long-term application of pesticides. The relationship between the content of pesticide residues in the soil and the microbial community structure was analyzed. The results indicated that the microbial diversity was strongly negatively correlated with the contents of pesticide residues in the soil. At a suitable dosage of 5kg fresh A. imbricata per square meter of soil area, the soil microbial diversity increased by 12.0%, and the contents of pesticide residues decreased by 26.8-72.1%. Sphingobacterium, Sphingopyxis, Thermincola, Sphingobium, Acaryochloris, Megasphaera, Ralstonia, Pseudobutyrivibrio, Desulfitobacterium, Nostoc, Oscillochloris, and Aciditerrimonas may play major roles in the degradation of pesticide residues. Thauera, Levilinea, Geothrix, Thiobacillus, Thioalkalispira, Desulfobulbus, Polycyclovorans, Fluviicola, Deferrisoma, Erysipelothrix, Desulfovibrio, Cytophaga, Vogesella, Zoogloea, Azovibrio, Halomonas, Paludibacter, Crocinitomix, Haliscomenobacter, Hirschia, Silanimonas, Alkalibacter, Woodsholea, Peredibacter, Leptolinea, Chitinivorax, Candidatus_Lumbricincola, Anaerovorax, Propionivibrio, Parasegetibacter, Byssovorax, Runella, Leptospira, and Nitrosomonas may be indicators to evaluate the contents of pesticide residues.

Restoration using Azolla imbricata increases nitrogen functional bacterial groups and genes in soil.

Microbial groups are major factors that influence soil function. Currently, there is a lack of studies on microbial functional groups. Although soil microorganisms play an important role in the nitrogen cycle, systematic studies of the effects of environmental factors on microbial populations in relation to key metabolic processes in the nitrogen cycle are seldom reported. In this study, we conducted a systematic analysis of the changes in nitrogen functional groups in mandarin orange garden soil treated with Azolla imbricata. The structures of the major functional bacterial groups and the functional gene abundances involved in key processes of the soil nitrogen cycle were analyzed using high-throughput sequencing (HTS) and quantitative real-time PCR, respectively. The results indicated that returning A. imbricata had an important influence on the composition of soil nitrogen functional bacterial communities. Treatment with A. imbricata increased the diversity of the nitrogen functional bacteria. The abundances of nitrogen functional genes were significantly higher in the treated soil compared with the control soil. Both the diversity of the major nitrogen functional bacteria (nifH bacteria, nirK bacteria, and narG bacteria) and the abundances of nitrogen functional genes in the soil showed significant positive correlations with the soil pH, the organic carbon content, available nitrogen, available phosphorus, and NH4+-N and NO3--N contents. Treatment with 12.5kg fresh A. imbricata per mandarin orange tree was effective to improve the quality of the mandarin orange garden soil. This study analyzed the mechanism of the changes in functional bacterial groups and genes involved in key metabolic processes of the nitrogen cycle in soil treated by A. imbricata.

Alcohol compounds in Azolla imbricata and potential source implication for marine sediments

This study investigated the composition of long-chain alkyl diols, triols, sec-alcohols, hydroxyl acids, and other hydroxylated compounds in Azolla imbricata and compared the organic alcohol components of Azolla filiculoides, Azolla microphylla, and South China Sea (SCS) sediments in order to investigate the possible indication of Azolla being the biological source of diols and triols in SCS sediment. Large amounts of diols, monohydroxy acids, and sec-alcohols with internal hydroxy groups at omega 20 were detected in the three types of Azolla. Among these, 1,omega 20-diol and omega 20-hydroxy acid exhibited strong even-odd predominance distribution, whereas omega 20-sec-alcohol exhibited strong odd-even predominance distribution. In addition, small amounts of diols, triols, and dihydroxy acids with internal hydroxy groups at 9, 10 or omega 9, omega 10 were detected, among which the chain length of C-29 was predominate. Compounds having similar structures as those in Azolla reflected a similar biosynthetic pathway: omega 20-hydroxy acid exhibiting even-odd predominance distribution is decarboxylated to omega 20-sec-alcohol exhibiting odd-even predominance distribution and converted to 1, omega 20-diol with even-odd predominance distribution by acyl reduction; omega 9, omega 10-hydroxy acid is converted to 1,20,21(1, omega 9, omega 10)-triol by acyl reduction, and then converted to 9,10-diol by hydrogenation and dehydration. The alcohol components in A. imbricata were clearly not the biological source of 1,13/1,14/1,15-C-28,C- 30,C- 32 diols and 1,3,4-C27-29 triols in the SCS sediment. Certain marine diatoms might be the source of 1,14-C-28,C- 30 diol in inshore sediment, but the biological source of diols and triols in the SCS sediment requires further investigation.

Molecular mechanism for cadmium-induced anthocyanin accumulation in Azolla imbricata

Anthocyanins inducibly synthesized by Cd treatment showed high antioxidant activity and might be involved in internal detoxification mechanisms of Azolla imbricata against Cd toxicity. In order to understand anthocyanin biosynthesis mechanism during Cd stress, the cDNAs encoding chalcone synthase (CHS) and dihydroflavonol reductase (DFR), two key enzymes in the anthocyanin synthesis pathway, were isolated from A. imbricata. Deduced amino acid sequences of the cDNAs showed high homology to the sequences from other plants. Expression of AiDFR, and to a lesser extent AiCHS, was significantly induced in Cd treatment plant in comparison with the control. CHS and DFR enzymatic activities showed similar pattern changes with these genes expression during Cd stress. These results strongly indicate that Cd induced anthocyanin accumulation is probably mediated by up-regulation of structural genes including CHS and DFR, which might further increase the activities of enzymes encoded by these structural genes that control the anthocyanin biosynthetic steps.

Toxic Effect of Cadmium on &lt;i&gt;Azolla Imbricata&lt;/i&gt; (&lt;i&gt;Roxb&lt;/i&gt;.) &lt;i&gt;Nakai&lt;/i&gt;

After cultivating 4 days in Steinberg medium with different concentrations of Cd2+ , the toxic effect of cadmiun on Azolla imbricata (Roxb.) Nakai was investigated for the purpose to find out if this plant is suitable to using on restoration of waterbody with cadmium pollution. The variations of chlorophyll content, soluble-protein content, peroxidase (POD) activity, catalase(CAT) activity, and malondialdehyde (MDA) content of Azolla imbricata (Roxb.) Nakai were measured in this study. The results show that the chlorophyll content of Azolla imbricata(Roxb.)Nakai has no significant changes in media with Cd2+ concentrations compare with control. The MDA content ascended significantly from the Cd2+ concentration was 5 mg•L-1, because of the intensified oxidative damage. When Cd2+ concentration is 0.1~20 mg•L-1, the souble protein content, POD activity and CAT activity increased to resist the oxidative damage. Azolla imbricata (Roxb.) Nakai is tolerance of cadmium pollution, it can be used to water bodies restoration with low level cadmium pollution.

Distribution patterns and changes of aquatic plant communities in Napahai Wetland in northwestern Yunnan Plateau, China

Using GPS technology and community research methods for plant communities, we investigated the distribution patterns of aquatic plant communities in the high plateaus of the Napahai Wetlands, Yunnan, China, as well as the species changes of plant communities compared with that of 24 years ago since 2005. We found that the types and numbers of aquatic plant communities have changed. Some pollution-tolerant, nutrient-loving plant communities such as Scirpus tabernaemontani, Zizania caduciflora, Myriophyllum spicatum, and Azolla imbricata flourished, while the primary aquatic plant communities were reduced or even disappeared. The number of aquatic plant communities were increased from nine to 12 with the addition of two new emergent plant communities and one new floating-leaved plant community. The increase in emergent plant communities was significant. From east to west and from south to north, various types of plant communities were continuously distributed, including floating-leaved plant communities, emergent plant communities and submerged plant communities. The composition of the communities became more complicated and the number of accompanying species increased, while the percentage ratio of dominant plant species declined. In 2005, the coverage of emergent plant communities was the largest (528.42 hm2) followed by submerged plant communities (362.50 hm2) and the floating-leaf plant communities was the smallest (70.23 hm2). The variations in the distribution of aquatic plant communities in the Napahai Wetlands reflect the natural responses to the change of the wetland ecological environment. This study indicates that human disturbances have led to an inward movement of the wetland shoreline, a decrease in water quality and a reduction in wetland habitat.

Characterization of polyamine oxidase from the aquatic nitrogen-fixing fern Azolla imbricata

Biochemical properties of a polyamine oxidase (PAO; EC 1.5.3.3) purified from the aquatic nitrogen-fixing fern Azolla imbricata (Roxb.) Nak. were studied. The native molecular mass of the enzyme estimated by Sephadex G 200 gel filtration was 66.2 kDa. SDS-PAGE gave a single protein band corresponding to a molecular mass of 65.5 kDa. The light yellow enzyme had absorption maxima at 278, 372 and 454 nm with 1 mol FAD per mole enzyme molecule as its cofactor. The PAO was active on both the triamine Spd and the tetraamine Spm as substrates. However, it was inactive on the diamines Put and Cad. It had a pH optimum of 6.5 for both Spd and Spm. The K ms for Spd and Spm were 6.71 × 10 −2 and 1.13 × 10 −1 mM, respectively. Pre-incubation with 10 mM of K + (KCl), Ca 2+ (CaCl 2) or Mg 2+ (MgCl 2) had no effect on PAO activity. However, 10 mM Cu 2+ (CuCl 2), Mn 2+ (MnCl 2) and Fe 2+ (FeSO 4) inhibited enzyme activity by 37%, 43% and 58%, respectively. The metal chelator EDTA (10 mM), the carbonyl reagent hydroxylamine (0.5 mM) and the sulfhydryl reagent p-chloro-mercuribenzoate (0.5 mM) had no effect on PAO activity.

Comparison of the Yield of Direct-sowed Paddy Rice and Conventionally Transplanted Paddy Rice Cultivated Using Green Manure.

緑肥作物としてレンゲを用いた湛水土中散播栽培水稲と, レンゲもしくはアゾラを用いた慣行移植栽培水稲の収量性を, 化学肥料を用いた各栽培法の収量性と比較し, 低コスト省力稲作と環境保全型稲作の両立の可能性について検討した. いずれの栽培法においても, レンゲ鋤込み後, 入水・代かきまでの乾田期間の長さによる収量関連形質への影響はみられなかった. また, いずれの栽培法においても, レンゲ施用区の収量は化学肥料施用区に対して劣り, 湛水土中散播栽培法では約3割減収, 慣行移植栽培法では約1割減収であった. 本試験ではアゾラによる水稲増収効果はみられず, アゾラの施用法には工夫が必要であると考えられた.