Isolation of the inorganic phosphorus-solubilizing bacteria Lysinibacillus sphaericus and assessing its role in promoting rice growth.

Soluble phosphorus scarcity severely limits plant growth and crop yield. In this study, a strain of inorganic phosphorus-solubilizing bacteria, Lysinibacillus sphaericus, was isolated from rice rhizosphere soil. The available phosphorus content in liquid inorganic phosphorus identification medium and in L. sphaericus-inoculated soil increased from 204.28 mg/L to 1124.68 mg/L and from 4.75 mg/kg to 7.04 mg/kg, respectively. The pH decreased significantly from 6.87 to 6.14. Incubation with L. sphaericus significantly increased malic and succinic acid content in the liquid inorganic phosphorus identification medium and increased acid phosphatase and alkaline phosphatase activity in the soil. Inoculation with L. sphaericus significantly increased rice growth, chlorophyll a/b content, and photosynthesis by increasing the soluble phosphorus content in the rice rhizosphere soil under phosphorus-deficient conditions. Further analysis revealed that L. sphaericus improved soil phosphorus release by decreasing soil pH and promoting acid phosphatase and alkaline phosphatase activity. This study supports the production of microbial fertilizers to improve rice yield in phosphorus-deficient conditions.

Interplay Impact of Exogenous Application of Abscisic Acid (ABA) and Brassinosteroids (BRs) in Rice Growth, Physiology, and Resistance under Sodium Chloride Stress.

The hormonal imbalances, including abscisic acid (ABA) and brassinosteroid (BR) levels, caused by salinity constitute a key factor in hindering spikelet development in rice and in reducing rice yield. However, the effects of ABA and BRs on spikelet development in plants subjected to salinity stress have been explored to only a limited extent. In this research, the effect of ABA and BRs on rice growth characteristics and the development of spikelets under different salinity levels were investigated. The rice seedlings were subjected to three different salt stress levels: 0.0875 dS m-1 (Control, CK), low salt stress (1.878 dS m-1, LS), and heavy salt stress (4.09 dS m-1, HS). Additionally, independent (ABA or BR) and combined (ABA+BR) exogenous treatments of ABA (at 0 and 25 µM concentration) and BR (at 0 and 5 µM concentration) onto the rice seedlings were performed. The results showed that the exogenous application of ABA, BRs, and ABA+BRs triggered changes in physiological and agronomic characteristics, including photosynthesis rate (Pn), SPAD value, pollen viability, 1000-grain weight (g), and rice grain yield per plant. In addition, spikelet sterility under different salt stress levels (CK, LS, and HS) was decreased significantly through the use of both the single phytohormone and the cocktail, as compared to the controls. The outcome of this study reveals new insights about rice spikelet development in plants subjected to salt stress and the effects on this of ABA and BR. Additionally, it provides information on the use of plant hormones to improve rice yield under salt stress and on the enhancement of effective utilization of salt-affected soils.

Unearthing the Alleviatory Mechanisms of Brassinolide in Cold Stress in Rice.

Cold stress inhibits rice germination and seedling growth. Brassinolide (BR) plays key roles in plant growth, development, and stress responses. In this study, we explored the underlying mechanisms whereby BR helps alleviate cold stress in rice seedlings. BR application to the growth medium significantly increased seed germination and seedling growth of the early rice cultivar "Zhongzao 39" after three days of cold treatment. Specifically, BR significantly increased soluble protein and soluble sugar contents after three days of cold treatment. Moreover, BR stimulated the activity of superoxide dismutase, catalase, peroxidase, and ascorbate peroxidase; thereby alleviating cold-induced damage and increasing glutathione content and the GSH/GSSG ratio while concomitantly reducing H2O2 content. BR upregulated the expression levels of cold-response-related genes, including OsICE1, OsFer1, OsCOLD1, OsLti6a, OsSODB, OsMyb, and OsTERF2, and downregulated that of OsWRKY45, overall alleviating cold stress symptoms. Thus, BR not only upregulated cellular osmotic content and the antioxidant enzyme system to maintain the physiological balance of reactive oxygen species under cold but, additionally, it regulated the expression of cold-response-related genes to alleviate cold stress symptoms. These results provide a theoretical basis for rice breeding for cold resistance using young seedlings.

[Research advance in the roles of water-nitrogen-oxygen factors in mediating rice growth, photosynthesis and nitrogen utilization in paddy soils.] / ç¨»ç”°æ°´æ°®æ°§çŽ¯å¢ƒå› å­å¯¹æ°´ç¨»ç”Ÿé•¿å‘è‚²ã€å ‰åˆä½œç”¨å’Œæ°®åˆ©ç”¨çš„è°ƒæŽ§ç ”ç©¶è¿›å±•.

Water and nitrogen are two important factors controlling rice growth and development. Suitable water-nitrogen interaction can alter nitrogen forms and oxygen environmental factors via regulating water content in the rhizosphere of paddy soil, promote the construction of root morphology, improve leaf photosynthesis and the allocation equilibrium of the photosynthetic products between the source and sink organs, and consequently increase rice population quality and grain yield. The microbial regulation mechanisms driven by the environmental factors (e.g. water, nitrogen and oxygen) also play an important role in improving nitrogen utilization efficiency in rice-soil system. Here, we reviewed the research progress in water-nitrogen interaction, and briefly discussed the effects of water, nitrogen form, and dissolved oxygen on rice growth, photosynthesis, carbon and nitrogen metabolism, nitrogen conversion and the underlying microbiological mechanism. We proposed several key directions for future researches: 1) to quantitatively investigate the spatial and temporal variations of dissolved oxygen in rhizosphere and their dominant environmental drivers under different water and nitrogen regimes; 2) to evaluate the responses of root-sourced signal to rhizosphere dissolved oxygen in different rice genotypes, and uncover its intrinsic mechanisms involved in rice growth and development; 3) to investigate the effects of key microbial process driven by the rhizosphere oxygen environment on the soil nitrogen conversion and rice nitrogen utilization.

Effects of nitric oxide on nitrogen metabolism and the salt resistance of rice (Oryza sativa L.) seedlings with different salt tolerances.

Salt stress inhibits rice productivity seriously. Nitric oxide (NO) is an endogenous signaling molecule in plants that can improve the resistance of rice to abiotic stresses. Previous studies also showed that nitrogen metabolism is essential for rice stress-tolerance. However, the physiological and molecular mechanisms by how NO affects the nitrogen metabolisms of rice seedlings remain unclear. A hydroponic experiment with two rice varieties, Jinyuan85 (salt tolerant) and Liaojing763 (salt sensitive), was carried out to explore whether NO could alleviate the negative effects of salt stress on nitrogen metabolism and increase salt resistance of rice seedlings. The results showed that (1) the application of NO alleviated the inhibitory effects of salt stress on plant height and biomass accumulation, and increased the nitrogen content of rice leaf. (2) the accumulation of the sucrose and proline was markedly increased in salt stress after application of NO, and peroxidase activities was increased by 107% and 67.7% for Jinyuan85 and Liaojing763, respectively. (3) NO significantly increased the activities of glutamate dehydrogenase, sucrose synthase and sucrose phosphate synthase in both rice varieties under salt stress. (4) Additionally, NO regulated the expression levels of AMT, NIA and SUT genes, but these regulation effects are different with rice varieties and treatments. The results suggested that NO mainly increased the glutamate dehydrogenase and peroxidase activities and sucrose accumulation to enhance the nitrogen metabolism and antioxidative capacity, and alleviated the negative effects of salt stress on rice performance.

Pyridoxal 5'-phosphate enhances the growth and morpho-physiological characteristics of rice cultivars by mitigating the ethylene accumulation under salinity stress.

Salinity-induced ethylene accumulation caused by high production of 1-aminocyclopropane-1-carboxylic acid (ACC) hinders rice plant growth and development. Nevertheless, ACC deaminase may alleviate salt stress and high ethylene production in rice cultivars under salinity stress. Pyridoxal 5'-phosphate (PLP), an ACC deaminase co-factor, could be a useful ACC inhibitor in plants; however, it has not been studied before. In the present study, the effects of PLP on the growth and morphophysiological characteristics of rice cultivars (Jinyuan 85 (JY85) and Nipponbare (NPBA) were investigated under salinity stress (control (CK), low salinity (LS), and high salinity (HS) in hydroponic conditions. The experiment was laid out in a completely randomized design (CRD) under factorial arrangement of treatments. The results showed that, compared with no PLP, exogenous application of PLP significantly inhibited ACC and ethylene production in the roots, leaves and panicles of both cultivars under salinity, and PLP was more effective at improving the physiological characteristics of both cultivars under salinity stress. Further, root morphophysiological traits and pollen viability were triggered in the PLP treatment compared to the no-PLP treatment under various salinity levels. ACC production inhibited by PLP was useful for improving the 1000-grain weight, grain yield per plant, and total plant biomass under the CK, LS and HS treatments in both rice cultivars. These results revealed that PLP, as an ACC deaminase cofactor, is a key tool for mitigating ethylene-induced effects under salinity stress and for enhancing the agronomic and morphophysiological traits of rice under saline conditions.

1-Methylcyclopropene Modulates Physiological, Biochemical, and Antioxidant Responses of Rice to Different Salt Stress Levels.

Salt stress in soil is a critical constraint that affects the production of rice. Salt stress hinders plant growth through osmotic stress, ionic stress, and a hormonal imbalance (especially ethylene), therefore, thoughtful efforts are needed to devise salt tolerance management strategies. 1-Methylcyclopropene (1-MCP) is an ethylene action inhibitor, which could significantly reduce ethylene production in crops and fruits. However, 1-MCPs response to the physiological, biochemical and antioxidant features of rice under salt stress, are not clear. The present study analyzed whether 1-MCP could modulate salt tolerance for different rice cultivars. Pot culture experiments were conducted in a greenhouse in 2016-2017. Two rice cultivars, Nipponbare (NPBA) and Liangyoupeijiu (LYP9) were used in this trial. The salt stress included four salt levels, 0 g NaCl/kg dry soil (control, CK), 1.5 g NaCl/ kg dry soil (Low Salt stress, LS), 4.5 g NaCl/kg dry soil (Medium Salt stress, MS), and 7.5 g NaCl/kg dry soil (Heavy Salt stress, HS). Two 1-MCP levels, 0 g (CT) and 0.04 g/pot (1-MCP) were applied at the rice booting stage in 2016 and 2017. The results showed that applying 1-MCP significantly reduced ethylene production in rice spikelets from LYP9 and NPBA by 40.2 and 23.9% (CK), 44.3 and 28.6% (LS), 28 and 25.9% (MS), respectively. Rice seedlings for NPBA died under the HS level, while application of 1-MCP reduced the ethylene production in spikelets for LYP9 by 27.4% compared with those that received no 1-MCP treatment. Applying 1-MCP improved the photosynthesis rate and SPAD value in rice leaves for both cultivars. 1-MCP enhanced the superoxide dismutase production, protein synthesis, chlorophyll contents (chl a, b, carotenoids), and decreased malondialdehyde, H2O2, and proline accumulation in rice leaves. Application of 1-MCP also modulated the aboveground biomass, and grain yield for LYP9 and NPBA by 19.4 and 15.1% (CK), 30.3 and 24% (LS), 26.4 and 55.4% (MS), respectively, and 34.5% (HS) for LYP9 compared with those that received no 1-MCP treatment. However, LYP9 displayed a better tolerance than NPBA. The results revealed that 1-MCP could be employed to modulate physiology, biochemical, and antioxidant activities in rice plants, at different levels of salt stress, as a salt stress remedy.

iTRAQ-Based Protein Profiling and Biochemical Analysis of Two Contrasting Rice Genotypes Revealed Their Differential Responses to Salt Stress.

Salt stress is one of the key abiotic stresses causing huge productivity losses in rice. In addition, the differential sensitivity to salinity of different rice genotypes during different growth stages is a major issue in mitigating salt stress in rice. Further, information on quantitative proteomics in rice addressing such an issue is scarce. In the present study, an isobaric tags for relative and absolute quantitation (iTRAQ)-based comparative protein quantification was carried out to investigate the salinity-responsive proteins and related biochemical features of two contrasting rice genotypes-Nipponbare (NPBA, japonica) and Liangyoupeijiu (LYP9, indica), at the maximum tillering stage. The rice genotypes were exposed to four levels of salinity: 0 (control; CK), 1.5 (low salt stress; LS), 4.5 (moderate salt stress; MS), and 7.5 g of NaCl/kg dry soil (high salt stress, HS). The iTRAQ protein profiling under different salinity conditions identified a total of 5340 proteins with 1% FDR in both rice genotypes. In LYP9, comparisons of LS, MS, and HS compared with CK revealed the up-regulation of 28, 368, and 491 proteins, respectively. On the other hand, in NPBA, 239 and 337 proteins were differentially upregulated in LS and MS compared with CK, respectively. Functional characterization by KEGG and COG, along with the GO enrichment results, suggests that the differentially expressed proteins are mainly involved in regulation of salt stress responses, oxidation-reduction responses, photosynthesis, and carbohydrate metabolism. Biochemical analysis of the rice genotypes revealed that the Na⁺ and Cl- uptake from soil to the leaves via the roots was increased with increasing salt stress levels in both rice genotypes. Further, increasing the salinity levels resulted in increased cell membrane injury in both rice cultivars, however more severely in NPBA. Moreover, the rice root activity was found to be higher in LYP9 roots compared with NPBA under salt stress conditions, suggesting the positive role of rice root activity in mitigating salinity. Overall, the results from the study add further insights into the differential proteome dynamics in two contrasting rice genotypes with respect to salt tolerance, and imply the candidature of LYP9 to be a greater salt tolerant genotype over NPBA.

Ammonium uptake and metabolism alleviate PEG-induced water stress in rice seedlings.

Ammonium (NH4+) can enhance the water stress induced drought tolerance of rice seedlings in comparison to nitrate (NO3-) nutrition. To investigate the mechanism involved in nitrogen (N) uptake, N metabolism and transcript abundance of associated genes, a hydroponic experiment was conducted in which different N sources were supplied to seedlings growing under water stress. Compared to nitrate, ammonium prevented water stress-induced biomass, leaf SPAD and photosynthesis reduction to a significantly larger extent. Water stress significantly increased root nitrate reductase (NR) and nitrite reductase (NiR) activities, but decreased leaf NiR and glutamate synthetase (GS) activities under NO3- supply, causing lower nitrate content in roots and higher in leaves. In contrast, under NH4+ supply root GS and glutamine oxoglutarate aminotransferase (GOGAT) activities were significantly decreased under water stress, but remained higher in leaves, compared to NO3- treatment, which was beneficial for the transport and assimilation of ammonium in leaves. 15N tracing assays demonstrated that rice 15N uptake rate and accumulation were significant reduced under water stress, but were higher in plants supplied with NH4+ than with NO3-. Therefore, the formers showed higher leaf soluble sugar, proline and amino acids contents, and in turn, associated with a higher photosynthesis rate and biomass accumulation. Most genes related to NO3- uptake and reduction in roots and leaves were down-regulated; however, two ammonium transporter genes closely related to NH4+ uptake (AMT1;2 and AMT1;3) were up-regulated in response to water stress. Overall, our findings suggest that ammonium supply alleviated waters tress in rice seedlings, mainly by increasing root NH4+ uptake and leaf N metabolism.

Nitrogen metabolism correlates with the acclimation of photosynthesis to short-term water stress in rice (Oryza sativa L.).

Nitrogen metabolism is as sensitive to water stress as photosynthesis, but its role in plant under soil drying is not well understood. We hypothesized that the alterations in N metabolism could be related to the acclimation of photosynthesis to water stress. The features of photosynthesis and N metabolism in a japonica rice 'Jiayou 5' and an indica rice 'Zhongzheyou 1' were investigated under mild and moderate soil drying with a pot experiment. Soil drying increased non-photochemical quenching (NPQ) and reduced photon quantum efficiency of PSII and CO2 fixation in 'Zhongzheyou 1', whereas the effect was much slighter in 'Jiayou 5'. Nevertheless, the photosynthetic rate of the two cultivars showed no significant difference between control and water stress. Soil drying increased nitrate reducing in leaves of 'Zhongzheyou 1', characterized by enhanced nitrate reductase (NR) activity and lowered nitrate content; whereas glutamate dehydrogenase (GDH), glutamic-oxaloacetic transaminase (GOT) and glutamic-pyruvic transaminase (GPT) were relative slightly affected. 'Jiayou 5' plants increased the accumulation of nitrate under soil drying, although its NR activity was increased. In addition, the activities of GDH, GOT and GPT were typically increased under soil drying. Besides, amino acids and soluble sugar were significantly increased under mild and moderate soil drying, respectively. The accumulation of nitrate, amino acid and sugar could serve as osmotica in 'Jiayou 5'. The results reveal that N metabolism plays diverse roles in the photosynthetic acclimation of rice plants to soil drying.

Nitrogen Metabolism in Adaptation of Photosynthesis to Water Stress in Rice Grown under Different Nitrogen Levels.

To investigate the role of nitrogen (N) metabolism in the adaptation of photosynthesis to water stress in rice, a hydroponic experiment supplying with low N (0.72 mM), moderate N (2.86 mM), and high N (7.15 mM) followed by 150 g⋅L-1 PEG-6000 induced water stress was conducted in a rainout shelter. Water stress induced stomatal limitation to photosynthesis at low N, but no significant effect was observed at moderate and high N. Non-photochemical quenching was higher at moderate and high N. In contrast, relative excessive energy at PSII level (EXC) was declined with increasing N level. Malondialdehyde and hydrogen peroxide (H2O2) contents were in parallel with EXC. Water stress decreased catalase and ascorbate peroxidase activities at low N, resulting in increased H2O2 content and severer membrane lipid peroxidation; whereas the activities of antioxidative enzymes were increased at high N. In accordance with photosynthetic rate and antioxidative enzymes, water stress decreased the activities of key enzymes involving in N metabolism such as glutamate synthase and glutamate dehydrogenase, and photorespiratory key enzyme glycolate oxidase at low N. Concurrently, water stress increased nitrate content significantly at low N, but decreased nitrate content at moderate and high N. Contrary to nitrate, water stress increased proline content at moderate and high N. Our results suggest that N metabolism appears to be associated with the tolerance of photosynthesis to water stress in rice via affecting CO2 diffusion, antioxidant capacity, and osmotic adjustment.

Amorphous In-Ga-Zn-O Powder with High Gas Selectivity towards Wide Range Concentration of C2H5OH.

Amorphous indium gallium zinc oxide (a-IGZO) powder was prepared by typical solution-based process and post-annealing process. The sample was used as sensor for detecting C2H5OH, H2, and CO. Gas-sensing performance was found to be highly sensitive to C2H5OH gas in a wide range of concentration (0.5-1250 ppm) with the response of 2.0 towards 0.5 ppm and 89.2 towards 1250 ppm. Obvious difference of response towards C2H5OH, H2, and CO was found that the response e.g., was 33.20, 6.64, and 2.84 respectively at the concentration of 200 ppm. The response time and recovery time of was 32 s and 14 s respectively towards 200 ppm concentration of C2H5OH gas under heating voltage of 6.5 V.

Elevational Variation in Soil Amino Acid and Inorganic Nitrogen Concentrations in Taibai Mountain, China.

Amino acids are important sources of soil organic nitrogen (N), which is essential for plant nutrition, but detailed information about which amino acids predominant and whether amino acid composition varies with elevation is lacking. In this study, we hypothesized that the concentrations of amino acids in soil would increase and their composition would vary along the elevational gradient of Taibai Mountain, as plant-derived organic matter accumulated and N mineralization and microbial immobilization of amino acids slowed with reduced soil temperature. Results showed that the concentrations of soil extractable total N, extractable organic N and amino acids significantly increased with elevation due to the accumulation of soil organic matter and the greater N content. Soil extractable organic N concentration was significantly greater than that of the extractable inorganic N (NO3--N + NH4+-N). On average, soil adsorbed amino acid concentration was approximately 5-fold greater than that of the free amino acids, which indicates that adsorbed amino acids extracted with the strong salt solution likely represent a potential source for the replenishment of free amino acids. We found no appreciable evidence to suggest that amino acids with simple molecular structure were dominant at low elevations, whereas amino acids with high molecular weight and complex aromatic structure dominated the high elevations. Across the elevational gradient, the amino acid pool was dominated by alanine, aspartic acid, glycine, glutamic acid, histidine, serine and threonine. These seven amino acids accounted for approximately 68.9% of the total hydrolyzable amino acid pool. The proportions of isoleucine, tyrosine and methionine varied with elevation, while soil major amino acid composition (including alanine, arginine, aspartic acid, glycine, histidine, leucine, phenylalanine, serine, threonine and valine) did not vary appreciably with elevation (p>0.10). The compositional similarity of many amino acids across the elevational gradient suggests that soil amino acids likely originate from a common source or through similar biochemical processes.

Synthesis of morphology-controlled ZnO microstructures via a microwave-assisted hydrothermal method and their gas-sensing property.

Controllable ZnO architectures with flower-like and rod-like morphologies were synthesized via a microwave-assisted hydrothermal method. By adjusting the concentration of Zn(2+) in the aqueous precursors, different morphologies of ZnO microstructures were obtained. The size of ZnO was uniform after ultrasonic treatment. The growth process of ZnO in solution was studied by monitoring the intermediate products, which were extracted at different stages of the reactions: (i) precursor preparation, (ii) microwave irradiation heating, (iii) natural cooling. Studies of the SEM images and XRD data revealed that the formation of ZnO occurred via in situ assembly or dissolution-reprecipitation of zinc hydroxide complexes. The morphology-dependent ethanol sensing performance was observed; the seven-spine ZnO structures exhibit the highest activity.

Field emission properties and growth mechanism of In2O3 nanostructures.

Four kinds of nanostructures, nanoneedles, nanohooks, nanorods, and nanotowers of In2O3, have been grown by the vapor transport process with Au catalysts or without any catalysts. The morphology and structure of the prepared nanostructures are determined on the basis of field emission scanning electron microscopy (FESEM), x-ray diffraction (XRD), and transmission electron microscopy (TEM). The growth direction of the In2O3 nanoneedles is along the [001], and those of the other three nanostructures are along the [100]. The growth mechanism of the nanoneedles is the vapor-liquid-solid (VLS), and those of the other three nanostructures are the vapor-solid (VS) processes. The field emission properties of four kinds of In2O3 nanostructures have been investigated. Among them, the nanoneedles have the best field emission properties with the lowest turn-on field of 4.9 V/µm and the threshold field of 12 V/µm due to possessing the smallest emitter tip radius and the weakest screening effect.

[Effects of straw incorporation on rice carbon sequestration characteristics and grain yield formation].

A field experiment was conducted to study the effects of straw incorporation on rice dry matter accumulation and transportation, rice carbon sequestration and grain yield formation. The experiment included four levels of straw incorporation: 0 (control), 4000, 6000 and 8000 kg · hm(-2). Hybrid rice cultivar Zhongzheyou 1 was used in this experiment. The results showed that the average rice dry matter accumulation amount of the three straw incorporation treatments was increased by 63.03 g · m(-2) compared with the control, and that of straw incorporation of 6000 kg · hm(-2) showed the most favorable result, which was 154.40 g · m(-2) higher than the control. Effects of straw incorporation on rice dry matter accumulation showed the best performance from the maximum tillering stage to the full heading stage, and the dry matter accumulation at this stage was 71.25 g · m(-2) higher than the control. Compared with the control, the average dry matter exportation rate and apparent transformation rate from rice stem and leaf in the straw incorporation treatments were increased by 4.2% and 3.7%, respectively. The highest dry matter exportation rate and apparent transformation rate from rice stem and leaf were observed in the straw incorporation treatment of 6000 kg · hm(-2), which were increased by 12.8% and 11.1% compared to the control, respectively. The average rice carbon sequestration from the straw incorporation treatments was increased by 55.38 g · m(-2) compared with the control, and straw incorporation of 6000 kg · hm(-2) performed best with an increase of 17.8% compared with the control. Straw incorporation played a positive role in regulating the carbon sequestration of stem and leaf at the early growth stage and carbon sequestration of spike at the late growth stage. The average grain yield from the straw incorporation treatments was increased by 794.59 kg · hm(-2) (9.5% higher) compared with the control. Rice grain yields from the straw incorporation treatments of 6000 and 4000 kg · hm(-2) were significantly higher than the control, while rice grain yield from the straw incorporation treatment of 8000 kg · hm(-2) did not show a significant increase compared to the control. The rice grain yield was closely related to the yield components, and the increase of effective panicles may be the main reason for the higher grain yields in the straw incorporation treatments. Effective panicles in the straw incorporation treatments was averagely 8.41 spikes · m(-2) more than the control.

[Selenium cycling and transformation in paddy field and selenium nutrition of rice: a review].

Due to the alternate variation of soil redox potential and the particularity of soil components in paddy field, the selenium (Se) cycling and transformation in paddy soil are obviously different from those in upland soil, and can affect the Se availability in soil and the Se absorption and accumulation by rice. To deeply understand the Se cycling and transformation in paddy soil and the Se absorption and accumulation by rice is of great importance in studying the transformation of soil inorganic Se to organic Se. This paper summarized the researches on the cycling mechanisms and form transformation of Se in paddy soil and the metabolic mechanisms and absorption characteristics of Se by rice, and discussed the present status and development trend of the studies on the Se transformation in soil-rice system and the Se translocation in rice plant, which could provide references for the study of soil Se availability and the cultivation of Se-enriched rice.

[Dynamic changes of rice (Oryza sativa L.) tiller angle under effects of photoperiod and effective accumulated temperature].

Using rice variety DI508 as test material, a field experiment of different seeding dates and a test with plant growth chamber were conducted to study the dynamic changes of rice tiller angle under effects of different photoperiod and effective accumulated temperature. Under field condition, the tiller angle of DI508 plants changed gradually into erect after 10-15 days of photoperiod becoming shorter (since the Summer Solstice on 21st June), irrespective of seeding dates (4th April, 5th May, and 4th June). Under controlled photoperiod, the tiller angle changed in the same way as in the field. Shorter lighting treatment (10 hours) advanced the tiller angle change, while longer lighting treatment (14 hours) delayed the change. Effective accumulated temperature had no effects on the tiller angle change of DI508.

[Effects of rice-duck farming system on biotic populations in paddy field].

A field experiment was conducted to study the effects of rice-duck farming on the related biotic populations in paddy field. The results showed that rice-duck farming had greater effects on the occurrence and damage of pests, pathogens and weeds, as well as the amount of pests' natural enemies in paddy field. The population of rice planthopper and leafhopper decreased by 64.8% and 78.5% after 12 and 42 days of duck-release, and the weeds decreased by 67.7% and 98.1% after 15 and 45 days of duck-release, respectively, compared with the control. The sheath blight index at the maximum tillering stage and full-heading stage in the rice-duck plots were 40.4% and 62.0% lower than those in the control plot, respectively. The population of spiders in duck-released field was increased obviously, which in turn decreased the damage of rice pests.