Water Submergence Research Articles

Recurrent Water Level Fluctuation Alleviates the Effects of Submergence Stress on the Invasive Riparian Plant Alternanthera philoxeroides.

Recurrent water level fluctuation and submergence of plants are common in riparian zones. Our study objectives were to test the independent and interactive effects of submergence level and fluctuation frequency on a globally important riparian invasive plant, Alternanthera philoxeroides. To this end, we conducted a greenhouse experiment, in which ramets of the plants, obtained from a wetland in China, were treated with four fluctuation frequencies (0, 3, 6, and 12 cycles over a 96-day experimental period) under three water levels (0, 10, and 30 cm). We found that effects of fluctuation frequency were non-significant, negative, and positive under water levels of 0, 10 and 30 cm, respectively. As fluctuation frequency increased, the effects of increasing water level decreased significantly. When water levels were high, A. philoxeroides allocated greater biomass to shoot production probably in order to elongate and escape from submergence. However, as fluctuation frequency increased, biomass investment in roots and leaves also increased, probably in order to maximize nutrient absorption and photosynthesis, respectively. These results suggest that water level fluctuation may alleviate the effects of submergence on A. philoxeroides. In addition, A. philoxeroides showed significant phenotypic plasticity, adjusting its functional traits, such as number of nodes and leaves per stem, as well as stem diameter and pith cavity diameter, according to recurrent water level fluctuation. We conclude that A. philoxeroides may perform better in shallow water zones under conditions of disturbance that include recurrent water level fluctuation. This ability to adapt to disturbance likely promotes its growth and invasion in disturbed habitats.

Effect of simulated flash flooding on rice and its recovery after flooding with nutrient management strategies

Rice grown in flood-prone areas must have submergence tolerance characteristics either through varietal selection or by management options like nutrient application. This study is conducted to investigate the effect of application methods of nitrogen and phosphorus on submerged rice productivity and nutrient absorption. The effect of basal phosphorus and post-flood nitrogen (six different nutrient schedules) on the performance of Sub1 (IR-64 Sub1 and Swarna Sub1) and non-Sub1 (IR-20) cultivars of rice was tested under clear and turbid water submergence for their tolerance to submergence. Photosynthesis, yield and N concentration of rice subjected to complete submergence for 15 days was decreased significantly over non-submerged rice plants. Turbid water submergence was fatal in terms of photosynthesis, stomatal conductance, effective tillers and yield because of low light and dissolved oxygen underwater. Rice plants fertilized with P tolerated flooding better and produced significantly higher grain yields than no P application. The crop fertilized with N produced more number of effective tillers and grain yield than the unfertilized crop under complete submergence at maximum tillering (MT) stage. When post-flood N was applied alone, grain yield was 25.8, 17.8 and 17.1% lower in IR-20, IR-64 Sub1 and Swarna Sub1, respectively, as compared to N and basal P application. Urea foliar spray after desubmergence significantly enhanced the photosynthesis and narrowed down the flowering time which led to higher grain yield and productivity. The findings of the study suggest that a simple alteration in the time and method of N application with basal P can significantly contribute to higher rice yield in flash-flood prone areas.

Combined application of silica and nitrogen alleviates the damage of flooding stress in rice

Flooding is the major abiotic stress in flood-prone rice ecosystems, where duration, severity and turbidity of flooding are the factors negatively affecting survival and crop growth worldwide. Advances in physiology, genetics, and molecular biology have greatly improved our understanding of plant responses to stresses, but nutrient-management options are still lacking. This study was conducted to investigate the combined effect of silica (Si), phosphorus (P) and nitrogen (N) with Sub1 and non-Sub1 cultivars of rice under clear and turbid water submergence. Submergence tolerance effects on allometry, metabolic changes, photosynthetic rate and ethylene accumulation were evaluated. Application of Si reduced elongation, lodging and leaf senescence, with more prominent effects when applied with basal P. Combined effect of Si, N and P significantly improved, growth, photosynthetic rate, concentrations of chlorophyll and soluble sugars of rice after flood recovery, which led to higher plant survival. The findings of the study suggest that combined application of Si, N and P can significantly contribute to higher survival of rice seedlings and establishment thereafter in flash-flood prone areas.

Experimental investigation of void distribution in suppression pool over the duration of a loss of coolant accident using steam–water two-phase mixture

Studies are underway to determine if a large amount gas discharged through the downcomer pipes in the pressure suppression chamber during the blowdown of Loss of Coolant Accident (LOCA) can potentially be entrained into the Emergency Core Cooling System (ECCS) suction piping of BWR. This may result in degraded ECCS pumps performance which could affect the ability to maintain or recover the water inventory level in the Reactor Pressure Vessel (RPV) during a LOCA. Therefore, it is very important to understand the void behavior in the pressure suppression chamber during the blowdown period of a LOCA. To address this issue, a set of experiments is conducted using the Purdue University Multi-Dimensional Integral Test Assembly for ESBWR applications (PUMA-E) facility. The geometry of the test apparatus is determined based on the basic geometrical scaling analysis from a prototypical BWR containment (MARK I) with a consideration of downcomer size, downcomer water submergence depth and Suppression Pool (SP) water level. Several instruments are installed in the test facility to measure the required experimental data such as the steam mass flow rate, void fraction, pressure and temperature.In the experiments, sequential flows of air, steam–air mixture and pure steam-each with the various flow rate conditions are injected from the Drywell (DW) through a downcomer pipe in the SP. Eight tests with two different downcomer sizes, various initial gas volumetric fluxes at the downcomer, and two different initial non-condensable gas concentration conditions in the DW are conducted. Three distinct phases, namely, an initial phase, a quasi-steady, and a chugging phase are observed. The maximum void penetration depth is observed in the initial phase. A reduction in the void penetration depth is observed in the quasi-steady phase. As a result of low non-condensable gas concentration, chugging is observed at the tail end of the experiment. Chugging provides renewed void penetrations comparable to those in the initial phase. It is determined that the void distribution and area of void penetration in the SP is governed by the gas volumetric flux at the downcomer and the non-condensable gas concentration in the downcomer.

Effects of crop establishment techniques on weeds and rice yield

Field and pot studies were conducted to evaluate the effects of seven rice establishment techniques {puddling transplanting (PT), no tillage transplanting (NTT), puddling drum wet seeding (PDWS), no tillage drum wet seeding (NTDWS), conventional tillage dry drilling (CTDD), furrow irrigated raised beds system dry drilling (FIRBSDD), and no-tillage dry-drilling (NTDD)} and water submergence stress on weeds and rice yield. The highest yield and least weed abundance were in the PT treatment. The direct seeded rice (DSR), both dry and wet exhibited severe weed infestation, and compared to transplanting showed reduced yield both in the presence and absence of weeds. The yield losses due to weeds in the DSR treatments ranged from 91.4 to 99.0%, compared to 16.0 and 42.0% in the transplanting treatments (PT and NTT). Weeds, including Cyperus rotundus L., Dactyloctenium aegyptium (L.) Willd., Digera arvensis Forsk., Phyllanthus niruri L., and Trianthema portulacastrum L. which were found in the un-puddled DSR treatments were absent in the puddled plots, particularly the PT treatments. In pot studies, continuous water-submergence (2.5 cm) for 20 days reduced the emergence of C. rotundus, D. aegyptium, T. portulacastrum, and Echinochloa crus-galli (L.) Beauv. by 99.4, 100, 100, and 24.4%, respectively, compared to alternate wetting–drying. In farmer's field studies, when compared to the PT treatments, the DSR treatments exhibited lower yields (15.8%) with coarse varieties (HKR-47 & IR-64), but fine cultivars (Sharbati & PB-1) exhibited similar yields under both systems. In view of the shortage of labour for manual transplanting, there is a need to develop suitable cultivars for aerobic system conditions (unpuddled DSR and NT machine-transplanting).

Integrating omic approaches for abiotic stress tolerance in soybean.

Soybean production is greatly influenced by abiotic stresses imposed by environmental factors such as drought, water submergence, salt, and heavy metals. A thorough understanding of plant response to abiotic stress at the molecular level is a prerequisite for its effective management. The molecular mechanism of stress tolerance is complex and requires information at the omic level to understand it effectively. In this regard, enormous progress has been made in the omics field in the areas of genomics, transcriptomics, and proteomics. The emerging field of ionomics is also being employed for investigating abiotic stress tolerance in soybean. Omic approaches generate a huge amount of data, and adequate advancements in computational tools have been achieved for effective analysis. However, the integration of omic-scale information to address complex genetics and physiological questions is still a challenge. In this review, we have described advances in omic tools in the view of conventional and modern approaches being used to dissect abiotic stress tolerance in soybean. Emphasis was given to approaches such as quantitative trait loci (QTL) mapping, genome-wide association studies (GWAS), and genomic selection (GS). Comparative genomics and candidate gene approaches are also discussed considering identification of potential genomic loci, genes, and biochemical pathways involved in stress tolerance mechanism in soybean. This review also provides a comprehensive catalog of available online omic resources for soybean and its effective utilization. We have also addressed the significance of phenomics in the integrated approaches and recognized high-throughput multi-dimensional phenotyping as a major limiting factor for the improvement of abiotic stress tolerance in soybean.

Magnetic properties of agricultural soil in the Pearl River Delta, South China — Spatial distribution and influencing factor analysis

Abstract Environmental magnetism has been widely applied to soil science due to its speediness, non-destructiveness and cost-effectiveness. However, the magnetic investigation of agricultural soil, so closely related to human activity, is limited, most probably because of its complexity. Here we present a magnetic investigation of 301 agricultural soil samples collected from the Pearl River Delta (PRD, 112°E–115°E and 22°N–24°N), China. The results showed that both low and high coercivity magnetic minerals coexist in agricultural soil. The values of concentration-dependent parameters, low-field susceptibility (χlf), anhysteretic remanence magnetization susceptibility (χARM), and saturation isothermal remanence magnetization (SIRM) were much higher in the PRD plain than in the surrounding areas. The S-ratio (S− 300) showed a similar spatial pattern to the aforementioned parameters. By contrast, frequency-dependent susceptibility (χfd%) and χARM/SIRM were higher in the surrounding hilly and mountainous areas than in the PRD plain. Natural and anthropogenic factors such as parent material, soil type and cultivation methods play important roles in determining agricultural soil magnetic properties. Magnetic minerals were coarser grained and overall indicated higher concentrations in soils from river alluvium and deposited materials. Soils which had suffered long-term water submergence have the lowest magnetic mineral concentration, a result consistent with previous studies. The magnetic properties of agricultural soils are strongly influenced by cultivation methods. Other human activities, such as industrial development and concomitant emitted pollutants, might have had an additional impact on the magnetic properties of agricultural soil.

Remote sensing based change analysis of rice environments in Odisha, India

The rainfed rice-growing environment is perhaps one of the most vulnerable to water stress such as drought and floods. It is important to determine the spatial extent of the stress-prone areas to effectively and efficiently promote proper technologies (e.g., stress-tolerant varieties) to tackle the problem of sustainable food production. This study was conducted in Odisha state located in eastern India. Odisha is predominantly a rainfed rice ecosystem (71% rainfed and 29% canal irrigated during kharif-monsoon season), where rice is the major crop and staple food of the people. However, rice productivity in Odisha is one of the lowest in India and a significant decline (9%) in rice cultivated area was observed in 2002 (a drought year). The present study analyzed the temporal rice cropping pattern in various ecosystems and identified the stress-prone areas due to submergence (flooding) and water shortage. The spatial distribution of rice areas was mapped using MODIS (MOD09Q1) 250-m 8-day time-series data (2000–2010) and spectral matching techniques. The mapped rice areas were strongly correlated (R2 = 90%) with district-level statistics. Also the class accuracy based on field-plot data was 84.8%. The area under the rainfed rice ecosystem continues to dominate, recording the largest share among rice classes across all the years. The use of remote-sensing techniques is rapid, cost-effective, and reliable to monitor changes in rice cultivated area over long periods of time and estimate the reduction in area cultivated due to abiotic stress such as water stress and submergence. Agricultural research institutes and line departments in the government can use these techniques for better planning, regular monitoring of land-use changes, and dissemination of appropriate technologies.

Impacts of water level fluctuations on substrate environments of lakeshore zone of the lakes in the middle and lower reaches of the Yangtze River

以长江中下游湖泊为对象,研究了水位波动对湖滨带底质环境的影响.结果表明,底质环境参数沿高程梯度变化明显.底质含水率沿高程梯度增加而减小,pH值沿高程梯度变化不大,有机质、总氮和总磷沿高程梯度呈先增大后减小的趋势.底质环境参数的季节变化也较大.分析表明,水位波动幅度、淹没深度、高水位持续时间等对湖滨带底质环境有较大影响.在中等波动幅度下,底质参数沿高程的变异系数最大,表明此时湖滨带底质异质性较高.夏季湖滨带淹没时间越长、淹没深度越大,底质养分流失越快.高水位持续时间越长,底质pH值变化就越大、营养盐流失越快.本研究结果可为湖滨带生态修复及管理提供依据.;The present paper dealt with the impacts of water level fluctuations on the lakeshore substrate environments of the shallow lakes in the middle and lower reaches of the Yangtze River. The results showed that substrate environments changed greatly with the elevation gradients. Moisture contents of substrate decreased as the elevation increased, and pH value changed little, while contents of organic matter, total nitrogen and total phosphorus in substrate increased at first and then decreased. Also, substrate environments showed clear seasonal dynamics. Analyses showed that the amplitude of water level fluctuations, submergence depth, and duration of high water level had great impacts on the substrates. The coefficients of variation of substrate parameters were the largest in the medium amplitude, indicating that the highest heterogeneity of substrate occurred under such a condition. Substrate nutrients would be lost at an increasing pace with the increase of time and depth submerged during summer. If the duration of high water level was long, the pH values would be changed greater and the nutrients would be lost faster. Our results offered a scientific foundation for ecological restoration and management of the lakeshore.

Generic unified rating for Cutthroat flumes

Computational fluid dynamics (CFD) software was used to generate water depth and discharge data for the 24 standard-size Cutthroat flumes (CTF), as well as an additional 27 intermediate sizes. The hydraulic model was validated using information from several sources, including physical model test data for 16 standard sizes and 3 intermediate sizes. Grid-size independence was also confirmed for a range of computational cell sizes, and the calibration results for 16 of the standard-size flumes were compared with previously published calibration parameters. Through the CFD simulations, a full set of calibration and validation data was generated for each of the 51 tested flume sizes, filling the gaps in the experimental data from physical models and permitting a full analysis of flume hydraulic performance. The study resulted in a “generic” (any CTF in the dimensional range of the 24 standard sizes and specified dimensional ratios according to the original design criteria) and “unified” (for both free- and submerged-flow conditions) calibrations. From these results, a single algebraic equation was developed for free and submerged flow, relating upstream water depth and submergence to discharge. The error in the CFD-predicted discharge for all flume sizes is less than 3 % of the full-scale discharge, and the equation is applicable to both standard and nonstandard sizes.

Dual-Injection Airlift Pumps: An Enhanced Performance

The airlift pump is a device for raising liquids or mixtures of liquids and solids through a vertical pipe, which partially submerged in the liquid, by using compressed air introduced at the lower end of the pipe. Airlift pumps are finding increasing use where reliability and low maintenance are required, and when compressed air or gas are readily available as an energy source for water and oil pumping applications. In comparison with other conventional pumps, the particular merit of the airlift pump is the mechanical simplicity. However, the main disadvantage of these pumps is their low efficiency especially at low liquid submergence ratio. In the present study, a dual injector is designed in order to increase the pump efficiency. The new injector is manufactured and tested for different water submergence ratios. The efficiency of the new design is found to be at least 30% higher than that of a conventional design. A proposed model for the analysis of the pump performance is presented and validated using the obtained experimental data. The model prediction of the pump performance is found to be in the range of ±15% of the obtained experimental data.

Artocarpus chaplasha: Establishment and Initial Growth Performance at Elevated Temperature and Saline Stresses

Like any other natural resources, forest flora may experience the extreme threat of elevated temperature and saline water submergence at different stages of their lives i.e. from germination to maturity due to climate change effects. The overall aim of the study was to measure the effect of higher temperatures along with saline water irrigation on survival and initial growth during seedling stage of Artocarpus chapalasha. The experiment was conducted in temperature- humidity-photoperiod regulated plant growth chamber during stipulated period to measure the growth performance of randomly selected seedlings. Within three different elevated temperatures viz. <TEX>$30^{\circ}C$</TEX>, <TEX>$32^{\circ}C$</TEX> and <TEX>$34^{\circ}C$</TEX>, the seedlings were given three different saline conditions such as 0.5 g/L, 1.5 g/L and 2.5 g/L NaCl concentrations. Results found from the experiment was that, seedlings of Artocarpus chaplasha reared at different temperatures and saline water treatments showed stunted growth than reared at existing outdoor temperature (<TEX>$26.31^{\circ}C$</TEX>) irrigated with regular fresh water. Seedling growth at three different parameters such as height, collar diameter and number of leaves showed that with increasing temperature individuals respond negatively to increasing saline condition. The seedling's growth occurred at every day in height, collar diameter and leaf. However, growth rate reduced later during the observation. The combined effect of high salinity and higher elevated temperature results in seedling mortality. Therefore, Artocarpus chaplasha may not thrive at higher temperature and salinity intrusion at its early growing period in plantation and natural forest areas.

Effect of the submergence, the bed form geometry, and the speed of the surface water flow on the mitigation of pesticides in agricultural ditches

Pesticides, which have been extensively used in agriculture, have become a major environmental issue, especially regarding surface and groundwater contamination. Of particular importance are vegetated farm drainage ditches, which can play an important role in the mitigation of pesticide contamination by adsorption onto ditch bed substrates. This role is, however, poorly understood, especially regarding the influence of hydrodynamic parameters, which make it difficult to promote best management practice of these systems. We have assessed the influence of three of these parameters (speed of the surface water flow, submergence, and geometrical characteristics of the bed forms) on the transfer and adsorption of selected pesticides (isoproturon, diuron, tebuconazole, and azoxystrobin) into the bed substrate by performing experiments with a tilted experimental flume, using hemp fibers as a standard of natural organic substrates that are found at the bottom of agricultural ditches. Results show the transfer of pesticides from surface water flow into bed substrate is favored, both regarding the amounts transferred into the bed substrate and the kinetics of the transfer, when the surface water speed and the submergence increase and when the bed forms are made of rectangular shapes. Extrapolation of flume data over a distance of several hundred meters suggests that an interesting possibility for improving the mitigation of pesticides in ditches would be to increase the submergence and to favor bed forms that tend to enhance perturbations and subsequent infiltration of the surface water flow.

Pongamia as a Source of Biodiesel in India

Pongamia Pinnata trees are normally planted along the highways, roads, canals to stop soil erosion. Billions of trees exist all over India. If the seeds fallen along road side are collected, and oil is extracted at village level expellers, few million tons of oil will be available for Lighting the Lamps in rural area. It is the best substitute for Kerosene. Since these are spread over a large area, collection of seeds for Biodiesel manufacture is not viable. (A compact plantation can support a Biodiesel plant. The seedlings of Pongamia can survive in 1.5 meters deep water submergence / inunda-tion for five to six months duration at a stretch. There are nearly 30,000 square km of water reservoirs in India. This tree can be cultivated in our water storage reservoirs up to 1.5 meters depth and reap additional economic value from unused reservoir lands. The estimated annual production of oil from its seeds is about 50,000 t. The oil has not yet found any significant commercial application. But due to increase in awareness and growth in research in this area the Pongamia it can be developed as the alternative source of fuel by replacing diesel. In the present study attempt has been made to study the scope of Pongamia in India.

Regulatory interplay of the Sub1A and CIPK15 pathways in the regulation of α‐amylase production in flooded rice plants

Rice (Oryza sativa L.) can successfully germinate and grow even when flooded. Rice varieties possessing the submergence 1A (Sub1A) gene display a distinct flooding-tolerant phenotype, associated with lower carbohydrate consumption and restriction of the fast-elongation phenotype typical of flooding-intolerant rice varieties. Calcineurin B-like interacting protein kinase 15 (CIPK15) was recently indicated as a key regulator of α-amylases under oxygen deprivation, linked to both rice germination and flooding tolerance in adult plants. It is still unknown whether the Sub1A- and CIPK15-mediated pathways act as complementary processes for rice survival under O(2) deprivation. In adult plants Sub1A and CIPK15 may perhaps play an antagonistic role in terms of carbohydrate consumption, with Sub1A acting as a starch degradation repressor and CIPK15 as an activator. In this study, we analysed sugar metabolism in the stem of rice plants under water submergence by selecting cultivars with different traits associated with flooding survival. The relation between the Sub1A and the CIPK15 pathways was investigated. The results show that under O(2) deprivation, the CIPK15 pathway is repressed in the tolerant, Sub1A-containing, FR13A variety. CIPK15 is likely to play a role in the up-regulation of Ramy3D in flooding-intolerant rice varieties that display fast elongation under flooding and that do not possess Sub1A.

Experimental study of boiling incipience in a closed loop vertical annular thermosiphon

Abstract The present study aims to identify the conditions of boiling incipience experimentally and relate them to the important relevant parameters such as heat flux, liquid submergence level and physical properties during boiling of liquids in an internally heated vertical annulus. The heating surface and liquid temperature distributions were therefore obtained with distilled water as a test fluid in the annulus. The test section is an annulus made of two concentric tubes, the inner made of stainless steel while the outer of corning glass through which flow during the boiling and non-boiling phenomenon along the annulus can be visualized. The maximum wall superheat, attained around boiling incipience, was taken from the wall temperature distributions. The computed values of (δ°/rc), which is ratio of the superheated layer to the radius of cavity on the heating surface, come out to be in the range of 8–18, which is quite comparable to the reported values in the literature. Correlations have been proposed in terms of the heat flux, physical properties of water and liquid submergence level.

Effect of hypoxia and post-hypoxia on the fluctuations in contents of malate and citrate, the activity of malic enzyme, and on the intensity of gas exchange in moss gametophores

Mosses are plants of simple anatomical structure and as they occur in habitats characterised not only by major changes in the concentrations of carbon dioxide, they suffer the stress of periodic water shortages or submergence in water. The condition of hypoxia (submergence in water or CaCl2 solution) prompted the increase in daily fluctuations in malate content, particularly in the gametophores of Polytrichum piliferum Hedw. No significant increases in daily fluctuations of citrate were found in the hypoxia and post-hypoxia conditions. Placing gametophores for 168 h in air with a concentration of CO2 at ∼ 350 μmol mol-1, and 21% of oxygen, after being submerged for 24 h in water, reduced the daily fluctuations of malate and citrate. Keeping the plants in these conditions for a long time (120-168 h) produced the increase in photosynthesis intensity in the gametophores of Mnium undulatum Hedw. and P. piliferum by 13% and 51%, respectively, when compared with plants submerged for 24 h. The intensity of respiration during post-hypoxia, however, was markedly lower compared with the intensity of the process recorded in hypoxia, particularly in the gametophores of P. piliferum. The increased daily fluctuations of malate and NAD(P)H in the studied species under hypoxia could constitute an important element of adaptive strategy to these conditions.

Chronosequential changes of selected pedogenic properties in paddy soils as compared with non-paddy soils

A series of paddy and non-paddy soil profiles that are developed in chronosequences from approximately 50 to 1000 years of exposure time on fairly uniform marine deposits under nearly identical landscape and climate conditions were sampled from Cixi, Zhejiang Province, China, where rice has been traditionally grown under water submergence. Master horizons were identified and sampled. Selected pedogenic properties such as soil organic carbon (SOC) content, clay content, fractions of iron, total manganese and pH were used to characterize the horizons. To compare the differences between paddy and non-paddy profiles, all paddy profiles are taken as one group and all non-paddy profiles as another. The measured properties were averaged over 0–100 cm soil depth. Results showed that paddy group contained significantly ( p < 0.05) higher amount of clay and total Fe than non-paddy group, but significantly lower amount of total Mn. The increased clay content was mainly found in horizons bellow about 40 cm of paddy profiles. SOC compared as such is insignificantly different between paddy and non-paddy groups. However, SOC in surface horizons (roughly 0–20 cm) is significantly higher in paddy profiles than that in non-paddy profiles. The chronosequence of soil development is obvious in paddy profiles in term of distribution/redistribution patterns of total Fe and free Fe oxyhydrates in the profiles, but is not seen in non-paddy profiles. Longer history of rice cultivation tended to result in more profound horizon differentiations, but longer history of non-rice cultivation did not have this effect. Fifty years of rice cultivation seem to be long enough to differentiate paddy profiles from non-paddy ones in terms of SOC contents in surface horizons. However, 100 years of rice cultivation do not seem to be long enough to differentiate them in terms of clay contents and distribution/redistribution of total Fe and free Fe oxyhydrates. In conclusion, our data demonstrate that paddy management has profound impact on soil formations. SOC accumulation in surface horizon, the increase of clay content in horizons bellow about 40 cm depth, horizon differentiation characterized by distribution/redistribution patterns of total Fe and free Fe oxyhydrates, and net losses of total Mn from the profiles are the characteristic soil-forming processes of paddy soils.

Germinação de sementes e sobrevivência de plântulas de Himatanthus sucuuba (Spruce) Wood. em resposta ao alagamento, nas várzeas da Amazônia Central

Himatanthus sucuuba é uma espécie que coloniza as várzeas na Amazônia Central. O objetivo desse trabalho foi estudar as estratégias de adaptação da planta ao alagamento prolongado dessas áreas. Para tanto, foram acompanhados a germinação das sementes e o desenvolvimento das plântulas, simulando as condições naturais de campo (seca e alagamento). A germinação foi realizada em dois substratos: areia+serragem (não-alagado), e em água (alagado). Durante 120 dias, as plântulas geradas foram submetidas a três tratamentos: controle (irrigação diária), submersão parcial (sistema radicular) e submersão total. Foram analisadas as alterações na morfologia das plântulas, na anatomia das raízes e a atividade da enzima álcool desidrogenase (ADH), nos tempos: 0, 15, 30, 60, 90 e 120 dias. Foi constatado que a espécie apresenta elevada taxa de germinação e produção de plântulas, ambas acima de 80%, mesmo para sementes em água. Sob submersão parcial foram formadas lenticelas hipertrofiadas, raízes adventícias e aerênquima radicular. A atividade da ADH se manteve elevada até o 60º dia, com decréscimo após esse período. Plântulas sob submersão total perderam as folhas, não formaram raízes adventícias ou lenticelas, mas desenvolveram aerênquima. Estas plântulas apresentaram os maiores valores da ADH, que permaneceram altos até o término do experimento, indicando o desvio do metabolismo anaeróbico para produção de etanol como principal via para a manutenção da carga energética. Apesar de ter ocorrido a morte de algumas plântulas no tratamento de submersão total, o percentual de sobreviventes foi alto com 70% ao final dos 120 dias de duração do período experimental. Desta maneira, as plântulas de H. sucuuba modulam morfo-fisiologicamente a tolerância ao alagamento em função do tempo de exposição ao estresse e altura da coluna de água.

Isolation and bioinformatics analyses of a COR413-like gene from Gossypium barbadense

A novel cDNA clone encoding a COR413-like gene was isolated by suppression subtraction hybridization and cDNA library screening from sea-island cotton (Gossypium barbadense). This gene (designated as GbCOR413, Accession number: AY761065) has a total length of 893 bp with an open reading frame of 600 bp, encoding a predicated polypeptide of 200 amino acids with a molecular weight of 22.74 kDa and a predicated pI of 9.2. Bioinformatics analyses revealed that this gene belonged to a novel stress-regulated multi-spanning transmembrane protein family without signal peptide. By means of semi-quantities RT-PCR analysis, the expression of GbCOR413 under short-term cold treatment at 4°C, water submergence and abscic acid treatment was investigated. Our studies suggested that the cloned gene was a new member of COR gene family which was slowly responsive to cold stress in cotton.