Balanced nitrogen economy as a flexible strategy on yield stabilizing and quality of aquatic food crops in wetland ecosystem

In wetland ecosystem, nitrogen along with other elements and its management is most imperative for the production of so many aquatic food, non-food and beneficial medicinal plants and for the improvement of soil and water characteristics. With great significant importance of INM (integrated nutrient management) as sources, emphasizing on management on nitrogen as a key element and its divergence, a case study was undertaken on such aquatic food crops (starch and protein-rich, most popular and remunerative) in the farmers' field of low-lying randomized block design, where, three important aquatic food crops (water chestnut (Trapa bispinosa Roxb.), makhana (Eurya/e ferox Salisb.) and water lily (Nymphaea spp.) as major factor and eleven combinations of organic and inorganic sources of nutrients as sub-factor was considered in the experiment. It revealed from the results that the production of fresh kernels or nuts of water chestnut (8.57 t ha-1), matured nut yield of makhana (3.06 t ha-1) and flower stalks of water-lily as vegetables (6.38 t ha-1) including its nutritional quality (starch, protein, sugar and minerals) was remarkably influenced with the application of both organic (neem oilcake @ 0.2 t ha-1) and inorganic sources (NPK @ 30:20:20 kg ha-1 along with spraying of NPK @ 0.5% each over crop canopy at 20 days interval after transplanting) than the other INM combinations applied to the crops. Among the crops, highest WCYE (water chestnut yield equivalence) exhibited in makhana due to its high price of popped-form in the country, which is being exported to other countries at now. Sole application of both (organic and inorganic sources) with lower range did not produce any significant outcome from the study and exhibited lower value for all the crops.Besides production of food crops, INM also greatly influenced the soil and water characterization and it was favourably reflected in this study. The physico-chemical characteristics of soil (textural class, pH, organic carbon, organic matter, ammoniacal nitrogen, nitrate nitrogen, available nitrogen, phosphorus and potassium) are most important and contributed a significant improvement due to cultivation of these aquatic crops. Analysis of such wet bodies represented the water characteristics (pH, BOD, COD, CO3-, HCO3-, NO3-N, SO4-S and Cl-) were most responsive,adaptable and quite favourable for the cultivation of these crops in this vast waste unused wetlands for the mankind without any environmental degradation.     

Balanced nitrogen economy as a flexible strategy on yield stabilizing and quality of aquatic food crops in wetland ecosystem

In wetland ecosystem, nitrogen along with other elements and its management is most imperative for the production of so many aquatic food, non-food and beneficial medicinal plants and for the improvement of soil and water characteristics. With great significant importance of INM (integrated nutrient management) as sources, emphasizing on management on nitrogen as a key element and its divergence, a case study was undertaken on such aquatic food crops (starch and protein-rich, most popular and remunerative) in the farmers' field of low-lying 'Tal' situation of New Alluvial Zone of Indian subtropics. The study was designed in factorial randomized block design, where, three important aquatic food crops (water chestnut (Trapa bispinosa Roxb.), makhana (Euryale ferox Salisb.) and water lily (Nymphaea spp.) as major factor and eleven combinations of organic and inorganic sources of nutrients as sub-factor was considered in the experiment. It revealed from the results that the production of fresh kernels or nuts of water chestnut (8.571 ha-1), matured nut yield of makhana (3.06 t ha-1) and flower stalks of water-lily as vegetables (6.38 t ha-1) including its nutritional quality (starch, protein, sugar and minerals) was remarkably influenced with the application of both organic (neem oilcake @ 0.2 t ha-1) and inorganic sources (NPK @ 30:20:20 kg ha-1 along with spraying of NPK @ 0.5% each over crop canopy at 20 days interval after transplanting) than the other INM combinations applied to the crops. Among the crops, highest WCYE (water chestnut yield equivalence) exhibited in makhana due to its high price of popped-form in the country, which is being exported to other countries at now. Sole application of both (organic and inorganic sources) with lower range did not produce any significant outcome from the study and exhibited lower value for all the crops. Besides production of food crops, INM also greatly influenced the soil and water characterization and it was favourably reflected in this study. The physico-chemical characteristics of soil (textural class, pH, organic carbon, organic matter, ammoniacal nitrogen, nitrate nitrogen, available nitrogen, phosphorus and potassium) are most important and contributed a significant improvement due to cultivation of these aquatic crops. Analysis of such wet bodies represented the water characteristics (pH, BOD, COD, CO3 =, HCO3-, NO3- N, SO4-S and Cl-) were most responsive, adaptable and quite favourable for the cultivation of these crops in this vast waste unused wetlands for the mankind without any environmental degradation.     

A comparison of nitrate transport in four different rice (Oryza sativa L.) cultivars

As rice can use both nitrate (NO ⁻₃ ) and ammonium (NH ⁺₄ ), we have tested the hypothesis that the shift in the pattern of cultivars grown in Jiangsu Province reflects the ability of the plants to exploit NO ⁻₃ as a nitrogen (N) source. Four rice cultivars were grown in solution culture for comparison of their growth on NO ⁻₃ and NH ⁺₄ nitrogen sources. All four types of rice, Xian You 63 (XY63), Yang Dao 6 (YD), Nong Keng 57 (NK) and Si You 917 (SY917), grew well and produced similar amounts of shoot biomass with 1 mmol/L NH ⁺₄ as the only N source. However, the roots of NK were significantly smaller in comparison with the other cultivars. When supplied with 1 mmol/L NO ⁻₃ , YD produced the greatest biomass; while NK achieved the lowest growth among the four cultivars. Electrophysiological measurements on root rhizodermal cells showed that the NO ⁻₃ -elicited changes in membrane potential (†E _m) of these four rice cultivars were significantly different when exposed to low external NO ⁻₃ (<1 mmol/L); while they were very similar at high external NO ⁻₃ (10 mmol/L). The root cell membrane potentials of YD and XY63 were more responsive to low external NO ⁻₃ than those of NK and SY917. The †E _m values for YD and XY63 rhizodermal cells were almost the same at both 0.1 mmol/L and 1 mmol/L NO ⁻₃ ; while for the NK and SY917 the values became larger as the external NO ⁻₃ increased. For YD cultivar, †E _m was measured over a range of NO ⁻₃ concentrations and a Michaelis-Menten fit to the data gave aK _m value of 0.17 mmol/L. Net N ⁻₃ uptake depletion kinetics were also compared and for some cultivars (YD and XY63) a single-phase uptake system with first order kinetics best fitted the data; while other cultivars (ND and SY917) showed a better fit to two uptake systems. These uptake systems had two affinity ranges: one had a similarK _m in all the cultivars (0.2 mmol/L); the other much higher affinity system (0.03 mmol/L) was only present in NK and SY917. The expression pattern of twelve different N ⁻₃ transporter genes was tested using specific primers, but onlyOsNRT1. 1 andOsNRT2.1 expression could be detected showing significant differences between the four rice cultivars. The results from both the physiological and molecular experiments do provide some support for the hypothesis that the more popular rice cultivars grown in Jiangsu Province may be better at using NO ⁻₃ as an N source.

     

A bacterial view of the periodic table: genes and proteins for toxic inorganic ions

Essentially all bacteria have genes for toxic metal ion resistances and these include those for Ag⁺, AsO ⁻₂ , AsO ³⁻₄ , Cd²⁺, Co²⁺, CrO ²⁻₄ , Cu²⁺, Hg²⁺, Ni²⁺, Pb²⁺, TeO ²⁻₃ , Tl⁺ and Zn²⁺. The largest group of resistance systems functions by energy-dependent efflux of toxic ions. Fewer involve enzymatic transformations (oxidation, reduction, methylation, and demethylation) or metal-binding proteins (for example, metallothionein SmtA, chaperone CopZ and periplasmic silver binding protein SilE). Some of the efflux resistance systems are ATPases and others are chemiosmotic ion/proton exchangers. For example, Cd²⁺-efflux pumps of bacteria are either inner membrane P-type ATPases or three polypeptide RND chemiosmotic complexes consisting of an inner membrane pump, a periplasmic-bridging protein and an outer membrane channel. In addition to the best studied three-polypeptide chemiosmotic system, Czc (Cd²⁺, Zn²⁺, and Co²), others are known that efflux Ag⁺, Cu⁺, Ni²⁺, and Zn²⁺. Resistance to inorganic mercury, Hg²⁺ (and to organomercurials, such as CH₃Hg⁺ and phenylmercury) involve a series of metal-binding and membrane transport proteins as well as the enzymes mercuric reductase and organomercurial lyase, which overall convert more toxic to less toxic forms. Arsenic resistance and metabolizing systems occur in three patterns, the widely-found ars operon that is present in most bacterial genomes and many plasmids, the more recently recognized arr genes for the periplasmic arsenate reductase that functions in anaerobic respiration as a terminal electron acceptor, and the aso genes for the periplasmic arsenite oxidase that functions as an initial electron donor in aerobic resistance to arsenite.

     

Optimization of aquatic-terrestrial ecosystem in relation to soil nitrogen status for the cultivation of fish and aquatic food crops of the Indian subtropics

A case study was undertaken during wet and postwet seasons to improve the perennial and alternate submerged saucer-shaped ponded lands (tal and semi-tal lands) in the coasts and northeastern plains of the Indian subtropics through pisciculture and cultivation of starch- and protein-rich aquatic food crops like water chestnut (Trapa bispinosa Roxb.) and makhana or fox nut (Euryale ferox Salisb.). The study revealed that the physico-chemical properties of soils (pH, organic C, organic matter, available N, P, and K) as well as quality of water (pH, EC, BOD, COD, CO3 +, HCO3-, NO3-N, SO4-S-, and Cl-), growing fish, makhana, and water chestnut was remarkably influenced by different moisture regimes and exhibited a significant improvement of soil health. The amount of organic C, available N, P, and K content were found significantly highest in the treatment where makhana was grown under alternate flooding and drying situation with a depth >2 m as compared to other treatments. Such enrichment of soil fertility, particularly in available N and P content, might be due to the accumulation of considerable amounts of biomass and fish excreta and their subsequent decomposition in situ in the soils. Therefore, the present study suggests that the N-enriched soil may effectively be utilized further for growing subsequent arable crops surroundings during summer season, which not only saves the amount of applied N fertilizer but also increases the apparent N efficiency with simultaneous increase in yield, and would benefit the farmers in this region.     

Ultrasonic and Thermal Inactivation of Catalases from Bovine Liver,the Methylotrophic Yeast Pichia pastoris,and the Fungus Penicillium piceum

The kinetics of inactivation of catalases from bovine liver (CAT), the fungus Penicillium piceum (CAT1), and the methylotrophic yeast Pichia pastoris (CAT2) was studied in phosphate buffer (pH 5.5 or 7.4) at 45 and 50°C or under the conditions of exposure to low-frequency ultrasound (LFUS; 27 kHz, 60 W/cm²). The processes were characterized by effective first-order rate constants (s^?1): k _in (total inactivation), k ^*_in (thermal inactivation), and k ^*_in (us) (ultrasonic inactivation). The values of k _in and k ^*_in increased in the following order: CAT1 < CAT < CAT2. Circular dichroic spectra of the enzyme solutions were recorded in the course of inactivation by high temperatures (45 and 50°C ) and LFUS, and the contents of secondary structures were calculated. Processes of thermal and ultrasonic inactivation of catalases were associated with a decrease in the content of α helices and an increase in that of antiparallel β structures and irregular regions (CAT1 < CAT < CAT2). We conclude that the enzymes exhibit the following rank order of resistance: CAT1 > CAT > CAT2. Judging from the characteristics of CAT1, it appears to be an optimum component for antioxidant enzyme complexes.

     

Identifying the species of copper that are toxic to plant roots in alkaline nutrient solutions

Background and aims

The pH of the growth medium influences Cu speciation in solution, the negativity of plasma membrane (PM) surface potential, and hence the rhizotoxicity of Cu.

Methods

Solution culture experiments were conducted with wheat (Triticum aestivum L.) seedlings to examine the toxicity of various Cu species at pH values ranging from 4.50 to 8.25. The toxic species of Cu was identified, giving particular consideration to the electrical properties at the plant cell membrane and ion activities at the PM surface.

Results

The solution culture studies showed that at pH?<?6.60 (i.e., free Cu²⁺ >95 % of total Cu), the addition of cations (Ca²⁺ or H⁺) decreased the toxic effects of Cu by decreasing the negativity of the PM surface potential (and hence decreasing the activity of Cu²⁺ at the PM surface). For solutions with pH values from 7.50 to 8.25 (CuCO ⁰₃ >50 % of total Cu), an increase in pH significantly enhanced the toxicity of Cu, whilst the addition of Ca had negligible influence on toxicity.

Conclusions

Root growth in solution cultures was influenced primarily by the surface activities of free Cu²⁺ and CuCO ⁰₃ . Across all experiments, the data indicate that it was CuCO ⁰₃ , rather than CuOH⁺, that contributed Cu toxicity over pH?>?7.00. Although our data do not explore the mechanism of toxicity, we propose that CuCO ⁰₃ has an important role in Cu rhizotoxicity in alkaline growth media.

     

Dissolved methane concentrations and fluxes to the atmosphere from a tropical floodplain lake

Large uncertainties in estimates of methane (CH₄) emissions from tropical inland waters reflect the paucity of information at appropriate temporal and spatial scales. CH₄ concentrations, diffusive and ebullitive fluxes, and environmental parameters in contrasting aquatic habitats of Lake Janauacá, an Amazon floodplain lake, measured for two years revealed patterns in temporal and spatial variability related to different aquatic habitats and environmental conditions. CH₄ concentrations ranged from below detection to 96 µM, CH₄ diffusive fluxes from below detection to 2342 µmol m⁻² h⁻¹, and CH₄ ebullitive fluxes from 0 to 190 mmol m⁻² d⁻¹. Vegetated aquatic habitats had higher surface CH₄ concentrations than open water habitats, and no significant differences in diffusive CH₄ fluxes, likely due to higher k values measured in open water habitats. CH₄ emissions were enhanced after a prolonged low water period, when the exposed sediments were colonized by herbaceous plants that decomposed after water levels rose, possibly fueling CH₄ production. Statistical models indicated the importance of variables related to CH₄ production (temperature, dissolved organic carbon) and consumption (dissolved nitrogen, oxygenated water column), as well as maximum depth, in controlling surface water CH₄ concentrations.

     

Sedimentary Organic Carbon and Nitrogen Sequestration Across a Vertical Gradient on a Temperate Wetland Seascape Including Salt Marshes,Seagrass Meadows and Rhizophytic Macroalgae Beds

Coastal wetlands are key in regulating coastal carbon and nitrogen dynamics and contribute significantly to climate change mitigation and anthropogenic nutrient reduction. We investigated organic carbon (OC) and total nitrogen (TN) stocks and burial rates at four adjacent vegetated coastal habitats across the seascape elevation gradient of Cádiz Bay (South Spain), including one species of salt marsh, two of seagrasses, and a macroalgae. OC and TN stocks in the upper 1 m sediment layer were higher at the subtidal seagrass Cymodocea nodosa (72.3 Mg OC ha⁻¹, 8.6 Mg TN ha⁻¹) followed by the upper intertidal salt marsh Sporobolus maritimus (66.5 Mg OC ha⁻¹, 5.9 Mg TN ha⁻¹), the subtidal rhizophytic macroalgae Caulerpa prolifera (62.2 Mg OC ha⁻¹, 7.2 Mg TN ha⁻¹), and the lower intertidal seagrass Zostera noltei (52.8 Mg OC ha⁻¹, 5.2 Mg TN ha⁻¹). The sedimentation rates increased from lower to higher elevation, from the intertidal salt marsh (0.24 g cm⁻² y⁻¹) to the subtidal macroalgae (0.12 g cm⁻² y⁻¹). The organic carbon burial rate was highest at the intertidal salt marsh (91 ± 31 g OC m⁻² y⁻¹), followed by the intertidal seagrass, (44 ± 15 g OC m⁻² y⁻¹), the subtidal seagrass (39 ± 6 g OC m⁻² y⁻¹), and the subtidal macroalgae (28 ± 4 g OC m⁻² y⁻¹). Total nitrogen burial rates were similar among the three lower vegetation types, ranging from 5 ± 2 to 3 ± 1 g TN m⁻² y⁻¹, and peaked at S. maritimus salt marsh with 7 ± 1 g TN m⁻² y⁻¹. The contribution of allochthonous sources to the sedimentary organic matter decreased with elevation, from 72% in C. prolifera to 33% at S. maritimus. Our results highlight the need of using habitat-specific OC and TN stocks and burial rates to improve our ability to predict OC and TN sequestration capacity of vegetated coastal habitats at the seascape level. We also demonstrated that the stocks and burial rates in C. prolifera habitats were within the range of well-accepted blue carbon ecosystems such as seagrass meadows and salt marshes.

     

Experimental and theoretical studies of the optical and electrical characteristics of a high-pressure pulsed discharge in argon

The optical and electrical characteristics of pulsed discharges in pure Ar at pressures of up to 7 atm, at which the discharge becomes unstable, are studied in a simple experimental device with automatic preionization. The gas temperature in the discharge is estimated from the width of the recorded emission spectrum. An analytical model of the vibrational relaxation of Ar ^*₂ (v) is used to better determine the constants of the vibrational-translational relaxation of Ar ^*₂ (v) molecules in their collisions with Ar atoms. The zerodimensional numerical model of a pulsed discharge in Ar is modified. The experimental and calculated results are compared in detail. Good agreement is achieved between the measured and calculated time dependences of the electrode voltage and the intensity of spontaneous emission in the pressure range of 1–6 atm, as well as between the measured and calculated values of the gas temperature at pressures of 3–6 atm. Preliminary results from numerical studies of the possibility of achieving generation are discussed.

     

Impact of long-term additions of chemical fertilizers and farm yard manure on carbon and nitrogen sequestration under rice-cowpea cropping system in semi-arid tropics

Restoration of soil organic carbon (SOC) in arable lands represents potential sink for atmospheric CO₂. The strategies for restoration of SOC include the appropriate land use management, cropping sequence, fertilizer and organic manures application. To achieve this goal, the dynamics of SOC and nitrogen (N) in soils needs to be better understood for which the long-term experiments are an important tool. A study was thus conducted to determine SOC and nitrogen dynamics in a long-term experiment in relation to inorganic, integrated and organic fertilizer application in rice-cowpea system on a sandy loam soil (Typic Rhodualf). The fertilizer treatments during rice included (i) 100% N (@ 100 kg N ha^?1), (ii) 100% NP (100 kg N and 50 kg P₂O₅ ha^?1), (iii) 100% NPK (100 kg N, 50 kg P₂O₅ and 50 kg K₂O ha^?1) as inorganic fertilizers, (iv) 50% NPK + 50% farm yard manure (FYM) (@ 5 t ha^?1) and (v) FYM alone @ 10 t ha^?1 compared with (vi) control treatment i.e. without any fertilization. The N alone or N and P did not have any significant effect on soil carbon and nitrogen. The light fraction carbon was 53% higher in NPK + FYM plots and 56% higher in FYM plots than in control plots, in comparison to 30% increase with inorganic fertilizers alone. The microbial biomass carbon and water-soluble carbon were relatively higher both in FYM or NPK + FYM plots. The clay fraction had highest concentration of C and N followed by silt, fine sand and coarse sand fractions in both surface (0–15 cm) and subsurface soil layers (15–30 cm). The C:N ratio was lowest in the clay fraction and increased with increase in particle size. The C and N enrichment ratio was highest for the clay fraction followed by silt and both the sand fractions. Relative decrease in enrichment ratio of clay in treatments receiving NPK and or FYM indicates comparatively greater accumulation of C and N in soil fractions other than clay.     

Cover crops do not increase soil organic carbon stocks as much as has been claimed: What is the way forward?

When compared to virgin land (forest and grassland), croplands store significantly lower amounts of organic carbon (OC), mainly as a result of soil tillage, and decreased plant inputs to the soil over the whole year. Doubts have been expressed over how much reduced and zero tillage agriculture can increase OC in soils when the whole soil profile is considered. Consequently, cover-crops that are grown in-between crops instead of leaving soils bare appear as the “last man standing” in our quest to enhance cropland OC stocks. Despite the claim by numerous meta-analyses of a mean carbon sequestration rate by cover crops to be as high as 0.32 ± 0.08 ton C ha⁻¹ year⁻¹, the present analysis showed that all of the 37 existing field studies worldwide only sampled to a depth of 30 cm or less and did not compare treatments on the basis of equivalent soil mass. Thirteen studies presented information on OC content only and not on OC stocks, had inappropriate controls (n = 14), had durations of 3 years or lower (n = 5), considered only one to two data points per treatment (n = 4), or used cover crops as cash crops (i.e., grown longer that in-between two crops) instead of catch crops (n = 2), which in all cases constitutes shortcomings. Of the remaining six trials, four showed non-significant trends, one study displayed a negative impact of cover crops, and one study displayed a positive impact, resulting in a mean OC storage of 0.03 ton ha⁻¹ year⁻¹. Models and policies should urgently adapt to such new figure. Finally, more is to be done not only to improve the design of cover-crop studies for reaching sound conclusions but also to understand the underlying reasons of the low efficiency of cover crops for improved carbon sequestration into soils, with possible strategies being suggested.     

Water chemistry and nutrient budgets in an undisturbed evergreen rainforest of southern Chile

In a pristine evergreen rainforest of Nothofagus betuloides, located at the Cordillera de los Andes in southern Chile (41 °S), concentrations and fluxes of nutrients in bulk precipitation, cloud water, throughfall water, stemflow water, soil infiltration and percolation water and runoff water were measured. The main objectives of this study were to investigate canopy-soil-atmosphere interactions and to calculate input-output budgets. From May 1999 till April 2000, the experimental watershed received 8121 mm water (86% incident precipitation, 14% cloud water), of which the canopy intercepted 16%. Runoff water volume amounted 9527 mm. Bulk deposition of inorganic (DIN) and organic (DON) nitrogen amounted 3.6 kg ha^–1 year^–1 and 8.2 kg ha^–1 year^–1 respectively. Occult deposition (clouds + fog) contributes for 40% to the atmospheric nitrogen input (bulk + occult deposition) of the forest. An important part of the atmospheric ammonium deposition is retained within the canopy or converted to nitrate or organic nitrogen by epiphytic bacteria or lichens. Also the export of inorganic (0.9 kg ha^–1 year^–1) and organic (5.2 kg ha^–1 year^–1) nitrogen via runoff is lower than the input to the forest floor via throughfall and stemflow water (3.2 kg DIN ha–1 year^–1 and 5.6 kg DON ha^–1 year^–1). The low concentrations of NO ₃ ^– and NH ₄ ⁺ under the rooting depth suggest an effective biological immobilization by vegetation and soil microflora. Dry deposition and foliar leaching of base cations (K⁺, Ca²⁺, Mg²⁺) was estimated using a canopy budget model. Bulk deposition accounted for about 50% of the total atmospheric input. Calculated dry and occult deposition are both of equal value (about 25%). Foliar leaching of K⁺, Ca²⁺, and Mg²⁺ accounted for 45%, 38% and 6% of throughfall deposition respectively. On an annual basis, the experimental watershed was a net source for Na⁺, Ca²⁺ and Mg²⁺.     

Biomanipulation of Lago di Candia (Northern Italy): a three-year experience of aquatic macrophyte management

A long-term experimental aquatic plant management programme has been in progress since 1985 in the eutrophic Lago di Candia (Northern Italy). 7.7 ha of water chestnut (Trapa natans L.) were harvested in 1986, 8.2 ha in 1987 and 11.0 ha in 1988, from August to October, removing 334, 290 and 418 tons of fresh plant material, respectively, from the lake. This annual harvesting of about 50% of the total water chestnut cover resulted in the removal from the lake of about 70 kg yr⁻¹ of phosphorus, a significant portion of the external annual loading originating mainly from run-off and precipitation. In addition, up to 38t yr⁻¹ of organic matter and 1t yr⁻¹ of nitrogen were removed. First results of the effect of the harvesting on Secchi-disc transparency, oxygen, total phosphorus, phytoplankton and zooplankton are discussed also in connection with a study of fish manipulation (Giussaniet al., 1990).     

Nitrogen transformations in limed and nitrogen fertilized soil in Norway spruce stands

Nitrogen transformations in the soil, and the resulting changes in carbon and nitrogen compounds in soil percolate water, were studied in two stands of Norway spruce (Picea abies L.). Over the last 30 years the stands were repeatedly limed (total 6000 kg ha^–1), fertilized with nitrogen (total about 900 kg ha^–1), or both treatments together. Both aerobic incubations of soil samples in the laboratory, and intact soil core incubations in the field showed that in control plots ammonification widely predominated over nitrification. In both experiments nitrogen addition increased the formation of mineral-N. In one experiment separate lime and nitrogen treatments increased nitrification, in the other, only lime and nitrogen addition together had this effect. In one experiment immobilization of nitrogen to soil microbial biomass was lower in soil only treated with nitrogen. Soil percolate water was collected by means of lysimeters placed under the humus layer and 10 cm below in the mineral soil. Total N, NH₄-N and NO₃-N were measured, and dissolved organic nitrogen was fractioned according to molecular weight. NO₃-N concentrations in percolate water, collected under the humus layer, were higher in plots treated with N-fertilizer, especially when lime was also added. The treatments had no effect on the N concentrations in mineral soil. A considerable proportion of nitrogen was leached in organic form.     

Production and characterization of exopolysaccharides by Geobacillus thermodenitrificans ArzA-6 and Geobacillus toebii ArzA-8 strains isolated from an Armenian geothermal spring

The thermal ecosystems, including geothermal springs, are proving to be source of thermophiles able to produce extracellular polysaccharides (EPSs). Among the sixteen thermophilic bacilli isolated from sediment sampled from Arzakan geothermal spring, Armenia, two best EPSs producer strains were identified based on 16S rRNA gene sequence analysis and phenotypic characteristics, and designated as Geobacillus thermodenitrificans ArzA-6 and Geobacillus toebii ArzA-8 strains. EPSs production was investigated under different time, temperature and culture media’s composition. The highest specific EPSs production yield (0.27 g g⁻¹ dry cells and 0.22 g g⁻¹ dry cells for strains G. thermodenitrificans ArzA-6 and G. toebii ArzA-8, respectively) was observed after 24 h when fructose was used as sole carbon source at 65 °C and pH 7.0. Purified EPSs displayed a high molecular mass: 5 × 10⁵ Da for G. thermodenitrificans ArzA-6 and 6 × 10⁵ Da for G. toebii ArzA-8. Chemical composition and structure of the biopolymers, determined by GC–MS, HPAE-PAD and NMR, showed that both the two EPSs are heteropolymers composed by mannose as major monomer unit. Optical rotation values [α] ^25 °C_D of the two EPSs (2 mg ml⁻¹ H₂O) were − 142,135 and − 128,645 for G. thermodenitrificans ArzA-6 and G. toebii ArzA-8, respectively.

     

Impact of DOC trends resulting from changing climatic extremes and atmospheric deposition chemistry on periphyton community of a freshwater tropical lake of India

Recent measurements have demonstrated unprecedented increase in atmospheric deposition of nutrients in many parts of India. To determine whether atmospheric nutrient inputs would increase phytoplankton growth and catchment dissolved organic carbon (DOC) flushing to constrain benthic algae, we analyzed NO₃ ^? and PO ₄ ^?3 in atmospheric deposits; nutrients and DOC in runoff and lake water and standing crop biomass of phytoplankton and periphyton at Jaisamand Lake of Rajasthan, India. Atmospheric deposition of NO₃ ^? (7.18–29.95 kg ha^?1 year^?1) and PO ₄ ^?3 (0.56–2.15 kg ha^?1 year^?1) showed a consistently rising trend across the year. Microbial biomass and activity in catchment increased in response to atmospheric deposition. Lake DOC and nutrients showed strong coherence with their terrestrial and atmospheric fluxes. Phytoplankton development showed significant linearity with atmospheric input of nutrients. Air-driven input appeared to have compensated the nutrient constraints to phytoplankton during drought. The N:P stoichiometry of deposition and that of lake water indicated that, although there was a seasonal switchover to N- or P-limitation, phytoplankton were mainly co-limited by N and P due probably to the synergistic effects of combined N + P enrichment in the pelagic zone of the lake. Periphyton standing crop showed inverse relationship with phytoplankton and lake DOC. The study indicated that enhanced phytoplankton development and terrestrial DOC flushing in response to atmospheric nutrient input attenuated light penetration to constrain algal periphyton. We suggests that data on these issues may be considered in developing aquatic ecosystem models to establish future links between changing air–water–land interactions and associated shifts in lake ecosystem functioning for more accurately predicting climate change drivers and designing integrated lake basin management strategies.     

Ammonium nutrition increases water absorption in rice seedlings (Oryza sativa L.) under water stress

Water stress is a primary limitation on plant growth. In previous studies, it has been found that ammonium enhances the tolerance of rice plants to water stress, but how water is related to nitrogen form and water stress remains unknown. To study the effects of nitrogen form (NH ₄ ⁺ , NO ₃ ^? , and a mixture of NH ₄ ⁺ and NO ₃ ^? ) on the growth and water absorption of rice (Oryza sativa L.) seedlings, a hydroponic experiment with water stress, simulated by the addition of polyethylene glycol (PEG, 10% w/v, MW 6000), was conducted in a greenhouse. The results showed that, compared with non-water stress, under water stress, the fresh weight of rice seedlings increased by 14% with NH ₄ ⁺ nutrition, whereas it had decreased by about 20% with either NO ₃ ^? or mixed nitrogen nutrition. No significant difference was found in the transpiration rate of excised shoots or in xylem exudation of excised roots in NH ₄ ⁺ supply between the two water situations, whereas xylem flow decreased by 57% and 24% under water stress in NO ₃ ^? and mixed nutrition, and root hydraulic conductivity decreased by 29% and 54% in plants in NH ₄ ⁺ and NO ₃ ^? nutrition conditions, respectively. Although water absorption ability decreased in both NH ₄ ⁺ and NO ₃ ^? nutrition, aquaporin activity was higher in NH ₄ ⁺ than in NO ₃ ^? nutrition, regardless of water stress. We conclude that NH ₄ ⁺ nutrition can improve water handling in rice seedlings and subsequently enhance their resistance to drought.     

Effects of supplemental nitrogen rate and source on biomass production by three weed species in fallow vegetable land

In 1983, a study was conducted to evaluate three weed species for their biomass yield potential on a fallowed tomato land with various nitrogen (N) rates and sources. Dogfennel (Eupatorium capillifolium (Lam.)Small), sida (Sida rhombifolia L.), and pigweed (Amaranthus hybridus L.), were grown with three N rates: residual, 1x and 2x (1x = 56 kg ha⁻¹ N) and with two N sources: NH₄NO₃ and isobutylidene diurea (IBDU). Sida produced the greatest fresh and dry biomass yields and percentage dry matter, 43·3, 23·3 Mg ha⁻¹ and 54·1%, respectively. Yields of the three crops increased with increasing N rates and were higher with NH₄NO₃ than with IBDU. Overall, sida at the 2x N rate with NH₄NO₃ had the highest fresh, 73·8 Mg ha⁻¹, and dry biomass, 37·9 Mg ha⁻¹, yield. Lowest residual soil total soluble salt concentration, 170 ppm, was found after pigweed, in plots which did not receive additional N. Additional N application increased residual soil total soluble salts after each of the three weeds. Thus, additional N, in NH₄NO₃ form, was necessary for high yields in a fallowed vegetable land, but the additional fertilizer also increased soil total soluble salts, regardless of the plant species.     

Microbial N turnover processes in three forest soil layers following clear cutting of an N saturated mature spruce stand

Microbial N turnover processes were investigated in three different forest soil layers [organic (O) layer, 0–10 cm depth (M₁), 10–40 cm depth (M₂)] after the clear cutting of a nitrogen (N) saturated spruce stand at the Höglwald Forest (Bavaria, Germany). The aim of the study was to provide detailed insight into soil-layer specific microbial production and the consumption of inorganic N within the main rooting zone. Furthermore, we intended to clarify the relevance of each soil layer investigated in respect of the observed high spatial variation of seepage water nitrate (NO ₃ ^? ) concentration at a depth of 40 cm. The buried bag and the ¹⁵N pool dilution techniques were applied to determine the net and gross N turnover rates. In addition, soil pH, C:N ratio, pool sizes of soil ammonium (NH ₄ ⁺ ) and NO ₃ ^? , as well as quantities of microbial biomass carbon (C_mic) and nitrogen (N_mic) were determined. The 40 cm thick upper mineral soil was found to be the main place of NO ₃ ^? production with a NO ₃ ^? supply or net nitrification three times higher than in the considerably thinner O layer. Nevertheless, O layer nitrification processes determined via in situ field experiments showed significant correlation with seepage water NO ₃ ^? . An improved correlation noted several months after the cut may result from a transport-induced time shift of NO ₃ ^? with downstream hydrological pathways. In contrast, the soil laboratory incubation experiments found no indication that mineral soil is relevant for the spatial heterogeneity of seepage water NO ₃ ^? . The results from our study imply that in situ experiments may be better suited to studies investigating N turnover in relation to NO ₃ ^? loss via seepage water in similar ecosystems in order to gain representative data.