Plant hemoglobins: important players at the crossroads between oxygen and nitric oxide

Plant hemoglobins constitute a diverse group of hemeproteins and evolutionarily belong to three different classes. Class 1 hemoglobins possess an extremely high affinity to oxygen and their main function consists in scavenging of nitric oxide (NO) at very low oxygen levels. Class 2 hemoglobins have a lower oxygen affinity and they facilitate oxygen supply to developing tissues. Symbiotic hemoglobins in nodules have mostly evolved from class 2 hemoglobins. Class 3 hemoglobins are truncated and represent a clade with a very low similarity to class 1 and 2 hemoglobins. They may regulate oxygen delivery at high O₂ concentrations. Depending on their physical properties, hemoglobins belong either to hexacoordinate non-symbiotic or pentacoordinate symbiotic groups. Plant hemoglobins are plausible targets for improving resistance to multiple stresses.     

Biotransformation of Meloxicam by <Emphasis Type="Italic">Cunninghamella blakesleeana</Emphasis>: Significance of Carbon and Nitrogen Source

Influence of carbon and nitrogen source, on biotransformation of meloxicam was studied by employing Cunninghamella blakesleeana NCIM 687 with an aim to achieve maximum transformation of meloxicam and in search of new metabolites. The transformation was confirmed by HPLC and based on LC–MS–MS data and previous reports the metabolites were predicted as 5-hydroxymethyl meloxicam, 5-carboxy meloxicam and a novel metabolite. The quantification of metabolites was performed using HPLC peak areas. The results obtained indicate that glucose as carbon source, ammonium nitrate as nitrogen source, were found to be optimum for maximum transformation of meloxicam. The study suggests the significance of these factors in biotransformation of meloxicam using microbial cultures. The fermentation was scaled up to 1 l level.     

Nitrogen cycling in tropical and temperate savannas

Savannas are the most common vegetation type in the tropics and subtropics, ranging in physiognomy from grasslands with scattered woody plants to woodlands with heterogeneous grass cover. Productivity and organic matter turnover in savannas are controlled by interactions between water and nutrient availability, and this basic environmental structure is modified by fire frequency and land management practices. We compared temperate and tropical savannas in order to understand the strength of nitrogen (N) limitation of productivity. American tropical and temperate savannas are N limited systems, and the N cycle differs according to the woody plant density, fire frequency, land use change, N deposition and N fixation. Grazing and conversion to pasture have been the predominant land-use changes in most savannas. In the Cerrado and the Llanos tropical savannas, intensified use of fire for pasture management is leading to decreased woody plant density. Oppositely, in the Chaco and North American temperate savannas, fire suppression and grazing are leading to increases in woody density. In addition, the higher soil P availability in the Gran Chaco and the higher N deposition in North American savannas may be contributing to increases of N cycling and net productivity rates. Some aspects of the N budget for savannas of the American continent are still unclear and require further analysis to determine rates of N fixation, and to understand how spatial and temporal soil heterogeneity control N fluxes through soil solution and into streams.     

The Relationships between Nitrogen Fixation and Several Kinds of Energy Metabolism by Gloeocapsa sp

Gloeocapsa sp., a species of anicellular blue-green alga, fixes dinitrogen mostly under light. The energy (ATP and reductant) needed for nitrogen fixation may be provided by photoreaction and aerobic catabolism. The nitrogenase activity (acetylene reduction) in vivo was decreased under the conditions of dark and inhibition of photo-phosphorylation or oxidative phosphorylation in the light. When photosystem Ⅱ was inhibited by the presence of DCMU, nitrogenase activities in both reactions of acetylene reduction and hydrogen evolution may be muchenhanced probably due to eliminating of the damage caused by the oxygen produced in the photolysis of water. The effects of the oxygen present in the atmosphere of the reaction systemand produced by the cells are different. It is shown that some trace oxygen seems to be required for nitrogen fixation by the energy supply of aerobic actabolism and oxidative phosphorylation. While the fixation of dinitrogen was inhibited by CO or no any reducible substrate was present, 70-100% of the energy accepted by nitrogenase was evolved as hydrogen. The algal cells also showed hydrogen uptake reaction, but no enhancement of nitrogen fixation by the hydrogen uptake was found.     

An economic assessment of algal turf scrubber technology for treatment of dairy manure effluent

Controlling the input of nitrogen (N) and phosphorus (P) from dairies and other livestock operations into the surrounding air- and water-sheds poses both technical and economic challenges to the agricultural community. The purpose of this paper is to assess the economics of algal turf scrubber treatment technology at the farm-scale for a hypothetical 1000-cow dairy. Costs were developed for farms with and without anaerobic pretreatment. The majority of capital costs were due to land preparation, installation of liner material, and engineering fees. The majority of operational costs were due to energy requirements for biomass drying, pumping water, and repayment of capital investment. On farms using anaerobic pretreatment, waste heat from burning of biogas could be used to offset the energy requirements of biomass drying. In addition, biogas combustion exhaust gas could then be recycled back to the algal system to supply dissolved inorganic carbon for optimal algal production and pH control. Under the best case (algal system coupled with anaerobic digestion pretreatment), the yearly operational costs per cow, per kg N, per kg P, and per kg of dried biomass were $454, $6.20, $31.10, and $0.70, respectively. Without anaerobic digestion pretreatment, the yearly operational costs were 36% higher, amounting to $631 per cow, $8.70 per kg N, $43.20 per kg P, and $0.97 per kg of dried biomass. For perspective, a recent survey of 36 Maryland dairy farms found long-term annual profits of about $500 per cow. As no market currently exists for manure grown algal biomass, our cost analysis does not include any value of the biomass generated during manure treatment. In addition, there are a variety of potential uses for the algal biomass from manure treatment that could defray treatment costs. Future opportunities for dairies to participate in nutrient trading approaches to watershed nutrient management may also become important.     

Nutrient dynamics of the highly productive C4 macrophyte Echinochloa polystachya on the Amazon floodplain

1. Echinochloa polystachya forms extensive monotypic stands on the lower levels of the Amazon floodplains. During its annual growth cycle c. 100t (dry mass) ha^–1 of biomass is formed as the floodplain is being submerged (December–September) and a phase of death and decomposition occurs when the water has retreated (October–November). This study examines the mineral nutrient dynamics of this plant and its potential significance to the nutrient status of the floodplain.
2. Echinochloa polystachya was sampled monthly from a study site in the central Amazon. N, P and K contents for different plant organs were determined and net uptake calculated from concurrent measurements of dry matter production and turnover.
3. Leaf N, P and K contents were c. 20, 1·7 and 19gkg^–1, values typical of nutrient-replete stands of C₄ plants. Stem concentrations were c. 12% of those of the leaves. Net N and P uptake followed the rise in the river level, whilst K appeared independent of water level.
4. The vegetation accumulated 377, 51 and 1136kgha^–2 of N, P and K, respectively, during the growth phase. Over a possible 5000km² of these stands in the Várzea, this represents a massive sequestration of nutrients in the flood phase and a high release during the following low-water period. It is suggested that the E. polystachya stands could have a role in maintaining the nutrient status of the Amazon floodplain.     

Growth and translocation of C and N in wheat (Triticum aestivum) grown with a split root system

The root system of wheat seedlings ( Triticum aestivum L. SUN 9E) was pruned to two seminal roots. One of the roots was supplied with different levels of NO₃, the other was deprived of N. Root respiration and the increment of C and N in roots and shoots were measured to determine the C/N ratio of the phloem sap feeding the N-deprived roots. Thus it was possible to determine translocation of N from the shoots to the roots. It was calculated that the C/N ratio of phloem sap feeding roots of plants growing at optimal and suboptimal N supply was ca 54. A supra-optimal N supply reduced, whilst shading increased, the C/N ratio of phloem sap. At optimal N supply 11% of all N transported to the shoots was retranslocated to the roots. Both a supra-optimal and a limiting N supply increased translocation of N back to the roots to 18% of the N translocated to the shoot, whilst shading of the plants decreased the proportion cycled to 7%. At the optimal N supply, 40% more N was translocated to the roots from the shoot than was incorporated by them. At a lower supply of N, 80% more N was imported from the shoots than was incorporated by these roots. It is suggested that the distribution of N between roots and shoots predominantly occurs in the shoots. The specific mass transfer rate in seminal roots was determined. The highest value was found for roots grown with an optimal N supply: 1.1 mg carbohydrate s⁻¹ cm⁻² (sieve tube) which is well within the range observed for other plant organs. Roots supplied with NO₃ produced more and longer laterals than N-deprived roots. It is suggested that this is due to the effect of NO₃ on import of carbon and other components transported in the mass flow with carbon.     

Amino acid uptake among wide-ranging moss species may contribute to their strong position in higher-latitude ecosystems

Plants that can take up amino acids directly from the soil solution may have a competitive advantage in ecosystems where inorganic nitrogen sources are scarce. We hypothesized that diverse mosses in cold, N-stressed ecosystems share this ability. We experimentally tested 11 sub-arctic Swedish moss species of wide-ranging taxa and growth form for their ability to take up double labelled (¹⁵N and ¹³C) glycine and aspartic acid in a laboratory setup as well as in a realistic field setting. All species were able to take up amino acids injected into the soil solution to some extent, although field uptake was marginal to absent for the endohydric Polytrichum commune. The 11 moss species on average took up 36 ± 5% of the injected glycine and 18 ± 2% of the aspartic acid in the lab experiment. Field uptake of both glycine (24 ± 5%) and aspartic acid (10 ± 2%) was lower than in the lab. Overall differences in uptake amongst species appeared to be positively associated with habitat wetness and/or turf density among different Sphagnum species and among non-Sphagnum species, respectively. Species from habitats of lower inorganic N availability, as indicated tentatively by lower tissue N concentrations, showed relatively strong amino acid uptake, but this was only significant for the field uptake among non-Sphagnum mosses. Further experiments are needed to test for consistent differences in amino acid uptake capacity among species and functional groups as determined by their functional traits, and to test how the affinity of cold-biome mosses for amino acids compares to that for ammonium or nitrate. Still, our results support the view that widespread moss species in cold, N-stressed ecosystems may derive a significant proportion of their nitrogen demand from free amino acids. This might give them a competitive advantage over plants that depend strongly on inorganic N sources. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Resource heterogeneity in oldfields

Abstract. Spatial heterogeneity of photosynthetically active radiation (PAR), soil moisture and soil N mineralization in a range of oldfield communities was analyzed using semi-variograms for transect data. Percent transmittance of PAR was examined in eight communities, and soil moisture and N mineralization were examined in the two most common communities. In general, the sites with the highest resource availability had the smallest coefficients of variation. For light, 63% of the transects showed significant non-zero spatial autocorrelation with sills at 1 - 70 cm distance intervals. Although the grass-dominated communities had the highest average PAR levels and the lowest coefficients of variation, they also were among those with the greatest percentage of transects that had non-zero spatial autocorrelation. For light, the average semivariogram range, or distance within which samples were autocorrelated, was 19 cm and different among communities at p = 0.07. For soil moisture, two of three shrub sites and one of three grass sites showed non-zero spatial autocorrelation with sills at 10 - 300 cm distance intervals. Average semivariance range was 249 cm for the shrub community and 170 cm for the grass community. For N-mineralization, none of the shrub and one of three grass sites showed non-zero spatial autocorrelation with a sill, with a semivariance range of 60 cm. Soil moisture and N-mineralization were higher in the shrub than in the grass communities. Overall, these results indicate that resource variability occurred within patches of uniform vegetation, and the range of resource spatial dependence was different among resources even within a single community type. Our results suggest that different seedlings invading these communities will experience very different patterns of microsite heterogeneity as a result of their specific resource requirements.