Cloning, sequencing and mutational analysis of the cytochrome c552 gene (cycB) from Bradyrhizobium japonicum strain 110

We report the cloning and nucleotide sequence analysis of the cytochrome c552 gene (cycB) of Bradyrhizobium japonicum strain 110. The gene was identified with help of an oligonucleotide that was designed on the basis of the amino acid sequence determined for purified cytochrome c552 of B. japonicum strain CC705. The cycB gene product has an N-terminal 23-amino acid signal peptide that is missing in the mature cytochrome c552 protein. A B. japonicum cycB insertion mutant was constructed which had no observable phenotypic defects in denitrification and symbiotic nitrogen fixation. Thus, the function of c552 remains unknown.     

Biomass allocation and nutrient use in fast-growing woody and herbaceous perennials used for phytoremediation

This study assessed the suitability of two deciduous woody perennials (Salix spp. and Populus spp.) and two summer green herbaceous perennials (Phragmites australis and Urtica dioica) for purification of nutrient enriched wastewater. The main hypothesis tested was that species with a particular trait combination of high relative growth rate (RGR), low nutrient productivity (A) and high mean residence time (MRT) of nutrients would be most effective in accumulating nutrients. The nitrogen and phosphorus use efficiency at the whole plant level was analysed. Four treatments comprising two possible phytoremediation substrates (municipal wastewater and landfill leachate) and two control plant nutrition situations (balanced nutrient solution and pure water) were applied in four replications to the four plant species. Generally, all four species studied showed a high RGR and a low P productivity in the balanced nutrient solution treatment, while the opposite (low RGR and high P productivity) was seen in the phytoremediation substrate and pure water treatments. The general conclusion is that if P is present in marginal proportions in the wastewater, a vegetation filter with Phragmites would have an advantage since biomass and nutrient accumulation in Phragmites does not decrease as much during phytoremediation as that in deciduous woody perennials.     

Nutrient concentrations in tidal creeks as indicators of the water quality role of mangrove wetlands in Southwest Florida

Coastal mangroves have the potential to improve the water quality of urban and rural runoff before it is discharged into adjacent coastal bays and oceans; but they also can be impaired by excessive pollutants from upstream. Nutrients (phosphorus and nitrogen), salinity, and other water quality parameters were measured in five mangrove tidal creeks in different hydrogeomorphic and urbanization settings during high and low tides over a calendar year of wet (June and August 2015) and dry (February and April 2016) seasons in the Greater Naples Bay area in Southwest Florida, USA. Nutrient concentrations (ave. ± std error) in the tidal creeks were 0.055 ± 0.008 mg-P/L for total phosphorus (TP) and 0.610 ± 0.020 mg-N/L for total nitrogen (TN), with an average N:P ratio of 11.4:1. Average wet season TP (0.075 ± 0.010 mg-P/L) was significantly higher than the dry season TP (0.033 ± 0.003 mg-P/L; p < 0.01, f = 15.17, f_crit = 3.89) and the average wet season TN (0.75 ± 0.03 mg-N/L) was significantly higher than dry season TN (0.52 ± 0.02 mg/L; p < 0.01, f = 64.14, f_crit = 3.89), suggesting that urban stormwater runoff is directly or indirectly affecting the nutrient conditions in these mangroves. Significant differences in nutrient concentrations between low tide and high tide were not found for either TP (p = 0.43, f = .63, f_crit = 3.88) or TN (p = 0.20, f = 1.66, f_crit = 3.89). These differences were confirmed by a PCA and cluster analyses, which found differences to be seasonal. We could not conclude from these results whether these five mangrove wetlands were sources nor sinks of nutrients based simply on the measurement of nutrient concentrations. But we illustrated that nutrient concentrations were indicators of the mangroves’ hydrogeomorphic settings, their tidal fluxes from Naples Bay, and the Bay's upstream watersheds, and less by direct urban runoff.     

人工湿地脱除富营养化水体氮磷的研究进展

水体中氮磷营养物质不断积累,部分藻类及水生生物的过度繁殖,导致了水体的富营养化。水体富营养化防治的关键是减小水中氮、磷的含量。人工湿地是一项新型的废水处理技术,近年来在脱除富营养化水体氮磷中获得广泛研究和应用。本文在简述脱氮除磷机理的基础上,较系统地阐述了影响人工湿地脱除氮磷的因素及工艺的在改善水体富营养化的研究进展,以便在构建人工湿地中对各项因素综合考虑及兼顾利用,提高人工湿地修复富营养化水体的综合效能。     

Ferricyanide reductase of rose plasma membranes is regulated by nitrogen supply

Summary The ability of suspension-cultured rose (Rosa damascena Mill. cv Gloire de Guilan) cells to reduce ferricyanide is decreased by 50% during an overnight incubation in a low-nutrient (1 mM CaCl₂, 0.1 mM KCl) solution. This loss is not observed when nitrate and/or glutamate is added to the low-nutrient medium, but it occurs in medium containing all the components needed for normal growth except nitrate plus glutamate. Thus, the cells possess both constitutive and inducible enzymes for the reduction of ferricyanide, and nitrate or glutamate is both necessary and sufficient to stimulate the production of the inducible enzyme.     

Reversible coupling of individual phycobiliprotein isoforms during state transitions in the cyanobacterium Trichodesmium analysed by single-cell fluorescence kinetic measurements

In the non-heterocyst, marine cyanobacterium Trichodesmium nitrogen fixation is confined to the photoperiod and occurs coevally with oxygenic photosynthesis although nitrogenase is irreversibly inactivated by oxygen. In previous studies it was found that regulation of photosynthesis for nitrogen fixation involves Mehler reaction and various activity states with reversible coupling of photosynthetic components. We now investigated these activity states in more detail. Spectrally resolved fluorescence kinetic measurements of single cells revealed that they were related to alternate uncoupling and coupling of phycobilisomes from and to the photosystems, changing the effective cross-section of PSII. Therefore, we isolated and purified the phycobiliproteins of Trichodesmium via ion exchange chromatography and recorded their UV/VIS absorption, fluorescence excitation and fluorescence emission spectra. After describing these spectra by mathematical equations via the Gauss-Peak-Spectra method, we used them to deconvolute the in vivo fluorescence spectra of Trichodesmium cells. This revealed that the contribution of different parts of the phycobilisome antenna to fluorescence quenching changed during the daily activity cycle, and that individual phycobiliproteins can be reversibly coupled to the photosystems, while the expression levels of these proteins did not change much during the daily activity cycle. Thus we propose that variable phycobilisome coupling plays a key role in the regulation of photosynthesis for nitrogen fixation in Trichodesmium.     

Evidence for increases in vegetation species richness across UK Environmental Change Network sites linked to changes in air pollution and weather patterns

We analysed trends in vegetation monitored at regular intervals over the past two decades (1993–2012) at the twelve terrestrial Environmental Change Network (ECN) sites. We sought to determine the extent to which flora had changed and link any such changes to potential environmental drivers. We observed significant increases in species richness, both at a whole network level, and when data were analysed within Broad Habitat groupings representing the open uplands, open lowlands and woodlands. We also found comparable increases in an indicator of vegetation response to soil pH, Ellenberg R. Species characteristic of less acid soils tended to show more consistent increases in frequency across sites relative to species with a known tolerance for strongly acidic soils. These changes are, therefore, broadly consistent with a response to increases in soil solution pH observed for the majority of ECN sites that, in turn, are likely to be driven by large reductions in acid deposition in recent decades. Increases in species richness in certain habitat groupings could also be linked to increased soil moisture availability in drier lowland sites that are likely to have been influenced by a trend towards wetter summers in recent years, and possibly also to a reduction in soil nitrogen availability in some upland locations. Changes in site management are also likely to have influenced trends at certain sites, particularly with respect to agricultural practices. Our results are therefore indicative of widescale responses to major regional-scale changes in air pollution and recent weather patterns, modified by local management effects. The relative consistency of management of ECN sites over time is atypical of much of the wider countryside and it is therefore not appropriate to scale up these observations to infer national scale trends. Nevertheless the results provide an important insight into processes that may be operating nationally. It will now be necessary to test for the ubiquity of these changes using appropriate broader spatial scale survey data.     

Cloning of the gene for phosphoenolpyruvate carboxylase from Azotobacter chroococcum, an enzyme important in aerobic nitrogen fixation

Summary Azotobacter chroococcum Fos 189 is a Tn1-induced mutant which, unlike the parent strain MCD1, does not fix nitrogen in air when provided with glucose or pyruvate as sole carbon sources. Fos 189 showed 5% of parental activity for phosphoenolpyruvate carboxylase though PEP synthetase activity was normal. The A. chroococcum phosphoenolpyruvate carboxylase (ppc) gene was isolated after complementation of an appropriate Escherichia coli mutant using a broad host range gene bank prepared from A. chroococcum genomic DNA. The gene was localised by transposon mutagenesis and subcloning on a minimum DNA fragment of 6.6 kb. Broad host range plasmids containing the A. chroococcum ppc gene complemented the mutation in Fos 189 thereby restoring aerotolerant nitrogen fixation.     

Can zinc influence nutrient resorption? A test with the drought-deciduous desert shrub Fouquieria splendens (ocotillo)

Paradoxically low nitrogen resorption efficiency in the drought-deciduous desert shrub Fouquieria splendens Engelm (ocotillo) triggered tests of the hypotheses that resorption is often low in this species and that resorption is influenced by zinc. Resorption efficiency and proficiency were measured in 1989 and 1994 at two sites in the Chihuahuan Desert in plants to which zinc, or zinc and nitrogen were added. Resorption of nitrogen, phosphorus, and zinc in unfertilized plants varied temporally and spatially, but was both efficient (66%, 49%, and 40%, respectively) and proficient (0.55%, 0.09%, and 9.4 μg g−1, respectively) as determined by comparison to worldwide resorption patterns in a wide variety of other species. Applications of zinc had no significant effect on the resorption of nitrogen and phosphorus, but did influence the resorption of zinc. Resorption of zinc was significantly less efficient in zinc-treated plants than controls at only one of the two sites in one of the 2 years, yet resorption of zinc was significantly less proficient in zinc-treated plants than controls in both years and at both sites. This pattern of zinc resorption adds insight into the continuing debate regarding the relationship between fertility and resorption because the data used to fuel the debate have almost exclusively described macronutrients, not trace metals. The high variability in resorption among individuals, sites, and years observed for F. splendens may well be an attribute of many desert-dwelling, drought-deciduous plants. When senescence is controlled primarily by water availability rather than photoperiod, especially in a landscape characterized by unpredictable amounts and timing of precipitation, high variability in associated processes such as resorption may be inevitable.     

Effects of nitrogen supply on growth, yield and yield components of safflower and sunflower

Safflower (Carthamus tinctorius L.) represents an important oil crop internationally and may have a certain production potential under low input conditions, particularly in organic farming systems, where the putatively low nutrient requirement would be an advantage. However, little is known about the nutrient requirements of safflower. This study was undertaken to determine the growth and yield response of safflower as compared to sunflower (Helianthus annuus L.) under different N supplies. Safflower and sunflower plants were grown in Mitscherlich pots containing equal volumes of sand, nutrient-poor limed soil, and perlite. Nitrogen supply was the same for both species (0.25, 0.5, 1.0, 1.5, and 2.0 g per pot) in the first year, but was raised for sunflower (0.5, 1.0, 2.0, 3.0, and 4.0 g per pot) in the second. Increased N supply enhanced plant growth and yield for both species. Growth and yield of safflower increased up to 1.0 g pot⁻¹, while the optimum for sunflower was 2.0 g pot⁻¹. Safflower out-yielded sunflower at low N supply, while at high N level the opposite occurred. Functional analysis according to Michaelis–Menten revealed that – in terms of yield formation – safflower is superior to sunflower under N-limited conditions. Safflower is generally more efficient than sunflower in concentrating N in their shoots. N concentration in the photosynthetically active youngest mature blade of both species exhibited the same functional relationship with the N supply, but safflower required a much lower leaf N concentration to produce optimal yield as compared to sunflower, indicating the higher efficiency of the former in terms of NUE. Yield components analysis revealed that in safflower, yield is tightly correlated with the number of capitula per plant and the mass per achene, both being strongly correlated, too. On the contrary, sunflower yield was merely determined by the number of achenes per capitulum, followed by the mass per achene. Path coefficient analysis showed that in safflower, the direct effects of the achene and leaf N content as well as the leaf dry matter on oil yield are small, and mediated principally via indirect effects on the number of achenes per capitulum, while for sunflower the number of achenes per capitulum exerts a strong direct effect. Dedicated to the late Prof. Dr. Burkhard Sattelmacher, who passed away on November 21, 2005.