Competitive effects of Phragmites australis on the endangered artesian spring endemic Eriocaulon carsonii

We investigated the relative importance of above- and below-ground competition by reeds (Phragmites australis (Cav.) Trin. ex Steud) on the growth rate of Eriocaulon carsonii F.Muell. subsp. carsonii, an endangered plant threatened by reeds on artesian springs in Australia. Soil-filled buckets containing E. carsonii were frequently watered to simulate artesian spring conditions and subject to three treatments: (1) no Phragmites (control), (2) Phragmites (ABG), and (3) Phragmites with shoots tied back (BG). After thirteen months, Phragmites mean below-ground biomasses had increased to c. 3 kg m⁻² and mean above-ground biomasses to c. 1 kg m⁻². After the same period, mean root biomass of E. carsonii plants was significantly lower in buckets subject to both Phragmites treatments compared with control plants, as was E. carsonii foliage area. Comparison of the two Phragmites treatments indicated that below-ground competition was the primary cause of this reduced growth in E. carsonii. The vulnerability of E. carsonii to competitive exclusion by P. australis is in part due to the highly synchronized phenologies of the two species.     

Nitrogen nutrition of Salvinia natans: Effects of inorganic nitrogen form on growth,morphology, nitrate reductase activity and uptake kinetics of ammonium and nitrate

In this study we assessed the growth, morphological responses, and N uptake kinetics of Salvinia natans when supplied with nitrogen as NO₃⁻, NH₄⁺, or both at equimolar concentrations (500 μM). Plants supplied with only NO₃⁻ had lower growth rates (0.17 ± 0.01 g g⁻¹ d⁻¹), shorter roots, smaller leaves with less chlorophyll than plants supplied with NH₄⁺ alone or in combination with NO₃⁻ (RGR = 0.28 ± 0.01 g g⁻¹ d⁻¹). Ammonium was the preferred form of N taken up. The maximal rate of NH₄⁺ uptake (V_max) was 6–14 times higher than the maximal uptake rate of NO₃⁻ and the minimum concentration for uptake (C_min) was lower for NH₄⁺ than for NO₃⁻. Plants supplied with NO₃⁻ had elevated nitrate reductase activity (NRA) particularly in the roots showing that NO₃⁻ was primarily reduced in the roots, but NRA levels were generally low (<4 μmol NO₂⁻ g⁻¹ DW h⁻¹). Under natural growth conditions NH₄⁺ is probably the main N source for S. natans, but plants probably also exploit NO₃⁻ when NH₄⁺ concentrations are low. This is suggested based on the observation that the plants maintain high NRA in the roots at relatively high NH₄⁺ levels in the water, even though the uptake capacity for NO₃⁻ is reduced under these conditions.     

免耕稻田氮肥运筹对土壤NH3挥发及氮肥利用率的影响

通过大田试验,设置5种不同的施肥比例(基肥:分蘖肥:拔节肥:穗肥-2:2:3:3(R1)、3:2:2:3(R2)、4:2:2:2(R3)、4:3:1:2(R4)与0:0:0:0(CK)),研究氮肥运筹对稻田NH₃挥发和氮肥利用率的影响。结果表明,(1)相对于不施肥,施肥显著提高了稻田NH₃挥发量。氮肥施用后,NH₃挥发损失量占施氮量的6.2%-8.5%,其中,以分蘖期NH₃挥发损失量最大,齐穗期次之,苗期和拔节期最小。施肥处理间,处理R1稻田累积NH₃挥发量最小,显著低于其它施肥处理,比处理R2、R3和R4分别低9.1%(P<0.05)、10.9%(P<0.05)和17.7%(P<0.05)。(2)相关分析表明,田面水NH₄⁺、pH值和土壤NH₄⁺和pH值均与稻田土壤NH₃挥发通量呈显著或者极显著相关;(3)处理R1水稻氮肥利用率相对于处理R2、R3和R4增加了28.4%(P<0.05)、55.4%(P<0.05)和74.9%(P<0.05)。研究表明,氮肥后移能有效降低免耕稻田NH₃挥发,提高水稻的氮肥利用率。     

Treatment of industrial wastewater with two-stage constructed wetlands planted with Typha latifolia and Phragmites australis

Industrial wastewater treatment comprises several processes to fulfill the discharge permits or to enable the reuse of wastewater. For tannery wastewater, constructed wetlands (CWs) may be an interesting treatment option. Two-stage series of horizontal subsurface flow CWs with Phragmites australis (UP series) and Typha latifolia (UT series) provided high removal of organics from tannery wastewater, up to 88% of biochemical oxygen demand (BOD₅) (from an inlet of 420 to 1000 mg L⁻¹) and 92% of chemical oxygen demand (COD) (from an inlet of 808 to 2449 mg L⁻¹), and of other contaminants, such as nitrogen, operating at hydraulic retention times of 2, 5 and 7 days. No significant (P < 0.05) differences in performance were found between both the series. Overall mass removals of up to 1294 kg COD ha⁻¹ d⁻¹ and 529 kg BOD₅ ha⁻¹ d⁻¹ were achieved for a loading ranging from 242 to 1925 kg COD ha⁻¹ d⁻¹ and from 126 to 900 kg BOD₅ ha⁻¹ d⁻¹. Plants were resilient to the conditions imposed, however P. australis exceeded T. latifolia in terms of propagation.     

Genetic diversity patterns in Phragmites australis at the population,regional and continental scales

Genetic diversity, population structure and interrelationships were investigated in eight populations of the common reed, Phragmites australis, in the Po Plain, Italy, by means of amplified fragments length polymorphisms (AFLPs) and random amplified polymorphic DNAs (RAPDs). Patterns of genetic diversity were analysed in relation to size, age and degree of human impact in the wetlands and compared with that of a distant population in Romania. Genetic distances between Po Plain clones and geographically distant clones were measured to determine the geographical extent of the gene pool.     

Evaluation of Phragmites australis (Cav.) Trin. evapotranspiration in Northern and Southern Italy

The design, operation, pollutant removal as well as hydraulic modeling of wetland systems for wastewater treatment can be improved by better understanding and simulating the evapotranspiration process. To this purpose, two experiments were carried out in Northern (Veneto region) and Southern (Sicily region) Italy to measure evapotranspiration (ET) and determine the crop coefficient of Phragmites australis (Cav.) Trin. using the FAO 56 approach. The experimental set-up consisted of a combination of vegetated and unvegetated plastic tanks (Veneto) or pilot sub-surface flow beds (Sicily). The ET values were obtained by measuring the amount of water needed to restore the initial volume in the tanks and in the beds after a certain period. All the needed climatic variables were measured and taken into account in the ET measurements. In the two experimental sites cumulative reference evapotranspiration (ET₀) was similar to the cumulative ET measured in the control tanks and beds (without vegetation, ET_con), while ET measured for P. australis (ET_phr) was significantly higher, underlining the strong effect of vegetation. From June 2009 to September 2009 the cumulative ET₀, ET_con and ET_phr in Veneto were 455, 424 and 3048 mm, in Sicily 653, 556 and 3899 mm, respectively. The plant coefficient trend of P. australis (K_p) estimated in Veneto was similar to that in Sicily, suggesting that the role of the plant in dispersing water is similar under different environmental conditions. Additional measurements made in the Veneto plant showed that K_p assumes different patterns and values in relation to plant age and growth stage. These results highlight the importance of the plants in regulating water losses from a wetland system, above all from small-scale constructed wetlands where the effect of the advection in ET rates is evident.     

Cultivable bacterial composition and BIOLOG catabolic diversity of biofilm communities developed on Phragmites australis

Biofilm samples formed on submerged young and old stems of reed, Phragmites australis (Cav.) Trin ex Steudel were taken during summer at different sites of Lake Velencei, Hungary. BIOLOG GN microplates were used to analyze the patterns of sole carbon source utilizations by microbial communities. From the carbon sources, carbohydrates and amino acids were preferred by all microbial communities. In the case of the old reed stem samples, higher number of carbohydrates, carboxylic acids and polymers were used than in young samples. Biofilm bacterial communities from the old reed samples of the nature conservation area of the lake used the highest number of (≥50% of the available) substrates. In principal component analysis (PCA), the metabolic potential of the microbial communities from the middle open water region of the lake showed the smallest variability. The variability within metabolic potential of the reed stem microbial communities from a given sampling site was the largest in the case of samples originating from the western, reed-covered nature conservation area. A total of 251 bacterial isolates obtained after serial dilutions and plating onto different media were characterized by traditional phenotypic tests. The strains showed high activities mainly in the hydrolysis of certain biopolymers (gelatine and casein). PCA was used to evaluate the phenotypic variability of strain groups of different sampling sites. The two open water regions were similar to each other, and separated from the western reed covered part of the lake. Similarly to the BIOLOG community-level physiological profiles, strain groups of the young and old reed stem samples originating from the nature conservation area had the largest metabolic potential. On the basis of 16S rDNA sequence analysis, 23 representative strains with different ARDRA patterns were identified. The cultivation-based investigations of bacterial diversity showed characteristic differences in the number of identified taxa in connection with the sampling sites. No characteristic differences could be observed according to medium or sample type (young, first year and more than 1-year old stems) among the identified species. 16S rDNA sequence comparisons resulted in the identification of the genera Aureobacterium, Arthrobacter, Kocuria, Microbacterium, Micrococcus, Rhodococcus, Bacillus, Marinibacillus, Rhodobacter, Defluvibacter, Pseudomonas, Klebsiella, Serratia and Aeromonas. The results of the cultivation-based and BIOLOG investigations revealed characteristic differences in the bacterial community composition and activities of the open water region and the reed covered nature conservation part of the lake.     

The influence of nitrogen concentration and ammonium/nitrate ratio on N-uptake,mineral composition and yield of citrus

In short-term water culture experiments with different ¹⁵N labeled ammonium or nitrate concentrations, citrus seedlings absorbed NH₄ ⁺ at a higher rate than NO₃ ^–. Maximum NO₃ ^– uptake by the whole plant occurred at 120 mg L^–1 NO₃ ^–-N, whereas NH₄ ⁺ absorption was saturated at 240 mg L^–1 NH₄ ⁺-N. ¹⁵NH₄ ⁺ accumulated in roots and to a lesser degree in both leaves and stems. However, ¹⁵NO₃ ^– was mostly partitioned between leaves and roots.Adding increasing amounts of unlabeled NH₄ ⁺ (15–60 mg L^–1 N) to nutrient solutions containing 120 mg L^–1 N as ¹⁵N labeled nitrate reduced ¹⁵NO₃ ^– uptake. Maximum inhibition of ¹⁵NO₃ ^– uptake was about 55% at 2.14 mM NH₄ ⁺ (30 mg L^–1 NH₄ ⁺-N) and it did not increase any further at higher NH₄ ⁺ proportions.In a long-term experiment, the effects of concentration and source of added N (NO₃ ^– or NH₄ ⁺) on nutrient concentrations in leaves from plants grown in sand were evaluated. Leaf concentration of N, P, Mg, Fe and Cu were increased by NH₄ ⁺ versus NO₃ ^– nutrition, whereas the reverse was true for Ca, K, Zn and Mn.The effects of different NO₃ ^–-N:NH₄ ⁺-N ratios (100:0, 75:25, 50:50, 25:75 and 0:100) at 120 mg L^–1 total N on leaf nutrient concentrations, fruit yield and fruit characteristics were investigated in another long-term experiment with plants grown in sand cultures. Nitrogen concentrations in leaves were highest when plants were provided with either NO₃ ^– or NH₄ ⁺ as a sole source of N. Lowest N concentration in leaves was found with a 75:25 NO₃ ^–-N/NH₄ ⁺-N ratio. With increasing proportions of NH₄ ⁺ in the N supply, leaf nutrients such as P, Mg, Fe and Cu increased, whereas Ca, K, Mn and Zn decreased. Yield in number of fruits per tree was increased significantly by supplying all N as NH₄ ⁺, although fruit weight was reduced. The number of fruits per tree was lowest with the 75:25 NO₃ ^–-N:NH₄ ⁺-N ratio, but in this treatment fruits reached their highest weight. Rind thickness, juice acidity, and colour index of fruits decreased with increasing NH₄ ⁺ in the N supply, whereas the % pulp and maturity index increased. Percent of juice in fruits and total soluble solids were only slightly affected by NO₃ ^–:NH₄ ⁺ ratio.     

Oral supplementation with a combination of l-citrulline and l-arginine rapidly increases plasma l-arginine concentration and enhances NO bioavailability

Background

Chronic supplementation with l-citrulline plus l-arginine has been shown to exhibit anti-atherosclerotic effects. However, the short-term action of this combination on the nitric oxide (NO)–cGMP pathway remains to be elucidated. The objective of the present study was to investigate the acute effects of a combination of oral l-citrulline and l-arginine on plasma l-arginine and NO levels, as well as on blood circulation.

Methods

Rats or New Zealand white rabbits were treated orally with l-citrulline, or l-arginine, or a combination of each at half dosage. Following supplementation, plasma levels of l-arginine, NO_x, cGMP and changes in blood circulation were determined sequentially.

Results

l-Citrulline plus l-arginine supplementation caused a more rapid increase in plasma l-arginine levels and marked enhancement of NO bioavailability, including plasma cGMP concentrations, than with dosage with the single amino acids. Blood flow in the central ear artery in rabbits was also significantly increased by l-citrulline plus l-arginine administration as compared with the control.

Conclusion

Our data show for the first time that a combination of oral l-citrulline and l-arginine effectively and rapidly augments NO-dependent responses at the acute stage. This approach may have clinical utility for the regulation of cardiovascular function in humans.     

Spatial dynamics and morphological plasticity of common reed (Phragmites australis) and cattails (Typha sp.) in freshwater marshes and roadside ditches

Over the last decades, the abundance of common reed has significantly increased in freshwater wetlands of eastern North America, and stands of this species are now commonly alternating with stands of cattails. Since these species share many characteristics, the contact zone between common reed and cattail stands may witness strong interspecific interactions. We surveyed stand dynamics in roadside ditches and freshwater marshes at these contact zones over three years, and we examined the morphological plasticity in response to neighbors. Results indicate that common reed is clearly gaining ground over time, while cattails stands are retreating. We also found annual variability in the spatial dynamics, suggesting that other factors, such as the effect of weather conditions on water level, may affect population processes. Interspecific interactions had a detrimental effect on both common reed and cattail biomass. However, common reed showed morphological plasticity in shoot height, number of nodes, and internodes length, while cattails did not. Our observations suggest that common reed has a net competitive advantage over cattails in roadside ditches and freshwater marshes.     

Synergistic impact of water level fluctuation and invasion of Glyceria on Typha in a freshwater marsh of Lake Ontario

The effects of multiple stressors on the native Typha marsh community (mainly Typha latifolia) were examined using historical records of water levels, human census population, and field vegetation maps. Percent cover of the major plant species was estimated in a GIS, and the percent cover of Typha was related to changes in water level, human population growth, and percent cover of exotic Glyceria maxima and invasive Phragmites australis. Water level fluctuation was the major natural disturbance and it alone accounted for 88% of the variation in Typha. After partitioning out the effect of water level, both human population growth and the presence of exotic species were still significantly related to the decline of native Typha. We suggest that multiple stressors interact with each other to influence changes in native Typha community and cause greater detrimental impact. An important implication of our results is that projected water level decline due to climate change may not necessarily favor the restoration of a desirable native marsh because of the presence of other disturbances such as exotic and invasive species and altered nutrient regime.     

Effects of macro elements and nitrogen source on adventitious root growth and ginsenoside production in ginseng (Panax ginseng C. A. Meyer)

We investigated the effects on ginseng adventitious root growth and ginsenoside production when macro-element concentrations and nitrogen source were manipulated in the culture media. Biomass growth was greatest in the medium supplemented with 0.5-strength NH₄PO₃, whereas ginsenoside accumulation was highest (9.90 mg g^-1 DW) in the absence of NH₄PO₃. At levels of 1.0-strength KNO₃, root growth was maximum, but a 2.0 strength of KNO₃ led to the greatest ginsenoside content (9.85 mg g^-l). High concentrations of MgSO₄ were most favorable for both root growth and ginsenoside accumulation (up to 8.89 mg g^-1 DW). Root growth and ginsenoside content also increased in proportion to the concentration of CaCI₂ in the medium, with the greatest accumulation of ginsenoside (8.91 mg g^-1 DW) occurring at a 2.0 strength. The NH₄/NO₃ ^-- ratio also influenced adventitious root growth and ginsenoside production; both parameters were greater when the NO₃ ^- concentration was higher than that of NH₄ ⁺. Maximum root growth was achieved at an NH₄ ⁺/NO₃ ^- ratio of 7.19/18.50, while ginsenoside production was greatest (83.37 mg L^-1) when NO₃ ^- was used as the sole N source.     

Nitrate uptake and storage in the seaweed Ulva rigida C. Agardh in relation to nitrate availability and thallus nitrate content in a eutrophic coastal lagoon (Sacca di Goro, Po River Delta, Italy)

The seasonal cycle of biomass and tissue composition of Ulva rigida C. Agardh, in relation to nitrogen availability in the water column, was studied in 1991-1992 in the Sacca di Goro, a highly eutrophic lagoon in the Po River Delta (Italy). Nitrate uptake rates and storage capacity were also determined in laboratory experiments. The seasonal growth of U. rigida was related to the seasonal trend of nitrogen concentration in the water column. U. rigida biomass increased exponentially during spring and attained peaks of about 300-400 g dry mass (DM) m⁻² in June. As biomass increased, U. rigida depleted nitrate in the water column. Thallus nitrate reserves also declined from 100 μmol N (g DM)⁻¹ to almost undetectable levels, and total thallus nitrogen declined from 4% to 2.5% DM and 1.25% DM in 1991 and 1992, respectively. During summer, U. rigida decomposition increased, and organic nitrogen concentrations in the water column increased. The uptake experiments demonstrated an inverse relationship between thallus nitrate content and nitrate uptake rates. A modified Michaelis-Menten equation that accounts for thallus nitrate fit the uptake data well. U. rigida can accumulate up to about 400-500 μmol nitrate (g DM)⁻¹ in cellular reserves. U. rigida in the Sacca di Goro has higher K_m and lower V_max/K_m ratios for nitrate uptake than other chlorophycean species, indicating a low efficiency of uptake at low nitrate concentrations. This low uptake efficiency, and the ability to exploit N availability by storing cellular nitrate pools in excess of immediate growth needs, may represent a physiological response to an eutrophic environment where nitrate is in large supply for most of the year.     

Ecophysiological responses of the euhalophyte Suaeda salsa to the interactive effects of salinity and nitrate availability

Effects of salinity and nitrate nitrogen (NO₃⁻-N) on ion accumulation and chlorophyll fluorescence were monitored for two populations of Suaeda salsa grown from seeds in a greenhouse experiment. One population inhabits the intertidal zone and the other occurs on inland saline soils. Ion contents in soils and in leaves of the two populations were also investigated in field. In the greenhouse, seedlings were exposed to a NaCl concentration of 0.6 and 35.1 ppt, with 0.1 or 5 mM NO₃⁻-N treatments for 20 days. The contents of Na⁺ and Cl⁻ were higher, but NO₃⁻ was lower in soils of the intertidal zone than at the inland site. In the field, ion concentrations and the estimated contribution of these ions to osmotic potential in leaves showed no difference between the two populations, except that the estimated contribution of Na⁺ to osmotic potential in leaves of the intertidal population was lower than that in the inland population. In the greenhouse, in contrast, the concentration of Cl⁻ was lower, but NO₃⁻ concentration and the estimated contribution of NO₃⁻ to osmotic potential were higher, in the leaves of plants from the intertidal zone. Salinity had no effect on the maximal efficiency of PSII photochemistry (Fv/Fm) and the actual PSII efficiency (ΦPSII). The results indicated that S. salsa from the intertidal zone was better able to regulate Cl⁻ to a lower level, and accumulate NO₃⁻ even with low soil NO₃⁻ concentrations. Tolerance of the PSII machinery to high salinity stress may be an important characteristic for the studied species supporting growth in highly saline environments.     

Reciprocal regulation between AtNRT2.1 and AtAMT1.1 expression and the kinetics of NH(4)(+) and NO(3)(-) influxes

Our results show that AtNRT2.1 expression has a positive effect on the NH₄⁺ ion influx, mediated by the HATS, as also occurs with AtAMT1.1 expression on the NO₃⁻ ion influx. AtNRT2.1 expression plays a key role in the regulation of AtAMT1.1 expression and in the NH₄⁺ ion influx, differentiating the nitrogen source, and particularly, the lack of it. Nitrogen starvation produces a compensatory effect by AtAMT1.1 when there is an absence of the AtNRT2.1 gene. Our results also show that, in the atnrt2 mutant lacking both AtNRT2.1 and AtNRT2.2, gene functions present different kinetic parameters on the NH₄⁺ ion influx mediated by the HATS, according to the source and availability of nitrogen. Finally, the absence of AMT1.1 also produces changes in the kinetic parameters of the NO₃⁻ influx, showing different V_max values depending on the source of nitrogen available.     

Growth rates of baldcypress (Taxodium distichum) seedlings in a treated effluent assimilation marsh

Wetlands have proven effective at improving water quality of treated wastewater effluent, which in turn promotes increased primary productivity and vertical accretion. Baldcypress (Taxodium distichum) seedlings grown under different conditions (bare root and potted) were planted in four subunits of an effluent assimilation marsh and a control marsh in southeast Louisiana, USA, and basal diameter growth was monitored over one growing season. Mean basal diameter growth for seedlings in the assimilation subunits ranged from 16.1 (±1.4) mm to 9.5 (±0.9) mm, whereas growth for seedlings planted in the control marsh was 6.4 (±0.9) mm. Seedlings planted nearest the outfall experienced greater basal diameter growth (18.1 ± 2.6) compared to those planted 700 m away (8.0 ± 0.9), with growth generally decreasing with distance. Potted seedlings experienced greater growth (19.1 ± 1.0 and 20.6 ± 1.0 for five-month-olds and ten-month olds, respectively) than bare root seedlings (4.6 ± 0.6 and 4.0 ± 0.4 for one-year-olds and two-year olds, respectively). Planting assimilation marshes with baldcypress seedlings can be an effective restoration tool for coastal Louisiana, which will provide hurricane protection and improved surface water quality. Wastewater treatment wetlands may offer an effective tool for restoring coastal baldcypress (T. distichum)-water tupelo (Nyssa aquatic) swamps in Louisiana.     

应用15N示踪研究欧美杨对PM2.5无机成分NH4+和NO3-的吸收与分配

通过气溶胶发生系统模拟PM2.5颗粒的发生,运用15N示踪技术研究了欧美杨107(Populus euramericana Neva.)对PM2.5中水溶性无机成分NH+4和NO-3的吸收与分配规律。结果表明,欧美杨能够有效吸收PM2.5中的NH+4和NO-3。轻度和重度污染下,欧美杨叶片对NH+4和NO-3的吸收速率均于处理后第1天达到峰值,之后,轻度污染下对NH+4和NO-3的吸收速率迅速降低以后趋于稳定,而重度污染下对NH+4和NO-3的吸收速率缓慢下降至趋于稳定。轻度污染下的欧美杨叶片的15N含量在处理后第1天达到峰值,15N(NH+4)的含量为0.11 mg/g,干重,15N(NO-3)的为0.14 mg/g,干重,之后15N含量迅速下降至趋于稳定。重度污染下的叶片15N含量在处理第1天迅速增长,之后缓慢增长至处理后第7天达到最高值,15N(NH+4)的含量为0.11 mg/g,干重,15N(NO-3)的为0.13 mg/g,干重。处理7 d后,欧美杨不同组织器官吸收或通过再分配获取的15N含量存在差异。轻度污染下,细根对NH+4和NO-3的吸收量最高,树皮、叶柄、叶片次之,髓最低。而重度污染下,叶片对NH+4和NO-3的吸收量最高,细根、叶柄、树皮次之,髓最低。欧美杨各组织器官中NH+4和NO-3的含量均表现为重度污染大于轻度污染,且两种污染程度下的欧美杨各组织器官对NO-3的吸收均大于对NH+4的吸收。重度污染下,欧美杨茎木质部对15N(NH+4和NO-3)的吸收征调能力(Ndff,Nitrogen derived from fertilizer)最大,其次为髓,叶片最小;欧美杨各组织器官中的15N分配率表现为叶片细根叶柄树皮粗根茎木质部髓。研究结果对进一步揭示植物吸收PM2.5的机制及有效利用植物降低颗粒物污染、净化环境提供了重要的科学理论依据。