Plant growth, community structure, and nutrient removal in monoculture and mixed constructed wetlands

The aim of this study was to compare the growth, community structure, and nutrient removal rates between monoculture and mixed wetlands, based on the hypothesis that it depends on the plant species used in the wetlands as to whether monoculture or mixed wetland is superior in plant growth and nutrient removal. Pilot-scale monoculture and mixed constructed wetlands were studied over 4 years. The monoculture wetland had a community height similar to the mixed wetland during the early years but a significantly lower height than the mixed wetland (P < 0.05) during the last year. The mixed wetland also displayed a higher plant density than the monoculture wetland (P < 0.05). The leaf area index in the monoculture wetland was significantly higher in the first year (P < 0.05) and significantly lower in the later years (P < 0.05) than that in the mixed wetland. The monoculture wetland had a similar vertical distribution of below-ground biomass over 4 years, while the mixed wetland showed a significant change in vertical distribution of below-ground biomass in the last 2 years. The monoculture wetland had a larger (P < 0.05) above-ground biomass and a similar leaf biomass in the first year, and a smaller above-ground biomass (P < 0.05) and a smaller leaf biomass (P < 0.05) than the mixed wetland during the latter 2 years. The amount of standing dead mass was smaller in the mixed wetland than in the monoculture wetland (P < 0.05). The mixed wetland exhibited a significantly lower NH₄-N removal rate in the first year (P < 0.05), and significantly higher NH₄-N removal rate in the last year, when compared to the monoculture wetland (P < 0.05). The study indicated that species competition and stubble growth resulted in significant differences between monoculture and mixed constructed wetlands in plant growth, community structure, and nutrient removal rates.     

Contaminant Removal of Domestic Wastewater by Constructed Wetlands： Effects of Plant Species

A comparative study of the efficiency of contaminant removal between five emergent plant species and between vegetated and unvegetated wetlands was conducted in small-scale （2.0 m×1.0 m×0.7 m, lengthxwidthxdepth） constructed wetlands for domestic wastewater treatment in order to evaluate the decontaminated effects of different wetland plants. There was generally a significant difference in the removal of total nitrogen （TN） and total phosphorus （TP）, but no significant difference in the removal of organic matter between vegetated and unvegetated wetlands. Wetlands planted with Canna indica Linn., Pennisetum purpureum Schum., and Phragmites communis Trin. had generally higher removal rates for TN and TP than wetlands planted with other species. Plant growth and fine root （root diameter ≤ 3 mm） biomass were related to removal efficiency. Fine root biomass rather than the mass of the entire root system played an important role in wastewater treatment. Removal efficiency varied with season and plant growth. Wetlands vegetated by P. purpureum significantly outperformed wetlands with other plants in May and June, whereas wetlands vegetated by P. communis and C. indica demonstrated higher removal efficiency from August to December. These findings suggest that abundance of fine roots is an important factor to consider in selecting for highly effective wetland plants. It also suggested that a plant community consisting of multiple plant species with different seasonal growth patterns and root characteristics may be able to enhance wetland performance.     

Effects of water level fluctuation on radial oxygen loss,root porosity,and nitrogen removal in subsurface vertical flow wetland mesocosms

Laboratory experiments were conducted to investigate the effects of water level fluctuation on plant radial oxygen loss (ROL), root porosity, plant growth performance, and nitrogen dynamics in vertical subsurface flow wetland mesocosms. Four types of mesocosms were used: control with static water level, control with fluctuating water level, static water level with plants, and fluctuating water level with plants. Typha orientalis, an emergent macrophyte, was used in this study. Changes of ROL, root porosity, and plant biomass were measured every six weeks. Shoot height and density of plants were also observed. Every two weeks, the nitrogen removal efficiency of the four systems was monitored. Maximum ROL values under static and fluctuating conditions were 7.58 and 2.73 μmol/g DW/h, respectively. The porosity values of roots under static and fluctuating conditions ranged between 33–47% and 30–37%, respectively. Average removal efficiency of both total nitrogen (TN) and ammonium nitrogen (NH₄-N) in the fluctuating condition with plants was about 65%, and nitrate nitrogen removal in the static condition with plants was about 75%. Although the water level fluctuation caused a considerable reduction in ROL and root porosity, it clearly produced a significant improvement in TN and NH₄-N removal.     

Plant growth and nutrient removal in constructed monoculture and mixed wetlands related to stubble attributes

The aim of this study is to test the hypothesis that it depends on plant species used in the wetlands and their stubble growth attributes, as to whether monoculture or mixed wetland is superior in plant growth and nutrient removal. Monoculture and mixed wetland microcosms of five wetland plant species were studied. Significant differences in growth and aboveground biomass were found in the monoculture wetlands. Species that showed faster growth and larger biomass in monoculture wetland were also dominant in the mixed wetland. The mixed wetland exhibited similar biomass and root growth to the averages of five monocultures. ANOVA showed that there were very significant differences among the wetlands in removal rates of all the nutrients studied except nitrate nitrogen (NO₃-N) and chemical oxygen demand (COD). The removal rates from the mixed wetland were generally comparable to the highest removal rates from the monocultures. The species exhibited different stubble growth attributes, with some species showing increasing stubble growth and removal rates, while other species showing decreasing stubble growth and removal rates. The results indicated that in both monocultures and mixed constructed wetlands, growth and nutrient removal rates depended on plant species, and attributes of plant stubble growth affected overall growth and nutrient removal capabilities.     

Relationships between plant photosynthesis,radial oxygen loss and nutrient removal in constructed wetland microcosms

The objective of this study was to investigate the relationships between root radial oxygen loss (ROL), photosynthesis, and nutrient removal, based on the hypothesis that ROL is primarily an active process which is affected positively by photosynthesis, and is correlated positively with nutrient removal. Four common wetland plants were studied in small-scale monoculture wetlands. Higher ROL coincided with faster growth among the four monocultures. Significant correlation between ROL and photosynthetic rate existed in Cyperus flabelliformis wetland (P < 0.01). Both ROL and photosynthesis represented close correlations with nutrient removal rates in all four monocultures. Significant differences in ROL, photosynthetic rate, removal rates of NH₄⁺, and soluble reactive phosphorus (SRP) were found among the four species. ROL and photosynthetic rates showed single-peak daily and seasonal patterns, with maximum daily values around noon, and with maximum yearly values in summer or autumn for the four monocultures. The results suggest that the ROL of wetland plants is related to active physiological processes. Both ROL and photosynthetic rate are indices which can be used to identify wetland plants with a higher nutrient removal capacity.     

蚯蚓对湿地植物光合特性及净化污水能力的影响

以香蒲、芦苇和美人蕉为研究对象,并以土壤+沙子+有机质混合物为供试基质模拟人工湿地处理污水,采用向基质中加入蚯蚓与未加入蚯蚓2种处理。研究加入蚯蚓后,香蒲、芦苇和美人蕉光合速率、蒸腾速率、SPAD值和水分蒸发、蒸腾量的变化及其对净化污水能力的影响。结果表明:与未加入蚯蚓相比,加入蚯蚓后,香蒲、芦苇和美人蕉的净光合速率、蒸腾速率、SPAD值和水分蒸发、蒸腾量均增加,其中芦苇的净光合速率、蒸腾速率和水分蒸发、蒸腾量增加达到显著水平(P <0.05),而香蒲的水分蒸发、蒸腾量增加也达到显著水平(P <0.05);加入蚯蚓后,香蒲、芦苇和美人蕉对COD_Mn、NH₄⁺-N、NO₃^--N、TN和TP的去除率均增加,且香蒲和芦苇对COD_Mn的去除率显著增加 (P <0.05)。加入蚯蚓后,香蒲、芦苇和美人蕉的SPAD值均增加,说明蚯蚓能提高湿地植物对氮的吸收,增加植株中的氮含量,促进湿地植物的光合速率和蒸腾速率从而提高对污水的净化能力。     

An oxygen-mediated positive feedback between elevated carbon dioxide and soil organic matter decomposition in a simulated anaerobic wetland

We examined the effects of elevated atmospheric CO₂ on soil carbon decomposition in an experimental anaerobic wetland system. Pots containing either bare C₄‐derived soil or the C₃ sedge Scirpus olneyi planted in C₄‐derived soil were incubated in greenhouse chambers at either ambient or twice‐ambient atmospheric CO₂. We measured CO₂ flux from each pot, quantified soil organic matter (SOM) mineralization using δ¹³C, and determined root and shoot biomass. SOM mineralization increased in response to elevated CO₂ by 83–218% (P<0.0001). In addition, soil redox potential was significantly and positively correlated with root biomass (P= 0.003). Our results (1) show that there is a positive feedback between elevated atmospheric CO₂ concentrations and wetland SOM decomposition and (2) suggest that this process is mediated by the release of oxygen from the roots of wetland plants. Because this feedback may occur in any wetland system, including peatlands, these results suggest a limitation on the size of the carbon sink presented by anaerobic wetland soils in a future elevated‐CO₂ atmosphere.     

Ecological indicators of nutrient enrichment, freshwater wetlands, Midwestern United States (U.S.)

Vegetation and soil indicators of nutrient condition were evaluated in 30 wetlands, 10 each in 3 Nutrient Ecoregions (NE) (VI-Corn Belt and Northern Great Plains, VII-Mostly Glaciated Dairy Region, IX-Temperate Forested Plains and Hills) of the Midwestern United States (U.S.) to identify robust indicators for assessment of wetland nutrient enrichment and eutrophication. Nutrient condition was characterized by surface water inorganic N (NH₄-N, NO₃-N) and P (PO₄-P) concentrations measured seasonally for 1 year, plant available and total soil N and P, and aboveground biomass, leaf N and P and species composition of emergent vegetation measured at the end of the growing season. Aboveground biomass, nutrient uptake and species composition were positively related to surface water NH₄-N (N) but not to PO₄-P or NO₃-N. Aboveground biomass and biomass of aggressive species, Typha spp. plus Phalaris arundinacea, increased asymptotically with surface water N whereas leaf P, senesced leaf N and senesced leaf P increased linearly with N. And, species richness declined with surface water N. Soil total P was positively related to surface water PO₄-P but it was the only soil indicator related to wetland nutrient condition. Individual regressions for each NE generally were superior to a single regression for all NEs. In NE VI (Corn Belt), few indicators were related to surface water N because of the high degree of anthropogenic disturbance (85% of the landscape is cleared) as compared to NEs VII and IX (24–53% cleared). Of the indicators evaluated, stem height (r² = 0.42 for all NEs, r² = 0.56 for NE VII + IX) and percent biomass of aggressive species, Typha spp. plus Phalaris, (r² = 0.46 for all NEs, r² = 0.54 for NE VII + IX), were the best predictors of wetland nutrient enrichment. Vegetation-based indicators are a promising tool for assessment of wetland nutrient condition but they may not be effective in NEs where landscape disturbance is intense and widespread.     

Nitrogen and phosphorus removal from wastewater by subsurface wetlands planted with Iris pseudacorus

Subsurface horizontal flow constructed wetlands are being evaluated for nitrogen (N) and phosphorus (P) removal from wastewater in this study through different gravel sizes, plant densities (Iris pseudacorus), effects of retention times (1 to 10 days) on N and P removal in continuously fed gravel wetland. The inlet and outlet samples were analyzed for TKN, NH₄-N, and NO₃-N, as standard methods. The planted wetland reactor with fine (SG) and coarse (BG) gravels removed 49.4% and 31.4% TKN, respectively, while unplanted reactors removed 43.4% and 26.8% TKN. Also, the efficiencies for NH₄-N were 36.7–43% and 21.6–25.4% for SG and BG planted reactors, respectively. The efficiencies for NO₃-N were 53.5–62.5% and 21.6–25.4% for SG and BG planted reactors, respectively. Roles of plants in SG reactors for O-PO₄ were 5–12% and 3–8% in BG. Also, the roles of plants in the reactors for TP were 9% and 7.4%. The minimum effective detention time for the removal of NO₃-N was 4–5 days. The subsurface constructed wetlands planted with I. pseudacorus can be an appropriate alternative in wastewater treatment natural system in small communities.     

Effect of plant root symbionts on performance of native woody species in competition with an invasive grass in multispecies microcosms

The majority of terrestrial plants form mutualistic associations with arbuscular mycorrhizal fungi (AMF) and rhizobia (i.e., nitrogen‐fixing bacteria). Understanding these associations has important implications for ecological theory and for restoration practice. Here, we tested whether the presence of AMF and rhizobia influences the performance of native woody plants invaded by a non‐native grass in experimental microcosms. We planted eight plant species (i.e., Acacia acuminata, A. microbotrya, Eucalyptus loxophleba subsp. loxophleba, E. astringens, Calothamnus quadrifidus, Callistemon phoeniceus, Hakea lissocarpha and H. prostrata) in microcosms of field‐conditioned soil with and without addition of AMF and rhizobia in a fully factorial experimental design. After seedling establishment, we seeded half the microcosms with an invasive grass Bromus diandrus. We measured shoot and root biomass of native plants and Bromus, and on roots, the percentage colonization by AMF, number of rhizobia‐forming nodules and number of proteaceous root clusters. We found no effect of plant root symbionts or Bromus addition on performance of myrtaceous, and as predicted, proteaceous species as they rely little or not at all on AMF and rhizobia. Soil treatments with AMF and rhizobia had a strong positive effect (i.e., larger biomass) on native legumes (A. microbotrya and A. acuminata). However, the beneficial effect of root symbionts on legumes became negative (i.e., lower biomass and less nodules) if Bromus was present, especially for one legume, i.e., A. acuminata, suggesting a disruptive effect of the invader on the mutualism. We also found a stimulating effect of Bromus on root nodule production in A. microbotrya and AMF colonization in A. acuminata which could be indicative of legumes’ increased resource acquisition requirement, i.e., for nitrogen and phosphorus, respectively, in response to the Bromus addition. We have demonstrated the importance of measuring belowground effects because the aboveground effects gave limited indication of the effects occurring belowground.     

Idaho forest growth response to post‐thinning energy biomass removal and complementary soil amendments

Utilization of woody biomass for biofuel can help meet the need for renewable energy production. However, there is a concern biomass removal will deplete soil nutrients, having short‐ and long‐term effects on tree growth. This study aimed to develop short‐term indicators to assess the impacts of the first three years after small‐diameter woody biomass removal on forest productivity to establish optimal biomass retention levels for mixed‐conifer forests in the Inland Northwest region, and to evaluate the ability of soil amendments to compensate for potential adverse effects from biomass removal. We examined impacts of four biomass retention‐level treatments at two study locations: full biomass removal (0x), full biomass retention (1x), double biomass retention (2x), and unthinned control. We combined biomass retention with four soil amendment treatments: biochar (B), fertilizer (F), fertilizer and biochar combined (FB), and an untreated control (C). We considered treatment effects on basal area and total stem volume growth for all trees per plot (plot trees) and for the six largest trees per plot (crop trees). Biomass removal had no effect on plot (P > 0.40) or crop tree growth (P > 0.65) compared to normal biomass retention. High biomass retention (2x) decreased plot tree growth as compared to normal biomass retention (1x) levels (P < 0.05) after three years. This growth difference was not explained by soil moisture, temperature, or nutrient uptake. While there were strong tree growth differences between study locations, patterns of biomass and amendment treatment responses did not differ. Fertilizer increased basal area growth and total volume growth (P < 0.10) as expected, because nitrogen is limiting in the region. Biochar had no effect on tree growth (P > 0.47). Initial findings after three years suggest removing small‐diameter biomass for biofuel feedstocks is feasible in the Inland Northwest without negative impacts on tree growth.     

Growth and Contaminant Removal Effect of Several Plants in Constructed Wetlands

The aim of the present study is to probe the relation between plant growth and its decontamination effect in constructed wetlands.Four species were studied in the small-scale mono-cuitured constructed wetlands, which were fed with domestic wastewater. Plant growth indexes were correlated with contaminant removal performance of the constructed wetlands. Wetlands planted with Cyperus flabelliformis Rottb. showed the highest growth indexes such as shoot growth, biomass, root activity, root biomass increment, and the highest contaminant removal rates, whereas wetlands planted with Vetiveria zizanioides L. Nash had the lowest growth indexes and the lowest removal rates. Above-ground biomass and total biomass were significantly correlated with ammonia nitrogen removal, and below-ground biomass with soluble reactive phosphorus removal. Photosynthetic rate had higher correlation with nitrogen removal in these species. Root activity and root biomass increment was more correlated with 5 d biochemical oxygen demand removal.Chemical oxygen demand removal had lower correlations with plant growth indexes. All four species had higher removal rates in summer and autumn. The results suggest that the effect of plant growth on contaminant removal in constructed wetlands were different specifically in plants and contaminants.     

The resprouting response of co‐occurring temperate woody plant and grass species to elevated [CO2]: An insight into woody plant encroachment of grasslands

The phenomenon of woody plant thickening in grasslands has been observed globally and is likely to have widespread ecological consequences. It has been proposed that woody plant thickening is driven in part by rising atmospheric [CO₂] enhancing the resprouting ability of woody plants relative to grasses so they respond more strongly after disturbances such as herbivory and fire. The aim of this study was to examine the CO₂ effect on the resprouting ability of 16 co‐occurring temperate woody plant and grass species (eight species from each growth form). Plants were grown in a controlled glasshouse experiment under ambient (400 ppm) and elevated [CO₂] (600 ppm) for 14 weeks after which their resprouting ability was measured. Root non‐structural carbohydrate (NSC_mass) and nitrogen (N_mass) storage was used as proxies to measure the resprouting ability of woody plants while for the grasses it was measured directly. We found that both the woody plants (22% on average; P = 0.003) and grasses (20% on average; P = 0.003) produced more biomass under elevated [CO₂]. Despite the woody plants not allocating additional carbon to belowground storage under elevated [CO₂], they had significantly greater root NSC_mass (23% on average; P = 0.007) due to increased root biomass production (8% on average; P = 0.007). In contrast, root N_mass of the woody plants did not differ between CO₂ treatments (P = 0.373). Surprisingly, the resprouting ability of the grasses did not significantly differ between the CO₂ treatments (P = 0.067). These results provide evidence that the differing resprouting response of woody plants and grasses under elevated [CO₂] may be contributing to woody plant encroachment of grasslands worldwide.     

Investigating CH4 and N2O emissions from eco-engineering wastewater treatment processes using constructed wetland microcosms

Methane (CH₄) and nitrous oxide (N₂O) are important greenhouse gases, because of their contribution to the global greenhouse effect. The present study assessed emissions of N₂O and CH₄ from constructed wetland microcosms, planted with Phragmites australis and Zizania latifolia, when treating wastewater under different biological oxygen demand (BOD) concentration conditions. The removal rate was 95% for BOD and more than 80% for COD in all three pollutant concentrations, both plants’ removal rates of pollutants were at almost the same level, and both were found to resist BOD concentrations as high as 200 mg L⁻¹. When BOD concentrations fell below 200 mg L⁻¹, the soil plant units reached an average of 80–92% T-N and T-P removal rates; however, as the concentrations increased to 200 mg mg L⁻¹ or when during the initial phases of winter, the removal rates for T-N and T-P decreased to less than 70%. With NH₃-N removal, the influences of BOD concentrations and air temperature were more obvious. When BOD concentrations increased to 100 mg L⁻¹ after October, an obvious decrease in NH₃-N removal was detected; almost no nitrification occurred beginning in December at BOD concentrations of 200 mg mg L⁻¹. N₂O and CH₄ emissions showed obvious seasonal changes; higher emissions were observed with higher BOD concentrations, especially among Z. latifolia units. The enumeration of methane-oxidizing bacteria and methane-producing bacteria was also conducted to investigate their roles in impacting methane emissions and their relationships with plant species. The pollutant purification potentials of P. australis and Z. latifolia plant units during wastewater treatment of different pollutant concentrations occurred at almost the same levels. The nutrient outflow and methane flux were consistently higher with Z. latifolia units and higher concentrations of BOD. The more reductive status and higher biomass of methanogens may be the reason for the lower nitrification and higher CH₄ emissions observed with Z. latifolia units and higher concentration systems. The Z. latifolia root system is shallow, and the activity of methanotrophs is primarily confined to the upper portion of the soil. However, the root system of P. australis is deeper and can oxidize methane to a greater depth. This latter structure is more favorable as it is better for reducing methane emissions from P. australis soil plant systems.     

Soil CO2 effluxes,temporal and spatial variations,and root respiration in shrub willow biomass crops fields along a 19‐year chronosequence as affected by regrowth and removal treatments

In shrub willow biomass crop (SWBC) production systems, the soil CO₂ efflux (F_c) component in the carbon cycle remains poorly understood. This study assesses (i) differences of F_c rates among the 5‐, 12‐, 14‐, and 19‐year‐old SWBCs with two treatments: continuous production (regrowth) willow fields that were harvested and allowed to regrow, and willow fields that were harvested, killed, and then stools and roots were ground into the soil (removal); (ii) temporal and spatial variations of F_c rates; (iii) root respiration contributions to total F_c; and (iv) climatic variables affecting F_c. During the growing season (May to September), F_c rates showed no statistically significant differences across different ages (P = 0.664), and between treatments (P = 0.351); however, there was an interaction between age and treatment (P = 0.001). Similarly, during the dormant season (October to April), F_c rates revealed no statistically significant differences across different ages (P = 0.305) and treatment interaction with age (P = 0.097). F_c rates differed significantly (P < 0.001) among different times of the day and times of the year. F_c rates, between 00 and 1059 h, between 1100 and 1659 h, and between 1700 and 2400 h displayed consistency from May to November; however, F_c rates in these three time intervals showed significant differences (P < 0.0001). In December, F_c rates remained constant over 24 h. F_c rates demonstrated higher temporal and spatial variations among willow age classes than between regrowth and removal treatments. Temporal and spatial variations of F_c were higher during the dormant season than during the growing season. The proportion of root respiration to total F_c ranged from 18 to 33% across age classes. F_c rates showed strong association with soil and air temperatures, and relative humidity.     

Aerobic cometabolic degradation of trichloroethene by methane and ammonia oxidizing microorganisms naturally associated with <Emphasis Type="Italic">Carex comosa</Emphasis> roots

The degradation potential of trichloroethene by the aerobic methane- and ammonia-oxidizing microorganisms naturally associated with wetland plant (Carex comosa) roots was examined in this study. In bench-scale microcosm experiments with washed (soil free) Carex comosa roots, the activity of root-associated methane- and ammonia-oxidizing microorganisms, which were naturally present on the root surface and/or embedded within the roots, was investigated. Significant methane and ammonia oxidation were observed reproducibly in batch reactors with washed roots incubated in growth media, where methane oxidation developed faster (2 weeks) compared to ammonia oxidation (4 weeks) in live microcosms. After enrichment, the methane oxidizers demonstrated their ability to degrade 150 μg l⁻¹ TCE effectively at 1.9 mg l⁻¹ of aqueous CH₄. In contrast, ammonia oxidizers showed a rapid and complete inhibition of ammonia oxidation with 150 μg l⁻¹ TCE at 20 mg l⁻¹ of NH₄ ⁺-N, which may be attributed to greater sensitivity of ammonia oxidizers to TCE or its degradation product. No such inhibitory effect of TCE degradation was detected on methane oxidation at the above experimental conditions. The results presented here suggest that microorganisms associated with wetland plant roots can assist in the natural attenuation of TCE in contaminated aquatic environments.     

Iron plaque formation on wetland plants and its influence on phosphorus,calcium and metal uptake

We investigated Fe plaque formation and Ca, Cu, Mn, Zn, and P uptake capacities of fifteen kinds of wetland plants. The test plants were cultured in 3 l nutrient solutions for 8 days. Fe plaque was induced by adding 200 mg l⁻¹ Fe²⁺ as FeSO₄·7H₂O for 4 days in one set of experiment and 8 days in another. This plaque ranged from 2.38 to 8.67 mg g⁻¹ of plant root after 4 days and from 4.56 to 15.71 mg g⁻¹ of plant root after 8-day treatment. In both experimental durations, the plaque was significantly correlated with root surface area (r = 0.904 and 0.878, P < 0.01). Thus, Canna generalis, Typha latifolia and Thalia dealbata, with their larger root surface areas (>1,400 cm²), formed relatively greater Fe plaque amounts. The amounts of Ca, Cu, Zn and P in the Fe plaques were significantly correlated with Fe plaque amount, (r = 0.819, 0.742, 0.693, 0.917, respectively, for these four elements for the 4-day treatment; and r = 0.917, 0.768, 0.949, 0.872, respectively, for 8-day treatment, P < 0.01). Plants varied widely in accumulating Ca, Cu, Mn, Zn, and P in their tissues. The amounts accumulated on root were significantly correlated with Fe plaque amount in both for 4- and 8-day exposure treatments with Fe (r = 0.973, 0.847, 0.709, 0.837, 0.892, respectively, for 4-day treatment; and r = 0.943, 0.691, 0.843, 0.957, 0.983, respectively, for 8-day treatment, P < 0.01). No such significant correlations were found for the Fe plaque in shoot. Canna generalis, Typha latifolia and Thalia dealbata were superior in Ca, P and Zn uptake, while Canna generalis and Thalia dealbata accumulated Cu and Mn well in case of concentrated wastewater treatment.     

Further reading in geomicrobiology

In the wetland rhizosphere, high densities of lithotrophic Fe(II)-oxidizing bacteria (FeOB) and a favorable environment (i.e., high Fe(II) availability and microaerobic conditions) suggest that these organisms are actively contributing to the formation of Fe plaque on plant roots. We manipulated the presence/absence of an Fe(II)-oxidizing bacterium (Sideroxydans paludicola, strain BrT) in axenic hydroponic microcosms containing the roots of intact Juncus effusus (soft rush) plants to determine if FeOB affected total rates of rhizosphere Fe(II) oxidation and Fe plaque accumulation. Our experimental data highlight the importance of both FeOB and plants in influencing short-term rates of rhizosphere Fe oxidation. Over time scales ca. 1 wk, the FeOB increased Fe(II) oxidation rates by 1.3 to 1.7 times relative to FeOB-free microcosms. Across multiple experimental trials, Fe(II) oxidation rates were significantly correlated with root biomass, reflecting the importance of radial O ₂ loss in supporting rhizosphere Fe(II) oxidation. Rates of root Fe(III) plaque accumulation (time scales: 3 to 6 wk) were ～ 70 to 83% lower than expected based on the short-term Fe(II) oxidation rates and were unaffected by the presence/absence of FeOB. Decreasing rates of Fe(II) oxidation and Fe(III) plaque accumulation with increasing time scales indicate changes in rates of Fe(II) diffusion and radial O ₂ loss, shifts in the location of Fe oxide accumulation, or temporal changes in the microbial community within the microcosms. The microcosms used herein replicated many of the environmental characteristics of wetland systems and allowed us to demonstrate that FeOB can stimulate rates of Fe(II) oxidation in the wetland rhizosphere, a finding that has implications for the biogeochemical cycling of carbon, metals, and nutrients in wetland ecosystems.     

Plant–microbe interactions and nitrogen dynamics during wetland establishment in a desert stream

In late-successional steady state ecosystems, plants and microbes compete for nutrients and nutrient retention efficiency is expected to decline when inputs exceed biotic demand. In carbon (C)-poor environments typical of early primary succession, nitrogen (N) uptake by C-limited microbes may be limited by inputs of detritus and exudates derived from contemporaneous plant production. If plants are N-limited in these environments, then this differential limitation may lead to positive relationships between N inputs and N retention efficiency. Further, the mechanisms of N removal may vary as a function of inputs if plant-derived C promotes denitrification. These hypotheses were tested using field surveys and greenhouse microcosms simulating the colonization of desert stream channel sediments by herbaceous vegetation. In field surveys of wetland (ciénega) and gravelbed habitat, plant biomass was positively correlated with nitrate (NO₃ ^?) concentration. Manipulation of NO₃ ^? in flow-through microcosms produced positive relationships among NO₃ ^? supply, plant production, and tissue N content, and a negative relationship with root:shoot ratio. These results are consistent with N limitation of herbaceous vegetation in Sycamore Creek and suggest that N availability may influence transitions between and resilience of wetland and gravelbed stable states in desert streams. Increased biomass in high N treatments resulted in elevated rates of denitrification and shifts from co-limitation by C and NO₃ ^? to limitation by NO₃ ^? alone. Overall NO₃ ^? retention efficiency and the relative importance of denitrification increased with increasing N inputs. Thus the coupling of plant growth and microbial processes in low C environments alters the relationship between N inputs and exports due to increased N removal under high input regimes that exceed assimilative demand.     

Nitrogen transformations and balance in a constructed wetland for nutrient-polluted river water treatment using forage rice in Japan

A pilot-scale surface-flow wetland planted with a new rice variety (Oryza sativa ’Kusahonami’) developed for livestock feed was constructed for treating nutrient-polluted river water. To calculate the balance between nitrogen removal and rice plant uptake of nitrogen, nitrogen removal from river water and nitrogen interactions among plants, soil water, and soil were investigated for this constructed wetland over two growing seasons in 2004 and 2005. The constructed wetland removed 33% of the total nitrogen entering with the river water. Rice plants were found to constitute the major nitrogen storage, with plant uptake being the major removal mechanism. The total inorganic nitrogen concentration in the rhizosphere changed seasonally because of plant uptake. Most nitrogen taken up by rice plants was contained in the aboveground biomass, with the mean amount being 34.0 g N m⁻². However, the nitrogen balance calculation suggested that rice plants uptake some nitrogen from soil, decreasing the available nitrogen in the soil of the lined impermeable wetland.