Unplanted Mesocosms Research Articles

A new incubation system to simultaneously measure N2 as well as N2O and CO2 fluxes from plant-soil mesocosms

AbstractThis study presents a novel plant-soil mesocosm system designed for cultivating plants over periods ranging from days to weeks while continuously measuring fluxes of N2, N2O and CO2. For proof of concept, we conducted a 33-day incubation experiment using six soil mesocosms, with three containing germinated wheat plants and three left plant-free. To validate the magnitude of N2 and N2O fluxes, we used 15N-enriched fertilizer and a 15N mass balance approach. The system inherent leakage rate was about 55 µg N m− 2 h− 1 for N2, while N2O leakage rates were below the detection limit (< 1 µg N m− 2 h− 1). In our experiment, we found higher cumulative gaseous N2 + N2O losses in sown soil (0.34 ± 0.02 g N m− 2) as compared to bare soil (0.23 ± 0.01 g N m− 2). N2 fluxes accounted for approximately 94–96% of total gaseous N losses in both planted and unplanted mesocosms. N losses, as determined by the 15N mass balance approach, were found to be 1.7 ± 0.5 g N m− 2 for the sown soil and 1.7 ± 0.6 g N m− 2 for the bare soil, indicating an inconsistency between the two assessment methods. Soil respiration rates were also higher in sown mesocosms, with cumulative soil and aboveground biomass CO2 respiration reaching 4.8 ± 0.1 and 4.0 ± 0.1 g C m− 2 over the 33-day incubation period, in sown and bare soil, respectively. Overall, this study measured the effect of wheat growth on soil denitrification, highlighting the sensitivity and utility of this advanced incubation system for such studies.

Salt-tolerant plant moderates the effect of salinity on soil organic carbon mineralization in a subtropical tidal wetland.

Although salinization is widely known to affect cycling of soil carbon (C) in tidal freshwater wetlands, the role of the presence or absence of plants in mediating the responses of soil organic carbon (SOC) mineralization to salinization is poorly understood. In this study, we translocated soils collected from a tidal freshwater wetland to sites with varying salinities along a subtropical estuarine gradient and established unplanted and planted (with the salt-tolerant plant Cyperus malaccensis Lam.) mesocosms at each site. We simultaneously investigated cumulative soil CO2 emissions, C-acquiring enzyme activities, availability of labile organic C (LOC), and structures of bacterial and fungal communities. Overall, in the planted mesocosm, the soil LOC content and the activities of β-1,4-glucosidase, cellobiohydrolase, phenol oxidase, and peroxidase increased with salinization. However, in the unplanted mesocosm, soil LOC content decreased with increasing salinity, whereas all the C-acquiring enzyme activities did not change. In addition, salinization favored the dominance of bacterial and fungal copiotrophs (e.g., γ-Proteobacteria, Bacteroidetes, Firmicutes, and Ascomycota) in the planted mesocosms. Contrarily, in the unplanted mesocosms salinization favored bacterial and fungal oligotrophs (e.g., α-Proteobacteria, Chloroflexi, Acidobacteria, and Basidiomycota). In both planted and unplanted mesocosms, cumulative soil CO2 emissions were affected by soil LOC content, activities of C-acquiring enzymes, and microbial C-use trophic strategies. Overall, cumulative soil CO2 emissions increased by 35% with increasing salinity in the planted mesocosm but decreased by 37% as salinity increased in the unplanted mesocosm. Our results demonstrate that the presence or absence of salt-tolerant plants can moderate the effect of salinity on SOC mineralization in tidal wetland soils. Future C prediction models should embed both planted and unplanted modules to accurately simulate cycling of soil C in tidal wetlands under sea level rise.

Plants affect the dissipation and leaching of anilide pesticides in soil mesocosms: Insights from compound-specific isotope analysis (CSIA)

The soil-plant system can act as a prevailing zone of pesticide dissipation in agroecosystems, which may influence pesticide leaching following rainfall events. Here we examined the contribution of leaching, dissipation and degradation of widely used anilide pesticides in planted and unplanted mesocosms with contrasting vineyard and forest soils. The mesocosms were spiked at 25 mg/kg with acetochlor, alachlor, S-metolachlor, butachlor and metalaxyl, and followed-up for 75 days. Successive rainfalls were applied on days 45, 60 and 75 to collect pesticide leachates. Bulk soil and rhizosphere samples were collected to evaluate pesticide dissipation. Up to 14% of initially spiked pesticides was exported by leaching. The first rainfall accounted for 69–99% of the total pesticide leaching. Pesticide dissipation in soil mesocosms on day 75 ranged from 58 to 99% and was larger in planted than in unplanted mesocosms. Compound-specific stable isotope analysis (CSIA) of the pesticides showed that biodegradation in both the vineyard and forest soil mesocosms occurred mainly in the soil solution that was leached following rainfall events rather than in the bulk soil. Changes in carbon isotope values (Δδ13C up to 13.9 ± 0.5‰) of acetochlor, alachlor, S-metolachlor and butachlor in leachates were more pronounced in planted than in unplanted mesocosms, indicating predominant pesticide degradation in the planted mesocosms. Pesticide biodegradation was favoured in the soil solution of soil-plant systems, independently of the soil type. Leaching of the soil solution, pesticide ageing and biodegradation in the bulk soil and the rhizosphere were the main processes of pesticide dissipation. Overall, this study emphasizes the variability of leaching and degradation of anilide pesticides in agricultural soils, and proposes a framework using CSIA to examine the contribution of dissipation processes in soil-plant systems.

Microbial community metabolic profiles in saturated constructed wetlands treating iohexol and ibuprofen

The aim of the present study was to elucidate the microbial community metabolic profiles in saturated constructed wetland (CW) mesocosms planted with five different wetland plant species fed with water individually spiked with 100 μg L−1 ibuprofen or iohexol. Community-level physiological profiling (CLPP) using Biolog Ecoplates was performed and coupled with the assessment of water quality parameters (water temperature, pH, DO and TOC, TN, NH4-N, PO4-P removal efficiency). The microbial community metabolic profiles (microbial activity, richness, and carbon source utilization), as well as the water quality parameters revealed similar trends among the control mesocosms and the mesocosms fed with water spiked with iohexol and ibuprofen. Significant differences were observed between the planted and unplanted mesocosms and between seasons (summer and winter) within each of the feeding lines (control, iohexol or ibuprofen). The microbial community metabolic profiles in the saturated CW were shaped by plant presence and plant species, while no negative impact of iohexol and ibuprofen presence was noticed at the 100 μg L−1. In addition, the microbial activity and richness were generally higher in planted mesocosms than in the unplanted systems in the summer. For the first time, a positive correlation between iohexol removal and the microbial community metabolic profiles (activity, richness and amines and amides utilization in summer, and carbohydrates utilization in winter) in the saturated mesocosms was observed. Putrescine utilization in the summer and d-cellobiose, d,l-alpha-glycerol phosphate in winter were linked with the metabolic processing of iohexol, while glycogen in summer and l-phenylalanine, Glycyl-l-glutamic acid in winter were linked with ibuprofen removal efficiency in the saturated CW.

Removal of the pesticide tebuconazole in constructed wetlands: Design comparison, influencing factors and modelling.

Constructed wetlands (CWs) are a promising technology to treat pesticide contaminated water, but its implementation is impeded by lack of data to optimize designs and operating factors. Unsaturated and saturated CW designs were used to compare the removal of triazole pesticide, tebuconazole, in unplanted mesocosms and mesocosms planted with five different plant species: Typha latifolia, Phragmites australis, Iris pseudacorus, Juncus effusus and Berula erecta. Tebuconazole removal efficiencies were significantly higher in unsaturated CWs than saturated CWs, showing for the first time the potential of unsaturated CWs to treat tebuconazole contaminated water. An artificial neural network model was demonstrated to provide more accurate predictions of tebuconazole removal than the traditional linear regression model. Also, tebuconazole removal could be fitted an area-based first order kinetics model in both CW designs. The removal rate constants were consistently higher in unsaturated CWs (range of 2.6-10.9cmd-1) than in saturated CWs (range of 1.7-7.9cmd-1) and higher in planted CWs (range of 3.1-10.9cmd-1) than in unplanted CWs (range of 1.7-2.6cmd-1) for both designs. The low levels of sorption of tebuconazole to the substrate (0.7-2.1%) and plant phytoaccumulation (2.5-12.1%) indicate that the major removal pathways were biodegradation and metabolization inside the plants after plant uptake. The main factors influencing tebuconazole removal in the studied systems were system design, hydraulic loading rate and plant presence. Moreover, tebuconazole removal was positively correlated to dissolved oxygen and all nutrients removal.

Effects of constructed wetland design on ibuprofen removal – A mesocosm scale study

This study aimed to investigate the effects of constructed wetland design (unsaturated, saturated and aerated saturated) and plant species (Juncus, Typha, Berula, Phragmites and Iris) on the mass removal and removal kinetics of the pharmaceutical ibuprofen. Planted systems had higher ibuprofen removal rates (29%–99%) than in the unplanted ones (15%–85%) in all designs. The use of forced aeration improved ibuprofen removal only in the unplanted mesocosms. In general, ibuprofen removal followed an area-based first-order removal kinetics model with removal rate coefficients (kA) varying between 3 and 35cm/d. The ibuprofen removal was mainly attributed to microbial degradation by the fixed bed biofilm, but plant uptake and degradation within plant tissues also occurred. The ibuprofen removal was positively correlated with the oxygen concentration in the water and the removal of nutrients, indicating that degradation may be due to co-metabolisation processes.

Plant community effects on CH4 fluxes, root surface area, and carbon storage in experimental wetlands

Wetland creation is a form of ecological engineering that often relies on establishing a plant community to increase ecosystem services. However, we still lack understanding about how species composition and diversity affect certain wetland ecosystem functions associated with these ecosystem services. Our objective was to investigate the link between plant community (diversity and composition) and plant carbon storage, root surface area and methane (CH4) emission. We hypothesized that more diverse mixtures would 1) store more carbon in above and belowground biomass and 2) emit less CH4 due to increased root surface area and aeration. Three plant groups that represented different growth forms (i.e., “functional groups”: ferns, reeds and tussocks) were planted in mesocosms to represent four levels of functional diversity and every combination of functional groups at each diversity level. Unplanted mesocosms served as the zero diversity treatment. At peak biomass in 2014 and 2015, we harvested aboveground biomass and took soil cores from each mesocosm at 0–10cm to determine the root biomass and surface area. Methane fluxes were measured in situ using a closed chamber system and a Picarro G2301 CRDS analyzer. Fluxes did not vary by functional group richness level or composition. Presence of the reed and tussock functional groups decreased fluxes; however, root surface area was not correlated with CH4 emission. Plant carbon storage was greater in all treatments containing tussocks (expect for the reed tussock mixture) compared with ferns grown alone. Functional group richness did not have a significant effect on plant carbon storage, however there was a positive trend. Root surface area increased 87% from the first to second year; however, there were no differences among functional group richness levels or mixtures. Our results indicate that planting reed and tussock functional groups in dense clumps during restoration could maintain a high level of carbon storage and relatively low CH4 emissions.

Functional Richness and Identity Do Not Strongly Affect Invasibility of Constructed Dune Communities.

Biotic effects are often used to explain community structure and invasion resistance. We evaluated the contribution of functional richness and identity to invasion resistance and abiotic resource availability using a mesocosm experiment. We predicted that higher functional richness would confer greater invasion resistance through greater resource sequestration. We also predicted that niche pre-emption and invasion resistance would be higher in communities which included functional groups similar to the invader than communities where all functional groups were distinct from the invader. We constructed communities of different functional richness and identity but maintained constant species richness and numbers of individuals in the resident community. The constructed communities represented potential fore dune conditions following invader control activities along the Australian east coast. We then simulated an invasion event by bitou (Chrysanthemoides monilifera ssp. rotundata DC. Norl.), a South African shrub invader. We used the same bitou propagule pressure across all treatments and monitored invasion success and resource availability for 13 months. Contrary to our predictions, we found that functional richness did not mediate the number of bitou individuals or bitou cover and functional identity had little effect on invasion success: there was a trend for the grass single functional group treatment to supress bitou individuals, but this trend was obscured when grasses were in multi functional group treatments. We found that all constructed communities facilitated bitou establishment and suppressed bitou cover relative to unplanted mesocosms. Abiotic resource use was either similar among planted communities, or differences did not relate to invasion success (with the exception of light availability). We attribute invasion resistance to bulk plant biomass across planted treatments rather than their functional group arrangement.

Biological denitrification inhibition (BDI) with procyanidins induces modification of root traits, growth and N status in Fallopia x bohemica

Nitrogen (N) limits plant growth in many ecosystems and denitrification is a major source of N loss from soils. Fallopia spp. is an invasive plant species complex adapted to low-fertility soils, which is responsible for biological denitrification inhibition (BDI) through the production of procyanidins. However, the extent to which procyanidins can affect Fallopia spp. via BDI has not yet been shown. We investigated how procyanidins can generate plant trait modifications in Fallopia x bohemica by adding them, or not, to soil mesocosms planted, or not, with F. x bohemica. Soil denitrification enzyme activity (DEA), soil substrate induced respiration (SIR), nitrification enzyme activity (NEA), N-mineralization and total N, and NO3− concentrations were measured in the soil of planted mesocosms. NO3− concentrations were measured in unplanted mesocosms. Leaf and root N contents and above- and belowground plant traits were measured. In unplanted soils, procyanidins induced a six-fold increase in NO3−. Procyanidins inhibited DEA but not SIR, NEA and N-mineralization in planted soil. Procyanidins increased root N content marginally and biomass allocation to roots, while modifying root traits associated with an increase in nutrient acquisition capacity. Our results suggest that a plant-soil feedback related to BDI could result from procyanidin production in Fallopia spp..

Planting richness affects the recovery of vegetation and soil processes in constructed wetlands following disturbance.

The resilience of constructed wetland ecosystems to severe disturbance, such as a mass herbivory eat-out or soil disturbance, remains poorly understood. In this study, we use a controlled mesocosm experiment to examine how original planting diversity affects the ability of constructed freshwater wetlands to recover structurally and functionally after a disturbance (i.e., aboveground harvesting and soil coring). We assessed if the planting richness of macrophyte species influences recovery of constructed wetlands one year after a disturbance. Mesocosms were planted in richness groups with various combinations of either 1, 2, 3, or 4 species (RG 1-4) to create a gradient of richness. Structural wetland traits measured include morphological regrowth of macrophytes, soil bulk density, soil moisture, soil %C, and soil %N. Functional wetland traits measured include above ground biomass production, soil potential denitrification, and soil potential microbial respiration. Total mesocosm cover increased along the gradient of plant richness (43.5% in RG 1 to 84.5% in RG 4) in the growing season after the disturbance, although not all planted individuals recovered. This was largely attributed to the dominance of the obligate annual species. The morphology of each species was affected negatively by the disturbance, producing shorter, and fewer stems than in the years prior to the disturbance, suggesting that the communities had not fully recovered one year after the disturbance. Soil characteristics were almost uniform across the planting richness gradient, but for a few exceptions (%C, C:N, and non-growing season soil moisture were higher slightly in RG 2). Denitrification potential (DEA) increased with increasing planting richness and was influenced by the abundance and quality of soil C. Increased open space in unplanted mesocosms and mesocosms with lower species richness increased labile C, leading to higher C mineralization rates.

Microbial community metabolic function in constructed wetland mesocosms treating the pesticides imazalil and tebuconazole

The objective of this research was to study the differences in microbial community metabolic function in planted and unplanted saturated constructed wetland mesocosm systems with five different wetland plant species, Typha latifolia, Phragmites australis, Iris pseudacorus, Berula erecta and Juncus effusus treating the pesticides imazalil and tebuconazole. Community level physiological profiling (CLPP) was used to determine the microbial community metabolic function from each mesocosm. Microbial activity and metabolic richness were in general not differentiated by pesticides presence. Significantly lower values in comparison with a non-pesticide control were only found in the Iris mesocosms exposed to imazalil and tebuconazole and in the Berula mesocosms exposed to tebuconazole during winter. Planted mesocosms had different microbial community carbon source utilization patterns in comparison to the unplanted mesocosms. In comparison to pesticide presence, plant species had a larger effect on differentiating the microbial community carbon source utilization patterns. Seasonal effects on carbon source utilization patterns were observed for both planted and unplanted mesocosms. In summer, microbial activity and metabolic richness were negatively correlated with TN, NH4+-N, TP concentration and pH in the control group, but not in the pesticide treatment groups, again suggesting a microbial community functional shift in the presence of pesticides. The main factors driving microbial community activity and functional diversity were plant species and season, while carbon source utilization revealed some pesticide adaptation in the summer period.

Characterization of microbial communities in wetland mesocosms receiving caffeine-enriched wastewater.

A 454 high-throughput pyrosequencing approach was used to characterize the structures of microbial communities in wetland mesocosms receiving caffeine-enriched wastewater at a concentration of 250μgL(-1). The removal efficiencies of caffeine in the planted beds (93.0%) were significantly (p < 0.05) higher than those in the unplanted beds (81.4%). Bacterial diversity was decreased by 25 and 22.4%, respectively, in both planted and unplanted mesocosms after 210-day operation. The results of taxonomic analyses suggested that chronic exposure of wetland ecosystems to caffeine could lead to moderate shifts in microbial community composition. In total, 2156 operational taxonomic units (OTUs) were generated and 20 phyla comprising 260 genera were identified. The major phylogenetic groups at phylum level included Firmicutes (39%), Actinobacteria (25.1%), Proteobacteria (17.1%), Synergistetes (5.6%), and Chloroflexi (5.5%). Bacilli and Synergistia increased in abundance in the planted mesocosms, while for the unplanted mesocosms, Actinobacterial, Clostridia and Betaproteobacteria exhibited increased proportion under the exposure of caffeine. At genus level, Propionibacterium, Staphylococcus, Bacillus, and Streptococcus were found to be increased in abundance after caffeine treatment. As for the response of fungal community to caffeine enrichment, genus like Cladosporium, Emericellopsis, Aspergillus, and Phoma were found to be resistant to caffeine disturbance. When compared to the microbial community between planted and unplanted mesocosms, a distinct community profile for both bacteria and fungi community was observed. The presence of plants had a remarkable effect on the structure of microbial community, helping buffer against the stress associated with caffeine exposure.

Ibuprofen removal in horizontal subsurface flow constructed wetlands: treatment performance and fungal community dynamics

ABSTRACTThe treatment performance of ibuprofen (IBP)-enriched wastewater by horizontal subsurface flow constructed wetlands planted with cattail (Typha angustifolia) and unplanted control mesocosms was investigated. Removal efficiencies of IBP were significantly (p < .05) enhanced in the planted mesocosms (78.5%) compared to those in the unplanted beds (57.9%). An 18S rRNA gene high-throughput pyrosequencing approach was used to investigate the effects of IBP on the structure of the fungal community in these wetland systems. The overall diversity of the fungal community was reduced under the IBP exposure. Taxonomic analysis revealed that 62.2% of the fungal sequences were affiliated with Basidiomycota, followed by Ascomycota (37.4%) at the phylum level. Uncultured fungus (48.2%), Chaetomium sp. (14.2%), Aspergillus sp. (12.4%), Trichoderma sp. (5.7%), Cladosporium sp. (5.4%), and Emericellopsis sp. (5.2%) were identified as dominant genera. At the genus level, a distinct profile of the fungal community in the IBP-enriched mesocosms was observed as compared to the control beds, and as well specific fungal genera were enhanced in the planted beds, regardless of IBP enrichment. However, despite these differences, the composition of the fungal community (as measured by Bray–Curtis similarity) was mostly unaffected by the significant IBP enrichment. On the other hand, a consistent similarity pattern of fungal community structure in the planted mesocosms suggests that the presence of higher macrophytes in the wetland systems may well help shape the fungal community structure.

Function of Leersia hexandra Swartz in constructed wetlands for Cr(VI) decontamination: A comparative study of planted and unplanted mesocosms

Constructed wetlands planted with Leersia hexandra Swartz can effectively remove Cr(VI) from water. This work aims to assess the function of L. hexandra in constructed wetlands that treat Cr(VI)-contaminated water. Cr(VI) removal performance of planted and unplanted mesocosms were compared under two different temperatures (25°C and 5°C). Results indicated that the Cr(VI) removal performance of the planted mesocosm was more efficient and stable than that of the unplanted mesocosm. The planted mesocosm showed enhanced Cr(VI) removal even in cold season (5°C) when the shoots were wilted. Therefore, L. hexandra played important roles in enhancing Cr(VI) removal. However, direct Cr uptake by plants only accounted for 9.3% of the total amount of Cr loading in the wetlands. This finding suggested that L. hexandra indirectly improved Cr(VI) removal by influencing other removal processes. Organic content and microbial abundance in the sediments of the planted mesocosm were significantly higher than those in the sediments of the unplanted mesocosm (p<0.05). The major functions of L. hexandra as an ecosystem engineer include producing organic matter and facilitating microbial growth, which are the key factors that influence Cr(VI) reduction and sequestration. A small proportion of Cr accumulated in biomass (4.7–8.6%) was released during plant litter decomposition, indicating that the effect of litter decomposition on water quality was negligible.

Arrival order among native plant functional groups does not affect invasibility of constructed dune communities

Different arrival order scenarios of native functional groups to a site may influence both resource use during development and final community structure. Arrival order may then indirectly influence community resistance to invasion. We present a mesocosm experiment of constructed coastal dune communities that monitored biotic and abiotic responses to different arrival orders of native functional groups. Constructed communities were compared with unplanted mesocosms. We then simulated a single invasion event by bitou (Chrysanthemoides monilifera ssp. rotundata), a dominant exotic shrub of coastal communities. We evaluated the hypothesis that plantings with simultaneous representation of grass, herb and shrub functional groups at the beginning of the experiment would more completely sequester resources and limit invasion than staggered plantings. Staggered plantings in turn would offer greater resource use and invasion resistance than unplanted mesocosms. Contrary to our expectations, there were few effects of arrival order on abiotic variables for the duration of the experiment and arrival order was unimportant in final community invasibility. All planted mesocosms supported significantly more invader germinants and significantly less invader abundance than unplanted mesocosms. Native functional group plantings may have a nurse effect during the invader germination and establishment phase and a competitive function during the invader juvenile and adult phase. Arrival order per se did not affect resource use and community invasibility in our mesocosm experiment. While grass, herb and shrub functional group plantings will not prevent invasion success in restored communities, they may limit final invader biomass.

The potential of four tropical wetland plants for the treatment of abattoir effluent

We investigated morphological characteristics and treatment potential of Cyperus papyrus, Typha domingensis, Miscanthidium violaceum, and Phragmites mauritianus receiving slaughterhouse wastewater in Kampala, Uganda, in experimental mesocosms. Unplanted mesocosms acted as controls. All planted mesocosms achieved significantly higher removals for nitrogen, phosphorus and organic matter than unplanted mesocosms. Among macrophytes, C. papyrus depicted highest pollutant uptake. The umbel of C. papyrus had the highest concentration of phosphorus (3.9 mg/g dry weight); while nitrogen concentration was highest in P. mauritianus shoot tissue (39.70 mg/g dry weight). Plants provided the necessary conditions that aided the removal of nutrients and organics through physical and biochemical processes. C. papyrus attained the highest biomass (31.0 kg dry weight/m2), compared to T. domingensis (7.5 kg dry weight/m2), P. mauritianus (7.2 kg dry weight/m2) and M. violaceum (5.0 kg dry weight/m2). C. papyrus had the largest total root surface area (200,634 cm2) in experimental mesocosms measuring 960 cm2

Purification processes involved in sludge treatment by a vertical flow wetland system: Focus on the role of the substrate and plants on N and P removal

Vertical-flow wetland systems were tested for treatment of liquid waste activated sludge with high content of organic compounds from a soft drink factory. A mesocosm experiment was carried out on planted and unplanted systems to understand the relative importance of substrate and plants in purification processes and to compare three species: Phragmites australis Cav., Typha latifolia L., or Iris pseudacorus L. All planted mesocosms performed better than unplanted mesocosms and Phragmites showed the highest efficiencies, both in volumes and loads, closely followed by Typha. Removal efficiencies were very high in all cases, and physical filtration by the organic substrate was identified as the main processes for nutrient removal (>50%). We showed that plants played direct and indirect roles such as nutrients uptake (up to 23% of the N for Phragmites), evapotranspiration reducing outflow volumes; or improvement of filtration by the root systems and stimulation of microbial activities (respiration rate was double compared to unplanted mesocosms).

Influence of plants on microbial activity in a vertical-downflow wetland system treating waste activated sludge with high organic matter concentrations

The rhizosphere is a key zone for pollutant removal in treatment wetlands; therefore, studies on microbial activity may provide helpful information for a better understanding of purification processes. We studied microbial activity in a vertical-downflow constructed wetland system treating waste activated sludge with high organic matter concentrations, under Mediterranean climate. The aims of the work were to study the influence of (i) the presence of plants, (ii) the plant species (Phragmites australis Cav., Typha latifolia L., Iris pseudacorus L.), and (iii) the plant growth stage (plant senescence and plant fast growing stage) on total respiration rate and phosphatase activity in the substrate (intented here as the solid support on which the plants grow). The presence of plants had a positive influence on microbial activity, since substrate respiration and both acid and alkaline phosphatase activity were always higher in planted than in unplanted mesocosms. Among the three tested species, Phragmites was the one that most stimulated both substrate respiration rate and phosphatase activity, followed by Typha and Iris. These differences of microbial activity between mesocosms were corresponding to differences of removal efficiency. Substrate respiration and phosphatase activity were of similar magnitude at the two growth stages, while the stimulating effect of plants seemed to have been delayed and microbial activity showed higher fluctuations at plant fast growing stage than at plant senescence.

Root production and methane dynamics: Impact of wetland functional group diversity and composition

Abstract Background/Question/Methods The loss of biodiversity worldwide has prompted a close investigation of the link between diversity and ecosystem functions. Most experimental studies have looked at the relationship between grassland plant diversity and aboveground productivity. Less is known about other ecosystems or how diversity affects belowground processes. Our objective was to investigate the link between plant community (diversity and composition) and key belowground processes such as root biomass production and CH4 dynamics in wetland ecosystems. We hypothesized that 1) root biomass would increase with functional group diversity due to complementarity and 2) the sediment pool of CH4 would decrease with diversity due to increased CH4 oxidation facilitated by root biomass. Four plant functional groups (facultative annuals, obligate annuals, reeds and tussocks) were planted in controlled mesocosms to represent five levels of functional diversity and every combination of functional groups at each diversity level. Unplanted mesocosms served as the zero diversity treatment. At peak biomass in 2007, porewater samplers were used to extract water at 5, 15, and 25 cm. The samples were frozen prior to headspace analysis of CH4 and CO2. Porewater was also analyzed for DOC. Afterward, we took soil cores from each mesocosm at 0-10 cm, 10-20 cm and 20-30 cm to determine the root biomass in each depth. Results/Conclusions Root biomass increased with functional diversity (F 3, 71 = 2.78, P &lt; 0.05), however only the lowest diversity treatment had significantly lower root biomass than the highest diversity level; 150.6 ± 24.94 (SE) g DW m-2 and 307.2 ± 49.9 g DW m-2, respectively. At each depth, root biomass increased with diversity (P &lt; 0.01), and root biomass at 0-10 cm &gt;10-20 cm &gt;20-30 cm. The facultative annual and obligate annual functional groups had significantly less root biomass than the other functional groups and combinations (P &lt; 0.001). Porewater concentrations of CH4 did not significantly differ between functional group combinations or diversity levels (P &gt; 0.05). However, CH4 was positively correlated with depth (F 1, 194 =19.75, P &lt; 0.001), CO2 concentration (F 1, 194 = 42.94, P &lt; 0.001) and DOC (F 1,194 = 4.98, P &lt; 0.001) and was not correlated with root biomass (P &gt; 0.05). Since this data is from the first year of sampling following mesocosm establishment, the insignificant relationship between root biomass and CH4 in the sediment pool may indicate that the microbial processes were influenced more by starting soil conditions than plant-mediated conditions.

Root production and methane dynamics: Impact of wetland functional group diversity and composition

Background/Question/MethodsThe loss of biodiversity worldwide has prompted a close investigation of the link between diversity and ecosystem functions. Most experimental studies have looked at the relationship between grassland plant diversity and aboveground productivity. Less is known about other ecosystems or how diversity affects belowground processes. Our objective was to investigate the link between plant community (diversity and composition) and key belowground processes such as root biomass production and CH4 dynamics in wetland ecosystems. We hypothesized that 1) root biomass would increase with functional group diversity due to complementarity and 2) the sediment pool of CH4 would decrease with diversity due to increased CH4 oxidation facilitated by root biomass. Four plant functional groups (facultative annuals, obligate annuals, reeds and tussocks) were planted in controlled mesocosms to represent five levels of functional diversity and every combination of functional groups at each diversity level. Unplanted mesocosms served as the zero diversity treatment. At peak biomass in 2007, porewater samplers were used to extract water at 5, 15, and 25 cm. The samples were frozen prior to headspace analysis of CH4 and CO2. Porewater was also analyzed for DOC. Afterward, we took soil cores from each mesocosm at 0-10 cm, 10-20 cm and 20-30 cm to determine the root biomass in each depth.Results/ConclusionsRoot biomass increased with functional diversity (F 3, 71 = 2.78, P < 0.05), however only the lowest diversity treatment had significantly lower root biomass than the highest diversity level; 150.6 ± 24.94 (SE) g DW m-2 and 307.2 ± 49.9 g DW m-2, respectively. At each depth, root biomass increased with diversity (P < 0.01), and root biomass at 0-10 cm >10-20 cm >20-30 cm. The facultative annual and obligate annual functional groups had significantly less root biomass than the other functional groups and combinations (P < 0.001). Porewater concentrations of CH4 did not significantly differ between functional group combinations or diversity levels (P > 0.05). However, CH4 was positively correlated with depth (F 1, 194 =19.75, P < 0.001), CO2 concentration (F 1, 194 = 42.94, P < 0.001) and DOC (F 1,194 = 4.98, P < 0.001) and was not correlated with root biomass (P > 0.05). Since this data is from the first year of sampling following mesocosm establishment, the insignificant relationship between root biomass and CH4 in the sediment pool may indicate that the microbial processes were influenced more by starting soil conditions than plant-mediated conditions.