Chong-Bang Zhang

Effects of plant diversity on nutrient retention and enzyme activities in a full-scale constructed wetland

This study focused on the relationship between plant diversity (six species richness levels) and nutrient retention and enzyme activities associated with carbon, nitrogen and phosphorus cycling in a full-scale constructed wetland (CW) fed with post-treatment domestic wastewater. Effects of plant species richness on nutrient retention and enzyme activities were assessed using soil chemical and zymological methods, respectively. Retention of NH(4)-N and NO(3)-N in the wetland substrate increased with increasing species richness, while phosphorus retention significantly decreased under the richness level of 16 species per plot. Activities of enzymes such as dehydrogenase, beta-glucosidase, invertase, phenol oxidase, L-arsparaginase, protease and nitrate reductase, while they were affected by plant species richness, were strongly depended on the presence or absence of plants in CW substrate, while activities of enzymes such as CM-cellulase, urease and acid phosphatase were strongly depended on plant species richness. We conclude that plant species richness influenced nutrient retention and enzyme activities in the substrate in our subtropical CW; increase plant species richness in CW will likely improve the efficiency of wastewater treatment.

Physiological responses and detoxific mechanisms to Pb, Zn, Cu and Cd in young seedlings of Paulownia fortunei

Paulownia fortunei has been successfully used in the phytoremediation of many Pb/Zn mine tailings. However, seed germination and young seedlings of P. fortunei rarely occurred in these mine tailings. The physiological responses and detoxific mechanisms of P. fortunei young seedling to Pb, Zn, Cu and Cd stress were investigated. The germinated rate, shoot length, chlorophyll and carotenoid contents in leaves of young seedlings had a great reduction under Zn and Cu treatments, but had little decrease under Pb and Cd treatments. The production rate of O2*-, H2O2 and malondialdehyde (MDA) contents significantly increased in response to added Zn and Cu indicating great oxidative stress for young seedlings, but they had no significant change to added Pb and Cd. Young seedlings had effective detoxific mechanism to Pb and Cd, as antioxidant enzymes activities, phytochelatins (PCs-SH) and proline contents increased with increasing rates of added Pb and Cd. However, young seedlings had un-effective detoxific mechanisms to Zn and Cu stress. Results revealed the heavy metals (such as Cu) that present at low concentrations in mine tailings may be major constraint for the survival of young seedlings.

Effects of monocot and dicot types and species richness in mesocosm constructed wetlands on removal of pollutants from wastewater

The effects of planting type and species richness on removal of BOD5, COD, nitrogen and phosphorus were studied in mesocosms with monocot alone (M), dicot alone (D) and mixed planting of M+D, where each planting type had four species richness levels. Above- and below-ground plant biomasses increased with the M and M+D species richness as shown by one-way ANOVA. The M+D type had the highest above-ground biomass, whereas the M type had the highest below-ground biomass among planting types. Carbon, nitrogen and phosphorus in the microbial biomass increased with the richness of the M and M+D type. Removals of BOD5, COD, inorganic P and total P did not change with the richness, but removals of NH4-N, NO3-N increased. Planting type impacted only removal of inorganic P, with higher removal of inorganic P in the M type.

Evaluation of Soil Chemical Properties and Actinomycete Community Structure following a Temporal Sequence of Revegetation through Paulownia Fortunei in the Heavy Metal-Contaminated Soil

The present work tested effects of a revegetation pattern conducted using Paulownia fortunei (Seem.) Hemsl. (Scrophulariaceae) on soil chemical properties and actinomycete community structure identified by terminal restriction fragment length polymorphism (T-RFLP) technology of 16S rDNA. The results indicated that P. fortunei planting with time effectively improved organic carbon and total nitrogen contents, as well as pH in heavy metal-contaminated soils and, at the same time, enhanced the retention of heavy metals such as Pb, Zn, Cu and Cd in soils. T-RFLP profiles of soil actinomycete communities digested from two restriction enzymes (HhaI and RsaI) showed different specific TRF patterns across four sites with different revegetation time. Nonetheless, number and diversity of terminal restriction fragments for soil actinomycete community increased gradually with P. fortunei planting time and followed consistent patterns with soil organic carbon, total nitrogen, pH and heavy metal contents. Our results revealed a great potential of P. fortunei to remediate heavy metal-contaminated soils.

Responses of Dissimilatory Nitrate Reduction to Ammonium and Denitrification to Plant Presence, Plant Species and Species Richness in Simulated Vertical Flow Constructed Wetlands

This study investigated the effects of plant presence, plant species and their species richness on plant biomass production, pH, dissolved oxygen (DO), oxidation-reduction potential (ORP), denitrification (DNF), dissimilatory NO3− reduction to ammonium (DNRA) and two associated bacterial community compositions in thirty vertical flow microcosm wetlands fed with the Hoagland solution, where three plant species richness levels (i.e. unvegetated, monocultured and 4-species polycultured treatment, respectively) were established using four macrophytes. Plant presence increased DO and ORP values, as well as the terminal restriction fragment (TRF) richness and Shannon-Weaver index of the DNRA community and also improved both potential DNF and DNRA rates. The microcosms monocultured with Cyperus alternifolius exhibited the greatest DO, ORP, smallest plant biomass parameters and DNF rates among all of the monocultured microcosms, whereas the microcosms monocultured with Canna glauca and Iris pseudacorus harbored the smallest pH, DO, ORP, the greatest plant biomass parameters and DNRA rates. Compared to both unvegetated and monocultured treatments, the 4-species polycultured treatment was effective in increasing both potential DNF and DNRA rates due to the greatest plant biomass parameters as confirmed by the correlation analysis, but was ineffective in terms of changing both DNF and DNRA community compositions.

Fungal Denitrification Activity in Vertical Flow Constructed Wetlands as Impacted by Plant Species Richness, Carbon, Nitrogen and pH Amendments

To control potential fungal denitrification rate (PFDR) in vertical flow simulated wetlands (VFSW) microcosms, thirty VFSW microcosms were established and planted with three plant species richness levels (i.e. unplanted, monoculture, and four-species polyculture treatment), and effects of carbon, nitrogen and pH amendments on the PFDR were investigated using a room-incubating method. Among seven carbon compounds, sodium citrate, glycerol, glucose and sodium succinate were more effective in enhancing PFDRs. These enhanced effects were dependant on a given species richness level. Sodium nitrite mostly stimulated PFDRs to a greater extent than the other three nitrogen compound amendments at any richness level. Treatments with pH 5.6 or 8.4 had significantly greater PFDRs than the treatment with pH 2.8 in the three species richness levels. However, no effect of plant species richness on the PFDR was observed among any carbon, nitrogen and pH amendments. Current results suggest carbon, nitrogen and pH factors should be considered when mediating fungal denitrification in VFSW microcosms.