Hydrological conditions determine the distribution of plant species in wetlands, where conditions such as water depth and hydrological fluctuations are expected to affect the interspecific interactions among emergent wetland species. To test such effects, we conducted a greenhouse experiment with three treatment categories, interspecific interaction (mixed culture or monoculture), water depth (10 or 30 cm depth), and hydrological fluctuation (static or fluctuating water level), and two common emergent wetland plant species, Scirpus planiculumis Fr. (Cyperaceae) and Phragmites australis var. baiyangdiansis (Gramineae). An increase in the water depth significantly restrained the growth of both S. planiculumis and P. australis, while hydrological fluctuations did not obviously alter the growth of either species. In addition, both water depth and hydrological fluctuations significantly affected the interspecific interaction between these two wetland species. P. australis benefited from interspecific interaction under increasing water depth and hydrological fluctuations, and the RII values were clearly positive for plants grown at a water depth that fluctuated around 30 cm. The results may have some implications for understanding how S. planiculumis and P. australis, as well as wetland communities, respond to the natural variation or human modification of hydrological conditions.
Estuarine wetlands provide a variety of ecosystem services, including carbon sinks, nitrogen removal, marine habitats, and climate regulation. However, many estuarine marshes are suffering from soil heavy metal pollution, which signi cantly affects soil enzyme activities that in uence the carbon and nitrogen biogeochemical cycles in wetlands. To date, studies on the effects of wetland plant biochars on heavy metal adsorption and enzyme activity in estuarine wetland soil are limited. The purpose of this study was to assess the effects of wetland plant biochars on the enzyme activity in heavy metal contaminated soil.The biochars were produced from Phragmites australis (PB), Suaeda salsa (SB), and Tamarix chinensis (TB) under different pyrolysis temperatures and times. The detected pyrolysis products showed that the ash, pH, electrical conductivity, and carbon content of the biochars increased signi cantly, while the production rate of the biochars decreased with increasing pyrolysis temperature and time. The results of the adsorption experiments indicated that biochar addition could effectively reduce the concentration of Pb and/or Cd in the Pb 2+ /Cd 2+ single or mixed solutions, but the Pb 2+ and Cd 2+ in the mixed solution indicated a competitive adsorption. A 30-day incubation experiment was conducted using salt marsh soil amended with different biochar application rates to investigate the short-term effects of biochar addition on Pb and Cd immobilization. The PB and SB signi cantly immobilized Pb within the rst 15 days, but Pb remobilized within the next 15-day period. In contrast, TB addition did not signi cantly x Pb. Moreover, biochar addition promoted the conversion of Cd from the residue to the less immobile fractions. The addition of three types of plant biochar had no signi cant effect on the urease activity in wetland soil but signi cantly increased soil sucrase activity. PB and SB signi cantly promoted catalase activity, while TB signi cantly inhibited soil catalase activity.
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