Phosphorus utilization and microbial community in response to lead/iron addition to a waterlogged soil

Constructed wetlands have emerged as a viable option for helping to solve a wide range of water quality problems. However, heavy metals adsorbed by substrates would decrease the growth of plants, impair the functions of wetlands and eventually result in a failure of contaminant removal. Typha latifolia L., tolerant to heavy metals, has been widely used for phytoremediation of Pb/Zn mine tailings under waterlogged conditions. This study examined effects of iron as ferrous sulfate （100 and 500 mg/kg） and lead as lead nitrate （0, 100, 500 and 1000 mg/kg） on phosphorus utilization and microbial community structure in a constructed wetland. Wetland plants （T. latifolia） were grown for 8 weeks in rhizobags filled with a paddy soil under waterlogged conditions. The results showed that both the amount of iron plaque on the roots and phosphorus adsorbed on the plaque decreased with the amount of lead addition. When the ratio of added iron to lead was 1：1, phosphorus utilized by plants was the maximum. Total amount of phospholipids fatty acids （PLFAs） was 23%-59% higher in the rhizosphere soil than in bulk soil. The relative abundance of Gram-negative bacteria, aerobic bacteria, and methane oxidizing bacteria was also higher in the rhizosphere soil than in bulk soil, but opposite was observed for other bacteria and fungi. Based on cluster analysis, microbial communities were mostly controlled by the addition of ferrous sulfate and lead nitrate in rhizosphere and bulk soil, respectively.

Monitoring Perennial Sub-Surface Waterlogged Croplands Based on MODIS in Jianghan Plain, Middle Reaches of the Yangtze River

Perennial waterlogged soil（PWS） is induced by the high level of groundwater, and has a persistent impact on natural ecosystems and agricultural production. Traditionally, distribution information regarding PWS is mainly collected from in situ measurements through groundwater level surveys and physicochemical property analyses. However, in situ measurements of PWS are costly and time-consuming, only rough estimates of PWS areas are available in some regions. In this paper, we developed a method to monitor the perennial waterlogged cropland using time-series moderate resolution imaging spectroradiometer（MODIS） data. The Jianghan Plain, a floodplain located in the middle reaches of the Yangtze River, was selected as the study area. Temporal variations of the enhanced vegetation index（EVI）, night land surface temperature（LST）, diurnal LST differences（ΔLST）, albedo, and the apparent thermal inertia（ATI） were used to analyze the ecological and thermodynamic characteristics of the waterlogged croplands. To obtain pure remote sensing signatures of the waterlogged cropland from mixed pixels, the croplands were classified into different types according to soil and land cover types in this paper, and a linear mixing model was developed by fitting the signatures using the multiple linear regression approach. Afterwards, another linear spectral mixing model was used to get the proportions of waterlogged croplands in each 1 km×1 km pixel. The result showed an acceptable accuracy with a root-mean-square error of 0.093. As a tentative method, the procedure described in this paper works efficiently as a method to monitor the spatial patterns of perennial sub-surface waterlogged croplands at a wide scale.

Driving factors of soluble organic nitrogen dynamics in paddy soils:Structure equation modeling analysis

Soil soluble organic nitrogen(SON)is one of the most active components in soil nitrogen pools;however,limited information is available with regard to its driving factors,as well as their pathways and degrees of influence.In this study,structural equation modeling was used to analyze the driving factors,their significance,and pathways that affected SON dynamics in a waterlogged experiment of two typical paddy soils incubated for 80 d after green manure application.Soil p H,Eh,microbial biomass,enzyme activity,and SON dynamics were used to construct the structural equation model.Results showed that soil microbial biomass carbon(MBC),protease,glutamine,and initial organic matter(OM)directly and significantly affected soil SON with path coefficients corresponding to 0.405,0.547,0.523,and-0.623(P<0.01),respectively.Soil microbial biomass carbon and initial OM affected the SON dynamics indirectly through protease and glutamine activity.In addition,pH indirectly affected SON dynamics by glutamine activity.It is implied that soil MBC,protease,glutamine,and initial OM are the key factors affecting SON dynamics in the waterlogged paddy soils after green manure application.Our research indicated that structural equation modeling could provide an effective method to clearly recognize the impact,significance,and pathways of multiple factors on SON dynamics in paddy soils.

Differential responses of three coastal grassland species to seawater flooding

Aims Supratidal plant communities fulfil a vital role in coastal protec-tion,but despite an increased likelihood of seawater flooding resulting from anthropogenic climate change,we understand little about how tidal inundation affects these habitats or interactions between their component species.Our aim was to determine how three common coastal grassland species responded to simulated seawater flooding and how subsequent changes to their ecophysi-ology,growth and survival might affect plant-plant interactions in mixed assemblages.Methods Seeds of three widely distributed European coastal grassland species(Leontodon autumnalis Asteraceae,Plantago lanceo-lata Plantaginaceae and Trifolium pratense Fabaceae)were collected from a coastal grassland site in South West England.in Experiment 1,we quantified changes in leaf ion(K^(+),Na^(+),Cl^(−))concentrations as a response to short-duration(0,2,8 or 24 h)immersion in seawater of the root-zone before monitoring longer-term effects on plant survival and growth.in a second experiment,we examined community-level responses by subjecting mixed assemblages of all three species to seawater immersion for(0,12,24 or 96 h).Important Findings When grown individually,one species(Trifolium)had markedly reduced survival with increasing soil immersion time,but a con-sistent decline in plant growth for all species with flooding dura-tion was most likely linked to osmotic and ionic stresses caused by salt ion accumulation.in mixed assemblages,all species suffered increased mortality and reduced growth following seawater flood-ing,although the relative contribution of one species(Leontodon)to total biomass increased in flooded microcosms.We thus demon-strate a number of species-specific responses to simulated seawater flooding and show that when grown together,interactions between plants are altered as a consequence.We argue that variation in the responses of component plant species will dictate how coastal plant communities respond to,and recover from,expected changes in sea levels and transient floods following storm surge events.Such infor-mation is vital in order to predict future impacts of seawater floods on supratidal vegetation.