Heavy metal phytoextraction by Sedum alfredii is affected by continual clipping and phosphorus fertilization amendment

Improving the efficacy of phytoextraction is critical for its successful application in metal contaminated soils. Mineral nutrition affects plant growth and metal absorption and subsequently the accumulation of heavy metal through hyper-accumulator plants. This study assessed the effects of di-hydrogen phosphates （KH2PO4, Ca（H2PO4）2, NaH2PO4 and NH4H2PO4） application at three levels （22, 88 and 352 mg P/kg soil） on Sedum alfredii growth and metal uptake by three consecutive harvests on aged and Zn/Cd combined contaminated paddy soil. The addition of phosphates （P） significantly increased the amount of Zn taken up by S. alfredii due to increased shoot Zn concentration and dry matter yield （DMY） （P 〈 0.05）. The highest phytoextraction of Zn and Cd was observed in KH2PO4 and NH4H2PO4 treatment at 352 mg P/kg soil. The amount of Zn removed by phytoextraction increased in the order of 1st clipping 〈 2nd clipping 〈 3rd clipping, and for Cd extraction the order was 2nd clipping 〈 1st clipping 〈 3rd clipping. These results indicate that the application of P fertilizers coupled with multiple cuttings can enhance the removal of Zn and Cd from contaminated soils by S. alfredii, thus shortening the time needed for accomplishing remediation goals.

Inhibition of ammonia-oxidizing bacteria promotes the growth of ammonia-oxidizing archaea in ammonium-rich alkaline soils

Disparities in the substrate affinity and tolerance threshold for ammonia have been believed to play a key role in driving niche differentiation between ammonia-oxidizing archaea (AOA) and bacteria (AOB);however, recent surveys argue that direct competition between AOA and AOB is also important in this phenomenon. Accordingly, it is reasonable to predict that diverse AOA lineages would grow in ammonium (NH_(4)^(+))-rich alkaline arable soils if AOB growth is suppressed. To test this hypothesis, a microcosm study was established using three different types of alkaline arable soils, in which a high NH_(4)^(+) concentration (200 μg N g^(-1) dry soil) was maintained by routinely replenishing urea and the activities of AOB were selectively inhibited by 1-octyne or 3,4-dimethylpyrazole phosphate (DMPP). Compared with amendment with urea alone, 1-octyne partially retarded AOB growth, while DMPP completely inhibited AOB. Both inhibitors accelerated the growth of AOA, with significantly higher ratios of abundance of AOA to AOB observed with DMPP amendment across soils. Nonmetric multidimensional scaling analysis (NMDS) indicated that different treatments significantly altered the community structures of both AOA and AOB and AOA OTUs enriched by high-NH_(4)^(+) amendment were taxonomically constrained across the soils tested and closely related to Nitrososphaera viennensis EN76 and N. garnensis. Given that these representative strains have been demonstrated to be sensitive to high ammonia concentrations, our results suggest that it is the competitiveness for ammonia, rather than disparities in substrate affinity and tolerance threshold for ammonia, that drives niche differentiation between these phylotypes and AOB in NH_(4)^(+)-rich alkaline soils.

Effect of elevated CO_2 concentration on photosynthetic characteristics of hyperaccumulator Sedum alfredii under cadmium stress

The combined effects of elevated CO2 and cadmi- um （Cd） on photosynthetic rate, chlorophyll fluorescence and Cd accumulation in hyperaccumulator Sedum alfredii Hance were investigated to predict plant growth under Cd stress with rising atmospheric CO2 concentration. Both pot and hydroponic experiments were conducted and the plants were grown under ambient （350 μL L^-1） or elevated （800μL L^-1） CO2. Elevated CO2 significantly （P 〈 0.05） increased Pn （105%- 149%）, Pnmax （38.8%-63.0%） and AQY （20.0%-34.8%） of S. alfredii in all the Cd treatments, but reduced chlorophyll concentra- tion, dark respiration and photorespiration. After lo days growth in medium with 50 μM Cd under elevated CO2, PSII activities were significantly enhanced （P 〈 0.05） with Pm, Fv/ Fm, φ（Ⅱ） and qP increased by 66.1%, 7.5%, 19.5% and 16.47o, respectively, as compared with ambient-grown plants. Total Cd uptake in shoot of S. alfredii grown under elevated CO2 wasincreased by 44.1%-48-5%, which was positively correlated with the increase in Pn. These results indicate that elevated CO2 promoted the growth of S. alfredii due to increased photosynthetic carbon uptake rate and photosynthetic light- use efficiency, and showed great potential to improve the phytoextraction of Cd by 5. alfredii.

Positive effects of applying endophytic bacteria in eggplant-Sedum intercropping system on Cd phytoremediation and vegetable production in cadmium polluted greenhouse

The combination of intercropping and phytoremediation in the remediation of cadmium contaminated soil is an emerging model in recent years,but the results of previous studies are inconsistent.In the field experiment,eggplant was intercropped with hyperaccumula-tor Sedum alfredii Hance(inoculated or not inoculated with endophytic bacteria)to study the effects of intercropping on vegetable safety production,phytoremediation efficiency of hyperaccumulator and variation of soil available nutrients.The results showed that the in-tercropping treatment had a negative effect on the growth of eggplant and Sedum,but en-dophyte SaMR12 alleviated the inhibition of intercropping on plant growth.Intercropping treatment increases the Cd concentration in edible part of eggplant to 1.34 mg/kg compared with eggplant monoculture(1.19 mg/kg).While the application of SaMR12 reduces the Cd concentration of eggplant fruit to 0.95 mg/kg and significantly promotes the Cd uptake by Sedum.What's more surprising is that compared with eggplant monocropping,the con-tent of soil available nitrogen,phosphorus and potassium in the treatment of intercropping with inoculated Sedum increased significantly.And according to the correlation analysis of various indexes of plants and soil,the Cd content of eggplant is negatively correlated with the available phosphorus and potassium in the soil,while the Cd content of Sedum is positively correlated with it,which suggested that the application of phosphorus and potas-sium fertilizers in this experimental site was beneficial to reduce Cd content in eggplant and improve Cd phytoextraction of Sedum.Therefore,in the daily production of moderately Cd-contaminated soil,intercropping eggplant with Sedum inoculated with endophytic bacteria is an excellent Phytoextraction Coupled with Agro-safe-production(PCA)pattern.

Compounded chelating agent derived from fruit residue extracts effectively enhances Cd phytoextraction by Sedum alfredii

Chelating agent is known as the enhancer for metal phytoextraction;however,there is still a lack of efficient and environmentally sustainable chelators.Here,lemon residue extraction(LRE),prepared from 11 kinds of fruit wastes,was combined with N,N-bis(carboxymethyl)glutamic acid(GLDA),and tea saponin(T.S.)for the compounded plant-derived chelator(CPC),and their influences on Cd phytoextraction by the hyperaccumulator Sedum alfredii was evaluated.Among these fruits,the lemon residue extracted the most significant amount of Cd from the soil.The most effective CPC was at the volume ratio of three agents being 15:4:1(LRE:GLDA:T.S.).Compared with the deionized water,the solubility of three Cd minerals was increased by 85–256 times,and Cd speciation was substantially altered after CPC application.In the pot experiment,CPC addition caused evident increases in plant shoot biomass,Cd phytoextraction efficiency,and organic matter content compared with EDTA and nitrilotriacetic acid(NTA)application.CPC induced fewer changes in bacterial community composition compared with EDTA and had no pronounced influence on microbial biomass carbon and bacterialα-diversity,suggesting CPC had a subtle impact on the microbiological environments.Our study provides a theoretical base for the reutilization of fruit wastes and the development of environmental-friendly chelator that assists Cd phytoextraction.

Elevated carbon dioxide stimulates nitrous oxide emission in agricultural soils: A global meta-analysis

Elevated carbon dioxide (CO_(2))(e CO_(2)) has been shown to affect the nitrous oxide (N_(2)O) emission from terrestrial ecosystems by altering the interaction of plants,soils,and microorganisms.However,the impact of e CO_(2) on the N_(2)O emission from agricultural soils remains poorly understood.This meta-analysis summarizes the effect of e CO_(2) on N_(2)O emission in agricultural ecosystems and soil physiochemical and biological characteristics using 50 publications selected.The e CO_(2) effect values,which equal to the percentage changes of N_(2)O emission under e CO_(2),were calculated based on the natural logarithm of the response ratio to e CO_(2).We found that e CO_(2) significantly increased N_(2)O emission (by 44%),which varied depending on experimental conditions,agricultural practices,and soil properties.In addition,e CO_(2) significantly increased soil water-filled pore space (by 6%),dissolved organic carbon content (by11%),and nitrate nitrogen content (by 13%),but significantly reduced soil p H (by 1%).Moreover,e CO_(2) significantly increased soil microbial biomass carbon(by 28%) and soil microbial biomass nitrogen (by 7%) contents.Additionally,e CO_(2) significantly increased the abundances of ammonia-oxidizing bacteria(AOB) amo A (by 21%),nir K (by 15%),and nir S (by 15%),but did not affect the abundances of ammonia-oxidizing archaea (AOA) amo A and nos Z.Our findings indicate that e CO_(2) substantially stimulates N_(2)O emission in agroecosystems and highlight that optimization of nitrogen management and agronomic options might suppress this stimulation and aid in reducing greenhouse effect.