Zhengyi Hu

Physiological and Biochemical Effects of Rare Earth Elements on Plants and Their Agricultural Significance: A Review

Abstract The rare earths include the elements scandium [Sc, atomic number (Z) = 21], yttrium (Y, Z = 39), and the lanthanides from lanthanum (La, Z = 57) to lutetium (Lu, Z = 71). Crop responses to application of rare earth elements (REEs) have only been documented in a few countries. The reasons for promoting growth or yield increases are still not sufficiently understood. Recently, physiological interaction of REEs with calcium (Ca), effects on structure and function of cytoplasm membranes, photosynthesis, hormone metabolism, enzyme activity, and water use efficiency have been discussed. This review covers the significance of REEs for agricultural plant production, beginning with a description of the history of their application. The recorded physiological and biochemical effects and responses of selected crops to REEs were also reviewed. Agricultural research needs on REEs are also suggested.

Rare Earth Elements in Soils

Abstract Rare earth elements (REEs) comprise a group of 17 elements with very similar chemical and physical properties, which include scandium (Sc, Z=21), yttrium (Y, Z=39), and the lanthanides with successive atomic numbers (Z from 57 to 71). Lanthanides are the elements lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu). REEs are required in modern industry, and their use in agriculture yielded positive effects in terms of crop yield and body weight of poultry. However, the question of whether the use of REEs in agriculture yields an enrichment of these elements in the environment remains open. It was the aim of this review to summarize the data about REEs in soils with view to their content, fractions, availability, chemical behavior, and translocation in soils and to elucidate further research needs.

Copper contamination in paddy soils irrigated with wastewater

Copper (Cu) contamination was investigated in paddy soils where Cu-rich wastewater (12 mg Cu/l) was used for irrigation. The results showed that Cu contamination increased the soil Cu content from 17.0 mg Cu/kg in the non-wastewater irrigated soils (NWIS) to 101.2 mg Cu/kg in the wastewater irrigated soils (WIS), and Cu accumulated mostly in the surface layer (0-10 cm) of the paddy soil. The average Cu contents in brown rice, rice hull and rice straw from NWIS were 1.4, 7.3 and 14.5 mg Cu/kg, while those from WIS were 15.5, 133.2, and 101.4 mg Cu/kg, respectively. Correlation analysis revealed that the relationship between the Cu content in the rice straw and the rice hull with the total Cu content of the soil could be described by an exponential function (R2 = 0.921 and 0.831, respectively; P <0.01). Rice plants grown in the WIS showed symptoms of black roots, less effective tiller, etc. Subsequently, the rice yield decreased by 18-25%, compared with that grown in NWIS.

Emissions of ammonia and greenhouse gases during combined pre-composting and vermicomposting of duck manure

Combined pre-composting and vermicomposting has shown potential for reclamation of solid wastes, which is a significant source of ammonia (NH3), and greenhouse gases (GHG), including nitrous oxide (N2O), methane (CH4), and carbon dioxide (CO2). Earthworms and amendments may both affect physico-chemical characteristics that control gas-producing processes, and thus affect NH3 and GHG emissions. Here, we used two-way ANOVA to test the effects of addition of reed straw and combined addition of reed straw and zeolite on NH3 and GHG emissions during pre-composting of duck manure, either with or without a follow-up phase of vermicomposting. Results showed that cumulative N2O, CH4, and CO2 emissions during pre-composting and vermicomposting ranged from 92.8, 5.8, and 260.6 mg kg(-)(1) DM to 274.2, 30.4, and 314.0 mg kg(-1) DM, respectively. Earthworms and amendments significantly decreased N2O and CH4 emissions. Emission of CO2 was not affected by earthworms, but increased in responses to addition of reed straw. Cumulative NH3 emission ranged from 3.0 to 8.1 g kg(-1) DM, and was significantly decreased by reed straw and zeolite addition. In conclusion, combined pre-composting and vermicomposting with reed straw and zeolite addition would be strongly recommended in mitigating emissions of N2O, CH4, and NH3 from duck manure. Moreover, this method also provides nutrient-rich products that can be used as a fertilizer.

The removal of nutrients from non-point source wastewater by a hybrid bioreactor

The aim of this project was to establish an economical and environmentally benign biotechnology for removing nutrients from non-point source wastewater. The proposal involves a hybrid bioreactor comprised of sequential anaerobic, anoxic and aerobic (A(2)/O) processes and an eco-ditch being constructed and applied in a suburban area, Kunming, south-western China, where wastewater was discharged from an industrial park and suburban communities. The results show that the hybrid bioreactor fosters heterotrophic and autotrophic microorganisms. When the hydraulic load is 200 m(3) per day with the running mode in 12h cycles, the removal efficiencies of the nutrients were 81% for TP, 74% for TDP, 82% for TN, 79% for NO(3)-N and 86% for NH(4)-N. The improved bacterial community structure and bacterial habitats further implied enhanced water quality and indicates that the easily-deployed, affordable and environmentally-friendly hybrid bioreactor is a promising bio-measure for removing high loadings of nutrients from non-point source wastewater.

Sulphur fractionation in calcareous soils and bioavailability to plants

Sulphur fractionation and availability to plants are poorly understood in calcareous soils. Sixty-four calcareous soils containing varying amounts of CaCO3 were collected from ten provinces in China and their S fractions determined. Organic S was the predominant fraction of S, accounting for on average 77% of the soil total S. The amounts of adsorbed sulphate were found to be negligible. 1 M HCl extracted substantially more sulphate than either 0.01 M CaCl2 or 0.016 M KH2PO4, indicating the existence of water-insoluble but acid-soluble sulphate, probably in the form of sulphate co-precipitated with CaCO3. The concentrations of water-insoluble sulphate correlated positively with the contents of CaCO3 and accounted for 0.03–40.3% (mean 11.7%) of soil total S. To test the bioavailability of water-insoluble sulphate, a sulphate-CaCO3 co-precipitate labelled with 35S was prepared and added to a calcareous soil in a pot experiment with either NH4+ or NO3− as the N source. In 29 days, wheat plants took up 10.6% and 3.0% of the 35S added to the soil in the NH4+ and NO3− treatments, respectively. At the end of the pot experiment, the decrease of water-insoluble, acid-soluble, sulphate was more apparent in the NH4+ than in the NO3− treatment. The results indicate that sulphate co-precipitated with CaCO3 in calcareous soils may become partly available for plant uptake, depending on rhizosphere pH, if the field precipitate is similar to the laboratory prepared sample studied.

Removal of cyanobacterial bloom from a biopond–wetland system and the associated response of zoobenthic diversity

Harmful cyanobacterial bloom in water bodies frequently occurs due to eutrophication, leading to the excessive growth of cyanobacteria which in turn may lead to a decrease in biodiversity. A biopond-wetland system to control cyanobacterial bloom and stabilize or even increase biodiversity is proposed and applied in a pond, Kunming, western China where cyanobacterial blooms frequently break out. The biopond-wetland system examined includes three main parts: filter-feeding fish, replanted pond macrophytes, and a terminal artificial wetland. When the hydraulic load of the biopond-wetland system was 500m(3)/d on non-rainy days, the system successfully decreased the level of chlorophyll-a (Chl-a). The declining levels of total nitrogen (TN), total phosphorus (TP) and ammonia in the water after establishing the biopond-wetland system also coincided with the disappearance of the cyanobacterial bloom. In the second summer, when the biopond-wetland system was in a relatively steady-state condition, the overall average nutrient removal efficiencies were as follows, Chl-a (83%), TN (57%), TP (70%) and ammonia (66%), while in the second winter, the overall average removal efficiencies were Chl-a (66%), TN (40%), TP (53%) and ammonia (49%). Simpsons diversity index of zoobenthos indicated that the system increased the zoobenthic diversity and improved the growth conditions of the zoobenthos habitat. The results demonstrated that the biopond-wetland system could control cyanobacterial blooms.

Eco-restoration: simultaneous nutrient removal from soil and water in a complex residential-cropland area.

An eco-restoration system to remove excess nutrients and restore the agricultural ecosystem balance was proposed and applied from August 2006 to August 2008 in a residential-cropland complex area (1.4 x 10(5) m(2)) in Kunming, western China, where the self-purifying capacity of the agricultural ecosystem had been lost. The proposed eco-restoration system examined includes three main foci: farming management, bioremediation, and wastewater treatment. The results showed that the removal efficiencies of total phosphorus (TP) and total nitrogen (TN) from the complex wastewater were 83% and 88%, respectively. The Simpsons diversity indices of macrophytes and zoobenthos indicated that the system had increased macrophyte and zoobenthic diversity as well as improved growth conditions of the plankton habitats. The results demonstrated that the proposed eco-restoration system is a promising approach for decreasing the output of nutrients from soil, improving agricultural ecosystem health, and minimizing the downstream eutrophication risk for surface waters.

Effect of crop growth on the distribution and mineralization of soil sulfur fractions in the rhizosphere

The effect of plant growth on the mineralization of organic matter and distribution of soil S fractions (plant available SO42—, adsorbed SO42—, carbon-bonded S, ester-bonded S, and residual-S) in the rhizosphere was studied in a greenhouse experiment using a rhizobag technique. In this study wheat, oilseed rape and radish were grown on two soils, a Haplic Acrisol and a Hortic Anthrosol. Significant differences between S fractions in the rhizosphere and non-rhizosphere were determined in dependence on soil type and crop species. In all cropped treatments lower amounts of ester-bonded S and higher levels of residual-S were found in the rhizosphere than in the non-rhizosphere, while the amount of carbon-bonded S fractions was similar. These results indicate firstly, that the arylsulfatase activity was higher in the rhizosphere than in the non-rhizosphere and secondly, that mass flow of SO42—-S to the rhizosphere increased after mineralization of residual-S. Compared to the non-vegetated soil, the ester-bonded S fraction of wheat and oilseed rape decreased in the rhizosphere revealing that the mineralization of organic S in the rhizosphere is related to the crop type. Einfluss des Pflanzenwachstums auf die Verteilung und Mineralisierung von Schwefelfraktionen in der Rhizosphare Der Einfluss des Pflanzenwachstums auf die Mineralisierung organischer Substanz und die Verteilung verschiedener Schwefel-fraktionen (pflanzenverfugbarer S, adsorbierter S, C-gebundener S, Ester-gebundener S und Residual-S) in der Rhizosphare und im nicht durchwurzelten Boden wurde in einem Gewachshausversuch untersucht, wobei eine ,Wurzelbeuteltechnik‘ angewandt wurde. Im Rahmen der vorliegenden Studie wurden Weizen, Raps und Rettich auf zwei Boden, einem Haplic Acrisol und einem Hortic Anthrosol kultiviert. Signifikante Unterschiede bestanden zwischen den Gehalten der einzelnen Schwefelfraktionen in der Rhizosphare und im nicht durchwurzelten Raum in Abhangigkeit vom Bodentyp und der Kulturart. Bei Pflanzenbewuchs waren im durchwurzelten Raum stets niedrigere Gehalte an Ester-gebundenem und hohere Gehalte an Residual-S zu finden als im nicht durchwurzelten Bodenbereich. Im Vergleich hierzu veranderten sich die Gehalte an C-gebundenem Schwefel nicht. Dies deutet darauf hin, dass die Arylsulfatase-Aktivitat in der Rhizosphare hoher war als im nicht durchwurzelten Boden. Des weiteren scheint die Mineralisation von Residual gebundenem Schwefel zu einem erhohten Massenfluss von Sulfat in den durchwurzelten Raum gefuhrt zu haben. Die Ester-gebundenen Schwefelgehalte lagen in der Rhizosphare von Weizen und Raps signifikant niedriger als im unbewachsenen Boden, wodurch kulturartspezifische Einflusse auf die Mineralisation organisch gebundenen Schwefels deutlich werden.

A multi-level bioreactor to remove organic matter and metals, together with its associated bacterial diversity.

The purpose of this study was to treat complex wastewater consisting of domestic wastewater, tobacco processing and building materials washings. The proposed multi-level bioreactor consists of a biopond-biofilter, anoxic/aerobic (A/O) fluidized beds and a photoautotrophic system. The results show that when the hydraulic load of the bioreactor was 200 m3/d, it successfully and simultaneously removed the organic matter and metals. When the bioreactor was in a relatively steady-state condition, the overall average organic matter and metals removal efficiencies are as follows, COD (89%), UV245 nm-matter (91%), Cu (78%), Zn (79%) and Fe (84%). The growth conditions of the native bacterial habitat were improved, which resulted from the increase of the in bacterial diversity under the rejuvenated conditions induced by the bioreactor. The results demonstrate that the multi-level bioreactor, without a sludge treatment system, can remove heterogeneous organic matter and metals from wastewater.