Enhanced phytoremediation of multi-metal contaminated soils by interspecific fusion between the protoplasts of endophytic Mucor sp. CBRF59 and Fusarium sp. CBRF14

The aim of this study was to isolate protoplasts from different metal resistant endophytic fungi and to carry out interspecific fusion of protoplasts to enhance bioremediation of contaminated soils. Three stable fusants (F1, F2, and F3) with resistance to Cd and Zn were constructed by interspecific fusion between inactivated protoplasts from Cd-resistant endophytic Mucor sp. CBRF59 and Zn-resistant endophytic Fusarium sp. CBRF14. The fusants increased concentrations of water soluble Cd, Pb, and Zn in soils, promoted rape growth, increased metal concentrations in the rape, elevated the extractable metal amount, and increased metal translocation from roots to shoots in soils containing single metals or multi-metals. Especially, the fusants showed much higher extraction efficacy than the parents in soils contaminated by multi-metals. The results indicated that protoplast fusion should be a feasible and efficient fungal method, which could be utilized to construct stable fusants by combining the genetic traits of parents for bioremediation of contaminated soils by multi-metals.     

Fungal and oomycete pathogen detection in the rhizosphere of organic tomatoes grown in cover crop-treated soils

Soil management practices, including the use of cover crops, affect soil and plant health through varied mechanisms. Impacts on microbial communities are known to be important, but are not well understood. Various techniques are used to measure the effect of treatments on microbial communities, but rarely are the results of more than one technique compared. This field study examined the impacts of a single-season application of cover crops on detection of pathogen species in the tomato crop rhizosphere. The study took place in Maryland, New York and Ohio (MD, NY and OH) in the summers of 2010 and 2011, with a total of 260 plots tested using both macroarray and T-RFLP analyses. The macroarray used in this study was specifically designed to detect thirty-one pathogens of solanaceous crops and had not previously been used for such a field study. The results of T-RFLP analysis, which is a common tool for examining microbial communities, were compared to the macroarray results and the limitations and benefits of each are presented. While not a quantitative measure, the macroarray was able to detect certain fungi with much greater sensitivity than T-RFLP. Our findings suggest that the results of PCR-based techniques used for microbial community studies should be compared to other methods to verify sensitivity.     

Aquaculture wastewater quality improvement by water spinach (Ipomoea aquatica Forsskal) floating bed and ecological benefit assessment in ecological agriculture district

The current ecological situation of aquaculture water quality in Wushe (Songjiang district, Shanghai city) district is not up to mark. In the present study, characteristic of ecological agriculture park was first investigated and then water spinach floating bed was used to improve the aquaculture wastewater quality. The results showed significant improvement in the aquaculture water quality at the experimental site with removal rates of TN, NH₄⁺-N, NO₂⁻-N and TP were 11.2%, 60.0%, 60.2% and 27.3%, respectively. Moreover, we found that the removal mechanism of ammonia nitrogen and nitrate nitrogen by water spinach was mostly by microorganism, whereas the removal mechanism of phosphorus was mainly by plant absorption. In addition, water spinach could be harvested at regular time intervals, which could achieve good economic benefits. This research could provide a good case study for sustainable development in ecological agricultural park for other cities around the world.     

Soil microbial community response to controlled-release urea fertilizer under zero tillage and conventional tillage

Soil microorganisms mediate many important biological processes for sustainable agriculture. The effect of a polymer-coated controlled-release urea (CRU, ESN^®) on soil microbial communities was studied at six sites across western Canada from 2004 to 2006. Fertilizer treatments were CRU, urea and an unfertilized control. Timing of fertilizer application (fall vs. spring) was studied in 9 of the 18 site-years (combinations of sites and years). Wheat (Triticum aestivum L.), canola (Brassica napus L.) and barley (Hordeum vulgare L.) were grown in rotation at five sites, and silage corn (Zea mays L.) was grown in all 3 years at one site, under conventional tillage (CT) or zero tillage (ZT). The fertilizers were side-banded at 50–60 kg N ha⁻¹ for wheat, barley and canola, and broadcast at 150 kg N ha⁻¹ for corn. Microbial biomass C (MBC) and bacterial functional diversity and community-level physiological profiles (CLPPs) were determined at about the flowering stage of each crop. In situ CO₂ evolution (soil respiration) was measured, and microbial metabolic quotient (qCO₂) determined, at one site in 2 years. In the rhizosphere, fertilizer effects on MBC and functional diversity were observed in 1 and 5 of 18 site-years, respectively; and in bulk soil in 4 site-years each. These effects were usually positive relative to the control. CRU increased MBC or functional diversity more than urea in 3 site-years, but the opposite was observed in 1 site-year. Time of fertilizer application affected MBC in 1, and functional diversity in 2, of 9 site-years in the rhizosphere, and no effects were observed in bulk soil. Fall-applied fertilizer increased MBC more than spring-applied fertilizer, but the opposite was observed for functional diversity. Tillage affected MBC and functional diversity in 4 and 5 of 18 site-years, respectively, in the rhizosphere, and in 3 and 4 site-years in bulk soil. Tillage effects were usually in favour of ZT. There were no treatment effects on CO₂ evolution, but an interactive effect of fertilizer and tillage on qCO₂ was observed in 1 year when qCO₂ in the control treatment was greater than that in either fertilizer treatment under CT, but urea increased qCO₂ relative to the control under ZT. Shifts in CLPPs were sometimes observed where the treatment effects described above were not significant. Notwithstanding the limitations of culture-dependent CLPPs, most fertilizer effects on soil microbiological properties were not statistically significant. Therefore, these fertilizers probably did not adversely affect most soil biological processes.     

Soils and the conditional allelopathic effects of a tropical invader

Allelopathy may contribute to the formation of mono-dominant stands of exotic species, but the effects of allelochemicals can be highly conditional. We explored variation in the production of phenolics in leaves, accumulation of phenolics in soils, and the inhibitory effects of soils under an aggressive invader Prosopis juliflora across a range of invaded sites and potential mechanisms by which soils alter the effects of P. juliflora leaf litter. For eight sites in Northwest India we compared the concentration of total phenolics and the seedling growth of Brassica campestris in soils from beneath P. juliflora to that in soils collected away from P. juliflora canopies. We then explored these effects in detail in soils from two sites that differed substantially in texture by germinating seeds of B. campestris in these soils amended with P. juliflora macerated leaf leachate. Finally, we tested the effects of l-tryptophan in soils from these two sites on the seedling growth of B. campestris. Across all sites soil beneath P. juliflora contained higher levels of total phenolics and suppressed the growth of B. campestris than soil that was not under P. juliflora. We observed much variation among P. juliflora-invaded sites in the total phenolic levels of soils and the degree to which they suppressed B. campestris and the concentration of phenolics in soils significantly correlated with the root length of B. campestris when grown in these soils. Soil from two sites amended with P. juliflora macerated leachate suppressed seedling growth of B. campestris, with the effect being higher in sandy soil than sandy loam soil. In soil amended with leachate the strong suppression of B. campestris corresponded with much higher total phenolic and l-tryptophan concentrations. However, in other tests l-tryptophan did not affect B. campestris. Our results indicate that the allelopathic effects of P. juliflora can be highly conditional and that variation in soil texture might contribute to this conditionality.     

红壤丘陵区坡长对作物覆盖坡耕地土壤侵蚀的影响

坡长对坡耕地土壤侵蚀的影响随雨强的不同而变化,为解决南方红壤丘陵区坡耕地水土流失问题,该文采用野外人工模拟降雨的方法,研究了南方红壤丘陵区作物覆盖坡耕地上不同雨强下坡长对其土壤侵蚀的影响,并探讨了侵蚀增强的临界雨强和设置水土保持措施的合理坡长,结果表明:产沙量随坡长延长整体呈增大趋势,但存在一定的波动,二者的关系可用幂函数(决定系数0.84)表示。坡长延长相同长度时,产沙量不呈比例增加,但每隔4 m产沙量增量有减少的趋势,且径流侵蚀产生的泥沙中主要为粒径0.002~0.02 mm的粉粒及粒径0.002 mm的黏粒,加剧了耕地土壤粗化,因此,可每隔4 m设置水土保持措施,有效减少坡耕地水土流失。坡面径流侵蚀产沙量随着雨强的增大而增加,坡长越长,产沙量随雨强增加速度越快,二者呈幂函数关系(决定系数0.76),60 mm/h是红壤丘陵区侵蚀增强的临界雨强;雨强、坡长与产沙量均呈正相关关系,且雨强对坡耕地产沙量的影响较坡长大。对不同雨强下坡长对作物覆盖坡耕地土壤侵蚀的影响研究,可以为南方红壤丘陵区坡耕地水土流失的治理提供一定的理论依据。     

Strategies for overcoming low agronomic nitrogen use efficiency in irrigated rice systems in China

Irrigated rice in China accounts for nearly 30% of global rice production and about 7% of global nitrogen (N) consumption. The low agronomic N use efficiency (AE_N, kg grain yield increase per kg N applied) of this system has become a threat to the environment. The objective of this study was to determine the possibility to improve the AE_N of irrigated rice in China by comparing the farmers’ N-fertilizer practices with other N management strategies such as real-time N management (RTNM) and fixed-time adjustable-dose N management (FTNM). Field experiments were conducted in farmers’ fields in four major rice-growing provinces in China in 2001 and 2002. The same experiment was repeated at the International Rice Research Institute (IRRI) farm in the dry seasons of 2002 and 2003. Agronomic N use efficiency was determined by the “difference method” using an N-omission plot. Maximum yield was achieved mostly at 60–120 kg N ha⁻¹, which was significantly lower than the 180–240 kg N ha⁻¹ applied in farmers’ practices at the Chinese sites. With the modified farmers’ fertilizer practice, a 30% reduction in total N rate during the early vegetative stage did not reduce yield but slightly increased yield and doubled AE_N compared with the farmers’ practice at the Chinese sites. The total N rate in RTNM and FTNM ranged from 30 to 120 kg ha⁻¹ at the Chinese sites, but their yields were similar to or higher than that of the farmers’ practice. Compared with the modified farmers’ practice, RTNM and FTNM further increased AE_N at the Chinese sites. Overall, FTNM performed better than RTNM at the Chinese sites because the total N rate of FTNM was closer to the optimal level than RTNM. A quantum leap in AE_N is possible in the intensive rice-growing areas in China by simply reducing the current N rate and by allocating less N at the early vegetative stage.     

基于薄膜扩散梯度技术的复合污染土壤镉的生物有效性研究

以两种典型的陆生植物小麦和玉米为供试材料,采用盆栽实验生物富积方式,对比研究了薄膜扩散梯度(DGT)技术与5种传统的化学提取方法评价铅(Pb)复合存在下土壤镉(Cd)的生物有效性。结果表明,Cd污染土壤中Pb的存在促进两种植物对Cd的吸收,并随Pb浓度的增加其促进作用更趋明显;DGT技术测定的土壤有效态Cd含量随土壤Pb浓度的增加而显著增加,土壤溶液中Cd的浓度和4种单一提取剂(醋酸、氯化钙、醋酸钠和乙二胺四乙酸)提取的土壤有效态Cd含量均与DGT技术表现出类似的变化趋势,从动力学和静态平衡两种角度揭示了土壤Pb的存在增强Cd的生物有效性;Pearson回归分析显示,6种方法表征的土壤有效态Cd含量均与两种植物体内Cd的含量呈显著正相关,但DGT、土壤溶液和CaCl2的相关系数明显高于其他3种化学提取方法。结果显示,DGT技术与传统方法(土壤溶液法和CaCl2提取法)均可用于预测土壤Cd的生物有效性。     

C to N ratio strongly affects population structure of Eisenia fetida in vermicomposting systems

Food quality influences not only the size of earthworm populations but also their growth and reproduction rates. Here we studied the effect of C to N ratio of pig slurry in microbial biomass and activity and in the growth and reproduction of the earthworm Eisenia fetida. We set up a batch of twelve vermireactors, six each for low (11) and high C to N ratio (19) of pig slurry applied; three of each without earthworms (control) and three containing 500 mature earthworms (E. fetida). After 36 weeks C to N ratio significantly affected earthworm numbers (sevenfold greater in high C to N ratio) and population structure. Thus, in the low C to N ratio treatment the population was composed mainly by mature earthworms (60%), with a higher mean weight than in the high C to N treatment. However, in the high C to N ratio treatment, the population was composed mainly by juvenile and hatchling earthworms (70%). A rapid depletion of dissolved organic C (DOC) content was observed in all treatments. Although earthworms produced an increase in microbial biomass and activity in young modules, finally a decrease in older modules was recorded. The decrease in available carbon did not seem to affect the relationships established between earthworms and microflora.     

Particle size fractionation and metal distribution in sewage sludges

A sequential step filtration technique has been used to investigate the different particle size fractions of suspended solids in several raw, activated and digested sewage sludge samples. Liquid sludge was passed through filters with progressively smaller pore sizes, from 100 µm down to 0.2 µm. The concentrations of Cd, Cu, Ni, Pb, and Zn associated with each particle size fraction were also determined. The particle size distributions indicated that there was a greater proportion of larger particles in the raw and activated sludges than in the digested sludges. Generally in activated sludge the metals tended to be associated with the large particles of > 100 µm, whereas in raw and particularly digested sludges the metals were found in the smaller particle size fractions from 20 µm, down to 2.5 µm. Calculating specific associations in terms of mg kg^?1 the 8 to 20 µm range appears important in complexing metals. This was especially evident when comparing the sludges from the same treatment works. Generally distributions were more widespread when results were expressed as mg kg^?1 as opposed to mg L^?1.