An incubation experiment was conducted to investigate the response of ammonia-oxidizing bacteria (AOB), ammonia-oxidizing archaea (AOA), and the nitrification rate to the contamination of Cu, Zn, and Cd in two New Zealand grassland soils. The soils spiked with different concentrations of Cu (20 and 50 mg kg−1), Zn (20 and 50 mg kg−1), and Cd (2 and 10 mg kg−1) were incubated for 14 days and then treated with 500 mg kg−1 urine-N before continuing incubation for a total of 115 days. Soils were sampled at intervals throughout the incubation. The nitrification rate in soils at each sampling period was determined, and the abundance of AOB and AOA was measured by real-time quantification polymerase chain reaction (qPCR) assay of the amoA gene copy numbers. The results revealed that moderate trace metal stress did not significantly affect the abundance of AOB and AOA in the two soils, probably due to the high organic matter content of the soils which would have reduced the toxic effect of the metals. Nitrification rates were much greater and the observable nitrification period was much shorter in the dairy farm (DF) soil, in which the AOB and AOA abundances were greater than those of the mixed cropping farm (MF) soil. AOB were shown to grow under high nitrogen conditions, whereas AOA were shown to grow under low N environments, with different metal concentrations. Therefore, nitrogen status rather than metal applications was the main determining factor for AOB and AOA growth in the two soils studied.

•Higher shoot and root Cd concentrations were observed in Cd-sensitive genotype H4.•The different Cd concentrations between two cultivars might be ascribed to root uptake and root-to-shoot translocation.•Higher Cd concentrations within all subcellular fractions were observed in both the root and leaf of H4.•Higher Cd concentrations and proportions extracted by water and 80% ethanol in root and 1 M NaCl in leaf were shown in H4.Cadmium (Cd) absorption and accumulation vary greatly not only among plant species but also among cultivars within the same species. In order to better understand the mechanisms of Cd absorption, transportation and distribution, we examined the differences of Cd absorption, translocation, subcellular distribution and chemical forms between L19, a Cd-tolerant genotype, and H4, a Cd-sensitive genotype, using kinetic analysis and soil culture experiment. Kinetic assays showed that the different Cd concentrations between the two cultivars might be ascribed to root absorption and translocation from root to shoot. The investigations of subcellular distribution and chemical forms verified that Cd concentrations of all subcellular fractions in H4 were all higher than in L19. Meanwhile, most of the Cd was associated with cell walls in the root of H4, but the Cd in the root of L19 and leaf of the two cultivars was mainly stored in soluble fraction, which could be one possible mechanism of tolerance to Cd toxicity. In addition, Cd fractions extracted by 1 M NaCl and 2% HAC were predominant in root and leaf of both cultivars and the concentrations and proportions extracted by water and 80% ethanol in root and 1 M NaCl in leaf were all higher in H4 than in L19. These results indicate that the Cd in H4 is more active than L19, which could be responsible for the sensitivity of H4 to Cd damage.

To investigate the effects of different nitrate sources on the uptake, transport, and distribution of molybdenum (Mo) between two oilseed rape (Brassica napus L.) cultivars, L0917 and ZS11.A hydroponic culture experiment was conducted with four nitrate/ammonium (NO3−:NH4+) ratios (14:1, 9:6, 7.5:7.5, and 1:14) at a constant nitrogen concentration of 15 mmol/L. We examined Mo concentrations in roots, shoots, xylem and phloem sap, and subcellular fractions of leaves to contrast Mo uptake, transport, and subcellular distribution between ZS11 and L0917.Both the cultivars showed maximum biomass and Mo accumulation at the 7.5:7.5 ratio of NO3−:NH4+ while those were decreased by the 14:1 and 1:14 treatments. However, the percentages of root Mo (14.8% and 15.0% for L0917 and ZS11, respectively) were low under the 7.5:7.5 treatment, suggesting that the equal NO3−:NH4+ ratio promoted Mo transportation from root to shoot. The xylem sap Mo concentration and phloem sap Mo accumulation of L0917 were lower than those of ZS11 under the 1:14 treatment, which suggests that higher NO3−:NH4+ ratio was more beneficial for L0917. On the contrary, a lower NO3−:NH4+ ratio was more beneficial for ZS11 to transport and remobilize Mo. Furthermore, the Mo concentrations of both the cultivars’ leaf organelles were increased but the Mo accumulations of the cell wall and soluble fraction were reduced significantly under the 14:1 treatment, meaning that more Mo was accumulated in organelles under the highest NO3−:NH4+ ratio.This investigation demonstrated that the capacities of Mo absorption, transportation and subcellular distribution play an important role in genotype-dependent differences in Mo accumulation under low or high NO3−:NH4+ ratio conditions.采用不同NO3−:NH4+比的营养液,探索不同氮源 对钼元素在两种甘蓝型油菜(L0917 和ZS11)中 的吸收、转运和分布的影响及品种间的差异。在不同氮源条件下,从组织分布、汁液运输、亚 细胞分布以及品种等方面研究了甘蓝型油菜的 钼营养状况。将甘蓝型油菜L0917 和ZS11 的幼苗在正常营养 液培养20 天后,分别转移至4 种NO3−:NH4+比 (14:1、9:6、7.5:7.5、1:14)且总氮为15 mmol/L 的营养液中培养15 天后收获。采用原子吸收分 光光度计-石墨炉法测定根、茎和叶不同部位钼含 量,木质部和韧皮部液钼含量,叶肉细胞细胞壁 组分、细胞器组分和可溶性组分钼含量。在高或低NO3−:NH4+比条件下,高的钼吸收能力、 木质部转运、韧皮部再迁移以及叶片亚细胞钼储 存在甘蓝型油菜钼积累上扮演重要角色。

•Sludge treatment beds were investigated in the subtropical condition in China.•Residual sludge is rich in N, P, and K for agriculture usage.•Bioavailability of Cu, Ni, Cr, Fe, and Pb is low due to the high proportion in residual state and oxidation state.•Cd needs to be considered before the treated sludge can be applied in agriculture.Sludge treatment bed has been used for sludge dewatering and stablilization due to the low operating and maintenance costs. However, there are still limiting information of this technology compare to conventional technologies, and very few information on using this technology in developing countries. In the present study, two sludge treatment beds were investigated under seven sludge loading rates and feeding frequencies under subtropical condition in China. The results showed that plants play an important role for sludge dewatering and stablilization. The best loading rate and feeding frequency for sludge dewatering and stablilization was 10L/4d in the planted system, with TS (total solid) and VS (volatile solid)/TS contents were 29% and 25%, respectively. The best pollutants removal efficiencies in leachate was observed at 12L/4d in the planted system, which were 99.8%, 91.1%, 98.6%, and 91.5% for COD (chemical oxygen demand), NH4+-N, TN (total nitrogen), and TP (total phosphorus), respectively. Heavy metals concentrations in the leachate were below the Chinese integrated wastewater discharge standard. In the accumulated sludge, TN + TP + TK (total potassium) > 30 g/kg which fulfill the standard of Chinese sludge for agriculture reuse. The bioavailability of Cu, Ni, Cr, Fe, and Pb was low thanks to the high proportion in residual state and oxidation state. However, Cd needs to be considered before the treated sludge can be applied for agriculture in China.

The effects of increasing Cd additions on plant growth and Cd fractionation and enzyme activities in rhizosphere soil of two radish cultivars were investigated. The results showed that Cd concentrations in shoot and root of cultivar 4 were both higher than for cultivar 19 under different Cd levels. Compared with cultivar 19, the total, shoot and root biomasses of cultivar 4 were significantly reduced with increasing Cd levels. A decrease in soil pH was observed for cultivar 4. The exchangeable Cd concentration of soil from cultivar 4 was significantly higher than for soil from cultivar 19, while the carbonate-bound Cd concentration of soil from cultivar 4 was significantly lower than for cultivar 19. Enzyme activities, especially acid phosphatase activity, were more susceptible to Cd in soil from cultivar 4. These results indicated that cultivar 19 exhibits a stronger ability to adapt to Cd stress than cultivar 4.

The aim of the study was to examine the remediation effect of biochar derived from three feedstocks on soil acidification.The effects of biochar derived from peanut hull, rice straw and rape straw on soil acidity, chemical and microbial properties, nutrients absorption, and growth of orange seedlings planted in an acidic soil were studied in a greenhouse experiment.Soil pH was increased 0.70, 0.92, and 0.63 by peanut hull, rice straw, and rape straw biochars. However, only peanut hull biochar significantly increased plant growth and the biomass of trifoliate orange seedlings. Soil microbial biomass C and basal respiration were increased by peanut hull and rice straw biochar, and the geometric mean of enzyme activities (GMea) were increased by the three biochars, peanut hull biochar result in the highest increase. Rice straw and rape straw biochars had more abundant mineral nutrient, led to greater influence on soil and plant nutrient contents than peanut hull biochar. However, peanut hull biochar resulted in higher plant nutrients accumulation due to the improvement of plant biomass.Although the three biochars effectively neutralized soil acidity, only peanut hull biochar raised plant growth and the biomass of orange seedlings significantly, and the increase of soil microbial properties and enzyme activity would be the key factors for the improvement of plant growth.

Molybdenum (Mo) is an essential micronutrient for plants. To obtain a better understanding of the molecular mechanisms of cold resistance enhanced by molybdenum application in winter wheat, we applied a proteomic approach to investigate the differential expression of proteins in response to molybdenum deficiency in winter wheat leaves under low-temperature stress. Of 13 protein spots that were identified, five spots were involved in the light reaction of photosynthesis, five were involved in the dark reaction of photosynthesis, and three were highly involved in RNA binding and protein synthesis. Before the application of cold stress, four differentially expressed proteins between the Mo deficiency (−Mo) vs. Mo application (+Mo) comparison are involved in carbon metabolism and photosynthetic electron transport. After 48 h of cold stress, nine differentially expressed proteins between the −Mo vs. +Mo comparison are involved in carbon metabolism, photosynthetic electron transport, RNA binding, and protein synthesis. Under −Mo condition, cold stress induced a more than twofold decrease in the accumulation of six differential proteins including ribulose bisphosphate carboxylase large-chain precursor, phosphoglycerate kinase, cp31BHv, chlorophyll a/b-binding protein, ribulose bisphosphate carboxylase small subunit, and ribosomal protein P1, whereas under +Mo condition cold stress only decreased the expression of RuBisCO large subunit, suggesting that Mo application might contribute to the balance or stability of these proteins especially under low-temperature stress and that Mo deficiency has greater influence on differential protein expression in winter wheat after low-temperature stress. Further investigations showed that Mo deficiency decreased the concentrations of chlorophyll a, chlorophyll b, and carotenoids; the maximum net photosynthetic rate; the apparent quantum yield; and carboxylation efficiency, even before the application of the cold stress, although the decrease rates were greater after 48 h of cold treatment, which is consistent with changes in the expressions of differential proteins in winter wheat under low-temperature stress. These findings provide some new evidence that Mo might be involved in the light and dark reaction of photosynthesis and protein synthesis.

The influence of different pretreatment methods on anaerobic mixed inoculum was evaluated for selectively enriching the hydrogen (H2) producing mixed culture using glucose as the substrate. The efficiency of H2 yield and the glucose fermentation pathway were found to be dependent on the type of pretreatment procedure adopted on the parent inoculum. The H2 yield could be increased by appropriate pretreatment methods including the use of heat, alkaline or acidic conditions. Heat pretreatment of the inoculum for 30 min at 80 °C increased the H2 yield to 53.20% more than the control.When the inoculum was heat-pretreated at 80 °C and 90 °C, the glucose degraded via ethanol (HEt) and butric acid (HBu) fermentation pathways. The degradation pathways shifted to HEt and propionate (HPr) types as the heat pretreatment temperature increased to 100 °C. When the inoculum was alkali- or acid-pretreated, the fermentation pathway shifted from glucose to a combination of the HPr and HBu types. This trend became obvious as the acidity increased. As the fermentation pathway shift from the HEt type to the HPr and HBu types, the H2 yield decreased.

Vegetable production is one of the most intensive agricultural systems with high rates of nitrogen (N) fertilizer use and irrigation, conditions conducive for nitrate (NO3−) leaching, and nitrous oxide (N2O) emissions. The objective of this study was to determine the effectiveness of a nitrification inhibitor, dicyandiamide (DCD), in decreasing NO3− leaching and N2O emissions in vegetable production systems.Twenty-four undisturbed soil monolith lysimeters (610 mm in diameter; 700 mm in depth; surface area, 0.29 m2) with two different soils, Huangzongrang (alfisol) and Chaotu (fluvisols), were collected and installed in a field lysimeter facility in Central China under irrigated vegetable production conditions. Urea fertilizer was applied at 650 kg N ha−1, and DCD was applied at 10 kg ha−1 to the lysimeters planted with three kinds of vegetables (capsicum, Capsicum annuum L.; amaranth, Amaranthus mangostanus L.; radish, Raphanus sativus L.).The results showed that DCD reduced NO3− leaching by 58.5% and 36.2% and N2O emissions factor by 83.8% and 72.7% in the two soils. The average NO3−–N concentration in the drainage water was decreased from 4.9 mg N L−1 to 2.3 mg N L−1 and from 4.4 mg N L−1 to 3.3 mg N L−1, in the Huangzongrang and Chaotu soils, respectively. In addition to the environmental benefits, the use of DCD also increased the yields of capsicum and radish in alfisol soil significantly (P < 0.01); only the amaranth yield in fluvisol soil was declined (P < 0.01), and the other vegetables yields were not affected. Total N concentrations of the three vegetables were increased significantly (P < 0.01) with the application of DCD with urea compared with urea alone. These results showed that the nitrification inhibitor DCD has the potential to significantly reduce NO3− leaching and N2O emissions and to make vegetable farming more environmentally friendly.These results demonstrated that the use of the nitrification inhibitor DCD can significantly reduce NO3− leaching, N2O emissions, and the average NO3−–N concentration in the drainage water, while increasing the fertilizer N efficiency in the vegetable production system.

Nitrate leaching from intensive vegetable production is an important contributor of nitrate contamination of water resources. The aim of this study was to quantify NO3− leaching losses under intensive vegetable production as affected by different rates of N fertilizer and to determine the optimum N application rates both for vegetable production and for meeting the drinking water standard.Twelve undisturbed soil lysimeters (590 mm diameter and 650 mm depth) were collected and installed in a field lysimeter facility in Central China to study nitrate leaching from a clay loam soil (alfisol) under irrigated vegetable production conditions. Urea was applied at 0 kg N/ha (N0), 370 kg N/ha (N1), 1,110 kg N/ha (N2), and 1,480 kg N/ha (N3) to the lysimeters planted with vegetables. Nitrate leaching losses and vegetable yields were measured for five vegetables [capsicum (Capsicum annuum L.), amaranth (Amaranthus mangostanus L.), radish (Raphanus sativus L.), Chinese cabbage 1 (Brassica chinensis L.), and Chinese cabbage 2), with rotations lasting a total of 13 months.The results showed that NO3−–N leaching losses were significantly affected by urea–N application rates, increasing from 32.8 to 63.3, 227.1, and 353.7 kg N/ha in the N0, N1, N2, and N3 treatments, respectively. These leaching losses represented 8.2%, 17.5%, and 21.7% of the total N applied, respectively. The average NO3−–N concentration in the drainage water ranged from 3.7 to 43.1 mg N/L. Only the NO3−–N concentrations of the control and N1 treatment were below the drinking water standard (10 mg N/L). Plant N removal accounted for 38.3%, 29.7%, and 22.9% of total N applied in the N1, N2, and N3 treatments, respectively. The N application rates for maximum yield, 90% maximum yield, and for meeting the drinking water standard (10 mg N/L) were 1,098.4, 699.5, and 445.2 kg N/ha, respectively.These results showed that the intensive vegetable production systems with high N fertilizer application rates and irrigation have a high NO3− leaching potential. Both the N application rates for optimum economic yield and for meeting the drinking standard were much lower than those often used by local farmers pursuing excessively high yields.The optimum fertilizer N application rate should be set as that which would not result in the NO3−–N concentration in the leachate above the drinking water standard. This rate is often lower than that for 90% maximum production.

Snowmelt is the most important hydrological event in cold climates. However, snowmelt effects on suspended sediment (SS) and phosphorus (P) loss are poorly documented in Canada. Using two agricultural watersheds in Eastern Canada, this study aimed to quantify SS and P loss during the snowmelt period and to investigate how snowmelt contributes SS and P loss. Water samples were collected from the outlets of the Bras d’Henri watershed (BHW, 2007–2009) and Black Brook watershed (BBW, 2008–2009) and measured for SS and P concentrations. Hydrological parameters (precipitation, snow water equivalent, and runoff discharge), soil frozen status and soil temperature were also measured. Results revealed inter-annual variation of snowmelt conditions and SS and P losses in each watershed. The 2008 snowmelt in BHW and BBW mainly occurred on unfrozen soils, while the 2007 and 2009 snowmelts in BHW and 2009 snowmelt in BBW mainly on frozen soils. In BHW, 2008 snowmelt caused much higher median concentrations of SS, total P (TP), dissolved P (DP) and particulate P (PP) in stream water than 2007 and 2009; ratios of PP fractions in TP were variable with events but the median values were similar, suggesting both DP and PP important contrubutors to TP loss. In BBW, the median concentration of dissolved reactive phosphorus (DRP) in stream water was greater in 2008 snowmelt than in 2009 snowmelt; PP dominated TP loss. This study also suggests that soil state (i.e. frozen status) and rainfall were the most important factors influencing SS and P losses during snowmelt. Furthermore, snowmelt P export represented more than 20% of the total annual P export in BHW, and more than 12% of the annual DRP export in BBW. Thus, we strongly recommend adopting Best Management Practices (BMPs) that specifically target sediment and P loss during snowmelt.Research highlights▶ This study is the first multi-year study on sediment and P losses in agricultural watersheds during snowmelt period in Eastern Canada; the only published study to date reported only one year of data. ▶ This study reports that phosphorus and sediment losses are major at snowmelt runoff in eastern Canada and that dissolved P fraction losses is significant which may have impacts on water quality and aquatic life. ▶ This study links the climate conditions, snowmelt runoff and surface water quality and shows that the inter-annual variability in climate conditions is very important for P and sediment losses. ▶ This study shows that it is fundamental to adapt agricultural BMPs to specifically mitigate and reduce soil erosion and nutrients loss caused by snowmelt runoff. In fact, most of the current BMPs target only the P and sediment losses occurring during the warm crop season.

•Fruit pulp mastication characteristic was related to the fruit pulp IDF and SDF.•The fruit pulp IDF content was influenced by the fruit pulp P, Ca and B contents.•The fruit pulp SDF content was influenced by the fruit pulp P and K contents.•Fruit pulp mastication characteristic was improved by applying Ca and Mg fertilizers.The objective of the present work was to examine the effect of soil-applied calcium (Ca) and magnesium (Mg) on the fruit pulp mastication characteristics of “Nanfeng” tangerine (Citrus reticulata Blanco cv. Kinokuni). A field experiment was conducted continuously in a red soil orchard from 2011 to 2013. Five fertilization treatments were involved; they were FF (farmer’s fertilization), RF (recommended fertilization), RF + Ca, RF + CaMg and RF + FMP (fused magnesium phosphate). In this study, the fruit pulp’s shear force and insoluble dietary fiber (IDF) contents of the RF + CaMg were significantly lower than those of the RF treatment, and fruit pulp’s boron (B) content and leaf potassium (K) and B contents were lower whereas the leaf Mg content was higher in the RF + CaMg treatment than in the other treatments. The fruit pulp’s shear force (higher shear forces meant inferior mastication characteristics) was significantly positively related with IDF but negatively related with the soluble dietary fiber (SDF). However, fruit segment shear force was significantly negatively correlated with fruit pulp N and P contents but positively with B content. We concluded that the fruit pulp mastication characteristic was significantly related to both IDF and SDF of the fruit pulp which were predominantly influenced by the fruit pulp B, P, Ca and K contents, so the mastication characteristic of NM fruit pulp could be improved by combining appropriate N, P and K fertilization rates with 500 g lime and 100 g magnesium oxide per tree.

•Application of Fe-EDDHA could induce zinc deficiency in citrus in calcareous soil.•Fe and Zn played different roles on citrus fruit yield improvement in calcareous soil.•Zn was more important factor than Fe on citrus fruit quality parameters.•Co-application of Fe-EDDHA and Zn could raise yield and quality of citrus in calcareous soil.The purpose of this study was to investigate citrus tissue's response to varying applications of Fe-EDDHA, zinc (Zn) and manganese (Mn) combinations and the resulting effects on citrus fruit yield and quality in calcareous soil. A field experiment was conducted for three years with satsuma mandarin trees planted in calcareous soil. Four treatments were conducted: (i) control; (ii) soil Fe application; (iii) soil Fe + Zn application; and (iv) soil Fe + Zn + Mn application. Soil available Fe and Zn concentrations were raised through the application of Fe-EDDHA and Zn, whereas the soil available Mn concentration was not increased through the application of Mn. Applying Fe-EDDHA raised the leaf active Fe content significantly without influencing the leaf and fruit Fe concentrations. The Zn concentrations in leaf and fruit decreased when Fe-EDDHA was applied exclusively, but increased when Fe + Zn and Fe + Zn + Mn were applied in the third year. There was no significant difference in leaf and fruit Mn concentrations among all treatments between 2010 and 2012. Soil Fe, Fe + Zn and Fe + Zn + Mn application increased fruit number by 23.5%, 26.7% and 24.9%, respectively, and soil Fe + Zn application increased the yield in 2012. Fruit TSS, TA and Vc content were higher through the application of Fe + Zn and Fe + Zn + Mn in 2012. The results revealed that Fe and Zn play different roles that affect fruit yield and quality in calcareous soil. The citrus yield was mainly affected by Fe, whereas fruit quality was improved by Zn. The application of Fe-EDDHA alone could induce Zn deficiency, so the co-application of Fe-EDDHA and Zn fertilizer was useful for obtaining higher yield and quality in satsuma mandarin in calcareous soil.

Iron deficiency chlorosis occurred frequently in many fruit trees grown on calcareous soils with a high pH. A field experiment of Fe–EDDHA application and a nutritional status survey on citrus orchards were conducted to observe the effects of Fe–EDDHA application on iron chlorosis of citrus trees. Three approaches, i.e., Sufficiency Range Approach (SRA), Diagnosis and Recommendation Integrated System (DRIS) and Compositional Nutrient Diagnosis (CND), were performed to evaluate the nutrient balance status of citrus trees. DRIS and CND were suitable to diagnose and evaluate nutrient balance status of citrus trees grown on calcareous soils with a high pH. The diagnosis results revealed that Fe–EDDHA application significantly improved Fe nutrition and decreased Zn in chlorotic citrus trees. The nutritional status of Zn, Mn, Fe, P and Mg were at the deficient levels and Cu, N, Ca and K at the excessive levels in iron treatment citrus trees. The results demonstrated that the leaf chlorosis of citrus trees grown on calcareous soils with a high pH was mainly caused by iron deficiency, but it was not the single cause leading to the nutrient imbalance in iron chlorotic citrus trees. DRIS and CND were suitable to diagnose and evaluate nutrient balance status of citrus trees grown on calcareous soils with a high pH. The results revealed that Zn and Mn deficiencies became the new limiting factors in iron deficiency citrus trees after iron chlorosis correction.Highlights► This paper studied the effects of EDDHA application on chlorotic citrus leaves. ► DRIS and CND were suitable to diagnose and evaluate the nutrient balance status. ► Iron deficiency was the main reason for the chlorosis. ► The deficiency of Zn and Mn could be the new limiting nutrients after iron correction.