Low NO3 Research Articles

Water connectivity in hillslope of upland–riparian zone and the implication for stream nitrate-N export during rain events in an agricultural and forested watershed

Water connectivity in the hillslopes of the upland–riparian zone has environmental implications for stream nitrate-N (NO3 −-N) export during rain events. This study was conducted to measure the shallow groundwater table over a hillslope with upland, interface, and riparian forest components and measure the stream NO3 −-N concentrations in a 36.6 km2 agricultural and forested watershed (AFW) in the Shibetsu area of northern Japan from July to November 2009. The groundwater and stream hydrographs at seasonal and rain event scales indicated that the hillslope water connectivity was first established from the riparian forest, and then expanded to the upland after several rain events. The hillslope water connectivity has important implications for NO3 −-N export in the watershed since the NO3 −-N export may primarily be explained by a flushing mechanism. The NO3 −-N export only flushed from riparian forest during the early water connection stage. While in the well water connection stage, the flush of NO3 −-N occurred with the subsurface flow from the upland which had a high shallow groundwater table and displayed higher stream NO3 −-N concentrations. However, lower stream NO3 −-N concentrations occurred during the late water connection stage and indicated that the N source in the upland might be limited due to denitrification and NO3 −-N leaching processes. Nevertheless, it was decided that the hydrology and biogeochemical reactions occurring in the upland controlled the stream NO3 −-N export. A conceptual model was formulated that explained the impacts of the hillslope water connectivity on the watershed stream NO3 −-N export during rain events in early, well, and late water connection stages within the AFW.

Influence of organic carbon and nitrate loading on partitioning between dissimilatory nitrate reduction to ammonium (DNRA) and N2 production

Biologically available nitrogen is removed from ecosystems through the microbial processes of anaerobic ammonium oxidation (anammox) or denitrification, while dissimilatory nitrate reduction to ammonium (DNRA) retains it. A mechanistic understanding of controls on partitioning among these pathways is currently lacking. The objective of this study was to conduct a manipulative experiment to determine the influence of organic C and NO3− loading on partitioning. Sediment was collected from a location on the southern New England shelf (78m water depth) and sieved. Half of the sediment was mixed with freeze-dried phytoplankton and the other half was not. Sediment was then spread into 1.5mm, “thin discs” closed at the bottom and placed in large aquarium tanks with filtered, N2/CO2 sparged seawater to maintain O2 limited conditions. Half of the discs received high NO3− loading, while the other half received low NO3− loading, resulting in a multifactorial design with four treatments: no C addition, low NO3− (−C−N); C addition, low NO3− (+C−N); no C addition, high NO3− (−C+N); and C addition, high NO3− (+C+N). Sediment discs were incubated in the tanks for 7weeks, during which time inorganic N (NH4+, NO3−, and NO2−) was monitored, and sediment discs were periodically removed from the tanks to conduct 15N isotope labeling experiments in vials to measure potential rates of anammox, denitrification, and DNRA. Temporal dynamics of inorganic N concentrations in the tanks were indicative of anoxic N metabolism, with strong response of the build up or consumption of the intermediate NO2−, depending on treatments. Vial incubation experiments with added 15NO2−+14NH4+ indicated significant denitrification and DNRA activity in sediment thin discs, but incubations with added 15NH4++14NO2− indicated anammox was not at all significant. Inorganic N concentrations in the tanks were fit to a reactive transport model assuming different N transformations. Organic C decomposition rates were inferred based on modeled rates as well as stoichiometric conversions of NH4+ production in pre-incubated vials. Based on model results, partitioning between DNRA and N2 production was positively linearly related to the ratio of C decomposition to NO3− reduction rates (C/NO3−) but not C decomposition alone. Based on vial results, partitioning was significantly related to C decomposition. Overall, this study supports the hypothesis that high organic C loading is a prerequisite for DNRA to be favored over denitrification but that N2 production may still be significant when organic C is high depending on NO3− availability.

Polyamines in conventional and organic vegetables exposed to exogenous ethylene

Relationships between endogenous levels of polyamines by thin layer chromatography (TLC) and gas chromatography (GC), nitrate and response to the application of ethylene were established between organic and conventional vegetables (broccoli, collard greens, carrots and beets), both raw and cooked. Responses to ethylene showed that organic plants were less responsive to the growth regulator. The levels of free polyamines obtained by TLC were higher in organic vegetables. Organic broccoli showed higher levels of putrescine (Put), and cooking resulted in lowering the overall content of these amines. Conventional collard green showed the highest level of putrescine in the leaves compared with organic. Tubers of carrots and beets contain the highest levels of Put. These plants also contain high levels of spermine. GC analysis showed the highest polyamines contents compared with those obtained by TLC. Cooking process decreased putrescine and cadaverine content, both in conventionally and organically grown vegetables. Organic beets contain lower NO3− compared with its conventional counterpart.

Denitrification in the shallow groundwater system of a lowland catchment: A laboratory study

Evidence for the occurrence of denitrification in shallow groundwater systems in New Zealand (NZ) is poorly documented; however, an observational study of the Toenepi dairying catchment in the Waikato region of NZ revealed a prevalence of reduced groundwater with very low nitrate (NO3−) concentrations (predominantly <0.5mgL−1N). Denitrification in the shallow groundwater system could play an important role in catchments with high NO3− leaching losses, by reducing the impact of land use and management practices on freshwater bodies. International studies have shown that denitrification below the root zone is often limited by the low availability of carbon (C) or other electron donors. In this laboratory incubation study we investigated three different profiles (to a maximum depth of 4.7m below ground surface) in the Toenepi catchment (15km2). Denitrification capacity was measured following the addition of 15N-enriched NO3−, while glucose was used as a readily available C source when ascertaining the denitrification potentials. The largest total 15N fluxes (without C amendment) were observed in samples from the Kereone (1.3–2.1nmolNg−1h−1) and Topehaehae sites (2.8nmolNg−1h−1); however, all sites had samples with fluxes of a similar magnitude (3.3–4.7nmolNg−1h−1) with no significant difference between sites (p>0.05) when glucose was added. The profiles were generally C-limited, as indicated by more than 80% of samples showing an increase (p<0.01) in total 15N gas (15N2+15N2O) production after C addition. The composition of the total 15N gas flux varied with depth but 15N2 was ≥69% of the total 15N flux and typically >92%. Extrapolation of denitrification capacity rates to field temperatures (14°C) indicates that much of the material found at depth, particularly at the Kereone and Topehaehae sites could contribute substantially towards attenuating the estimated NO3− leaching losses (29–42kgNha−1year−1) from the root zone and is likely the cause of the very low NO3− concentrations prevalent throughout the catchment.

A survey of nitrate and nitrite concentrations in conventional and organic-labeled raw vegetables at retail.

A national survey of the nitrate ( NO3(-)) and nitrite ( NO2(-)) concentrations in raw and highly consumed vegetables available at retail in the United States was conducted. A total of 194 samples of fresh broccoli, cabbage, celery, lettuce, and spinach categorized as conventional or organic by label were collected from 5 major cities in different geographic regions of the United States and analyzed to determine NO3(-) and NO2(-) concentrations. There were no differences in the mean NO2(-) values of conventional compared with organic vegetables taken from the 5 metropolitan areas. However, significant differences in mean pairwise comparisons between some conventional and organic vegetables for NO3(-) content were observed. The mean NO2(-) concentration of both conventional and organic vegetables ranged between 0.1 and 1.2 mg/kg of fresh weight (FW) with the exception of conventional spinach that contained 8.0 mg/kg FW. Mean NO3(-) contents of conventional broccoli, cabbage, celery, lettuce, and spinach were 394, 418, 1496, 851, and 2797 mg/kg FW, respectively, while their organic-labeled counterparts averaged 204, 552, 912, 844, and 1318 mg/kg FW. In most cases, organic vegetables were numerically lower in NO3(-) content than their conventional counterparts. Based on survey results, the finding that low NO3(-) levels were observed in some organic vegetables in different cities may warrant further study to determine if true differences exist, due to production practices, seasonal differences, and the magnitudes of those differences. Furthermore, the geographic differences in NO3(-) content of vegetables may flaw estimates of daily NO2(-) and NO3(-) exposure.

Stoichiometric determination of nitrate fate in agricultural ecosystems during rainfall events.

Ecologists have found a close relationship between the concentrations of nitrate (NO3 -) and dissolved organic carbon (DOC) in ecosystems. However, it is difficult to determine the NO3 - fate exactly because of the low coefficient in the constructed relationship. In the present paper, a negative power-function equation (r 2 = 0.87) was developed by using 411 NO3 - data points and DOC:NO3 - ratios from several agricultural ecosystems during different rainfall events. Our analysis of the stoichiometric method reveals several observations. First, the NO3 - concentration demonstrated the largest changes when the DOC:NO3 - ratio increased from 1 to 10. Second, the biodegradability of DOC was an important factor in controlling the NO3 - concentration of agricultural ecosystems. Third, sediment was important not only as a denitrification site, but also as a major source of DOC for the overlying water. Fourth, a high DOC concentration was able to maintain a low NO3 - concentration in the groundwater. In conclusion, this new stoichiometric method can be used for the accurate estimation and analysis of NO3 - concentrations in ecosystems.

Preliminary Evaluation of a Permeable Reactive Barrier for Reducing Groundwater Nitrate Transport from a Large Onsite Wastewater System

A permeable reactive barrier was installed between a large Onsite Wastewater System (OWS) and a monitoring well located down-gradient from the OWS. Groundwater samples from the well had shown elevated and increasing concentrations of NO3--N (>20 mg L-1 for 2 years). The barrier was constructed using woodchips from various tree species that were placed in a trench excavated to approximately the same depth as the well which was experiencing elevated NO3--N concentrations. Groundwater samples (5) were collected from the well between two weeks and four months after the barrier was installed. Groundwater NO3--N concentrations dropped by an average of 5 mg L-1, while Dissolved Organic Carbon (DOC) concentrations increased by 11 mg L-1 and Cl concentrations stayed relatively stable (<2 mg L-1 increase). The data suggest that denitrification fueled by the DOC from the barrier may be contributing to the lower NO3--N concentrations. Monitoring will continue at the site to determine the longer-term water quality trends. More research should be conducted to evaluate the applicability of permeable barriers as a best management practice for non-point sources of pollution in nutrient sensitive areas.

Applicability of a novel osmotic membrane bioreactor using a specific draw solution in wastewater treatment

This study aims to develop a new osmotic membrane bioreactor by combining a moving bed biofilm reactor (MBBR) with forward osmosis membrane bioreactor (FOMBR) to treat wastewater. Ethylenediaminetetraacetic acid disodium salt coupled with polyethylene glycol tert-octylphenyl ether was used as an innovative draw solution in this membrane hybrid system (MBBR–OsMBR) for minimizing the reverse salt flux and maintaining a healthy environment for the microorganism community. The results showed that the hybrid system achieved a stable water flux of 6.94L/m2h and low salt accumulation in the bioreactor for 68days of operation. At a filling rate of 40% (by volume of the bioreactor) of the polyethylene balls used as carriers, NH4+-N and PO43−-P were almost removed (>99%) while producing relatively low NO3−-N and NO2−-N in the effluent (e.g. <0.56 and 0.96mg/L, respectively). Furthermore, from analysis based on scanning electron microscopy, Fourier transform infrared spectroscopy, and fluorescence emission–excitation matrix spectrophotometry, there was a thin gel-like fouling layer on the FO membrane, which composed of bacteria as well as biopolymers and protein-like substances. Nonetheless, the formation of these fouling layers of the FO membrane in MBBR–OsMBR was reversible and removed by a physical cleaning technique.

High-affinity nitrate/nitrite transporter genes (Nrt2) in Tisochrysis lutea: identification and expression analyses reveal some interesting specificities of Haptophyta microalgae.

Microalgae have a diversity of industrial applications such as feed, food ingredients, depuration processes and energy. However, microalgal production costs could be substantially improved by controlling nutrient intake. Accordingly, a better understanding of microalgal nitrogen metabolism is essential. Using in silico analysis from transcriptomic data concerning the microalgae Tisochrysis lutea, four genes encoding putative high-affinity nitrate/nitrite transporters (TlNrt2) were identified. Unlike most of the land plants and microalgae, cloning of genomic sequences and their alignment with complementary DNA (cDNA) sequences did not reveal the presence of introns in all TlNrt2 genes. The deduced TlNRT2 protein sequences showed similarities to NRT2 proteins of other phyla such as land plants and green algae. However, some interesting specificities only known among Haptophyta were also revealed, especially an additional sequence of 100 amino acids forming an atypical extracellular loop located between transmembrane domains 9 and 10 and the function of which remains to be elucidated. Analyses of individual TlNrt2 gene expression with different nitrogen sources and concentrations were performed. TlNrt2.1 and TlNrt2.3 were strongly induced by low NO3 (-) concentration and repressed by NH4 (+) substrate and were classified as inducible genes. TlNrt2.2 was characterized by a constitutive pattern whatever the substrate. Finally, TlNrt2.4 displayed an atypical response that was not reported earlier in literature. Interestingly, expression of TlNrt2.4 was rather related to internal nitrogen quota level than external nitrogen concentration. This first study on nitrogen metabolism of T. lutea opens avenues for future investigations on the function of these genes and their implication for industrial applications.

Mixed Agricultural Pollutant Mitigation Using Woodchip/Pea Gravel and Woodchip/Zeolite Permeable Reactive Interceptors

Dairy soiled water (DSW) is water from concreted areas, hard stand areas and holding areas for livestock that has become contaminated by livestock faeces or urine, chemical fertilisers and parlour washings. Losses of DSW occur as point (e.g. storage, pivot irrigators) and diffuse losses (e.g. during or shortly after land application). The concept of a permeable reactive interceptor (PRI), comprising a denitrifying bioreactor woodchip cell to convert nitrate (NO3−) to dinitrogen (N2) gas and an adsorptive media cell for phosphorus (P) and ammonium (NH4+) mitigation, attempts to simultaneously treat mixed pollutants. This study is the first attempt to test this concept at laboratory-scale. Washing of woodchip media prior to PRI operation produced low NO3− but high NH4+, dissolved reactive P (DRP) and dissolved organic carbon losses. Dairy soiled water was then treated in replicated PRIs containing woodchip in combination with zeolite or gravel compartments. In general, all PRIs were highly efficient at reducing NO3−, NH4+, DRP, dissolved unreactive phosphorus (DUP) and dissolved organic nitrogen (DON) from an influent water replicating DSW. Longitudinal and hydrochemical PRI profiles, as well as zeolite batch experiments, showed that woodchip can both enhance NO3− reduction and adsorb nutrients. Since woodchip is likely to become saturated, it is important to place the reactive media cell further into the sequence of treatment. Even though the majority of the dissolved nutrients were mitigated, the PRIs also emitted greenhouse gases, which would need further remediation sequences.

An assessment of the influence of sulfidic mine wastes on rainwater quality in a semiarid climate (SE Spain)

This study assessed the influence of the Sierra Minera de Cartagena – La Unión mining wastes on the surrounding areas, due to the sediment transport in the atmosphere. Monitoring of 15 weather stations located in the Campo de Cartagena land (SE Spain) was performed in the period December, 2004–March, 2008. A total of 920 rainfall water samples were collected and analyzed in this study. The network of weather stations covered a wide range of soil use and human activities (industrial, urban, agricultural, and mining sites). The physicochemical characterization involved determination of pH, EC, major ions, and the metals of interest in the soluble fraction of rainwater. Precipitations had an alkaline pH (7.0–7.9) and, compared to World Health Organization guidelines for drinking-water quality, samples were characterized by low EC (76–930 μS/cm), Ni (0.1–8 μg/L), Cu (3–88 μg/L), As (0.04–2 μg/L), Na+ (3–16 mg/L), K+ (0.41–30 mg/L), Ca2+ (6–51 mg/L), Mg2+ (up to 5 mg/L), Cl– (4–23 mg/L), NO3– (1–30 mg/L), and SO42− (4–35 mg/L) values. In certain locations, Zn, Cd, and Pb exceeded the guideline limits. A downward trend of H+, Zn, Cd, and Pb concentrations in total depositions was observed while the distance to the area affected by mining activities increased in the first 20 km. Rainwater quality was found to be just subtly affected by the metal-sulfide abandoned minesites, but without presenting a current threat to neither public health nor natural ecosystem. Nevertheless, greater attention should be paid in the future projections of climate change, where a significant increase in aridity may favor the atmospheric transport of pollutant particles.

Nitrate reutilization mechanisms in the tonoplast of two Brassica napus genotypes with different nitrogen use efficiency

Nitrate (NO3−) can accumulate in high concentrations in plant cell vacuoles if it is not reduced, reutilized or transported into the cytoplasm. Such accumulation of NO3− in the vacuole occurs when mechanisms for NO3− assimilation in the cytoplasm are saturated. Moreover, other processes such as efflux across the plasma membrane might affect NO3− accumulation in the vacuole. These are the main reasons limiting nitrogen use efficiency (NUE) in plants. This study elucidates mechanisms for NO3− transport from the cytoplasm to vacuoles by the V-proton pump (V-ATPase and V-PPase) and their relationship with different NUE in four Brassica napus genotypes. Pot experiments were conducted in a greenhouse under normal (15.0 mmol L−1) and limited N (7.5 mmol L−1) concentrations of nitrate using B. napus genotypes that demonstrated either high (742 and Xiangyou 15) or low (814 and H8) NUE (g g−1). Specific inhibitors of V-ATPase and V-PPase increased nitrate reductase (NR) activity, resulting in greatly decreased NO3− in plant tissues. Nitrate reductase activity and NO3− content correlated more highly to V-PPase activity than they did to V-ATPase activity, and correlation between V-PPase activity and NO3− content was significantly higher than it was to V-ATPase. Genotypes with high NUE had significantly lower activities of V-ATPase and V-PPase than those with low NUE. In the high-NUE plants, lower activities of V-proton pump underlie mechanisms that result in significantly lower NO3− content in plant tissues of the high-NUE genotypes than those found in plant tissues of the low-NUE genotypes. Our results show that the tonoplast proton pumps V-PPase and V-ATPase strongly negatively affect NR activity and positively affect NO3− content. V-PPase contributed more to this regulatory mechanism than did V-ATPase.

Response of nitrogen use efficiency and soil nitrate dynamics to soil mulching in dryland maize (Zea mays L.) fields

Plastic film (FM) and gravel mulching (GM) have been used extensively to increase dryland agricultural productivity. Understanding mulching effects on nitrogen (N) use efficiency (NUE) and soil nitrogen dynamics is important for optimizing N management strategies. A 3-year field experiment was performed on the Loess Plateau of China to investigate the GM and FM effects on plant N accumulation, N translocation, N harvest index (NHI), NUE and soil NO3 −-N dynamics in dryland maize fields. Compared with the control (CK, non-mulching), the mulching treatments markedly promoted plant N accumulation and especially maintained higher N uptake rates during the post-silking stage. At harvest, the total N accumulation was 12.8–41.2 and 33.2–55.8 % higher in the GM and FM treatments, respectively, than in the CK treatment. The NHIs of the mulching treatments were significantly higher by 9.6–32.4 % than the CK treatment, primarily due to greater N translocation and N accumulation post-silking. Overall, compared with the CK treatment, the GM and FM NUEs increased significantly by 17.1 and 28.3 % in 2010, 70.3 and 87.6 % in 2011, and 16.7 and 38.2 % in 2012, respectively. In the wet years of 2010 and 2011, the increased amount of soil NO3 −-N in the 100–200 cm layer after harvest was 27.1–57.1 and 47.9–85.7 % lower in the GM and FM treatments, respectively, than in the CK treatment, indicating a lower NO3 −-N leaching loss. These results suggest that mulching (especially FM) is an effective measure for increasing NUE and grain yield and decreasing N leaching loss in dry farmland.

Dry deposition, seasonal variation and source interpretation of ionic species at Abali, Firouzkouh and Varamin, Tehran Province, Iran

Using a passive sampler, the results of the analyses of water soluble ions (Na+, Cl−, K+, NH4+, NO3−, SO42−, Ca2+ and Mg2+) in Abali, Firouzkouh and Varamin stations were registered. Dry deposition fluxes of water soluble ions were collected weekly for 14months (Oct. 2010 to Dec. 2011). The results showed that the weekly dry deposition mass fluxes ranged from 16.48 to 922.68mgm−2day−1, with annual average deposition of 159.37, 124.46 and 237.09 in mg m−2day−1 in Abali, Firouzkouh and Varamin, respectively. In Abali, Na+, SO42− and NO3− the dominant ionic species were Na+, SO42− and NO3−, SO42−, Ca2+ and NO3− and SO42−, Na+ and Ca2+, accounting for 28%, 23% and 17%, 36%, 25% and 18% and 30%, 20% and 19% of the total mass of ions, in Abali, Firouzkouh and Varamin, respectively. Dry deposition flux of major ions was higher during the dust storm and other weather phenomena. Air mass back trajectories calculated for all three sampling sites on October 2011 (when there was pollution), revealed four sectors of air mass origin: NW to N of Siberia/Russia and Caspian Sea, local, Middle East and W to SW of Oman Sea. Seasonal variation of total ion flux was significant, with the highest depositions observed in winter 2011, autumn 2010 and autumn 2011 and the lowest depositions in spring 2011, spring 2011 and autumn 2010 in Abali, Firouzkouh and Varamin, respectively. These major ions were mainly in the form of Ca(NO3)2, CaSO4, CaCl2, and NaCl. Firouzkouh had the lowest NO3−/SO42− flux value among the two other sampling sites, indicating that the stationary source of the air pollution was the more dominant one. Stationary emissions were still the dominant source in all three sampling sites demonstrated by the NO3−/SO42− ratio being lower than one. NO3−, SO42− and NH4+ were primarily affected by anthropogenic emissions, while SO42− might have been partially influenced by the sea. Na+ and K+ were derived from both soil crust and marine sources, but Ca2+ was mainly coming from the soil.

Influence of two different cover crops on soil N availability, N nutritional status, and grape yeast-assimilable N (YAN) in a cv. Tempranillo vineyard

The aim was to study the effects of two different cover crops (leguminous versus gramineous) on soil NO3 −-N availability, grapevine N status, and yeast-assimilable N (YAN) and amino acid profile in the must of a cv. Tempranillo vineyard from La Rioja (Spain) over 3 years. Three treatments were established: gramineous (barley) and leguminous (Persian clover) cover crops and conventional tillage. Soil total N and extractable NH4 +-N at bloom, soil NO3 −-N content from budbreak to postharvest, leaf N content at bloom, and free amino acids and ammonia in must were monitored. Each year, the barley cover crop treatment had lower soil NO3 −-N than tillage, while the clover treatment showed lower soil NO3 −-N than tillage in 2009 and showed higher values in 2010 and 2011. In 2011 leaf N content, yeast-assimilable N (YAN), and some amino acids in the grapes were lower in barley cover crop treatment thus affecting the amino acid profile. Meanwhile, the clover cover crop did not have these effects. Furthermore, relationships between leaf N content and various amino acids were also found. With the barley cover crop treatment, soil N availability decreased from the first year of the experiment, provoking a decrease in N grapevine status and in content of YAN and various amino acids at the third year. In contrast, clover cover crop maintained N grapevine status, YAN, and amino acid profile similar to conventional tillage. Therefore, our study shows how soil N can be managed both within a year and from year to year when two different cover crops are sown and how the grapevine N nutritional status and YAN content and amino acid profile can be modified in the must.

Determining nitrate and ammonium requirements for optimal in vitro response of diverse pear species

Inorganic nitrate (NO3 −) and ammonium (NH4 +) are the two major components in nitrogen (N) nutrition of typical tissue culture growth media, and the total amounts and ratios influence both shoot induction and differentiation. This study was designed to determine the optimal N requirements and interactions of NH4 + × NO3 − to complete the optimization of a pear shoot culture medium. Pyrus communis ‘Horner 51’ and ‘OH × F 87’, P. cordata, P. pyrifolia ‘Sion Szu Mi’, and P. ussuriensis ‘Hang Pa Li’ from the pear germplasm collection of the US Department of Agriculture, National Clonal Germplasm Repository–Corvallis (NCGR) were evaluated. Response surface design was used to create and analyze treatment combinations of NH4 +, K+, and NO3 −. Cultures were evaluated for overall quality, shoot length, multiplication, leaf color and size, leaf spotting and necrosis, and callus production. Significant improvement was observed in multiplication and length for most genotypes. Reduced callus amounts were seen in two genotypes, and greener leaves were also seen in two genotypes. Each species had a distinct response, and the N form could be manipulated to produce longer shoots, more shoots, or less callus. For the best-quality shoots, both P. communis cultivars required high NO3 − and low to moderate NH4 +, P. cordata quality was best with high NO3 − and NH4 +, P. pyrifolia ‘Sion Szu Mi’ quality improved with moderate NO3 − and high NH4 +, and P. ussuriensis ‘Hang Pa Li’ required low NO3 − and high NH4 +. This study illustrates that optimizing the N components of a growth medium is very important when working with diverse plant germplasm.

Does low stomatal conductance or photosynthetic capacity enhance growth at elevated CO2 in Arabidopsis?

The objective of this study was to determine if low stomatal conductance (g) increases growth, nitrate (NO3 (-)) assimilation, and nitrogen (N) utilization at elevated CO2 concentration. Four Arabidopsis (Arabidopsis thaliana) near isogenic lines (NILs) differing in g were grown at ambient and elevated CO2 concentration under low and high NO3 (-) supply as the sole source of N. Although g varied by 32% among NILs at elevated CO2, leaf intercellular CO2 concentration varied by only 4% and genotype had no effect on shoot NO3 (-) concentration in any treatment. Low-g NILs showed the greatest CO2 growth increase under N limitation but had the lowest CO2 growth enhancement under N-sufficient conditions. NILs with the highest and lowest g had similar rates of shoot NO3 (-) assimilation following N deprivation at elevated CO2 concentration. After 5 d of N deprivation, the lowest g NIL had 27% lower maximum carboxylation rate and 23% lower photosynthetic electron transport compared with the highest g NIL. These results suggest that increased growth of low-g NILs under N limitation most likely resulted from more conservative N investment in photosynthetic biochemistry rather than from low g.

Conservation tillage positively influences the microflora and microfauna in the black soil of Northeast China

Soil food webs are important in maintaining agricultural productivity and ecosystem health. However, our understanding is still limited with respect to the influences of tillage transitions on soil food webs. The present study aimed to quantify the response of microflora and microfauna, and their linkage to different tillage treatments: no tillage (NT), ridge tillage (RT) and conventional tillage (CT). Soil samples were collected from 0 to 20cm depth in April of 2011 after 10 years of conservation tillage. The abundance and richness of bacteria and arbuscular mycorrhizal fungi were greater in NT and RT than in CT. In case of microfauna also, similar patterns were observed with greater protozoa, bacterivores and omnivores–carnivores in NT and RT compared to CT. The connectance of the bacterial and predator–prey pathways was greater in NT and RT than in CT and that of fungal pathway was greatest in RT. The trophic relationship of the bacterial and predator–prey pathways was strengthened due to the higher water content of soil and the lower NO3–-N after the conversion of CT to NT and RT. Our study suggested that 10 years of conservation tillage can effectively enhance the structure and function of soil food webs through bottom–up effects in the black soil region of Northeast China.

Microbial regulation of nitrogen dynamics along the hillslope of a natural forest

Topography affects the soil physicochemistry, soil N dynamics, and plant distribution and growth in forests. In Japan, many forests are found in mountainous areas and these traits are often highly variable along steep slopes. In this study, we investigated how the microbial population dynamics reflected the bioavailable N dynamics with the physicochemical gradient along the slope in soils of a natural forest in Japan. We measured the gross rates of NH4+ production, nitrification, and NH4+/ NO3− immobilization using the N isotope dilution method to analyze the N dynamics in the soils. We also determined the abundance of the bacterial 16S rRNA gene and bacterial and archaeal ammonia monooxygenase gene (amoA) using qPCR to assess the populations of total bacteria and nitrifiers. We found that gross rates of NH4+ production and nitrification were higher in the lower part of the slope, they were positively correlated with the abundance of the bacterial 16S rRNA gene and archaeal amoA, respectively; and the availability of N, particularly NO3−, for plants was higher in the lower part of the slope because of the higher microbial nitrification activity and low microbial NO3− immobilization activity. In addition, path analysis indicated that gross rates of NH4+ production and nitrification were regulated mainly by the substrate (dissolved organic N and NH4+) concentrations and population sizes of total bacteria and nitrifiers, respectively, and their population sizes were strongly affected by the soil physicochemistry such as pH and water content. Our results suggested that the soil physicochemical gradient along the slope caused the spatial gradient of gross rates of NH4+ production and nitrification by altering the communities of ammonifiers and nitrifiers in the forest slope, which also affected plant distribution and growth via the supply of bioavailable N to plants.

黄河三角洲盐碱地不同造林模式下的土壤碳氮分布特征

PDF HTML阅读 XML下载 导出引用 引用提醒 黄河三角洲盐碱地不同造林模式下的土壤碳氮分布特征 DOI: 10.5846/stxb201311282837 作者: 作者单位: 滨州学院,滨州学院,滨州市水利局,滨州学院 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目(31370702); 国家"十一五"科技支撑计划项目(2009BADB2B0502); 山东省高校科研发展计划项目(J13LE58, J13LC03); 山东省科技发展计划项目(2013YD17001) Distribution characteristics of soil carbon and nitrogen under different afforestation modes of saline land in the Yellow River Delta Author: Affiliation: Binzhou University,Shandong Provincial Key Laboratory of Eco-Environmental Science for Yellow River Delta,Binzhou,Binzhou University,Shandong Provincial Key Laboratory of Eco-Environmental Science for Yellow River Delta,Binzhou,, Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:为了探讨不同造林模式对土壤碳氮影响的生态效应,以黄河三角洲盐碱地白蜡+棉花(FC)、香花槐+棉花(RC)、竹柳+棉花(SC)、白蜡林(F)、竹柳林(S)等5种造林模式为研究对象,分析比较各造林模式土壤的碳氮形态及分布特征,为重度退化刺槐林的经营改造和造林模式选择提供理论依据。结果显示:(1)不同造林模式下土壤的可溶性总碳和可溶性有机碳含量均高于裸地,农林间作高于纯林,其中SC模式含量最高,其次为FC和RC模式,而F和S纯林模式较低;5种造林模式不同土层可溶性有机碳含量均表现为0-20 cm高于20-40 cm。(2)农林间作模式0-40 cm土层的可溶性全氮和可溶性有机氮平均含量均高于纯林模式,其中SC模式的含量最高。FC、SC和S纯林模式 0-20 cm土层可溶性有机氮含量显著高于20-40 cm土层,分别为其1.4、1.5和2.7倍;而RC模式 20-40 cm土层可溶性有机氮含量显著高于0-20 cm土层。(3)5种造林模式中,除F纯林土壤硝态氮低于裸地外,其他造林模式下的土壤各种氮养分含量均显著高于裸地。土壤可溶性有机碳与全氮和铵态氮的相关性达到极显著水平(P<0.01)。研究表明农林间作模式可显著提高重度退化刺槐林皆伐后土壤中有效态碳、氮含量,其中SC模式改良效果较好,而纯林模式较差。 Abstract:The Yellow River Delta is the largest estuarine wetland ecosystem in the warm temperate zone of in China and the most active land-ocean interacion regions among the large river deltas in the word. However, here rainfall was less and the mineral content in underground water was higher. These conditions caused soil salinization and alkalization. Soil affected by saline and alkaline constitute nearly 50 percent of total and surface. Therefore, the development of management strategies designed to reduce soil salinity has become a high priority in this region. However, a better understanding of ecological effects of different afforestation is necessary before targeted management strategies can be conceived. Thus, the objective of this study is to assess the effects of agro-forestry and pure forest on the organic carbon and nitrogen of saline soil in the Yellow River Delta. Total soluble carbon (TOC), dissolved organic carbon (DOC), total soluble nitrogen (TSN), soluble organic nitrogen (SON), NH4+-N, NO3-N and total nigrogen (TN) in soil taken from different afforest measures were analyzed. Five afforestation models were Fraxinus chinensis + Gossypium hirsutum (FC), Robinia pseudoacacia cv. Idaho + Gossypium hirsutum (RC), Salix babylonica + Gossypium hirsutum (SC), Fraxinus chinensis (F) and Salix babylonica (S). Compared with bare land, soil TOC and DOC contents in the combination of SC were highest among all treatments, followed by FC, RC,Soil DOC content in all systems tended to be higher in surface layer (0-20 cm) than in deeper layer (20-40 cm). Regardless of soil layers, the contents of TSN and SON were higher in agro-forestry than in pure forest,SC had the highest level of soil TSN and SON. The contents of SON in 0-20 cm soil layers were significantly higher than 20-40 cm soil layers under FC, SC and S, respectively was 1.4, 1.5 and 2.7 times of them. Conversely, the contents of soil SON in 20-40 cm were significantly higher than in 0-20 cm under RC. Among five afforestation measures, the contents of all kinds of soil nitrogen were significantly higher than bare land, excepted for the lower NO3--N contents under F. There was a positive correlation between the DOC,and TN and NH4+-N (P<0.01). The conclusion indicates that the agro-forestry could significantly improve the contents of soil effective carbon and nitrogen, in particular, SC was the best afforestation model, while the pure forest was poor. 参考文献 相似文献 引证文献