Rapid immobilization of applied nitrogen in saline–alkaline soils

The dynamics of inorganic N are important in soil, and this applies particularly to the saline–alkaline soils of the former lake Texcoco in Mexico with high pH and salinity where a forestation program was started in the 1970s. In soils of lake Texcoco, in Mexico, more than 50% of applied N could not be accounted for one day after application of 200 mg kg^–1 soil along with glucose amendment. It was not clear whether this was due to abiotic or biotic processes, the form of inorganic N applied or the result of applying an easily decomposable substrate. We investigated this by adding glucose and 200 mg kg^–1 soil as (NH₄)₂SO₄-N or KNO₃-N to sterilized and unsterilized soil. The changes in inorganic and ninhydrin N, microbial biomass C and production of CO₂ were then monitored. Between the time of applying N and extraction with 0.5 M K₂SO₄, i.e., after ca 2 h, approximately 110 mg NH₄ ⁺-N kg^–1 dry soil could not be accounted for in the unsterilized and sterilized soil and that remained so for the entire incubation in the sterilized soil. After 1 day this increased to 140 mg NH₄ ⁺-N kg^–1 dry soil in the unsterilized control and 170 mg NH₄ ⁺-N kg^–1 dry soil in C amended soil. Volatilization of NH₃ accounted for 56 mg NH₄ ⁺-N kg^–1 so the rest appeared to be adsorbed on the soil matrix. The NH₃ volatilization and NH₄ ⁺ fixed in the soil matrix remained constant over time and no oxidation to NO₂ ^– or NO₃ ^– had occurred, so unaccounted N in unsterilized soil was probably incorporated into the microbial biomass in excess of what was required for metabolic activity. The unaccounted N was ca 70 mg NO₃ ^––N in nitrate amended soil after 3 days and 138 NO₃ ^––N when glucose was additionally added. Losses through abiotic processes were absent as inferred from changes in sterilized soil and the aerobic incubation inhibited possible losses through denitrification. It was inferred that NO₃ ^– that could not be accounted for was taken up by micro-organisms in excess of what was required for metabolic activity.     

The role of nitrogen in climate change and the impacts of nitrogen–climate interactions in the United States: foreword to thematic issue

Producing food, transportation, and energy for seven billion people has led to large and widespread increases in the use of synthetic nitrogen (N) fertilizers and fossil fuel combustion, resulting in a leakage of N into the environment as various forms of air and water pollution. The global N cycle is more severely altered by human activity than the global carbon (C) cycle, and reactive N dynamics affect all aspects of climate change considerations, including mitigation, adaptation, and impacts. In this special issue of Biogeochemistry, we present a review of the climate–nitrogen interactions based on a technical report for the United States National Climate Assessment presented as individual papers for terrestrial and aquatic ecosystems, agriculture and human health within the US. We provide a brief overview of each of the paper’s main points and conclusions is presented in this foreword summary.     

Does nitrogen availability control rates of litter decomposition in forests?

The effects of increased exogenous N availability on rates of litter decomposition were assessed in several field fertilization trials. In a jack pine (Pinus banksiana Lamb.) forest, needle litter decomposed at the same rate in control plots and in plots fertilized with urea and ammonium nitrate (1350 kg N ha^-1) with or without P and K. Mixed needle litter of western hemlock (Tsuga heterophylla (Raf.) Sarg.), western red cedar (Thuja plicata Donn) and Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) incubated in plots recently amended with sewage sludge (500 kg N ha^-1) lost less weight during 3 years than did litter in control plots. Forest floor material also decomposed more slowly in plots amended with sewage sludge. Paper birch (Betula papyrifera Marsh.) leaf litter placed on sewage sludge (1000 kg N ha^-1), pulp sludge, or sewage-pulp sludge mixtures decomposed at the same rate as leaf litter in control plots. These experiments demonstrate little effect of exogenous N availability on rates of litter decomposition.The influence of endogenous N availability on rates of litter decomposition was examined in a microcosm experiment. Lodgepole pine (Pinus contorta var. latifolia Engelm.) needle litter collected from N-fertilized trees (525 kg N ha^-1 in ammonium nitrate) were 5 times richer in N than needles from control trees (1.56% N versus 0.33% N in control trees), but decomposed at the same rate. Green needles from fertilized trees contained twice as much N as needles from control trees (1.91% N versus 0.88% N), but decomposed at the same rate. These experiments suggest that N availability alone, either exogenous or endogenous, does not control rates of litter decomposition. Increased N availability, through fertilization or deposition, in the absence of changes in vegetation composition, will not alter rates of litter decomposition in forests.     

A “toy model” analysis of causes of nitrogen limitation in terrestrial ecosystems

Nitrogen (N) limitation to net primary production is widespread and influences the responsiveness of ecosystems to many components of global environmental change. Logic and both simple simulation (Vitousek and Fieldin in Biogeochemistry 46: 179–202, 1999) and analytical models (Menge in Ecosystems 14:519–532, 2011) demonstrate that the co-occurrence of losses of N in forms that organisms within an ecosystem cannot control and barriers to biological N fixation (BNF) that keep this process from responding to N deficiency are necessary for the development and persistence of N limitation. Models have focused on the continuous process of leaching losses of dissolved organic N in biologically unavailable forms, but here we use a simple simulation model to show that discontinuous losses of ammonium and nitrate, normally forms of N whose losses organisms can control, can be uncontrollable by organisms and can contribute to N limitation under realistic conditions. These discontinuous losses can be caused by temporal variation in precipitation or by ecosystem-level disturbance like harvest, fire, and windthrow. Temporal variation in precipitation is likely to increase and to become increasingly important in causing N losses as anthropogenic climate change proceeds. We also demonstrate that under the conditions simulated here, differentially intense grazing on N- and P-rich symbiotic N fixers is the most important barrier to the responsiveness of BNF to N deficiency.

     

Dissolved nitrogen in drinking water resources in Al-Mahareth village of Assir – Saudi Arabia

A water quality study was carried out on ground water wells, which serve as drinking water sources in farming communities in Al-Mahareth village of Assir region of the Kingdom of Saudi Arabia. The objective of this research was to determine concentrations of different forms of nitrogen in drinking water samples. Water samples were collected from these sources every 3 months (from January to December 2008) and analyzed for ammonia, nitrate and nitrite using the Plaintest Photometer Method. Results indicated that the annual mean concentration of nitrate, nitrite and ammonia varied from 23.09 to 25.06 mg/l, 0.006 to 0.36 mg/l and 0.008 to 0.179 mg/l, respectively. An important observation was that, in general, higher nitrate and nitrite concentrations were found during the rainy season compared to the dry season. Concentrations of these potentially toxic substances were below WHO acceptable limits for surface and ground waters, indicating that these water resources appear safe for drinking from a dissolved nitrogen perspective.     

What is the function of nitrogen catabolite repression in Saccharomyces cerevisiae?

In contrast to the previously held notion that nitrogen catabolite repression is primarily responsible for the ability of yeast cells to use good nitrogen sources in preference to poor ones, we demonstrate that this ability is probably the result of other control mechanisms, such as metabolite compartmentation. We suggest that nitrogen repression is functionally a long-term adaptation to changes in the nutritional environment of yeast cells.     

Immunogenicity of “viable” tumor cells after storage in liquid nitrogen

Summary Injection of vaccines containing BCG and irradiated L10 hepatoma cells into strain 2 guinea pigs led to arrest and regression of viable L10 cells injected contralateral to and simultaneous with the vaccine. If the tumor cells in the vaccine had been stored in LN2, the vaccine was significantly less effective. The diminished immunogenicity of the stored cells could not be attributed to the sequence of freezing and irradiation, nor to the presence of dead cells which had been killed during cryopreservation. We concluded that cells which had been stored in LN2 had undergone changes which decreased their immunogenicity but which did not alter permeability to trypan blue.     

Can mineralization of soil organic nitrogen meet maize nitrogen demand?

Background and aims

It is generally assumed that very large herbivores, such as elephants, make foraging decisions at large spatial scales, but the extent to which seasonal foraging decisions are driven by soil quality, and its link to plant nutrient levels, is uncertain.

Methods

We studied the diet selection of African elephants Loxodonta africana in Ithala Game Reserve in northern KwaZulu-Natal, South Africa, using data on elephant feeding preferences and spatial distributions from a published paper. Elephants were present in the eastern half with granite soils in the wet season, and in the western half with sedimentary soils in the dry season. The quality of these two soil types and of seven key tree species for elephants was assessed in both seasons.

Results

Soil quality was higher on the sedimentary soils in terms of total nitrogen, soil respiration, water-holding capacity, organic carbon and pH. Leaf quality was higher on the sedimentary soils in the dry season, while in the wet season there was no significant difference in leaf quality of the seven key tree species growing on the two substrates.

Conclusion

Soil quality may explain elephants’ foraging decisions in the dry season, but not in the wet season. Elephants preferred trees with higher protein and lower concentrations of fibre on both granite and sedimentary soils.

     

Inefficient nitrogen resorption in genets of the actinorhizal nitrogen fixing shrubComptonia peregrina: physiological ineptitude or evolutionary tradeoff?

Nutrient resorption was measured in an actinorhizal nitrogen-fixing shrub,Comptonia peregrina, for five years in the understory of a deciduous oak forest in Rhode Island, USA. Mean resorption of nitrogen was extremely inefficient (11%) compared to most deciduous species (50%+), yet resorption of phosphorus was efficient (53%) and comparable to other species. Of the seven additional nutrients studied, only copper (6%) and zinc (10%) were resorbed from senescing leaves. Resorption of nitrogen (5%–20%) and phosphorus (40%–71%) varied significantly among years. Copper was resorbed from leaves in three years and accreted into leaves in two years. Five-year resorption means differed among individual genets by as much as a factor of 2.5 for nitrogen, and 1.3 for phosphorus. Resorption of nitrogen, copper, and zinc were highly correlated, yet resorption of phosphorus remained autonomous from other nutrients. The ecophysiological tradeoffs inComptonia which have resulted in the cooccurence of actinorhizal nitrogen fixation, inefficient nitrogen resorption, and efficient phosphorus resorption suggest that plant nutrient status does have an impact on resorption efficiency and that the evolution of nutrient conservation strategies is nutrient-specific.     

Does genotypic variation in nitrogen remobilisation efficiency contribute to nitrogen efficiency of winter oilseed-rape cultivars (Brassica napus L.)?

Aims

Winter oilseed-rape production is characterized by a low N efficiency, due to low N uptake and insufficient N remobilisation to the seeds. In particular, a reduction of leaf N losses might be one way to improve N efficiency of this crop. It was tested if variations in leaf N losses and in stem residual N amounts at maturity exist between cultivars differing in N efficiency.

Methods

In a 3-year field experiment, four oilseed rape cultivars were cultivated at limiting, medium, and high N supply.

Results

N harvest indices in this study were comparatively high (around 0.79) and leaf N losses amounted to at most 13 kg N ha^?1. 86 % of the leaf N present at the beginning of flowering was remobilised, irrespective of N rate or cultivar. Nevertheless, genotypic variation in leaf N loss existed. They were mainly due to differences in leaf N accumulation until flowering. Residual N in stems (up to 33 kg N ha^?1) was higher than leaf N losses and varied more between treatments but was not related to genotypic variation in yield.

Conclusions

N uptake after flowering was more important than N remobilisation from vegetative biomass for genotypic variation in seed yield both at low and high N supply.     

Studies on nitrogen metabolism during somatic embryogenesis in carrot. I. Utilization of α-alanine as a nitrogen source

α-Alanine added to a culture medium was incorporated into cells and/or embryos during rapid cell proliferation and globular embryo formation, in which an active protein synthesis was occurring. After the incorporation into cells, α-alanine seemed to be quickly transformed to glutamic acid by alanine aminotransferase and utilized as a nitrogen source. Alanine aminotransferase activity was observed in cells and/or embryos, although the activity decreased during culture period. Utilization of α-alanine by cultured cells as a nitrogen source was discussed in relation to its stimulative effect on somatic embryogenesis.     

Temperature-sensitive photosynthesis-deficient mutants of the cyanobacteriumAnabœna variabilis impaired in nitrogen assimilation

Temperature-sensitive (Ts) mutants ofAnabœna variabilis exhibited differences in the rates of oxygen evolution at 28 and 40°C. They were unable to perform photosynthesis and nitrogen fixation at 40°C beyond a period of 3 d in a nitrogen-deficient medium. However, the addition of combined nitrogen sources enhanced the growth of all the Ts mutants at both temperatures. Studies on nitrate uptake ty Ts mutants revealed the existence of a low affinity system, whereK _m values were found to be lower than 1 mmol/L. The activity of nitrate reductase gradually increased with time at 28°C with the exception of Ts-161 where the activity decreased with time at 40°C. The rate of ammonia uptake byA. variabilis and its Ts mutants greatly differed and the results suggest the existence of a single phase of uptake. The activity of glutamate-ammonia ligase (GAL) of the parent and Ts mutants was slightly higher in cells from nitrogen-deficient medium when compared to nitrate grown cells at 28°C. At 40°C, the GAL activity decreased after 3 d. The inability of the Ts mutants to grow at 40°C appears to be due to an impairment in nitrogen asimilation.     

Temporal–spatial distributions of high nitrogen concentrations in headwater areas of regions with low precipitation

Temporal–spatial distributions of nitrogen in the low-precipitation headwater areas of the Sanuki Mountain Range, Kagawa Prefecture, Japan, was studied to clarify the natural loading from forests to rivers as basic knowledge for elucidating the eutrophication in dead-water regions downstream. The survey to clarify temporal variations was carried out once every two weeks at the headwaters of five rivers in the Sanuki Mountain Range and the Shikoku Mountains on Shikoku Island, Japan, between May 6, 2002, and April 22, 2003. The survey to clarify the spatial distribution was carried out at 23 stations on the headwaters of the Sanuki Mountain Range between August 13 and 15, 2002. In the Kazuratani and Tarobei Rivers, which originate in the Sanuki Mountain Range, where precipitation is scarce, total N was consistently high – greater than 1mgl^–1 throughout the year. The maximum value of total N was 3.2mgl^–1 in the Kazuratani River. The spatial distribution of total N in the headwater areas was 0.47–3.8mgl^–1. High concentrations over 1mgl^–1 were found in the central region of the Sanuki Mountain Range and the maximum value was 3.8mgl^–1. From these results, it became clear that nitrogen concentrations in headwater areas of the Sanuki Mountain Range are high compared with those in other regions. Various factors were considered in relation to low precipitation and drying as the causes of the high nitrogen concentrations. Furthermore, It was noted that the majority of the regions with the highest NO₃ ^–-N concentrations in our study were composed of granitic rock.     

Shift in soil–plant nitrogen dynamics of an alpine–nival ecotone

We investigated the nitrogen (N) dynamics of an alpine–nival ecotone on Mt. Schrankogel, Tyrol, Austria, in relation to temperature. Natural abundance of ¹⁵N was used as a tool to elucidate differences in N cycling along an altitudinal transect ranging from 2,906 to 3,079 m, corresponding to a gradient in mean annual temperature of 2.4 °C. The amount of total soil N, of plant available N and soil C/N ratio decreased significantly with increasing altitude, whereas soil pH increased. Soil δ ¹⁵N decreased with increasing altitude from +2.2 to −2.1‰ and δ ¹⁵N of plant tissues (roots and leaves) decreased from −3.7 to −5.5‰. The large shift in soil δ ¹⁵N of 4.3‰ from the lowest to the highest site suggested substantial differences in N cycling in alpine and nival ecosystems in the alpine nival ecotone investigated. We concluded that N cycling at the alpine–nival ecotone is likely to be controlled by various factors: temperature, soil age and development, atmospheric N deposition and plant competition. Our results furthermore demonstrate that the alpine–nival ecotone may serve as a sensitive indicator of global change.     

Effect of p,p′ DDT on nitrogen fixation of white clover in volcanic soils of Chile

Summary The effect of increasing concentrations of p,p DDT on dry matter production and nitrogen fixation of white clover (Trifolium repens L.) growing in pots with volcanic soils of the southern region of Chile was studied. The chlorinated insecticides content of the soils ranged from low to very high (>20 mg/kg), being associated with the amount of insecticide applied. A detrimental effect of medium and high levels of DDT on growth, dry matter production and N-accumulation of clover was observed. The effects on nodulation and nitrogenase activity were smaller. These effects were higher when nutrient solutions were used instead of soil, because of the protective effects of soil colloids.

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Resumen Se estudió el efecto de concentraciones crecientes de p,p DDT sobre la producción y parámetros de fijación de N del trébol blanco (Trifolium repens L.) en condiciones de invernadero en suelos volcánicos de la zona sur de Chile. Los contenidos de insecticidas clorados de los suelos de la región son desde bajos hasta muy altos (>20 mg/kg), dependiendo de las aplicaciones. Se apreció un efecto depresivo del DDT a dosis medias y altas sobre el crecimiento, producción de materia seca y N-acumulado del trébol y un efecto menor sobre nodulación y actividad nitrogenásica. Estos efectos fueron más acentuados cuando se trabajó con soluciones nutritivas que con suelo, debido a la protección ejercida por los coloides del suelo.

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Résumé On a étudié l'effet de concentrations croissantes de p,p-DDT sur la production de matière sèche et sur la fixation de l'azote par le trèfle blanc (Trifolium repens L.) cultivé en serre sur des échantillons de sols volcaniques du sud du Chili. Dans les sols de cette région, la teneur en résidus d'insecticides chlorés varie entre <1 et >20 mg/kg suivant le niveau des prelévements. Le DDT inhibe la croissance, la production de matière sèche et l'accumulation d'azote par le trèfle. De plus, nous avons constaté un effet secondaire sur la nodulation et l'activité nitrogénasique. Ces effets sont plus marqués lorsqu'on utilise des solutions nutritives au lieu de terre, ce qui est dû à une protection éxercée par les colloides du sol.

     

Changes in needle nitrogen partitioning and photosynthesis during 80 years of tree ontogeny in Picea abies

Needle nitrogen partitioning and photosynthesis of Norway spruce were studied in a forest chronosequence in Järvselja Experimental Forest, Estonia. Current- and previous-year shoots were sampled from upper and lower canopy positions in four stands, ranging in age from 13 to 82 years. A/c _i curves were determined to obtain maximum carboxylation rate (V _cmax) and maximum rate of electron transport (J _max), whereas needle nitrogen partitioning into carboxylation (P _R), bioenergetics associated with electron transport (P _B) and thylakoid light harvesting components (P _L) was calculated from the values of V _cmax, J _max and leaf chlorophyll concentration. The greatest changes in studied needle characteristics took place between tree ages of 13 and 26 years, and this pattern was independent of needle age and canopy position. Needle mass per projected area (LMA) was lowest in the 13-year-old stand and mass-based nitrogen concentration (N^M) was generally highest in that stand. The values of LMA were significantly higher and those of N^M lower in the 26-year-old stand. Mass-based V _cmax and J _max were highest in the 13-year-old stand. Area-based photosynthetic capacity was independent of tree age. The proportion of photosynthetic nitrogen (P _R, P _B and P _L) was highest and that of non-photosynthetic nitrogen lowest in the 13-year-old stand. Current-year needles had lower LMA and P _L, but higher photosynthetic capacity compared to 1-year-old foliage. Needles from lower canopy positions exhibited lower LMA, area-based nitrogen concentration and photosynthetic capacity than needles from upper canopy. The period of substantial reductions in needle photosynthetic capacity and changes in nitrogen partitioning coincides with the onset of reproductive phase during tree ontogeny.     

Microbial transformations of some particulate pollution deposits in soils — A source of plant-available nitrogen and sulphur

Summary Atmospheric pollution deposits, largely consisting of soot, were removed from sycamore leaves growing downwind of a coking plant, and added to soil. Increases in plant available S-ions (S₂O₃ ²⁻; S₄O₆ ²⁻ and SO₄ ²⁻) and N (NH₄ ⁺ and NO₃ ⁻) occurred due to the action of soil microorganisms on the deposits. Although the detrimental effects of air pollution on plant growth have been previously emphasised, supply of nutrients resulting from the microbial transformation of particulate pollutants may prove important to the growth of pollution-resistant plant communities.     

Changes in stable isotopic signatures of soil nitrogen and carbon during 40 years of forest development

Understanding what governs patterns of soil δ¹⁵N and δ¹³C is limited by the absence of these data assembled throughout the development of individual ecosystems. These patterns are important because stable isotopes of soil organic N and C are integrative indicators of biogeochemical processing of soil organic matter. We examined δ¹⁵N of soil organic matter (δ¹⁵N_SOM) and δ¹³C_SOM of archived soil samples across four decades from four depths of an aggrading forest in southeastern USA. The site supports an old-field pine forest in which the N cycle is affected by former agricultural fertilization, massive accumulation of soil N by aggrading trees over four decades, and small to insignificant fluxes of N via NH₃ volatilization, nitrification, and denitrification. We examine isotopic data and the N and C dynamics of this ecosystem to evaluate mechanisms driving isotopic shifts over time. With forest development, δ¹³C_SOM became depth-dependent. This trend resulted from a decline of ~2‰ in the surficial 15 cm of mineral soil to −26.0‰, due to organic matter inputs from forest vegetation. Deeper layers exhibited relatively little trend in δ¹³C_SOM with time. In contrast, δ¹⁵N_SOM was most dynamic in deeper layers. During the four decades of forest development, the deepest layer (35–60 cm) reached a maximum δ¹⁵N value of 9.1‰, increasing by 7.6‰. The transfer of >800 kg ha⁻¹ of soil organic N into aggrading vegetation and the forest floor and the apparent large proportion of ectomycorrhizal (ECM) fungi in these soils suggest that fractionation via microbial transformations must be the major process changing δ¹⁵N in these soils. Accretion of isotopically enriched compounds derived from microbial cells (i.e., ECM fungi) likely promote isotopic enrichment of soils over time. The work indicates the rapid rate at which ecosystem development can impart δ¹⁵N_SOM and δ¹³C_SOM signatures associated with undisturbed soil profiles.