Nitrogen Deposition Rates Research Articles

Retention of surface nitrate additions in a temperate old field: implications for atmospheric nitrogen deposition over winter and plant nitrogen availability

In many temperate ecosystems, rates of atmospheric nitrogen deposition remain high over winter despite decreased agricultural activity over this season. The extent to which this nitrogen is accessible for plant growth over the following growing season may depend strongly on uptake by plants and soil microorganisms from late fall through early spring, when the majority of aboveground plant tissue has senesced. We added Ca(15NO3)2 (5 atom %15N) at a rate of 2 g m−2 of N (corresponding to 100 mg 15N m−2) to the surface of plots in a temperate old field during either late fall, winter, spring melt or early spring. We quantified the recovery of excess 15N in the soil microbial biomass and soil extracts following spring melt and in aboveground plant tissue at the peak of the plant growing season. Nitrate additions had no significant effect on total aboveground plant biomass, relative species abundance or percent tissue nitrogen. However, mean excess 15N in aboveground plant tissue varied significantly among treatments, with values of 8.1, 2.6, 0.3 and 7.3 mg m−2 for late fall, winter, spring melt and early spring addition plots, respectively. Corresponding values of excess 15N were 3.1, 1.4 and 0.2 mg m−2 in microbial biomass, and 0.17, 0.07 and 0.03 mg m−2 in soil extracts, for late fall, winter and spring melt addition plots, respectively. Overall, these results indicate that nitrogen retention from late fall through early spring may depend highly on plant uptake in this system, and that only a small fraction of the nitrogen that accumulates in the winter snow pack may be available to plants.

Mass invariance of population nitrogen flux by terrestrial mammalian herbivores: an extension of the energetic equivalence rule

According to the energetic equivalence rule, energy use by a population is independent of average adult body mass. Energy use can be equated with carbon flux, and it has been suggested that population fluxes of other materials, such as nitrogen and phosphorus, might also be independent of body mass. We compiled data on individual nitrogen deposition rates (via faeces and urine) and average population densities of 26 species of mammalian herbivores to test the hypothesis of elemental equivalence for nitrogen. We found that the mass scaling of individual nitrogen flux was opposite to that of population density for the species in our dataset. By computing the product of individual nitrogen flux and average population density for each species in our dataset, we found that population-level nitrogen flux was independent of species mass, averaging c. 3.22 g N ha(-1) day(-1). Results from this analysis can be used to understand the influence of mammalian herbivore communities on nitrogen cycling in terrestrial ecosystems.

Changes in the distribution area of vascular plants in Flanders (northern Belgium): eutrophication as a major driving force

In large parts of Western Europe agricultural intensification after World War II has led to an increased use of fertilisers. The resulting nutrient enrichment (=eutrophication) has a huge impact on the occurrence and distribution of plant species and is one of the main pressures on native plant communities. We used the distribution maps (grid size: 16 km²) of individual plant species, obtained through two consecutive survey projects (1939–1971 and 1972–2004) in Flanders (northern Belgium), to estimate the relative change in their distribution area. The comparison of changes in range size among groups of taxa classified according to habitat preference and Ellenberg indicator values, demonstrated a marked decline in distribution area in species that are characteristic for nutrient-poor habitats. To assess geographic patterns in the change of species assemblages, we calculated the mean Ellenberg N- and R-values for every grid cell during each of both survey periods. Differences between these values were analysed in relation to soil type and estimates of atmospheric nitrogen deposition. The largest shifts in Ellenberg N-values, reflecting a decline of species from nutrient-poor conditions and/or an increase of nitrophilous plants, were observed in areas with nutrient-poor, acid sandy soils and high nitrogen deposition rates. Hence, shifts in species composition were modulated by geographic variation in soil type and levels of nitrogen deposition. As the levels of atmospheric nitrogen deposition are still very high in Flanders, it is likely that species from nutrient-poor habitats such as heathlands, will further decline in the near future.

Global nitrogen deposition and carbon sinks

Land and ocean uptake of carbon dioxide plays a critical role in determining atmospheric carbon dioxide levels. Future increases in nitrogen deposition have been predicted to increase the size of these terrestrial and marine carbon sinks, but although higher rates of nitrogen deposition might enhance carbon uptake in northern and tropical forests, they will probably have less of an impact on ocean sink strength. Combined, the land and ocean sinks may sequester an additional 10% of anthropogenic cabon emissions by 2030 owing to increased nitrogen inputs, but a more conservative estimate of 1 to 2% is more likely. Thus nitrogen-induced increases in the strength of land and ocean sinks are unlikely to keep pace with future increases in carbon dioxide. Land and ocean carbon sinks play a critical role in determining atmospheric carbon dioxide levels. Nitrogen-induced increases in land and ocean sink strength are unlikely to keep pace with future increases in carbon dioxide.

Potential geographic distribution of atmospheric nitrogen deposition from intensive livestock production in North Carolina, USA

To examine the consequences of increased spatial aggregation of livestock production facilities, we estimated the annual production of nitrogen in livestock waste in North Carolina, USA, and analyzed the potential distribution of atmospheric nitrogen deposition from confined animal feeding operations (“CAFO”) lagoons. North Carolina is a national center for industrial livestock production. Livestock is increasingly being raised in CAFOs, where waste is frequently held, essentially untreated, in open-air lagoons. Reduced nitrogen in lagoons is volatilized as ammonia (NH 3), transported atmospherically, and deposited to other ecosystems. The Albemarle-Pamlico Sound, NC, is representative of nitrogen-sensitive coastal waters, and is a major component of the second largest estuarine complex in the U.S. We used GIS to model the area of water in the Sound within deposition range of CAFOs. We also evaluated the number of lagoons within deposition range of each 1 km 2 grid cell of the state. We considered multiple scenarios of atmospheric transport by varying distance and directionality. Modeled nitrogen deposition rates were particularly elevated for the Coastal Plain. This pattern matches empirical data, suggesting that observed regional patterns of reduced nitrogen deposition can be largely explained by two factors: limited atmospheric transport distance, and spatial aggregation of CAFOs. Under our medium-distance scenario, a small portion (roughly 22%) of livestock production facilities contributes disproportionately to atmospheric deposition of nitrogen to the Albemarle-Pamlico Sound. Furthermore, we estimated that between 14–37% of the state receives 50% of the state's atmospheric nitrogen deposition from CAFO lagoons. The estimated total emission from livestock is 134,000 t NH 3 yr − 1 , 73% of which originates from the Coastal Plain. Stronger waste management and emission standards for CAFOs, particularly those on the Coastal Plain nearest to sensitive water bodies, may help mitigate negative impacts on aquatic ecosystems.

Separation of effects of moderate N deposition from natural change in ground vegetation of forests and bogs

The effect of moderate rates of nitrogen deposition on ground floor vegetation is poorly predicted by uncontrolled surveys or fertilization experiments using high rates of nitrogen (N) addition. We compared the temporal trends of ground floor vegetation in permanent plots with moderate (7–13 kg ha −1 year −1) and lower bulk N deposition (4–6 kg ha −1 year −1) in southern Sweden during 1982–1998. We examined whether trends differed between growth forms (vascular plants and bryophytes) and vegetation types (three types of coniferous forest, deciduous forest, and bog). Trends of site-standardized cover and richness varied among growth forms, vegetation types, and deposition regions. Cover in spruce forests decreased at the same rate with both moderate and low deposition. In pine forests cover decreased faster with moderate deposition and in bogs cover decreased faster with low deposition. Cover of bryophytes in spruce forests increased at the same rate with both moderate and low deposition. In pine forests cover decreased faster with moderate deposition and in bogs and deciduous forests there was a strong non-linear increase with moderate deposition. The trend of number of vascular plants was constant with moderate and decreased with low deposition. We found no trend in the number of bryophyte species. We propose that the decrease of cover and number with low deposition was related to normal ecosystem development (increased shading), suggesting that N deposition maintained or increased the competitiveness of some species in the moderate-deposition region. Deposition had no consistent negative effect on vegetation suggesting that it is less important than normal successional processes.

Growth and production of California sea cucumbers (Parastichopus californicus Stimpson) co-cultured with suspended Pacific oysters (Crassostrea gigas Thunberg)

Growth and production of California sea cucumbers (Parastichopus californicus Stimpson), co-cultured with suspended Pacific oysters (Crassostrea gigas Thunberg), were investigated in a 12-month (January 2004–January 2005) study conducted at two sites of deep-water, suspended oyster culture in British Columbia, Canada. Rates of oyster biodeposition (faeces and pseudofaeces) and the utilization of this particulate material as a food source by P. californicus were also examined. Peaks in sedimentation rates through 8.5 m water depth, below the oyster rafts, were observed in April (93.6 g dry wt m−2 d−1) and July (91.9 g dry wt m−2 d−1) 2004. At the two study sites, maximum mean total organic carbon deposition rate at 8.5 m depth occurred in July 2004 and amounted to 3123 and 3830 mg dry wt C m−2 d−1. Maximum mean total nitrogen deposition rate at the two sites was 524 and 568 mg dry wt N m−2 d−1 which occurred in November and July 2004, respectively. Mean C/N ratios of particulate material in the sediment trap samples collected at the two sites between January and November 2004 ranged between 5.9 and 12.4 and may be considered to be of high nutritional value. Growth and survivorship of sea cucumbers held in experimental trays below the suspended oysters were measured, growth being assessed using split weight as well as muscle and skin wet weights. There were no sea cucumber mortalities in any of the trays deployed at either site during the study. Sea cucumbers grown in trays at both sites successfully utilized biodeposits from the cultured oysters and showed a mean weight increase of 42.9 g in approximately 12 months (average growth rates at both sites ranged from 0.061 to 0.158 g d−1). Overall growth was affected by the absence of visceral organs and the cessation of feeding activity observed in the November 2004 sampling period. Overall mean values (for the two study sites) for organic content were significantly higher in the foregut of the sea cucumbers (24.7 % or 224.6 mg g−1 dry sediment) than in the sediment (5.9% or 51.6 mg g−1 dry sediment) or in the hindgut (14.5% or 157.9 mg g−1 dry sediment), showing both active selection of organic material from the sediments and digestion/assimilation of these organics in the gut. Organic material deposited in the trays was assimilated by P. californicus at the two study sites with an average efficiency of 40.4%. The successful utilization of the naturally-available biodeposits from the cultured Pacific oysters by California sea cucumbers suggests the feasibility of developing a commercial-scale co-culture system that would both reduce the amount of organic deposition underneath shellfish farms and produce a secondary cash crop.

Control of morphology (ZrN crystallite size and SiN x layer thickness) in Zr–Si–N nanocomposite thin films

DC reactive magnetron sputtering was used for the deposition of Zr–Si–N thin films. Four series of samples have been deposited at various substrate temperatures T S: 300 K, 510 K, 710 K and 910 K. Depending on T S, different N 2 partial pressures p N2 were required to obtain nearly stoichiometric ZrN films. Si content ( C Si) was varied in each series by changing the power applied on the Si target, whereas the power on the Zr target was kept constant. The microstructure of the coatings was examined by XRD and in cross-section by transmission electron microscopy (TEM). Depending on T S and p N2, the deposition rate showed significant variations from 0.04 to 0.18 nm/s. The correlation between film morphology (preferential orientation of crystallites, grain size, column dimensions, thickness of the SiN x layer covering ZrN crystallites) and the deposition conditions (power applied on Si target, temperature, nitrogen partial pressure and deposition rate) provides useful information for optimizing the deposition process.

Nitrogen deposition interacts with climate in affecting production and decomposition rates in Sphagnum mosses

AbstractIncreasing rates of atmospheric nitrogen (N) deposition may reduce growth and accelerate decomposition of Sphagnum mosses in bogs. Sphagnum growth and rates of Sphagnum litter decomposition may also vary because of climate change as both processes are controlled by climatic factors. The initial purpose of this study was to assess if growth and litter decomposition of hummock and lawn Sphagnum species varied with increasing N input in a factorial mid‐term (2002–2005) experiment of N and phosphorus (P) addition, in a bog on the southern Alps of Italy. However, as the experimental period was characterized by an exceptional heat wave in summer 2003, we also explored the interacting effects of fertilization and strongly varying climate on growth and decomposition rates of Sphagnum. The heat wave implied strong dehydration of the upper Sphagnum layer even if precipitation in summer 2003 did not differ appreciably from the overall mean. Sphagnum production was somewhat depressed by high levels (3 g m−2 yr−1) of N addition without concomitant addition of P presumably because of nutrient imbalance in the tissues, but production rates were much lower than the overall means in 2003, when no effect of nutrient addition could be observed. Adding N at high level also increased the potential decay of Sphagnum litter. Higher CO2 emission from N‐fertilized litter was due to amelioration of litter chemistry showing lower C/N quotients in the N‐fertilized treatments. Rates of CO2 emission from incubated litter also were more strongly affected by water content than by nutrient status, with practically no CO2 emission detected when litter was dry. We conclude that higher rates of atmospheric N availability input may depress Sphagnum growth because of P, and presumably potassium, (co‐)limitation. Higher N availability is also expected to promote potential decay of Sphagnum litter by ameliorating litter chemistry. However, both effects are less pronounced if the growing Sphagnum apex and the underlying senescing tissues dry out.

Plant and soil natural abundance δ 15N: indicators of relative rates of nitrogen cycling in temperate forest ecosystems

Watersheds within the Catskill Mountains, New York, receive among the highest rates of nitrogen (N) deposition in the northeastern United States and are beginning to show signs of N saturation. Despite similar amounts of N deposition across watersheds within the Catskill Mountains, rates of soil N cycling and N retention vary significantly among stands of different tree species. We examined the potential use of delta (15)N of plants and soils as an indicator of relative forest soil N cycling rates. We analyzed the delta (15)N of foliage, litterfall, bole wood, surface litter layer, fine roots and organic soil from single-species stands of American beech (Fagus grandifolia), eastern hemlock (Tsuga canadensis), red oak (Quercus rubra), and sugar maple (Acer saccharum). Fine root and organic soil delta (15)N values were highest within sugar maple stands, which correlated significantly with higher rates of net mineralization and nitrification. Results from this study suggest that fine root and organic soil delta (15)N can be used as an indicator of relative rates of soil N cycling. Although not statistically significant, delta (15)N was highest within foliage, wood and litterfall of beech stands, a tree species associated with intermediate levels of soil N cycling rates and forest N retention. Our results show that belowground delta (15)N values are a better indicator of relative rates of soil N cycling than are aboveground delta (15)N values.

Effects of Nitrogen Deposition on Bryophyte Species Composition of Calcareous Grasslands

Regular additions of NH4NO3 (35–140 kg N ha−1 yr−1) and (NH4)2SO4 (140 kg N ha−1 yr−1) to a calcareous grassland in northern England over a period of 12 years have resulted in a decline in the frequency of the indigenous bryophyte species and the establishment of non-indigenous calcifuge species, with implications for the structure and composition of this calcareous bryophyte community. The lowest NH4NO3 additions of 35 kg N ha−1 yr−1 produced significant declines in frequency of Hypnum cupressiforme, Campylium chrysophyllum, and Calliergon cuspidatum. Significant reductions in frequency at higher NH4NO3 application rates were recorded for Pseudoscleropodium purum, Ctenidum molluscum, and Dicranum scoparium. The highest NH4NO3 and (NH4)2SO4 additions provided conditions conducive for the establishment of two typical calcifuges — Polytrichum spp. and Campylopus introflexus, respectively. Substrate-surface pH measurements showed a dose-related reduction in pH with increasing NH4NO3 deposition rates of 1.6 pH units between the control and highest deposition rate, and a further significant fall in pH, of >1 pH unit, between the NH4NO3 and (NH4)2SO4 treatments. These results suggest that indigenous bryophyte composition may be at risk from nitrogen deposition rates of 35 kg N ha−1 yr−1 or less. These effects are of particular concern for rare or endangered species of low frequency.

Controls on surface water chemistry in two lake‐watersheds in the Adirondack region of New York: differences in nitrogen solute sources and sinks

AbstractThe southwestern Adirondack region of New York receives among the highest rates of atmospheric nitrogen (N) deposition in the USA. Atmospheric N deposition to sensitive ecosystems, like the Adirondacks, may increase the acidification of soils through losses of exchangeable nutrient cations, and the acidification of surface waters associated with enhanced mobility of nitrate (NO3−). However, watershed attributes, including surficial terrestrial characteristics, in‐lake processing, and geological settings, have been found to complicate the relationships between atmospheric N deposition and N drainage losses. We studied two lake‐watersheds in the southwestern Adirondacks, Grass Pond and Constable Pond, which are located in close proximity (∼26 km) and receive similarly high N deposition, but have contrasting watershed attributes (e.g. wetland area, geological settings). Since the difference in the influence of N deposition was minimal, we were able to examine both within‐ and between‐watershed influences of land cover, the contribution of glacial till groundwater inputs, and in‐lake processes on surface water chemistry with particular emphasis on N solutes and dissolved organic carbon (DOC). Monthly samples at seven inlets and one outlet of each lake were collected from May to October in 1999 and 2000. The concentrations of NO3− were high at the Grass Pond inlets, especially at two inlets, and NO3− was the major N solute at the Grass Pond inlets. The concentrations of likely weathering products (i.e. dissolved Si, Ca2+, Mg2+, Na+) as well as acid neutralizing capacity and pH values, were also particularly high at those two Grass Pond inlets, suggesting a large contribution of groundwater inputs. Dissolved organic N (DON) was the major N solute at the Constable Pond inlets. The higher concentrations of DON and DOC at the Constable Pond inlets were attributed to a large wetland area in the watershed. The DOC/DON ratios were also higher at the Constable Pond inlets, possibly due to a larger proportion of coniferous forest area. Although DON and DOC were strongly related, the stronger relationship of the proportion of wetland area with DOC suggests that additional factors regulate DON. The aggregated representation of watershed physical features (i.e. elevation, watershed area, mean topographic index, hypsometric‐analysis index) was not clearly related to the lake N and DOC chemistry. Despite distinctive differences in inlet N chemistry, NO3− and DON concentrations at the outlets of the two lakes were similar. The lower DOC/DON ratios at the lake outlets and at the inlets having upstream ponds suggest the importance of N processing and organic N sources within the lakes. Although an inverse relationship between NO3− and DOC/DON has been suggested to be indicative of a N deposition gradient, the existence of this relationship for sites that receive similar atmospheric N deposition suggest that the relationship between NO3− and the DOC/DON ratio is derived from environmental and physical factors. Our results suggest that, despite similar wet N deposition at the two watershed sites, N solutes entering lakes were strongly affected by hydrology associated with groundwater contribution and the presence of wetlands, whereas N solutes leaving lakes were strongly influenced by in‐lake processing. Copyright © 2006 John Wiley & Sons, Ltd.

Are Current Rates of Atmospheric Nitrogen Deposition Influencing Lakes in the Eastern Canadian Arctic?

Although arctic lakes rank among the most pristine ecosystems remaining on Earth, widespread paleoecological analyses have revealed rapid recent changes in lake ecology that largely surpass Holocene natural variability and that are generally attributed to climate warming since the end of the Little Ice Age. However, the possibility that climate is only one dimension of these unprecedented ecological shifts remains an untested possibility, especially given that current warming may not yet exceed maximum, naturally mediated, postglacial warmth. In this paper, we assess whether increased anthropogenic nitrogen (N) deposition from distant sources is contributing to directional changes in the biogeochemistry and ecology of two remote lakes on Baffin Island in the eastern Canadian Arctic. Paleolimnological analyses, including diatom assemblages and a suite of biogeochemical proxies (total organic matter, biogenic silica, organic N and C contents, and stable isotopic ratios) reveal a complex suite of progressive changes that are coherently expressed in both lakes. Diatom assemblages began to change as early as the mid-19th century, but major inflections in the biogeochemical proxies occurred significantly later, being most pronounced after 1950. Among these changes are increases in sediment organic matter, depletions of 2‰ in sediment δ15N, and decoupling of δ13C and δ15N signatures. It seems likely that climate warming, subsequently coupled to anthropogenic N deposition, is synergistically driving these ecosystems towards states for which no prior natural analogs exist.

Contribution of dissolved organic nitrogen deposition to total dissolved nitrogen deposition under intensive agricultural activities

For elucidating the atmospheric deposition contribution of dissolved organic nitrogen (DON) to the total dissolved nitrogen (TDN) deposition rate, dissolved inorganic nitrogen (DIN: NH4+ + NO3–) and DON deposition rates were annually and monthly estimated during 4 and half-yr monitoring period in an experimental multi-farm under intensive agricultural activities of N fertilizer use and animal husbandry in Central Japan. Annual NH4+, DON and NO3– deposition rates in bulk and wet deposition data accounted for 48%, 32% and 20% of TDN deposition, respectively, which indicated that this area is strongly affected by the intensive agricultural activities. The DIN and DON deposition rates were respectively estimated at 21.6 and 10.1 kg N ha−1 yr−1, which ranked high in a worldwide regional data set. Consequently, this area has been exposed to a large amount of N deposition including DON with N fertilizer input. The difference between bulk and wet deposition rates (NH4+ and DON) is one of important factors controlling the N deposition in this area. Monthly DON deposition showed positive correlations with DIN and NH4+ deposition rates, respectively, with a significant linear regression curve. The linear regression curve of our monthly data (n = 127) indicates the same trend as the worldwide annual data set (n = 31).

Nitrogen limitation constrains sustainability of ecosystem response to CO2

Enhanced plant biomass accumulation in response to elevated atmospheric CO2 concentration could dampen the future rate of increase in CO2 levels and associated climate warming. However, it is unknown whether CO2-induced stimulation of plant growth and biomass accumulation will be sustained or whether limited nitrogen (N) availability constrains greater plant growth in a CO2-enriched world. Here we show, after a six-year field study of perennial grassland species grown under ambient and elevated levels of CO2 and N, that low availability of N progressively suppresses the positive response of plant biomass to elevated CO2. Initially, the stimulation of total plant biomass by elevated CO2 was no greater at enriched than at ambient N supply. After four to six years, however, elevated CO2 stimulated plant biomass much less under ambient than enriched N supply. This response was consistent with the temporally divergent effects of elevated CO2 on soil and plant N dynamics at differing levels of N supply. Our results indicate that variability in availability of soil N and deposition of atmospheric N are both likely to influence the response of plant biomass accumulation to elevated atmospheric CO2. Given that limitations to productivity resulting from the insufficient availability of N are widespread in both unmanaged and managed vegetation, soil N supply is probably an important constraint on global terrestrial responses to elevated CO2.

The Effect of Nitrogen Depostition and Edaphic Conditions on Microbial Activity in the Alpine Zone of the Grand Teton National Park

Atmospheric nitrogen (N) deposition rates show increasing N loadings since the 1980s in the western U.S. associated with increasing N emissions from industrial, urban, and agricultural sources (Fenn et al., 2003). Compared to the eastern U.S., the number of NADP/NTN (National Atmospheric Deposition Program/ National Trends Network) and CASTNet (Clean Air Status Network) monitoring sites is much more limited in the west, and they are rarely located in the highest-elevations, where ecosystems are likely to be more sensitive (Bums 2004). Although N deposition tends to increase with elevation in this region (Williams and Tonnesen 2000), there are considerable uncertainties about the actual N deposition levels in the Rocky Mountains. Model-simulations indicate a "hotspot" of N deposition near Grand Teton National Park (GRTE) (Fenn et al., 2003; Nanus et al. 2003), with feedlot and fertilizer N emissions in Southern Idaho, as potential sources impacting the alpine communities in GRTE. However, little data is currently available on the actual atmospheric N inputs to alpine ecosystems in GRTE, either as snow during winter or wet and dry deposition during the short snow-free period.

A comparison between feeding a single diet or phase feeding a series of diets, with either the same or reduced crude protein content, to growing finishing pigs

Abstract A study was designed to determine if pig performance and lysine conversion ratio would be improved by phase feeding a series of diets with either the same, or with reduced overall mean crude protein (lysine) content, compared with providing a single diet throughout the growing-finishing period. Four hundred and forty-eight group-penned pigs (no. = 32 groups) were assigned at random to one of four treatments: single diet (SD: 11·1 g lysine per kg), high lysine (HL: 12·2, 11·6, 11·1, 10·5 and 10·0 g lysine per kg), medium lysine (ML: 11·1, 10·5, 10·0, 9·5 and 8·9 g lysine per kg) and low lysine series of diets (LL: 10·0, 9·5, 8·9, 8·4 and 7·8 g lysine per kg). The mean lysine contents of the treatments were 11·1, 11·1, 10·0 and 8·9 g/kg for SD, HL, ML and LL respectively. There were five 2-week phases from 38·3 kg to slaughter at 97·3 kg live weight. LL pigs had lower carcass average daily gain (709 v. 742 g/day;P< 0·05) and poorer carcass FCR (P< 0·05: 2·95 v. 2·84 kg/kg) than SD pigs. Daily lysine intake was lower for pigs on HL (P< 0·05: 22·5 g/day), ML (P< 0·001: 20·9 g/day) and LL (P< 0·001: 18·2 g/day) compared with SD (23·4 g/day). Live weight lysine conversion ratio was better for HL (P< 0·05: 26·9 g/kg), ML (P< 0·001: 24·5 g/kg) and LL (P< 0·001: 22·6 g/kg) pigs compared with SD pigs (27·6 g/kg), but carcass lysine conversion ratio was only better for pigs on the ML (P< 0·001: 27·9 g/kg) and LL (P< 0·001: 25·7 g/kg) treatments compared with SD (31·6 g/kg). Nitrogen intake was lower for LL pigs than SD pigs (P< 0·001: 3·45 v. 4·03 kg). Estimated nitrogen excretion was lower for ML (P< 0·01: 2·16 kg) and LL (P< 0·001: 1·85 kg) pigs than SD pigs (2·47 kg). Nitrogen deposition rate was lower for pigs on the LL compared with the SD treatment (P< 0·05: 22·3 v. 23·2 g/day). Although phase feeding diets with the same mean lysine content (11·1 g/kg) as a single diet over the growing-finishing period resulted in similar pig performance, reduced overall daily lysine intake and improved lysine conversion ratio, there was no effect on carcass characteristics or carcass lysine conversion ratio. Reducing the overall mean lysine content to either 10·0 or 8·9 g/kg improved lysine conversion ratio and reduced nitrogen excretion. However, reducing the overall mean lysine content of the diet to 8·9 g/kg had a negative effect on pig growth performance.

Elevated NH3 and NO2 air concentrations and nitrogen deposition rates in the vicinity of a highway in Southern Bavaria

Abstract A transect study consisting of air concentration and deposition measurements of nitrogen compounds was performed to estimate the potential influence of car emissions on the nitrogen input to ecosystems. Therefore, two transects each consisting of 4 plots, the first in a coniferous forest and the second one in an extensively farmed grassland, were installed perpendicular to a highway south of Munich (Bavaria). Both profiles were influenced mainly by car emissions and showed only small local influences caused by agricultural activities. In the framework of a pilot study based upon denuder measurements we found a strong temporal dependency of both nitrogen dioxide (NO2) and ammonia (NH3) concentrations on traffic density. In the main study air concentrations of NO2 and NH3 were measured by passive samplers; they used as the basis for the estimation of dry deposition. These estimations have been compared with the results of analyses from simultaneously conducted canopy throughfall deposition and open air bulk measurements of nitrate (NO3−) and ammonium (NH4+). Additionally, within the forest transect the variety of different soil vegetation species was recorded and quantified. We obtained a strong gradient of gas concentrations along both profiles. Whereas the bulk deposition remained quite constant along the non-forested transect, the nitrogen throughfall deposition rate diminished substantially with the distance from the highway. The deposition rate at the forest edge was twice of that inside. The nitrogen load estimated for the examined forest in the vicinity of the highway was comparable to other forest ecosystems situated near diffuse emission sources from agriculture. It could be shown that changes in soil composition and soil vegetation along the forest transect are caused by decreasing nitrogen deposition with distance from the highway. The application of road salt in winter leads to further impacts.

The fate of experimentally deposited nitrogen in mesocosms from two Canadian peatlands

In large regions of Europe and North America, peatlands have been exposed to elevated rates of atmospheric nitrogen (N) deposition. We investigated the fate of experimentally added N (NH 4 15NO3) at two different N loads (1.2 and 4.7 g N m − 2 yr − 1 ) and water tables (1 and 32 cm) in intact cores from two peatlands, located in Central and Eastern Canada. The sites receive an estimated total N load of 0.6 g m − 2 a − 1 and 1.5 g m − 2 yr − 1 , excluding nitrogen fixation. In all treatments, experimentally added nitrate (NO 3 −) was fully (96–99%) and ammonium (NH 4 +) mostly (81–97%) retained by the plant cover, mainly consisting of Sphagnum mosses, or in the unsaturated zone below. However, on average only 48% of the 15N were recovered from the plant cover, and substantial amounts were found in depth layers of 2–6 cm (21–46%) and 8–12 cm (1.4–10.8%) below the moss surface. The amount of 15N retained also significantly decreased with a lower water table from 56 ± 9% to 40 ± 10%. These findings document a substantial mobility of N, particularly during water table drawdown. Analysis of 15N by a sequential diffusion procedure revealed a transfer of 15N from NO 3 − into NH 4 + and dissolved organic N (DON), but the contents of 15N in these pools accounted for less than 1% of the total N, natural background subtracted. The mass flux of dissolved 15N into the peat was small compared to the total mass flux of 15N. The accumulation of 15N in the bulk peat must have been caused by a mechanism that was not investigated, possibly by transport of particulate organic N.

Aphid infestation causes different changes in carbon and nitrogen allocation in alfalfa stems as well as different inhibitions of longitudinal and radial expansion.

Alfalfa (Medicago sativa) stem elongation is strongly reduced by a pea aphid (Acyrthosiphon pisum Harris) infestation. As pea aphid is a phloem feeder that does not transmit virus or toxins, assimilate withdrawal is generally considered as the main mechanism responsible for growth reduction. Using a kinematic analysis, we investigated the spatial distributions of relative elemental growth rates of control and infested alfalfa stems. The water, carbon, and nitrogen contents per unit stem length were measured along the growth zone. Deposition rates and growth-sustaining fluxes were estimated from these patterns. Severe short-term aphid infestation (200 young adults over a 24-h period) induced a strong and synchronized reduction in rates of elongation and of water and carbon deposition. Reduced nitrogen content and associated negative nitrogen deposition rates were observed in some parts of the infested stems, especially in the apex. This suggested a mobilization of nitrogen from the apical part of the growth zone, converted from a sink tissue into a source tissue by aphids. Calculation of radial growth rates suggested that aphid infestation led to a smaller reduction in radial expansion than in elongation. Together with earlier observations of long-lasting effects of a short-term infestation, this supports the hypothesis that in addition to nutrient withdrawal, a thigmomorphogenesis-like mechanism is involved in the effect of aphid infestation on stem growth.