Effects Of Atmospheric Nitrogen Deposition Research Articles

Cascading impacts of nitrogen deposition on soil microbiome and herbivore communities in desert steppes

Human activities in the last century have intensified global nitrogen deposition, resulting in the degradation of ecosystem function and loss of biodiversity worldwide. Nitrogen addition is a crucial method for examining the effects of atmospheric nitrogen deposition on species composition and structure of soil microbiome and biotic community, as exogenous nitrogen inputs can trigger cascading effects on ecosystem functions. In a 6-year experiment, we evaluated the impact of nitrogen addition on soil microbial-plant-insect systems in desert steppes. Our results show that nitrogen addition significantly altered soil microbial composition and ecological function, leading to a decrease in nitrogen-fixing bacteria and an increase in saprophytic fungi. High levels of nitrogen addition increased total plant biomass while decreasing species diversity. Additionally, high nitrogen addition levels suppressed below-ground biomass of gramineae and legumes compared to low nitrogen addition. Nitrogen addition also increased herbivore abundance by altering insect community structure, particularly benefiting chewing pests over sucking pests, thus heightening the risk of biological disasters through trophic cascading effects. Consequently, excessive nitrogen addition may destabilize desert steppe ecosystems by disturbing soil microbial-plant-insect interactions, hindering the maintenance of biotic community diversity and steppe productivity.

The effects of atmospheric nitrogen deposition in coral-algal phase shifts on remote coral reefs

Remote seawater has been considered a potential refuge for corals in the face of anthropogenic disturbances. However, these remote areas may receive increased atmospheric N deposition, and the ecological consequences remain unclear. This field survey revealed coral-algal phase shifts in the mid-north of the South China Sea. These shifts were observed in 44%, 13.6%, and 26.5% of the sampled reef sites at depths of 1-4 m, 5-8 m, and 10-15 m, respectively. Over 50% of sections in the deeper depths hosted fewer corals compared to shallower areas, coinciding with a higher abundance of macroalgae in the deeper layers. Furthermore, based on long-term observation of atmospheric N flux, laboratory experiments were conducted to explore the cause of coral declines. The results indicate that N supply efficiently promoted macroalgae growth. The saturation of N absorption by macroalgae occurred within 2 weeks, leading to nutrient accumulation in seawater, especially nitrate, which had a direct impact on corals. While moderate N fluxes appeared to mitigate coral bleaching, high N fluxes, even with a balanced P supply or medium level of nutrients with an imbalanced N/P ratio, can both increase the susceptibility of corals to heat bleaching. This study explains the coral-algal phase shift in remote and relatively deep seawater and improves understanding of the cause-and-effect relationship between atmospheric N deposition and coral reef decline.

Effects of simulated atmospheric nitrogen deposition on the bacterial community structure and diversity of four distinct biocolonization types on stone monuments: a case study of the Leshan Giant Buddha, a world heritage site

AbstractAtmospheric nitrogen deposition may affect the biodeterioration process of stone monuments through direct and indirect pathways, but relevant studies are lacking. Therefore, taking the biologically colonized rocks around the Leshan Giant Buddha (World Heritage - Mixed Property) as the research objects, we studied the effects of multiple nitrogen addition levels (0, 9, 18, 36, 72 kg N hm-2 a-1; N0, N1; N2 ; N3; N4) on the bacterial community structure and soil nutrients on the surfaces of stones with four biocolonization types, including naked rock (NR), and lichen (LR), bryophyte (BS) and vascular plant (VS) colonization, to investigate the potential effect of atmospheric nitrogen deposition on the rock weathering of the Leshan Giant Buddha. The results demonstrated that nitrogen addition impacted soil carbon, nitrogen and phosphorus nutrients, as well as bacterial community structure and composition, but the responses to nitrogen input varied among different colonization types. Nitrogen fertilization promoted the accumulation of total organic carbon and total nitrogen in NR and LR, and increased the content of total phosphorus in VS. Bacterial α-diversity decreased with nitrogen addition in NR but increased with nitrogen addition in VS. Nitrogen addition significantly (R > 0.9, p < 0.01) changed the bacterial community composition in the four biocolonization types, and the changes were dominated by species replacement (contributed to 60.98%, 76.32%, 67.27% and 72.14% for bacterial diversity in NR, LR, BS and VS, respectively). Total nitrogen, dissolved organic nitrogen, dissolved organic nitrogen and total phosphorus were the most important ecological factors affecting bacterial community structure in NR, LR, BS and VS, respectively. Nitrogen addition enriched different bacterial taxa in the four biocolonization types. The results of this study provide basic data for the protection of stone monuments and the formulation of sustainable development strategies under a changing climate.

The threat of groundwater pollution for petrifying springs; defining nutrient threshold values for an endangered bryophyte dominated habitat

Eutrophication by human activities is increasingly affecting ecosystem functioning and plant community composition. So far, studies mainly focus on the effects of atmospheric nitrogen deposition, surface water eutrophication or soil nutrient accumulation. Groundwater pollution of spring habitats, however, has received much less attention, although numerous papers report groundwater nutrient enrichment worldwide. This study presents a survey on groundwater pollution (with emphasis on nitrate and phosphate) and bryophyte composition in 51 ambient petrifying springs in 5 NW European countries, which were compared to published data from 173 other sites in 11 European countries.The reviewed dataset covers a broad range of unpolluted to heavily polluted springs with nitrate concentrations between 0.7 and 3227 μmol l−1. Most petrifying springs in the rural lowlands of NW Europe were found to have elevated concentrations of nitrate and phosphate with the most polluted springs occurring in The Netherlands.The cover of individual characteristic bryophyte species significantly correlates with groundwater nutrient concentrations indicating that nutrient pollution of spring waters affects bryophyte composition. Palustriella commutata, Eucladium verticillatum and Brachythecium rivulare prefer unpolluted petrifying springs whereas Cratoneuron filicinum and Pellia endiviifolia show a much broader tolerance to groundwater pollution. In order to sustain at least the basic conditions for the typical bryophyte composition of petrifying springs habitats, threshold values of 288 μmol (18 mg l−1) NO3− l−1 and 0.42 μmol (0.04 mg l−1) ortho-PO43- l−1 were defined.Data analysis of the spring water composition indicates that the main source for nutrient and nutrient induced base cation enrichment are nitrate losses from intensively used agricultural fields. The anthropogenically induced but regionally different chemical processes in subsoil and aquifers can result in different levels of nutrient pollution in springs.Further regulations for nitrate and phosphate application are required to conserve and restore groundwater fed ecosystems in Europe.

The Effects of Atmospheric Nitrogen Deposition on the Marine Ecosystem of the Northern South China Sea

AbstractThe rapid economic developments in countries surrounding the South China Sea have caused a significant increase in the atmospheric deposition of nitrogen (AD‐N) into the ocean. The impact of AD‐N on the regional ecosystem has not been quantitatively assessed, and its driving mechanism has not been explored, either. Here, we applied a one‐dimensional European Regional Seas Ecosystem Model to examine the responses of the ecosystem to AD‐N. The physical‐biological coupled model reproduced the seasonal and interannual variabilities of observed nutrients, chlorophyll a, phytoplankton community structure, and particulate organic carbon (POC) exports at the South East Asia Time‐series Station. Seasonally, the increase of POC flux by AD‐N was most significant in winter, with a ∼2‐month lag behind the associated surface response. It can exist in the following spring, as supported by the larger population size of zooplankton after the previous winter's feeding up. Notably, the ratio of POC export to primary production varied seasonally and interannually, which was controlled by the phytoplankton and zooplankton's size compositions. The surface nutrient input thus caused a significant seasonal change in the biological carbon pump efficiency. Interannually, the modulation of the POC flux by AD‐N was inversely phase‐locked with wind variations. The out‐of‐phase of the surface‐ and subsurface‐nutrient‐driven POC fluxes suggested a potentially more considerable contribution of AD‐N to the total carbon export during years under the weak subsurface influence. This study highlights the importance of AD‐N in the regional ecosystem, which needs a better representation in the present biogeochemical modeling framework.

Simulated nitrogen deposition promotes the carbon assimilation of shrubs rather than tree species in an evergreen broad-leaved forest

Although understory addition of nitrogen (UAN) is commonly used to simulate nitrogen deposition in field studies in forest ecosystems, it ignores the effects of atmospheric nitrogen deposition on the canopy. We studied the effects of nitrogen deposition simulated by UAN and by canopy addition of nitrogen (CAN) on leaf structure, chemical properties, Calvin cycle, and photosynthate distribution strategy of representative woody plant species in a subtropical evergreen broadleaved forest in South China. The results showed that maximum photosynthetic rate (Amax) of shrub species Blastus cochinchinensis and Ardisia quinquegona under CAN treatments was significantly higher than that of UAN treatments at the same N addition concentration. The concentrations of intermediates (PGK, DPGA and G3P) in Calvin cycle of B. cochinchinensis and A. quinquegona, and Castanea henryi were significantly increased with CAN treatments, but the opposite was true with UAN treatments. CAN25 significantly increased starch concentrations of shrub species Lasianthus chinensis and B. cochinchinensis, and significantly decreased sucrose concentrations of shrub species A. quinquegona and tree species C. henryi. Correlation analyses showed that nitrogen application amount under different modes helped explain the changes in Amax and Calvin cycle intermediates. In summary, nitrogen deposition may promote the Amax and Calvin cycle of shrub species, and the adaptability of shrub species to nitrogen deposition is higher than that of tree species, which may help to explain the degradation of subtropical evergreen broad-leaved forest.

Effects of atmospheric nitrogen deposition on productivity and growth allocation. First results of a long-term experiment in a pre-alpine beech forest

Atmospheric nitrogen deposition is an important global change driver, potentially affecting forest health and productivity. In order to evaluate the potential effects on tree growth and above-ground biomass production in southern European conditions, a long-term manipulation experiment was carried out in a prealpine beech forest (Pian Cansiglio, BL). Four treatments are compared: (i) control, (ii) moderate soil fertilization, (iii) high soil fertilization (iv) and moderate above canopy fertilization. Results, 7 years into the experiment, do not show any effect of soil fertilization treatments on the monitored parameters, but show instead positive effects of the canopy fertilization on the allocation of resources to the canopy and on the production of leaf biomass, with values that in 2021 exceeded those observed in the control treatment by 0.72 Mg DM ha-1. The contribution of N due to atmospheric deposition does not seem to decrease the growth of pre-alpine beech forests in the short term, but could substantially alter their ecological dynamics.

Modeling Effects of Atmospheric Nitrogen Deposition on the Water Quality of the MR-SNWDP

Modeling the effects of atmospheric deposition on the water quality of the middle route of the South-to-North Water Diversion Project (MR-SNWDP) can provide a basis for scientific protection and optimal allocation of water resources. Considering the total nitrogen (TN) as a representative water quality index, this study analyzed the water quality variations along the MR-SNWDP and in the Miyun Reservoir under atmospheric deposition, using the hydrodynamic and environmental numerical models. The results in 2016 revealed that the atmospheric deposition significantly affected the water quality of the MR-SNWDP, and the effects of atmospheric deposition on the water quality of the middle route and Miyun Reservoir showed different variation rules. However, the clearer water from the MR-SNWMP would significantly deteriorate after storage in the Miyun Reservoir as the TN concentration increased significantly. Based upon the scenario analysis, it was found that the constant water diversion scheme helped reduce the effects of atmospheric deposition. Further, it is recommended that the storage amounts in the Miyun Reservoir should be as low as possible.

Effects of Atmospheric Nitrogen Deposition on Nitrous Oxide Emission from Mountainous Forest Soils in Southwest Karst Region

Effects of Atmospheric Nitrogen Deposition on Nitrous Oxide Emission from Mountainous Forest Soils in Southwest Karst Region

Effects of simulated nitrogen deposition on the soil microbial community diversity of a Deyeuxia angustifolia wetland in the Sanjiang Plain, Northeastern China

PurposeThe soil microbial community is an important bioactive component of terrestrial ecosystems. Its structural and functional diversity directly affects carbon and nitrogen processes. This study aimed to investigate the variations in the diversity and composition of soil bacterial communities in a wetland with different nitrogen deposition conditions.MethodsA long-term simulated nitrogen deposition experiment was conducted in the Ecological Locating Research Station of the Institute of Nature and Ecology of Heilongjiang Academy of Sciences. Three different treatments were evaluated, including low nitrogen (LK; 40 kg N·hm-2·a-1), high nitrogen (HN; 80 kg N·hm-2·a-1), and control (CK; 0 kg N·hm-2·a-1). Bacterial 16S rDNA was then sequenced and analyzed using the next-generation sequencing technology.ResultHigher levels of N deposition resulted in an α-diversity increase followed by a decrease, with significant reductions in the HN treatment. Simulated nitrogen deposition resulted in changes in the structure and abundance of bacterial communities in wetland soils. The dominant phyla in all three plots were Proteobacteria and Acidobacteria. Compared with CK, the relative abundance of Chloroflexi increased significantly under the HN treatment (P < 0.05), whereas the relative abundance of Firmicutes and Bacteroidetes decreased significantly (P < 0.05). Nitrogen input changed the composition and relative abundance of the bacterial community, which was possibly due to N-induced soil acidification.ConclusionThis study thus provides a theoretical basis for predicting the effects of atmospheric nitrogen deposition on soil microorganisms, as well as changes in the wetland ecosystem in Sanjiang Plain.

Effect of atmospheric nitrogen deposition and its components on carbon flux in terrestrial ecosystems in China

Long-term atmospheric nitrogen (N) deposition increases bioavailable N in terrestrial ecosystems, thereby influencing ecosystem productivity. However, how N deposition and its components (i.e., NO3−–N and NH4+–N) influence the spatial pattern of productivity in terrestrial ecosystems in China remains unknown. Here, we utilize published data including carbon (C) fluxes from eddy flux tower (gross ecosystem productivity, ecosystem respiration, and net ecosystem productivity) and the corresponding climate and N deposition data for 60 typical ecosystems in China. The objective was to investigate the effect of N deposition on ecosystem productivity and explore the variations of N use efficiency (NUE). Our results reveal that atmospheric total N deposition is significantly correlated with C fluxes of terrestrial ecosystems in China. Ecosystems respond variably to different components of N deposition. In detail, forest ecosystem marginally correlated with NO3−–N and wet deposition, while grassland ecosystem significantly correlated with NH4+–N and dry deposition. NUE of productivity induced by N deposition in Chinese terrestrial ecosystems was 53.95 ± 40.30 g C g−1 N, and it was influenced by precipitation and aridity index. This study quantifies the contribution of total N deposition and its associated components to productivity in terrestrial ecosystems in China, offering vital information for regional C and N management.

Nighttime climate warming enhances inhibitory effects of atmospheric nitrogen deposition on the success of invasive Solidago canadensis

Nighttime climate warming enhances inhibitory effects of atmospheric nitrogen deposition on the success of invasive Solidago canadensis

Nitrogen application and osmotic stress antagonistically affect wheat seed germination and seedling growth

Atmospheric nitrogen (N) deposition (AtNiDe) and drought stress (DS) have strongly affected plant growth. However, previous research has primarily focused on the effects of AtNiDe with various levels and DS on plant growth (especially seed germination and seedling growth). This study aimed to evaluate the single and combined effects of AtNiDe with four types (compounds: NH4–N, NO3–N, CO(NH2)2–N, and a mixture of the three types of N) and DS (three levels: control, low, and high) on wheat seed germination and seedling growth. The AtNiDe treatment increased wheat seed germination and seedling growth. Mixed N exerted a greater positive effect on wheat seed germination and seedling growth than single N forms. Organic N also had a greater positive effect on wheat seed germination and seedling growth than reduced inorganic N. The DS treatment decreased wheat seed germination and seedling growth. The AtNiDe treatment alleviated the adverse effects of DS on wheat seed germination and seedling growth. Mixed N had the greatest effect on alleviating the adverse effects of DS on wheat seed germination and seedling growth. Thus, AtNiDe and DS antagonistically affected wheat seed germination and seedling growth. NOVELTY STATEMENT This study assessed the single and combined effects of atmospheric nitrogen deposition with four types and drought stress at three levels on wheat seed germination and seedling growth. Generally, nitrogen and drought antagonistically affected wheat seed germination and seedling growth.

大气氮沉降对中亚草地生态系统净初级生产力的影响

氮沉降作为除气候变化、CO₂浓度升高以及土地利用变化之外的第四大主要影响陆地生态系统结构和功能的因素，其对碳循环过程的影响研究相对薄弱，同时也是不确定性最大的环节之一。近年来，由于长期高强度的放牧导致草地生态系统的生产力降低，氮成为典型草地植物生长和生态系统净初级生产力的主要限制因子。据研究，亚洲的氮沉降平均增速极有可能高于全球氮沉降平均增速，成为未来氮沉降增加最快的区域。在此背景下，研究大气氮沉降对于中亚草地生态系统的影响具有重要的意义。利用反硝化-分解模型（DNDC）分析1979-2014年中亚地区草地生态系统净初级生产力（NPP）的时空分异，探讨氮沉降对草地NPP影响。结果表明：（1）1979-2014年间，中亚地区平均草地NPP约为（173.10±31.80） g C m^-2 a^-1，草地NPP时空分异明显，各草地类型的NPP从大到小依次为森林草甸、温带草原和荒漠草原，并且草地NPP以（2.67±1.30） g C m^-2 a^-1的速度逐年增长；（2）当前氮沉降情景总体上促进了中亚地区草地NPP的增长，1979-2014年氮沉降使得中亚草地NPP增加了0.42 Pg C。;Climate change, increased CO₂ concentration, nitrogen deposition and land use change are currently recognized as the main factors affecting the structure and function of ecosystems. Among them, the research on the influence of nitrogen deposition on carbon cycling process is still insufficient with great uncertainty. In recent years, as the productivity of grassland ecosystem is reduced due to long-term intensive grazing, nitrogen has become a limiting factor of typical grassland. The increasing rate of nitrogen deposition in Asia is probably higher than the global average as reported by previous research. In view of this, it is of significant importance to study the effect of atmospheric nitrogen deposition on grassland ecosystem in Central Asia. In this study, Denitrification-Decomposition (DNDC) model was utilized to analyze the temporal and spatial variation of grassland net primary productivity (NPP) in Central Asia from 1979 to 2014, to explore the effects of nitrogen deposition on grassland NPP. The results showed that:(1) During 1979-2014, the annual averaged temperature in Central Asia showed a significant increase trend((0.03±0.01)℃ a^-1, R²=0.40), while the precipitation decreased with the trend of (2.26±1.78)mm a^-1(R²=0.35). (2) from 1979 to 2014, the average NPP of grassland in Central Asia was about(173.10±31.80)g C m^-2 a^-1, and the spatial and temporal differences of grassland NPP were obvious. The highest NPP of grassland was found in forest meadow, followed by temperate grassland, and desert grassland NPP. Moreover, the grassland NPP increased at the rate of(2.67±1.30)g C m^-2 a^-1. (3) The current nitrogen deposition scenario generally benefits the growth of grassland NPP in central Asia, which increases the grassland NPP by 0.42 Pg C in the last 36 years. Based on the existing studies, we cannot determine whether the decrease of NPP in this part of grassland is caused by reaching the critical load of nitrogen, and more in-depth studies are needed.

模拟大气氮沉降对细根形态和解剖结构影响的研究进展

模拟大气氮沉降对细根形态和解剖结构影响的研究进展

Carbon–nitrogen interactions in European forests and semi-natural vegetation – Part 2: Untangling climatic, edaphic, management and nitrogen deposition effects on carbon sequestration potentials

Abstract. The effects of atmospheric nitrogen deposition (Ndep) on carbon (C) sequestration in forests have often been assessed by relating differences in productivity to spatial variations of Ndep across a large geographic domain. These correlations generally suffer from covariation of other confounding variables related to climate and other growth-limiting factors, as well as large uncertainties in total (dry + wet) reactive nitrogen (Nr) deposition. We propose a methodology for untangling the effects of Ndep from those of meteorological variables, soil water retention capacity and stand age, using a mechanistic forest growth model in combination with eddy covariance CO2 exchange fluxes from a Europe-wide network of 22 forest flux towers. Total Nr deposition rates were estimated from local measurements as far as possible. The forest data were compared with data from natural or semi-natural, non-woody vegetation sites. The response of forest net ecosystem productivity to nitrogen deposition (dNEP ∕ dNdep) was estimated after accounting for the effects on gross primary productivity (GPP) of the co-correlates by means of a meta-modelling standardization procedure, which resulted in a reduction by a factor of about 2 of the uncorrected, apparent dGPP ∕ dNdep value. This model-enhanced analysis of the C and Ndep flux observations at the scale of the European network suggests a mean overall dNEP ∕ dNdep response of forest lifetime C sequestration to Ndep of the order of 40–50 g C per g N, which is slightly larger but not significantly different from the range of estimates published in the most recent reviews. Importantly, patterns of gross primary and net ecosystem productivity versus Ndep were non-linear, with no further growth responses at high Ndep levels (Ndep &gt; 2.5–3 g N m−2 yr−1) but accompanied by increasingly large ecosystem N losses by leaching and gaseous emissions. The reduced increase in productivity per unit N deposited at high Ndep levels implies that the forecast increased Nr emissions and increased Ndep levels in large areas of Asia may not positively impact the continent's forest CO2 sink. The large level of unexplained variability in observed carbon sequestration efficiency (CSE) across sites further adds to the uncertainty in the dC∕dN response.

A modelling approach to assess the effects of atmospheric nitrogen deposition on the marine ecosystem in the Bohai Sea, China

Atmospheric deposited nitrogen (AD-N) approximates or exceeds riverine input in many coastal ecosystems, such as the Bohai Sea (BHS) which is one of the most eutrophic coastal waters in China. We construct a three-dimensional (3D) physical-biogeochemical model to understand the influence of atmospheric dissolved inorganic nitrogen (DIN) on the intra- and inter-annual variations of phytoplankton blooms and nutrient dynamics in the BHS. The biological component, which is coupled to the Regional Ocean Modelling System (ROMS), is a simple but widely used Nutrient-Phytoplankton-Zooplankton-Detritus (NPZD) model with eight state variables. The model simulation successfully reproduces the spatial and temporal variations of observed DIN and dissolved inorganic phosphorus (DIP) and the climatological features of phytoplankton biomasses (chlorophyll a), which confirms the major role of air-transported nutrients in controlling standing stocks and nutrient limitations. The modelling results show that the relative contributions of deposited nitrogen to the total DIN in the seawater for the Bohai, Laizhou and Liaodong Bays and Central Bohai Basin reach 84.8%, 49.3%, 37.4% and 44.4% on average, respectively. The relative contribution ratio is approximately 54% for the entire Bohai region, causing a 56.5% increase in the phytoplankton biomass on average. These results also indicate that the effects of AD-N on nutrient and phytoplankton dynamics vary widely in regional areas because of the uneven spatial distribution of nitrogen deposition fluxes and also partially because of the hydrodynamic conditions, shortwave radiation and water temperatures.

Does canopy nitrogen uptake enhance carbon sequestration by trees?

Temperate forest 15N isotope trace experiments find nitrogen (N) addition‐driven carbon (C) uptake is modest as little additional N is acquired by trees; however, several correlations of ambient N deposition against forest productivity imply a greater effect of atmospheric nitrogen deposition than these studies. We asked whether N deposition experiments adequately represent all processes found in ambient conditions. In particular, experiments typically apply 15N to directly to forest floors, assuming uptake of nitrogen intercepted by canopies (CNU) is minimal. Additionally, conventional 15N additions typically trace mineral 15N additions rather than litter N recycling and may increase total N inputs above ambient levels. To test the importance of CNU and recycled N to tree nutrition, we conducted a mesocosm experiment, applying 54 g N/15N ha−1 yr−1 to Sitka spruce saplings. We compared tree and soil 15N recovery among treatments where enrichment was due to either (1) a 15N‐enriched litter layer, or mineral 15N additions to (2) the soil or (3) the canopy. We found that 60% of 15N applied to the canopy was recovered above ground (in needles, stem and branches) while only 21% of 15N applied to the soil was found in these pools. 15N recovery from litter was low and highly variable. 15N partitioning among biomass pools and age classes also differed among treatments, with twice as much 15N found in woody biomass when deposited on the canopy than soil. Stoichiometrically calculated N effect on C uptake from 15N applied to the soil, scaled to real‐world conditions, was 43 kg C kg N−1, similar to manipulation studies. The effect from the canopy treatment was 114 kg C kg N−1. Canopy treatments may be critical to accurately represent N deposition in the field and may address the discrepancy between manipulative and correlative studies.

Combined effect of atmospheric nitrogen deposition and climate change on temperate forest soil biogeochemistry: A modeling approach

Atmospheric N deposition is known to severely impact forest ecosystem functioning by influencing soil biogeochemistry and nutrient balance, and consequently tree growth and overall forest health and biodiversity. Moreover, because climate greatly influences soil processes, climate change and atmospheric N deposition must both be taken into account when analysing the evolution of forest ecosystem status over time.Dynamic biogeochemical models have been developed to test different climate and atmospheric N deposition scenarios and their potential interactions in the long term. In this study, the ForSAFE model was used to predict the combined effect of atmospheric N deposition and climate change on two temperate forest ecosystems in France dominated by oak and spruce, and more precisely on forest soil biogeochemistry, from today to 2100. After a calibration step and following a careful statistical validation process, two atmospheric N deposition scenarios were tested: the current legislation in Europe (CLE) and the maximum feasible reduction (MFR) scenarios. They were combined with three climate scenarios: current climate scenario, worst-case climate scenario (A2) and best-case climate scenario (B1). The changes in base saturation and inorganic N concentration in the soil solution were compared across all scenario combinations, with the aim of forecasting the state of acidification, eutrophication and forest ecosystem recovery up to the year 2100.Simulations highlighted that climate had a stronger impact on soil base saturation, whereas atmospheric deposition had a comparative effect or a higher effect than climate on N concentration in the soil solution. Although deposition remains the main factor determining the evolution of N concentration in soil solution, increased temperature had a significant effect. Results also highlighted the necessity of considering the joint effect of both climate and atmospheric N deposition on soil biogeochemistry.

Year-round grazing to counteract effects of atmospheric nitrogen deposition may aggravate these effects

Excessive nitrogen input in natural ecosystems is a major threat to biodiversity. A coastal dune area near Amsterdam in the Netherlands suffers from high atmospheric nitrogen deposition affecting sensitive habitats such as fixed coastal dunes with herbaceous vegetation (‘grey dunes’). To mitigate its effect year round grazing was applied from 2007 until 2012. In winter, when natural food supply is low, the cattle received supplementary hay that caused additional inputs of nitrogen. Estimates based on nitrogen contents of hay, as well as of manure, showed the input through winter feeding (c. 3–14 kg N ha−1.y−1) is in the same order of magnitude as both the actual deposition (c. 17 kg N ha−1.y−1) and the critical load for a number of herbaceous habitat types (10–15 kg N ha−1.y−1). Locally, the effect of winter feeding adds to the effect of nitrogen redistribution within the area caused by the cattle's terrain usage. We conclude that winter feeding may aggravate effects of atmospheric nitrogen deposition.