High Atmospheric Nitrogen Deposition Research Articles

Drought effects on growth and density of temperate tree regeneration under different levels of nitrogen deposition

Temperate forests in Central Europe suffer from climate change-induced productivity and vitality reductions and increased tree mortality. Most field work assessing climate change effects in forests refers to mature trees and does not cover interaction between climate change and nitrogen deposition. Here we show in a study of 54 forest sites representing different combinations of climatic conditions and atmospheric nitrogen deposition across Germany that nitrogen significantly affects the drought tolerance of tree regeneration in the field. We compared shoot length increment and regeneration density of Central Europe’s naturally most dominant tree species, European beech (Fagus sylvatica) with three species, which are discussed as potentially more drought-tolerant replacement tree species for climate change adaptation of forestry. Growth of beech was reduced with increasing nitrogen deposition identifying high reactive nitrogen loads as an additional threat for this species, but between-site variation of beech growth was not dependent on climatic parameters despite growth reductions after the drought summer 2018 across all study sites. Remarkably, the only species in the between-site comparisons where low growth was attributable to dry climate was Douglas fir (Pseudotsuga menziesii), as shoot length increment was reduced at sites with dry spring climate. Silver fir (Abies alba) showed increasing growth with increasing nitrogen deposition in combination with increasing drought, probably due to reduced ammonium uptake. Shoot length increment in sessile oak (Quercus petraea) was not affected by the between-site variation of either drought or nitrogen. Our results (combined with results of regeneration density) indicate that high atmospheric nitrogen deposition, which is primarily found in regions with intensive livestock farming in Central Europe, modifies the climate change response of temperate tree species. Interaction of drought and nitrogen deposition should thus be addressed in the debate on climate change adaptation of forestry.

Atmospheric N Deposition Significantly Enhanced Soil N2O Emission From Eastern China Forests

AbstractNitrous oxide (N2O) is an influential greenhouse gas (GHG) and an unregulated ozone‐depleting substance. The extent to which N2O emissions from natural forest soils have been enhanced by high atmospheric nitrogen (N) deposition in China during past decades is unclear; however, assessing land‐related N2O emissions for 2060 national “carbon neutrality” goal is urgent. In this study, we proposed a “gray box” conceptual model and deduced a linear relationship between soil N2O emissions and N deposition on a large scale. On this basis, we created a “process‐augmented data‐driven” approach using which we combined experimental N addition data from 38 Chinese forests with N deposition observation data to estimate regional soil N2O emissions. We found that the N2O emission budget of eastern China forest soils averaged 0.24 ± 0.07 TgN yr−1 from 1996 to 2015; of this, ∼36% (0.087 TgN yr−1) was directly induced by N deposition. Soil N2O emission rates (RN2O) fluctuated slightly after 2006, and the RN2Os of different ecoregions were significantly different (p < 0.001). Soil factors and N‐deposition‐related factors dominated the spatial variation of RN2O. Our findings provide country‐specific and ecoregion‐specific emission factors for national GHG inventories in China. Our approach bridges the gap between site‐level experiments and demand for regional N2O emissions, and is applicable for estimating N2O emissions in other countries/regions. Meanwhile, more N addition experiments are needed to comprehensively understand N cycling processes and extend the predictive capability of the approach.

Foliar phosphorus allocation and photosynthesis reveal plants' adaptative strategies to phosphorus limitation in tropical forests at different successional stages

High atmospheric nitrogen (N) deposition and low soil phosphorus (P) availability occur simultaneously in tropical areas, and thus tropical plants need to adapt nutrient-use strategies to maintain growth and survival. Therefore, identifying the adaptative strategies of tropical plants at different successional stages under low soil P availability is indispensable. Here, we separately investigated foliar traits, photosynthetic characteristics, and P fractions of 8 species in the primary and secondary tropical forests after 10 years of N and P fertilization. P addition increased foliar P concentrations and deceased N:P ratio in the primary forest and secondary forest. The foliar photosynthetic rates did not significantly respond to nutrient additions, and the foliar photosynthetic P-use efficiency (PPUE) reduced under the P addition in the primary forest. In contrast, the foliar photosynthetic rates and photosynthetic nitrogen (N)-use efficiency (PNUE) were enhanced with nutrient additions in the secondary forest. The allocations of foliar nucleic acid P and residual P were reduced by P addition in the primary forest, whereas the allocation of metabolic P was enhanced and the allocation of residual P was reduced by P addition in the secondary forest. Additionally, a higher proportion of structural P was found in the primary forest, and a higher proportion of metabolic P was observed in the secondary forest. Interesting, structural equation model analysis revealed that the plants decreased the allocation of foliar nucleic acid P and increased the allocation of structural P in the primary forest, thereby reducing photosynthetic rates. Whereas the plants enhanced photosynthetic rates by promoting PPUE and the allocation of foliar metabolic P in the secondary forest.Our findings highlighted tropical plants at different successional stages can reasonably allocate foliar P to regulate photosynthetic rates and acclimate to low P environments.

Blowout dynamics in lime‐rich and lime‐poor coastal dunes in the Netherlands

AbstractBlowouts can mitigate the negative effects of acidification in the topsoil, especially in industrialized countries with high atmospheric nitrogen (N) deposition. However, blowout activity may differ between lime‐rich and lime‐poor dunes, which creates different regional responses and interactions between processes and patterns.To further explore this, five Dutch dune sites were selected over the gradient from lime‐rich and lime‐poor dunes. We mapped blowout activity in 5 years between 1996 and 2017 with aerial photographs, and used transport potential, atmospheric N‐deposition and rabbit density as explanatory variables. We also studied soil and plant parameters in the field in different stages of succession.All sites showed fluctuations, but blowout activity net increased in the lime‐rich sites, and decreased in the lime‐poor sites. Differences in blowout activity could not be explained by sand transport potential, which differed between years, but not sites. Differences in blowout activity could to some extent be explained by rabbit density and exceedance of the critical N load, although the transition site between lime‐rich and lime‐poor dunes showed high blowout activity despite low rabbit density.Differences in blowout activity between lime‐rich and lime‐poor dunes were also related to differences in topsoil chemistry, especially with respect to lime content, Fe content and different forms of phosphorus (P). High pH was a key factor, which reduced sensitivity to high N deposition through reduced P‐availability to the vegetation, higher proportion of arbuscular mycorrhizal plants, which may improve food quality for rabbits, and lower root biomass, which may increase erodibility of the dune soil. High pH and low P availability may even occur in lime‐poor dunes with a little lime, as long as blowouts stay active and counteract acidification. However, when pH values drop below 6.5, P availability to the vegetation will increase and start feedback processes leading to blowout stabilization.

Levels and variations of soil bioavailable nitrogen among forests under high atmospheric nitrogen deposition

To examine the perturbation of atmospheric nitrogen (N) deposition on soil N status and the biogeochemical cycle is meaningful for understanding forest function evolution with environmental changes. However, levels of soil bioavailable N and their environmental controls in forests receiving high atmospheric N deposition remain less investigated, which hinders evaluating the effects of enhanced anthropogenic N loading on forest N availability and N losses. This study analyzed concentrations of soil extractable N, microbial biomass N, net rates of N mineralization and nitrification, and their relationships with environmental factors among 26 temperate forests under the N deposition rates between 28.7 and 69.0 kg N ha−1 yr−1 in the Beijing-Tianjin-Hebei (BTH) region of northern China. Compared with other forests globally, forests in the BTH region showed higher levels of soil bioavailable N (NH4+, 27.1 ± 0.8 mg N kg−1; NO3−, 7.0 ± 0.8 mg N kg−1) but lower net rates of N mineralization and nitrification (0.5 ± 0.1 mg N kg−1 d−1 and 0.4 ± 0.1 mg N kg−1 d−1, respectively). Increasing N deposition levels increased soil nitrification and NO3− concentrations but did not increase microbial biomass N and N mineralization among the study forests. Soil moisture and C availability were found as dominant factors influencing microbial N mineralization and bioavailable N. In addition, by budgeting the differences in soil total N densities between the 2000s and 2010s, atmospheric N inputs to the forests were more retained in soils than lost proportionally (84% vs. 16%). We concluded that the high N deposition enriched soil N without stimulating microbial N mineralization among the study forests. These results clarified soil N status and the major controlling factors under high anthropogenic N loading, which is helpful for evaluating the fates and ecological effects of atmospheric N pollution.

Phosphorus fluxes in two contrasting forest soils along preferential pathways after experimental N and P additions

The assessment of impacts of an altered nutrient availability, e.g. as caused by consistently high atmospheric nitrogen (N) deposition, on ecosystem phosphorus (P) nutrition requires understanding of P fluxes. However, the P translocation in forest soils is not well understood and soil P fluxes based on actual measurements are rarely available. Therefore, the aims of this study were to (1) examine the effects of experimental N, P, and P+N additions on P fluxes via preferential flow as dominant transport pathway (PFPs) for P transport in forest soils; and (2) determine whether these effects varied with sites of contrasting P status (loamy high P/sandy low P). During artificial rainfall experiments, we quantified the P fluxes in three soil depths and statistically analyzed effects by application of linear mixed effects modeling. Our results show that the magnitude of P fluxes is highly variable: In some cases, water and consequently P has not reached the collection depth. By contrast, in soils with a well-developed connection of PFPs throughout the profile fluxes up to 4.5 mg P m−2 per experiment (within 8 h, no P addition) were observed. The results furthermore support the assumption that the contrasting P nutrition strategies strongly affected P fluxes, while also the response to N and P addition markedly differed between the sites. As a consequence, the main factors determining P translocation in forest soils under altered nutrient availability are the spatio-temporal patterns of PFPs through soil columns in combination with the P nutrition strategy of the ecosystem.

High atmospheric wet nitrogen deposition and major sources in two cities of Yangtze River Delta: Combustion-related NH3 and non-fossil fuel NOx

High ammonia (NH3) and nitrogen oxide (NOx) emissions are related to serious air pollution in urban areas and the negative impacts of excessive reactive nitrogen (N) deposition on many ecosystems. However, whether there is a relationship between N deposition rates and their sources with urbanization or not remains unclear in many areas. Here, we investigated the deposition rates of ammonium (NH4+), nitrate (NO3−), dissolved organic N, and water-insoluble particular N from July 2017 to June 2018 at two urban and two suburban sites in the Yangtze River Delta (YRD). The δ15N values of precipitation NH4+ and NO3− were measured, and major sources were analyzed using a Bayesian isotope mixing model. Wet N deposition rates were higher in Yangzhou (developing city, 20.3–22.7 kg N ha−1 yr−1) than those in Nanjing (developed city, 19.4–20.5 kg N ha−1 yr−1), and were higher at urban sites (20.4–22.5 kg N ha−1 yr−1) than those at suburban sites (18.7–20.3 kg N ha−1 yr−1). δ15N values of precipitation NH4+ increased with an increase in precipitation pH because ambient acidity affects the equilibrium isotope fractionation between NH3 and NH4+ and wet scavenging coefficients of NH3 and particulate NH4+. For NH4+, combustion-related NH3 sources (62%–65% with 5.5–6.4 kg N ha−1 yr−1, including coal combustion, vehicle exhaust, and biomass burning) contributed more than volatilization NH3 sources (35%–38% with 2.9–3.9 kg N ha−1 yr−1, including fertilizer application and waste volatilization). For NO3−, non-fossil fuel NOx sources (50%–63% with 3.4–4.1 kg N ha−1 yr−1, including biomass burning and microbial N cycle) were comparable to fossil fuel NOx sources (37%–50% with 2.4–3.4 kg N ha−1 yr−1, including coal combustion and vehicle exhaust). This study evidenced high N deposition rates and the importance of combustion-related NH3 emissions and non-fossil fuel NOx emissions in city areas of the YRD.

Denitrification rates in lake sediments of mountains affected by high atmospheric nitrogen deposition

During the last decades, atmospheric nitrogen loading in mountain ranges of the Northern Hemisphere has increased substantially, resulting in high nitrate concentrations in many lakes. Yet, how increased nitrogen has affected denitrification, a key process for nitrogen removal, is poorly understood. We measured actual and potential (nitrate and carbon amended) denitrification rates in sediments of several lake types and habitats in the Pyrenees during the ice-free season. Actual denitrification rates ranged from 0 to 9 μmol N2O m−2 h−1 (mean, 1.5 ± 1.6 SD), whereas potential rates were about 10-times higher. The highest actual rates occurred in warmer sediments with more nitrate available in the overlying water. Consequently, littoral habitats showed, on average, 3-fold higher rates than the deep zone. The highest denitrification potentials were found in more productive lakes located at relatively low altitude and small catchments, with warmer sediments, high relative abundance of denitrification nitrite reductase genes, and sulphate-rich waters. We conclude that increased nitrogen deposition has resulted in elevated denitrification rates, but not sufficiently to compensate for the atmospheric nitrogen loading in most of the highly oligotrophic lakes. However, there is potential for high rates, especially in the more productive lakes and landscape features largely govern this.

Nitrification is the primary source for NO in N-saturated subtropical forest soils: Results from in situ 15 N labeling.

Acidic subtropical forest soils that receive high atmospheric nitrogen (N) deposition have been identified as important sources of nitric oxide (NO). The relative importance of major processes producing NO is unclear. To partition NO sources, we conducted an in situ tracing experiment with 15 NH4 NO3 and NH4 15 NO3 in well-drained acid soils of an N-saturated subtropical forest in Chongqing, southwest China. In the 15 NH4 NO3 treatment, the 15 N signature of NO emitted from the foot of the hillslope (Lower site) was similar to that of the NH4 + pool, indicating predominant autotrophic nitrification for NO formation. In the NH4 15 NO3 treatment, the 15 N enrichment of NO was smaller than that of the NO3 - pool, suggesting minor contribution of denitrification to NO production (~15%). Nitrification is the main process responsible for NO emissions, even in monsoonal summers when soil water-filled pore space values are relatively high.

Effects of decomposing beech (Fagus sylvatica) logs on the chemistry of acidified sand and loam soils in two forest reserves in Flanders (northern Belgium)

We studied the effect of coarse woody debris (CWD) on the soil nutrient status in two beech (Fagus sylvatica) dominated forest reserves in Flanders, Belgium: Wijnendale Forest, on a sandy soil and Kersselaerspleyn in Sonian Forest, on a loamy soil. More specifically, we looked at the chemical composition of beech logs of different stages of decay. In addition, we examined the chemical composition of the organic and the mineral soil at five distances from the decomposing logs. We considered the concentrations of the following elements: C, N, P, S, Ca, K, Mg, Mn, Fe, and Al.The results indicate a difference in wood and soil chemical composition between the two forest sites. The soil and the aboveground biomass of Wijnendale had the highest total N concentration and the lowest concentrations of P and base elements (Ca, K, Mg, and Mn). There is an increase in element concentrations in CWD of both forests during the decomposition, except for K and C. The higher N concentration in Wijnendale, explained by high atmospheric nitrogen deposition in this forest, persisted during decomposition. By contrast, the concentrations of P, Ca, K, and Mg in dead wood of both forests became similar when decomposition proceeded. The effect of CWD was more pronounced in the organic soil layer than in the mineral soil. The organic soil in the proximity of CWD had a higher pH and higher concentrations of C, N, P, Ca, Mg, and Mn (in Sonian forest) and a lower Al concentration (in Wijnendale forest) and this is highly significant for Ca, a limiting nutrient in moderate to highly acidic forests. The percentage of the soil surface impacted by the logs is 0.92% and 0.36% for Sonian and Wijnendale respectively, which is expected to increase with time, considering the fact that both reserves are only recently left unmanaged. The results of this study highlight the contribution of CWD in sustaining the nutrient status and buffering capacity of forest sites, in particular on soils sensitive to acidification and exposed to high nitrogen deposition.

Effects of long-term nitrogen addition on phosphorus cycling in organic soil horizons of temperate forests

High atmospheric nitrogen (N) deposition is expected to impair phosphorus (P) nutrition of temperate forest ecosystems. We examined N and P cycling in organic soil horizons of temperate forests exposed to long-term N addition in the northeastern USA and Scandinavia. We determined N and P concentrations, enzyme activities and net N and P mineralization rates in organic soil horizons of two deciduous (Harvard Forest, Bear Brook) and two coniferous (Klosterhede, Gardsjon) forests which had received experimental inorganic N addition between 25 and 150 kg N ha−1 year−1 for more than 25 years. Long-term N addition increased the activity of phosphatase (+ 180%) and the activity of carbon (C)- and N-acquiring enzymes (cellobiohydrolase: + 70%, chitinase: + 25%). Soil N enrichment increased the N:P ratio of organic soil horizons by up to 150%. In coniferous organic soil horizons, net N and P mineralization were small and unaffected by N addition. In deciduous organic soil horizons, net N and P mineralization rates were significantly higher than at the coniferous sites, and N addition increased net N mineralization by up to 290%. High phosphatase activities concomitant with a 40% decline in P stocks of deciduous organic soil horizons indicate increased plant P demand. In summary, projected future global increases in atmospheric N deposition may induce P limitation in deciduous forests, impairing temperate forest growth.

Tracing the Fate of Atmospheric Nitrate in a Subalpine Watershed Using Δ17O.

Nitrogen is an essential nutrient for life on Earth, but in excess, it can lead to environmental issues (e.g., N saturation, loss of biodiversity, acidification of lakes, etc.). Understanding the nitrogen budget (i.e., inputs and outputs) is essential to evaluate the prospective decay of the ecosystem services (e.g., freshwater quality, erosion control, loss of high patrimonial-value plant species, etc.) that subalpine headwater catchments provide, especially as these ecosystems experience high atmospheric nitrogen deposition. Here, we use a multi-isotopic tracer (Δ17O, δ15N and δ18O) of nitrate in aerosols, snow, and streams to assess the fate of atmospherically deposited nitrate in the subalpine watershed of the Lautaret Pass (French Alps). We show that atmospheric N deposition contributes significantly to stream nitrate pool year-round, either by direct inputs (up to 35%) or by in situ nitrification of atmospheric ammonium (up to 35%). Snowmelt in particular leads to high exports of atmospheric nitrate, most likely fast enough to impede assimilation by surrounding ecosystems. Yet, in a context of climate change, with shorter snow seasons, and increasing nitrogen emissions, our results hint at possibly stronger ecological consequences of nitrogen atmospheric deposition in the close future.

Spatial and temporal variability of soil nitric oxide emissions in N-saturated subtropical forest

Acidic subtropical forest soils, receiving high atmospheric nitrogen (N) deposition, are characterized by fast N turnover, making them potential “hot spots” for nitrous oxide (N2O) and nitric oxide (NO) emissions. Production of NO in soils is mediated by microbial nitrification and denitrification and/or chemical decomposition of microbially produced nitrite (NO2 −). In monsoonal forests, soil microbial processes are exposed to strong soil moisture and temperature fluctuations, known to cause pronounced variability in NO emission. We quantified in situ fluxes of NO throughout two summers in the N-saturated TieShanPing forest, Chongqing, SW China. Additional N2O measurements were carried out in the second summer to infer likely source processes. To address spatial variability, fluxes were measured along two transects, one covering well-drained Acrisols on a forested hill slope, and the other hydrologically connected terraces with poorly drained Cambisols situated in a groundwater discharge zone. Hill slope sites emitted on average 48.4 ± 60.6 µg NO–N m−2 h−1 in the relatively wet summer of 2015 and 88.4 ± 94.6 µg NO–N m−2 h−1 in the dry summer of 2016, illustrating the strong effect of soil moisture regime. The NO emission in the groundwater discharge zone, measured in the dry summer of 2016 only, while it was flooded in the summer of 2015, was significantly smaller (26.4 ± 52.7 µg N m−2 h−1). The mean N2O-N emission on the hillslope (18.1 ± 13.9 µg N m−2 h−1) was smaller than NO-N flux, while it was larger (38.3 ± 39.3 µg N m−2 h−1) in the groundwater discharge zone. The temporal variability of the NO flux was largely explained by soil moisture fluctuations, whereas soil organic matter pool sizes contributed most to spatial variability. Hourly measurements showed that the NO flux doubled with 8 °C increase of soil temperature, indicating that soil temperature was another important driver for NO emissions. Our study indicates that acid N-saturated subtropical forest soils are a large source for NO, particularly during dry summers.

Long-term nitrogen and phosphorus enrichment alters vegetation species composition and reduces carbon storage in upland soil

Reactive nitrogen (N) deposition can affect ecosystem processes, particularly in oligotrophic upland habitats. Phosphorus (P) addition has been proposed to reduce the effects of N enrichment on N leaching and acidification, since P limitation can reduce biomass production and consequent sequestration of reactive N. However, biodiversity is often reduced in more productive ecosystems and P limitation may protect against this effect. Responses to P availability in instances of high N deposition are poorly understood. This study investigated the ecosystem response to alleviation of P limitation, using a long-term nutrient addition experiment (1996–2012) three years after ceasing N inputs and 15years after a single P application. Substantial differences were observed in the structure and composition of vegetation species and above-ground vegetation biomass. Vegetation height was greater in the N+P addition treatments (+38% cf. control), with increased cryptogam cover (+47%), whereas N addition increased graminoid species cover (+68%). Vegetation diversity was significantly reduced by the addition of P (−21%), indicating that P limitation is likely to be an important mechanism that limits biodiversity loss in upland habitats exposed to chronic N deposition. Significant differences in soil C and N contents were also observed between treatments. Relative to control, the addition of N increased soil C (+11%) and N (+11%) pool sizes, whereas the addition of N and P reduced soil C (−12%) and N (−13%) pool sizes. This demonstrated the importance of P availability for upland ecosystem processes, and highlights the long-term effects of P addition on vegetation species composition and C storage. Thus, the addition of P cannot be endorsed as a method for reducing impacts of N deposition.Capsule: Phosphorus limitation is a major mechanism governing ecosystem processes in situations of high atmospheric nitrogen deposition.

北京地区典型落叶阔叶乔木叶片含氮量和δ15N值对大气氮沉降的响应

PDF HTML阅读 XML下载 导出引用 引用提醒 北京地区典型落叶阔叶乔木叶片含氮量和δ15N值对大气氮沉降的响应 DOI: 10.5846/stxb201511202348 作者: 作者单位: 北京林业大学,北京林业大学自然保护区学院,北京林业大学自然保护区学院,北京林业大学自然保护区学院,北京林业大学 作者简介: 通讯作者: 中图分类号: 基金项目: 北京市优秀人才培养资助项目（2014000020124G073）；国家自然科学基金资助项目（41503077）；北京林业大学科技创新计划资助项目（BLX20120022） Responses and Indications of Foliar Nitrogen Contents and δ15N values to Atmospheric Nitrogen Deposition in Beijing, China Author: Affiliation: Beijing Forestry University,,,,Beijing Forestry University Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:为探究植物对大气氮沉降的响应和对这部分氮素的来源指示作用，本研究通过对北京地区198个采样点，典型落叶阔叶乔木杨属（Populus）和柳属（Salix）植物叶片进行采样，测定其叶片样品含氮量和δ15 N值。结果表明：北京地区杨属植物叶片含氮量为16.5-38.6 g/kg，平均（24.0±4.0）g/kg；柳属植物叶片含氮量为17.2-36.2 g/kg，平均（25.9±4.1）g/kg。研究区域范围内杨属、柳属植物叶片的含氮量均呈现出西北低、东南高的对角线型分布，与该区域大气氮沉降的空间变异相吻合。由于研究区域范围内气候因子无明显的变异，植物叶片的含氮量变化反应了大气氮沉降对植物元素化学计量特征的影响和植物对大气氮沉降的响应。北京地区杨属植物叶片δ15N值为-3.95‰-8.10‰，平均（1.15±2.48）‰；柳属植物叶片δ15N值为-3.04‰-9.73‰，平均（2.31±2.60）‰。杨属和柳属植物叶片的δ15N值均呈现出西北高、中部高、东南低的空间分布，与叶片含氮量空间分布趋势相反。中部城区较高的δ15N值反应了交通污染对大气含氮化合物增加的影响；西北部较高的δ15N值反应了该区域受人为活动排放源的影响较少，自然的氮循环是其较高δ15N值的主要原因；东南部较低的δ15N值则有可能是由农业活动和交通共同作用的结果。 Abstract:With 60% of the total area located in the North China Plain, Beijing suffered with very high atmospheric nitrogen (N) deposition in the south part, which was as high as 100 kg hm-2 a-1 including both organic and inorganic nitrogenous species from both wet and dry deposition. To test the responses of foliar N contents of plants, a collection of deciduous broadleaf tree leaves was conducted across Beijing areas. Typical deciduous broadleaf trees, Populus and Salix were selected at 189 sites, which were firstly designed at 5-decimal minute in latitude and longitude grid resolution and then excluded sites without Populus or Salix species. Leaf sampling collection was carried out in the end of August corresponding to annual peak-standing biomass in late summer. Five trees of every species at each site were selected, and five mature leaves of every tree were collected. All the leaf samples were over-dried at 105℃ for 10 minutes and then 65℃ for 48 hours to constant mass. Samples of each species at each site were put together and grounded with a mill to pass 1-mm sieve for N contents analysis. Foliar N was determined following Kjeldehl digestion and δ15N values were determined by continuous flow isotope-ratio mass spectrometer. The foliar N contents were (24.0±4.0) g/kg and (25.9±4.1) g/kg on average for Populus and Salix, respectively. Spatial variations of both the two genus showed similar trends, with higher foliar N contents in the southeast and lower foliar N contents in the northwest, consisting with the spatial variation of atmospheric N deposition in Beijing area. The foliar δ15N values were (1.15±2.48)‰ and (2.31±2.60)‰ on average for Populus and Salix, respectively. However, the spatial variation trends of δ15N values were contrary with the foliar N contents. Higher δ15N values were found in the city center and northwest, while lower δ15N values were found in the southeast. With the different δ15N values of potential sources, the higher δ15N values in the city center indicated the traffic emission sources, the higher δ15N values in the northwest indicated the natural N cycling, while the lower δ15N values indicated both the agricultural and traffic pollution. 参考文献 相似文献 引证文献

Heterogeneous responses to ozone and nitrogen alter the species composition of Mediterranean annual pastures.

Air pollution represents a threat to biodiversity throughout the world and particularly in the Mediterranean area, where high tropospheric ozone (O3) concentrations and atmospheric nitrogen (N) deposition are frequently recorded. Mediterranean annual pastures are among the most important ecosystems in southern Europe due to their high biodiversity and extension. Aiming to study the responses of these communities to the main atmospheric pollutants in the Mediterranean region, an experimental study was performed in an open-top chamber (OTC) facility. A mixture of six species representative of annual pastures was grown under field conditions inside the OTC. Plants were exposed for 39days to four O3 treatments and three doses of N. The species responded heterogeneously to both factors. Legumes did not react to N but were very sensitive to O3: Trifolium species responded negatively, while Ornithopus responded positively, taking advantage of the greater sensitivity of clovers to O3. The grasses and the herb were more tolerant of O3 and grasses were the most responsive to N. Significant interactions between factors indicated a loss of effectiveness of N in O3-polluted atmospheres and an ability of O3 to counterbalance the damage induced by N input, but both effects were dependent on O3 and N levels. The inclusion of plant competition in the experimental design was necessary to reveal results that would otherwise be missed, such as the positive growth responses under elevated O3 levels. Surprisingly, competition within the legume family played the most important role in the overall response of the annual community to O3. Both tropospheric O3 and N deposition should be considered important drivers of the structure and biodiversity of Mediterranean annual pastures.

Phosphorus nutrition of beech (Fagus sylvatica L.) is decreasing in Europe

Foliar phosphorus concentrations have decreased in Europe during the last 20 years. High atmospheric nitrogen deposition and climate change might be responsible for this trend. Continued decrease in foliar P concentrations might lead to reduced growth and vitality of beech forests in Europe. Increased forest soil acidification, atmospheric nitrogen deposition, and climate change have been shown to affect phosphorus nutrition of forest trees. Low foliar phosphorus levels and high nitrogen/phosphorus ratios have been observed in different European countries and have been related to reduced growth in forests. We test the hypothesis that phosphorus concentrations of European beech (F. sylvatica L.) foliage are decreasing at the European scale. Foliar phosphorus concentrations in beech were monitored on the basis of the “International Co-operative Programme on Assessment and Monitoring of Air Pollution Effects on Forests.” Here, data from 12 European countries, comprising 79 plots and a 20-year sampling period (1991–2010), were evaluated. Foliar phosphorus concentrations ranged from 0.81 to 1.66 mg g−1 dw (plot median of the 20-year sampling period). On 22 % of the plots, phosphorus concentrations were in the deficiency range of beech (Mellert and Gottlein 2012). On 62 % of the plots, the nitrogen/phosphorus ratio was above 18.9, which is considered to be disharmonious for beech. In addition, foliar phosphorus concentrations were significantly decreasing by, on average, 13 % from 1.31 to 1.14 mg g−1 in Europe (p < 0.001). Our results show that phosphorus nutrition of beech is impaired in Europe. Possible drivers of this development might be high atmospheric nitrogen deposition and climate change. Continued decrease in foliar phosphorus concentrations, eventually attaining phosphorus deficiency levels, might lead to reduced growth and vitality of beech forests in Europe.

Impact of bioenergy production on ecosystem dynamics and services-a case study on U.K. Heathlands.

For sustainability's sake, the establishment of bioenergy production can no longer overlook the interactions between ecosystem and technological processes, to ensure the preservation of ecosystem functions that provide energy and other goods and services to the human being. In this paper, a bioenergy production system based on heathland biomass is investigated with the aim to explore how a system dynamics approach can help to analyze the impact of bioenergy production on ecosystem dynamics and services and vice versa. The effect of biomass harvesting on the heathland dynamics, ecosystem services such as biomass production and carbon capture, and its capacity to balance nitrogen inputs from atmospheric deposition and nitrogen recycling were analyzed. Harvesting was found to be beneficial for the maintenance of the heathland ecosystem if the biomass cut fraction is higher than 0.2 but lower than 0.6, but this will depend on the specific conditions of nitrogen deposition and nitrogen recycling. With 95% recycling of nitrogen, biomass production was increased by up to 25% for a cut fraction of 0.4, but at the expense of higher nitrogen accumulation and the system being less capable to withstand high atmospheric nitrogen deposition.

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.

Aboveground persistence of vascular plants in relationship to the levels of airborne nutrient deposition

This paper examines whether high atmospheric nitrogen deposition affects aboveground persistence of vascular plants. We combined information on local aboveground persistence of vascular plants in 245 permanent plots in the Netherlands with estimated level of nitrogen deposition at the time of recording. Aboveground persistence of vascular plants was studied using two types of survival statistic technique: Kaplan–Meier analysis and Cox’ regression. We expected a link between nitrogen deposition and loss of plant species due to intensified herbivory or other forms of tissue loss that would lead to diminishing local aboveground persistence. This could not be detected. In contrast, a positive relation was found between local aboveground persistence of plants and high levels of ammonia deposition. This result is considered to be an indication of lower colonization access, for example due to limited space (e.g. the chance of successful establishment of individuals from new species is lower). The results are discussed in relation to the extremely high levels of nitrogen deposition in the studied plots. This study provides an indication that management practices aiming for restoration of colonization access (e.g. mowing, grazing and sod cutting) are vital under heavily eutrophied conditions.