Enzai Du

Nitrogen deposition and its ecological impact in China: an overview.

Nitrogen (N) deposition is an important component in the global N cycle that has induced large impacts on the health and services of terrestrial and aquatic ecosystems worldwide. Anthropogenic reactive N (N(r)) emissions to the atmosphere have increased dramatically in China due to rapid agricultural, industrial and urban development. Therefore increasing N deposition in China and its ecological impacts are of great concern since the 1980s. This paper synthesizes the data from various published papers to assess the status of the anthropogenic N(r) emissions and N deposition as well as their impacts on different ecosystems, including empirical critical loads for different ecosystems. Research challenges and policy implications on atmospheric N pollution and deposition are also discussed. China urgently needs to establish national networks for N deposition monitoring and cross-site N addition experiments in grasslands, forests and aquatic ecosystems. Critical loads and modeling tools will be further used in N(r) regulation.

Changes in wet nitrogen deposition in the United States between 1985 and 2012

The United States (US) is among the global hotspots of nitrogen (N) deposition and assessing the temporal trends of wet N deposition is relevant to quantify the effectiveness of existing N regulation policies and its consequent environmental effects. This study analyzed changes in observed wet deposition of dissolved inorganic N (DIN?=?ammonium?+?nitrate) in the US between 1985 and 2012 by applying a Mann?Kendall test and Regional Kendall test. Current wet DIN deposition (2011?2012) data were used to gain insight in the current pattern of N deposition. Wet DIN deposition generally decreased going from Midwest?>?Northeast?>?South?>?West region with a national mean rate of 3.5 kg N ha?1 yr?1. Ammonium dominated wet DIN deposition in the Midwest, South and West regions, whereas nitrate and ammonium both contributed a half in the Northeast region. Wet DIN deposition showed no significant change at the national scale between 1985 and 2012, but profound changes occurred in its components. Wet ammonium deposition showed a significant increasing trend at national scale (0.013 kg N ha?1 yr?2), with the highest increase in the Midwest and eastern part of the South region. Inversely, wet nitrate deposition decreased significantly at national scale (?0.014 kg N ha?1 yr?2), with the largest reduction in the Northeast region. Overall, ratios of ammonium versus nitrate in wet deposition showed a significant increase in all the four regions, resulting in a transition of the dominant N species from nitrate to ammonium. Distinct magnitudes, trends and patterns of wet ammonium and nitrate deposition suggest the needs to control N emissions by species and regions to avoid negative effects of N deposition on ecosystem health and function in the US.

Effects of nitrogen and phosphorus supply on growth rate, leaf stoichiometry, and nutrient resorption of Arabidopsis thaliana

BackgroundNitrogen (N) and phosphorus (P) availabilities affect plant growth and the balance of elements, yet how these plant traits respond to N and P supply remains unclear.MethodsWe explored the effects of N and P supply on the growth rate, leaf N and P concentration, and nutrient resorption of Arabidopsis thaliana in a greenhouse fertilization experiment.ResultsRelative growth rate increased with mature green-leaf N:P ratio (N:Pgr) when N-limited, but decreased with N:Pgr when P-limited, suggesting that the growth rate hypothesis might be related to the type of nutrient limitation. In N-limited A. thaliana, addition of P did not significantly affect the leaf N concentration. However, in P-limited A. thaliana, addition of N decreased the leaf P concentration. Addition of N increased P resorption efficiency, and addition of P stimulated N resorption efficiency. Consistent with the predictions of the relative resorption hypothesis, the difference in the proportionate resorption of N vs. P declined with increasing N:Pgr.ConclusionsOur results suggest that N and P jointly regulate growth rate, leaf stoichiometry, and nutrient resorption of A. thaliana, and highlight that the interacting effects of nutrients should be considered when predicting future responses of plant functional traits to global change.

Spatial boundary of urban ‘acid islands’ in southern China

Elevated emissions of sulfur dioxide, nitrogen oxides and ammonia in China have resulted in high levels of sulfur and nitrogen deposition, being contributors to soil acidification, especially in and near large cities. However, knowledge gaps still exist in the way that large cities shape spatial patterns of acid deposition. Here, we assessed the patterns of pH, sulfate, nitrate and ammonium in bulk precipitation and throughfall in southern China’s forests by synthesizing data from published literature. Concentrations and fluxes of sulfate, nitrate and ammonium in bulk precipitation and throughfall exhibited a power-law increase with a closer distance to the nearest large cities, and accordingly pH showed a logarithmic decline. Our findings indicate the occurrence of urban ‘acid islands’ with a critical radius of approximately 70 km in southern China, receiving potential acid loads of more than 2 keq ha−1 yr−1. These urban acid islands covered an area of 0.70 million km2, accounting for nearly 30% of the land area in southern China. Despite a significant capacity to neutralize acids in precipitation, our analysis highlights a substantial contribution of ammonium to potential acid load. Our results suggest a joint control on emissions of multiple acid precursors from urban areas in southern China.

Liu et al. suspect that Zhu et al. (2015) may have underestimated dissolved organic nitrogen (N) but overestimated total particulate N in wet deposition in China.

In a recent publication in the journal Science of the Total Environment, Zhu et al. (2015) reported the composition, spatial patterns, and factors influencing atmospheric wet nitrogen (N) deposition based on one years data from 41-monitoring sites in China. We suspect their results may largely underestimate dissolved organic N (DON) but overestimate total particulate N (TPN) in wet deposition due to the uncertainty resulting from the sampling, storage and analysis methods in their study. Our suspicions are based mainly on our experience from earlier measurements and the literature. We therefore suggest that enhanced data quality control on atmospheric N deposition measurements should be taken into account in future studies.

High Rates of Wet Nitrogen Deposition in China: A Synthesis

Anthropogenic reactive nitrogen emissions (especially NH 3 and NO x ) have been increasing rapidly since the late 1970s in China and may lead to increased atmospheric input of reactive nitrogen to the Earths surface through wet and dry deposition. Analyzing the temporal and spatial patterns of nitrogen (N) deposition is a high priority in order to assess environmental impacts of N deposition on a national scale. To this end, we have established a database for China, based on wet N deposition measured between 1995 and 2007. High rates of wet N deposi- tion have been observed in large areas, particularly in central and eastern China. Average rates of wet deposition for dissolved inorganic nitrogen (DIN), NH 4 + -N and NO x − -N were 17.36 ± 10.53, 10.66 ± 6.54 and 6.57 ± 4.93 kg N ha −1 year −1 . The average ratios of NH 4 + -N/NO x − -N in wet deposition were as high as 1.96 ± 1.27 and showed no significant difference among urban, rural and remote sites. Average wet deposition for DON was 4.84 ± 2.80 kg N ha −1 year −1 accounting for 25.4 ± 13.5 % of the total dissolved nitrogen (TDN) deposition. Wet N deposition exceeded 15 kg N ha −1 year −1 at 52 % of the rural sites. The high rates of wet N deposition in central and eastern China suggest heavy atmospheric reactive nitrogen pollution and substantial negative effects on the terrestrial and aquatic ecosystems of China.

Reduced nitrogen dominated nitrogen deposition in the United States, but its contribution to nitrogen deposition in China decreased

Recently, Li et al. (1) report that reduced nitrogen (N) dominated both wet and dry deposition of inorganic N, following long-term N oxides (NO x ) emission controls introduced in 1990. They systematically compare wet deposition of inorganic N, measured by the US National Atmospheric Deposition Program (NADP) between 1990–1992 and 2010–2012, and calculate N dry deposition from measurements of concentrations made by Clean Air Status and Trends Network, NADP Ammonia Monitoring Network, and Interagency Monitoring of Protected Visual Environments NH x in 2011–2013. Their results show the transition from oxidized N-dominated wet deposition in the early 1990s to reduced N-dominated wet deposition in the early 2010s. According to their analysis (1), this transition reflects increases in agricultural ammonia (NH3) emissions and … [↵][1]1To whom correspondence should be addressed. Email: liu310{at}cau.edu.cn. [1]: #xref-corresp-1-1

Direct effect of acid rain on leaf chlorophyll content of terrestrial plants in China

Anthropogenic emissions of acid precursors in China have resulted in widespread acid rain since the 1980s. Although efforts have been made to assess the indirect, soil mediated ecological effects of acid rain, a systematic assessment of the direct foliage injury by acid rain across terrestrial plants is lacking. Leaf chlorophyll content is an important indicator of direct foliage damage and strongly related to plant productivity. We synthesized data from published literature on experiments of simulated acid rain, by directly exposing plants to acid solutions with varying pH levels, to assess the direct effect of acid rain on leaf chlorophyll content across 67 terrestrial plants in China. Our results indicate that acid rain substantially reduces leaf chlorophyll content by 6.71% per pH unit across the recorded plant species. The direct reduction of leaf chlorophyll content due to acid rain exposure showed no significant difference across calcicole, ubiquist or calcifuge species, implying that soil acidity preference does not influence the sensitivity to leaf injury by acid rain. On average, the direct effects of acid rain on leaf chlorophyll on trees, shrubs and herbs were comparable. The effects, however varied across functional groups and economic use types. Specifically, leaf chlorophyll content of deciduous species was more sensitive to acid rain in comparison to evergreen species. Moreover, vegetables and fruit trees were more sensitive to acid rain than other economically used plants. Our findings imply a potential production reduction and economic loss due to the direct foliage damage by acid rain.

Weak growth response to nitrogen deposition in an old-growth boreal forest

Nitrogen (N) deposition has been enhanced globally due to the dramatic increase in anthropogenic N emissions, but the effects of N deposition on the growth of old-growth forests remain poorly understood. A three-year N enrichment experiment (0, 20, 50 and 100 kg N ha−1 yr−1) was conducted in an old-growth boreal forest in Northeast China to explore its growth response to enhanced N deposition. Nitrogen enrichment significantly increased N availability but caused only a very weak stimulation of growth (<3 kg C/kg N), indicating a minor N limitation. Nitrogen enrichment did not significantly influence the mass production of needle-leaves but increased the production of woody biomass, leading to a slight improvement in growth efficiency. Nitrogen content increased and phosphorus (P) content decreased in freshly fallen needle-leaves, leading to an increase of N:P ratios. The failure of P acquisition to match the increased N uptake suggests a limitation of soil P availability. Our results support the hypothesis of progressive N saturation and indicate that N deposition may cause a very weak stimulation of carbon sequestration in old-growth forests.

Progress in Monitoring and Modelling Estimates of Nitrogen Deposition at Local, Regional and Global Scales

This chapter discusses the status and progress of activities around the world to measure and model dry and wet deposition of reactive nitrogen (Nr), i.e. the final removal processes from the atmosphere, at the local, regional and global scales. It gives an overview of present status and developments in networks and techniques for measuring deposition of Nr. We describe recent developments in the modelling of emissions and deposition, and finish by giving research and policy recommendations regarding N-deposition measurement and modelling, including the need for;