Allocation patterns of nonstructural carbohydrates in response to CO_(2)elevation and nitrogen deposition in Cunninghamia lanceolata saplings

Stored nonstructural carbohydrates(NSC)indicate a balance between photosynthetic carbon(C)assimilation and growth investment or loss through respiration and root exudation.They play an important role in plant function and whole-plant level C cycling.CO_(2)elevation and nitrogen(N)deposition,which are two major environmental issues worldwide,aff ect plant photosynthetic C assimilation and C release in forest ecosystems.However,information regarding the eff ect of CO_(2)elevation and N deposition on NSC storage in diff erent organs remains limited,especially regarding the trade-off between growth and NSC reserves.Therefore,here we analyzed the variations in the NSC storage in diff erent organs of Chinese fi r(Cunninghamia lanceolata)under CO_(2)elevation and N addition and found that NSC concentrations and contents in all organs of Chinese fi r saplings increased remarkably under CO_(2)elevation.However,N addition induced diff erential accumulation of NSC among various organs.Specifi cally,N addition decreased the NSC concentrations of needles,branches,stems,and fi ne roots,but increased the NSC contents of branches and coarse roots.The increase in the NSC contents of roots was more pronounced than that in the NSC content of aboveground organs under CO_(2)elevation.The role of N addition in the increase in the structural biomass of aboveground organs was greater than that in the increase in the structural biomass of roots.This result indicated that a diff erent tradeoff between growth and NSC storage occurred to alleviate resource limitations under CO_(2)elevation and N addition and highlights the importance of separating biomass into structural biomass and NSC reserves when investigating the eff ects of environmental change on biomass allocation.

Changes in soil microbial communities induced by warming and N deposition accelerate the CO 2 emissions of coarse woody debris

Warming and nitrogen(N)deposition are two important drivers of global climate changes.Coarse woody debris(CWD)contains a large proportion of the carbon(C)in the total global C pool.The composition of soil microbial communities and environmental changes(i.e.,N deposition and warming)are the key drivers of CWD decomposition,but the interactive impact between N deposition and warming on the composition of soil microbial communities and CWD decomposition is still unclear.In a laboratory experiment,we study and simulate respiration during decomposition of the CWD(C 98)of Cryptomeria japonica(CR)and Platycarya strobilacea(PL)in response to warming and N deposition over 98 days.Resuts show that either warming or N addition signifi cantly accelerated the C 98 of the two tree species by altering the soil microbial community(bacterial:fungi and G+:G–).The combined treatment(warming+N)resulted in a decomposition eff ect equal to the sum of the individual eff ects.In addition,the species composition of bacteria and fungi was obviously aff ected by warming.However,N deposition had a remarkable infl uence on G+:G–.Our results indicated that N deposition and warming will observably alter the composition and growth of the microbial community and thus work synergistically to accelerate CWD decomposition in forest ecosystems.We also present evidence that N deposition and warming infl uenced the composition and balance of soil microbial communities and biogeochemical cycling of forest ecosystems.

Effect of Simulated N Deposition on Soil Exchangeable Cations in Three Forest Types of Subtropical China

The effects of simulated nitrogen(N)deposition on soil exchangeable cations were studied in three forest types of subtropical China.Four N treatments with three replications were designed for the monsoon evergreen broadleaf forest (mature forest):control(0 kg N ha-1 year-1),low N(50 kg N ha-1 year-1),medium N(100 kg N ha-1 year-1)and high N(150 kg N ha-1 year-1),and only three treatments(i.e.,control,low N,medium N)were established for the pine and mixed forests.Nitrogen had been applied continuously for 26 months before the measurement.The mature forest responded more rapidly and intensively to N additions than the pine and mixed forests,and exhibited some significant negative symptoms,e.g.,soil acidification,Al mobilization and leaching of base cations from soil.The pine and mixed forests responded slowly to N additions and exhibited no significant response of soil cations.Response of soil exchangeable cations to N deposition varied in the forests of subtropical China,depending on soil N status and land-use history.

Preliminary Response of Soil Fauna to Simulated N Deposition in Three Typical Subtropical Forests

A field-scale experiment arranged in a complete randomized block design with three N addition treatments including a control (no addition of N), a low N (5 g m-2 year-1), and a medium N (10 g m-2 year-1) was performed in each of the three typical forests, a pine (Pinus massoniana Lamb.) forest (PF), a pine-broadleaf mixed forest (MF) and a mature monsoon evergreen broadleaf forest (MEBF), of the Dinghushan Biosphere Reserve in subtropical China to study the response of soil fauna community to additions of N. Higher NH4+ and NO3- concentrations and a lower soil pH occurred in the medium N treatment of MEBF, whereas the NO3- concentration was the lowest in PF after the additions of N. The response of the density, group abundance and diversity index of soil fauna to addition of N varied with the forest type, and all these variables decreased with increasing N under MEBF but the trend was opposite under PF. The N treatments had no significant effects on these variables under MF. Compared with the control plots, the medium N treatment had significant negative effect on soil fauna under MEBF. The group abundance of soil fauna increased significantly with additions of higher N rates under PF. These results suggested that the response of soil fauna to N deposition varied with the forest type and N deposition rate, and soil N status is one of the important factors affecting the response of soil fauna to N deposition.

Response of soil fauna to simulated nitrogen deposition: A nursery experiment in subtropical China

We studied the responses of soil fauna to a simulated nitrogen deposition in nursery experimental plots in Subtropical China. Dissolved NH4NO3 was applied to the soil by spraying twice per month for 16 months, starting January 2003 with treatments of 0, 5, 10, 15 and 30 gN/（m^2·a）. Soil fauna was sampled after 6, 9, 13 and 16 months of treatment in three soil depths （0-5 cm, 5-10 cm, 10-15 cm）. Soil available N increased in correspondence with the increasing N treatment, whereas soil pH decreased. Bacterial and fungal densities were elevated by the N treatment. Soil fauna increased in the lower nitrogen treatments but decreased in the higher N treatments, which might indicate that there was a threshold around 10 gN/（m^2·a） for the stimulating effects of N addition. The N effects were dependent on the soil depth and sampling time. The data also suggested that the effects of the different N treatments were related to the level of N saturation, especially the concentration of NO3^- in the soil.

Response of Nitrogen Leaching to Nitrogen Deposition in Disturbed and Mature Forests of Southern China

Current nitrogen (N) leaching losses and their responses to monthly N additions were investigated under a disturbed pine (Pinus massoniana) forest and a mature monsoon broadleaf forest in southern China. N leaching losses from both disturbed and mature forests were quite high (14.6 and 29.2 kg N ha-1 year-1, respectively), accounting for 57% and 80% of their corresponding atmospheric N inputs. N leaching losses were substantially increased following the first 1.5 years of N applications in both forests. The average increases induced by the addition of 50 and 100 kg N ha-1 year-1 were 36.5 and 24.9 kg N ha-1 year-1, respectively, in the mature forest, accounting for 73.0% and 24.9% of the annual amount of N added, and 14.2 and 16.8 kg N ha-1 year-1 in the disturbed forest, accounting for 28.4% and 16.8% of the added N. Great N leaching and a fast N leaching response to N additions in the mature forest might result from long-term N accumulation and high ambient N deposition load (greater than 30 kg N ha-1 year-1 over the past 15 years), whereas in the disturbed forest, it might result from the human disturbance and high ambient N deposition load. These results suggest that both disturbed and mature forests in the study region may be sensitive to increasing N deposition.

Effects of six years of simulated N deposition on gross soil N transformation rates in an old-growth temperate forest

Elevated atmospheric nitrogen(N) deposition has been detected in many regions of China, but its effects on soil N transformation in temperate forest ecosystems are not well known. We therefore simulated N deposition with four levels of N addition rate(N0, N30, N60, and N120) for6 years in an old-growth temperate forest in Xiaoxing’an Mountains in Northeastern China. We measured gross N transformation rates in the laboratory usingN tracing technology to explore the effects of N deposition on soil gross N transformations taking advantage of N deposition soils. No significant differences in gross soil N transformation rates were observed after 6 years of N deposition with various levels of N addition rate. For all N deposition soils, the gross NH~+ immobilization rates were consistently lower than the gross N mineralization rates,leading to net N mineralization. Nitrate(NO~-) was primarily produced via oxidation of NH~+(i.e., autotrophic nitrification), whereas oxidation of organic N(i.e., heterotrophic nitrification) was negligible. Differences between the quantity of ammonia-oxidizing bacteria and ammonia-oxidizing archaea were not significant for any treatment, which likely explains the lack of a significant effect on gross nitrification rates. Gross nitrification rates were much higher than the total NO~- consumption rates,resulting in a build-up of NO~-, which highlights the high risk of N losses via NO~- leaching or gaseous N emissions from soils. This response is opposite that of typical N-limited temperate forests suffering from N deposition,suggesting that the investigated old-growth temperate forest ecosystem is likely to approach N saturation.

Variations in diversity,composition,and species interactions of soil microbial community in response to increased N deposition and precipitation intensity in a temperate grassland

Background Global climate change has resulted in precipitation regimes exhibiting an increasing trend in rainfall intensity but a reduction in frequency.In addition,nitrogen(N)deposition occurs simultaneously in arid and semi-arid regions.Microbial biomass,diversity,composition,and species interactions are key determinants of ecological functions.We examined the effects of changes in precipitation intensity and N addition on the soil bacterial and fungal communities in a semi-arid grassland in Inner Mongolia,China.Methods The microbial biomass(bacterial PLFAs and fungal PLFAs)was determined through phospholipid fatty acid(PLFA)analysis,and microbial diversity(Shannon index and evenness index)was determined with high-throughput sequencing(16S and ITS).Species interactions were determined using a molecular ecological network analysis.The relationships between microbial community(bacterial community and fungal community)and environmental variables were examined by Mantel tests.Results We found that N addition decreased fungal PLFA under moderate,high,and extreme precipitation intensity treatments and increased fungal community complexity under the high precipitation intensity treatment.Furthermore,N addition increased bacterial diversity under moderate and high precipitation intensity treatments.N addition caused greater environmental stress to the fungal community,which was dominated by deterministic processes.Conclusions The effects of N deposition on soil bacterial and fungal communities were altered by precipitation intensity.The changes in soil bacterial and fungal communities were different,implying that composition and functional traits adapt differently to projected global changes at a regional scale.

Determining Total N Deposition Using ^(15)N Dilution Technique in the North China Plain

本文采用定量氮沉降总量的ITNI（Integrated Total Nitrogen Input）系统,利用15N稀释原理和生物监测技术,定量研究了华北平原大气氮沉降的农田输入总量及其在推荐施肥中的作用。结果表明,以玉米和小麦为指示植物,监测到在玉米-小麦轮作体系中整个华北平原大气氮沉降的输入总量高达80-90 kgN ha-1yr-1,对玉米和小麦植物有效性的沉降氮总量约为50 kgN ha-1yr-1。以黑麦草为指示植物,监测到华北平原大气氮沉降的输入总量约为100 kgN ha-1yr-1,对其植物有效性的沉降氮约为76 kgN ha-1yr-1,占总沉降氮的77%。由于华北平原小麦季扬尘较多,因此干沉降可能是该时期大气氮沉降输入总量的主要贡献。

Interactive effect of climate warming and nitrogen deposition may shift the dynamics of native and invasive species

Aims Projections of invasive species expansion under a warmer world often do not explicitly consider the concurring nitrogen(N)deposition.It remains largely unknown how the convoluted effect of climate warming and N deposition will shift the native and invasive species dynamics.Here,we hypothesize that the concurring in creases in N and temperature would promote growth of invasive species greater than that of native species.Methods A controlled greenhouse experiment was conducted to quantify the growth response of an invasive species(Solidago canadensis L.)and a co-existing native species(Artemisia argyi Levi,et Van)under the effects of climate warming,N deposition and their interactions.Important Findings Due to the strong positive effect of N addition,the interactive effect of temperature increase and N addition resulted in an overall significant increase in growth of both in vasive and native species,demonstrating that these manipulations may make microhabitats more favorable to plant growth.However,the relative increases in biomass,height and diameter of invasive S.canadensis were signifiesntly lower than those of native A.argyi.This suggests that the vegetative growth superiority of invasive S.canadensis over the native species A.argyi is reduced by the enhanced N availability in the warmer world.Therefore,the inclusion of N deposition may mitigate the projection of invasive species S.canadensis expansion under climate warming.

Simulated NH_4^+-N Deposition Inhibits CH_4 Uptake and Promotes N_2O Emission in the Meadow Steppe of Inner Mongolia, China

Few studies are conducted to quantify the effects of enhanced N deposition on soil nitrous oxide （N2O） emission and methane （CH4） uptake in the meadow steppe of Inner Mongolia, China. A two-year field experiment was conducted to assess the effects of nitrogen （N） deposition rates （0, 10, and 20 kg N ha-1 year-1 as （NH4）2SO4） on soil N2O and CH4 fluxes. The seasonal and diurnal variations of soil N2O and CH4 fluxes were determined using the static chamber-gas chromatography method during the two growing seasons of 2008 and 2009. Soil temperature, moisture and mineral N （NH4＋-N and NO3-N） concentration were simultaneously measured. Results showed that low level of （NH4）2SO4 （10 kg N ha-1 year-1） did not significantly affect soil CH4 and N20 fluxes and other variables. High level of （NH4）2SO4 （20 kg N ha-1 year-1） significantly increased soil NO3-N concentration by 24.1% to 35.6%, decreased soil CH4 uptake by an average of 20.1%, and significantly promoted soil N2O emission by an average of 98.2%. Soil N2O emission responded more strongly to the added N compared to CH4 uptake. However, soil CH4 fluxes were mainly driven by soil moisture, followed by soil NO3--N concentration. Soil N2O fluxes were mainly driven by soil temperature, followed by soil moisture. Soil inorganic N availability was a key integrator of soil CH4 uptake and N2O emission. These results suggest that the changes of availability of inorganic N induced by the increased N deposition in soil may affect the CH4 and N2O fluxes in the cold semi-arid meadow steppe over the short term.

Effects of Atmosphere Deposition on Nitrogen Content of Two Poaceae Plants

[Objective] It was to study nitrogen use efficiency under the condition of deposition of perennial ryegrass (Lolium perenne L.) and barley (Hordeum vulgare L.), further revealing the difference in gene variation.[Method] A pot experiment was conducted under 3 treatments of rainwater, ammonium-N (aN) and nitrate-N (nN).[Result] In the treatments of aN and nN, the biomass and N contents in plants were obviously higher than those in rainwater treatment, while the largest biomass(36.116 g) was observed in nN treatment. The absorption to aN was best to perennial ryegrass while nN to barley. According to the differential analysis of N content, treatments of both aN and nN was nitrogen superfluous, which led to release excessive N to the atmosphere, and the rainwater treatment and the control were N deficient, the largest N absorption from atmosphere was 0.698 g in rainwater treatment.[Conclusion] Average N use efficiency contributed by atmosphere N deposition ranged from 1.321%-6.116%, while the control of barley had the highest of 6.116%.

Influence of nitrogen wet deposition on nitrogen output in a typical watershed in the Three Gorges Reservoir Area

In order to explore the influence of wet nitrogen(N)deposition on N output in watersheds,this study selected a typical small watershed(Chenjiagou,CJG)in the Three Gorges Reservoir(TGR)area based on one-year observation of rainfallrunoff N forms.Characteristics and sources of N output were clarified by chemical statistics and isotopic abundance,and the contribution of N deposition to the N output was quantified by the output coefficient method.The N flux of wet deposition was estimated at 18.53 kg N ha^(-1) yr^(-1),and originated mostly from agricultural activities.Watershed N was significantly accumulated from upper to lower reaches due to frequent human activities.Seasonal changes of riverine N were strongly affected by chemical fertilizer,with the highest concentration in spring and the lowest in winter.Nitrate was mainly derived from chemical fertilizer,accounting for 38.83% of all sources.N concentration in processes of different rainfall events had a hysteresis effect corresponding to the flow rate.Three rainfall events greatly changed DTN(Dissolved total N)outputs:rainstorm caused 91.26 kg DTN output,which was 11 times that of moderate rain(8.46 kg)and 4 times that of heavy rain(20.80 kg).N deposition contributed 19.89% of riverine N output in the watershed.The results can provide theoretical support for the control of N pollution in the TGR area.

Assessment of Nitrogen Pollutant Sources in Surface Waters of Taihu Lake Region

The nitrogen （N） pollution status of the 12 most important rivers in Changshu, Taihu Lake region was investigated. Water samples were collected from depths of 0.5-1.0 m with the aid of the global positioning system （GPS）. The seasonal variations in the concentrations of different N components in the rivers were measured. Using tension-free monolith lysimeters and ^15N-labeled fertilizer, field experiments were carried out in this region to determine variations of iSN abundance of NO3^- in the leachate during the rice and wheat growing seasons, respectively. Results showed that the main source of N pollution of surface waters in the Taihu Lake region was not the N fertilizer applied in the farmland but the urban domestic sewage and rural human and animal excreta directly discharged into the water bodies without treatment. Atmospheric dry and wet N deposition was another evident source of N pollutant of the surface waters. In conclusion, it would not be correct to attribute the N applied to farmlands as the source of N pollution of the surface waters in this region.

Dynamics of soil inorganic nitrogen and their responses to nitrogen additions in three subtropical forests, south China

Three forests with different historical land-use, forest age, and species assemblages in subtropical China were selected to evaluate current soil N status and investigate the responses of soil inorganic N dynamics to monthly ammonium nitrate additions. Results showed that the mature monsoon evergreen broadleaved forest that has been protected for more than 400 years exhibited an advanced soil N status than the pine （Pinus massoniana） and pine-broadleaf mixed forests, both originated from the 1930＇s clear-cut and pine plantation. Mature forests had greater extractable inorganic N pool, lower N retention capacity, higher inorganic N leaching, and higher soil C/N ratios. Mineral soil extractable NH4^＋-N and NO3-N concentrations were significantly increased by experimental N additions on several sampling dates, but repeated ANOVA showed that the effect was not significant over the whole year except NH4^＋-N in the mature forest. In contrast, inorganic N （both NH4^＋-N and NO3^--N） in soil 20-cm below the surface was significantly elevated by the N additions. From 42% to 74% of N added was retained by the upper 20 cm soils in the pine and mixed forests, while 0%-70% was retained in the mature forest. Our results suggest that land-use history, forest age and species composition were likely to be some of the important factors that determine differing forest N retention responses to elevated N deposition in the study region.

Litter decomposition and C and N dynamics as affected by N additions in a semi-arid temperate steppe, Inner Mongolia of China

Litter decomposition is the fundamental process in nutrient cycling and soil carbon（C） sequestration in terrestrial ecosystems. The global-wide increase in nitrogen（N） inputs is expected to alter litter decomposition and,ultimately, affect ecosystem C storage and nutrient status. Temperate grassland ecosystems in China are usually N-deficient and particularly sensitive to the changes in exogenous N additions. In this paper, we conducted a 1,200-day in situ experiment in a typical semi-arid temperate steppe in Inner Mongolia to investigate the litter decomposition as well as the dynamics of litter C and N concentrations under three N addition levels（low N with 50 kg N/（hm2？a）（LN）, medium N with 100 kg N/（hm2？a）（MN）, and high N with 200 kg N/（hm2？a）（HN）） and three N addition forms（ammonium-N-based with 100 kg N/（hm2？a） as ammonium sulfate（AS）, nitrate-N-based with 100 kg N/（hm2？a） as sodium nitrate（SN）, and mixed-N-based with 100 kg N/（hm2？a） as calcium ammonium nitrate（CAN）） compared to control with no N addition（CK）. The results indicated that the litter mass remaining in all N treatments exhibited a similar decomposition pattern： fast decomposition within the initial 120 days, followed by a relatively slow decomposition in the remaining observation period（120–1,200 days）. The decomposition pattern in each treatment was fitted well in two split-phase models, namely, a single exponential decay model in phase I（〈398 days） and a linear decay function in phase II（≥398 days）. The three N addition levels exerted insignificant effects on litter decomposition in the early stages（〈398 days, phase I; P〉0.05）. However, MN and HN treatments inhibited litter mass loss after 398 and 746 days, respectively（P〈0.05）. AS and SN treatments exerted similar effects on litter mass remaining during the entire decomposition period（P〉0.05）. The effects of these two N addition forms differed greatly from those of CAN after 746 and 1,053 days, respectively（P〈0.05）. During the decomposition period, N concentrations in the decomposing litter increased whereas C concentrations decreased, which also led to an exponential decrease in litter C：N ratios in all treatments. No significant effects were induced by N addition levels and forms on litter C and N concentrations（P〉0.05）. Our results indicated that exogenous N additions could exhibit neutral or inhibitory effects on litter decomposition, and the inhibitory effects of N additions on litter decomposition in the final decay stages are not caused by the changes in the chemical qualities of the litter, such as endogenous N and C concentrations. These results will provide an important data basis for the simulation and prediction of C cycle processes in future N-deposition scenarios.

Fate of ^(15)N Labeled Nitrate and Ammonium Salts Added to an Alpine Meadow in the Qinghai-Xizang Plateau, China

To understand the dynamics of added nitrogen (N) in alpine meadow and the role of alpine plants and soil microorganisms in the retention of deposited N, the fate of 15 N labeled nitrate and ammonium salts was determined in an alpine meadow for two months. Two weeks after 15 N application, total recovery of 15 N from NO - 3_ 15 N was 73.5% while it was 78% from NH + 4_ 15 N. More 15 N was recovered in plants than in soil organic matter or in microbial biomass, irrespective of forms of N added. After one month, 70.6% of added NO - 3_ 15 N and 57.4% of NH + 4_ 15 N were recovered in soils and plants. 15 N recovered in soil organic matter decreased greatly while that recovered in plants varied little, irrespective of the form N. Compared with the results of two weeks after 15 N application, more NO - 3_ 15 N than NH + 4_ 15 N was recovered in microbial biomass. Total recovery was 58.4% (six weeks) and 67% (eight weeks) from NO - 3_ 15 N, and 43.1% and 49% from NH + 4_ 15 N, respectively. Both plants and soil microorganism recovered more NO - 3_ 15 N than NH + 4_ 15 N. But plants recovered more 15 N than soil microorganisms. During the whole experiment plants retained more NO - 3_N and 15 N than soil microorganisms while 15 N recovered in inorganic N pool did not exceed 1% due to lower amount of inorganic N. This indicates that plants play more important roles in the retention of deposited N although microbial biomass can be an important sink for deposited N in early days after N application.

Contrasting effects of nitrogen addition on litter decomposition in forests and grasslands in China

Nitrogen(N)addition has profound impacts on litter-mediated nutrient cycling.Numerous studies have reported different effects of N addition on litter decomposition,exhibiting positive,negative,or neutral effects.Previous meta-analysis of litter decomposition under N addition was mainly based on a small number of samples to allow comparisons among ecosystem types.This study presents the results of a meta-analysis incorporating data from 53 published studies(including 617 observations)across forests,grasslands,wetlands,and croplands in China,to investigate how environmental and experimental factors impact the effects of N addition on litter decomposition.Averaged across all of the studies,N addition significantly slows litter decomposition by 7.02%.Considering ecosystem types,N addition significantly accelerates litter decomposition by 3.70%and 11.22%in grasslands and wetlands,respectively,clearly inhibits litter decomposition by 14.53%in forests,and has no significant effects on litter decomposition in croplands.Regarding the accelerated litter decomposition rate in grasslands due to N addition,litter decomposition rate increases slightly with increasing rates of N addition.However,N addition slows litter decomposition in forests,but litter decomposition is at a significantly increasing rate with increasing amounts of N addition.The responses of litter decomposition to N addition are also influenced by the forms of N addition,experiential duration of N addition,humidity index,litter quality,and soil pH.In summary,N addition alters litter decomposition rate,but the direction and magnitude of the response are affected by the forms of N addition,the rate of N addition,ambient N deposition,experimental duration,and climate factors.Our study highlights the contrasting effects of N addition on litter decomposition in forests and grasslands.This finding could be used in biogeochemical models to better evaluate ecosystem carbon cycling under increasing N deposition due to the differential responses of litter decomposition to N addition rates and ecosystem types.

Foliar C/N stoichiometry in urban forest trees on a global scale

Foliar C/N stoichiometry is an indicator of geochemical cycling in forest ecosystems,but the driving changes for its response to urbanization at the wide scale is not clear.In this study,data on tree-leaf C and N stoichiometry were collected in papers from across 105 tree species from 82 genera and 46 families.The foliar C/N of urban forest trees varied among different climate zones and tree taxonomic variation and tended to be higher in trees of urban forests near the equator and in eastern regions,mainly driven by lowered foliar N concentration.Neither the foliar C concentration nor foliar C/N for trees of urban forests was statistically higher than those of rural forests.For variation by taxonomic classification,C_4 species Amaranthus retroflexus and Chenopodium ambrosoides(Amaranthaceae) had lower foliar C/N than did other species and families.Myrsine guianensis(Primulaceae) and Myconia fallax(Asteraceae) had the highest foliar C/N.Therefore,urbanization has not caused a significant response in forest trees for foliar C/N.The change in foliar N concentration was globally the main force driving of the differences in foliar C/N for most tree species in urban forests.More work is needed on foliar C/N in trees at cities in polar regions and the Southern Hemisphere.

Linnebjer—A South Swedish Oak Forest and Meadow Area—Revisited after Half a Century

An oak forest and three wet meadows/fens were reinvestigated after 50 years concerning tree vitality, biomass and productivity, and soil chemistry. Sulphur and nitrogen deposition has changed dramatically during these years, and the aim was to analyse the differences in both the oak forest and the open field ecosystems. Trees were re-measured and soil profiles were resampled. Important visible changes in the oak forest were stated concerning the vitality of oaks. Aboveground there was a decrease in tree biomass, production and litter fall, but a huge increase in standing dead logs. During the years, the deposition of sulphur had decreased drastically, but nitrogen deposition was still high. Soil acidification in the forest had decreased, reflected in an increased base saturation in the forest, in spite of slightly lowered pH-values. Strongly increased amounts of exchangeable Ca and Mg now appeared in the forest soil, and a substantial transport of calcium and magnesium had obviously taken place from the forest soil to the meadow and fens during the years. However, the most important soil change was the accumulation of organic matter. The increased accumulation of organic matter in turn meant increased amounts of colloid particles and microsites for ion exchange in the soil. This favoured 2-valence base cations, and especially Ca and Mg that increased very much in all the studied ecosystems. Carbon as well as nitrogen had strongly increased in the forest, meadow and fen soils. This was interpreted as a natural result of increased vegetation growth due to high nitrogen deposition, increased global annual temperature and increased carbon dioxide concentration in air. It was concluded that the decreased deposition of sulphur had had a positive effect on soil chemistry, and that the deposition of nitrogen probably had stimulated vegetation growth in general, and contributed to increased amount of organic matter in the soils. However, in this studied oak forest, the decreased vitality and many killed trees were also suspected to be a result of high nitrogen deposition. Obviously increased tree growth was counteracted by decreased stress resistance, and increased appearance of pathogens in the oak trees.