Experimental investigations of the effects of air pollutants on aphids on coniferous trees

Summary The relative growth, rates of two aphid species feeding on Sitka spruce (Picea sitchensis) and one species on Scots pine (Pinus sylvestris) were measured on two year old trees prefumigated with either ozone (O₃ or nitrogen dioxide (NO₂) and compared with the growth rates of aphids grown, on trees which were exposed to filtered air. All three species showed increased growth rates on trees which were prefumigated with 100ppb NO₂ for periods in excess of 24 hours. However the effects of prefumigation with O₃ were more complex. Only on species,Cinara pilicornis, responded to this treatment and there was a strong interaction between the fumigation treatment and the temperature experienced by the plants during fumigation.

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Experimentelle Untersuchungen der Wirkung von Luftschadstoffen auf Bauml?use an Nadelb?umen

Zusammenfassung Relative Wachstumsraten von zwei Arten von Bauml?usen an Sitkafichte (Picea sitchensis) und von einer an der gemeinen Kiefer (Pinus sylvestris) an 2j?hrigen Pflanzen, die vorher entweder Ozon (O₃) oder Stickstoffdioxyd (NO₂) ausgesetzt worden waren, wurden verglichen mit solchen von Bauml?usen, die auf Wirtspflanzen in gefilterter Luft wuchsen. Allen drei Arten zeigten schnelleres Wachstum an Pflanzen, die vorher über 24 Studen lang einer Konzentration von 100 ppb NO₂ ausgesetzt waren. Vielf?ltiger waren jedoch die Auswirkungen von O₃. Nur eine Art,Cinara pilicornis, reagierte auf diese Behandlung, und es gab eine starke Wechselwirkung zwischen der Begasung als solcher und der Temperatur, der die Pflanzen w?hrend dieser Behandlung ausgesetzt waren.

     

O_3浓度升高对桢楠和闽楠幼苗光合作用、抗氧化能力及生物量的影响

[目的]探讨O_3浓度升高对两种亚热带树木幼苗的影响,并分析其敏感性差异及原因。[方法]本试验以1年生桢楠和闽楠幼苗为材料,采用开顶式气室(OTCs),研究未过滤大气、100 nmol·mol-1(E1)、150 nmol·mol-1(E2)O_3处理对光合作用、抗氧化能力和生物量的影响。[结果]研究表明:(1) O_3熏蒸主要通过非气孔限制因素降低了两树种的净光合速率(Pn)。其中对于桢楠,E2对Pn的不利影响大于E1。而对于闽楠,8月份E2的Pn大于E1,而9月份和10月份小于E1。(2) O_3熏蒸提高了两树种的抗氧化能力,表现为总酚含量和总抗氧化能力随着O_3浓度的升高逐渐升高,而E2的还原型抗坏血酸含量低于E1。(3) O_3熏蒸降低了两树种根、茎、叶及总干质量,及降低了闽楠的根茎比。[结论]O_3熏蒸降低了两树种的光合作用,提高了抗氧化能力,最终减少了生物量。根据Pn和生物量,确定闽楠较桢楠对O_3浓度升高更加敏感。两树种间的O_3敏感性差异与气孔导度和抗氧化物质的背景水平及其对O_3浓度升高的响应有关。     

Injury to Eastern White Pine by Sulfurdioxide and Ozone Alone and in Mixtures

Clones of eastera white pine (Pinus strobus) selected for their sensitivity to sulfur dioxide (SO₂) were fumigated in a controlled environment chamber. Sulfur dioxide alone and in combination with ozone (O₃) at concentration 5 parts per hundred million (pphm) of air by volume of each gas for independent 2-hr exposures was toxic to new needles. Severest injury resulted from a discontinuous fumigation with 5 pphm O₃ and 5 pphm SO₂for 2 hr in separate fumigations, followed 24 hr later by a 2-hr exposure to a mixture of these gases, each at 5 pphm. The rapidity of lesion development and total injury to new needles were less following a single 2-hr fumigation with an O₃-SO₂mixture than when a single 2-hr fumigation with SO₂alone was used. Ozone and SO₂reacted to reduce injury. These plants were not injured by O₃used alone. New needles receiving only filtered air or new needles on resistant plants were not visibly affected by any treatment. Acute injury induced by the O₃-SO₂mixture developed differently from injury induced by SO₂alone.     

Growth recovery of mature Norway spruce and European beech from chronic O<Subscript>3</Subscript> stress

Elevated O₃ levels can strongly impair the health and vitality of forest ecosystems. Free-air exposure systems reveal that forest tree and stand growth can be reduced strongly under chronic O₃ stress. Detailed knowledge of the effect of O₃ exposure on photosynthesis, carbon sequestration, allometry and growth during chronic stress is available. However, knowledge of growth response after O₃ reduction is scarce. Here, we analyse the growth of mature Norway spruce (Picea abies (L.) Karst.) and European beech (Fagus sylvatica L.) in the free-air O₃ fumigation experiment at Kranzberg Forest. We compare tree growth over a 9-year period (2008–2016) after exposure to O₃ (2000–2007). During 2?×?O₃ exposure, the annual basal area growth of Norway spruce and European beech decreased by 24 and 32%, respectively. After cessation of 2?×?O₃ exposure, the annual basal area growth of Norway spruce and European beech not only recovered but exceeded the growth of the trees in the control condition by 14 and 24%, respectively. The growth resilience and resistance of trees previously exposed to 2?×?O₃ towards drought stress and late frost was hardly lower than that of the trees in the control condition. The capacity for growth recovery even after long-term chronic O₃ stress emphasizes the strong beneficial effect of air pollution control on the health of forest ecosystems and on the global land carbon sink.     

Effects of crown release on basal area growth rates of some broad-leaved tree species with different shade-tolerance

We compare three or four years effects of crown release on stem growth rates among four deciduous broad-leaved tree species,Fagus crenata, Quercus crispula, Magnolia obovata andAcer mono, in an even-aged coppice forest, central Japan. The crown release significantly improved relative growth rates for basal-area (RGR_BA) of the four species. However the effects of neighboring gap area (GAPA) on the RGR_BA differed among the species. The effects were significant forQ. crispula andM. obovata, indicating that growth rates of these two species increase with intensity of the crown release. In contrast, the RGR_BA ofF. crenata andA. mono were not correlated with the GAPA, suggesting that their growth rates are unrelated to the intensity. We considered that such differences among species were closely related to their photosynthetic characteristics of light use; less-tolerant species (Q. crispula andM. obovata) exhibit greater growth rates relative to the intensity of crown release than tolerant species (F. crenata andA. mono). Based on these results, we proposed implications for thinning practices in mixed forests of species with different shade-tolerance.     

Long lasting effects of O3 and SO2 on the sensitivity to drought in two clones of Picea abies (L.) Karst.

Rooted cuttings of two Picea abies-clones were fumigated with O₃ and O₃+ SO₂ for 12 weeks. After 4 and 16 months without fumigation the treated plants showed much higher sensitivity to drought (expressed in osmotic potential of cell sap and in percent survival) than the untreated ones.     

Risk assessment of ozone impact on the carbon absorption of Japanese representative conifers

A risk assessment of ozone (O₃) impact on the annual carbon absorption (ACA) of Japanese representative conifers was conducted based on the results of an experimental study, monitoring data of oxidant concentrations and vegetation surveys. The areas with high O₃-induced reduction in ACA did not necessarily correspond to the areas with relatively high O₃-exposure. Widespread distribution of O₃-sensitive tree species such as Pinus densiflora and Larix kaempferi, and high ACA were important factors that induced a high risk of O₃ impact on the ACA. Therefore, we concluded that not only the accumulated O₃-exposure but also the variety of tree habitat, the tree sensitivity to O₃ and the ACA among the tree species must be taken into account to assess the risk of O₃ impact on the ACA of Japanese conifers. The O₃-induced reduction in the total ACA of the three tree species in Japan was estimated to be 0.8%.     

Effect of Ca on Al-induced activation of antioxidant enzymes in the needles of hinoki cypress (Chamaecyparis obtusa)

The effect of CA(NO₃)₂ on the active oxygen scavenging system in hinoki cypress (Chamaecyparis obtusa) seedlings cultured in a nutrient solution containing aluminum was examined. The hinoki cypress seedlings were transferred to nutrient solutions containing 5 mM AlCl₃ together with various concentrations of Ca(NO₃)₂ in pots containing glass beads and Teflon tips. The growth in height and dry matter allocation to each organ was little influenced over a period of 12 weeks by either Al or the concentration of Ca(NO₃)₂. The activity of superoxide dismutase (SOD) in the needles was stimulated by Al, and the effect of Al was lowered significantly by simultaneous application of 25 mM Ca(NO₃)₂. At week 1, the activity of catalase (CAT) in the needles was increased by Al, but the effect was no longer observed at week 12. The Al concentration in the roots was increased by treatment with Al, whereas the Al concentration in needles was not. These results indicate that rhizospheric Al stress stimulates antioxidative enzyme activities in hinoki cypress needles and the activation of the enzymes is suppressed by addition of Ca. The transmission of Al stress to the needles, which induced a change in the enzyme activity, is not caused by the transfer of the Al ion itself from roots to needles. This work was supported in part by funding from the Japan Science and Technology Corporation, the CREST program 1996–2001, and the Center for Forest Decline Studies.     

Application of a polymeric coating can protect coniferous trees from acute pollution injury

SO₂ and NO_x are main primary pollutants which often occur together in Europe. In three experiments small spruce trees were exposed to SO₂ or to SO₂ + NO₂ in controlled environmental conditions. A polymeric coating (spodnam), based on a natural terpenoid compound was applied to half the trees fumigated in each experiment and the influence of this material on the sensitivity to pollutant injury was observed. Picea abies and Picea rubens (Norway and Red spruce) were more sensitive than Picea sitchensis (Sitka spruce) to acute damage from 8000 ppb SO₂ experienced for 12-h periods during dormancy. A single application of 15% (ν/ν) of the polymeric coating substantially decreased the extent of acute injury in all three species. Dormant P. sitchensis fumigated with 250 ppb SO₂ and SO₂ + NO₂ also showed less pollutant injury at the end of a 2-month fumigation when 5% (ν/ν) spodman had been applied. Exposure of coated and uncoated seedlings of P. sitchensis to 400 ppb SO₂ during growth in 8-h and 16-h photoperiods confirmed the strong protective effect of a 15% (ν/ν) application. After 6 weeks in 16-h photoperiods, the coated plants grown in SO₂ had larger dry weights than uncoated plants in SO₂. Spodnam also caused decreases of dry weight which were greater in the 8-h daylength, indicating that growth rate was important in determining the physiological cost of having an additional coating over the foliage. Further analysis of the effects of the coating on plant growth and of its protective function against air pollutants are required to determine whether application would be beneficial in forest areas were large concentrations of gaseous air pollutants occur. The timing, concentration and degree of coverage achieved during application would influence the impact of this material; and the benefit gained would depend on the severity of pollutant damage and on the way in which spodnam effects other factors which influence growth.     

Seasonal dynamics of mineral N pools and N-mineralization in soils under homegarden trees in South Andaman,India

Agroforestry trees are now well known to play a central role in the build up of nutrients pools and their transformations similar to that of forest ecosystem, however, information on the potential of homegarden trees accumulating and releasing nitrogen (mineralization) is lacking. The present study reports seasonal variations in pool sizes of mineral N (NH₄⁺-N and NO₃⁻-N), and net N-mineralization rate in relation to rainfall and temperature under coconut (Cocos nucifera L.), clove (Eugenia caryophyllata Thunb) and nutmeg (Myristica fragrans Houtt. Nees) trees in a coconut-spice trees plantation for two annual cycles in the equatorial humid climate of South Andaman Island of India. Concentration of NH₄⁺-N was the highest during wet season (May–October) and the lowest during post-wet season (November–January) under all the tree species. On the contrary, concentration of NO₃⁻-N was the lowest in the wet season and the highest during the post-wet season. However, concentrations of the mineral N were the highest under the nutmeg and the lowest under the coconut trees. Like the pool sizes, mean annual mineralization was the highest under the nutmeg (561 mg kg⁻¹ yr⁻¹) and the lowest under the coconut trees (393 mg kg⁻¹ yr⁻¹). Rate of mineralization was the highest during the post-wet season and the lowest during the dry season (February–April) under all the tree species. High rainfall during the wet season, however, reduced the rate of nitrification under all the tree species. The mean annual mineralization was logarithmically related with rainfall amount and mean monthly temperature.     

Photosynthese,Transpiration und Spaltöffnungsverhalten verschiedener Holzarten nach Begasung mit SO2

Photosynthesis, transpiration and stomatal response of various species of woody plants exposed to sulfur dioxide. Photosynthesis of Fraxinus excelsior, Piceaabies, Abies alba and Pinus sylvestris declined after 6 and 12 h of fumigation at SO₂ concentrations of 5 and 9mg m^?3. Transpiration also declined, but the maximum depression was only 38%. Stomata began to close after fumigation with ～ 1 mg SO₂m^?3 for 6 h. The diffusion resistance of needles of Pices and Abies increased after fumigation with 9 mg SO₂ for 6h to a peak value of 35–40 scm^?1 and decreased rapidly (Picea) or remained stable (Abies) during the following 30h.     

Effects of acidic fog and ozone on the growth and physiological functions of Fagus crenata saplings

The effects of simulated acid fog (SAF) and ozone (O₃) stress on the growth and physiology of beech (Fagus crenata) saplings were investigated. Three-year-old beech saplings were exposed to SAFs of pH 3 and pH 5 (control) during May 2007 to July 2008. In each SAF treatment group, half of the saplings were exposed to 60 ppb of O₃ during September 2007 to July 2008. In comparison to the control saplings, those from the pH 3 treatment had lower total plant biomasses, epicuticular wax amounts, Ca²⁺ concentrations in their leaves, and lower starch concentrations in their leaves and roots. The effect of O₃ was significant only for the starch concentration in the roots, but the O₃ exposure also negatively affected the growth and physiology of beech saplings. Results show that acid fog exerts various severe effects, and that both chronic acid fog and O₃ exposure suppressed the physiological functions of beech saplings.     

Growth and photosynthetic responses of Gallesia integrifolia (Spreng.) Harms and Schinus terebinthifolius Raddi seedlings in dense shade

We analyzed the growth and photosynthetic behavior of Gallesia integrifolia (‘pau-d’alho’) and Schinus terebinthifolius (‘aroeirinha’) under shade, seeking to obtain ecophysiological information for introducing seedlings of those species in previously established cacao agroforestry systems. Considering that light intensity under the shade of cacao trees varied between 5 and 10% daylight, 5 months old seedlings were exposed to four irradiance levels (25, 17, 10 and 5% daylight) for 92 days. With shade increase both species displayed trends of decrease leaf mass per unit leaf area, leaf area per plant (LA), relative growth rate (RGR) and net assimilation rate (NAR), and increase leaf area ratio (LAR). The mean values of light-saturated net photosynthetic rate (P _nmax) in 25 and 5% daylight were 12.8 and 8.0 μmol CO₂ m⁻² s⁻¹ for G. integrifolia and 17.9 and 7.4 μmol CO₂ m⁻² s⁻¹, respectively, for S. terebinthifolius. Based on the measurements of photosynthetic photon flux density and estimated values of photosynthetic saturated irradiance (Is) we concluded that, in all shaded conditions, the leaves of both species were under sub optimal light conditions to reach P _nmax. In spite of the lowest P _nmax values, RGR and NAR were significantly higher for G. integrifolia in all irradiance levels. Differences in growth rates can be explained by the higher values of LA, LAR and leaf mass ratio (LMR), as well as by the lower values of Is, photosynthetic compensation irradiance and dark respiration rates observed for G. integrifolia. Even though seedlings of G. integrifolia presented higher capacity to adapt under conditions of dense shade, we concluded that both species were under stress conditions induced by shade in light environments below 25% daylight. On a practical point of view it is possible to conclude that seedlings of both species should be introduced in light gaps, formed after the fall of big trees, or in places in which cacao trees are cultivated using large plant spacing.     

Nitrogen form and concentration interact to affect the performance of two ecologically distinct Mediterranean forest trees

Most studies examining inorganic N form effects on growth and nutrition of forest trees have been conducted on single species from boreal or temperate environments, while comparative studies with species from other biomes are scarce. We evaluated the response of two Mediterranean trees of contrasting ecology, Quercus ilex L. and Pinus halepensis Mill., to cultivation with distinct inorganic N forms. Seedlings were fertilized with different NH₄ ⁺/NO₃ ^? proportion at either 1 or 10 mM N. In both species, N forms had small effects at low N concentration, but at high N concentration they markedly affected the plant performance. A greater proportion of NH₄ ⁺ in the fertilizer at high N caused toxicity as it reduced growth and caused seedling death, with the effect being greater in Q. ilex than in P. halepensis. An increase in the proportion of NO₃ ^? at high N strongly enhanced growth relative to low N plants in P. halepensis but had minor effects in Q. ilex. Relatively more NH₄ ⁺ in the fertilizer enhanced plant P concentration but reduced K concentration in both species, while the opposite effect occurred with NO₃ ^?, and these effects were enhanced under high N concentration. We conclude that species responses to inorganic N forms were related to their ecology. P. halepensis, a pioneer tree, had improved performance with NO₃ ^? at high N concentration and showed strong plasticity to changes in N supply. Q. ilex, a late successional tree, had low responsiveness to N form or concentration.     

Effect of pruning on branch production and water relations in widely spaced ponderosa pines

This study dealt with the effects of pruning on branch and leaf area (F _a) production of ponderosa pines growing in silvopastoral systems in Patagonia. We hypothesized that pruning positively influences the number of branches per whorl and their basal area growth rate, changing F _a production. In addition, we studied some water relations in order to explain potential differences in branch growth rates between treatments. Two mathematical models were developed to estimate branch and total F _a. The averaged diameter at the third year of pruning was, for high-pruned trees 3.1 and 3.6 cm at the bottom and middle of the crown, against 4 and 4.4 cm for low-pruned trees. Pruning did not produce changes in the number of branches per whorl (approximately 7.6 branches per whorl). Water stress may be responsible of this lower branch growth in pruned trees. Water potential, stomatal conductance and transpiration were lower in high- than in low-pruned trees.     

Risk assessment of ozone impact on <Emphasis Type="Italic">Fagus crenata</Emphasis> in Japan: consideration of atmospheric nitrogen deposition

Tropospheric ozone (O₃) is considered to be the air pollutant relating to the decline of Fagus crenata forest in Japan. In the present study, we assessed a risk of O₃ impact on the growth of F. crenata in Japan, giving consideration to the effects associated with atmospheric nitrogen (N) deposition based on the experimental study, national monitoring data for oxidant concentration and atmospheric N deposition, and a national vegetation survey. The average and maximum O₃-induced relative growth reduction (RG_red) of F. crenata across Japan were estimated to be 3.2 and 9.7%, respectively. Current levels of atmospheric N deposition were found to significantly affect the sensitivity of F. crenata to O₃. When the N deposition was assumed as zero, the estimated average and maximum RG_red were 2.3% and 5.7%, respectively. The inclusion of atmospheric N deposition data thus increased the estimated values for average and maximum RG_red (by 38% and 71%, respectively). Our results demonstrate that a change in the sensitivity to O₃ associated with atmospheric N deposition is an important consideration in the risk assessment of O₃ impact on the growth of F. crenata in Japan.     

Adaptation to exploit nitrate in surface soils predisposes yellow-cedar to climate-induced decline while enhancing the survival of western redcedar: A new hypothesis

Yellow-cedar (Chamaecyparis nootkatensis (D. Don) Spach) and western redcedar (Thuja plicata Donn), two valuable tree species of Pacific Northwest forests, are competitive in low productivity forests on wet, nearly saturated soils with low nitrogen (N) availability and turnover. We propose a mechanism where cedar trees survive in marginal conditions through exploiting a coupled Ca–NO₃⁻ nutrient cycle where trees assimilate N as nitrate (NO₃⁻), but must accumulate a counter-ion to NO₃⁻ such as calcium (Ca⁺²) to control their internal cell pH and provide electrochemical balance. The availability of NO₃⁻ in cedar forests is favored by increased microbial activity and shifts in microbial community composition that is conducive to N mineralization and nitrification at higher pH. Cedars influence the soils under their canopy by enriching the forest floor with calcium compounds leading to increases in pH. Cedars are also prone to precocious dehardening in the spring when N is released from freeze–thaw events in the soils and conditions appear to favor nitrifying microbial communities. Cedars must concentrate fine-root biomass near the soil surface to access Ca and NO₃⁻, but this beneficial physiological adaptation also creates a vulnerability to periodic root freezing injury that is leading to the decline and mortality of at least one of them—yellow-cedar.     

Interactive Influences of Fertility and Nodulation on Growth,Nutrition, and Water Relations of European Alder in a Mine Soil

Abstract

Actinorhizal nodulation of European alder (Alnus glutinosa[L.] Gaertn.) as influenced by substrate fertility was assessed for its effects on seedling growth and physiology. After a brief period in seed flats, seedlings were transplanted to a mine soil where they resided for 18 months, and three fertility regimes were imposed by application of differing nutrient solution concentrations while two distinct levels of nodulation were created through methyl bromide fumigation. Ultimately, seedlings in nonfumigated soil had > 5Xthe nodules of those grown in fumigated soil, and rising fertility stimulated nodule formation in the former. Heavy nodulation resulted in a 35% increase in shoot mass and a 60% increase in root mass on average, responses that exceeded those to fertilization for the latter. Seedlings with abundant nodules had higher foliar concentrations of total N, NO₃, K, and Cu and lower concentrations of Ca, Mg, S, Fe, Mn, Zn, Mo, and Al overall, than were found in those with minimal nodulation. In turn, soil in which heavily nodulated seedlings were grown had higher total N, NO₃, Ca, Mg, S, Fe, Mn, Zn, and Al concentrations but a lower Mo concentration than fumigated soil. Fertility regime effects on nutrition were readily apparent, although considerably more so in the mine soil than in foliage. During a simulated drought episode, predawn and midday xylem pressure potentials within the high fertility treatment were lower in heavily nodulated seedlings than in those with few nodules, and the water potentials in soil in which the heavily nodulated seedlings resided were lower overall as well. Collectively, these results provide insight into approaches to most effectively exploit the benefits European alder offers as a reforestation species for difficult sites.     

Ozone,Acid Deposition,and Mycorrhization Effects on Loblolly Pine and White Oak

Abstract

Above- and below-ground responses of juvenile loblolly pine (Pinus taedaL.) and white oak (Quercus albaL.) to tropospheric ozone (0.0, 0.06, and 0.12 μL L^-1 O₃), acid precipitation (pH 4.8, 4.2, and 3.6), and induced ectomycorrhizal colonization (Pisolithus tinctorius [Pers.] Coker & Couch vs. natural mycobiont), alone and in combination, were examined. After 30 weeks, the filtered air treatment (ozone 0.0) reduced foliar injury but also produced smaller stem diameters, lower total foliage and total shoot dry weights, decreased needle density, and shorter root systems in inoculated pine, growth responses not found in uninoculated pine. Height growth of inoculated oak was increased by the filtered air treatment while leaf density was reduced by 0.12 μL L^-1 O₃, results also not found in uninoculated oak. Ectomy-corrhizal colonization percentages in pine decreased with increasing O₃ concentration regardless of mycorrhizal treatment, and the filtered air treatment produced the highest infection percentages in inoculated oak as well. Rains of pH 4.2 stimulated height growth in inoculated pine while diameter decreased in inoculated oak but increased in uninoculat-ed oak with declining pH. Also, pH 4.2 rainfall increased root weight in inoculated oak while that of pH 4.8 reduced foliar injury but also shoot weight in oak regardless of mycorrhizal treatment. Generally, the my-corrhization response to increasing rainfall acidity was reduced colonization. Independent of the other treatments, inoculation produced a substantial increase in above- and below-ground growth of both pine and oak, and also increased foliage density but reduced specific root length in each species. Overall, these results indicate that the growth responses to O₃ and acid deposition of loblolly pine and white oak are strongly influenced by mycorrhization, but that the magnitude of these responses is exceeded by those to mycorrhization alone. However, the propensity revealed here for both O₃ and acid precipitation to suppress mycorrhizal colonization in these two species may indicate the potential for a gradual reduction in long-term forest productivity in the southeastern United States.     

Seedling growth response of two tropical tree species to nitrogen deposition in southern China

Seedling growth response of two tropical tree species (Schima superba and Cryptocarya concinna) to simulated N deposition was studied during a period of 11 months. One-year-old seedlings were grown in forest soil treated with N as NH₄NO₃ at Control–no N addition, N5–5, N10–10, N15–15, and N30–30 g N m⁻² year⁻¹. The objective was to examine the effects of N addition on seedling growth and compare this effect between the two tropical tree species of different species-N-requirement. Results showed that both species responded significantly to N addition and exhibited positive effect to lower rate of N addition and negative effect to higher rate of N addition on growth parameters (height and stem base diameter, biomass production, and net photosynthetic rate). The highest values were observed in the N10 plots for S. superba and in the N15 plots for C. concinna, but the lowest values were observed in the N30 plots for both species. However, the reduction in the N30 plots was more pronounced for S. superba than for C. concinna relative to the control plots. Our findings suggest that response of seedling growth of tropical tree species to atmospheric N deposition may vary depending on rate of N deposition and species-N-requirement.