Species mixing effect on Norway spruce response to elevated CO2 and climatic variables: root and radial growth response

A 7-year study was conducted to examine the growth (diameter and root) response of Norway spruce (Picea abies (L.) Karst.) seedlings to elevated CO₂ (CO_2ELV, 770 μmol (CO₂) mol^?1) in different mixture types (monospecific (M): a Norway spruce seedling surrounded by six spruce seedlings, group-admixture (G): a spruce seedling surrounded by three spruce and three European beech seedlings, single-admixture (S): a spruce seedling surrounded by six beech seedlings). After seven years of treatments, no significant effect from elevated CO₂ was found on the root dry mass (p?=?0.90) and radial growth (p?=?0.98) of Norway spruce. Neither did we find a significant interaction between [CO₂]?×?mixing treatments (p?=?0.56), i.e. there was not a significant effect of CO₂ concentrations [CO₂] in all the admixture types. On the contrary, spruce responses to admixture treatments were significant under CO_2AMB (p?=?0.05), which demonstrated that spruce mainly increased its growth (diameter and root) in M and neighbouring with beech was not favourable for spruce seedlings. In particular, spruce growth diminished when growing beside high proportions/numbers of European beech (S). Here, we also evaluated the association between tree-ring formation and climatic variables (precipitation and air temperature) in different admixture types under elevated and ambient CO₂ (CO_2AMB, 385 μmol (CO₂) mol^?1). Overall, our result suggests that spruce responses to climate factors can be affected by tree species mixing and CO₂ concentrations, i.e. the interaction between climatic variables?×?admixture types?×?[CO₂] could alter the response of spruce to climatic variables.

     

Soil properties and microbial functional structure in the rhizosphere of Pinus densiflora (S. and Z.) exposed to elevated atmospheric temperature and carbon dioxide

Rhizosphere-induced changes of Pinus densiflora (S. and Z.) grown at elevated atmospheric temperature and carbon dioxide are presented based on experiments carried out in a two-compartment rhizobag system filled with forest soil in an environmentally controlled walk-in chamber with four treatment combinations: control (25°C, 500 μmol mol^?1 CO₂), T2 (30°C, 500 μmol mol^?1 CO₂), T3 (25°C, 800 μmol mol^?1 CO₂), and T4 (30°C, 800 μmol mol^?1 CO₂). Elevated temperature and atmospheric carbon dioxide resulted in higher concentration of sugars and dissolved organic carbon in soil solution, especially at the later period of plant growth. Soil solution pH from the rhizosphere became less acidic than the bulk soil regardless of treatment, while the electrical conductivity of soil solution from the rhizosphere was increased by elevated carbon dioxide treatment. Biolog EcoPlate? data showed that the rhizosphere had higher average well color development, Shannon–Weaver index, and richness of carbon utilization compared with bulk soil, indicating that microbial activity in the rhizosphere was higher and more diverse than in bulk soil. Subsequent principal component analysis indicated separation of soil microbial community functional structures in the rhizosphere by treatment. The principal components extracted were correlated to plant-induced changes of substrate quality and quantity in the rhizosphere as plants’ response to varying temperature and atmospheric carbon dioxide.     

Pathogenic variability of various isolates of Seiridium cardinale,S. cupressi and S. unicorne inoculated on selected Cupressus clones and seedlings

Comparative studies of the pathogenicity of eight isolates of three Seiridium species were carried out by stem inoculations on Cupressus sempervirens and C. glabra seedlings and clones. Seiridium cardinale and S. cupressi caused bigger and more severe cankers than all strains of S. unicorne. During the first nine months after inoculation, the canker length of S. cardinale was larger than the cankers of S. cupressi. However, during the second year after inoculation, S. cupressi cankers were larger and more severe than those of 5. cardinale.     

Increased atmospheric carbon dioxide concentration: effects on eucalypt rust (Puccinia psidii), C:N ratio and essential oils in eucalypt clonal plantlets

Evaluation of impacts of high CO₂ atmospheric concentration is strategically important for the development of adaptation measures and sustainable crop management. The objective of this study was to evaluate the effects of increased atmospheric CO₂ concentration on eucalypt rust (Puccinia psidii), C:N ratio, yield and chemical composition of essential oils and growth of eucalypt clonal plantlets. Two clones with different levels of rust resistance were studied: a Eucalyptus urophylla × E. camaldulensis hybrid (VM 01) and an E. urophylla (clone MN 463). The experiments were performed in open‐top chambers (OTCs) with CO₂ mean concentrations (μmol mol^?1) of 399 (unenclosed control), 412 (OTCs with ambient CO₂ concentration) and 508 (OTCs with high CO₂ concentration) and in closed chambers (CCs) with CO₂ mean concentrations of 390, 405, 520 and 700. Increased atmospheric CO₂ concentrations resulted in a decrease in rust pustules per leaf, uredinia per leaf area, spores per uredinia and area under the disease progress curve in VM 01 (hybrid) clonal plantlets. The disease did not occur in MN 463 clonal plantlets, which demonstrated that high CO₂ concentrations did not change the level of rust resistance. Plant growth of the two clones was stimulated by up to 23% in height and 26% in stem diameter in OTCs and by 18% for both clones in CCs. An increased C:N ratio in leaves, stems and roots was observed only for the VM 01 clonal plantlets. Essential oils produced by VM 01 (2.8 g 100 g^?1) and MN 463 (1.4 g 100 g^?1), as well as the major essential oil compounds (80% 1.8‐cineole for VM 01; 50% 1.8‐cineole and 32% α‐pinene for MN 463), were not altered. In this study, increased concentrations of atmospheric CO₂ favourably impacted eucalypt growth and reduced rust severity, while not influencing the production of essential oils.     

Growth responses of seedlings of six Betula pubescens Ehrh. Provenances to six ozone exposure regimes

Seedlings of six provenances of Betula pubescens Ehrh. from different latitudes (59–70°N) were grown under six ozone exposure regimes by combining different concentrations and daily exposure periods. The different treatments at increasing O₃ exposure over 40 nmol mol^?1 (AOT40 given in parentheses) were: 19 nmol mol^?1/24 h day^?1 (0.1 μmol mol^?1‐h), 42 nmol mol^?1/12 h day^?1 (2.5 μmol mol^?1‐h), 44 nmol mol^?1/24 h day^?1 (7.1 μmol mol^?1‐h), 76 nmol mol^?1/6 h day^?1 (9.4 μmol mol^?1‐h), 75 nmol mol^?1/12 h day^?1 (17.8 μmol mol^?1) and 116 nmol mol^?1/6 h day^?1 (19.8 μmol mol^?1) for 40 days at a 24 h day^?1 photoperiod in growth chambers placed in a greenhouse. The effect of increasing the O₃ exposure from 19 nmol mol^?1/24 h (0.1 μmol mol^?1‐h AOT40) to 42 nmol mol^?1/12 h (2.5 μmol mol^?1‐h AOT40) was a decrease in root but not shoot dry weight. A further increase in the exposure to 44 nmol mol^?1/24 h (7.1 μmol mol^?1‐h AOT40) also decreased the shoot dry weight. An increase in the O₃ concentration to 75 (9.4–17.8 μmol mol^?1‐h AOT40) and 116 nmol mol^?1 (19.8 μmol mol^?1‐h AOT40) further decreased shoot and root dry weights. A moderate O₃ exposure (42 nmol mol^?1/12 h = 2.5 μmol mol^?1‐h AOT40) increased the plant height and leaf size, while a further increase in O₃ concentration and exposure time decreased both of these variables. The birch provenances generally had a similar response to the O₃ treatments. The accumulated O₃ exposure over the 0, 10, 20, 30, 40 and 50 nmol mol^?1 concentrations (AOT0, AOT10, AOT20, AOT30, AOT40 and AOT50, respectively) was calculated for all O₃ treatments. The shoot and root dry weights were correlated best with AOT40 and AOT30, and were estimated to decrease by 10% at an AOT40 of 7.0 and 5.5 μmol mol^?1‐h, respectively. The development of O₃ injury (yellow stipples/chlorosis) was most marked when correlated with AOT40.     

Stomatal response ofPinus sylvestriformis to elevated CO2 concentrations during the four years of exposure

Four-year-oldPinus sylvestriformis were exposed for four growing seasons in open top chambers to ambient CO₂ concentration (approx. 350 μmol·mol⁻¹) and high CO₂ concentrations (500 and 700 μmol·mol⁻¹) at Research Station of Changbai Mountain Forest Ecosystems, Chinese Academy of Sciences at Antu Town, Jilin Province, China (42°N, 128°E). Stomatal response to elevated CO₂ concentrations was examined by stomatal conductance (g _s), ratio of intercellular to ambient CO₂ concentration (c _i/c _a) and stomatal number. Reciprocal transfer experiments of stomatal conductance showed that stomatal conductance in high-[CO₂]-grown plants increased in comparison with ambient-[CO₂]-grown plants when measured at their respective growth CO₂ concentration and at the same measurement CO₂ concentration (except a reduction in 700 μmol·mol⁻¹ CO₂. grown plants compared with plants on unchambered field when measured at growth CO₂ concentration and 350 μmol·mol⁻¹CO₂). High-[CO₂]-grown plants exhibited lowerc _i/c _a ratios than ambient-[CO₂]-grown plants when measured at their respective growth CO₂ concentration. However,c _i/c _a ratios increased for plants grown in high CO₂ concentrations compared with control plants when measured at the same CO₂ concentration. There was no significant difference in stomatal number per unit long needle between elevated and ambient CO₂. However, elevated CO₂ concentrations reduced the total stomatal number of whole needle by the decline of stomatal line and changed the allocation pattern of stomata between upper and lower surface of needle. Foundation Item: This research was supported by National Basic Research Program of China (2002CB412502), Project of Key program of the National Natural Science Foundation of China (90411020) and National Natural Science Foundation of China (30400051). Biography: ZHOU Yu-mei (1973-), female, Ph. Doctor, assistant research fellow, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110016, P. R. China. Responsible editor: Song Funan     

The ecology of fungal cankers on Cupressus macrocarpa in southern England

Bark isolations from cankers on Cupressus macrocarpa in southern England yielded Seiridium cardinale, Pestalotiopsis funerea and Pestalotiopsis monochaetioides. The recovery pattern of the three fungi indicated that only S. cardinale was a primary pathogen; the two Pestalotiopsis species being secondary. Pathogenicity data obtained following the inoculation of C. macrocarpa branches with mycelium of the three fungi confirmed this view. No evidence of vegetative incompatibility was found in S. cardinale, but five vegetative-compatibility (vc) groups were found in P. funerea and six in P. monochaetioides. Different vc groups of the two Pestalatiopsis species were often found in the same S. cardinale lesion, suggesting that a number of separate colonization events were involved. It is possible that this sometimes leads to complete replacement of the pathogen.     

Effect of ambient SO2 levels on S fractions in Pinus sylvestris foliage growing in the subarctic

The total S and SO₄‐S concentrations of Scots pine (Pinus sylvestris L.) needles growing at a distance of 10–80 km from the metallurgical complex in Monchegorsk in subarctic Russia were measured, and organic S was calculated as the difference between them, in order to study the impact of SO₂ (3–28 μg m^?3 a^?1) on foliar S fractions. Total S concentrations of currentand previous‐year needles collected in April 1991 and July 1992 amounted to 658–2548 ppm, SO₄‐S concentrations to 99–1297 ppm and organic S concentrations to 447–1599 ppm. The SO₄‐S concentrations and the S/N ratios (0.032–0.113 on a gram atom basis) show that S in excess of the growth requirements of trees was entering the needles at all the five sites studied. Foliar K and Ca, but not Mg, increased with increasing SQ₄‐S. It is hypothesized that exposure to SO₂ concentrations of ≥2 μg m^?3 as a growing season mean together with pollution episodes of ～ 100 μg m^?3 h^?1 result in an oxidative stress high enough to damage Scots pine needles, which derive SO₂ effectively from the atmosphere, and that cellular acidification is a secondary effect.     

Effects of elevated CO2 concentration on the respiratory behavior of the branches of field-grown hinoki cypress (Chamaecyparis obtusa)

The effects of elevated atmospheric CO₂ concentrations on the nighttime respiration were examined for two sample branches of a hinoki cypress tree (Chamaecyparis obtusa) growing in the field with an open gas exchange system for a one-year period from July 1994 to June 1995. The branches were of a similar size and located at a similar position within the crown. One branch was subjected to an elevated CO₂ concentration of 800 μmol mol⁻¹ and the other was subjected to ambient air which had a CO₂ concentration of about 370 μmol mol⁻¹. Nighttime respiration rate was higher in elevated CO₂ level than in ambient CO₂ level. The relationship between nighttime respiration and the corresponding nighttime air temperature was fitted by the exponential function in every month of the year. The segregation of regression lines between the two CO₂ treatments increased gradually as the seasons progressed during the treatment period. TheQ ₁₀ values for nighttime respiration were lower in elevated CO₂ (1.9 ≤Q ₁₀ ≤ 3.7) than in ambient CO₂ (2.4 ≤Q ₁₀ ≤ 4.5) in every month of the year. TheQ ₁₀ was inversely related to the monthly mean nighttime air temperature in both elevated and ambient CO₂. The estimated daily nighttime respiration rate under both CO₂ treatments had a similar seasonal pattern, which almost synchronized with the temperature change. The respiration ratio of elevated CO₂ to ambient CO₂ increased gradually from 1.1 to 1.6 until the end of the experiment. Our results indicate that the CO₂ level and the temperature have a strong interactive effect on respiration and suggest that a potential increase in respiration of branches will occur when ambient CO₂ increases.     

Response of seedlings of different tree species to elevated C02 in Changbai Mountain

Eco-physiological responses of seedlings of eight species,Pinus koraiensis, Picea koraiensis, Larix olgensis, Populus ussuriensis, Betula platyphylla, Tilia amurensis, Traxinus mandshurica andAcer mono from broadleaved/Korean pine forest, to elevated CO₂ were studied by using open-top chambers under natural sunlight in Changbai Mountain, China in two growing seasons (1998–1999). Two concentrations of CO₂ were designed: elevated CO₂ (700 μmol·mol⁻¹) and ambient CO₂ (400 μmol·mol⁻¹). The study results showed that the height growth of the tree seedlings grown at elevated CO₂ increased by about 10%–40% compared to those grown at ambient CO₂. And the water using efficiency of seedlings also followed the same tendency. However, the responses of seedlings in transpiration and chlorophyll content to elevated CO₂ varied with tree species. The broad-leaf tree species were more sensitive to the elevated CO₂ than conifer tree species. All seedlings showed a photosynthetic acclimation to long-term elevated CO₂. Foundation item: The project was supported by National Key Basic Development of China (G1999043400) and the grant KZCX 406-4, KZCX1 SW-01 of the Chinese Academy of Sciences Biography: WANG Miao (1964-), maie, associate professor in Institute of applied Ecology, Chinese Academy of Sciences, Shenyang 110016, P. R. China. Responsible editor: Song Funan     

长白山阔叶红松林CO2廓线和CO2贮存的动态

从1999年8至10月,2000年的4至6月,2002年8月至2003年9月,在平均树高为26米的长白山阔叶红松林内,用红外气体分析仪(2250D,LI-CORInc.和LI-COR,820)测定了不同高度的二氧化碳浓度。根据测定的数据,分析了阔叶红松林二氧化碳廓线的日变化和季节变化动态。结果表明:CO2浓度的垂直分布在白天和夜间是不同的,在接近地面处CO2浓度始终最大。从季节CO2廓线看出,在植物生长季节林冠处CO2浓度有明显的成层现象,不同高度(60~2.5m)的CO2浓度3月份变化较小差值为10mmol穖ol-1,而在7月份变化较大,差值为60mmol穖ol-1。7月份林冠处(22,26,32m)CO2浓度梯度较大,浓度差为8mmol穖ol-1。计算位于涡度相关仪器之下的40米高空气柱中CO2贮存状况表明,年际贮存是负值,但对NEE的贡献很小。图4参11。     

Effects of [CO2] and nitrogen on morphological and biomass traits of white birch (Betula papyrifera) seedlings

To investigate the interactive effects of CO₂ concentration ([CO₂]) and nitrogen supply on the growth and biomass of boreal trees, white birch seedlings (Betula papyrifera) were grown under ambient (360 μmol mol⁻¹) and elevated [CO₂] (720 μmol mol⁻¹) with five nitrogen supply regimes (10, 80, 150, 220, and 290 μmol mol⁻¹) in greenhouses. After 90 days of treatment, seedling height, root-collar diameter, biomass of different organs, leaf N concentration, and specific leaf area (SLA) were measured. Significant interactive effects of [CO₂] and N supply were found on height, root-collar diameter, leaf biomass, stem biomass and total biomass, stem mass ratio (SMR), and root mass ratio (RMR), but not on root mass, leaf mass ratio (LMR), leaf to root ratio (LRR), or leaf N concentration. The CO₂ elevation generally increased all the growth and biomass parameters and the increases were generally greater at higher levels of N supply or higher leaf N concentration. However, the CO₂ elevation significantly reduced SLA (13.4%) and mass-based leaf N concentration but did not affect area-based leaf N concentration. Increases in N supply generally increased the growth and biomass parameters, but the relationships were generally curvilinear. Based on a second order polynomial model, the optimal leaf N concentration was 1.33 g m⁻² for height growth under ambient [CO₂] and 1.52 g m⁻² under doubled [CO₂]; 1.48 g m⁻² for diameter under ambient [CO₂] and 1.64 g m⁻² under doubled [CO₂]; 1.29 g m⁻² for stem biomass under ambient [CO₂] and 1.43 g m⁻² under doubled [CO₂]. The general trend is that the optimal leaf N was higher at doubled than ambient [CO₂]. However, [CO₂] did not affect the optimal leaf N for leaf and total biomass. The CO₂ elevation significantly increased RMR and SMR but decreased LMR and LRR. LMR increased and RMR decreased with the increasing N supply. SMR increased with increase N supply up to 80 μmol mol⁻¹ and then leveled off (under elevated [CO₂]) or stated to decline (under ambient [CO₂]) with further increases in N supply. The results suggest that the CO₂ elevation increased biomass accumulation, particularly stem biomass and at higher N supply. The results also suggest that while modest N fertilization will increase seedling growth and biomass accumulation, excessive application of N may not stimulate further growth or even result in growth decline.     

在长白山生态系统中长期的高浓度CO2熏蒸对土壤酶的影响

从1999年到2006年在中科院长白山森林生态系统定位站（42°24＇N,128°28＇E,海拔738m）对长期高浓度CO2熏蒸对土壤酶活性的影响进行了研究.采用开顶箱（OTC）的方式对红松和长白松进行高浓度CO2处理, CO2浓度分别受控于高浓度CO2箱（500 μmol·mol^-1）、对照箱（370 μmol·mol^-1））和裸地（370 μmol·mol^-1）.经高浓度CO2（500 μmol·mol^-1）熏蒸8年后,土壤样品分别在2006年春季、夏季和秋季进行采集和分析.结果表明：在高CO2浓度（500 μmol mol^-1）条件下,转化酶活性除了红松夏季样品之外都是显著降低的;而脱氢酶活性却是增加的,但只有部分结果显著;长白松的多酚氧化酶活性都显著降低;过氧化氢酶活性在春季增加,而在其他季节均降低.总而言之,在高CO2浓度条件下,土壤酶的活性与树种有关.     

长白赤松和红松土壤微生物活性对高浓度CO2的响应

Responses of soil microbial activities to elevated CO₂ in experiment sites ofPinus sylvestriformis andPinus koraiensis seedlings were studied in summer in 2003. The results indicated the number of bacteria decreased significantly (p<0.05) under elevated CO₂ forPinus sylvestriformis andPinus koraiensis. Amylase and invertase activities in soil increased forPinus sylvestriformis and decreased forPinus koraiensis with CO₂ enrichment compared with those at ambient (350 μmol·mol⁻¹). The size of microbial biomass C also decreased significantly at 700 μmol·mol⁻¹ CO₂. Bacterial community structure had some evident changes under elevated CO₂ by DGGE (Denaturing Gradient Gel Electrophoresis) analysis of bacterial 16S rDNA gene fragments amplified by PCR from DNA extracted directly from soil. The results suggested that responses of soil microorganisms to elevated CO₂ would be related to plant species exposed to elevated CO₂. Foundation item: The study was supported by Major State Basic Research Development Program of China (2002CB412502) and the Knowledge Innovation Project from Chinese Academy of Sciences (KZCX1-SW-01-03). Biography: JIA Xia (1975), female, Ph. D. candidate of Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110016, P. R. China. Responsible editor: Song Funan     

Histopathologie du chancre cortical du cypres à Seiridium cardinale

Histopathology of cankers on Cupressus caused by Seiridium cardinale . The purpose of this work was to understand host defense reactions of cypress trees against S. cardinale canker to improve selection of clones resistant to the disease. Following infection, bark recovery depends on the neophellogenic efficiency to build a necrophylactic periderm (NP) that compartmentalizes the diseased tissue. The thicker the NP the more resistant the bark. Neophellogenic activity can be estimated by measuring the thickness of constitutive phelloderm of the bark of trees from natural plantings or seedlings. Potentially resistant clones having phelloderms thicker than 100μm will be selected for further experiments.     

Effects of CO2 enrichment at varying photon flux density on the growth of picea abies (L) karst. seedlings

Seedlings of Norway spruce (Picea abies (L.)) were grown at 335 and 1000 μl CO₂ 1^?1 for 118 days in growth rooms at different irradiance levels. Photon flux density ranging from 8.6 to 34.6 mol m^?2 day^?t (PAR) was given either as constant light or as alternating levels in intervals of two or six hours. CO₂ enrichment increased the plant dry weight from 36% to 105% by increasing photon flux density from 8.6 to 25.9 mol m^?2 day^?1. At constant light the dry weight apparently reached its maximum at a photon flux density of 25.9 mol m^?2 day^?t. At the lower radiation levels alternating in CO₂ enriched air gave slightly higher dry weights compared to constant light levels. At the highest radiations the effect on dry weight was the opposite. High CO₂ concentration and 300 μmol m^?2 s^?1 constant light (25.9 mol m^?2 day^?1) gave the best growth and quality of plants. Top, root, stem and foliage weight were proportionally affected. Shoot length was enhanced by CO₂ enrichment. Shoot weight per cm was substantially increased both by CO₂ enrichment and increasing photon flux density.     

A medium to enhance identification of Septoria musiva from poplar cankers

A series of experiments was conducted to determine the relative tolerance in vitro of an isolate of Septoria musiva (a fungus that causes a severely damaging stem canker disease of poplars) for selected chemicals. Inhibition of diameter growth of this fungus on a V‐8 vegetable juice‐based medium with captan, chlorothalonil, iprodione, mancozeb and streptomycin sulphate at concentrations, respectively, of 50, 1, 10, 10, and 100 mg l^–1 was relatively low compared to inhibition of eight other fungi cultured from cankers on poplars. In addition, the presence of captan stimulated profuse sporulation of the fungus. These properties assisted in the identification of S. musiva from cankers resulting from artificial inoculation of poplar branches in the field.     

Seasonal dynamics and impact factors of urban forest CO<Subscript>2</Subscript> concentration in Harbin,China

CO₂ concentrations in different plant communities (larch, birch, lilac, and grassland) were measured during the growing season in the Heilongjiang Forest Botanical Garden to study diurnal variation, seasonal and annual dynamics and factors that impact CO₂ concentration in different spaces. CO₂ concentration in different communities in green lands had an obvious diurnal variation, chronically decreasing, and temperature influenced the lilac area and the grassland. Seasonally, CO₂ was lowest in the larch green land (344.03 ± 23.03 μmol/mol) and highest in the grassland (360.13 ± 22.43 μmol/mol). The overall trend in CO₂ concentration was autumn > spring > summer; temperature is the main factor controlling variation in CO₂ concentrations during the growing season; the CO₂ concentration at the larch, birch, lilac, and grassland types of sites was negatively correlated with land surface temperature and air temperature, and the CO₂ concentration at the larch and birch sites was positively correlated with atmospheric pressure. Without any obvious annual change law, further study and observation are needed.     

Effect of elevated CO2 concentration on growth course of tree seedlings in Changbai Mountain

One-year-old seedlings ofPinus koraiensis, Pinus sylvestriformis, Phellodendron amurense were grown in open-top chambers (OTCs) with 700 and 500 ώmol/mol CO₂ concentrations, control chamber and on open site (ambient CO₂, about 350 ώmol/mol CO₂) respectively at the Open Research Station of Changbai Mountain Forest Ecosystems, Chinese Academy of Sciences, and the growth course responses of three species to elevated CO₂ and temperature during one growing season was studied from May to Oct. 1999. The results showed that increase in CO₂ concentration enhanced the growth of seedlings and the effect of 700 (ώmol/mol CO₂ was more remarkable than 500 ώmol/mol CO₂ on seedling growth. Under the condition of doubly elevated CO₂ concentration, the biomass increased by 38% in average for coniferous seedlings and 60% for broad-leaved seedlings. With continuous treatment of high CO₂ concentration, the monthly-accumulated biomass of shade-tolerantPinus koraiensis seedlings was bigger in July than in August and September, while those ofPinus sylvestriformis andPhellodendron amurense seedlings showed an increase in July and August, or did not decrese until September. During the hot August, high CO₂ concentration enhanced the growth ofPinus koraiensis seedlings by increasing temperature, but it did not show dominance in other two species. Foundation Item: This paper was supported by Chinese Academy of Sciences and the Open Research Station of Changbai Mountain Forest Ecosystem.     

Photosynthetic responses to lightflecks ofFagus crenata seedlings grown in a gap and understory of a deciduous forest

Photosynthetic responses to a series of 1-min lightflecks (1,000μmol m⁻² s⁻¹) superimposed on a background with different duration (1, 5, and 10 min) and intensity (25 and 50μmol m⁻² s⁻¹) of low background photosynthetic photon flux density (PPFD) were measured in the leaves ofFagus crenata grown in a gap and understory of aFagus crenata forest in the Naeba Mountains. The two background PPFD intensities most frequently occurred in understory and gap sites respectively. The maximum net photosynthetic rate (P _Nmax) and maximum stomatal conductance (g _smax) were higher in the gap seedlings than in the understory seedlings. However, when the background PPFD was 25μmol m⁻²s⁻¹, the net photosynthetic rate (P ₂₅) and stomatal conductance (g _s25) were almost the same between the gap and understory. When the background PPFD duration was 1-min, the net photosynthetic rate (P _N ) at the end of each lightfleck increased progressively. When the background PPFD duration was 5- and 10-min, the increase inP _N at the end of each lightfleck was less. This indicates that background PPFD duration is important to photosynthetic responses to lightflecks. The higher ratios ofP ₂₅/P _Nmax andg _s25/g _smax in the understory seedlings indicate that the understory seedlings can maintain relatively lower levels of biochemical and stomatal limitations than the gap seedlings under low light conditions. The ratios ofP _N /P _Nmax at the end of each lightfleck (IS) and light utilization efficiency of single lightflecks (LUE _s) that showed the influence of lightflecks on carbon gain were higher in the understory seedlings than in the gap seedlings when the background PPFD was 25μmol m⁻² s⁻¹. This means that understory seedling are capable of utilizing fluctuating light more efficiently under low light conditions than the gap seedlings although the net carbon gain of single lightflecks (CG _s) in the understory seedlings was not higher than that in the gap seedlings. There were no significant differences inIS andLUE _s between understory seedlings at a background PPFD of 25μmol m⁻² s⁻¹ and gap seedlings at a background PPFD of 50μmol m⁻² s⁻¹. However,CG _s in gap seedlings was higher than in understory seedlings. These results provide more evidence thatF. crenata acclimate to a natural light environment in respect to relative induction state at low background PPFD and can capture the fluctuating light at the same efficiency in both the gap and understory seedlings under natural light environments. This study was funded by the research project, Evaluation of Total CO₂ Budget in Forest Ecosystems, coordinated by the Ministry of Agriculture, Forestry and Fisheries of Japan.