Linking water and carbon-use traits to drought and warming response strategies in three high-elevation species.

• Allometry of sapwood/heartwood is essential for understanding tree growth, water transport and carbon allocation, timber production and use, but such an allometry is lacking for Chinese temperate tree species. • We studied the allometry and development of heartwood and sapwood for seven Chinese temperate tree species: Korean pine (Pinus koraiensis Sieb. et Zucc), Dahurian larch (Larix gmelinii Rupr.), Japanese elm (Ulmus davidiana Planch var. japonica (Rehd.) Nakai), Manchurian ash (Fraxinus mandshurica Rupr.), Manchurian walnut (Juglans mandshurica Maxim.), Amur cork-tree (Phellodendron amurense Rupr.), and Mongolian oak (Quercus mongolica Fisch.). • All heartwood parameters investigated, including heartwood radius (HR), heartwood formation rate (HFR), heartwood ring number (HRN), heartwood initiation age (HIA), and heartwood volume ratio (HVR), were positively correlated with tree cambial age (CA). The HR, sapwood width (SW), sapwood area (SA), heartwood and sapwood volumes were significantly related to stem diameter at breast height (DBH) or xylem diameter. There was a polynomial relationship between the sapwood ring longevity (SRL) and sapwood ring number (SRN). However, most of the allometric relationships were species-dependent. The hardwood formation patterns were different between coniferous and broadleaved tree species. A power function was suitable to scale SA from DBH, but the exponent varied from 1.32 for the larch to 2.19 for the cork-tree. • Our allometry provided a practical means to assess wood development and related physiology for the temperate tree species.

Effects of soil rewatering on mesophyll and stomatal conductance and the associated mechanisms involving leaf anatomy and some physiological activities in Manchurian ash and Mongolian oak in the Changbai Mountains

通过室内模拟试验，阐明阔叶红松林中已测得含量较高的3种酚酸物质（苯甲酸、丁香酸和香草酸）对红松种子萌发及苗木生长的影响，为探索阔叶红松林内化感作用机理及解决红松更新障碍问题提供科学依据。采用培养皿培养法及室内盆栽培养法，以红松种子和3年生红松苗为试验对象，设置不同浓度（2、20、200 mg/L）苯甲酸、丁香酸、香草酸处理液，以蒸馏水为对照（CK），进行红松种子萌发试验及红松苗木生长试验，研究3种酚酸物质对红松种子发芽、苗木生长、光合色素、抗氧化酶活性、膜脂过氧化作用及渗透调节物质的影响。结果表明，（1）不同浓度3种酚酸均抑制红松种子萌发，但酚酸浓度变化仅对红松种子发芽率影响差异显著。（2）3种酚酸对红松苗木生长及物质积累抑制作用显著。浓度变化对红松苗株高及地径影响不显著，对生物量、根干重和茎干重影响显著。（3）针叶叶绿素a、叶绿素b、类胡萝卜素含量变化对酚酸处理反应一致，20 mg/L的3种酚酸均显著抑制光合色素产生，而200 mg/L丁香酸溶液及2 mg/L香草酸溶液均显著促进叶绿素a和类胡萝卜素积累。（4）酚酸处理使红松苗针叶中POD、CAT活性降低，SOD活性增加。针叶中MDA含量显著增加，200 mg/L丁香酸溶液处理组针叶MDA含量高于CK处理组70.51%。（5）不同浓度苯甲酸溶液促进可溶性糖增加，抑制可溶性蛋白增加；不同浓度丁香酸溶液促进可溶性蛋白增加，而不同浓度香草酸溶液抑制可溶性蛋白增加，二者对可溶性糖含量影响受浓度变化影响显著。苯甲酸、丁香酸、香草酸影响红松种子萌发，通过对红松苗光合色素、抗氧化酶活性及渗透调节物质的影响导致其生长受抑制、生物量减少，产生膜脂过氧化伤害。因此，解决阔叶红松林内红松更新障碍问题时，凋落物及土壤中酚酸物质的化感作用不容忽视。;Through the relevant indoor simulation experiments, this research aims to clarify the effects of three phenolic acids (benzoic acid, syringic acid, and vanillic acid) with high content in broad-leaved Pinus koraiensis forest on the seed germination and seedling growth of Pinus koraiensis, so as to provide scientific basis for exploring the allelopathy mechanism of broad-leaved Pinus koraiensis forest and solving the problem of regeneration obstacle of Pinus koraiensis. The experiment adopts petri dish culture method and the indoor potted culture method. The Pinus koraiensis seeds and triennial Pinus koraiensis seedlings as experimental object were treated with different concentrations (2, 20, and 200 mg/L) of benzoic acid, syringic acid, vanillic acid solution, and distilled water was used as control. The germination experiment of Pinus koraiensis seed and the Pinus koraiensis seedling growth test were carried out to study the effects of three phenolic acids on germination, seedling growth, photosynthetic pigment, antioxidant enzyme activity, membrane lipid peroxidation, and osmoregulation substances of Pinus koraiensis seeds. The results show that: (1) all the three phenolic acids with different concentrations had the effects of inhibiting germination of Pinus koraiensis seeds, but the change of phenolic acid concentration only had a significant difference in the germination rate of Pinus koraiensis seeds. (2) The three phenolic acids had significant inhibitory effects on the growth and substance accumulation of Pinus koraiensis seedlings. Phenolic acid concentration had no significant effect on plant height and root length, but had significant effect on biomass, root weight and stem weight. (3) The changes in the contents of chlorophyll a, chlorophyll b, and carotenoids in needles had same reaction to the phenolic acid treatment. All the three phenolic acids of 20 mg/L had significant inhibition on the production of photosynthetic pigments, while the syringic acid solution of 200 mg/L and the vanillic acid solution of 2 mg/L had significant effects on promoting the accumulation of chlorophyll a and carotenoids. (4) Phenolic acid treatment reduced the activity of peroxidase and catalase and increased the activity of superoxide dismutase. The content of malondialdehyde in needles was significantly increased, while the content of MDA in needles treated with 200 mg/L syringic acid group was 70.51% higher than that in control group. (5) Benzoic acid solutions of different concentrations could promote the increase of soluble sugar and inhibit the increase of soluble protein. Different concentrations of syringic acid could promote the increase of soluble protein, while different concentrations of vanillic acid could inhibit the increase of soluble protein. The concentration changes of both had a significant influence on the change of soluble sugar content. Benzoic acid, syringic acid, and vanillic acid affected the germination of Pinus koraiensis seeds, which led to growth inhibition, biomass reduction and membrane lipid peroxidation of Pinus koraiensis seedlings by affecting photosynthetic pigment, antioxidant enzyme activity and osmotic regulation substances. Therefore, allelopathy of phenolic acids in litter and soil should not be ignored when solving the problem of Pinus koraiensis regeneration in broad-leaved Pinus koraiensis forests.

Although many studies have focused on the cutting performance of ceramic blades in processing different materials, few have reported on their application in wood processing. Thus, it is necessary to explore the cutting performance of ceramic tools in solid wood machining. The aims of this paper were to evaluate the cutting performance of Al2O3 and Si3N4 ceramic tools in the process of machining Manchurian ash (Fraxinus mandshurica Rupr.) and Chinese fir (Cunninghamia lanceolata) by means of analysing cutting force and surface roughness and to provide guidelines for factories for applying ceramic tools in the manufacture of solid wood furniture. Up-milling tests were conducted for each combination of cutting speed, tool material, and workpiece material, and each combination was replicated five times. Results showed that (1) cutting force and surface roughness decreased with increase of cutting speed and (2) cutting force and surface roughness resulting from using Al2O3 ceramic cutting tools were larger than those of Si3N4 ceramic cutting tools, especially when cutting Manchurian ash with its extractives. Overall, ceramic tools can be used in high-speed cutting of solid wood. Compared with Al2O3 ceramic cutting tools, Si3N4 ceramic cutting tools are more suitable for cutting solid wood, especially those with extractives. Si3N4 ceramic tools provided not only chemical stability, but improved final product quality.

To better understand the eco-physiological characteristics of dominant tree species in Korean pine broad-leaved forests, and to provide fundamental data for modelling and predicting carbon dynamics of forest ecosystems, we measured leaf CO2 assimilation rate versus intercellular CO2 concentration curves of four canopy dominant tree species in a Korean pine broad-leaved forest, in situ, for the first time, using a canopy crane in the Changbai Mountain Forest Ecosystem Research Station. Several important photosynthetic parameters were fitted with the FvCB model. Photosynthe-tic rate (A), maximum carboxylation rate (Vc max) and stomatal conductance (gs) were lowest in Pinus koraiensis (Pk), while stomatal limitation on photosynthesis (Ls) was highest in Pk. There were significant variations of photosynthetic characteristics among the three broad-leaved tree species [i.e., Fraxinus mandshurica (Fm), Quercus mongolica (Qm) and Tilia amurensis (Ta)]. The rank of tree species with respect to area-based Vc max was: Fm (83.2 μmol·m-2·s-1) and Qm (89.3 μmol·m-2·s-1) > Ta (68.4 μmol·m-2·s-1) and Pk (68.8 μmol·m-2·s-1) (P<0.05), and their rank with respect to mass-based Vc max was: Fm (1.36 μmol·g-1·s-1) > Qm (1.03 μmol·g-1·s-1) > Ta (0.90 μmol·g-1·s-1) > Pk (0.42 μmol·g-1·s-1) (P<0.05). From July to September, A value significantly declined in Fm and Qm, but remained stable in Ta and Pk. By contrast, Vc max significantly decreased in all tree species from July to September. Our results indicated that seasonal variation of Vcmax should be taken into consideration in the modelling and predicting of forest ecosystem carbon dynamics in northeastern China.

Selective cutting changes tree species composition and stand structure, modifies tree competition intensity in the stand, with consequences on tree growth and population dynamics. Key tree species play a crucial role in maintaining community structure and ecosystem function. To clarify the competitive characteristics of three key species (Pinus koraiensis, Tilia amurensis, and Fraxinus mandshurica, which accounted for about 70% of growing stock) of typical forest types in broadleaved-Korean pine mixed forest, Hegyi competition index was used in four permanent 1-hm2 plots, i.e. virgin forest (VF), low-intensity cutting forest (LCF), moderate-intensity cutting forest (MCF) and high-intensity cutting forest (HCF). Compared with VF, the stand density and mean DBH of big trees (DBH≥20 cm) significantly decreased in MCF and HCF, but the stand density of young trees (2 cm≤DBH<10 cm) increased, but no significant changes of stand or DBH in LCF. In all the four forest types, individual competition index (CI) of the three species decreased with increasing DBH. There was a power function relation between CI and DBH. CI curve turned to be gentle at DBH reaching 20 cm, and this rule was not affected by selective cutting. In VF, LCF and HCF, most of competition pressure of young trees of all key species derived from other tree species in secondary canopy or understory, but the competition pressure of small trees (10 cm≤DBH<20 cm) and big trees of P. koraiensis originated mainly from intra-species and other species in secondary canopy or understory. The competition stress of F. mandshurica was mainly affected by P. koraiensis and other species in secondary canopy or understory. T. amurensis was mainly affected by intra-species and P. koraiensis. Betula platyphylla contributed most of the competition stress (over 50%) to all three key species in HCF. Our results suggested that removing the trees which are in secondary canopy or understory but suppress the three key trees species intensively would be beneficial to the regeneration and growth of key species before tree DBH exceeds 20 cm. We proposed to regulate the density of key tree species in overstory to cultivate large diameter timber according to the competition among the key trees species. Once tree DBH exceeds 20 cm, tree growth would not be affected by competition. This study had guiding significance for the cultivation of key tree species and rapid recovery of natural forests after selective cutting.

细根(直径≤ 2 mm)的生长和死亡动态及其影响因子是森林生态系统能量流动和物质循环的重要研究内容,但因受到研究方法的限制而了解甚少。于2010年5-10月采用微根管技术对东北东部山区5种温带森林生态系统的细根生长量(FRP)和死亡量(FRM)进行了动态跟踪测定,并同步测定了土壤温度(<em>T</em>s)、土壤湿度(<em>M</em>s)、叶面积指数(LAI)等相关因子。结果表明: 不同林型和取样时间的FRP和FRM均差异显著(<em>P</em> < 0.001)。杨桦林、硬阔叶林、兴安落叶松林、红松林、蒙古栎林的FRP和FRM分别为:(13.34±0.90) μm·cm^-2·d^-1(平均值±标准误)和(5.02±0.36) μm·cm^-2·d^-1、(13.04±0.82) μm·cm^-2·d^-1 和(6.85±0.32) μm·cm^-2·d^-1、(8.74±1.44) μm·cm^-2·d^-1和(5.05±0.61) μm·cm^-2·d^-1、(8.02±2.27) μm·cm^-2·d^-1和(3.88±0.35) μm·cm^-2·d^-1、(7.59±0.82) μm·cm^-2·d^-1和(3.88±0.61) μm·cm^-2·d^-1。所有林型生长季期间FRP的时间变化均呈现明显的单峰型,但峰值出现的时间却因林型而异。FRM随生长季的进程而逐渐增加,杨桦林和硬阔叶林FRM在8月初出现峰值,而红松林、兴安落叶松林和蒙古栎林的FRM峰值均出现在生长季末期。<em>T</em>s、<em>M</em>s和LAI对FRP和FRM均存在显著的正效应(<em>P</em> < 0.05),3个因子的综合作用对各个林型FRP和FRM变异性的解释率分别达68%和53%以上,表明这些温带森林生态系统细根生长和死亡的时间动态主要受土壤温湿度和叶面积变化的联合影响。;Production and mortality of fine roots (diameter ≤ 2mm) and influencing factors are important to energy flow and nutrient cycling in forest ecosystems, but remain poorly understood mainly due to the limitation of methodology. In this study, we used a minirhizotron technique to investigate the temporal dynamics in fine root length production (FRP) and mortality (FRM) of five representative forest ecosystems in Northeast China during the period between May and October of 2010. Soil temperature (<em>T</em>s), soil moisture (<em>M</em>s), and leaf area index(LAI)were simultaneously measured for each stand. The stands were aspen-birch forest dominated by <em>Populus davidiana</em> and <em>Betula platyphylla</em>, hardwood forest dominated by <em>Fraxinus mandshurica</em> and <em>Juglans mandshurica</em>, Mongolian oak forest dominated by<em> Quercus mongolica</em>, Korean pine (<em>Pinus Koraiensis</em>) plantation, and Dahurian larch (<em>Larix gmelinii</em>) plantation. The experimental design included five forest types, three 20 m×30 m replicate plots in each forest type. The results showed that the FRP and FRM were significantly (<em>P</em> < 0.001) affected by forest types, sampling times and their interactions. The FRP was (13.34±0.90) μm·cm^-2·d^-1(mean±SE), (13.04±0.82) μm·cm^-2·d^-1, (8.74±1.14) μm·cm^-2·d^-1, (8.02±2.77) μm·cm^-2·d^-1, and (7.59±0.82) μm·cm^-2·d^-1 for the aspen-birch, hardwood, larch, pine, and oak stands, respectively; and the FRM was (5.02±0.36) μm·cm^-2·d^-1, (6.85±0.32) μm·cm^-2·d^-1, (5.05±0.61) μm·cm^-2·d^-1, (3.88±0.35) μm·cm^-2·d^-1, and (3.88±0.61) μm·cm^-2·d^-1, correspondingly. The FRP showed a unimodal seasonal pattern with peaks varying with forest types. The FRM increased gradually as the growing season proceeded, and reached its maximum at the end of the growing season for all the stands except for the aspen-birch and hardwood stands where it peaked in early August. <em>T</em>s, <em>M</em>s, and LAI all exerted significant positive effects on FRP and FRM (<em>P</em> < 0.05), which, together, explained more than 68% and 53% of variability in FRP and FRM, respectively. These results illustrated that the temporal dynamics of fine root production and mortality in these temperate forest ecosystems were jointly influenced by changes in soil temperature, moisture and leaf area index.

The maximum rate of carboxylation in leaves (Vcmax) is an important parameter used to determine the photosynthetic rate. An accurate estimation of Vcmax is important for evaluating the photosynthetic capacity of vegetation productivity and the carbon budget of forest ecosystems. In this study, we measured the light use efficiency (LUE) and Vcmax of leaves and their corresponding spectral characteristics. Spectral analysis was used to find a modified photochemical reflectance index (PRI) of leaves to estimate LUE and thereby estimate leaf Vcmax. The results showed that the precision with which the modified ratio PRI index estimated LUE was significantly increased. The R2 of the estimation model was 0.69, and the root mean square error (RMSE) was 0.0024. The R2 of the model for estimating leaf Vcmax based on the LUE was 0.72, and the RMSE was 8.439 μmol/m2/s. The Vcmax values of conifer trees (Scots pine, Korean pine, and larch) were higher than those of broadleaf trees (white birch, Manchurian walnut, Siberian elm, Manchurian ash, Mongolian oak, Korean aspen, and Amur linden). This method avoids problem that conventional PRI is not sensitive to high leaf LUE values and provides important parameter data for the quantitative estimation of the gross primary productivity of forest ecosystems.

Mungbean seedlings were grown in a nutrient solution with combined concentrations of aluminum (Al) (0, 2, and 5 mM) and calcium (Ca) (0–10 mM) in a randomized complete block design experiment for 16 days. The results showed that under no Al stress, Al0 + Ca0 decreased chlorophyll content by 10%, increased soluble protein, free proline content, and electrolyte leakage by 51%, 533%, and 111%, respectively, compared with a control (Al0 + Ca0.5). Under 2mMAl stress, Al2 + Ca0 decreased chlorophyll content by 19%, increased soluble protein, free proline content, and electrolyte leakage by 48%, 405%, and 55%, respectively, compared with a control (Al2 + Ca0.5). The ratio of Al/Ca = 1:2 increased chlorophyll content by 3%, decreased free proline content and electrolyte leakage by 64% and 34%, respectively. However, all of Al/Ca = 2:1, 1:1 and 1:2 at 2AlmM significantly increased soluble protein, compared with Al2 + Ca0.5. Under 5mMAl stress, Al5 + Ca0 decreased chlorophyll content by 11%, and increased soluble protein, free proline content, and electrolyte leakage by 77%, 85%, and 30%, respectively, compared with a control (Al5 + Ca0.5). The ratio of Al/Ca = 1:2 increased chlorophyll content by 14%, decreased free proline content by 80%, and electrolyte leakage by 34%, compared with Al5 + Ca0.5. However, all ratios of Al/Ca = 2:1, 1:1 and 1:2 at 5mMAl also significantly increased soluble protein, compared with the control. Furthermore, it was observed that Al/Ca = 1:2 could accumulate more Al and Ca in the seedlings than Al/Ca = 2:1 and 1:1 regardless of Al stress (2mM or 5mMAl). Lack of Ca affected the synthesis of chlorophyll, increased soluble protein and free proline, and enhanced electrolyte leakage. Al/Ca = l:2 might be an appropriate ratio for physiological alleviation of Al toxicity to mungbean seedling growth. High concentration of Ca in the solution at appropriate Al/Ca ratio (e.g. Al/Ca = 1:2) could increase chlorophyll content, an indication of alleviation effect. On the contrary, the high Ca caused a significant increase of soluble protein. It suggests the involvement of various proteins that have properties to resist Al toxicity for mungbean seedling growth.

Light is one of the most important environmental cues that affects plant development and regulates its behavior. Light stress directly inhibits physiological responses and plant tissue development and even induces mortality in plants. Korean pine (Pinus koraiensis) is an evergreen conifer species widely planted in northeast China that has important economic and ecological value. However, the effects of light stress on the growth and development of Korean pine are still unclear. In this study, the effects of different shading conditions on physiological indices, molecular mechanisms and metabolites of Korean pine were explored. The results showed that auxin, gibberellin and abscisic acid were significantly increased under all shading conditions compared with the control. The contents of chlorophyll a, chlorophyll b, total chlorophyll and carotenoid also increased as the shading degree increased. Moreover, a total of 8556, 3751 and 6990 differentially expressed genes (DEGs) were found between the control and HS (heavy shade), control and LS (light shade), LS vs. HS, respectively. Notably, most DEGs were assigned to pathways of phytohormone signaling, photosynthesis, carotenoid and flavonoid biosynthesis under light stress. The transcription factors MYB-related, AP2-ERF and bHLH specifically increased expression during light stress. A total of 911 metabolites were identified, and 243 differentially accumulated metabolites (DAMs) were detected, among which flavonoid biosynthesis (naringenin chalcone, dihydrokaempferol and kaempferol) metabolites were significantly different under light stress. These results will provide a theoretical basis for the response of P. koraiensis to different light stresses.

We have limited understanding of architecture and morphology of fine root systems in large woody trees. This study investigated architecture, morphology, and biomass of different fine root branch orders of two temperate tree species from Northeastern China—Larix gmelinii Rupr and Fraxinus mandshurica Rupr —by sampling up to five fine root branch orders three times during the 2003 growing season from two soil depths (i.e., 0–10 and.10–20 cm). Branching ratio (R b) differed with the level of branching: R b values from the fifth to the second order of branching were approximately three in both species, but markedly higher for the first two orders of branching, reaching a value of 10.4 for L. gmelinii and 18.6 for F. mandshurica. Fine root diameter, length, SRL and root length density not only had systematic changes with root order, but also varied significantly with season and soil depth. Total biomass per order did not change systematically with branch order. Compared to the second, third and/or fourth order, the first order roots exhibited higher biomass throughout the growing season and soil depths, a pattern related to consistently higher R b values for the first two orders of branching than the other levels of branching. Moreover, the differences in architecture and morphology across order, season, and soil depth between the two species were consistent with the morphological disparity between gymnosperms and angiosperms reported previously. The results of this study suggest that root architecture and morphology, especially those of the first order roots, should be important for understanding the complexity and multi-functionality of tree fine roots with respect to root nutrient and water uptake, and fine root dynamics in forest ecosystems.

Longitudinal compression can help wood form some folds on the wood cell walls after a suitable softening procedure. These folds can enhance the one- and multi-dimensional bending performances of wood. The longitudinal compression properties of alkali-treated juvenile and mature northeast Chinese ash (Fraxinus mandshurica Rupr.) were analyzed. Elastic and elastic-plastic stages were inferred from the longitudinal compression curves. Scanning electron microscopy images showed that some folds formed in the wood cell wall vessels and fibers. X-ray microdensitometer test results showed a decrease in the fluctuation of the wood cell wall density of the specimens. The swelling and degradation or extraction of hemicellulose, lignin, and extractive occurred after alkaline treatment. Slippage between cellulose chains and curving within a cellulose chain were inferred during longitudinal compression. Juvenile wood specimens had higher modulus of elasticity and larger variability than mature wood after alkaline treatment. This finding can be attributed to the higher extent of degradation or extraction of hemicelluloses, lignin, and extractive, as well as the smaller microfibril angle and the similar cellulose crystallinity of treated juvenile wood compared to those of mature wood specimens after alkaline treatment.

The soil saturated water content, soil water permeability and the soil water content dynamic process under six forest types (Pinus koraiensis plantation, Fraxinus mandshurica-Populus davidiana forest, Fraxinus mandshurica- Larix olgensis forest, Tilia mandshurica forest Quercus monglica forest and Juglans mandshurica forest) beside Songhua River were measured in the sample forests and experiment room during May to September 2006. The soil saturated water contents under six forest types were from 2693.50 t/hm2 to 3184.31 t/hm2, the biggest value occurred under Fraxinus mandshurica-Populus davidiana forest, and the smallest value occurred under Quercus monglica forest. The initial permeability coefficient and stable permeability coefficient of the various soil layers under six forest types were bigger than that of bare land, and the biggest value occurred under Tilia mandshurica forest. The soil water content under six forest types had the same change tendency during growth season that was, high-low-high-low in May-June-July and August-September. The results would provide the theories basis for the forest management beside Songhua River.

The observed variation in the reflectance in the region of chlorophyll absorption (450 to 900 nanometers) of mature Pinus ponderosa. (Ponderosa Pine) is explained in terms of pigment concentrations and stress associated with pollutant exposure . Reflectance and chlorophyll concentrations were measured on each years growth on each of 20 trees at four sites along an ozone exposure gradient the southern Sierra Nevada. Additionally, each of these sites was characterized in terms of stand density and age. Exposure to ozone, a strong oxidant, results in chloroplast injury. Granulation of the chloroplast stroma is an early metabolic response to ozone exposure. Thus, an examination of the reflectance changes observed along the ozone gradient provide a means for quantifying the spectral changes associated with chloroplast damage and reduced photosynthetic efficency. Additionally, the spectral trends associated with increasing needle age were related to the effects of cumulative ozone exposure and changes in overall chlorophyll concentration. It was found that the within site variation of the reflectance spectra was directly related to total chlorophyll concentration; an increase in chlorophyll concentration resulted in both a shift in the red-edge inflection to longer wavelength and an increase in the depth of the chlorophyll absorption well. Similarly, an increase in chloroplast damage, associated with higher levels of ozone exposure, also produced shift to 10I)ger wavelengths of the red­ edge but a decrease in the depth of the absorption well. The absorption band broadening observed in the high ozone exposure sites is indicative of an increase in the disorder of

Cultivar renewing is important for the increases of wheat yield. Studying changes of different physiological characteristics in the succession process of wheat varieties has great implications for future breeding. The senescence rate of flag leaf is a key factor affecting winter wheat yield. The variation of photosystem II function during senescence of flag leaves of wheat from different ages is still not clear. 31 wheat varieties planted in Henan Province from different ages since 1941 were examined in this experiment. The variation of photosystem II function was analyzed through measu-ring the relative chlorophyll content, and chlorophyll fluorescence induction dynamics during the senescence of flag leaves which were induced by continued dark. The results showed that the chlorophyll content of flag leaves was gradually increased in the succession of winter wheat. The chlorophyll degradation rate in the leaves of modern varieties was lower than the earlier varieties during the senescnece of flag leaves. Meanwhile, J point of the fluorescence induction kinetics curves in flag leaves of modern varieties increased less than I point. The photosystem II maximum photochemical efficiency and the amount of active reaction centers per unit area gradually increased during succession of wheat varieties, but the reduced extent in leaves of modern varieties was lower than that in the earlier ones. There was no significant correlation between the change of chlorophyll content and Fv/Fm in senescent leaves. There was significant positive correlation when the leaves aging degree increased, with the slope of trend line gradually increased. The photosystem II unit area and the amount of active reaction center was positively related with the aging degree, and both the correlation degree and slope of trend line increased with the increases of senescence extent of the leaves. The results suggested that chlorophyll content of flag leaf increased and the degradation rate slowed down gradually during the succession of wheat varieties. The anti-aging ability of photosynthetic electron transfered from QA to QB was improved, which contributed to the slowing down of the decline of Fv/Fm and the amount of active reaction center. The increased chlorophyll content and anti-aging ability of photosystem II also contributed to the increases of yield in the succession of winter wheat.