Changes in leaf expansion and epidermal screening effectiveness in Liquidambar styraciflua and Pinus taeda in response to UV-B radiation

Absorption or screening of ultraviolet-B (UV-B) radiation by the epidermis may be an important protective method by which plants avoid damage upon exposure to potentially harmful UV-B radiation. In the present study we examined the relationships among epidermal screening effectiveness, concentration of UV-absorbing compounds, epidermal anatomy and growth responses in seedlings of loblolly pine (Pinus taeda L.) and sweetgum (Liquidambar styraciflua L.). Seedlings of each species were grown in a greenhouse at the University of Maryland under either no UV-B radiation or daily supplemental UV-B radiation levels of 4, 8 or 11 kJ m^?2 of biologically effective UV-B (UV-B_BE) radiation. Loblolly pine seedlings were subsequently grown in the field under either ambient or supplemental levels of UV-B radiation. At the conclusion of the growing season, measurements of epidermal UV-B screening effectiveness were made with a fiber-optic microprobe. In loblolly pine, less than 0.5% of incident UV-B radiation was transmitted through the epidermis of fascicle needles and about 1% was transmitted in primary needles. In contrast, epidermal transmittance in sweetgum ranged from about 20% in leaves not preconditioned to UV-B exposure, to about 10% in leaves grown under UV-B radiation. The concentration of UV-absorbing compounds was unaffected by UV-B exposure, but generally increased with leaf age. Increases in epidermal thickness were observed in response to UV-B treatment in loblolly pine, and this accounted for over half of the variability in UV-B screening effectiveness. In spite of the low levels of UV-B penetration into the mesophyll, delays in leaf development (both species) and final needle size (loblolly pine) were observed. Seedling biomass was reduced by supplemental UV-B radiation in loblolly pine. We hypothesize that the UV-induced growth reductions were manifested by changes in either epidermal anatomy or epidermal secondary chemistry that might negatively impact cell elongation.     

Foliar nutrients in relation to growth, allocation and leaf traits in seedlings of a wide range of woody plant species and types

This study aimed to identify functional correlates of seedling leaf nutrient content among woody species and to characterise functional species groups with respect to leaf nutrient attributes. Seedlings of 81 woody species from the temperate zone of western Europe were grown in a standard laboratory environment with standard, near-optimal nutrient availability. Weight-based leaf N content (N_wght) was positively correlated with mean relative growth rate (RGR), but the correlation with mean RGR was tighter when leaf N was expressed on a whole-plant weight basis: leaf nitrogen weight ratio (LNWR). Area-based leaf N content (N_area) was not associated with mean RGR, but was closely correlated with the quotient of saturated leaf weight and leaf area. Weight-based leaf K content (K_wght) was a close correlate of the saturated/dry weight ratio of the foliage. Within the lower range, K_wght corresponded with growth-related nutrient attributes, but higher values appeared to indicate succulence or remobilisable stored water. Functional groups of species and genera could be distinguished with respect to seedling leaf nutrient attributes. Deciduous woody climbers and scramblers had consistently higher leaf N_wght, LNWR and (apparently) leaf K_wght than other deciduous species or genera, and shrubs had higher values than trees. These differences seemed due partly to variation in specific leaf area. Evergreens had consistently higher leaf N_area than deciduous plants, but there were no significant differences in weight-based leaf nutrient attributes between these two groups, possibly because of `luxury nutrient consumption' by the slow-growing evergreens. Another functional group was that of the nitrogen-fixing species, which had consistently high innate leaf N_wght compared to non-N-fixers. The ecological significance of the leaf nutrient attributes in this study is discussed by comparing the seedling data with those from field-collected material, and by brief reference to the natural habitats of the species. Received: 22 September 1996 / Accepted: 1 March 1997     

陆生植物体内酶系统对UV-B辐射增强的响应

臭氧层减薄导致地表中波紫外线UV-B(280～320 nm)辐射的增强,UV-B辐射能量远高于可见光,且能被植物体内蛋白质和核酸等生物大分子吸收.酶是植物体内起催化作用的一类蛋白质,酶的数量和活性对UV-B辐射增强有强烈的响应.本文将近年来增强UV-B辐射对植物体内酶影响的研究工作进行了综述.主要包括抗氧化酶、核酮糖-1,5-二磷酸羧化酶、硝酸还原酶和谷氨酰胺合成酶.并就今后该方面的研究提出建议.     

青藏高原草地植物叶解剖特征

运用常规石蜡制片技术对我国青藏高原66种草地植物优势种的叶解剖特征进行研究,并分析了叶解剖特征与海拔、生长季降水及生长季均温之间的关系.结果表明:青藏高原草地植物叶片具有很多适应高寒环境的结构特征,如表皮层厚且表皮细胞大小差异显著,表皮毛等表皮附属物发达,异细胞丰富,通气组织普遍发达等;叶片各组成部分厚度的变异程度不同,其中海绵组织厚度变异最大,其次为上角质层、下表皮层、下角质层、上表皮层、栅栏组织,叶片厚度的变异最小;青藏高原草地植物叶片各组成部分的厚度存在协同进化,上下角质层厚度呈强烈正相关,海绵组织厚度与叶片厚度相关性最强;青藏高原草地植物叶片各组成部分的厚度与海拔、生长季降水、生长季均温3个重要环境变量呈较弱的相关性,总体表现为随海拔升高叶片各组成部分的厚度减小,而随生长季降水和生长季均温的增加叶片厚度增加.     

UV-B effects on the nutritional chemistry of plants and the responses of a mammalian herbivore

Stratospheric ozone depletion has caused ground-level ultraviolet-B (UV-B) radiation to rise in temperate latitudes of both hemispheres. Because the effects of enhanced UV-B radiation on the nutrition of food consumed by mammalian herbivores are unknown, we measured nutritional and chemical constituents of 18 forages and related changes to in vitro dry matter digestibility. We also measured intake and in vivo digestibility of Pacific willow (Salix lasiandra) and alfalfa (Medicago sativa L.) by blue duikers (Cephalophus monticola). Forages were irradiated for 3 months with ambient (1×) or supplemental (1.6×) UV-B radiation representing a 15% ozone depletion for Pullman, Washington, USA. Enhanced UV-B radiation had minimal and inconsistent effects on the nutritional content, in vitro dry matter digestibility, and protein-binding capacity of forages. However, flavonoid compounds increased in seven of the 13 forbs and woody dicots that were evaluated. Flavonoids were found to decrease only in yarrow (Achillea millefolium). When offered simultaneously, blue duikers preferred 1× and 1.6× UV-B irradiated plants of alfalfa equally, but ate 26% less willow grown under 1.6× UV-B radiation. However, when fed to duikers in separate feeding experiments, total dry matter intake and in vivo digestibility of dry matter, fiber, protein, and apparent energy did not differ between alfalfa and willow grown under 1× and 1.6× UV-B radiation. We conclude that expected increases in UV-B radiation from ozone depletion would have minimal effects on intake and digestion of ruminant herbivores.     

Penetration of UV-B radiation in foliage: evidence that the epidermis behaves as a non-uniform filter

In some plants, particularly herbaceous species, a considerable proportion of incident ultraviolet-B radiation (UV-B, 280-320 nm) penetrates into the leaf mesophyll where it is potentially damaging to nucleic acids and the photosyn-thetic machinery. We used optical techniques to look at the spatial variation in UV-B penetration through the epidermis of foliage of two herbaceous species (Chenopodium album and Smilacina stellata)and a conifer (Picea pun-gens). Measurements of UV-B penetration in intact foliage with a fibre-optic microprobe revealed that 300 nm radiation reached 161±36μm (mean±SD) into leaves of C. album, 154±40μm in S. stellata and 17±2μm in P. pungens, with epidermal transmittance being 39±14%, 55±19% and 0%, respectively. A thin polymer film was developed which fluoresced blue when irradiated by UV-B. Fresh epidermal leaf peels were placed over the film and irradiated with UV-B, and microscopic examination of the film from below allowed us to determine the spatial pattern of UV-B penetration through the epidermis. In herbaceous species, film fluorescence below cell walls, but not epidermal and guard cell protoplasts indicated that UV-B transmittance was much greater through anticlinal cell wall regions than protoplasts. Ultraviolet-B transmittance through large areas of epidermal cells could be induced by plasmolysis. Epidermal transmittance was also relatively high through stomal pores (and what appear to be nuclei in Smilacina), but relatively low through stomatal guard cells. Results from the fluorescing film technique were substantiated by direct measurements of UV-B transmittance through epidermal peels with a fibre-optic microprobe run paradermally along the bottom or inner side of irradiated peels. In Smilacina, we estimate that UV-B epidermal transmittance was up to 90% through anticlinal cell wall regions, but <10% through protoplast areas. In contrast to herbaceous species, we did not detect any UV-B transmittance through the epidermis of P. pungens with either the fluorescing film or the fibre-optic microprobe technique. The epidermis appears to be a much more spatially uniform UV-B filter in conifers than in these herbaceous species.     

Responses of the flavonoid pathway to UV-B radiation stress and the correlation with the lipid antioxidant characteristics in the desert plant Caryopteris mongolica

Caryopteris mongolica is a dwarf shrub mainly found in grassland and desert areas of north-west China, and which can survive severe environmental stress. This study aimed to assess the responses of the flavonoid pathway to UV-B radiation treatments and its correlation to the lipid peroxide and antioxidant systems in C. mongolica. In UV-B radiation experiments, plants were exposed to UV-B radiation treatments with a intensity of 30 J/s for 1, 4 and 24 h, respectively. A control group without UV-B radiation treatment was also used. The chlorophyll fluorescence parameters, contents of chlorophyll and carotenoid, levels of lipid peroxidation, activities of antioxidant system enzymes, accumulations of total flavonoids and anthocyanins, and activities of phenylalanine ammonialyase (PAL) and chalcone isomerase (CHI) under different UV-B radiation treatments were investigated. The correlations between products and key enzymes in the flavonoid pathway and the lipid peroxide and antioxidant systems were also analyzed. The results showed that chlorophyll fluorescence parameters decreased within 24 h of treatment. The chlorophyll contents decreased within 4 h and remained stable after 24 h. Carotenoid content significantly increased. The level of MDA, the activities of superoxide dismutase (SOD), ascorbate peroxidase (APX) and peroxidase (POD) and the contents of total flavonoids and anthocyanidins increased, while catalase (CAT) activity decreased under UV-B stress. The activities of PAL and CHI also increased with the increased content of total flavonoids. The flavonoid products anthocyanidins had a significant positive correlation with MDA level, as well as the activities of antioxidant enzyme SOD. In conclusion, UV-B radiation induced the degradation of photosynthetic pigments and decreased photochemical efficiency of Photosystem II; increased the contents of MDA, total flavonoids and anthocyanidins; and also enhanced activities of antioxidant enzymes (SOD, APX and POD) and key enzymes (PAL and CHI) in the flavonoid pathway in C. mongolica. Thus, we speculate that the flavonoid pathway were involved in the regulation of stress resistance in C. mongolica.     

Growth under UV-B radiation increases tolerance to high-light stress in pea and bean plants

Pea (Pisum sativum L.) and bean (Phaseolus vulgaris L.) plants were exposed to enhanced levels of UV-B radiation in a growth chamber. Leaf discs of UV-B treated and control plants were exposed to high-light (HL) stress (PAR: 1200 mol m^–2 s^–1) to study whether pre-treatment with UV-B affected the photoprotective mechanisms of the plants against photoinhibition. At regular time intervals leaf discs were taken to perform chlorophyll a fluorescence and oxygen evolution measurements to assess damage to the photosystems. Also, after 1 h of HL treatment the concentration of xanthophyll cycle pigments was determined. A significantly slower decline of maximum quantum efficiency of PSII (F _v/F _m), together with a slower decline of oxygen evolution during HL stress was observed in leaf discs of UV-B treated plants compared to controls in both plant species. This indicated an increased tolerance to HL stress in UV-B treated plants. The total pool of xanthophyll cycle pigments was increased in UV-B treated pea plants compared to controls, but in bean no significant differences were found between treatments. However, in bean plants thiol concentrations were significantly enhanced by UV-B treatment, and UV-absorbing compounds increased in both species, indicating a higher antioxidant capacity. An increased leaf thickness, together with increases in antioxidant capacity could have contributed to the higher protection against photoinhibition in UV-B treated plants.     

地表臭氧浓度增加和UV-B辐射增强及其复合处理对大豆光合特性的影响

基于开顶式气室(OTC),系统开展了地表O3增加和UV-B增强及其复合处理下(自然空气,CK;10%UV-B增强,T1;100nmol/mol O3,T2;100 nmol/mol O3+10%UV-B增强,T3)大豆光合气体交换、光响应、光合色素和类黄酮含量等参数的观测与分析研究。结果表明,与对照相比,T1和T2单因子处理组的如下指标有相似变化:气孔导度、气孔限制值下降,胞间二氧化碳浓度上升,净光合速率、最大净光合速率、半饱和光强显著降低,表观量子效率和暗呼吸速率先升后降。T1的叶绿素含量降低不显著,类胡萝卜素含量先降后升,类黄酮含量上升,而T2的叶绿素和类胡萝卜素含量显著降低,类黄酮含量先降后升。复合处理下,与CK相比各指标的变化和单因子相似,影响程度均强于两单因子组。因此,100 nmol/mol O3浓度增加和10%UV-B辐射增强复合处理对大豆叶绿素含量的影响存在协同作用,且O3胁迫起了主导作用。光合作用下降的主要原因均是非气孔因素,复合处理对大豆光合作用的影响比两因子单独胁迫有所加深,是O3和UV-B共同作用的结果。     

紫外线-B辐射对植物DNA及蛋白质的影响

大气平流层中的臭氧衰减,导致太阳辐射中的紫外辐射量有明显的增加,其中UV-B辐射对植物会产生不同程度的影响。分子生态学理论认为,UV-B辐射对植物造成的损伤,首先伤害植物的生物大分子,即进行光化学修饰。本文就臭氧衰减对生态环境和植物的影响途径进行了讨论,重点论述了UV-B辐射对植物蛋白质合成的抑制和DNA的损伤修复途径。并应用分子生物学技术研究植物对UV-B辐射的抗性机理和DNA修复技术的前景进行了展望。     

Comparison of responses of bean, pea and rape plants to UV-B radiation in darkness and in light

Effect of UV-B radiation on leaves of bean, pea and rape plants was studied. UV-B radiation (11.2 kJ·m⁻²) induced more distinct reduction of the primary photosynthesis activity when applied in darkness than the same UV-B dose, extended in time, and applied with photosynthetic active radiation (PAR). The pea plants were more susceptible to UV-B in darkness, but in the presence of PAR their tolerance was higher. The CO₂ fixation in the bean and rape plants, exposed to UV-B was decreased, but for the pea plants it remained unchanged. The UV-B irradiation caused an increase in the content of ultraviolet-absorbing pigments. Additionally, the bean plants grown at UV-B increased the thickness of leaves, described as SLW.     

水稻对UV-B辐射增强的抗性遗传及其生理生化特性研究

本研究结果表明紫外线B(UVB,280～330nm)能严重影响水稻秧苗生长发育,从而引起植株矮化,叶片干枯,叶绿素含量降低,单株干物质减少甚至死亡。不同水稻基因型对紫外线的反应存在明显差异。在3个供试品种(HR、M63、Hr)中,HR最抗UVB危害。遗传分析表明水稻抗UVB的性状为数量遗传性状且受多对隐性基因控制,生化分析表明水稻秧苗经UVB处理后,在0～3d内,随着时间推移,秧苗保护酶活性明显增强,之后,保护酶活性逐惭下降,MDA含量相应增加。抗UVB品种HR比感UVB品种Hr保护酶活性一直较高,膜质过氧化程度较低,反映了保护酶对抵抗UVB危害的重要作用。     

Responses of the ecological characteristics and antioxidant enzyme activities in Rotaria rotatoria to UV-B radiation

Hydrobiologia - UV-B radiation is an increasing threat to aquatic organisms and also a potential driving force for zooplankton population dynamics. To explore the ecological effects of UVR on...     

增强的UV-B辐射对植物影响的研究

综述了国内外有关UV－B辐射对植物影响的研究现状与动态,讨论了增强的UV－B辐射对植物生长及形态结构、植物生理生化代谢、植物遗传物质、UV－B吸收物质及某些基因表达和种群及生态系统的影响。展望了增强的UV－B辐射对植物影响领域中值得深入探讨的问题。     

Influence of enhanced UV-B radiation on biomass allocation and pigment concentrations in leaves and reproductive structures of greenhouse-grown Brassica rapa

We assessed the effects of enhanced ultraviolet-B radiation (UV-B; 280–320 nm) on biomass allocation to roots, shoots, leaves and flowers in the annual Brassica rapa. In addition, we investigated how concentrations of chlorophyll and UV-B-absorbing compounds in leaves, ovaries and pollen changed in response to enhanced UV-B. Plants were grown for 38 d in a greenhouse under lampbanks providing daily biologically effective UV-B doses equivalent to those under ambient mid-March stratospheric ozone levels or 16% (low-enhanced UV-B) or 32% (high-enhanced UV-B) ozone depletion levels for Morgantown, WV, USA. Total and aboveground biomass of plants was less under low-enhanced UV-B, but similar to ambient controls under high-enhanced UV-B. Concentrations of UV-B-absorbing compounds in leaves (area basis) increased under high-enhanced UV-B by about 20%, but were similar to ambient controls under low-enhanced UV-B. More effective protection due to higher screening-compound concentrations in plants under high-enhanced UV-B may explain why biomass production was not reduced. Plants under high-enhanced UV-B also had more reproductive biomass and produced more flowers, and had less root mass, than plants under ambient or low-enhanced UV-B. Concentrations of leaf total chlorophyll were not affected by UV-B treatment. While UV-B treatment had no affect on concentrations of UV-B-absorbing compounds in ovaries, concentrations in pollen from plants under both enhanced-UV-B treatments were >40% greater than ambient controls.     

The involvement of low-molecular antioxidants in cross-adaptation of medicine plants to successive action of UV-B radiation and salinity

Artemisia (Artemisia lercheana Web.), common basil (Ocimum basilicum L.), and black cumin (Nigella sativa L.) plants grown in water culture until the stage of 4–5 true leaves were subjected to 10-min UV-B irradiation, treated with 100 mM NaCl, or subjected to the successive action of both stressors. The contents of proline, anthocyanins, flavonoids, soluble phenols, and carotenois were measured. Superoxide dismutase activity was also assayed. Experimental plants could tolerate UV-B irradiation due to the accumulation of phenolic compounds (anthocyanins, soluble phenols, and flavonoids). Anthocyanins contributed mostly in the defnse effect; their content in black cumin and common basil increased 3–5-fold after irradiation. Dynamics of the anthocyanin content in tested plants of all treatments indicates the activation of their biosynthesis by UV-B irradiation and suppression by salinity. Successive action of stressors resulted in synergism of their effects on accumulation of low-molecular compounds in artemisia and common cumin plants. When these plants were irradiated with UV-B and then treated with NaCl, they accumulated more low-molecular compounds than after separate treatment with these stressors, especially in Artemisia. Plant pretreatment with UV-B reduced the adverse action of salinity; this was manifested in the turgor maintenance in salt-treated plants after preliminary irradiation. For basil, salinity was the stronger stressor than UV-B, which was manifested in a decrease in the content of low-molecular compounds.     

Leaf thickness and UV-B absorbing pigments of plants in relation to an elevational gradient along the Blue Mountains,Jamaica

Terrestrial plant species vary widely in their adaptation to (increasing) solar UV-B radiation. Among the various responses of higher plants to enhanced UV-B are increasing leaf thickness and increasing concentrations of UV-B absorbing compounds. In some (UV-B resistant) plant species increased leaf thickness and UV-B absorbance may form part of mechanisms protecting plants from UV-B damage. However, in UV-B sensitive plant species leaf thickness and UV-B absorbance may increase as well with enhanced UV-B radiation. In the latter case however, this response cannot prevent plant damage and disturbance. In the present field study the relationship between these plant parameters and a natural elevational UV-B gradient on the tropical island of Jamaica was described. Four plant species of the Blue Mountain Tropical Montane Forest, occurring on open forest sites along the roadside and paths were studied along an elevational gradient. Plant species studied are Redbush (Polygonum chinense), Wild ginger (Hedychium gardneranum), John Crow Bush (Bocconia frutescens) and White clover (Trifolium repens). The elevational sites were at 800, 1000, 1200, 1400 and 1600 m above sea level. Leaf thickness was measured of leaves of intact plants around midday in the field. Leaf disks (5 mm) were sampled and extracted with a methanol/HCl mixture. UV-B absorption of these leaf extracts was measured spectrophotometrically. For all species leaves from higher elevations were thicker than those from lower elevations. In addition, the absorption of UV-B of leaf extracts increased with increasing elevations. It is assumed that the calculated gradient of the UV-B_BE from 800 m above sea level: 9.45 kJ m^-2 day^-1 to 9.75 kJ m^-2 day^-1 at 1600 m is related to the measured increase of leaf thickness and UV-B absorbing compounds. The responsiveness of these plant parameters to the elevational gradient does not necessarily imply that the plant species are UV-B resistant. One possibility is that the species studied, which are growing on open, disturbed sites on the forest floor and along mountain-roads, are relatively sensitive to UV-B. In addition to clear sky conditions, mist and clouds occur frequently in this tropical mountane forest at Jamaica. Also, the low nutrient status of the soil (low pH, nutrient deficiency) and the high content of polyphenols in leaves of many plant species of the tropical montane rain forest may relate to the marked response of the species studied with increasing elevation. Abbreviations: asl – above sealevel, UV-B – ultraviolet-B radiation (280–320 nm), TMCF – Tropical Montane Cloud Forest.     

Seasonal occurrence and distribution of myxomycetes on different types of leaf litter in a warm temperate forest of western Japan

The seasonal occurrence and distribution of myxomycetes on different types of newly defoliated leaf litter were examined in a secondary forest in a warm temperate region of western Japan. The two types of leaf litter (deciduous trees, Prunus verecunda and Quercus variabilis, and evergreen trees, Q. glauca and Cinnamomum camphora) were incubated in trays on the forest floor. A total of 45 myxomycete species were recorded from 3021 collected samples that occurred at the July peak during the warmest and humidest season from April to November. The occurrence of species was significantly related to the changes in mean temperature and minimum temperature on both leaf types under humid conditions. Myxomycete assemblages were divided into three seasonal phases. Most of the species occurred in June–September, while a few species demonstrated characteristic distributions; i.e., Didymium melanospermum appeared in April– May and Diderma umbilicatum appeared in October– November. The respective leaf types supported the reproduction of myxomycetes with high species richness and diversity, with 34 species and H’ = 2.59 on deciduous trees and similarly 30 species and H’ = 2.49 on evergreen trees. Several species, however, exhibited a preference for either the deciduous tree or evergreen tree leaves. Thus, a mixed forest that defoliates during different two seasons yields a greater species diversity of myxomycete assemblage.     

UV-B辐射胁迫下不同起源时期的3种木本植物幼苗的生长及光合特性

平流层臭氧的减薄导致到达地表UV-B辐射增强是全球所面临的环境问题之一。UV-B辐射胁迫对植物的生物学效应研究成为继全球大气二氧化碳浓度升高对植物影响研究之后的又一热点领域。设置了UV-B滤光减弱组、UV-B辐射增强组和自然光对照组3组大田实验,选择不同起源时期的乐东拟单性木兰(Parakmeria lotungensi)、青冈(Cyclobalanopsis glauca)、山核桃(Carya cathayensis)幼苗为实验材料,测定每组中3种植物的生长量与光合特征参数,通过对比组间和种间差异,研究不同起源时期的3种木本植物对UV-B辐射胁迫的响应模式,分析3种植物对于UV-B辐射胁迫的适应性与自身起源和进化时间的关系,为"起源时间越早的木本植物生长发育和光合生理能否更好地适应UV-B辐射胁迫"这一科学命题的探讨提供一定实验参考。得到如下结果:(1)相对于自然光照条件,增强UV-B辐射胁迫对3种木本植物的地径和株高都有抑制作用;对乐东拟单性木兰、青冈的Pn和Amax有一定的抑制作用,对山核桃Pn和Amax则具有一定的促进作用。减弱UV-B辐射胁迫对3种木本植物的地径起到抑制作用,对乐东拟单性木兰、青冈幼苗的株高生长有促进作用,但对山核桃的株高却具有抑制作用;对乐东拟单性木兰以及山核桃的Pn和Amax有一定的抑制作用,而对青冈Pn和Amax则有促进作用。(2)对比种间差异,发现3种不同的UV-B光照条件下青冈的地径生长量都最大,乐东拟单性木兰次之,山核桃最小;株高生长量种间大小排序不一致;相对于自然光照条件,增强UV-B辐射强度下山核桃Pn、Amax的比值都最大,青冈次之,乐东拟单性木兰最小;减弱UV-B辐射强度下青冈的Pn、Amax的比值都最大,乐东拟单性木兰次之,山核桃最小;表明不同起源时间对植物抗UV-B辐射胁迫能力有一定的影响,但不是决定性因素。UV-B辐射增强和过滤减弱胁迫对3个树种幼苗的生长发育、光合作用、叶绿素均有影响,但不同起源时期3种木本植物幼苗光合特征参数的响应模式不一,其机制尚待进一步开展实验进行求证。本研究结果可丰富和补充UV-B辐射胁迫对木本植物的影响研究,为从进化角度筛选UV-B胁迫抗性较强的植物提供了一定的依据。