UV—B辐射增强对植物光合作用的影响及植物的相关适应性研究

综述了UV－B辐射增强对植物光合作用的影响,植物对光破坏的响应与适应性方面的国内外研究进展,许多研究表明UV－B辐射增强对植物具有破坏作用能引起植物光抑制,光氧化和光损伤,植物依靠自身修复系统而对其破坏又具有一定的适应性。     

UV-B辐射对植物花粉萌发率和花粉管生长的累积效应

研究了19种植物花粉在不同UV－B辐射强度和辐照时间下其萌发率和花粉管伸长的变化,结果表明,UV－B辐射增加显著抑制大多数植物花粉的萌发率和花粉管生长;与对照相比,较高强度的UV－B对花粉的抑制作用大于较低强度;几个种的花粉萌发率及花粉管生长对UV－B增强不敏感,甚至被UV－B辐射所促进;辐射时间越长,对花粉抑制作用愈大,说明具有辐射累积效应,由此可知,植物花粉的萌发过程对UV－B的敏感性变化在自然条件下将会产生严重的生态学后果。     

增强UV—B辐射对高山植物麻花艽净光合速率的影响

在高寒矮嵩草（Kobresia humilis)草甸地区以太阳短波辐射为背景,建立了人工增强UV－B辐射的实验装置,每天增补15．8kJ.m^-2的辐射剂量,模拟平流层臭氧破坏约5％时近地表面太阳UV－B辐射的增强。观测表明：UV－B辐射的增强对麻花艽（Gentiana stramianea)植物的光合作用无明显的抑制或伤害作用。相反,在早晨补充UV－B辐射的短时间内,叶片的Pn随Gs的增大而有所提高。随着UV－B辐射时间的延长,在11：30－12：30,Pn和Gs有所降低。UV－B辐射时间进一步延长后（约14：00以后）,处理和对照组叶片Pn和Gs的差异趋向不明显,增强太阳UV－B辐射后,麻花艽叶片的光合色素并无明显变化,UV－B吸收物质的含量无明显变化,麻花艽叶片厚度的直接测量表明,增强UV－B辐射能明显提高叶片的厚度。叶片厚度的增加可补偿增强UV－B辐射辐后引起的光合色素的光降解,改善单位叶面积为基础的光合速率,是高原植物对强UV－B辐射的一种适应方式。     

增强UV-B辐射与干旱复合处理对小麦幼苗生理特性的影响

为研究由于平流层臭氧层减薄紫外线B辐射增强在干旱地区对春小麦生理特性的影响的特殊性,模拟平流层臭氧减少20％时辐射到地表的紫外线B（UV－B,280－315nm)的增强和水分胁迫（－0.5Mpa,聚乙二醇PEG－6000处理获得）,通过测定两种胁迫下春小麦（Triticum aestivum L.)叶绿素含量、类黄酮含量、水势、细胞膜相对透性、超氧歧化酶（SOD）活性及丙二醛（MDA）含量,研究了增强UV－B辐射和水分胁迫复合作用对温室种植的小麦幼苗生理生化的影响。实验结果表明,虽然水分胁迫和UV－B辐射单独或复合处理都使春小麦的叶绿素含量降低,但仅UV－B辐射增强单独处理显著地降低小麦叶绿素a、b和总叶绿素的含量,而水分胁迫以及复合处理对叶绿素的含量的降低作用不显著。两种胁迫无论是单独作用还是复合作用均能使类黄酮含量升高,并且处理第3天比第1天高出近50％,复合处理下类黄酮的含量大于两个因子单独处理。UV－B辐射和水分胁迫处理1d对春小麦叶片的相对电导率的影响不明显,处理3d后两种胁迫下相对电导率均上升,表明膜透性增加,其中水分胁迫作用下增加尤其明显。膜质过氧化产物丙二醛的含量,在两种因子单独和复合作用下都升高,说明膜的生理功能受到了一定的不利影响。活性氧清除剂超氧化物歧化酶（SOD）的活性在各种处理下,都没有发生改变。虽然增强的UV－B辐射和干旱处理一样,会显著降低植物水势,但是,UV－B辐射与干旱同时处理时叶片水势降低的程度,不但没有比两者分别处理时降低程度之和低,而且比单做干旱处理时的降低程度还低,这表明UV－B辐射和干旱胁迫同时处理时,UV－B辐射不但没有加重水分胁迫,反而减轻了干旱对春小麦生长的胁迫。由此可以认为,在干旱条件下,增强UV－B辐射不会加剧而是有利于提高小麦对干旱的抗性。     

重金属镉（Cd）和增强UV—B辐射复合对大豆生长和生理代谢的影响

研究了大豆的生长、生物量、抗氧化酶活性和吲哚乙酸（IAA）氧化酶活性在Cd^2 、UV－B辐射和二者复合胁迫（Cd UV-B)下的变化。结果表明,Cd^2 和UV－B辐射都抑制大豆生长,并显著抑制根的伸长,二者复合后加强了对根伸长的抑制。UV－B辐射显著增强了POD、SOD活性,Cd^2 对POD活性影响不明显,但却拮抗UV－B对POD活性的诱导,SOD活性在各种胁迫下显著增强。虽然Cd%2 对叶片类黄酮含量影响不明显,但对UV－B诱导的类黄酮合成有一定影响。IAA氧化酶活性在复合作用下下降,可能是复合胁迫影响大豆生长的重要因素之一。     

大豆作物响应增强UV—B辐射的品种差异

田间条件下模拟20％平流层臭氧层衰减,紫外线（UV－B,280－315nm)辐射增强,研究了UV－B对2个大豆（Glycin max (L.)Merr.)品种黑豆和晋豆生长,光合作用和稳定碳同位素组成的影响,结果表明,晋豆比黑豆对UV－B有较强的抗性或不敏感,表现为增强的UV－B辐射显著抑制黑豆的生长和株高,叶、茎、根和总生物量以及株高全部降低,而晋豆仅茎重和株高降低;晋豆的色素含量（叶绿素a,b,类胡萝卜素和类黄酮）不受UV－B辐射影响,在UV－B辐射下黑豆的净光合作用,气孔导度,胞间CO2浓度和蒸腾作用以及不分利用效率明显下降,而晋豆只有气孔导度和蒸腾作用减少,这可能与晋豆本身含有较高的类黄酮及较多的表皮毛和遗传特性有关,用叶片稳定碳同位素组成（δ^13C值）的分析也证明晋豆对UV－B辐射不敏感,由此看来,大豆品种对UV－B辐射的反应差异可以通过δ^13C值来判定。     

田间增强UV—B辐射对麦田生态系统K营养和累积的影响

研究大田栽培和自然光条件下,模拟UV－B辐射（UV－B,280－315nm)增强对麦田生态系统K营养和累积的影响,UV－B辐射显著影响春小麦不同生育期各部位K含量和群体K累积,并显著降低群体K总累积,在5．31kJ.m^-2UV-B辐射下,春小麦群体K总累积的降低最显著,UV－B辐射降低春小麦群体K输出,标志着麦田生态系统K产投比降低,K循环功能下降,麦田土壤速效K含量增加是春小麦群体K输出降低的结果,并将导致土壤库中K储量的增加。     

温室条件下增强UV-B辐射对小麦、谷子大小等级性和异速生长的影响

通过温室盆栽试验,研究了小麦与谷子种群在增强UV—B辐射条件下个体大小等级性与异速生长的变化模式。结果如下：①UV—B辐射处理组与对照组相比株高和生物量极显著下降（P〈0．01）,并且其株高和生物量的频率分布均向左偏移。②增强的UV—B辐射使小麦、谷子株高和各部位生物量的Gini系数极显著增大（P〈0．001）。③在增强UV-B辐射下,小麦和谷子株高．生物量之间仍表现为“简单异速生长关系”（P〈0．05）,但株高一生物量之间这种关系发生较大的偏离。结果表明增强UV—B辐射对不同大小的植物个体影响是不均匀的。     

UV-B辐射对香蕉光合作用和不同氮源利用的影响

生长在NO3^--N、NH4^--N和NH4NO3－N的香蕉叶片有相近似的最大光合速率,UV－B辐射引起生长在不同氮源的香蕉叶片光合速率、表现量子产率和光肥利用效率的降低。UV－B辐射使生长在不同氮源的植株叶面积干重和叶氮含是降低。生长在NH4^--N的植株Vcmax和Jmax均较生长在其它氮源的高。UV－B辐射引起生长在NH4^-N的植株Vcmax和Jmax降低较相同处理的NO3^-－N和NH4NO3－N植株明显,表明生长在NH4^ －N的香蕉对UV－B辐射更加敏感。UV－B辐射改变植株的叶片的碳氢比和碳氮比。经过UV－B辐射处理的NH4^ －N生长植株的碳氮生长在NO3^--N和NH4NO3－N的低。UV－B辐射可能改变植株对不同氮源的吸收利用,从而引起碳氮代谢和酸碱调节的变化。UV－B辐射降低叶氮在Rubisco和生物力能学组分的分配系数,可能使这些组分合成减少,使叶片光调节的变化。UV－B辐射降低叶氮在Rubisco和生物力能学组分的分配系数,可能使这些组分合成减少,使叶片光合速率下降。结果表明,生长在不同氮源的香蕉植树对UV－B辐射有不同响应,NH4^ -N有利于主要光合参数增高,但其对UV－B辐射亦最为敏感。氮供应受限制或植株生长在中性盐如NH4NO3－N则对UV－B辐射不甚敏感。     

增强紫外B辐射对植物及生态系统影响研究的发展趋势

介绍了一些有关紫外B辐射增强对植物及生态系统影响研究的新进展：1．许多研究已深入到分子水平;2．注意到对植物生长调控的研究;3．更加重视对植物防御、修复的研究;4．有关信号传导的研究日渐增多;5．对植物群体及生态系统影响的研究在不断扩大与加深;6．复合效应研究正在升温。推断今后在一段时间内,有关UV－B辐射对植物和生态系统影响的研究不但不会削弱,可能还会加强,特别分子水平的研究会大大增加,今后对群体和生态系统的研究会重视野外和长期效应的观测。我国在这一领域的研究起步晚,但近些年发展得较快,有部分研究已赶上国际研究进展的步伐。     

Metabolite specific effects of solar UV-A and UV-B on alder and birch leaf phenolics

We measured the concentrations of ultraviolet (UV)‐absorbing phenolics varying in response to exclusion of either solar UV‐B or both solar UV‐A and UV‐B radiations in leaves of grey alder (Alnus incana) and white birch (Betula pubescens) trees under field conditions. In alder leaves 20 and in birch leaves 13 different phenolic metabolites were identified. The response to UV exclusion varied between and within groups of phenolics in both tree species. The changes in concentration for some metabolites suggest effects of only UV‐A or UV‐B, which band being effective depending on the metabolite. For some other metabolites, the results indicate that UV‐A and UV‐B affect concentrations in the same direction, while for a few compounds there was evidence suggesting opposite effects of UV‐A and UV‐B radiation. Finally, the concentration of some phenolics did not significantly respond to solar UV. We observed only minor effects on the summed concentration of all determined phenolic metabolites in alder and birch leaves, thus indicating that measuring only total phenolics concentration may not reveal the effects of radiation. Here, we show that the appropriate biological spectral weighting functions for plant‐protective responses against solar UV radiation extend in most cases – but not always – into the UV‐A region and more importantly that accumulation of different phenolic metabolites follows different action spectra. This demonstrates under field conditions that some of the implicit assumptions of earlier research simulating ozone depletion and studying the effects of UV radiation on plant secondary metabolites need to be reassessed.     

Responses to solar ultraviolet-B radiation in a shrub-dominated natural ecosystem of Tierra del Fuego (southern Argentina)

A study was made of the effects of solar ultraviolet‐B radiation (UV‐B) on the growth of the dominant plant species of a shrub‐dominated ecosystem in Tierra del Fuego. This part of southern Argentina can be under the direct influence of the Antarctic ‘ozone hole’ during the austral spring and lingering ozone‐depleted air during the summer. The plant community is dominated by an evergreen shrub (Chiliotrichum diffusum) with an herbaceous layer of Gunnera magellanica and Blechnum penna‐marina in the interspaces between the shrubs. Inspections of ozone trends indicate that the springtime and summertime ozone column over Tierra del Fuego has decreased by 10–13% from 1978/9 to 1998/9. In a set of well‐replicated field plots, solar UV‐B was reduced to approximately 15–20% of the ambient UV‐B using plastic films. Polyester films were used to attenuate UV‐B radiation and UV‐transparent films (～90% UV‐B transmission) were used as control. Treatments were imposed during the growing season beginning in 1996 and continued for three complete growing seasons. Stem elongation of the shrub C. diffusum was not affected by UV‐B attenuation in any of the three seasons studied. However, frond length of B. penna‐marina under attenuated UV‐B was significantly greater than that under near‐ambient UV‐B in all three seasons. Attenuation of solar UV‐B also promoted the expansion of G. magellanica leaves in two of the growing seasons. Differences between treatments in leaf or frond length in B. penna‐marina and G. magellanica did not exceed 12%. Another significant effect of UV‐B attenuation was a promotion of insect herbivory in G. magellanica, with a 25–75% increase in the leaf area consumed. Changes in plant phenology or relative species cover were not detected within the time frame of this study. The results suggest that the increase in UV‐B radiation associated with the erosion of the ozone layer might be affecting the functioning of this ecosystem to some degree, particularly by inhibiting the growth of some plant species and by altering plant–insect interactions.     

Aphid orientation and performance in glasshouses under different UV‐A/UV‐B radiation regimes

Visual cues leading to host selection and landing are of major importance for aphids and evidence suggests that flight activity is very dependent on ultraviolet (UV)‐A radiation in the environment. At the same time research on insect plant hosts suggest that the UV‐B component can deter some pests via changes in secondary metabolite chemistry. Here, we examine the potential of UV (UV‐A/UV‐B) radiation to control insect pests in the glasshouse environment. We first examined artificial exposure to UV‐B and the potential to trigger morphological and biochemical modifications in pepper (Capsicum annuum L., Solanaceae) with implications for the fitness of green peach aphid, Myzus persicae Sulzer (Hemiptera: Aphididae). UV‐B caused accumulation of leaf secondary metabolites and soluble carbohydrates, and stimulated photosynthetic pigments. However, UV‐B did not impact on foliar protein content and aphid performance was unaffected. Next, we studied how altering the UV‐A/UV‐B ratio environment affected aphid orientation and spatial distribution over time, either directly or by exposing plants to supplemental UV before insect introduction. Aphids directly settled and dispersed on their host pepper plants more readily in the presence of supplemental UV‐A and UV‐B. In the control treatment with ambient glasshouse UV‐A and UV‐B, insects remained more aggregated. Furthermore, insects were less attracted to peppers pre‐exposed to supplemental UV‐A and UV‐B radiation. Our results suggest that suppression of UV‐A and UV‐B inside the protected environment reduces aphid colonization and dispersal. Furthermore, application of moderate exposure of young pepper plants to supplemental UV‐B radiation could aid in protection from the colonization by phytophagous insects.     

UV‐B impact on aphid performance mediated by plant quality and plant changes induced by aphids

Plants face various abiotic and biotic environmental factors and therefore need to adjust their phenotypic traits on several levels. UV‐B radiation is believed to impact herbivorous insects via host plant changes. Plant responses to abiotic challenges (UV‐B radiation) and their interaction with two aphid species were explored in a multifactor approach. Broccoli plants [Brassica oleracea L. convar. botrytis (L.), Brassicaceae] were grown in two differently covered greenhouses, transmitting either 80% (high UV‐B) or 4% (low UV‐B) of ambient UV‐B. Three‐week‐old plants were infested with either specialist cabbage aphids [Brevicoryne brassicae (L.), Sternorrhyncha, Aphididae] or generalist green peach aphids [Myzus persicae (Sulzer), Sternorrhyncha, Aphididae]. Plants grown under high‐UV‐B intensities were smaller and had higher flavonoid concentrations. Furthermore, these plants had reduced cuticular wax coverage, whereas amino acid concentrations of the phloem sap were little influenced by different UV‐B intensities. Cabbage aphids reproduced less on plants grown under high UV‐B than on plants grown under low UV‐B, whereas reproduction of green peach aphids in both plant light sources was equally poor. These results are likely related to the different specialisation‐dependent sensitivities of the two species. The aphids also affected plant chemistry. High numbers of cabbage aphid progeny on low‐UV‐B plants led to decreased indolyl glucosinolate concentrations. The induced change in these glucosinolates may depend on an infestation threshold. UV‐B radiation considerably impacts plant traits and subsequently affects specialist phloem‐feeding aphids, whereas aphid growth forces broccoli to generate specific defence responses.     

Multivariate analysis of intraspecific responses to UV-B radiation in white clover (Trifolium repens L.)

White clover (Trifolium repens L.) is experiencing increased levels of ultraviolet‐B (UV‐B) radiation in temperate pastures due to the depletion of the stratospheric ozone layer. Based on 17 morphological, morphogenetic and physiological attributes, this study analysed the consequences of enhanced UV‐B on 26 white clover populations using principal components analysis (PCA). After 18 d of exposure to 13·3 kJ m ^{? 2} d ^{? 1} UV‐B in controlled environments, UV‐B significantly decreased above‐ground and below‐ground plant growth attributes, epidermal cell surface area and maximum quantum efficiency of photosystem II photochemistry (F_v/F_m). Aspects of cell division and cell expansion both were negatively affected by UV‐B. Stomatal density, specific leaf mass, root‐to‐shoot ratio and levels of UV‐B‐absorbing compounds increased in response to UV‐B. In the multivariate analysis, the main dimension of UV‐B sensitivity was characterized by changes in plant growth attributes. Alterations in partitioning within and between plant organs constituted a secondary tier of UV‐B responsiveness. Plant characteristics related to UV‐B tolerance included lower growth rate, smaller epidermal cell surface area and higher UV‐B‐induced levels of UV‐B‐absorbing compounds. The results suggest overall UV‐B tolerance for slower‐growing populations from less productive habitats with higher natural UV‐B irradiance.     

Solar UV‐B radiation and ethylene play a key role in modulating effective defenses against Anticarsia gemmatalis larvae in field‐grown soybean

Solar UV‐B radiation has been reported to enhance plant defenses against herbivore insects in many species. However, the mechanism and traits involved in the UV‐B mediated increment of plant resistance are unknown in crops species, such as soybean. Here, we studied defense‐related responses in undamaged and Anticarsia gemmatalis larvae‐damaged leaves of two soybean cultivars grown under attenuated or full solar UV‐B radiation. We determined changes in jasmonates, ethylene (ET), salicylic acid, trypsin protease inhibitor activity, flavonoids, and mRNA expression of genes related with defenses. ET emission induced by Anticarsia gemmatalis damage was synergistically increased in plants grown under solar UV‐B radiation and was positively correlated with malonyl genistin concentration, trypsin proteinase inhibitor activity and expression of IFS2, and the pathogenesis protein PR2, while was negatively correlated with leaf consumption. The precursor of ET, aminocyclopropane‐carboxylic acid, applied exogenously to soybean was sufficient to strongly induce leaf isoflavonoids. Our results showed that in field‐grown soybean isoflavonoids were regulated by both herbivory and solar UV‐B inducible ET, whereas flavonols were regulated by solar UV‐B radiation only and not by herbivory or ET. Our study suggests that, although ET can modulate UV‐B‐mediated priming of inducible plant defenses, some plant defenses, such as isoflavonoids, are regulated by ET alone.     

Integration and scaling of UV‐B radiation effects on plants: from molecular interactions to whole plant responses

A process based model integrating the effects of UV‐B radiation to molecular level processes and their consequences to whole plant growth and development was developed from key parameters in the published literature. Model simulations showed that UV‐B radiation induced changes in plant metabolic and/or photosynthesis rates can result in plant growth inhibitions. The costs of effective epidermal UV‐B radiation absorptive compounds did not result in any significant changes in plant growth, but any associated metabolic costs effectively reduced the potential plant biomass. The model showed significant interactions between UV‐B radiation effects and temperature and any factor leading to inhibition of photosynthetic production or plant growth during the midday, but the effects were not cumulative for all factors. Vegetative growth were significantly delayed in species that do not exhibit reproductive cycles during a growing season, but vegetative growth and reproductive yield in species completing their life cycle in one growing season did not appear to be delayed more than 2–5 days, probably within the natural variability of the life cycles for many species. This is the first model to integrate the effects of increased UV‐B radiation through molecular level processes and their consequences to whole plant growth and development.     

Temporal variation in epidermal flavonoids due to altered solar UV radiation is moderated by the leaf position in Betula pendula

The physiological mechanisms controlling plant responses to dynamic changes in ambient solar ultraviolet (UV) radiation are not fully understood: this information is important to further comprehend plant adaptation to their natural habitats. We used the fluorimeter Dualex to estimate in vivo the epidermal flavonoid contents by measuring epidermal UV absorbance (A(375) ) in Betula pendula Roth (silver birch) leaves of different ages under altered UV. Seedlings were grown in a greenhouse for 15 days without UV and transferred outdoors under three UV treatments (UV-0, UV-A and UV-A+B) created by three types of plastic film. After 7 and 13 days, Dualex measurements were taken at adaxial and abaxial epidermis of the first three leaves (L1, L2 and L3) of the seedlings. After 14 days, some of the seedlings were reciprocally swapped amongst the treatments to study the accumulation of epidermal flavonoids in the youngest unfolded leaves (L3) during leaf expansion under changing solar UV environments. A(375) of the leaves responded differently to the UV treatment depending on their position. UV-B increased the A(375) in the leaves independently of leaf position. L3 quickly adjusted A(375) in their epidermis according to the UV they received and these adjustments were affected by previous UV exposure. The initial absence of UV-A+B or UV-A, followed by exposure to UV-A+B, particularly enhanced leaf A(375) . Silver birch leaves modulate their protective pigments in response to changes in the UV environment during their expansion, and their previous UV exposure history affects the epidermal-absorbance achieved during later UV exposure.     

Physical disturbance of an upland grassland influences the impact of elevated UV-B radiation on metabolic profiles of below-ground micro-organisms

This investigation determined the response of soil microbial communities to enhanced UV‐B radiation and disturbance in upland grassland. A factorial field experiment encompassing two levels of UV‐B supplementation (simulating ambient and a 30% increase in stratospheric ozone) and two levels of disturbance (disturbed and undisturbed) was established at Buxton Climate Change Impacts Laboratory, Derbyshire, UK, and maintained for 7 years prior to sampling. Enhanced UV‐B increased microbial utilization of carbohydrates, carboxylic acids, polymers and aromatic compounds present in Biolog® GN plates when inoculated with soils taken from disturbed plots, but did not affect carbon utilization of soil microbial communities associated with undisturbed plots (UV‐B×Disturbance interaction, P<0.05 for each substrate type). UV‐B treatment did not affect numbers of bacteria or fungi. Direct microscopic counts showed fewer bacteria in soil originating from disturbed plots than from undisturbed plots (Disturbance, P<0.001), although a greater number of culturable bacteria and fungi were isolated from disturbed than from undisturbed soils (Disturbance, P<0.001). No UV‐B‐ or disturbance‐related differences in protein, starch or urea hydrolysis were exhibited by bacterial isolates. UV‐B treatment did not affect total plant biomass within undisturbed plots or the biomass of individual groupings of grasses, forbs and mosses. Per cent root length colonized by arbuscular mycorrhizal fungi (AMF) was not affected by enhanced UV‐B radiation in the undisturbed plots. Neither AMF nor plant biomass was measured in disturbed plots. The key findings of this study show that UV‐B‐mediated alterations in carbon utilization occurred in soil microbial communities subjected to disturbance, but such changes were not observed in communities sampled from undisturbed grassland. Differences in the catabolic potential of microbial communities from disturbed grassland subjected to enhanced UV‐B are probably related to plant‐mediated changes in resource availability or quality.