Effects of lanthanum(Ⅲ) on nitrogen metabolism of soybean seedlings under elevated UV-B radiation

The hydroponic culture experiments of soybean bean seedlings were conducted to investigate the effect of lanthanum （La） on nitrogen metabolism under two different levels of elevated UV-B radiation （UV-B, 280-320 nm）. The whole process of nitrogen metabolism involves uptake and transport of nitrate, nitrate assimilation, ammonium assimilation, amino acid biosynthesis, and protein synthesis. Compared with the control, UV-B radiation with the intensity of low level 0.15 W/m^2 and high level 0.45 W/m^2 significantly affected the whole nitrogen metabolism in soybean seedlings （p 〈 0.05）. It restricted uptake and transport of NO3^-, inhibited activity of some key nitrogen-metabolism-related enzymes, such as： nitrate reductase （NR） to the nitrate reduction, glutamine systhetase （GS） and glutamine synthase （GOGAT） to the ammonia assimilation, while it increased the content of free amino acids and decreased that of soluble protein as well. The damage effect of high level of UV-B radiation on nitrogen metabolism was greater than that of low level. And UV-B radiation promoted the activity of the anti-adversity enzyme glutamate dehydrogenase （GDH）, which reduced the toxicity of excess ammonia in plant. After pretreatment with the optimum concentration of La （20 mg/L）, La could increase the activity of NR, GS, GOGAT, and GDH, and ammonia assimilation, but decrease nitrate and ammonia accumulation. In conclusion, La could relieve the damage effect of UV-B radiation on plant by regulating nitrogen metabolism process, and its alleviating effect under low level was better than that under the high one.

Effects of UV-B radiation on the growth interaction of Ulva pertusa and Alexandrium tamarense

Enhanced UV-B(280-320 nm) radiation resulting from ozone depletion is one of global environmental problems. Not only marine organisms but also marine ecosystems can be affected by enhanced UV-B radiation. The effects of UV-B radiation on interaction of macro-algae and micro-algae were investigated using Ulva pertusa Kjellman and Alexandrium tamarense as the materials in this study. The results demonstrated that UV-B radiation could inhibit the growth of Ulva pertusa and Alexandrium tamarense when they were both mono-cultured, and the growth inhibition of algae was more significant with increasing doses of UV-B radiation. Alexandrium tamarense could inhibit the growth of Ulva pertusa in mixed culture, and the growth inhibition was more significant when increasing the initial cell density. However, Ulva pertusa could inhibit the growth of Alexandrium tamarense in early phase and stimulate the growth in latter phase when they were grown in mixed culture. Lower initial cell density(10~2 cell/ml) of Alexandrium tamarense could inhibit the growth of Ulva pertusa under UV-B radiation treatment,however, with the initial cell density increasing(10~3 and 10~4 cell/ml), the growth of Ulva pertusa was stimulated under lower dose of UV-B radiation and inhibited under higher dose of UV-B radiation by Alexandrium tamarense. Compared with that in mixed culture, Ulva pertusa showed more positive inhibition to the growth of Alexandrium tamarense under UV-B radiation treatment.

The effect of UV-B radiation enhancement on the interspecific competition between Skeletonema costatum and Heterosigma akashiwo

The responses of the interspecific competition between Skeletonema costatum and Heterosigma akashiwo to UV-B radiation enhancement were studied by the co-culture method. The results showed that Heterosigma akashiwo exhibited inhibition on the growth of Skeletonema costatum, and with the increase of initial inoculation density of Heterosigma akashiwo, heavier inhibition on Skeletonema costatum appeared. Under different inoculation proportions, Heterosigma akashiwo could always be in predominance in competition with Skeletonema costatum. The UV-B radiation treatment could change the competition relationship between Skeletonema costatum and Heterosigma akashiwo, which could increase the competitive dominance of Skeletonema costatum and decrease the competitive dominance of Heterosigma akashiwo. When the inoculation proportions of Heterosigma akashiwo and Skeletonema costatum were H∶S=1∶4 and H∶S=1∶1,Skeletonema costatum was in predominance in this competition; however, Heterosigma akashiwo was in predominance when the inoculation proportion was H∶S=4∶1.

Effect of UV-B Radiation on Ingesting and Nutritional Selecting Behavior of Rotifer Brachionus urceus

Effect of UV-B radiation on ingesting and nutritional selecting behavior of the roifer Brachionus urceus on 5 species of microlgae were studied under controlled laboratory conditions. Restdts showed that enhanced UV-B radiation significantly inhibited ingesting of the rotifer B. urceus when it was fed with 5 species of micro-algae （p〈0.05）. The ingesting selectivity rate varied with the UV-B radiation enhancement when it was fed with 5 species micro-algal mixture. Results indicated that the enhanced UV-B radiation could affect ingesting and nutritional selectivity of B. urceus.

Effect of atmospheric aerosols on UV-B radiation reaching the ground

Solar ultraviolet radiation reaching the ground can be reduced due to light scattering of atmospheric aerosols. Aerosol pollution has led to the decrease in biological active UV-B radiation by about 45% and 10% in city and rural areas, respectively. In populated areas, effect of aerosol scattering on UV-B radiation may offset the increased amount of UV-B caused by ozone depletion, but in clean areas such as two poles, ozone depletion may have great damage effects on ecosystems.

The effects of enriched C0_(2) and enhanced UV-B radiation on ultrastructure of Dunaliella salina, singly and in combination

The effects of ambient CO2/ambient UV-B, enriched CO2/ambient UV-B, ambient CO2/enhanced UV-B, and enriched CO2/enhanced UV-B on the ultrastructure of Dunaliella salina were investigated. （1） The ultrastructure of D..salina cell in the control experiment showed that the arrangement of thylakoid lamellae was regular, and there were many large starch grains among the thylakoid lamellae. A prominent well-developed pyrenoid was found in the middle of the chloroplast. Nucleus envelope and nucleolus were clearly observed. The Golgi apparatus accompanied by numerous vesicles with a compact arrangement of cisternae and the peripheral tips of the cisternae were swollen to a size comparable to that of some of the associated vesicles. （2） The ultrastructure of D. salina cell in enriched CO2 showed that the arrangement of thylakoid was regular and the lamellae were vivid. Developed pyrenoids were found in the low-CO2-grown cells, but not in the high-CO2-grown cells. The mitochondria cristae were vivid. The arrangement of Golgi apparatus was compact. （3） The ultrastructure of D. salina cell in enhanced UV-B showed that the thylakoid was dissolved and the cells had a less developed pyrenoid or no detectable pyrenoid. Part of the nucleus envelope was dissolved. The number ofmitochondria was increased and some mitochondria cristae were disintegrated. The starch grains were broken apart into many small starch grains. The Golgi apparatus with a loose arrangement ofcistemae and the peripheral tips of the Golgi cistemae were not especially swollen, with several large associated vesicles. （4） The ultrastructure of D. salina cell in the enriched CO2/enhanced UV-B showed that part of the thylakoid and nucleus envelopes of some cells were dissolved. The pyrenoid was larger than that of the enhanced UV-B. There were many mitochondria between stroma and chloroplast membrane, but mitochondria cristae were partly dissolved. Many small starch grains were accumulated in cells. The starch sheath was broken into several discontinuous starch grains with different sizes. The arrangement of Golgi apparatus was loose. Above all, although the enriched CO2 can alleviate the damage induced by the UV-B radiation, the effects of experimental UV-B radiation were larger than the effects of actual UV-B radiation, the damage induced by the UV-B radiation was so severe, therefore, CO2 enrichment could not restore the ultrastructure to the control level.

Effects of UV-B radiation and different light repair conditions on the early development of the tetraspores of Chondrus ocellatus Holm

The effects of exposure to UV-B radiation, 280-315 nm, and dark or dark repair conditions on the early development of Chondrus ocellatus Holm collected from Qingdao coast were studied under the laboratory condition. After being exposed to different doses [0, 36, 72, 108, 144 and 180 J/（m2.d）] of UV-B radiation, one treatment of tetraspores were put back to normal culture condition （PAR）, the other treatment were put into dark condition to repair for 2 h. During the cultivation, the diameter of the tetraspores were recorded every 4 d till the 50th day when vertical branches formed in all treatments. Then at the 50th day, CPDs, phycoerythrin, chlorophyll a and MAAs （Palythine and asterina-330） were measured. The results showed that low doses UV-B radiation could significantly accelerate the growth rate of the rate reduced gradually with UV-B radiation keep on tetraspores of C. ocellatus and the growth increasing. The variation trend of both the phycoerythrin and chlorophyll a concentration reduced significantly （P 〈0.05） once given the UV- B radiation. Under UV-B stress, the CPDs were induced, and the concentrations of CPDs were significant low in dark repair groups. The data of MAAs analyzed by LC/MS in the tetraspores of C. ocellatus suggested that there were two MAAs formed （palythine and asterina-330） after UV-B radiation induced, and low dose of UV-B irradiation could significantly induced the concentration of MAAs. From the growth and development state of the tetraspores, negative effects of UV-B radiation on the dark repair groups were more serious than PAR.

Changes of proteins in the Antarctic ice microalga Chlamydomonas sp. cultured under UV-B radiation stress

Antarctic ice microalga Chlamydomonas sp. can thrive undisturbed under high UV radiation in the Antarctic ice layer. However, it is unknown that the initial adaptation mechanisms in protein level occurring in response to high UV radiation. Global-expression profiling of proteins in response to stress was analyzed by two-dimensional electrophoresis （2-DE） and image analysis. In the 2-DE analysis, protein preparation is the key step. Three different protein extract methods were compared, and the results showed that the trichloroacetic acid （TCA）-acetone fractional precipitation method was the fittest one. At the same time, the proteins in Chlamydomonas sp. were compared in 2-DE way, and the synthesis of seven protein spots was found disappeared and 18 decreased after exposed to UV-B radiation. In addition, 14 protein spots were enhanced or induced, among which two new peptides （20 and 21 kDa） appeared whose isoelectric point （pI） was 7.05 and 4.60 respectively. These changed proteins might act as key role in the acclimation of Antarctic ice microalga to UV-B radiation

Effects of UV-B Radiation and Water Stress on Soybean Yield

Soybean Dongnong 47 was subjected to the experiments of increasing UV-B radiation and water stress on soybean yield components in different growth periods. The results showed that 100-seed weight greatly increased during the early stage of pod filling in the treatment of weak UV-B radiation, seed number per plant as well as seed weight per plant and Dongnong47 yield also increased, while the yield and yield components of Dongnong47 during the blossom to mature period were negatively affected in the treatment of intensive UV-B radiation. 100-seed weight of Dongnong47 all increased in the double factor treatments of UV-B radiation and water stress, with the drought intensified, seed number per plant, seed weight per plant and yield of Dongnong47 decreased, the change of 100-seed weight were various and the antagonistic action of UV-B radiation and water stress were related with their intensity.

Effects of UV-B radiation intensity and timing on epidemiological components of wheat stripe rust

Stripe rust caused by Puccinia striiformis f. sp. tritici is an important wheat disease worldwide that is greatly influenced by environmental conditions. Ultraviolet B(UV-B) radiation is one important environmental factor affecting the occurrence and epidemiology of wheat stripe rust. Investigating UV-B radiation effects on the epidemiology of stripe rust may be conducive to monitoring and predicting this disease. In this study, wheat seedlings were exposed to UV-B radiation during different periods under laboratory conditions and radiation effects on epidemiological components of wheat stripe rust were investigated. Results showed that incubation period was shortened, and the infection efficiency, sporulation quantity and disease index increased when UV-B radiation was performed only pre-inoculation. When the UV-B radiation was performed only postinoculation or both pre-and post-inoculation, the incubation period was prolonged, and the infection efficiency, sporulation quantity and disease index were reduced. When healthy wheat seedlings were inoculated using urediospores collected from wheat leaves irradiated by UV-B only post-inoculation or both pre-and post-inoculation, infection efficiency, sporulation quantity and disease index were also reduced. However, in the latter, the disease incubation period did not differ under varying UV-B radiation intensities compared to that when wheat leaves were not treated with UV-B radiation. Overall, the effects of direct exposure of wheat plants to UV-B radiation with different intensities in different periods on epidemiological components of wheat stripe rust were systematically explored, and the results suggest that the effects of UV-B radiation increased gradually with the increase of UV-B radiation intensity. This information provides a basis for monitoring and predicting this disease as well as for conducting further studies on pathogen virulence variation.

UV-B irradiation and allelopathy by Sargassum thunbergii affects the activities of antioxidant enzymes and their isoenzymes in Corallina pilulifera

Intertidal macroalgae can cope with the dual effects of UV-B irradiation and allelopathy.To study the impacts of the two stressors,we co-cultured Corallina pilulifera with Sargassum thunbergii in 1:1 and 1:10 ratios under different doses of UV-B radiation.The response of the antioxidant defense system,focusing on activities of superoxide dismutase(SOD),ascorbate peroxidase(APX),peroxidase(POX)and glutathione reductase(GR),was monitored.In addition,isoenzyme patterns were analyzed using nondenaturing poly acry lamide gel electrophoresis.The results show that the activities of SOD,APX,and GR were all significantly affected by both UV-B radiation and allelopathy,and the effect of their interaction was significant.However,POX activity was only influenced by UV-B radiation.The enzymatic assay revealed four distinct bands of SOD.The SODⅢband weakened significantly when the co-cultures were exposed to extremely high dosage of UV-B irradiation under both co-culturing ratios of 1:1 and 1:10.When the coculturing ratio was 1:10,both POXⅡand APXⅡenzy me activities increased with different UV-B doses.GR activity was at its greatest when the co-culture ratio was 1:10 and exposure was to the higher UV-B doses.The activities of GRⅢand GRⅣwere elevated under all UV treatments whereas the activities of GRI and GRII were reduced under the lower UV-B treatments but were elevated under the higher UV-B treatments.However,lipid peroxidation,as indicated by the thiobarbituric acid-reacting substance(TBARS)assay,increased significantly under the dual stressors.Our data sugge st that allelopathy and UV-B radiation stre ss can each affect the antioxidant enzyme activities of C.pilulifera.Critically,the adverse effects of UV-B on C.pilulifera were intensified by the compounding effects of allelopathy.

Effect of UV-B radiation on the population dynamics of the rotifer Brachionus urceus

The effect of UV-B radiation enhancement at experimental doses of 0.00,0.24,0.48,0.72,0.96,and 1.20 kJ/m 2 on the population dynamics of the rotifer Brachionus urceus feeding on the alga Chlorella sp.was studied under controlled laboratory conditions using clonal culture and life-table techniques.The results show that UV-B radiation treatment significantly shortened the survival time of the rotifer （P 0.05）： The longest survival time （336 h） occurred in the control （0.00 kJ/m 2 ） while the shortest （222 h） occurred when exposed to the highest UV-B radiation treatment （1.20 kJ/m 2 ）.The fecundity of the rotifer B.urceus was enhanced by the lower UV-B radiation treatment （0.24 and 0.48 kJ/m 2 ） but inhibited by the higher treatments （0.96 and 1.20 kJ/m 2 ）.Life expectancy also was obviously affected by UV-B radiation （P 0.05）.The highest life expectancy occurred in the control （0.00 kJ/m 2 ）,and it became shorter with increasing doses of UV-B radiation.The resutls in the present study indicate that the life expectancy of the rotifer B.urceus can be used as an indicator for UV-B radiation enhancement.

Comparative analysis of the mass elevation effect and its implication for the treeline between the Tibetan and Bolivian plateaus based on solar radiation

As one of the main non-zonal factors,the mass elevation effect(MEE)has significant impacts on both regional climates and mountain ecological patterns.In recent years,with the development of quantitative techniques and methods,quantitative studies on the MEE and its implication on mountain altitudinal belts have developed rapidly.However,some issues have not been solved yet,such as high errors in spatial temperature estimations and difficulties in the definition and extraction of intramountain base elevation.Moreover,there is still a lack of comparative studies on the MEE and its influence on treelines and snowlines as most studies were conducted on specific mountains or plateaus.To compare the MEE magnitudes of the Tibetan Plateau(TP)and the Bolivian Plateau(BP),we estimated the correspondent air temperatures and simulated the solar radiations based on MODIS surface temperature,station observation,and treeline data.Then,we analyzed the elevation of the 10℃isotherms on the two plateaus,the temperatures at the same elevation,and the solar radiations.According to the mechanism of the MEE and the relationship of solar radiation and treeline,we constructed treeline models for the two plateaus through a stepwise regression analysis by considering several influencing factors of the MEE(e.g.,air temperature and precipitation)and using solar radiation as its proxy.The results showed that:(1)the MEE magnitude on the TP is equivalent to that on the BP although the former is slightly higher than the latter;(2)the MEE strongly influences the highest treelines in the northern and southern hemispheres,which both occur on the two plateaus.Notably,the treeline distribution models based on solar radiation had higher accuracies than those models with parameters of temperature and precipitation(the adjusted R^(2) values were 0.76 for the TP and 0.936 for the BP),indicating that solar radiation can be used to quantify the MEE and its implications on treelines.Overall,the results of this study can serve as a basis for subsequent analyses on the MEE’s impact factors.

Comparative Analysis of Photosynthetic Activity and PSII Protein Profiles of Some Plants Grown under Enhanced Solar UV-B Radiation

The deleterious effects of ultraviolet B(UV-B)radiation on photosynthesis and photosynthetic proteins of tropical and temperate plants have been studied.Like tropical plants(black gram and green gram),the temperate plants(carrot and radish)also successfully grown in the tropical region.They were exposed to enhanced UV-B radiation under field condition.Comparative studies show that under enhanced UV-B radiation photosynthetic activity was increased in black gram.In green gram and radish the UV-B radiation slightly enhanced the photosynthetic activity,but it inhibited the photosynthetic activity in carrot.The comparative results showed changes in contents of thylakoid 55,47,43,33,29,27-25,23 and 17 kDa polypeptides that were significantly lowered in UV-B treated carrot plant when compared to other plants.The PSII protein profile results showed a strong correlation between the presence of a membrane polypeptide and photosynthetic activity.In black gram and green gram the UV-B radiation did not produce any significant difference in the PSII polypeptides.As in the case of radish the UV-B radiation increased the accumulation of 33-28 kDa protein and affected expression of the 63 kDa protein.In the case of carrot,severe degradation of 32 kDa and 33 kDa,corresponding to D1 and D2 core proteins of PSII,was observed.It could be concluded that the ability of plants to tolerate increased levels of UV-B radiation,relative to photosynthetic capacity,depends on acclimation processes of the plant in the growing region.

Different Doses of the Enhanced UV-B Radiation Effects on Wheat Somatic Cell Division

Being sessile, plants are continuously exposed to DNA-damaging agents presenting in the environment such as ultraviolet (UV). Sunlight acts as an energy source for photosynthetic plants;hence, avoidance of UV radiations (namely, UV-A, 315 - 400 nm;UV-B, 280 - 315 nm;and UV-C, 1 group: 4.05 kJ&#8226m-2&#8226d-1, B2 group: 10.08 kJ&#8226m-2&#8226d-1, B3 group: 7.05 kJ&#8226m-2&#8226d-1, B4 group: 23.02 kJ&#8226m-2&#8226d-1) treatment wheat, then, explored on the growth of wheat root and wheat root tip cell of chromosome aberration effect. In wheat, root-tip cells were observed with confocal laser scanning microscopy (CLSM), the results showed that low doses of B1 group (4.05 kJ&#8226m-2&#8226d-1) promoted the growth of wheat root and cell mitosis frequency. But high dose of B2 group (10.08 kJ&#8226m-2&#8226d-1), B3 group (17.05 kJ&#8226m-2&#8226d-1), B4 group (23.02 kJ&#8226m-2&#8226d-1) inhibited the growth of wheat root tip, and made crooked growth of wheat root, and inhibited the wheat root tip cell mitotic frequency and processed that induce root tip cells of wheat produce all kinds of aberration of chromosome in the interphase containing “multiple nucleoli nuclei”, “incomplete nuclei”, “long round nuclei”, “bean sprouts nucleus”. In mitosis M period contains “dissociative chromosome”, “chromosome bridge”, “adhesion chromosome”, “multi-bundle divide”, “nuclear anomalies”. After, high doses of enhanced UV-B radiation treatment, most of the cell cycle anomaly concentrated in mitosis interphase. In mitosis M period, with UV-B radiation dose enhanced chromosome aberration rate was on the rise and the aberration types also increasing.

Effect of Rare Earths on Plants under Supplementary Ultraviolet-B Radiation: Ⅱ. Effect of Cerium on Antioxidant Defense System in Rape Seedlings under Supplementary Ultraviolet-B Radiation

Effects of cerium （Ce^3＋ ） on membranous protective enzymes in rape seedlings exposed to two levels of enhanced uhraviolet-B radiation （UV-B, 280 - 320 nm） were studied by hydroponics in the laboratory. The results show that the chlorophyll content decreases and membrane permeability increases in the leaves under UV-B irradiation with an intensity of 0.15 and 0.35 W·m^-2. The activities of SOD, CAT and POD are first increased and then decreased in leaves exposed to a low level of UV-B radiation. POD activity in leaves exposed to a high level of UV-B radiation is enhanced constantly. The sensitivities of these enzymes to UV-B radiation are SOD 〉 CAT 〉 POD. The injury by UV-B radiation on the functions of protective enzymes is lightened, their ability to scavenge radicals is improved, and the membrane permeability is maintained by Ce. Furthermore, the protective effect of cerium is more obvious in plants exposed to low levels of UV-B radiation than to high levels of it. Accordingly, all results prove that the protective effect of Ce on plants under UV-B radiation is realized through the protective system of plants.

Responses of antioxidant enzyme and photosynthesis in rape seedling to the combined stresses of acid rain and ultraviolet-B radiation

Effects of the simulated acid rain（AR） and ultraviolet-B（UV-B, 280-320 nm） radiation with a single or two ways simultaneously （AR ＋ UV-B） on the antioxidant enzyme and photosynthesis of the rape seedlings were investigated by the hydroponic culture. The results of static experiment indicated that the tolerance of rape seedling to single stress（AR or UV-B） is stronger than that to dual stresses（AR ＋ UV-B）. Furthermore, the dual stresses had additive effect on catalase activity, and a synergistic effect on MDA content, net photosynthesis rate, water use efficiency as well as intercellular CO2 concentration. Meanwhile, it has an independent effect on chlorophyll content, stomatal conductance, and transpiration rate as well as membrane permeability. During 64 h restoration course, the dynamic change in the curves of physiological and biochemical indices were not identical, and none of them show a simple linear variation. According to the static and dynamic experiments, it was found that a responsive sequence of catalase activity, membrane permeability, MDA content and photosynthetic characteristics to the above-mentioned stresses was as follows： AR ＋ UV-B 〉 UV-B 〉 AR.

Deriving the slope-mean shielded astronomical solar radiation spectrum and slope-mean possible sunshine duration spectrum over the Loess Plateau

Solar radiation is often shielded by terrain relief, especially in mountainous areas, before reaching the surface of the Earth. The objective of this paper is to study the spatial structures of the shielded astronomical solar radiation(SASR) and the possible sunshine duration(PSD) over the Loess Plateau. To this end, we chose six test areas representing different landforms over the Loess Plateau and the software package of Matlab was used as the main computing platform. In each test area, 5-m-resolution digital elevation model established from 1:10,000 scale topographic maps was used to compute the corresponding slope, SASR and PSD. Then, we defined the concepts of the slope-mean SASR spectrum and the slope-mean PSD spectrum, and proposed a method to extract them from the computed slope, SASR and PSD over rectangular analysis windows. Using this method, we found both spectrums in a year or in a season for each of the four seasons in the six test areas. Each spectrum was found only when the area of the corresponding rectangular analysis window was greater than the corresponding stable area of the spectrum. The values of the two spectrums decreased when the slope increased.Furthermore, the values of the stable areas of the spectrums in a year or in a season were positively correlated with the variable coefficients of the slope or the profile curvature. The values of the stable areas of the two spectrums in a year or in a season may represent the minimum value of test areas for corresponding future research on the spatial structures of the SASR or PSD. All the findings herein suggest that the spatial structures of the PSD and the SASR are caused by the interactions between solar radiation and terrain relief and that the method for extracting either spectrum is effective for detecting their spatial structures. This study may deepen our understanding of the spatial structure of solar radiation and help us further explore the distribution of solar energy in mountainous regions.

Effects of cerium on growth and physiological mechanism in plants under enhanced ultraviolet-B radiation

Effect of cerium （Ce^3＋） on the growth, photosynthesis and antioxidant enzyme system in rape seedlings （Brassica juncea L.） exposed to two levels of UV-B radiation （T1： 0.15 W/m^2 and T2：0.35 W/m^2） was studied by hydroponics under laboratory conditions. After 5 d of UV-B treatment, the aboveground growth indices were obviously decreased by 13.2%-44. 1%（T1） and 21.4%-49.3% （T2）, compared to CK, and except active absorption area of roots, the belowground indices by 14.1%-35.6%（T1） and 20.3%-42.6% （T2）. For Ce＋UV-B treatments, the aboveground and belowground growth indices were decreased respectively by 4.1%-23.6%, 5.2% -23.3%（Ce＋T1） and 10.8%-28.4%, 7.0%-27.8%（Ce＋T2）, lower than those of UV-B treatments. The decrease of growth indices appeared to be the result of changes of physiological processes. Two levels of UV-B radiation induced the decrease in chlorophyll content, net photosynthesis rate, transpiration rate, stomatal conductance and water use efficiency by 11.2%-25.9%（T1） and 20.9%- 56.9%（T2）, whereas increase in membrane permeability and activities of antioxidant enzymes including superoxide dismutase（SOD）, catalase （CAT） and peroxidase （POD） by 6.9%, 22.8%, 21.5%, 9.5%（T1） and 36.6%, 122.3%, 103.5%, 208.9%（T2）, respectively. The reduction of the photosynthetic parameters in Ce＋UV-B treatments was lessened to 3.2%-13.8%（Ce＋T1） and 4.9%-27.6%（Ce＋T2）, and the increase of membrane permeability and activities of antioxidant enzymes except POD in the same treatments were lessened to 2.4%, 8.4%, 6.6%（Ce＋T1） and 30.1%, 116.7%, 75.4%（Ce＋T2）. These results indicate that the regulative effect of Ce on photosynthesis and antioxidant enzymatic function is the ecophysiological basis of alleviating the suppression of UV-B radiation on growth of seedlings. Furthermore, the protective effect of Ce on seedlings exposed to TI level of UV-B radiation is superior to T2 level.

Distributed modeling of direct solar radiation on rugged terrain of the Yellow River Basin

Due to the influences of local topographical factors and terrain inter-shielding, calculation of direct solar radiation （DSR） quantity of rugged terrain is very complex. Based on digital elevation model （DEM） data and meteorological observations, a distributed model for calculating DSR over rugged terrain is developed. This model gives an all-sided consideration on factors influencing th a resolution of 1 km × 1 km for thDSR. Using the developed model, normals of annual DSR quantity wie Yellow River Basin was generated, with DEM data as the general characterization of terrain. Characteristics of DSR quantity influenced by geographic and topographic factors over rugged terrain were analyzed thoroughly. Results suggest that： influenced by local topographic factors, i.e. azimuth, slope and so on, and annual DSR quantity over mountainous area has a clear spatial difference; annual DSR quantity of sunny slope （or southern slope） of mountains is obviously larger than that of shady slope （or northern slope）. The calculated DSR quantity of the Yellow River Basin is provided in the same way as other kinds of spatial information and can be employed as basic geographic data for relevant studies as well.