Elevated UV-B radiation modifies the extractability of carbohydrates from leaf litter of Quercus robur

We examined the influence of elevated UV-B radiation on the extractability of carbohydrates from leaf litter of Quercus robur. Saplings were exposed to a 30% elevation above the ambient level of erythemally weighted UV-B (280-315 nm) radiation for eight months at an outdoor facility. UV-B radiation was applied under arrays of fluorescent lamps filtered with cellulose diacetate, which transmitted both UV-B and UV-A (315-400 nm) radiation. Saplings were also exposed to elevated UV-A radiation under arrays of polyester-filtered lamps and to ambient radiation under arrays of non-energised lamps. Abscised leaves were collected, ground and sequentially treated with seven solvents in order to fractionate extractable carbohydrates based on the way in which they are held in the cell wall. Elevated UV-B radiation reduced the extractability of carbohydrates from cell walls of Q. robur. Sodium phosphate buffer at pH 7 extracted 10% less total carbohydrate from leaf material exposed during growth to elevated UV-B radiation under cellulose diacetate-filtered lamps than from leaf material grown under polyester-filtered and non-energised lamps. The cumulative amount of carbohydrate released by sequential extraction with phosphate buffer, CDTA, urea and sodium carbonate was between 5.1% and 7.8% lower from leaf material grown under cellulose diacetate-filtered lamps relative to that from leaves grown under non-energised lamps. Abscised leaves were also digested with Driselase, an enzyme mixture extracted from a basidiomycete fungus. No effects of elevated UV radiation were recorded on the amount of carbohydrate released by Driselase digestion. Regression analyses, using data from a previous field decomposition study, suggested that reduced availability of carbohydrates enhanced the colonisation of Q. robur litter by basidiomycete fungi, which then accelerated the decomposition rate of the litter in soil. We recommend that future studies into the effects of UV-B radiation on plant litter decomposition measure not only the concentrations of chemical constituents of litter, but also determine the availability of litter carbon sources to soil microbes, using methods similar to those used here.     

Selenium treatment alters the effects of UV radiation on chemical and production parameters in hybrid buckwheat

Ambient UV radiation is recognised as an important environmental factor in the regulation of plant growth and development, and selenium (Se) as a beneficial nutrient that can increase plant tolerance to different environmental constraints. The effects on hybrid buckwheat plants of full (+UV) and reduced (?UV) ambient UV radiation without (?Se) and with (+Se) foliar Se treatment (10?mg?L^?1 sodium selenate) provided the four conditions of Se?UV–, Se–+UV, +Se?UV and +Se+UV. Plant morphological, biochemical and physiological properties were examined, along with leaf elemental composition and content, efficiency of Se enrichment, and production parameters. Leaf anatomical parameters under all conditions were mainly affected by UV radiation, and less so by Se. +Se+UV plants showed a trade-off between primary and secondary metabolism, which resulted in high levels of protective substances (e.g. anthocyanins, UV absorbing compounds), and low levels of photosynthetic pigments. All +UV plants were significantly shorter in comparison to those under the reduced ?UV, while biomass production was highest for ?Se+UV plants and lowest for +Se+UV plants. +Se plants accumulated ～20-fold greater Se content compared to ?Se plants, and full ambient UV radiation partly reduced this effect. +UV plants showed increased phosphorus content in leaves, independent of Se status, while +Se plants showed increased K content. Si content was increased by Se treatment and decreased by the full UV exposure. Se treatment and the ambient UV radiation, separately have positive effects on growth and production of this hybrid buckwheat, while the combination of the Se treatment and ambient UV resulted in lower yields. However, under these conditions (+Se+UV), the buckwheat plants established good protection against the different environmental constraints that are becoming more and more frequent due to changes to our climate.     

Effects of UV-B filtration on the chemistry and decomposition of Fraxinus excelsior leaves

Several studies have demonstrated a range of effects of outdoor UV-B supplementation during the growing season on leaf chemistry including carbohydrate extractability and on the subsequent decomposition of leaf litter. However, this study investigates the effects of several levels of UV radiation on leaf carbohydrate chemistry and subsequent decomposition using filtration of ambient sunlight. Fraxinus excelsior seedlings were grown outdoors in the UK under ambient solar irradiation and under filtration treatments which excluded either UV-B or both UV-A and UV-B. After one year of decomposition in the litter layer of a mixed semi-natural woodland, the loss of dry mass was 10% greater, relative to starting mass, in the leaves which had received no UV at all or no UV-B throughout the growing season (P < 0.05). Analysis of the cell wall material before decomposition revealed no significant trends in total carbohydrate and lignin content with UV exclusions, no change in foliar nitrogen and C-to-N ratio and a 2% increase in foliar carbon (P < 0.05) only with the combined exclusion of UV-A and UV-B. A sequential extraction of carbohydrate with a series of extractants (phosphate buffer, ammonium oxalate, urea, sodium hydroxide and formic acid) showed no trends with UV exclusions but digestion with the fungal enzyme mixture Driselase revealed that exclusion of UV-B only caused rhamnose and mannose residues of the cell-wall polysaccharides to resist Driselase digestion whist exclusion of all UV had the opposite effect. Whereas some studies have reported that elevated UV-B radiation from lamp supplementation can increase rates of subsequent leaf decomposition, the higher UV-B levels in the ambient controls of this filtration study resulted in 29% lower decomposition rates than the filtered-UV treatments.     

紫花苜蓿、黑麦草和狼尾草对Cu、Pb复合污染土壤修复能力的研究

随着经济和社会的发展,土壤重金属污染对粮食安全及人类的身体健康构成了巨大的威胁,而目前对于土壤重金属污染的治理主要以植物修复为主。为了寻找适宜修复Cu、Pb复合污染土壤的牧草,采用盆栽试验法,将试验的植物设置9组处理:1组对照组(CK),不添加任何重金属盐;4组单一污染,即单一Cu低(Cu1,200 mg×kg-1)、高浓度(Cu2 400 mg×kg-1),单一Pb低(Pb1 300 mg×kg-1)、高浓度(Pb2 800 mg×kg-1);4组Cu、Pb复合污染(Cu1Pb1、Cu1Pb2、Cu2Pb1、Cu_2Pb_2)。通过比较紫花苜蓿(Medicago sativa)、黑麦草(Lolium perenne)、狼尾草(Pennisetum alopecuroides)的适应能力和富集特征,研究了这3种常见牧草植物对受Cu、Pb复合污染土壤的修复效果。结果表明:1)紫花苜蓿地上部和根部生物量均在Pb1处理组时最大,显著高于其他处理组;黑麦草地上部生物量在Cu1Pb1处理组最大,根部生物量在Pb1处理组最大;狼尾草地上部生物量在Cu_2Pb_2处理组最大,根部生物量在Cu2处理组最大。2)Cu单一污染下,狼尾草抗性系数最大;Pb单一污染下,紫花苜蓿抗性系数最大;Cu-Pb复合污染下,狼尾草的抗性系数较大。高浓度Cu处理组3种牧草植物的地上部生物量、根部生物量和抗性系数均呈现:狼尾草黑麦草紫花苜蓿,且狼尾草显著大于黑麦草和紫花苜蓿。3)种植3种牧草植物后,土壤重金属Cu、Pb含量均有所降低。在一定浓度下,土壤Cu-Pb重金属间会相互促进对方在牧草植物中的吸收。4)3种牧草中紫花苜蓿地上部对Cu的富集系数在Cu_2Pb_2处理组最大,达1.61;黑麦草根部对Cu的富集系数在Cu_2Pb_2处理组最大,达3.80;3种牧草地上部和根部对Pb的富集系数只在黑麦草根部的Cu1Pb1处理组时大于1,达1.46。5)黑麦草对Pb的吸收能力较强,且主要积累在根系;紫花苜蓿对Cu-Pb复合污染综合修复效果最好。紫花苜蓿和黑麦草分别在Cu-Pb复合污染和Pb单一污染土壤中对Pb的转运系数大于1,分别为2.72和2.06,反映其对土壤中的Pb具有富集潜力。综合表明,黑麦草对重金属Pb具有较强的耐性,在Pb单一污染土壤的植物修复及尾矿废弃地的植被重建中,可优先作为选择的材料;紫花苜蓿对重金属Cu、Pb均具有较强的耐性,在重金属Cu单一或Cu-Pb复合污染土壤的植物修复及尾矿废弃地的植被重建中,可优先作为选择的材料。     

Yield and N assimilation of winter wheat (Triticum aestivum L., var. Norstar) inoculated with rhizobacteria

The effects of bacterial inoculants on the growth of winter wheat were studied in a growth chamber. Azospirillum brasilense, Azotobacter chroococcum, Bacillus polymyxa, Enterobacter cloacae, or a mixture of the four rhizobacteria were the inoculants tested. Inoculation effects on yield, yield components, and N-derived from fertilizer (Ndff) were assessed. The response of plants inoculated with individual bacteria was inconsistent and varied with treatment. At the first harvest (58 days after planting-DAP) plants inoculated with the mixture exhibited increases in plant dry weight, total-N and Ndff. At the second harvest (105 DAP), plants inoculated with A. brasilense and the mixture exhibited increases in shoot biomass, whereas at maturity (170 DAP), the inoculated plants showed no differences in total-N or shoot dry matter yield, as compared to the uninoculated controls. Inoculation with A. brasilense, however, increased the Ndff in the shoots, and B. polymyxa tended to enhance grain yield. Practical use of these rhizobacteria as inoculants for winter wheat may have limited value until such time as we better understand factors which influence rhizosphere competence of bacterial inoculants.     

大田条件下模拟UV-B辐射滤减对水稻生长及内源激素含量的影响

对大田栽培条件下人工模拟的UV-B辐射滤减环境对晚稻品种“协优432”的叶绿素含量、株高、内源激素吲哚乙酸(IAA)、脱落酸(ABA)、赤霉素(GA3)、玉米素(Zeatin)含量的影响研究结果表明,在正常日光处理组与UV-A滤光组之间叶绿素a含量变化显著;正常日光处理组与UV-A滤光组、UV-A UV-B滤光组之间株高无明显变化。UV-A UV-B滤光组IAA、GA3、Zeatin含量分别比正常日光处理组降低了40.42%、48.60%、36.21%;分别比UV-A滤光处理组降低了36.52%、70.94%、54.54%。单因素方差分析及多重比较结果显示,UV-A UV-B滤光组与正常日光处理组之间IAA、GA3含量差异显著;UV-A UV-B滤光组与UV-A滤光处理组之间GA3、Zeatin含量差异显著。UV-A UV-B滤光组ABA含量比正常日光处理组降低了29.74%,比UV-A滤光处理组降低了5.19%,经单因素方差分析后发现差异不显著。     

紫茎泽兰和黄顶菊入侵对土壤微生物群落结构和旱稻生长的影响

为比较入侵植物与本地植物对土壤微生态影响的差异, 探索外来植物入侵的土壤微生物学机制, 本研究通过同质园试验, 比较分析了2种入侵菊科植物(紫茎泽兰、黄顶菊)和2种本地植物(马唐、猪毛菜)对土壤肥力和微生物群落的影响, 并通过盆栽反馈试验验证入侵植物改变后的土壤微生物对本地植物旱稻生长的反馈作用。同质园试验结果表明: 2种入侵植物和2种本地植物分别对土壤微生态产生了不同的影响, 尤其是紫茎泽兰显著提高了土壤有效氮、有效磷和有效钾含量,紫茎泽兰根际土壤中有效氮含量为39.80 mg·kg^-1,有效磷含量为48.52 mg·kg^-1。磷脂脂肪酸指纹图谱结果表明, 2种入侵植物与2种本地植物相比, 较显著增加了土壤中放线菌数量, 而紫茎泽兰比其他3种植物显著增加了细菌和真菌数量。盆栽结果表明: 黄顶菊生长过的土壤灭菌后比灭菌前旱稻株高增加113%, 紫茎泽兰也使旱稻的株高增加17%。由以上结果可知, 紫茎泽兰和黄顶菊可能通过改变入侵地土壤的微环境, 形成利于其自身生长扩散的微生态环境从而实现其成功入侵。     

UV-B辐射增强对大麦生理生态的影响

在大田条件下,研究了UV-B辐射增强对大麦的生长发育、光合作用、蒸腾作用及其产量构成的影响。结果表明,UV-B辐射增强明显抑制大麦生长,使株高变矮、绿叶数减少、叶面积和干物质量下降,但抑制程度随生育期而异。在UV-B辐射增强条件下,大麦叶片叶绿素含量、净光合速率、气孔导度和蒸腾速率都有不同程度的降低,水分利用率也随之降低。UV-B辐射增强对大麦形态学和生理学上的不利影响,导致了大麦产量下降24.96%。     

Direct and indirect effects of ultraviolet-B radiation on soil biota, decomposition and nutrient fluxes in dune grassland soil systems

 Enhanced UV radiation did not show any effect on the decomposition of a mixed litter of the dune grassland plant species Calamagrostis epigeios and Carex arenaria. Also, leaching of nutrients from lysimeters filled with dune grassland soils was not affected by enhanced UV radiation. Negative UV effects on the fungal biomass in the first part of the experiment were later reversed into positive ones. Clear effects of both UV-A and UV-B were found on Collembola, both on total number of individuals and on the number of species. The decreased number of species under UV radiation could have been due to a decrease in UV-sensitive species. The role of pigmentation is discussed. Received: 6 July 1999     

Deterioration of rhizospheric soil health due to elevated ultraviolet-B

Enhancements in ultraviolet-B radiation (UV-B) due to stratospheric ozone depletion affect biological forms directly and indirectly. To investigate how belowground processes are affected under increased UV-B, a field experiment with mung bean cultivars (HUM-1 and HUM-12) was conducted. The responses of selected soil enzymes (β-glucosidase, cellobiohydrolase, polyphenol oxidase, glycine aminopeptidase, and phosphatase), microbial biomass C and N were assessed in rhizospheric and non-rhizospheric zones, along with measurements of phenol and flavanoid contents in roots and leaves. Test plants were exposed to two UV-B levels: (1) UVB, simulating 20% stratospheric O₃ depletion; and (2) UV0, the ambient UV-B. Elevated UV-B depressed shoot biomass by 24.8 and 15.9% and root biomass by 43.7 and 38.4% in cv. HUM-1 and HUM-12 compared with UV0. Although elevated UV-B caused an increase in phenol and flavonoid contents in leaves and roots, a reduction in the number of root nodules (32.4 and 24% in HUM-1 and HUM-2, respectively) and their fresh weight (27 and 23% in HUM-1 and HUM-2, respectively) was observed. Elevated UV-B caused microbial activity to shift from the rhizosphere to non-rhizosphere as indicated by increased microbial biomass N and soil enzyme activities in this zone.     

狗牙根与空心莲对水库消落带土壤氮磷释放影响的模拟

通过水库水位涨落室内模拟试验,探究丹江口库区消落带优势物种狗牙根和空心莲2种草本植物对土壤氮磷释放过程影响。结果表明:(1)水淹结束后(32天),空心莲子草土壤TN、TP分别降低11.75%,25.28%,狗牙根分别降低3.62%,25.77%。(2)干湿交替环境主要影响土壤中NH_4~+-N、NO_3~--N和AP的含量的变化,对土壤中的TN、TP含量的影响较小。(3)狗牙根的死亡增加土壤TN、NH_4~+-N、TP量,即不耐淹植被过滤带虽然能净化径流中N、P等污染物,但截留的污染物和植物吸收的养分随着植物体的分解再次进入水体或土壤,无法达到有效防控农业面源污染的目的。该研究为丹江口水库利用植被缓冲带防控水体富营养化提供一定理论依据。     

Effect of Elevated Ultraviolet-B Radiation on Microbial Biomass Carbon and Nitrogen in Barley Rhizosphere Soil

As one of the important problems in global change, elevated ultraviolet-B (UV-B) radiation induced by the depletion of stratospheric ozone layer has received more and more attentions around the world. Field experiment with barley was conducted to investigate the effects of elevated UV-B radiation on microbial biomass carbon and nitrogen in rhizosphere and nonrhizosphere soil. The experiment was designed with two UV-B radiation levels, i.e., elevated (E, simulating 25% stratospheric ozone depletion) and ambient (A, control), and performed at the Station of Agricultural Meteorology, Nanjing University of Information Science and Technology, Nanjing, China. Compared with the control, elevated UV-B radiation significantly depressed shoot biomass by 13.2?C42.6% and root biomass by approximately 50% from jointing to ripening stage. Elevated UV-B radiation significantly increased microbial biomass C and N in nonrhizosphere soil in most cases, but significantly decreased microbial biomass C and N in rhizosphere soil. Further researches are needed to elucidate whether the above findings are connected with the changes in composition and amount of root exudates induced by elevated UV-B radiation, which can mainly affect the dynamics of soil microbial biomass.     

Responses in Some Growth and Mineral Elements of Mono Maple Seedlings to Enhanced Ultraviolet-B and to Nitrogen Supply

The effects of enhanced ultraviolet-B (UV-B) and nitrogen supply on the growth and mineral elements of mono maple (Acer mono Maxim) seedlings were studied in open semi-field conditions. Mono maple is a common species in reforestation processes in the southeast of the Qinhai-Tibetan Plateau of China. The experimental design included two levels of UV-B treatments (ambient UV-B, 11.02 KJ/m²/day; enhanced UV-B, 14.33 KJ/m²/day) and two nitrogen levels (0; 20 g N/m²/a). No visible symptoms of nutrient deficiency were observed in seedlings grown under enhanced UV-B radiation during the experiment. However, there was visible damage of enhanced UV-B radiation on leaves. Enhanced UV-B significantly reduced plant height and biomass of plants, and changed biomass allocation between organs under supplemental nitrogen supply, which lead to a decrease in root/shoot ratio. On the other hand, nitrogen supply significantly increased plant height and biomass under ambient UV-B, whereas it reduced root mass and root weight ratio, and increased stem mass and stem weight ratio under enhanced UV-B. In addition, enhanced UV-B radiation and nitrogen supply significantly affected the concentration and allocation of most nutrients in various organs, and nitrogen supply could changed the effects of enhanced UV-B on mineral element in plant parts to some extent, which may have significant impacts on nutrient cycling and may lead to the disorder of nutrient balanced and influence the growth of plants.     

胶质芽孢杆菌与苜蓿根瘤菌双接种对排土场紫花苜蓿生长和土壤性质的影响

为了明确胶质芽孢杆菌和苜蓿根瘤菌在矿区排土场复垦中的协同作用,以矿区排土场土壤作为基质进行盆栽试验,设置两菌单接种处理、双接种处理及对照,其中胶质芽孢杆菌和苜蓿根瘤菌用量分别为1.50%和0.25%,测定紫花苜蓿产量指标、叶片生理指标、土壤速效养分含量和土壤微生物指标。结果表明,接种胶质芽孢杆菌和苜蓿根瘤菌的各处理均能显著提高紫花苜蓿的产量指标,其中以双接种处理效果最优,将生物量和结瘤量分别比对照显著提高110.27%和124.32%;在生理指标方面,双接种处理效果低于单接种处理,未表现出协同作用;在土壤养分和微生物性质方面,单接种胶质芽孢杆菌仅显著提高土壤速效钾含量,单接种苜蓿根瘤菌对大部分指标均有显著效果,而双接种处理效果最佳,土壤碱解氮、速效钾含量比对照分别显著提高94.14%和84.55%,土壤微生物指标MBC含量、呼吸强度、蔗糖酶、脲酶、磷酸酶、过氧化氢酶活性比对照分别显著提高204.02%,65.86%,212.32%,91.87%,30.57%,51.87%。双接种处理对紫花苜蓿产量指标、养分和微生物指标表现出显著的协同作用。因此,1.50%用量胶质芽孢杆菌和0.25%用量苜蓿根瘤菌双接种能够有效提高排土场土壤的复垦效果,具有协同作用,可以作为矿区排土场复垦的高效方法。     

Responses of co-occurring populations of Dendrobaena octaedra (Lumbricidae) and Cognettia sphagnetorum (Enchytraeidae) to soil pH, moisture and resource addition

Dendrobaena octaedra (Lumbricidae) and Cognettia sphagnetorum (Enchytraeidae) are the two most dominating soil invertebrates in terms of biomass in boreal coniferous forest soils. A microcosm experiment was set up in order to study the influence of pH, moisture and resource addition on D. octaedra and C. sphagnetorum when both species are simultaneously present. Two kinds of coniferous forest humus were used as substrate, pine stand humus (pH 4.2), and spruce stand humus (pH 4.6); in the third treatment the pine stand humus was adjusted with slaked lime (CaOH₂) to the same initial pH as the spruce stand humus. Each substrate was adjusted to water contents of 25%, 42.5% and 60% of WHC (referred to as ‘dry’, ‘moist’ and ‘wet’). In the second part of the experiment, spruce needle litter and birch leaf litter were separately added into the pine stand humus (‘moist’, unlimed) and compared with a control without litter. The microcosms were plastic jars with 75 g (d.m.) of humus, into which 4 specimens of D. octaedra and 70 specimens of C. sphagnetorum were added. D. octaedra showed the highest biomass and C. sphagnetorum the lowest biomass in the spruce stand humus with higher pH. Moisture did not affect earthworms, while C. sphagnetorum thrived best at the highest moisture. Addition of both kinds of litter increased the numbers and biomass of D. octaedra, while on C. sphagnetorum resource addition had little effect. The results help to explain the abundance of these two species in coniferous forests differing in soil acidity, moisture and fertility.     

Defoliation effects on Plantago lanceolata resource allocation and soil decomposers in relation to AM symbiosis and fertilization

Plants can mediate interactions between aboveground herbivores and belowground decomposers as both groups depend on plant-provided organic carbon. Most vascular plants also form symbiosis with arbuscular mycorrhizal fungi (AMF), which compete for plant carbon too. Our aim was to reveal how defoliation (trimming of plant leaves twice to 6 cm above the soil surface) and mycorrhizal infection (inoculation of the fungus Glomus claroideum BEG31), in nutrient poor and fertilized conditions, affect plant growth and resource allocation. We also tested how these effects can influence the abundance of microbial-feeding animals and nitrogen availability in the soil. We established a 12-wk microcosm study of Plantago lanceolata plants growing in autoclaved soil, into which we constructed a simplified microfood-web including saprotrophic bacteria and fungi and their nematode feeders. We found that fertilization, defoliation and inoculation of the mycorrhizal fungus all decreased P. lanceolata root growth and that fertilization increased leaf production. Plant inflorescence growth was decreased by defoliation and increased by fertilization and AMF inoculation. These results suggest a negative influence of the treatments on P. lanceolata belowground biomass allocation. Of the soil organisms, AMF root colonization decreased with fertilization and increased with defoliation. Fertilization decreased numbers of bacterial-feeding nematodes, probably because fertilized plants produced less root mass. On the other hand, bacterial feeders were more abundant when associated with defoliated than non-defoliated plants despite defoliated plants having less root mass. The AMF inoculation per se increased the abundance of fungal feeders, but the reduced and increased root AM colonization rates of fertilized and defoliated plants, respectively, were not reflected in the numbers of fungal feeders. We found no evidence of plant-mediated effects of the AM fungus on bacterial feeders, and against our prediction, soil inorganic nitrogen concentrations were not positively associated with the concomitant abundances of microbial-feeding animals. Altogether, our results suggest that (1) while defoliation, fertilization and AMF inoculation all affect plant resource allocation, (2) they do not greatly interact with each other. Moreover, it appears that (3) while changes in plant resource allocation due to fertilization and defoliation can influence numbers of bacterial feeders in the soil, (4) these effects may not significantly alter mineral N concentrations in the soil.     

土壤微生物对紫茎泽兰生长与竞争的反馈: 不同灭菌方法的比较

土壤微生物去除是验证土壤微生物反馈调节入侵植物竞争排斥本地植物群落的重要手段。为了确定土壤微生物反馈效应的最佳土壤微生物去除方法,以及土壤微生物对紫茎泽兰与本地植物竞争中的反馈作用,本试验比较了添加蛭石和未添加蛭石下,3种常见土壤微生物灭菌方式(干热灭菌、湿热灭菌、辐照灭菌)处理的紫茎泽兰单优群落根际土壤对紫茎泽兰与本地植物香茶菜生长的影响。结果表明:与未灭菌处理土壤相比,3种灭菌处理土壤均显著抑制了紫茎泽兰和香茶菜的生长;添加蛭石灭菌的土壤相对于未添加蛭石的灭菌土壤显著促进了2种植物的生长;灭菌土壤添加蛭石的情况下辐照灭菌土壤的两种植物的生物量显著地高于干热灭菌和湿热灭菌土壤两种植物的生物量,其中辐照灭菌下紫茎泽兰的生物量分别比干热灭菌和湿热灭菌条件下增加30.8%和66.5%,香茶菜生物量分别显著增加109.5%和63.4%。辐照灭菌土壤添加蛭石的处理方式最接近真实地反映土壤微生物对植物生长的反馈效应。进一步进行辐照灭菌土壤添加蛭石处理与未灭菌土壤添加蛭石处理的紫茎泽兰与香茶菜混种的盆栽试验,结果显示,土壤微生物显著增强了紫茎泽兰对香茶菜的竞争优势,相对竞争优势度增加16.0%,说明土壤微生物在紫茎泽兰竞争排斥本地植物的入侵过程中具有正反馈偏利调节作用     

Response of three eastern tree species to supplemental UV-B radiation: leaf chemistry and gas exchange

Quantitative changes in foliar chemistry in response to UV-B radiation are frequently reported but less is known about the qualitative changes in putative UV-screening compounds. It has also not been conclusively shown whether qualitative differences in screening compounds or differences in localization patterns influence the sensitivity of plants to damage from UV-B radiation and there is some question as to whether differences in the amounts of soluble screening compounds correlate with physiological sensitivity to UV-B radiation. This study represents the first part of a multiple-year study designed to answer the above questions. In this study we evaluated whether differences in soluble UV-screening compounds were linked with possible effects on gas exchange and photosynthetic carbon assimilation. Branches of mature trees of sweet gum (Liquidambar styraciflua), tulip poplar (Liriodendron tulipifera) and red maple (Acer rubrum) were exposed to supplemental levels of UV-B radiation over three growing seasons. Controls for UV-A were also measured by exposing branches to supplemental UV-A only and additional branches not irradiated were also used for controls. These species demonstrated differing levels of screening compounds with poplar being the most responsive in terms of epidermal accumulation of phenolics. These were separately identified as flavonols, chlorogenic acid and hydroxycinnamates (HCAs). Red maple had the highest levels of constitutive UV-absorbing compounds but these showed little response to supplemental UV-B radiation. Leaf area was marginally influenced by UV exposure level with both UV-A and UV-B tending to reduce leaf area in red maple and poplar and increase it in sweet gum, when averaged over the 3-year period. Assimilation was generally not reduced by UV-B radiation in these species and was enhanced in red maple by both UV-B and UV-A and by UV-A in sweet gum. These findings are consistent with a hypothesis that epidermal attenuation of UV-B would only be reduced in poplar, which accumulated the additional epidermal screening compounds. It is possible that photosynthetic efficiency was enhanced in red maple by the increased absorption of blue light within the mesophyll due to elevated levels of HCAs. Stomatal conductance was generally reduced and this led to an increase in water use efficiency (WUE) in red maple and poplar. Since few detrimental effects of supplemental UV-B were observed, these results suggest that these tree species utilized a range of UV-screening compounds and deposition patterns to achieve UV-B tolerance and further, that subtle responses to UV-B could have ecological significance in the absence of reduced productivity or photosynthetic efficiency.     

UV-B辐射增强对不同品种大麦田土壤微生物量碳和土壤呼吸的影响

利用田间模拟UV-B辐射装置,从大麦分蘖期开始进行UV-B辐射增强处理,以后各主要生育期各选择一典型日分别观测作物根际、非根际土壤微生物量碳含量和土壤呼吸速率.UV-B辐射设对照(Ambient)和增强(Elevated,14.4kJ·m-2·d-1)两个水平,增强处理相当于南京地区4-5月自然光UV-B辐射量的120％.3个大麦品种分别为单2号、苏啤3号和苏啤4号.结果表明:3个品种中作物根际、非根际土壤微生物量碳含量均随生育进程表现出一致的规律,即分蘖、拔节、孕穗和抽穗期逐渐增加并达到最大值,成熟期则显著下降,UV-B辐射增强没有改变这种变化趋势;UV-B辐射增强后,各品种在多数生育时期观测的根际与非根际土壤微生物量碳含量显著低于对照(自然光)(P＜0.05),而单2号和苏啤4号在孕穗期(4月23日)观测的非根际土壤微生物量碳含量却明显高于对照(P＜0.05);UV-B辐射增强条件下,单2号在孕穗期和成熟期、苏啤3号在抽穗期与成熟期观测的土壤呼吸速率显著低于对照(P＜0.05),其它阶段的差异不显著,各处理中土壤呼吸速率由分蘖到拔节、孕穗、抽穗期逐渐增加,抽穗期、成熟期逐渐下降的趋势没有改变;在UV-B辐射增强条件下,单2号和苏啤3号两个品种的Q10值显著低于对照(P＜0.05),苏啤4号的Q10值则显著增大,明显高于其它品种(P＜0.05).研究认为,不同大麦品种土壤微生物量碳和土壤呼吸速率对UV-B辐射增强的响应存在差异.     

施用外源物对尾矿土壤种植胡枝子修复效应初探

采用土培试验在两种尾矿土壤(废弃地和尾矿渣土)上种植耐性不同的两个胡枝子品种,通过添加客土、锯末,调控有机肥或无机肥等外源物,分析不同处理条件下胡枝子生物量、植株和土体内重金属含量,以明确外源物对尾矿土壤的修复效应。结果表明,二色胡枝子生物量整体上显著高于截叶胡枝子生物量;在所有处理中,废弃地上同时添加客土和有机无机肥的处理是二色胡枝子生物量最高的处理。外源肥料添加提高了两个品种地上部和根部的生物量,客土添加可能对改善立地生存的理化条件有较大帮助作用,更能体现出肥料的效果。两种土壤上添加客土或肥料,均较为显著地减少了截叶胡枝子根部和地上部重金属的吸收,而二色胡枝子效果不明显。两种土壤上添加外源物、种植不同品种胡枝子可以降低部分处理土壤中重金属含量,但通过植物种植直接摄取土壤中重金属的量是相对较少的。总之,客土添加、肥料施入均较为明显地改善了废弃地和尾矿渣土两类土壤的立地条件,增加了两种胡枝子的生物量,一定程度上限制了植物对重金属的吸收,土壤改良的基础上优先选择耐性品种是提高植物修复效果的上佳方案。