The impact of Gunnera tinctoria (Molina) Mirbel invasions on soil seed bank communities

Aims In recent years, there has been an increasing interest in the impact of invasive alien plant species on the soil seed bank. Soil seed banks play an important role in determining the composition and dynamics of the vegetation through time. Therefore, an ability to form a persistent seed bank and/or a capacity to alter the structure of the seed bank of invaded communities could be important factors in determining the success of many alien plant species. In this study, we report on a detailed assessment of the characteristics of the seed bank community associated with the herbaceous plant invader, Gunnera tinctoria, a newly emerging and potentially globally significant invasive plant species. This species, native to South America, is invasive in a range of wet habitats in Europe, Australasia and the USA.Methods A comprehensive assessment of the seed bank of invaded and comparable uninvaded areas was made at two points in time (May and October), at three sites in western Ireland. The seedling emergence approach was used to assess the structure (diversity, dominance and abundance) of the soil seed bank. Differences between invaded and uninvaded seed bank communities were investigated at the spatial scales of site, plot and depth.Important findings Gunnera tinctoria formed a large persistent seed bank at the study sites. Approximately 30-000 seedlings per square metre emerged from soils collected from invaded areas, of which 30% were found in deep soil layers. Seedlings of this invader represented 53–86% of the total number of seedlings associated with invaded areas. Both the transient and the more persistent component of the seed bank of invaded communities were significantly less diverse and abundant than those of uninvaded areas, and were characterized by higher dominance, even when seedlings of the invader were not included in the analysis. The seed bank of invaded areas was largely composed of seeds of agricultural weeds in addition to those of the invader. These results suggest that G. tinctoria has the capacity to profoundly alter the seed bank of invaded communities. These results have direct relevance for the development of control and management strategies, for this and other comparable invasive species, which should account for both quantitative and qualitative alterations in the seed bank community. Our study also suggests that control measures that result in disturbance of areas colonized by G. tinctoria could promote the germination of undesirable weeds.     

Growth,phenology and N-utilization by invasive populations of Gunnera tinctoria

智利大叶草(Gunnera tinctoria)是一种不同寻常的固氮植物,已入侵到了世界各地,通常入侵到低蒸发需求和/或高降雨的环境。 在许多可以解释其作为一个成功的引入物种的机制中,差异性的物候特征可能起重要作用,但这可能取决于在次优化条件下生长和利用 营养物质的能力。我们研究了智利大叶草在物候和固氮能力方面是否具有优势,并将其与受智利大叶草入侵影响最大的本地物种灯芯草 (Juncus effusus)进行了比较。2016–2017年,我们每周或每两周对爱尔兰阿奇尔岛的长期种群进行物候学评估。在测量土壤温度,湿度和氧化还原电位的同时,收集了叶和花序数,叶总面积,光截获和地上生物量的数据。利用δ ¹⁵N 同位素并结合原位乙炔还原测量的方法评估了用于支持季节生长的固氮能力的重要性。研究结果表明,2016–2017年,智利大叶草和灯芯草开始生长的时间不同,智利大叶草叶片出现和展叶的时间较早,水分利用率较高时地上生物量最大。智利大叶草的早期生长依赖于预先形成的结构,5月下旬冠层发育达到最大,并且早于灯芯草。虽然在3月份观察到固氮作用,但这对冠层发育后期的生长有更显著的贡献。基于δ ¹⁵N 同位素分析结果表明,早期生长主要与根状茎的氮转移有关,而幼苗主要依赖于固氮作用。这一发现强调了养分调动对早期生长的重要性,并表明固氮能力的重要性可能在不同的发育过程中有所不同,并且其在入侵过程的不同阶段也是如此。     

Effects of nitrogen source on the synthesis of the UV-screening compound, scytonemin, in the cyanobacterium Nostoc punctiforme PCC 73102

The effects of nitrogen source (N(2), NO(3)(-) and NH(4)(+)) on scytonemin synthesis were investigated in the heterocystous cyanobacterium Nostoc punctiforme PCC 73102. With the required UVA radiation included, Nostoc synthesized three to seven times more scytonemin while fixing nitrogen than when utilizing nitrate or ammonium. A similar increase in scytonemin synthesis occurred when nitrate or ammonium became depleted by growth and Nostoc switched to diazotrophic metabolism with the differentiation of heterocysts. In addition, UVA-exposed cultures grown in medium with both NO(3)(-) and NH(4)(+) synthesized some scytonemin but synthesis increased when NH(4)(+) was depleted and growth had become dependent on NO(3)(-) reduction. Although the mechanism is unclear, these results suggest that the greater the restriction in nitrogen accessibility, the greater the production of scytonemin. Perhaps the entire response may be an interaction between this restriction and a resultant sensitivity to UV radiation that acts as a cue for determining the level of scytonemin synthesis. Scytonemin is a stable UVR screening compound and appears to be synthesized by cyanobacteria as a long-term solution for reducing UVR exposure and damage, but mainly or solely, when metabolic activity is absent. It is likely that during metabolic resurgence, the presence of a dense scytonemin sheath would facilitate the recovery process without the need for active defenses against UV radiation.     

Sub-Cellular Element Analysis of a Cyanobacterium (Nostoc sp.) in Symbiosis with Gunnera manicata by ESI and EELS

Element analysis using electron spectroscopic imaging (ESI) and electron energy loss spectroscopy (EELS) was performed in a symbiotic Nostoc sp. strain found in the upper stem tissue of Gunnera manicata, and in Nostoc PCC 9229, a free-living heterocyst-forming cyanobacterium able to enter into symbiosis with the angiosperm Gunnera in reconstitution experiments. ESI and EELS unequivocally identified the four elements nitrogen (N), sulphur (S), phosphorus (P) and oxygen (O) in different inclusion bodies of these biological specimens. High amounts of nitrogen were solely detected in huge cyanophycin granules in vegetative cells of the symbiotic Nostoc strain, whereas large polyphosphate bodies, containing high amounts of phosphorus, sulphur and oxygen, could be seen in the free-living Nostoc PCC 9229. The latter were usually not present or, when found, very small in vegetative cells of the cyanobiont.     

葡萄糖和氢对Gunnera／Nostoc固氮共生体固氮活力的影响

Ｇｕｎｎｅｒａ／Ｎｏｓｔｏｃ固氮共生体固氮相对效率（ＲＥ）可在０．２６～０．８０之间变动,而不是一个常数。外加１．５％葡萄糖液可使其固氮活力提高约１００％,同时也使组织的呼吸速率提高了近１６０％。加外源Ｈ２可使其固氮活力提高近１００％,但却使组织的呼吸速率降低了近５０％。正常生长条件下的组织净放Ｈ２量较低．而外源２％葡萄糖液可使组织净放Ｈ２量提高近２倍。外加５ｍｍｏｌ／Ｌ的ＮＨ１Ｃｌ溶液可使其固氮活力下降约７０％。故认为Ｇｕｎｎｅｒａ／Ｎｏｓｔｏｃ共生体固氮活力受碳水化合物供应状况及比代谢两者构成的“还原力库”或“电子库”的调节,在此“还原力库”中,Ｈ２代谢起到了一个“中间调节者”的作用。     

Cloning and expression of a putative cyclodextrin glucosyltransferase from the symbiotically competent cyanobacterium Nostoc sp. PCC 9229

A polymerase chain reaction-based method was used to isolate a Nostoc sp. PCC 9229 cDNA from infected glands of Gunnera chilensis. The complete gene sequence was isolated from a genomic Nostoc sp. PCC 9229 library. Sequence analysis showed 84% amino acid similarity to a putative cyclodextrin glycosyltransferase from Nostoc sp. PCC 7120 and the gene was therefore termed cgt. Southern blot revealed that the cgt gene was present in symbiotically competent cyanobacteria. The cgt gene was expressed in free-living nitrogen-fixing cultures in light or in darkness when supplemented with fructose. This is the first expression analysis of a cgt gene from a cyanobacterium.     

Phycobiliprotein fluorescence of Nostoc punctiforme changes during the life cycle and chromatic adaptation: characterization by spectral confocal laser scanning microscopy and spectral unmixing

Many cyanobacteria are highly adaptable to light quality, and many species undergo a complex life cycle. In this study we show that adaptive changes in the photosynthetic apparatus of cyanobacteria are not only caused by environmental, but also by developmental factors. Spectral confocal laser scanning microscopy (CLSM) was used to analyse in vivo the fluorescence spectra of the photosynthetic pigments chlorophyll a (Chl a), allophycocyanin (APC), phycocyanin (PC) and phycoerythrin (PE) of two Nostoc punctiforme strains. Changes in pigment fluorescence emission occurred in different developmental stages. Strain 1:1-26 showed an emission maximum at 674 nm in motile hormogonia stages, whereas vegetative stages showed maxima at 658 and 575 nm. These changes were not caused by chromatic adaptation. In contrast, the second strain (1:1-26lg) showed distinct fluorescence spectra, pigment localization and clear chromatic adaptation in red light. When these properties are known, both strains can be easily distinguished by the spectral CLSM method, which also allows the localization of the pigments within single cells. To calculate the contribution of individual phycobiliproteins to the observed changes, fluorescence spectra were analysed by spectral unmixing. This allowed the mathematical estimation of fluorescence shares for the individual phycobiliproteins in different developmental stages and both before and after chromatic adaptation. It is concluded that care should be taken when characterizing cyanobacteria by differences in pigment fluorescence, because these differences are influenced not only by chromatic adaptation, but also developmental stages. Spectral CLSM offers a powerful method to study the phycobiliprotein composition in vivo.     

Relationships between nitrogen fixation and photosynthesis as the main components of the productivity in alfalfa

Alfalfa (Medicago sativa L.) plants were inoculated with Sinorhizobium meliloti Tn-5 mutants featuring various nitrogen-fixing effectiveness and then grown in sand culture to study relations between CO₂ exchange, plant productivity, and nitrogen fixation. At the flowering stage, the relationship between nitrogen fixation and photosynthesis of whole alfalfa plants was described with the logarithmic curve. At the same stage of plant development, a close relationship was observed between nitrogen fixation rate and plant weight; this relationship showed a trend toward saturation at high rates of nitrogen fixation. The increase in nitrogenase activity of root nodules was accompanied by stimulation of root respiration; the relation of respiration to nitrogen-fixing activity was manifested stronger than its relation to the total root weight. It is concluded that highly effective strains of root nodule bacteria can realize their potential only in combination with complementary plant genotypes featuring active photosynthesis that provides a balanced supply of assimilates for both the symbiotic apparatus and growth processes in the macrosymbiont.     

Interaction between atmospheric and pedospheric nitrogen nutrition in spruce (Picea abies L. Karst) seedlings

The effect of NO₂ fumigation on root N uptake and metabolism was investigated in 3-month-old spruce (Picea abics L. Karst) seedlings. In a first experiment, the contribution of NO₂ to the plant N budget was measured during a 48 h fumigation with 100mm³m^?3 NO₂. Plants were pre-treated with various nutrient solutions containing NO₂ and NH₄⁺, NO₃^? only or no nitrogen source for 1 week prior to the beginning of fumigation. Absence of NH₄⁺ in the solution for 6d led to an increased capacity for NO₃^? uptake, whereas the absence of both ions caused a decrease in the plant N concentration, with no change in NO₃^? uptake. In fumigated plants, NO₂ uptake accounted for 20–40% of NO₃^? uptake. Root NO₃^? uptake in plants supplied with NH₄⁺plus NO₃^? solutions was decreased by NO₂ fumigation, whereas it was not significantly altered in the other treatments. In a second experiment, spruce seedlings were grown on a solution containing both NO₂ and NH₄⁺ and were fumigated or not with 100mm³m^?3 NO₂ for 7 weeks. Fumigated plants accumulated less dry matter, especially in the roots. Fluxes of the two N species were estimated from their accumulations in shoots and roots, xylem exudate analysis and ¹⁵N labelling. Root NH₄⁺ uptake was approximately three times higher than NO₃^? uptake. Nitrogen dioxide uptake represented 10–15% of the total N budget of the plants. In control plants, N assimilation occurred mainly in the roots and organic nitrogen was the main form of N transported to the shoot. Phloem transport of organic nitrogen accounted for 17% of its xylem transport. In fumigated plants, neither NO₃^? nor NH₄⁺ accumulated in the shoot, showing that all the absorbed NO₂ was assimilated. Root NO₃^? reduction was reduced whereas organic nitrogen transport in the phloem increased by a factor of 3 in NO₂-fimugated as compared with control plants. The significance of the results for the regulation of whole-plant N utilization is discussed.     

Phenolic profile,antioxidant and cytotoxic properties of polar extracts from leaves and flowers of Isatis tinctoria L. (Brassicaceae) growing in Sicily

This study was designed to define and compare the antioxidant and cytotoxic properties of polar extracts obtained from basal leaves (It-BL), cauline leaves (It-CL) and flowers (It-F) of Isatis tinctoria L. growing wild around Acireale (Sicily, Italy). The phenolic profile was characterized by HPLC-PDA-ESI-MS analysis and the correlation between phenolic content and the observed biological effects was established. Further, LC/MS analysis showed that the extracts contain glucosinolates at very low concentrations. The antioxidant activity of the extracts was tested in vitro; It-F was the most effective in the DPPH test (IC₅₀ = 0.437 ± 0.003 mg/mL), whilst It-CL showed the best reducing power (1.546 ± 0.006 ASE/mL) and ferrous ions chelating activity (IC₅₀ = 0.564 ± 0.011 mg/mL). The extracts exhibited anti-proliferative effects against three different human thyroid carcinoma cell lines, and It-BL displayed the strongest activity; particularly, it markedly inhibited the growth of CAL-62 cells, causing nearly 85% reduction of viability at the highest tested dose. No cytotoxicity against Artemia salina was observed. The results of our investigations indicate that the polar extracts obtained from I. tinctoria are a potential source of antioxidant and anticancer compounds, which could be suitable for nutraceutical and therapeutic applications.     

The role of iron nutrition in photosynthesis and nitrogen assimilation in SCENEDESMUS QUADRICAUDA (Chlorophyceae) 1

The rate of photosynthesis and nitrate uptake are related to the iron concentration in the medium for the green alga Scenedesmus quadricauda (Turp.) Breb. Increased iron leads to changes in chlorophyll a concentration, carbon fixation rate per chlorophyll a and in vivo fluorescence characteristics. These parameters all indicate that the efficiency of photosynthesis is related to iron nutrition. Nitrate uptake rate is also a function of both Fe and light Iron-limited cultures had decreased nitrate uptake at low light whereas ammonium uptake was relatively constant. Iron-limited cultures fixed about twice as much carbon into protein relative to the total carbon fixed. Iron plays a crucial role in the bioenergetics of carbon and nitrogen metabolism and may be important in controlling patterns of productivity.     

Distribution and ecology of the edible cyanobacterium Ge-Xian-Mi (Nostoc) in rice fields of Hefeng County in China

Ge-Xian-Mi (an edible species of Nostoc) grows insome mountain paddy fields in China during winter and forms macroscopicallyvisible subspherical colonies. The geology and climate at one of its locations,Hefeng County, were investigated, and the present-day situation of Ge-Xian-Miwas assessed in order to raise awareness that it may be endangered. There wereformerly 796 ha of rice fields suited to its growth in HefengCounty and the maximum annual yield ever reached was 25 t. Theannual mean temperature is about 12.2 °C, and the annualrainfall is 1934 mm with mean relative humidity of 78–87%.The distribution of Ge-Xian-Mi was found to be associated with the source ofwater and the pH values of water suited to its growth were 6.2–6.3. Soilsin its habitats were enriched with phosphorus and contained more microbes thanthose without its distribution. With changing agricultural techniques most ofthe habitats are endangered or already extinct. The widespread use ofherbicides, pesticides and fertilizers containing chlorine had been suggestedtobe an important factor limiting its distribution. The taxonomic identity ofGe-Xian-Mi is discussed.     

底质营养盐负荷对轮叶黑藻生长和光合荧光特性的影响

在实验室条件下,研究了用不同营养盐负荷底泥作为底质培育的轮叶黑藻(Hydrilla verticillata(L.f)Royle)的生长的效应,结果表明,在上覆水TN/TP为20-50,TP变化范围在0.03-0.05mg/L内,底质磷相对释放速率为0.33mg/(m.2d)时培育的轮叶黑藻生长最好。轮叶黑藻对环境有较强的适应性,培育期间各组光合荧光参数Fv/Fm,qP,ETRmax随培养时间均明显的升高;在非最佳生长条件下轮叶黑藻能通过自身光合荧光参数qN的升高,耗散掉过剩的光能,来对自身进行保护。     

水稻光合功能相关性状QTL分析

利用粳稻Kinmaze／籼稻DV85杂交后代单粒传衍生的81个F11家系所组成的重组自交系（Recombinant Inbred Lines,RILs）群体,研究水稻光合功能相关性状的数量性状基因座（QTL）。在水稻抽穗后7d测定叶片全氮含量（TLN）、叶绿素a／b比值（Chl．a：b）和叶绿素含量（Chl）。共检测到6个QTL,各QTL的LOD值为2．66～4．81,贡献率为11．2％-29．6％,其中,在第1、2和11染色体上检测到3个与全氮含量相关的QTL,相应贡献率为17．3％、15．3％、13．7％;在第3和4染色体检测到2个与叶绿素a／b比值相关的QTL,贡献率为13．8％和29．6％;在第1染色体检测到1个与叶绿素含量相关的QTL,贡献率为11．2％。4个QTL为本研究新检测的基因座。有趣的是,控制叶绿素含量的qCC-1位于第1染色体上RFLP标记C122附近,与已报道的NADH-谷氨酸合成酶基因位置一致,而叶绿素合成始于谷氨酸,暗示该基因座与水稻光合功能关系极为密切。然而,对抽穗后30d叶绿素含量进行QTL分析,结果未检测到与其相关的QTL,表明控制叶绿素含量qCC-1效应随水稻叶片的衰老而降低。     

Community structure and physiological characterization of microbial mats in Byers Peninsula, Livingston Island (South Shetland Islands, Antarctica)

The community structure and physiological characteristics of three microbial mat communities in Byers Peninsula (Livingston Island, South Shetland Islands, Antarctica) were compared. One of the mats was located at the edge of a stream and was dominated by diatoms (with a thin basal layer of oscillatorian cyanobacteria), whereas the other two mats, located over moist soil and the bottom of a pond, respectively, were dominated by cyanobacteria throughout their vertical profiles. The predominant xanthophyll was fucoxanthin in the stream mat and myxoxanthophyll in the cyanobacteria-dominated mats. The sheath pigment scytonemin was absent in the stream mat but present in the soil and pond mats. The stream mat showed significantly lower delta13C and higher delta15N values than the other two mats. Consistent with the delta15N values, N2 fixation was negligible in the stream mat. The soil mat was the physiologically most active community. It showed rates of photosynthesis three times higher than in the other mats, and had the highest rates of ammonium uptake, nitrate uptake and N2 fixation. These observations underscore the taxonomic and physiological diversity of microbial mat communities in the maritime Antarctic region.     

Utilization of inorganic carbon in the edible cyanobacterium Ge-Xian-Mi (Nostoc) and its role in alleviating photo-inhibition

The present work investigated the inorganic carbon (C_i) uptake, fluorescence quenching and photo‐inhibition of the edible cyanobacterium Ge‐Xian‐Mi (Nostoc) to obtain an insight into the role of CO₂ concentrating mechanism (CCM) operation in alleviating photo‐inhibition. Ge‐Xian‐Mi used HCO₃^– in addition to CO₂ for its photosynthesis and oxygen evolution was greater than the theoretical rates of CO₂ production derived from uncatalysed dehydration of HCO₃^–. Multiple transporters for CO₂ and HCO₃^– operated in air‐grown Ge‐Xian‐Mi. Na⁺‐dependent HCO₃^– transport was the primary mode of active C_i uptake and contributed 53–62% of net photosynthetic activity at 250 µmol L^?1 KHCO₃ and pH 8.0. However, the CO₂‐uptake systems and Na⁺‐independent HCO₃^– transport played minor roles in Ge‐Xian‐Mi and supported, respectively, 39 and 8% of net photosynthetic activity. The steady‐state fluorescence decreased and the photochemical quenching increased in response to the transport‐mediated accumulation of intracellular C_i. Inorganic carbon transport was a major factor in facilitating quenching during the initial stage and the initial rate of fluorescence quenching in the presence of iodoacetamide, an inhibitor of CO₂ fixation, was 88% of control. Both the initial rate and extent of fluorescence quenching increased with increasing external dissolved inorganic carbon (DIC) and saturated at higher than 200 µmol L^?1 HCO₃^–. The operation of the CCM in Ge‐Xian‐Mi served as a means of diminishing photodynamic damage by dissipating excess light energy and higher external DIC in the range of 100–10000 µmol L^?1 KHCO₃ was associated with more severe photo‐inhibition under strong irradiance.     

Hormogonia mass differentiation from Nostoc sphaeroides Kütz. (cyanobacterium) and the comparison of structural characteristics between hormogonia and vegetative filaments

It was found that, after colonies of Nostoc sphaeroides Kütz. in exponential phase of growth were transferred to fresh complete BG‐11₀ medium, the hormogonia differentiated independent of the type of preculture used. This provided evidence that the hormogonia differentiation was not directly related to phosphorus and potassium status, nor to the osmotic effect of the media. In contrast, all the cultures in the stationary growth phase had no hormogonium differentiation after being transferred to fresh medium. However, the incomplete media for preculture seemed to favor the liberation of hormogonia from colonies to the medium. The result showed that the morphology and ultrastruc‐tures of the vegetative filament, the main stage of Nostocacean life history, determine its adaptability in changing environments, while the hormogonium remains as a propagule of the species.     

不同品种小豆光合作用和生长发育对弱光的响应

为确定小豆作为林果行间套种作物的适宜性,通过田间试验和盆栽试验,测定全光和弱光处理(全光的48%)下3个小豆品种(阜南绿小豆、早熟黑小豆、晚熟黑小豆)在初花期的叶片光合特征参数、光合色素含量和RuBPCase活性,研究小豆生长发育对弱光的响应.结果表明: 弱光使3个品种小豆叶片的最大净光合速率、光饱和点、光补偿点等光合参数不同程度地向耐荫的方向变化,净光合速率、水分利用效率和RuBPCase活性也显著下降;遮阴后,阜南绿小豆的叶绿素a和b含量显著增加,Chl a/b和类胡萝卜素含量显著降低,其他小豆的叶绿素和类胡萝卜素含量无明显变化;弱光使3个品种小豆的生物量和干物质积累效率降低,根冠比降低,根瘤量减少,叶片数和叶面积指数减小;弱光胁迫下,阜南绿小豆提前开花、提前成熟,早熟黑小豆推迟开花、延迟成熟,而晚熟黑小豆只开花不结实.从遮阴后小豆的光合特性变化和生长发育差异等方面综合考虑,3个小豆品种的耐阴能力大小为:阜南绿小豆>早熟黑小豆>晚熟黑小豆.