Developmental and growth controls of tillering and water-soluble carbohydrate accumulation in contrasting wheat (Triticum aestivum L.) genotypes: can we dissect them?

In wheat, tillering and water-soluble carbohydrates (WSCs) in the stem are potential traits for adaptation to different environments and are of interest as targets for selective breeding. This study investigated the observation that a high stem WSC concentration (WSCc) is often related to low tillering. The proposition tested was that stem WSC accumulation is plant density dependent and could be an emergent property of tillering, whether driven by genotype or by environment. A small subset of recombinant inbred lines (RILs) contrasting for tillering was grown at different plant densities or on different sowing dates in multiple field experiments. Both tillering and WSCc were highly influenced by the environment, with a smaller, distinct genotypic component; the genotypeenvironment range covered 350750 stems m(2) and 25210mg g(1) WSCc. Stem WSCc was inversely related to stem number m(2), but genotypic rankings for stem WSCc persisted when RILs were compared at similar stem density. Low tilleringhigh WSCc RILs had similar leaf area index, larger individual leaves, and stems with larger internode cross-section and wall area when compared with high tilleringlow WSCc RILs. The maximum number of stems per plant was positively associated with growth and relative growth rate per plant, tillering rate and duration, and also, in some treatments, with leaf appearance rate and final leaf number. A common threshold of the red:far red ratio (0.390.44; standard error of the difference0.055) coincided with the maximum stem number per plant across genotypes and plant densities, and could be effectively used in crop simulation modelling as a ocut-off' rule for tillering. The relationship between tillering, WSCc, and their component traits, as well as the possible implications for crop simulation and breeding, is discussed.

Relationships among the contents of total phenolics, soluble carbohydrate, and free amino acids of 15 aquatic macrophytes

In order to examine how carbon and nitrogen status of a macrophyte may affect its total phenolics (TP) production, the contents of free amino acids (FAA), soluble carbohydrate (SC) and TP were examined in leaves of seven submersed, four floating-leaved, and four emergent macrophytes. The floating-leaved and emergent macrophytes had much higher contents of SC and TP than the submersed macrophytes. The contents of FAA were not significantly different among the submersed, floating-leaved, and emergent macrophytes. Correlations among the contents of FAA, SC, and TP indicated that the production of TP was more dependent on the SC content than on the FAA content.

Association of candidate genes with flowering time and water-soluble carbohydrate content in Lolium perenne (L.)

Sk?t, L., Humphreys, J., Humphreys, M. O., Thorogood, D., Gallagher, J. A., Sanderson, R., Armstead, I. P., Thomas, I. D. (2007). Association of candidate genes with flowering time and water-soluble carbohydrate content in Lolium perenne (L.). Genetics, 177 (1), 535-547. Sponsorship: BBSRC RAE2008

Free Cyclitol, Soluble Carbohydrate and Protein Contents in Vigna unguiculata and Phaseolus vulgaris Bean Sprouts

Seeds sprouts have been used as a good source of basic nutrients and nutraceutical compounds. The high nutritional value of seeds derives from the deposition of compounds during development. However some of these molecules are used in metabolic processes like germination, which leads to a considerable variation in their concentrations once these events are completed. In this work, we investigate the levels of inositols (myo-inositol, D-pinitol and ononitol), soluble carbohydrates and proteins in cotyledons of Phaseolus vulgaris and Vigna unguiculata sprouts. Sprouting increased myo-inositol and glucose content and reduction of raffinose and ononitol was observed. The protein levels increased in P. vulgaris and decreased in V. unguiculata sprouting. The level of sucrose was maintained in both sprouts. D-Pinitol was detected only in quiescent seeds. Our results suggested that bean sprout is an important source of proteins, sucrose, glucose and myo-inositol. Additionally, bean sprouts have low levels of raffinose, an antinutritional compound.

Effects of Different Feeding Regimes on the Digestibility and Faecal Excretion of Nitrogen, Soluble Carbohydrates and Fibre Fractions in Water Buffaloes kept under Subtropical Conditions

In the course of the ‘Livestock Revolution’, extension and intensification of, among others, ruminant livestock production systems are current phenomena, with all their positive and negative side effects. Manure, one of the inevitable secondary products of livestock rearing, is a valuable source of plant nutrients and its skillful recycling to the soil-plant interface is essential for soil fertility, nutrient - and especially phosphorus - uses efficiency and the preservation or re-establishment of environmentally sustainable farming systems, for which organic farming systems are exemplarily. Against this background, the PhD research project presented here, which was embedded in the DFG-funded Research Training Group 1397 ‘Regulation of soil organic matter and nutrient turnover in organic agriculture ’ investigated possibilities to manipulate the diets of water buffalo (Bubalus bubalis L.) so as to produce manure of desired quality for organic vegetable production, without affecting the productivity of the animals used. Consisting of two major parts, the first study (chapter 2) tested the effects of diets differing in their ratios of carbon (C) to nitrogen (N) and of structural to non-structural carbohydrates on the quality of buffalo manure under subtropical conditions in Sohar, Sultanate of Oman. To this end, two trials were conducted with twelve water buffalo heifers each, using a full Latin Square design. One control and four tests diets were examined during three subsequent 7 day experimental periods preceded each by 21 days adaptation. Diets consisted of varying proportions of Rhodes grass hay, soybean meal, wheat bran, maize, dates, and a commercial concentrate to achieve a (1) high C/N and high NDF (neutral detergent fibre)/SC (soluble carbohydrate) ratio (HH), (2) low C/N and low NDF/SC ratio (LL); (3) high C/N and low NDF/SC ratio (HL) and (4) low C/N and high NDF/SC (LH) ratio. Effects of these diets, which were offered at 1.45 times maintenance requirements of metabolizable energy, and of individual diet characteristics, respectively, on the amount and quality of faeces excreted were determined and statistically analysed. The faeces produced from diets HH and LL were further tested in a companion PhD study (Mr. K. Siegfried) concerning their nutrient release in field experiments with radish and cabbage. The second study (chapter 3) focused on the effects of the above-described experimental diets on the rate of passage of feed particles through the gastrointestinal tract of four randomly chosen animals per treatment. To this end, an oral pulse dose of 683 mg fibre particles per kg live weight marked with Ytterbium (Yb; 14.5 mg Yb g-1 organic matter) was dosed at the start of the 7 day experimental period which followed 21 days of adaptation. During the first two days a sample for Yb determination was kept from each faecal excretion, during days 3 – 7 faecal samples were kept from the first morning and the first evening defecation only. Particle passage was modelled using a one-compartment age-dependent Gamma-2 model. In both studies individual feed intake and faecal excretion were quantified throughout the experimental periods and representative samples of feeds and faeces were subjected to proximate analysis following standard protocols. In the first study the organic matter (OM) intake and excretion of LL and LH buffaloes were significantly lower than of HH and HL animals, respectively. Digestibility of N was highest in LH (88%) and lowest in HH (74%). While NDF digestibility was also highest in LH (85%) it was lowest in LL (78%). Faecal N concentration was positively correlated (P≤0.001) with N intake, and was significantly higher in faeces excreted by LL than by HH animals. Concentrations of fibre and starch in faecal OM were positively affected by the respective dietary concentrations, with NDF being highest in HH (77%) and lowest in LL (63%). The faecal C/N ratio was positively related (P≤0.001) to NDF intake; C/N ratios were 12 and 7 for HH and LL (P≤0.001), while values for HL and LH were 11.5 and 10.6 (P>0.05). The results from the second study showed that dietary N concentration was positively affecting faecal N concentration (P≤0.001), while there was a negative correlation with the faecal concentration of NDF (P≤0.05) and the faecal ratios of NDF/N and C/N (P≤0.001). Particle passage through the mixing compartment was lower (P≤0.05) for HL (0.033 h-1) than for LL (0.043 h-1) animals, while values of 0.034 h-1 and 0.038 h-1 were obtained for groups LH and HH. At 55.4 h, total tract mean retention time was significantly (P≤0.05) lower in group LL that in all other groups where these values varied between 71 h (HH) and 79 h (HL); this was probably due to the high dietary N concentration of diet LL which was negatively correlated with time of first marker appearance in faeces (r= 0.84, P≤0.001), while the dietary C concentration was negatively correlated with particle passage through the mixing compartment (r= 0.57, P≤0.05). The results suggest that manure quality of river buffalo heifers can be considerably influenced by diet composition. Despite the reportedly high fibre digestion capacity of buffalo, digestive processes did not suppress the expression of diet characteristics in the faeces. This is important when aiming at producing a specific manure quality for fertilization purposes in (organic) crop cultivation. Although there was a strong correlation between the ingestion and the faecal excretion of nitrogen, the correlation between diet and faecal C/N ratio was weak. To impact on manure mineralization, the dietary NDF and N concentrations seem to be the key control points, but modulating effects are achieved by the inclusion of starch into the diet. Within the boundaries defined by the animals’ metabolic and (re)productive requirements for energy and nutrients, diet formulation may thus take into account the abiotically and biotically determined manure turnover processes in the soil and the nutrient requirements of the crops to which the manure is applied, so as to increase nutrient use efficiency along the continuum of the feed, the animal, the soil and the crop in (organic) farming systems.

Changes in soluble carbohydrates and starch amounts during somatic and zygotic embryogenesis of Acca sellowiana (Myrtaceae)

Comparative analysis of zygotic and somatic embryogenesis of Acca sellowiana showed higher amounts of sucrose, fructose, raffinose, and myo-inositol in zygotic embryos at different developmental stages than in corresponding somatic ones. These differences were mostly constant. In general, glucose levels were significantly lower than the other soluble carbohydrates analyzed, showing minor variation in each embryo stage. Despite the presence of sucrose in the culture medium, its levels conspicuously diminished in somatic embryos compared with the zygotic ones. Raffinose enhanced parallel to embryo development, regardless of its zygotic or somatic origin. Analysis of the soluble carbohydrate composition of mature zygotic cotyledon used as explant pointed out fructose, glucose, myo-inositol, sucrose, and raffinose as the most important. Similar composition was also found in the corresponding somatic cotyledon. Total soluble carbohydrates varied inversely, decreasing in zygotic embryos and increasing in somatic embryos until the 24th d, at which time they increased rapidly about sixfold in zygotic embryos until the 27th d, a period coinciding with the zygotic proembryos formation. Such condition seems to reflect directly the variation of endogenous sucrose level, mainly because glucose and fructose diminished continuously during this time period. This means that, in terms of soluble sugars, zygotic embryo formation occurred under a situation represented by high sucrose amounts, simultaneously with low fructose and glucose levels, while in contrast, somatic embryo formation took place under an endogenous sugar status characterized by a substantial fructose enhancement. Starch levels increased continuously in zygotic embryos and decreased in somatic ones, the reverse to what was found in fructose variation. Starch accumulation was significantly higher in somatic torpedo and cotyledonary embryos than in the corresponding zygotic ones.

Concentration of mannitol and other soluble carbohydrates in the crustose lichen Rhizocarpon geographicum

In symbiotic lichens which have Trebouxia as the algal partner, photosynthesis by the algae results in the production of the soluble carbohydrate ribitol which is then transported to the fungus where it is converted to arabitol and mannitol. Within the fungus, arabitol may act as a short-term carbohydrate reserve while mannitol may have a more protective function and be important in stress resistance. The concentrations of ribitol, arabitol, and mannitol were measured, using gas chromatography, in the central areolae and marginal hypothallus of the crustose lichen Rhizocarpon geographicum (L.) DC. growing on slate rocks in north Wales, UK. The concentrations of all three soluble carbohydrates were greater in the central areolae than in the marginal prothallus. In addition, the ratio of mannitol in the prothallus to that in the areolae was least in July. The concentration of an individual carbohydrate in the prothallus was correlated primarily with the concentrations of the other carbohydrates in the prothallus and not to their concentrations in the areolae. Low concentration of ribitol, arabitol, and mannitol in the marginal prothallus compared with the central areolae suggests either a lower demand for carbohydrate by the prothallus or limited transport from areolae to prothallus and may explain the low growth rates of this species. In addition, soluble carbohydrates appear to be partitioned differently through the year with an increase in mannitol compared with arabitol in more stressful periods.

Nutritional analysis of gastric contents and body condition score at a single time point in feral horses in Australia

Objective: To determine the impact of a free-choice diet on nutritional intake and body condition of feral horses. Animals: Cadavers of 41 feral horses from 5 Australian locations. Procedures: Body condition score (BCS) was determined (scale of 1 to 9), and the stomach was removed from horses during postmortem examination. Stomach contents were analyzed for nutritional variables and macroelement and microelement concentrations. Data were compared among the locations and also compared with recommended daily intakes for horses. Results: Mean BCS varied by location; all horses were judged to be moderately thin. The BCS for males was 1 to 3 points higher than that of females. Amount of protein in the stomach contents varied from 4.3% to 14.9% and was significantly associated with BCS. Amounts of water-soluble carbohydrate and ethanol-soluble carbohydrate in stomach contents of feral horses from all 5 locations were higher than those expected for horses eating high-quality forage. Some macroelement and microelement concentrations were grossly excessive, whereas others were grossly deficient. There was no evidence of ill health among the horses. Conclusions and Clinical Relevance: Results suggested that the diet for several populations of feral horses in Australia appeared less than optimal. However, neither low BCS nor trace mineral deficiency appeared to affect survival of the horses. Additional studies on food sources in these regions, including analysis of water-soluble carbohydrate, ethanol-soluble carbohydrate, and mineral concentrations, are warranted to determine the provenance of such rich sources of nutrients. Determination of the optimal diet for horses may need revision.

Crop and environmental attributes underpinning genotype by environment interaction in synthetic-derived bread wheat evaluated in Mexico and Australia

Synthetic backcrossed-derived bread wheats (SBWs) from CIMMYT were grown in the north-west of Mexico (CIANO) and sites across Australia during 3 seasons. A different set of lines was evaluated each season, as new materials became available from the CIMMYT crop enhancement program. Previously, we have evaluated both the performance of genotypes across environments and the genotype x environment interaction (G x E). The objective of this study was to interpret the G x E for yield in terms of crop attributes measured at individual sites and to identify the potential environmental drivers of this interaction. Groups of SBWs with consistent yield performance were identified, often comprising closely related lines. However, contrasting performance was also relatively common among sister lines or between a recurrent parent and its SBWs. Early flowering was a common feature among lines with broad adaptation and/or high yield in the northern Australian wheatbelt, while yields in the southern region did not show any association with the maturity type. Lines with high yields in the southern and northern regions had cooler canopies during flowering and early grain filling. Among the SBWs with Australian genetic backgrounds, lines best adapted to CIANO were tall (>100 cm), with a slightly higher ground cover. These lines also displayed a higher concentration of water-soluble carbohydrates in the stem at flowering, which was negatively correlated with stem number per unit area when evaluated in southern Australia (Horsham). Possible reasons for these patterns are discussed. Selection for yield at CIANO did not specifically identify the lines best adapted to northern Australia, although they were not the most poorly adapted either. In addition, groups of lines with specific adaptation to the south would not have been selected by choosing the highest yielding lines at CIANO. These findings suggest that selection at CIMMYT for Australian environments may be improved by either trait based selection or yield data combined with trait information. Flowering date, canopy temperature around flowering, tiller density, and water-soluble carbohydrate concentration in the stem at flowering seem likely candidates.

Effect of defoliation interval and height on the growth and quality of Arachis pintoi cv. Amarillo

The effect of defoliation on Amarillo (Arachis pintoi cv. Amarillo) was studied in a glasshouse and in mixed swards with 2 tropical grasses. In the glasshouse, Amarillo plants grown in pots were subjected to a 30/20°C or 25/15°C temperature regime and to defoliation at 10-, 20- or 30-day intervals for 60 days. Two field plot studies were conducted on Amarillo with either irrigated kikuyu (Pennisetum clandestinum) in autumn and spring or dryland Pioneer rhodes grass (Chloris gayana) over summer and autumn. Treatments imposed were 3 defoliation intervals (7, 14 and 28 days) and 2 residual heights (5 and 10 cm for kikuyu; 3 and 10 cm for rhodes grass) with extra treatments (56 days to 3 cm for both grasses and 21 days to 5 cm for kikuyu). Defoliation interval had no significant effect on accumulated Amarillo leaf dry matter (DM) at either temperature regime. At the higher temperature, frequent defoliation reduced root dry weight (DW) and increased crude protein (CP) but had no effect on stolon DW or in vitro organic matter digestibility (OMD). On the other hand, at the lower temperature, frequent defoliation reduced stolon DW and increased OMD but had no effect on root DW or CP. Irrespective of temperaure and defoliation, water-soluble carbohydrate levels were higher in stolons than in roots (4.70 vs 3.65%), whereas for starch the reverse occured (5.37 vs 9.44%). Defoliating the Amarillo-kikuyu sward once at 56 days to 3 cm produced the highest DM yield in autumn and sprong (582 and 7121 kg/ha DM, respectively), although the Amarillo component and OMD were substantially reduced. Highest DM yields (1726 kg/ha) were also achieved in the Amarillo-rhodes grass sward when defoliated every 56 days to 3 cm, although the Amarillo component was unaffected. In a mixed sward with either kikuyu or rhodes grass, the Amarillo component in the sward was maintained up to a 28-day defoliation interval and was higher when more severely defoliated. The results show that Amarillo can tolerate frequent defoliation and that it can co-exist with tropical grasses of differing growth habits, provided the Amarillo-tropical grass sward is subject to frequent and severe defoliation.

Caracterização das estratégias ecofisiológicas de samambaias em resposta à inundação na restinga de Maricá, Rio de Janeiro, Brasil

As matas inundáveis e brejos presentes nas restingas desencadeiam uma série de processos que influenciam as características físico-químicas e biológicas do solo, levando as plantas a apresentarem mecanismos de aclimatação ou adaptação ao estresse da inundação, como alterações morfológicas e fisiológicas de forma a minimizar os efeitos da falta de oxigênio. Dentre as espécies vegetais de samambaias ocorrentes em ambientes inundáveis nas restingas, se destacam três espécies: Acrostichum danaeifolium Langsd. & Fisch., Blechnum serrulatum Rich. e Thelypteris interrupta (Willd.) K.Iwats. O objetivo deste trabalho é caracterizar os aspectos ecofisiológicos que os esporófitos dessas samambaias apresentam para sobreviver em ambientes de inundação na restinga de Maricá, estado do Rio de Janeiro. Neste sentido, foi determinada a caracterização física e química dos sítios de ocorrências destas samambaias, as variações foliares entre elas, espessura, densidade, massa por unidade de folha, teor de clorofilas e atributos quantitativos das células epidérmicas, além da quantificação e determinação à distribuição dos carboidratos. Para as variáveis dos vegetais foram feitas coletas na estação chuvosa e seca e para variáveis do solo na estação seca. Os sítios analisados se mostraram extremamente ácidos, de baixa fertilidade e com toxidez por macro e micro nutrientes, indicando que as samambaias apresentam tolerância a estes fatores. Na época chuvosa (inundação), as samambaias apresentaram queda na densidade foliar, acompanhada de um aumento de massa por unidade de folha. Esta habilidade de conseguir ganhar massa seca por área classifica todas as samambaias analisadas como tolerantes à inundação. Os altos valores de carboidratos solúveis nas folhas indicam aumento da degradação do amido foliar e o menor teor de carboidrato solúvel encontrado nos caules explicita a redução na respiração das raízes destas plantas sob anoxia/ hipoxia, para evitar a oxidação e o incremento do estoque de amido de reserva, elucidando estratégia de tolerância à inundação. A menor disponibilidade de água na estação seca afeta diretamente os atributos foliares diminuindo o índice estomático, a suculência e a massa por unidade de folha, no qual reflete na queda das concentrações de clorofilas. Os menores valores nas concentrações de clorofila têm influencia direta na presença de amidos foliar que são estocado e, alterando toda a dinâmica dos carboidratos nestas espécies. A análise do sítio onde cresce Acrostichum danaeifolium indica níveis críticos de Na no solo e provavelmente, a produção de mucilagem no caule e no pecíolo é uma estratégia de tolerância ao ambiente salino e inundado. O elevado índice de cobertura de Blechnum serrulatum em ambientes inundados indica que esta espécie possui adaptações a solos hidromórficos, entre elas, grande capacidade de estocagem de amido no caule. A maior sinuosidade das células epidérmicas em T. interrupta permite uma alta suculência mantendo o status hidrológico da folha em ambas as estações. Os resultados apresentados, além de agregar informações sobre a biologia das samambaias nos neotrópicos, irão contribuir para a compreensão da dinâmica de ocupação de espécies herbáceas em ambientes alagáveis nas restingas brasileiras

根茎克隆植物羊草分株种群对去叶干扰的生长对策

克隆植物具有多种不同于非克隆植物的生长和繁殖策略。本研究首先综述了这些生长与繁殖策略之中，与我们的实验研究相关的尤其是对于去叶干扰适应策略的四个方面，包括克隆整合、克隆分株大小与密度之权衡( tradeoff)过程、碳水化合物贮备与利用、营养繁殖和芽种群(bud population)调节等。预测克隆植物选择什么样的对策以及某种对策发生作用的条件及程度如何，对克隆植物生态学研究者来说，将是富有挑战意味的课题。 羊草(Leymus chinensis (Trin,) Tzvel.)是禾本科的一种多年生根茎型克隆植物，常常处于由放牧或刈割造成的去叶干扰( defoliation)的胁迫下。在我们的第一个实验（2002年）中，考察了去叶干扰和根茎切割( rhizome severing)是否影响根茎本身和分株地上部分的生长、以及营养繁殖芽的数量特征。同时我们检验如下的假设：直接受到去叶干扰的分株除了会受益于可能的补偿作用之外，还会受益于克隆整合作用，即与之保持根茎联系的未受去叶处理的分株将转移碳水化合物或养分给受去叶干扰的分株，使之得以尽快恢复光合组织。实验结果显示：单次去叶干扰影响根茎生长和芽的产生，而对地上部分的生长影响甚微。只有重度去叶干扰才显著影响营养繁殖芽的产生，而轻度去叶干扰作用不明显。所以，当去叶强度不大时，补偿作用机制将弥补植物由于去叶干扰而受到的损失。我们的实验并未检测到克隆整合的发生，可能的原因是本实验持续的时间不足够长或者是由于根茎中的碳水化合物贮备在去叶干扰发生后发挥了作用，缓解了去叶干扰对羊草分株生长及芽生产的所造成的冲击。 在第二个实验（200 3年）中，为了考查相继数次的去叶干扰是否能够启动羊草分株间的克隆整合，以及启动克隆整合所需达到的去叶干扰的频次，我们将实验样方设计为两部分：核心区( Core section)和外围区(Periphery section)。不同频次的去叶处理（0去叶，作为对照; 1次去叶;3次去叶;5次去叶）仅施加于实验样方的核心区。结果表明，经历3次和5次去叶处理的样方外围区的生物量及水溶性碳水化合物( wsc)含量均明显少于经历1次去叶处理及0去叶处理的样方外围区，这意味着克隆整合在3次去叶和5次去叶两种处理中发生了，而在其它两种处理中没有发生。此外，分株的大小一数目之权衡可能在基株(genet)水平上发生，因此，一个克隆植物基株，当部分分株受到去叶干扰后，将增加其分株数目，但优先增加未受到去叶干扰部分的分株数目。我们将羊草的这种行为视为克隆基株试图逃避干扰的“逃逸行为”( escaping behavior)。 同时在实验中，我们监测了实验样方核心区分株的wsc浓度，目的是查明羊草枝条与根茎中wsc浓度随时间的变化格局及其对去叶干扰的响应，意在发现羊草枝条地上、地下部分和根茎中wsc浓度的时间变化之间的联系。在生长旺季，对照处理（即O去叶处理）的wsc浓度显著降低，这是由于植物在此时期的高生长速率和高呼吸速率所致;相比之下，其它经历去叶干扰的三个处理中羊草wsc浓度降低不如对照处理那么明显和迅速，甚至在高频次去叶处理中还有所上升，其原因大概是由于去叶而使叶面积减小，引起枝条的总呼吸下降所致。羊草枝条中最终的wsc浓度没有受到单次去叶处理的显著影响，却很可观地受到相继数次去叶干扰（3次和5次去叶处理）的影响。去叶干扰可能加速了碳水化合物在气温降低时自地上向地下的转移。枝条的地下部分wsc浓度比地上部分更稳定。在地上部分受到去叶干扰后，根茎中的wsc必然向上输出到地上枝条，而强烈的生长会消耗wsc，但可能的克隆整合（通常在相对频繁的去叶干扰条件下发生）将在一定程度上缓解这种wsc消耗。 在此实验中，我们还监测了羊草平均每分株所拥有的芽的数目，包括每分株分蘖节芽（tiller bud）数目和根茎芽(thizomatous bud)数目。从平均每分株芽数目的时间动态来看，各种去叶处理之间的差异程度不大，这主要是羊草在受到去叶干扰后补偿作用的贡献。与对照处理相比，受不同频次去叶干扰的三个处理的根茎芽具有相对于分蘖节的更强的增长优势。去叶干扰对根茎芽生长的促进作用大于对分蘖节芽的促进作用。我们认为这种反应是羊草克隆基株的一种逃避干扰的适应性努力，可视为一种“逃逸行为”，也可看作克隆植物觅养行为(foraging behavior)的一种特殊形式。芽的增长在中等频度的去叶干扰条件下最强，似乎同样符合中度干扰理论。有趣的是，特定频度的去叶干扰可能会造成芽种群中两大类型芽之间比例（根茎芽／分蘖节芽）的振荡现象（Oscillation）。 最后展望了对于羊草今后应继续开展的工作主要集中在两大方面：一是有性繁殖与无性繁殖之间在不同生境或不同干扰条件下的权衡关系;二是处于不同斑块对比度( patch contrast)的生境中的羊草克隆分株之问的生理整合，及其强度与斑块对比度的定量关系。

Effects of Organic-Rich Sediment and Below-Ground Sulfide Exposure on Submerged Macrophyte, Hydrilla verticillata

The effects of organic-rich sediment and sulfide exposure on Hydrilla verticillata were investigated. The organic richness of sediment was simulated by adding sucrose into sediments, and sulfide exposure was conducted by adding sodium sulfide to plant roots. The length, biomass and density of shoot reduced in the sucrose-amended sediments, and the largest reduction occurred in the highest 1.0% addition treatment by 84.2%, 56.7% and 92.4%, respectively. However, the 0.1% addition treatment stimulated the growth of root. The effects of below-ground sulfide exposure on the physiological activities of H. verticillata were determined by adding sulfide to the below-ground tissue. Significantly inhibitory effects of sulfide were observed on plant photosynthesis, root carbohydrate and nitrogen synthetic reserves. The net photosynthetic rates, soluble carbohydrate and soluble protein contents in root were reduced by 104%, 71.8% and 49.8%, respectively, in the 0.6 mM sulfide treatment.

Microcystin-RR induces physiological stress and cell death in the cyanobacterium Aphanizomenon sp DC01 isolated from Lake Dianchi, China

The phytoplankton community in Lake Dianchi (Yunnan Province, Southwestern China) is dominated in April by a bloom of Aphanizomenon, that disappears Suddenly and is displaced by a Microcystis bloom in May. The reasons for the rapid bloom disappearance phenomenon and the temporal variability in the composition of phytoplankton assemblages are poorly understood. Cell growth, ultrastructure and physiological changes were examined in cultures of Aphanizomenon sp. DC01 isolated from Lake Dianchi exposed to different closes of rnicrocystin-RR (MC-RR) produced by the Microcystis bloom. MC-RR concentrations above 100 mu g L-1 markedly inhibited the pigment (chlorophyll-a, phycocyanin) synthesis and caused an increase of soluble carbohydrate and protein contents and nitrate reductase activity of toxin-treated blue-green algae. A drastic. reduction in photochemical efficiency of PSII (Fv/Fm) was also found. Morphological examinationn showed that the Aphanizomenon filaments disintegrated and file cells lysed gradually after 48 h Of toxin exposure. Transmission electron microscopy revealed that cellular inclusions of stressed cells almost leaked out completely and the cell membranes were grossly damaged. These findings demonstrate the allelopathic activity of Microcystis aeruginosa inducing physiological stress and cell death of Aphanizomenon sp. DC01 Although the active concentrations of microcystin were rather high, we propose that microcystin may function as allelopathic Substance due to inhomogeneous toxin concentrations close to Microcystis cells. Hence, it may play a role in species Succession of Aphanizomenon and Microcystis in Lake Dianchi.

Exploitation of intertidal Zostera species by Brent geese (Branta bernicla hrota): Why dig for your dinner?

Exploitation of intertidal Zostera spp by Pale-bellied Brent geese Branta bernicla hrota in Strangford Lough, Co. Down, was studied with respect to feeding method employed, plant parts exploited, the quality of the forage, and assimilation efficiency. Most Brent geese feeding activity involved digging behaviour, which, along with faecal analyses, indicated that birds were exploiting above (shoot) and below ground portions (rhizome) of the food plant. Nutritional information indicated that while rhizome was lower in overall energy, it contained more accessible energy in the form of water soluble carbohydrate and was lower in indigestible fibre than shoot. Feeding experiments indicated that Brent geese feeding on whole plants of Zostera noltii achieved 43% assimilation efficiency. Dig feeding of intertidal Zostera spp by Brent geese is likely to significantly increase the amount and quality of the forage available. Why dig feeding is not employed on all intertidal systems, and its potential effects on the food plants are discussed.