禾-豆混播草地种间竞争与共存

以羊草分别与沙打旺、兴安胡枝子、花苜蓿、紫花苜蓿、山野豌豆5种豆科牧草在混播数量比为1:0、2:1、1:2、0:1的条件下建立两物种混播草地,以相对产量、相对密度和相对产量总值为指标,比较各个混播草地中种间竞争的相对激烈程度;各个物种组合的种间竞争优势以及是否发生氮素资源分离;并探索不同禾-豆混播群落达到共存状态的可能途径.研究结果表明,各个禾-豆组合的相对产量总值分别在不同收获时期大于1,禾草与豆科牧草的生态位发生了不同程度的分离.沙打旺和紫花苜蓿对羊草具有显著的竞争优势,即使其种内竞争大于种间竞争时,混生的羊草亦受到强烈的种间竞争压力.与此相反,羊草对兴安胡枝子、花苜蓿和山野豌豆具有种间竞争优势.刈割对竞争双方的优劣地位产生很大影响,减少强竞争力物种的混播比例,可促进混播物种双方均受益,形成共存格局.实验采用的相对密度指标在预测未来混播种群组成上比相对产量更为可行,并且具有维持低个体大小、高构件密度能力是竞争关系中忍耐型物种能够长期存在的可能原因之一.     

A model of the competitive relationships between R. cochinchinensis and Z. mays

An understanding of the competitive relationship between weed and crop can be used in assessing what physiological aspects of the association can be exploited in the control of the weed. Field and greenhouse studies were conducted with Z. mays L. and Rottboellia cochinchinensis (Lour.) W D Clayton using a modified replacement series model in which the overall weed crop density in each treatment was maintained as a constant, but the proportion of the two species varied. The results indicated that the crop had greater competitive ability (K_mr) than the weed even at increasing weed densities. Under field conditions, the values of the Plant Relative Yield (PRY) indicated that severe specific competition was occurring and suggested that some environmental factor was limiting, while the Relative Yield Total (RYT) suggest that either the crop and the weed were exploiting the resources in mutual antagonism or that allelopathy was occurring. The limiting environmental factor that both species exploited in mutual antagonism in the field was light under conditions of adequate soil moisture and nutrients.     

A new index of interspecific competition for replacement and additive designs

The literature is reviewed to summarize the major indices of interspecific competition used in De Wit replacement experiments. Of the many indices that have been defined, some are less than clear as to their meaning, so interpretations are often difficult to make. In an effort to explore the performance of individual indices and to permit cross-correlation among indices, a series of hypothetical results in different competition scenarios is created. A standardized notation for all indices is also provided, along with equations and proofs. Nine indices are reviewed and analyzed for their behavior under the hypothetical scenarios and a new index that provides increased clarification and interpretability over other indices is proposed. Relative Yield Total, Aggressivity, and Relative Replacement Rate were shown to be poor measures of competition. Relative Crowding Coefficient has many restrictions to its use. The clearest index that includes two or more species is Relative Yield of Mixture. Indices that describe single species accurately were found to be Relative Yield (RY) and Relative Competition Intensity (RCI), both of which are mathematically convertible. An index introduced here, Change in Contribution (CC), is a single species index that differs from RY and RCI because it takes into account the overall biomass each species contributes.     

Interspecific interactions under fertilization among Elymus nutans,Festuca sinensis and Festuca ovina on the eastern Qinghai‐Tibetan plateau

A field replacement experiment was used to study the interspecific interaction among three perennial grasses (Elymus nutans, Festuca sinensis and Festuca ovina) that are distributed widely on the east Qinghai‐Tibetan plateau. The experiment consisted of four different species mixtures at four seeding densities and two fertilizer levels. Above‐ground biomass, relative yield and complementary effect were determined from harvested shoot dry weights. The results showed that above‐ground biomass was greater in all species mixtures than in monocultures. The difference between the observed and expected relative yield was greater than zero in all mixtures for E. nutans and was greater than zero in the F. sinensis/F. ovina mixture, but was below zero in all other mixtures for F. sinensis, and was below zero in all mixtures for F. ovina. The complementary effect was more negative across all seeding densities except at a seeding density of 400 seeds/m², and was negative across all mixtures except the F. sinensis/F. ovina mixture. In addition, fertilization had an insignificant impact on the relative yield, but a significant impact on the complementary effect. Fertilization enhanced negative interspecific interaction among the species.     

Arbuscular mycorrhizal impacts on competitive interactions between Acacia etbaica and Boswellia papyrifera seedlings under drought stress

Aims Arbuscular mycorrhizal fungi can have a substantial effect on the water and nutrient uptake by plants and the competition between plants in harsh environments where resource availability comes in pulses. In this study we focus on interspecific competition between Acaia etbaica and Boswellia papyrifera that have distinctive resource acquisition strategies. We compared the extent of interspecific competition with that of intraspecific competition.Methods In a greenhouse study we examined the influence of Arbuscular Mycorrhiza (AM) and pulsed water availability on competitive interactions between seedlings of the rapidly growing species A. etbaica and the slowly growing species B. papyrifera. A factorial experimental design was used. The factors were AM, two water levels and five species combinationsImportant findings Seedlings of both species benefitted from AM when grown alone, and the positive growth response to pulsed water availability in B. papyrifera seedlings was in contrast with the negative growth response for A. etbaica seedlings. AM also affected the competitive performance of both species. B. papyrifera was not affected by intraspecific competition, whereas A. etbaica was negatively affected compared to the seedlings grown alone. This effect was stronger in the presence of AM. In interspecific competition, A. etbaica outcompeted B. papyrifera. Mycorrhiza and pulsed water availability did not affect the outcome of interspecific competition, and the aggressivity index of A. etbaica remained unchanged. The extent to which AM influences plant competition in a drought-stressed environment may depend on belowground functional traits of the species. AM and pulsed water availability could modify the balance between intraspecific and interspecific competition. By affecting the balance between intraspecific and interspecific competition, both factors could impact the establishment and survival of seedlings.     

Seed and seedling vigour in relation to crop growth and yield

In theory, seed germination, vigour and size (three aspects of seed quality) may influence crop yield through both indirect and direct effects. The indirect effects include those on percentage emergence and time from sowing to emergence. These influence yield by altering plant population density, spatial arrangement, and crop duration. Direct effects on subsequent plant performance are more difficult to discern. A number of different approaches to testing the hypothesis that seed quality affects subsequent plant performance (implicit in some definitions of vigour) are illustrated. The results show that it is possible to detect such effects in some circumstances.     

Identification of an index tissue to predict zinc status of wheat

The critical concentration of Zn in wheat tissues for the prediction of Zn response and diagnosis of Zn deficiency was examined in a glasshouse experiment with wheat (Triticum aestivum, line QT 4118) grown to anthesis in two Vertisols at Zn application rates of 0, 1.25, 2.5, 5, 10, 15 and 30 kg ha^-1 equivalent as ZnSO₄ 7H₂O. The wheat tissues examined were the youngest mature leaf blade (YMB), the leaf immediately below the youngest mature leaf blade (YMB-1), the older leaves, the ear, the stem and the whole tops. The minimum Zn concentration required in a tissue at 0.90 relative yield, referred to as the critical Zn concentration, was determined using the Cate-Nelson graphical and statistical models, the Mitscherlich equation and a two-intersecting straight lines model. The Zn status of wheat was best defined by the Zn concentration in the YMB. Although the critical Zn concentration of the YMB did not vary much with the method of estimation, the Cate-Nelson statistical procedure explained a higher percentage of the variation in Zn concentration in the YMB and relative yield than the Mitscherlich and the two intersecting straight lines models. The critical concentration of Zn in the YMB was 16.0 mg kg^-1 dry matter. It is concluded that determination of Zn concentration in the YMB is the best procedure for evaluating the Zn status of wheat plants.     

Soil nutrient heterogeneity and competitive ability of three grass species (<Emphasis Type="Italic">Festuca ovina,Arrhenatherum elatius</Emphasis> and <Emphasis Type="Italic">Calamagrostis epigejos</Emphasis>) in experimental conditions

We studied the effects of differences in root growth and nutrient pool on the competitive ability of Festuca ovina (short grass), Arrhenatherum elatius and Calamagrostis epigejos (tall grasses) grown in monocultures and in mixtures of homogeneous and heterogeneous environments during two growing seasons. Analysis of variance revealed a significant effect of plant species on nutrient concentrations in above-ground biomass and of substrate type on contents of N, K, Ca, Mg in biomass. The ANOVA also confirmed the significant effect of competitive environment on the concentration of N, K in above-ground biomass. In heterogeneous environments, both tall grasses (in competition with F. ovina) were able to produce more roots in the nutrient-rich patches and to accumulate more nitrogen in plant tissues, which was associated with higher yield of their above-ground biomass. Thus, the relative competitive ability for nutrients of both tall grasses was higher than that of F. ovina. This competitive ability of A. elatius to C. epigejos increased in heterogeneous treatments.     

Specific interactions of alcohols and non‐alcohols with a biologically active boronic acid derivative: a spectroscopic study

The photophysical properties of 4‐fluoro‐2‐methoxyphenyl boronic acid (4FMPBA) are characterized using absorption and fluorescence techniques in series of non‐alcohols and alcohols. The results are analyzed using different solvent polarity functions and Kamlet and Catalan's multiple regression approaches. The excited state dipole moment and change in dipole moment are calculated using both the solvatochromic shift method and Reichardt's microscopic solvent polarity parameter . The ground state dipole moment is evaluated using quantum chemical calculations. It is found that general solute–solvent and hydrogen bond interactions are operative in this system. A red shift of ~ 9 nm in the emission spectra is observed with an increase in the solvent polarity, which depicts π→π^* transitions, as well as the possibility of an intramolecular charge transfer (ICT) character in the emitting singlet state of 4FMPBA. The relative quantum yield, radiative and non‐radiative decay constants are calculated in alkanes and alcohols using the single point method. It is found that the quantum yield of the molecule varies from 16.81% to 50.79% with the change in solvent polarity, indicating the dependence of fluorescence on the solvent environment. Copyright © 2015 John Wiley & Sons, Ltd.     

解磷菌株B25的筛选、鉴定及其解磷能力

从安徽省铜陵市铜官山尾矿库木贼根际分离筛选出多株解磷细菌,经过多次筛选纯化获得一株解磷能力较好的菌株B25.采用透射电镜观察和DNA分子技术,确定此菌株属于芽孢杆菌属.研究了解磷菌株B25在培养168 h内的解磷能力、溶液pH值以及菌株生长量的变化情况,并比较了B25在不同条件下的解磷能力.结果表明：解磷菌株B25的解磷能力与溶液pH值之间存在微弱的相关性,在碳源为葡萄糖、初始pH值为7.0、培养温度为30 ℃时解磷效果较好.     

Solvent effect on the relative quantum yield and fluorescence quenching of a newly synthesized coumarin derivative

We estimated the relative florescence quantum yield (Φ) of 8‐methoxy‐3‐[1‐(4,5‐dicarbomethoxy‐1,2,3‐triazoloacetyl)]coumarin [8MDTC] using a single‐point method with quinine sulfate in 0.1 M of sulfuric acid used as a standard reference. The fluorescence lifetimes, radiative and non‐radiative decay rate constants are calculated. Relative quantum yields were found to be less in the non‐polar solvents, indicating that the solute exhibits less fluorescence in a non‐polar environment. The fluorescence quenching of [8MDTC] by aniline was studied at room temperature by examining the steady state in five different solvents in order to explore various possible quenching mechanisms. The experimental results show a positive deviation in Stern–Volmer plots in all solvents. Ground state complex and sphere of action static quenching models were used to interpret the results. Many quenching rate parameters were calculated using these models. The values of these parameters suggest that the sphere of action static quenching model agrees well with the experimental results. Further, a finite sink approximation model was used to check whether these bimolecular reactions were diffusion limited or not. The values of the distance parameter R′ and the diffusion coefficient D were determined and are compared with the values of the encounter distance R and diffusion coefficient D calculated using the Stokes–Einstein equation. Copyright © 2014 John Wiley & Sons, Ltd.     

Effects of tillage systems on wheat and weed water relationships over time when growing together,in semiarid conditions

Water availability directly influences interactions and competition between weeds and crops. This article is based on the idea that relative water content (RWC) indicates the water uptake within plants and that it is possible to explain the water relationships between plants that are growing together. A field experiment carried out for 3 years (2013–2014, 2014–2015 and 2015–2016) compared the short-term effects of years and tillage systems on wheat grain yield, weed density, wheat-RWC, weed-RWC and soil water content (SWC), at tillering and flowering stages in a winter wheat monoculture system. The three tillage treatments were conventional tillage (CT), minimum tillage (MT) and no-tillage (NT). Wheat grain yield was low all years of study, because of low interannual rainfall, and we did not observe differences between tillage systems. Weed density was also affected by year and not by tillage systems. Lowest winter rainfall (73.4 mm from Nov to Feb) in the last year of the study (2015–2016), decreased the weed density in all tillage systems. Despite the rainfall variability over the 3 years of study, the NT system presented higher weed density (73 plants/m²) than MT and CT systems (39.83 and 46.33 plants/m²). We also observed a higher number of weed species for the NT system, facilitated by a high soil water storage in this system. The wheat-RWC, at tillering stage, varied with years and tillage systems; we found that high winter rainfall (2013–2014) led to higher values in CT (64.5%) compared with MT (52.9%) and NT plots (52.9%). Weed-RWC values did not vary and SWC was greater in NT than in CT and MT. At flowering stage, the year (2015–2016) with highest spring rainfall favoured higher wheat-RWC in NT (56.9%) compared with CT (48.3%). However, the lowest spring rainfall coincided with the lowest weed-RWC, (18% in NT plots) and SWC was always higher in NT soils. The results showed that climatic conditions affected the water competence dynamics between weeds and wheat in different ways. Seemingly, weeds can tolerate a lack of water availability until crop tillering stage independently of tillage system; however, the competition for water was not a problem as crops overcame the high weed density by flowering stage.     

Theories and methods on plant nutrition and growth

A theory comprising two basic concepts relating nutrition and growth is presented. The first concept is a nutrient flux model and is based upon studies of plants at constant internal nutrient concentrations, where a formal mathematical derivation shows that the relative uptake rate (R_U) and the relative growth rate (R_G) are equal. Deviations from equality are results of experimental insufficiencies and errors. The second concept is based on the observation that R_G is linearly related to the internal nutrient concentration. The slope represents nutrient productivity (P_n), an important parameter expressing growth rate per unit of nutrient. Light and the plant genome, for example, influence the value of the proportionality factor, P_n, but not the formal relationship between the internal nutrient concentration and R_G Not only the theory itself but many results and conclusions are very different from those obtained with traditional methods. In experiments where R_U was controlled during the exponential period of growth, the relationships between treatment (the relative addition rate, R_A), nutrient uptake (R_U) and growth (R_G) were reproduced with extremely low variability. In agreement with theory, internal nutrient concentration and R_G remained stable over time (steady-state). An extension of the theory is based upon the empirical assumption that after exponential growth, self-shading and ageing reduce P_n in proportion to biomass. This assumption has been successfully applied in predicting growth of forest stands, but the nature of the growth reduction is little understood. The generalized model has few parameters and can easily be rewritten to suit different experimental aims, for example to establish reference values and to model changes in soil fertility. Further extension and understanding of the model and different interpretations of the parameters are discussed.     

Ten Years of the Relative Risk Model and Regional Scale Ecological Risk Assessment

It has been 10 years since the publication of the relative risk model (RRM) for regional scale ecological risk assessment. The approach has since been used successfully for a variety of freshwater, marine, and terrestrial environments in North America, South America, and Australia. During this period the types of stressors have been expanded to include more than contaminants. Invasive species, habitat loss, stream alteration and blockage, temperature, change in land use, and climate have been incorporated into the assessments. Major developments in the RRM have included the extensive use of geographical information systems, uncertainty analysis using Monte Carlo techniques, and its application to retrospective assessments to determine causation. The future uses of the RRM include assessments for forestry and conservation management, an increasing use in invasive species evaluation, and in sustainability. Developments in risk communication, the use of Bayesian approaches, and in uncertainty analyses are on the horizon.     

灌溉水稻生长发育和潜力产量的模拟模型

本文提出的HDRICE模型是灌溉水稻生长的生理生态模型,它由相互衍接的水稻形态发育、干物质积累和叶面积发育三模块组成。形态发育模块用以模拟逐日温度和日长对水稻发育的影响,其参数可反映水稻品种的基本营养性、感温性和感光性;干物质积累模块用以模拟冠层CO_2同化、作物的维持呼吸和生长呼吸及干物质分配等过程;叶面积发育模块用以模拟叶面积指数的动态。本文还讨论了模型的输入参数和模型检验。模型可应用于模拟水稻的生长发育,预测水稻品种潜在产量及为取得潜在产量所必需的群体数量指标。     

基于HNP三态模型及相对熵方法的蛋白质折叠研究

把20种氨基酸简化为3类:疏水氨基酸(hydrophobic,H)、亲水氨基酸(hydrophilic,P)及中性氨基酸(neutral,N),每个氨基酸简化为一个点,用其C!原子来代替.采用非格点模型,以相对熵作为优化函数,进行蛋白质三维结构预测.为了与基于相对熵方法的蛋白质设计工作进行统一,采用了新的接触强度函数.选用蛋白质数据库中的天然蛋白质作为测试靶蛋白,结果表明,采用该模型和方法取得了较好的结果,预测结构相对于天然结构的均方根偏差在0.30～0.70nm之间.该工作为基于相对熵及HNP模型的蛋白质设计研究打下了基础.     

长期氮磷钾肥配施对贵州黄壤玉米产量和土壤养分可持续性的影响

为明确长期氮磷钾肥配施下贵州典型黄壤玉米产量、氮磷钾肥增产效应及土壤养分的演变特征,利用国家贵阳黄壤肥力与肥效长期定位试验,研究氮磷钾平衡施肥(NPK)与缺素施肥(N、NK、NP、PK)对玉米相对产量、氮磷钾肥增产贡献率及土壤氮磷钾素养分可持续性指数等的影响.结果表明: 氮磷钾平衡施肥有显著增产效果,玉米相对产量均值为:NPK>NP>NK>PK>CK;氮、磷、钾肥增产贡献率和农学利用率均为氮肥>磷肥>钾肥,施肥依存度为氮、磷、钾肥配施>氮肥>磷肥>钾肥,但缺磷处理(NK)玉米相对产量以每年1.4%的速度极显著下降,磷肥贡献率和依存度则以每年2.3%和1.4%的速度极显著上升,最终磷肥对玉米生产的影响逐渐与氮肥持平;缺磷处理土壤pH值和有机质含量均最低,而缺氮处理则较高;施用化学磷肥可提高黄壤磷素可持续性指数,但氮肥和钾肥对黄壤氮素和钾素可持续性指数无显著影响.综上,平衡施肥是贵州典型黄壤地区玉米高产的重要保障,其中磷肥与氮肥同等重要,但长期单施化肥尤其是缺磷处理不利于黄壤养分的可持续利用.