Supply pre-emption, not concentration reduction, is the mechanism of competition for nutrients

Concentration reduction theory is the leading theory regarding the mechanism of competition for nutrients in soils among plants, yet it has not been rigorously tested. Here we used a spatially explicit, fine-scale grid-based model that simulated diffusion and plant uptake of nutrients by plants in soil to test whether concentration reduction theory was appropriate for terrestrial plant competition for nutrients. In the absence of competition, increasing the rate of diffusion allows a plant to maintain positive growth rates below the lowest average concentration to which it can reduce nutrients in soil solution (R*). As such, differences among plants in the reduction of soil moisture, which here primarily affects nutrient diffusion, can cause R* to predict competitive success incorrectly. The stronger competitor for nutrients captures the largest proportion of the nutrient supply by ensuring nutrients contact its roots before those of a competitor. Although the metric derived from concentration reduction theory, R*, might have predictive power for competitive outcomes in terrestrial ecosystems, this evidence suggests that plants outcompete other plants for nutrients by pre-empting the supply, not reducing the average concentration.     

Competition both drives and impedes diversification in a model adaptive radiation

Competitors are known to be important in governing the outcome of evolutionary diversification during an adaptive radiation, but the precise mechanisms by which they exert their effects remain elusive. Using the model adaptive radiation of Pseudomonas fluorescens, we show experimentally that the effect of competition on diversification of a focal lineage depends on both the strength of competition and the ability of the competitors to diversify. We provide evidence that the extent of diversification in the absence of interspecific competitors depends on the strength of resource competition. We also show that the presence of competitors can actually increase diversity by increasing interspecific resource competition. Competitors that themselves are able to diversify prevent diversification of the focal lineage by removing otherwise available ecological opportunities. These results suggest that the progress of an adaptive radiation depends ultimately on the strength of resource competition, an effect that can be exaggerated or impeded by the presence of competitors.     

小麦浆片在开花过程中的结构与作用观察

小麦可育株系和杂种F1花期早,开花张角大,开闭花持续时间短,其浆片吸胀快,体积大,增重幅度大,浆片解剖结构有3个部分;表皮层细胞外壁厚,有角质层,无气孔（器）;基本组织薄壁细胞（GPC）含丰富的原生质,在浆片吸胀和萎缩过程中,GPC体积增大至内膜系统破裂,细胞自溶后内溶物撤离;维管束分散于基本组织中,由导管,筛管薄壁细胞所组成。     

Identification of the ammonium-dependent isoenzyme of glutamate dehydrogenase as the form induced by senescence or darkness stress in the first leaf of wheat

The level of glutamate dehydrogenase activity increases nearly 3 fold in detached wheat ( Triticum aestivum L. cv. Capitole) leaves during 72 h incubation with 15 mM ammonia. De novo synthesis of one of the glutamate dehydrogenase isoenzymes is shown to be correlated with the activity increase, by using an immunochemical approach. The identification of the ammonia inducible isoenzyme as the form previously reported induced by darkness stress or senescence (Laurière et al. 1981, Physiol. Plant. 52: 151-155), provides new information on the possible physiological significance of the response to ammonia.     

The absorption and translocation of diclofop-methyl and amitrole in wheat and oat roots

The absorption and translocation of diclofop-methyl (methyl 2-[4(2',4'-dichlorophenoxy)phenoxy]propanoate) was examined by using a specially designed treatment apparatus that separated excised roots or roots of seedlings into four zones. [¹⁴C]-Diclofop-methyl was absorbed along the entire root length of both wheat ( Triticum aestivum L.) and oat ( Avena sativa L.). In both species, absorption was greatest in the apical region of the root. Absorption by the apical region of wheat roots was more than three times greater than the basal portions, and more than twice as great as the apical region of oat roots. Less than 5% of the absorbed diclofop-methyl was translocated in both wheat and oat roots. Diclofop-methyl and diclofop(2-[4(2',4'-dichlorophenoxy)phenoxy]propanoic acid) were the predominant translocated forms. The absorption and translocation of amitrole (3-amino-1,2,4-triazole) were also examined. Amitrole was absorbed along the entire length of wheat roots and translocated primatily in the basipetal direction. The usefulness of the specially designed apparatus for biochemical and physiological studies is discussed.     

水曲柳苗木地下竞争与地上竞争的定量研究

对3种密度进行栽培试验,利用通径分析的方法,研究了水曲柳地下竞争和地上竞争的关系及对总竞争的影响。结果表明,水曲柳苗木的地下部分生物量、地上部分生物量和总生物量与营养空间有密切关系。随着苗木空间距离增加,由生物量计算的竞争指数下降。在同一密度条件下,地下竞争指数明显大于地上竞争指数。由于地下生长与地上生长的相互作用,各竞争指数之间具有明显的相关性。但是地下竞争和地上竞争对总竞争的影响是不同的,通径分析可以定量的区分地下竞争和地上竞争的相对大小。地下竞争对总竞争的直接作用范围在0．5543～0．7426之间,明显大于地上竞争对总竞争的直接作用(0．2851～0．5282)。随着距离的增加,单株苗木的生长空间加大,地上部分的竞争作用增加,地下部分的竞争程度减弱。但是,地下根系的竞争在水曲柳苗木总的竞争中占有重要地位。     

A burst of CO2 from photosynthesizing leaves after a temperature decrease under constant light conditions

A transient CO₂ burst from seedlings of some plant species was observed after a rapid temperature decrease. The magnitude of the CO₂ release depended on initial temperature, oxygen concentration and light intensity. To obtain a maximal value of CO₂ release, the temperature had to decrease by more than 8°C. The phenomenon was detected only in the light, and was confined to C₃ species. It was inhibited by low oxygen concentration, indicating its possible connection with photorespiration.     

小麦小孢子发生过程的超微结构

采用透镜电镜技术对小麦（Ｔｒｉｔｉｃｕｍ ａｅｓｔｉｖｕｍ）小孢子发生过程进行了超微结构观察。造孢细胞时期细胞质中含有丰富的核糖体,质体和线粒体。在小孢子母细胞减数分裂过程中,有核糖体数量存在逐渐减少的现象,质体和线袜体结构在双线期／终变期和中期１简化,二分体时期,质体和线粒体形态结构基本恢复正常。结果表明,啵麦小孢子母细胞减数分裂过程中存在质体和线粒体的脱人化与再分化过程,但该过程与核糖体数量增     

Nutrient availability and atmospheric CO2 partial pressure modulate the effects of nutrient heterogeneity on the size structure of populations in grassland species

BACKGROUND AND AIMS: Size-asymmetric competition occurs when larger plants have a disproportionate advantage in competition with smaller plants. It has been hypothesized that nutrient heterogeneity may promote it. Experiments testing this hypothesis are inconclusive, and in most cases have evaluated the effects of nutrient heterogeneity separately from other environmental factors. The aim of this study was to test, using populations of Lolium perenne, Plantago lanceolata and Holcus lanatus, two hypotheses: (a) nutrient heterogeneity promotes size-asymmetric competition; and (b) nutrient heterogeneity interacts with both atmospheric CO2 partial pressure (P(CO2)) and nutrient availability to determine the magnitude of this response. METHODS: Microcosms consisting of monocultures of the three species were grown for 90 d in a factorial experiment with the following treatments: P(CO2) (37.5 and 70 Pa) and nutrient availability (NA; 40 and 120 mg of N added as organic material) combined with different spatial distribution of the organic material (NH; homogeneous and heterogeneous). Differences in the size of individual plants within populations (size inequality) were quantified using the coefficient of variation of individual above-ground biomass and the combined biomass of the two largest individuals in each microcosm. Increases in size inequality were associated with size-asymmetric competition. KEY RESULTS: Size inequality increased when the nutrients were heterogeneously supplied in the three species. The effects of NH on this response were more pronounced under high nutrient supply in both Plantago and Holcus (significant NA x NH interactions) and under elevated P(CO2) in Plantago (significant P(CO2) x NA x NH interaction). No significant two- and three-way interactions were found for Lolium. CONCLUSIONS: Our first hypothesis was supported by our results, as nutrient heterogeneity promoted size-asymmetric competition in the three species evaluated. Nutrient supply and P(CO2) modified the magnitude of this effect in Plantago and Holcus, but not in Lolium. Thus, our second hypothesis was partially supported.     

不同供水条件对小麦强、弱势籽粒中淀粉粒度分布的影响

以3个淀粉含量不同的冬小麦品种山农12、鲁麦21和济南17为材料,设灌溉和旱作2种栽培处理,对不同水分条件下小麦强、弱势籽粒中淀粉粒的体积、数目和表面积的分布特征进行了研究.结果表明,小麦强、弱势籽粒均含有A(＞9.8 μm)、B(2.0～9.8 μm)、C(＜2.0 μm)3种类型的淀粉粒,但不同类型淀粉粒的分布状况存在明显差异.在强势籽粒中,淀粉粒的体积和表面积分布均表现为三峰分布,而弱势籽粒中淀粉粒的体积和表面积分布则表现为双峰分布.与弱势粒相比较,强势粒中C型淀粉粒(＜2.0 μm)的体积百分比为7.25%～9.31%,表面积百分比为34.88%～41.51%,而弱势粒的体积和表面积百分比分别为5.33%～6.40%和26.31%～33.54%.强、弱势籽粒中＜0.6 μm和0.6～2.0 μm范围内的淀粉粒数目存在明显差异,强势粒为1.86%～6.13%和83.77%～87.77%,而弱势粒为25.72%～37.42%和52.77%～58.48%.与灌溉栽培相比较,旱作栽培条件下籽粒中B、C型淀粉粒体积和表面积百分比显著增加,而A型淀粉粒体积和表面积显著减少;弱势粒中＜0.6 μm的淀粉粒数目显著增加,强势籽粒中淀粉粒的数目无显著变化.与弱势粒相比较,强势粒中的蛋白质含量较高,C型淀粉粒的体积和表面积所占比例较大,而强势粒中的淀粉含量较低,且A、B型淀粉粒比例也较小.与灌溉栽培相比较,旱作栽培条件下强、弱势籽粒中B、C型淀粉粒体积和表面积百分比增加,蛋白质含量也显著增加,淀粉含量降低.表明水分亏缺能提高籽粒中B、C型淀粉粒体积和表面积百分比及蛋白质含量.     

Induction of haploid and diploid plants though in vitro anther culture of haploid wheat (n=3x=21)

Summary Five haploid plants of wheat were used for anther culture. Embryos were formed and six plants were regenerated. Of these, two were haploid (n=3x=21) and two diploid (2n=6x=42). The two diploids derived from the anthers of the same haploid wheat plant gave seeds, but the fertility was reduced in one of them showing, abnormalities at meiosis.     

壳聚糖对镉胁迫条件下小麦生长及生理的影响

以小麦为材料,研究了镉对水培小麦幼苗的胁迫作用及壳聚糖对镉胁迫的缓解效应。结果表明:250μmol·L-1的镉胁迫处理后,小麦幼苗的生长受到严重抑制,叶片中叶绿素含量明显下降,金属硫蛋白和丙二醛的含量显著上升(P<0.05);培养液中添加0.01%的壳聚糖能降低小麦幼苗中镉的积累,对小麦幼苗的镉胁迫具有明显地缓解效应。     

普通小麦特殊染色体构型环状单价体和类等臂单价的研究

在植物花粉母细胞减数分裂中期Ⅰ出现的单价体,因不配对常呈捧状或弯曲成V形而独立于赤道板之外,然而有时其自身的两臀也会配对发生交叉而成环状,这种环状单价体在黑麦、大麦和小麦中已有报道。环状单价体的研究对染色体特异性配对等基本理论问题有重要的意义。1987和1988年,我们在鉴定(中国春单体×小偃6号)F_1单     

Solute adjustments in leaves of two species of wheat at two different stages of growth in response to salinity

Changes in leaf solute concentrations in response to salinity were measured at two growth stages in two species of wheat, Triticum turgidum L. cv. Aldura (Durum group) and Triticum aestivum L., cv. Probred that differed in their salt tolerances. Both species at 55 days of age were Na⁺-excluders, but the concentration of Na⁺ was 10 times higher in T. turgidum than T. aestivum at low to moderate levels of stress. The ratio then decreased until it was 2:1 at – 1.2 MPa. In T. turgidum, K⁺ concentrations decreased with increasing Na⁺ concentrations so that the sum of the two cations remained constant at all stress levels, but in T. aestivum K⁺ decreased more rapidly than Na⁺ increased. In both species growing in media at 0 to –0.6 MPa, the amounts of Mg²⁺ and Ca²⁺ in 55-day-old plants that could be extracted with hot water were below 0.1 mmol (g dry weight)^?1. Then, as osmotic potentials of media decreased further, hot water-extractable Ca²⁺ increased greatly until, at – 1.2 MPa, Ca²⁺ concentrations were almost equal to the sum of Na⁺ and K⁺. In the range of 0 to –1.0 MPa, the ratio of Cl^? to total cationic charge remained constant at 1:6 in T. aestivum and 1:2 in T. turgidum. However, at – 1.2 MPa, the ratio in both species had changed to 2:3. Sucrose and betaine concentrations were 4 and 48 μmol (g dry weight)^?1, respectively, in non-stressed plants of both species. At – 1.2 MPa, sucrose had increased 30-fold but betaine had increased only 2.5-fold. Proline increased exponentially relative to foliar Na⁺ in T. turgidum. In T. aestivum only plants grown at –1.2 MPa contained sufficient Na⁺ to stimulate the accumulation of proline. Although the quantities of the solutes in leaves of non-stressed 96-day-old plants differed from those in non-stressed younger plants, the patterns of change of organic solutes as the older plants were subjected to increasing saline stresses were the same as in younger plants with the exception of sucrose. Sucrose concentrations were much higher in leaves of non-stressed older plants and this sugar first increased and then decreased with decreasing osmotic potentials of media.     

半干旱条件下春小麦种群不整齐性动态及其水分生理生态基础

在黄土高原半干时生态条件下设置了低、中、高３个密度梯度的以水为限制因子的实验,各密度种群个体重量分布偏倚度（Ｇ）随时间的延续而增大,增大的幅度随密度增高而上升,在此基础之上,在人工气候室内模拟自然条件,对竞争中不同大小个体之间的关生理生态指标进行测定与比较,发现在生长发育过程中,由于对有限水资源的争夺性利用相邻的不同大小个体之间吸水能力差异迅速增 大,竞争使不同大小邻体的根系吸水效率,总蒸腾速率和