Effect of host plant resistance and chemical control of the head bug, Calocoris angustatus Leth., on grain quality and seedling establishment in sorghum

The sorghum head bug, Calocoris angustatus Lethiery (Hemiptera: Miridae), is one of the most important pests of grain sorghum in India. Studies were conducted to quantify the effect of head bug damage on grain quality and seedling establishment on head bug-resistant cultivars (IS 17610 and IS 21443), a moderately susceptible cultivar (IS 9692), and a susceptible commercial cultivar (CSH 11). Differences in 1000-grain mass, seed germination and percentage of floaters were significant between protected and unprotected plots in CSH 11 and IS 9692, but not in IS 17610 and IS 21443. Grain damage ratings were significantly lower in IS 17610 than in IS 9692 and CSH 11 across different protection levels. Head bug-damaged grain had greater protein content than the undamaged grain, possibly because of depletion in starch, and a marginal increase in soluble sugars. Amounts of proline and tyrosine were greater in the bug-damaged grain than in the undamaged grain, while the reverse was true for aspartic acid, methionine, leucine and lysine. Head bug damage also increased the tannin content in IS 9692 (which is a high-tannin genotype). Moisture regimes and insecticide protection levels significantly affected seedling emergence. Seedling emergence of CSH 11 was lower than that in IS 17610. In the latter genotype, the differences between protected and unprotected plots were not significant. Head bug damage thus not only leads to quantitative loss in grain yield, but also spoils the grain quality and renders the grain unfit for seed purposes. These qualitative effects should be taken into account while estimating losses due to bug damage and determining economic thresholds.     

dlt操纵子赋予苏云金芽胞杆菌对阳离子抗菌肽的抗性和对昆虫的毒力

【目的】革兰氏阳性菌中的dlt操纵子编码细胞壁中磷壁酸发生D-丙氨酰化修饰所必需的酶。D-丙氨酰化使细胞表面产生正电荷,并因此排斥带正电的分子,例如阳离子抗菌肽,从而赋予对宿主的抗性。本文中,我们研究了dlt操纵子对苏云金芽胞杆菌表型性状的影响及在对昆虫毒力中发挥的作用。【方法】通过同源重组构建了Δdlt ABt基因缺失突变株,并对其进行形态学观察、表面电荷差异分析、抗逆性分析和毒力测定。【结果】结果表明,dlt A的失活显著降低了细胞表面的净负电荷,对阳离子抗菌肽(多粘菌素B和溶菌酶)的抗性和碱耐受性显著下降。同时,Δdlt ABt的生长曲线发生明显改变,细胞表面粗糙且形状不规则,生物膜形成减少和群游运动能力增强。此外,dlt A的失活降低了对昆虫中肠上皮细胞的粘附能力,并减弱了对家蚕的毒力。【结论】研究结果表明,dlt操纵子介导的磷壁酸发生D-丙氨酰化修饰与苏云金芽胞杆菌的许多表型性状密切相关,并且在苏云金芽胞杆菌对昆虫的致病性及抵抗昆虫体液免疫保护中具有重要作用。     

羊草基因型数目与氮添加对土壤微生物群落的交互影响

物种多样性(或同一物种遗传多样性)减少和氮富集都是影响陆地生态系统进程的主要因素,它们之间的交互作用是否对土壤微生物群落产生显著影响已成为研究者关心的主要科学问题。研究羊草基因型数目(1、2、4三种基因型数目组合)和氮添加(无氮添加、低氮添加和高氮添加3种水平)对土壤微生物群落的总磷脂脂肪酸(PLFA,Phospholipid Fatty Acid)含量、细菌PLFA生物标记含量、真菌PLFA生物标记含量、真菌/细菌比、以及基于每个PLFA生物标记相对含量百分比所得微生物群落的Shannon-Wiener多样性指数和Simpson优势度指数的影响。结果表明:氮添加对细菌PLFA生物标记含量,以及土壤微生物PLFA生物标记的Shannon-Wiener多样性指数和Simpson优势度指数具有显著影响(P0.05);基因型数目对所测变量无显著影响(P0.05),但基因型数目和氮添加的交互作用对细菌PLFA生物标记含量和真菌/细菌比具有显著影响(P0.05)。研究结果为全球变化背景下氮沉降及重要物种种群数量减少对土壤微生物群落的影响提供了科学数据,为合理解释群落动态变化提供了数据支持。     

Influence of plant development and environment on transgene expression in potato and consequences for insect resistance

Clonal replicates of different transformed potato plants expressing transgene constructs containing the constitutive Cauliflower Mosaic Virus (CaMV) 35S promoter, and sequences encoding the plant defensive proteins snowdrop lectin (Galanthus nivalis agglutinin; GNA), and bean chitinase (BCH) were propagated in tissue culture. Plants were grown to maturity, at first under controlled environmental conditions, and later in the glasshouse. For a given transgene product, protein accumulation was found to vary between the different lines of clonal replicates (where each line was derived from a single primary transformant plant), as expected. However, variability was also found to exist within each line of clonal replicates, comparable to the variation of mean expression levels observed between the different clonal lines. Levels of GNA, accumulated in different parts of a transgenic potato plant, also showed variation but to a lesser extent than plant–plant variation in expression. With the majority of the clonal lines investigated, accumulation of the transgene product was found to increase as the potato plant developed, with maximum levels found in mature plants. The variation in accumulation of GNA among transgenic plants within a line of clonal replicates was exploited to demonstrate that the enhanced resistance towards larvae of the tomato moth, Lacanobia oleracea L., caused by expression of this protein in potato, was directly correlated with the level of GNA present in the plants, and that conditions under which the plants were grown affect the levels of GNA expression and subsequent levels of insect resistance.     

Pod hairs as a factor in Vigna vexillata resistance to the pod-sucking bug, Clavigralla tomentosicollis

Two varieties of Vigna vexillata Benth proved more highly resistant, both under field (free-choice) and screenhouse (no-choice) conditions, to infestation and damage by the pod-sucking bug Clavigralla tomentosicollis (Stål.) (Hemiptera: Coreidae) than cowpea (Vigna unguiculata Walp.) varieties. Trichomes on the pod of V. vexillata partly accounted for the resistance. However, other factors in the pod or seeds are involved in the resistance. Because the pod wall of V. vexillata is not tougher than that of cowpeas, biochemical characteristics of pods and seeds of V. vexillata will be further investigated.

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Résumé Deux variétés de Vigna vexillata se sont avérées plus résistantes aux infestations et dégâts causés par la punaise des cosses Clavigralla tomentosicollis (Stål.) (Hemiptera: Coreidae) que les variétés de Vigna unguiculata, tant en champ (condition de libre choix) qu'en serre (sans choix possible). Les trichomes des cosses de V. vexillata sont en partie responsables de cette résistance. Cependant d'autres facteurs de la cosses ou des fèves sont impliqués dan la résistance. Comme la paroi de la cosse de V. vexillata n'offre pas plus de résistance mécanique que celle de V. unguiculata, les études futures se porteront sur les caractéristiques biochimiques des cosses et des fèves de V. vexillata.

     

Orientation of males of sorghum midge,Contarinia sorghicola to sex pheromones from virgin females in the field

The orientation of males of the sorghum midge,Contarinia sorghicola Coq. (Diptera: Cecidomyiidae) towards virgin female baited sticky traps was studied in the field. Male response increased linearly with an increase in the number of virgin females in the sticky traps. Five females per vial were optimum for monitoring midge populations in the field. Numbers of males trapped were significantly greater in traps placed at 0.5 and 1.5 m above ground level compared with those placed at 2.5 m. Peak trap catches occurred at 0900 h. The number of males trapped decreased significantly after 1400 h; male catches continued till sunset. Trap catches followed the same pattern as the number of ovipositing females on sorghum panicles at the half-anthesis stage. Midge activity decreased with an increase in temperature and a decrease in relative humidity. Peak midge density was observed during the second fortnight of October in the rainy season and during February-March in the post-rainy season. Sex pheromones can be used to monitor midge population dynamics for integrated pest management and to screen for host plant resistance to this insect.     

Plasmid-borne resistance to arsenate, arsenite, cadmium, and chloramphenicol in a Rhodococcus species

Summary A primarily genetic approach was employed to obtain plasmids in Rhodococcus erythropolis ATCC 12674 which carried genes conferring increased resistance to sodium arsenate and arsenite, cadmium chloride, and chloramphenicol. The plasmids were large, migrating more slowly than chromosomal DNA in agarose gels, and were made up of resistance determinants from the host organism together with part of the genome of nocardiophage Q4. Purified plasmid was used to transform a suitable recipient to increased resistance to sodium arsenate, sodium arsenite, and cadmium chloride.     

Genetic variation in chrysanthemum for resistance toFrankliniella occidentalis

In a choice-experiment, 42 chrysanthemum cultivars were screened for resistance toFrankliniella occidentalis (Pergande). Oviposition preference, two types of feeding damage and thrips numbers per flower were recorded as measures of resistance. A large genetic variation in thrips resistance was found among the cultivars screened. The amount of feeding damage was strongly determined by oviposition preference. Besides, a positive correlation was found between the oviposition preference in non-flowering chrysanthemums (number of eggs) and flowering chrysanthemums (number of thrips per flower). Thrips feeding on young, developing tissues, causes growth damage because affected cells are unable to expand and leaves become distorted. Thrips feeding on older, expanded leaves causes cells to become filled with air, resulting in ‘silver’ damage. The amounts of growth-and ‘silver’ damage were negatively correlated suggesting that thrips chose either young or older leaves to feed on. The order of resistance among cultivars did not change during the experiment. In order to get more insight in resistance mechanisms the influence of some plant- and flower characters on resistance was examined. The plant characters height, number of leaves, flower production and flower weight were all negatively correlated with resistance. It is suggested that tall chrysanthemum cultivars with many and large flowers may invest less in defence than smaller cultivars, and therefore are more damaged by thrips.     

Foliar pubescence and resistance to potato moth, Phthorimaea operculella, in Lycopersicon hirsutum

Pubescence characteristics for six accessions of Lycopersicon hirsutum Dunal and five accessions of L. hirsutum f. glabratum CH Mull. were determined and compared with those of an accession of cultivated tomato (L. esculentum Mill.). Removal of trichome exudates from excised leaflets using ethanol solution resulted in a reduced mortality and increased survival of potato moth (Phthorimaea operculella (Zeller)) neonates for the accessions that were most lethal when not treated with ethanol solution. No such treatment effect was evident for L. esculentum or for the L. hirsutum accession with least effect on neonates when its trichomes were intact. In a glasshouse experiment with caged intact plants, mortality of neonate P. operculella placed on the abaxial surface was greater on seven accessions than for L. esculentum.Neonates were less severely affected on the adaxial surface. Eleven days after inoculation, no live larvae were found on LA 1927, PI 127827, PI 134418, and PI 134428, and numbers on other accessions were lower than for L. esculentum. Eventual emergence of adults followed a similar trend. Multiple regression of insect data against pubescence indicated a significant correlation between density of type IV and VI trichomes and neonate mortality, decreased larval development and decreased adult emergence. Non-glandular type V trichomes were positively correlated with high survival of insects to 11 days and to adult. Though factors other than glandular trichomes are likely to be important, increased density of type IV and VI, along with reduced type V, are shown to be important to select in breeding for P. operculella resistance.     

rpoS基因缺失突变对荧光假单胞菌胁迫耐受性、群体感应及腐败活性的影响

【目的】微生物活动是引起食品腐败的主要原因,研究食品腐败菌的腐败作用调控机制对于保证食品的质量和安全具有重要意义。荧光假单胞菌是一种代表性的食品腐败菌,本文旨在研究RNA聚合酶的选择性sigma因子Rpo S在荧光假单胞菌致腐败过程中的作用。【方法】运用同源重组的方法构建荧光假单胞菌冷藏鱼分离株的rpo S基因缺失突变株,比较野生型和突变株暴露于不同胁迫条件下的存活率;通过液相色谱-串联质谱(LC-MS/MS)分析野生型和突变株产生高丝氨酸内酯类(AHLs)群体感应信号分子的种类和含量;检测野生型和突变株接种于灭菌三文鱼汁后4°C贮存过程中的菌落总数和挥发性盐基氮的生成量。【结果】成功构建了荧光假单胞菌rpo S基因缺失突变株。rpo S基因的缺失导致荧光假单胞菌对10 mmol/L H2O2和15%乙醇的耐受性显著降低,对150μg/m L结晶紫和175 mmol/L醋酸的耐受性有一定程度增强,不影响其对47°C和20%Na Cl的耐受性。荧光假单胞菌在rpo S基因缺失突变后长链信号分子C_(10)-HSL、C_(12)-HSL和C_(14)-HSL的含量增加。在灭菌三文鱼汁中的腐败活性检测表明rpo S基因缺失可导致荧光假单胞菌挥发性盐基氮的生成量显著降低。【结论】荧光假单胞菌的Rpo S不仅调节细菌对多种胁迫条件的耐受性,还影响AHL群体感应和腐败活性。     

The mechanism of trichome resistance in Anaphalis margaritacea to the meadow spittlebug Philaenus spumarius

This study demonstrated how simple, lanate trichomes on the stem of Anaphalis margaritacea (D.C.) inhibit feeding by young nymphs of Philaenus spumarius (L.). Nymphs were caged on stems which were subsequently sectioned and examined for feeding marks. The lack of stylet punctures at sites where nymphs were unable to feed indicated that trichomes prevented the start of stylet penetration rather than interfering with the progress of the stylets after penetration had begun. Trichome resistance declined progressively with spittlebug instar from complete resistance to first instar nymphs through complete absence of resistance to fifth instar nymphs. Discriminant analysis of the effect of number of trichomes per mm², vertical density, and height on trichome resistance to third instar nymphs revealed that trichome height was the critical factor in resistance. Variation in the percent of nymphs in each instar able to feed when caged on the stem was (1) positively correlated with degree to which the average rostrum length of the instar exceeded the trichome height, (2) independent of trichome density, which was uniformly high on all stems. Trichomes prevented stylet penetration where trichome height exceeded the length of the nymph's rostrum, probably because the necessary stimuli were not received when the sensilla on the tip of the rostrum could not touch the surface of the stem. A similar mechanism may explain resistance of simple trichomes to crop pests in the Cicadellidae.

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Résumé Ce travail montre comment des trichomes simples et laineux sur les tiges d'Anaphalis margaritacea (D.C.) inhibent la prise d'aliments par les jeunes larves de Philaenus spumarius L. Les larves ont été encagées sur des tiges qui ont été ultérieurement coupées et les piqûres alimentaires dénombrées. L'absence de piqûres par les stylets aux lieux où les larves ont été incapables de s'alimenter a montré que les trichomes ont empêché le début de la pénétration des stylets plus qu'ils n'ont entravé leur progression après le début de la pénétration. La résistance des trichomes diminue progressivement: totale pour le premier stade larvaire, elle est devenue nulle au cinquième stade. Une analyse discriminante des effets de la densité des trichome par mm², de la densité verticale, de leur hauteur sur la résistance des trichomes aux larves de 3ème stade, a révélé que la hauteur du trichome est le facteur de résistance. La variation dans le pourcentage de larves de chaque stade encagées sur la tige, capables de consommer, présentait une relation positive avec le degré par lequel la longueur du rostre dépasse la hauteur du trichome, quelle que soit la densité des trichomes qui est toujours élevée sur toutes les tiges. Les trichomes ont empêché la pénétration des stylets quand leur hauteur a dépassé la longueur du rostre, probablement parce que les stimuli nécessaires n'ont pas été reçus quant l'extrémité du rostre ne pouvait pas atteindre la surface de la tige. Un mécanisme semblable peut expliquer la résistance de trichomes simples aux Cicadellidae.

     

Seasonal dynamics of fine root biomass, root length density, specific root length, and soil resource availability in a Larix gmelinii plantation

Fine root turnover is a major pathway for carbon and nutrient cycling in terrestrial ecosystems and is most likely sensitive to many global change factors. Despite the importance of fine root turnover in plant C allocation and nutrient cycling dynamics and the tremendous research efforts in the past, our understanding of it remains limited. This is because the dynamics processes associated with soil resources availability are still poorly understood. Soil moisture, temperature, and available nitrogen are the most important soil characteristics that impact fine root growth and mortality at both the individual root branch and at the ecosystem level. In temperate forest ecosystems, seasonal changes of soil resource availability will alter the pattern of carbon allocation to belowground. Therefore, fine root biomass, root length density (RLD) and specific root length (SRL) vary during the growing season. Studying seasonal changes of fine root biomass, RLD, and SRL associated with soil resource availability will help us understand the mechanistic controls of carbon to fine root longevity and turnover. The objective of this study was to understand whether seasonal variations of fine root biomass, RLD and SRL were associated with soil resource availability, such as moisture, temperature, and nitrogen, and to understand how these soil components impact fine root dynamics in Larix gmelinii plantation. We used a soil coring method to obtain fine root samples (⩽2 mm in diameter) every month from May to October in 2002 from a 17-year-old L. gmelinii plantation in Maoershan Experiment Station, Northeast Forestry University, China. Seventy-two soil cores (inside diameter 60 mm; depth intervals: 0–10 cm, 10–20 cm, 20–30 cm) were sampled randomly from three replicates 25 m × 30 m plots to estimate fine root biomass (live and dead), and calculate RLD and SRL. Soil moisture, temperature, and nitrogen (ammonia and nitrates) at three depth intervals were also analyzed in these plots. Results showed that the average standing fine root biomass (live and dead) was 189.1 g·m⁻²·a⁻¹, 50% (95.4 g·m⁻²·a⁻¹) in the surface soil layer (0–10 cm), 33% (61.5 g·m⁻²·a⁻¹), 17% (32.2 g·m⁻²·a⁻¹) in the middle (10–20 cm) and deep layer (20–30cm), respectively. Live and dead fine root biomass was the highest from May to July and in September, but lower in August and October. The live fine root biomass decreased and dead biomass increased during the growing season. Mean RLD (7,411.56 m·m⁻³·a⁻¹) and SRL (10.83 m·g⁻¹·a⁻¹) in the surface layer were higher than RLD (1 474.68 m·m⁻³·a⁻¹) and SRL (8.56 m·g⁻¹·a⁻¹) in the deep soil layer. RLD and SRL in May were the highest (10 621.45 m·m⁻³ and 14.83m·g⁻¹) compared with those in the other months, and RLD was the lowest in September (2 198.20 m·m⁻³) and SRL in October (3.77 m·g⁻¹). Seasonal dynamics of fine root biomass, RLD, and SRL showed a close relationship with changes in soil moisture, temperature, and nitrogen availability. To a lesser extent, the temperature could be determined by regression analysis. Fine roots in the upper soil layer have a function of absorbing moisture and nutrients, while the main function of deeper soil may be moisture uptake rather than nutrient acquisition. Therefore, carbon allocation to roots in the upper soil layer and deeper soil layer was different. Multiple regression analysis showed that variation in soil resource availability could explain 71–73% of the seasonal variation of RLD and SRL and 58% of the variation in fine root biomass. These results suggested a greater metabolic activity of fine roots living in soil with higher resource availability, which resulted in an increased allocation of carbohydrate to these roots, but a lower allocation of carbohydrate to those in soil with lower resource availability. __________ Translated from Acta Phytoecologica Sinica, 2005, 29(3): 403–410 [译自: 植物生态学报, 2005, 29(3): 403–410]     

Utilization of chemical inducers of resistance and Cryptococcus flavescens OH 182.9 to reduce Fusarium head blight under greenhouse conditions

Four chemicals [salicylic acid (SA), sodium salt of salicylic acid (NaSA), isonicotinic acid (INA), and DL-β-amino-n-butyric acid (BABA)] and the yeast antagonist Cryptococcus flavescens (=C. nodaensis nomen nudum) OH 182.9 were evaluated separately or together for the ability to reduce Fusarium head blight (FHB) of wheat in the greenhouse. When sprayed onto wheat heads at 3 days prior to pathogen challenge with Gibberella zeae, NaSA and INA at 10 mM significantly reduced FHB severity compared to the non-treated disease control. Applied at concentrations of 1 and 5 mM at 3 days before pathogen challenge, NaSA or INA in combination with OH 182.9 did not significantly reduce FHB severity compared to either treatment alone, though the lowest disease severity values frequently were associated with the combination treatments. When sprayed onto wheat heads just beginning to emerge from boot at 10 days prior to pathogen inoculation, NaSA, INA, and BABA at 1 mM significantly reduced FHB severity indicating that induced systemic resistance was at least partially responsible for the reduction of FHB disease. Induced FHB resistance was achieved by treating wheat with INA at concentrations as low as 0.1 mM. In only one instance was 100-kernel weight affected by any chemical or combination of chemicals with OH 182.9 treatment. Data from our studies in the greenhouse suggest that chemical inducers can induce resistance in wheat against FHB, and that further efforts are warranted to explore the potential of improved control of FHB disease by incorporating chemical inducers with the FHB biocontrol agent OH 182.9.     

末端氧化酶CyxA增强肺炎克雷伯菌对外界环境的抵抗力及致病性

【背景】细胞色素bd末端氧化酶存在于许多致病菌中,保护细菌免受各种不利环境应激的损害,促进多种致病菌的毒力,由于真核生物缺乏这种酶,被认为是开发新型抗菌药物的一个有前景的靶标,肺炎克雷伯菌(以下简称“肺克”)中末端氧化酶的作用至今尚不清楚。【目的】探究末端氧化酶CyxA在肺炎克雷伯菌中的生物学功能。【方法】构建cyxA基因无痕缺失株与回补株,通过体外实验比较野生株WT及敲除株ΔcyxA的生长能力、生物被膜和荚膜合成能力、对不同环境因素(酸性、高渗、氧化、还原)及抗生素的抵抗力,同时结合体内感染实验分析CyxA对肺克致病性的作用。【结果】缺失cyxA基因后肺克体外有氧生长能力明显降低,生物被膜和荚膜合成能力无差异,对pH 5.5、1.9%氯化钠、过氧化氢、β-巯基乙醇和部分β-内酰胺类及氨基糖苷类抗生素的抵抗力降低。通过小鼠滴鼻实验发现缺失cyxA基因后肺克的致病性降低。【结论】本研究首次证实末端氧化酶CyxA促进肺克有氧生长,增强该菌对酸性、高渗、氧化还原环境及部分抗生素的抵抗力,从而增强肺克的致病性。该研究为进一步阐明末端氧化酶对肺克致病性的分子机制奠定基础,为后续开发靶向肺克末端氧化酶的新型抗菌药物提供参考。     

Mechanisms and genetic diversity for host plant resistance to spotted stem borer,Chilo partellus in sorghum,Sorghum bicolor

Levels of resistance to spotted stem borer, Chilo partellus, in the germplasm are low to moderate and therefore we evaluated 25 sorghum genotypes for resistance to stem borer to identify lines with diverse mechanisms of resistance to this insect. Leaf glossiness was significantly and negatively associated with low deadheart formation. Dwarf genotypes with fewer nodes showed more deadheart formation. Antixenosis and/or antibiosis for leaf feeding, and reduced deadheart formation, tunnelling, and number of exit holes resulted in lower losses owing to C. partellus damage. Axillary tillers compensated for loss in grain yield owing to borer infestation as a result of deadheart formation, but their synchrony for maturity with the main plant is quite important. Path coefficient analysis revealed that direct effects of stem tunnelling on loss in grain yield were greater than leaf feeding and deadhearts. However, leaf feeding via stem tunnelling showed maximum indirect effects on loss in grain yield. Estimates for broad‐sense heritability and genetic advance suggested that it is possible to improve for grain yield under stem borer infestation. Heritability estimates for grain yield were usually higher than for stem borer damage parameters. Multi‐trait cluster analysis placed the test genotypes into four and five clusters in rainy and post‐rainy seasons, respectively. The genotypes placed in different groups, and showing resistance to leaf feeding, deadheart formation, stem tunnelling, and/or compensation in grain yield can be used for sorghum improvement.     

植株密度和氮素互作对垂穗披碱草生物量分配的影响

垂穗披碱草（Elymus nutans）是高寒地区建植和改良栽培草地的首选草种。虽然合理植株密度和氮素添加量是垂穗披碱草栽培草地稳产的关键因子,但两者之间是否存在最佳互作组合仍不清楚。采用盆栽试验,通过分析不同植株密度（58、102、146株/m²）和氮素添加量（0、200、400 mg/kg）组合状态下垂穗披碱草株高、单株分蘖数、地上生物量、地下生物量、根系体积和地上地下生物量比,以确定理论上是否存在植株密度和氮素添加量的最佳组合。结果表明：随植株密度增加,垂穗披碱草株高、地上生物量和地上地下生物量比值均先增加后降低,而单株分蘖数逐渐减小,根系体积和地下生物量先增加后保持相对稳定;随氮素添加量增加,垂穗披碱草单株分蘖数、地上生物量和地上地下生物量比值均表现为先增加后降低,地下生物量逐渐降低。植株密度与氮素添加量互作虽然对垂穗披碱草的根系体积和单株分蘖数没有显著影响,但两者互作显著影响了垂穗披碱草株高、地上生物量、地下生物量、地上地下生物量比（P<0.01）,这些指标与植株密度和氮素添加量的关系均表现为一个开口向下的抛物面。当植株密度为102株/m²和氮素添加量为200 mg/kg时,垂穗披碱草栽培草地产量最大,生物量分配最优。垂穗披碱草植株密度和氮素添加互作时理论上存在最佳组合,这为垂穗披碱草栽培草地的田间管理提供了理论依据。     

贵南沙蜥洞穴空间分布与昆虫资源分布特征的关系

贵南沙蜥分布在青海省贵南县的一片长×宽约为30 km×20 km的连续沙丘,该沙丘被周缘草地隔离,贵南沙蜥主要在沙地与草地接触带的沙地一侧活动。采用3条样线共150个陷阱研究贵南沙蜥在草地与沙地交界线两侧的活动洞穴空间分布特征与潜在的可利用性昆虫食物资源多样性,并分析洞穴空间分布特征与昆虫种类以及数量分布的关系。研究共捕获1236个昆虫个体,隶属于2纲10目26科42种,其中昆虫纲有7目21科37种978个,蛛形纲有3目5科5种258个;草地采集的昆虫有2纲9目22科37种570个,沙地有2纲9目21科33种666个。草地昆虫的Shannon-Wiener,Simpson多样性指数与均匀度指数均大于沙地,表明草地的昆虫食物资源较丰富且分布均匀。研究表明贵南沙蜥在沙地环境活动洞穴数量较多,且离交界线越近洞穴分布数量越多;草地生境活动洞穴空间分布与离交界线距离无相关性,相对沙地数量较少且空间上分布较均匀。草地样方捕获的昆虫种类和数量以及沙地样方捕获的昆虫数量都与离分界线的距离无关,但沙地上昆虫种类与离分界线的距离呈高度负相关。研究表明贵南沙蜥沙地活动洞穴空间分布与昆虫种类分布特征显著相关。     

Influence of olfactory stimulants on resistance/susceptibility of pearl millet, Pennisetum americanum to the rice weevil, Sitophilus oryzae

The orientation responses of the rice weevil, Sitophilus oryzae (L.) (Coleoptera: Curculionidae) as influenced by the olfactory stimulants emanating from either resistant or susceptible pearl millet, Pennisetum americanum, kernels were studied using a Y-tube olfactometer. The rice weevils were more attracted towards odours from millet grains than to blank controls and to susceptible entries more than to resistant entries, in general. However, there were exceptions. Odours from some resistant entries caused statistically the same, or even more positive orientations than those from some susceptible entries, and this suggests that the relative resistance of an entry and its olfactory attractiveness may not be strongly related, or that the resistance to infestation might be influenced by factors other than attractiveness. The partial damage of the millet kernel pericarp by abrasion slightly increased the orientational response of the weevils to odours from some susceptible and some resistant entries alike.     

南宁市桉树人工林土壤有机碳密度与地形因子的关系

桉树人工林土壤有机碳密度与地形因子的关系还不明确,且当前的研究较少地关注复合地形因子,对两者的线性和非线性关系强度的对比研究也较少。以南宁市高峰林场中的桉树人工林地为研究区,采用条件拉丁超立方抽样法布设采样点,通过建立数字高程模型提取和计算得到地形因子的指标;采用线性回归和回归树分别建立桉树人工林土壤有机碳密度-地形因子的线性和非线性回归模型。结果表明:研究区土壤表层、0—50 cm和全剖面的土壤有机碳密度均值分别为2.8、7.7、10.9 kg/m2,属于中等水平;仅坡度在0.05显著性水平上与表层和全剖面土壤有机碳密度显著相关,总体而言,简单地形因子与土壤有机碳密度的相关性普遍好于复合地形因子;随着土壤层次厚度的增加,线性和非线性回归模型对土壤有机碳密度空间变异解释能力都提升;回归模型对土壤有机碳密度空间变异的解释能力大小顺序为:回归树全变量多元线性回归逐步线性回归,因此,桉树人工林土壤有机碳密度与地形因子之间的非线性关系比线性关系强。     

青霉素钠对萼花臂尾轮虫适合度的促进作用及其与藻密度的关系

以萼花臂尾轮虫（Brachionus calyciflorus）为受试动物,在1.0×10⁶（较低）、2.0×10⁶（中等）和4.0×10⁶个细胞/mL （较高）的斜生栅藻（Scenedesmus obliquus）密度下,研究了不同浓度（0、200、400、600、800和1000 μg/L）的青霉素钠对轮虫各生命表统计学参数的影响。结果表明,与各藻密度下的对照组相比,当藻密度为2.0×10⁶个细胞/mL时,200-1000 μg/L的青霉素钠处理组中轮虫的生命期望和世代时间分别延长了40.67%-70.67%和34.04%-50.23%（P<0.05）,净生殖率和内禀增长率分别提高了204.35%-358.70%和36.26%-62.09%（P<0.05）;藻密度的降低或升高均显著降低青霉素钠对轮虫存活、生殖和种群增长的促进幅度。1.0×10⁶ 个细胞/mL的斜生栅藻密度下,400 μg/L的青霉素钠处理组中轮虫的生命期望延长了21%（P<0.05）,200-400μg/L的青霉素钠处理组中轮虫的世代时间延长了23.15%-33.13%（P<0.05）,200-600和1000 μg/L的青霉素钠处理组中轮虫的净生殖率分别升高了40%-81.05%和41.05%（P<0.05）;但4.0×10⁶个细胞/mL的斜生栅藻密度下,各青霉素钠处理组中轮虫的所有生命表统计学参数均与对照组之间无显著性差异（P>0.05）。藻密度对轮虫的生命期望、净生殖率、内禀增长率和后代混交率均具有显著性影响（P<0.01）,青霉素钠浓度对轮虫的世代时间、净生殖率和内禀增长率均具有显著性影响（P<0.05）,藻密度和青霉素钠浓度的交互作用对轮虫的生命期望、净生殖率和内禀增长率也具有显著性影响（P<0.05）。在实验设置的青霉素钠浓度范围内,1.0×10⁶个细胞/mL藻密度下轮虫的生命期望、世代时间和净生殖率与青霉素钠浓度之间均具有显著的剂量-效应关系（P<0.05）;2.0×10⁶个细胞/mL藻密度下,轮虫的生命期望、世代时间和内禀增长率与青霉素钠浓度之间均具有显著的剂量-效应关系（P<0.05）。本研究结果提示,环境相关浓度的青霉素钠不会对萼花臂尾轮虫的存活、生殖和种群增长产生显著性影响。