Risk analysis for biological weed control – simulating dispersal of Sclerotinia sclerotiorum (Lib.) de Bary ascospores from a pasture after biological control of Cirsium arvense (L.) Scop.

Biological control of Cirsium arvense(L.) Scop. in pasture by the plurivorous plantpathogenic fungus Sclerotiniasclerotiorum (Lib.) de Bary mayresult in the formation, escape and aerialdispersal of ascospores, creating an additionaldisease risk in down-wind market garden crops. To determine the width of a safety zone for apasture subjected to this form of weed control,we simulated the spatial pattern in the ratioof added (due to biocontrol) to naturallyoccurring airborne ascospores (due to marketgarden crops) around a 1ha virtual biocontrolpasture under either sheep or dairy cattlegazing over a 91-day emission period in 1996 inCanterbury, New Zealand. This was achievedusing a unique combination of two computermodels; SPORESIM-1D (for spore escape from avegetation source) and PC-STACKS (a modernGaussian plume model for dispersal beyond asource). Plumes of dispersing ascospores weremodelled for each hour of the emission periodfor both the virtual market garden andbiocontrol sites, and the aerial density of theascospores was averaged over the period. Assuming that a 1:1 ratio of added to naturallypresent spores is acceptable, no safety zonewas necessary for either of the modeledpastures. A ten-fold ratio (1:10 added tonatural) necessitated safety zones of 300 and150 m for the sheep and dairy pasturerespectively. Uncertainties associated withextrapolation of this conclusion to individualpasture management scenarios, and to otheryears and climatically different regions arediscussed.     

黑龙江省大豆菌核病菌核盘菌遗传多样性分析

了解黑龙江省不同地区侵染大豆核盘菌菌株分离物间的主要特性差异,利用PDA培养基对核盘菌进行分离和纯化,同时利用RAPD和rDNA-ITS标记方法对核盘菌进行遗传多样性分析,获得了50株纯化的核盘菌,用RAPD标记确定的遗传相似系数范围为0.54-0.98,平均相似系数为0.76,说明供试的核盘菌菌株的基因型具有一定的差异。对50个测定序列有差异的32个核盘菌ITS和5.8S rDNA片段的多序列对位分析,在ITS1区域的1-40bp种间变化较大,主要以碱基颠换和转换为进化形式。ITS2区域非常保守没有变异位点。黑龙江省核盘菌菌株在DNA水平上和ITS间隔区上具有较显著的遗传变异,显示出丰富的遗传多样性。     

Populations of strongyloid nematode infective stages in sheep pastures: Comparison between direct pasture sampling and tracer lambs as estimators of larval abundance

Waller P.J., Dobson R.J., Donald A.D. and Thomas R.J. 1981. Populations of strongyloid nematode infective stages in sheep pastures : comparison between direct pasture sampling and tracer lambs as estimators of larval abundance. International Journal for Parasitology11: 359–367. Over a 2-year period, numbers of infective larvae in samples of pasture herbage, and numbers of worms in previously worm-free “tracer” lambs allowed 4 weeks grazing, were compared as estimators of the abundance of infective larvae on pastures.Transformation of sample estimates of infective larval numbers per 100 g herbage dry matter (DM) and of worm numbers in tracer sheep, according to the expression y = log₁₀ (x+25), was effective in stabilizing variances. Estimates of error variance for each technique did not differ significantly among the genera Haemonchus, Ostertagia or Trichostrongylus and the pooled estimate for the tracer sheep method was 4 times greater than that for pasture sampling. From these results, more tracer sheep than pasture samples would be required to achieve the same level of precision with the two techniques. Using conventional statistical methods, the effects of numbers of pasture samples or tracer sheep on the size of the difference between two means which can be detected as significant and on the width of the confidence interval about a single mean, are illustrated. These can be used as a guide in the choice of sample sizes. Error variances for Nematodirus spp. were significantly less than for the other genera by pasture sampling, and greater by the tracer sheep technique. Possible reasons for this are discussed, but it is concluded that pasture sampling is likely to be much the more precise method for estimating Nematodirus spp. infective larval availability.Changes with time in infective larval abundance, for Haemonchus, Trichostrongylus and Nematodirus spp. which were present in moderate to low numbers, followed similar trends by both techniques. However, for Ostertagia spp. larvae, which were much more abundant, peak levels were defined more sharply and occurred earlier by pasture sampling than by the tracer method. It is suggested that worm counts from tracer sheep, especially those grazing for 4 weeks rather than shorter periods, may systematically underestimate the infective larval population on pasture at high levels of abundance owing to density-dependent worm loss.     

Breeding objectives for sheep should be customised depending on variation in pasture growth across years

Breeding programmes for livestock require economic weights for traits that reflect the most profitable animal in a given production system, which affect the response in each trait after selection. The profitability of sheep production systems is affected by changes in pasture growth as well as grain, meat and wool prices between seasons and across years. Annual pasture growth varies between regions within Australia’s Mediterranean climate zone from low growth with long periods of drought to high growth with shorter periods of drought. Therefore, the objective of this study was to assess whether breeding objectives need to be adapted for regions, depending on how reliable the pasture growth is across years. We modelled farms with Merino sheep bred for wool and meat in 10 regions in Western Australia. Across these 10 regions, mean annual pasture growth decreased, and the CV of annual pasture growth increased as pasture growth for regions became less reliable. We calculated economic values for nine traits, optimising management across 11 years, including variation for pasture growth and wool, meat and grain prices between and within years from 2002 to 2012. These economic values were used to calculate responses to selection for each trait for the 10 regions. We identified two potential breeding objectives, one for regions with low or high reliability and the other for regions with medium reliability of pasture growth. Breeding objectives for high or low pasture growth reliability had more emphasis on live weight traits and number of lambs weaned. Breeding objectives for medium reliability of pasture growth had more emphasis on decreasing fibre diameter. Relative economic weights for fleece weight did not change across the regions. Regions with low or high pasture reliability had similar breeding objectives and response to selection, because the relationship between the economic values and CV of pasture growth were not linear for live weight traits and the number of lambs weaned. This non-linearity was caused by differences in distribution of pasture growth between regions, particularly during summer and autumn, when ewes were pregnant, with increases in energy requirements affecting the value of lambs weaned. In addition, increasing live weight increased the intake capacity of sheep, which meant that more poor quality pasture could be consumed during summer and autumn, which had more value in regions with low and high pasture reliability. We concluded that breeding values for sheep production systems should be customised depending on the reliability of pasture growth between years.     

Changes in fatty acid profile of Bovec sheep milk due to different pasture altitude

Sheep rearing on mountain pastures is an ancestral tradition in northwestern Slovenia. The indigenous Bovec sheep are widespread there and are well adapted to the rough Alpine rearing conditions. Every year, after weaning, the sheep start grazing in the lowlands (L) and then gradually move to mountain pastures, and finally, to the highland (H) pastures of the Alps. Grazing positively affects the fatty acid (FA) composition in sheep milk fat with increased availability of polyunsaturated FA (PUFA) in grass, and subsequently, in milk. Consequently, the objective of this work was to study the FA profile in sheep milk during grazing in four geographical areas in the Alps. A total of 15 ewes of the Bovec sheep breed were randomly selected and milk samples from these ewes were taken at four different pasture locations that differed with regard to altitude: the L pasture location at an altitude of 480 m, the mountain pastures (M1 and M2) at altitudes of 1100 to 1300 m and 1600 to 1900 m, respectively, and the H pastures at altitudes of 2100 to 2200 m. Milk samples from the ewes were taken during the grazing season from April to September. The chemical and FA composition of the milk samples from each pasture location were determined. There were significant differences in the concentrations of FA among the L, M1, M2 and H milk samples. We observed decreases of the concentrations of saturated FA (SFA) in milk from L to H pastures. The concentration of α-linolenic FA, monounsaturated FA (MUFA), PUFA and n-3 PUFA in milk were increased significantly with pasture altitude. The n-6/n-3 PUFA ratio was reduced by the change of pasture altitude with the lowest value at the M1 pasture (1.5). The concentrations of total SFA decreased significantly and was lowest at the L pasture. Our results underline the importance of the effect of grazing in the Alpine region associated with pasture altitude on the FA profile of sheep milk. The first variation in FA concentration in sheep milk occurred between L and M1, although it was more evident on H pastures in the Alpine mountains. Changes of the FA profile in sheep milk due to pasture altitude were related to variation in FA concentration in the pasture and the botanical composition of the pasture location.     

西藏羽藓科植物的地理分布及区系成分的初步分析

关于西藏苔藓植物的研究,过去报道甚少,据有关资料,W.Mitten(1859)整理鉴定了T.Thomson(1847-1849)在西藏西部及其邻近地区所采标本,发表了66种藓类,其中至今仍隶属于或已调入羽藓科的植物计23种,其后尚有E.S.Salmon(1900),V.F.Brotherus(1948,1929)有过报道。     

森林草地转换对景观视觉效果的影响

基于景观保护的视点,定量研究了森林草地转换对景观视觉效果的影响．结果表明,中景域的可视区域比近景域和远景域大,草地建设对中景域景观视觉效果的影响也最大,因此,中景域是重要的景观保护对象．对草地内林地的可视量分析可知,各景域的可视林地多分布在400～600m高海拔上。25°以上的坡度范围内分布偏少．并探讨了草地建成后应采取的景观管理和保护对策,以增加草地景观的视觉效果．     

'Nucleating’ succession in recovering neotropical wet forests: The legacy of remnant trees

Question: What is the influence of remnant trees on secondary forest structure and composition in tropical pastures many years after abandonment? Location: Neotropical lowland wet forest, La Selva Biological Station, Costa Rica. Methods: Tree and sapling density, basal area, and species richness were quantified at three distances from remnant trees, 0–10 m (inner), 20–30 m (intermediate), and ca. 50 m (distal) zones. A total of 15 remnant trees were sampled in pastures ~23 years after abandonment. Results: Tree density decreased along a gradient from inner (1117 ± 377 individuals/ha) to distal (592 ± 282 individuals/ha) zones, and the number of large‐seeded individuals (seeds > 1 cm diameter) was significantly greater in the inner zone. Basal area of tree individuals was greater in the inner (25.6 ± 12 m²/ha) and intermediate (28.3 ± 15.6 m²/ha) zones than the distal zone (14.7 ± 7.2 m²/ha), but there were no differences between inner and intermediate zones. Similar patterns are reported for species richness. Additionally, saplings (1 ‐ 5 cm DBH) had higher density directly beneath and adjacent to remnants, suggesting that remnant trees can affect recruitment even many years after pasture abandonment and the formation of a surrounding secondary forest. Conclusions: Results indicate that remnant trees facilitate forest recovery over a broad temporal range, and appear to ‘nucleate’ forest regeneration by expanding their sphere of influence outward over time.     

Preferences for sheep or goats in Indonesia

This paper aims to explore farmers’ preferences for sheep or goats based on feeding practices, animal and flock performances and economic benefits of sheep and goats in different agro-ecological zones in Central Java, Indonesia. In total, 150 smallholder farmers were selected from three agro-ecological zones: the lowlands, the middle zone, and the uplands. Feeding and performance parameters were estimated through weekly farm visits and farm records, from September 2001 to August 2003. In the lowlands, small ruminants were fed mainly with field grass and crop residues, whereas in the middle zone and uplands feeds fed were mainly field grass and leaves. Sheep were given more opportunities to graze than goats, however, grazing was not a major component in the diets. In the lowlands and the middle zone the differences in feed intakes, ADG and reproductive performances between sheep and goats were small. In all zones, does had significantly larger litters than ewes. In the uplands, goats had a significantly higher DMI, grew slightly faster, and had a higher weaning rate than sheep. Consequently, in the uplands, the total economic benefits from goat flocks were 25% higher than from sheep flocks. The major differences in agro-ecological conditions that affect the choice for sheep or goats were the availability of cassava peels in the lowlands, favouring a choice for sheep, and the abundance of leaves in the middle zone and uplands, which favours keeping goats. The promotion of goats by the government, the family tradition of keeping sheep or goats, the preference for sacrificing sheep for religious festivities, and the high initial investment needed to buy goat breeding stock could be other important motives to keep sheep or goats. Sheep fattening based on rice bran supplementation could be a feasible innovation in the lowlands. In the middle zone and uplands goat breeding could make a positive contribution to rural livelihoods.     

Dispersal kernels of the invasive alien western corn rootworm and the effectiveness of buffer zones in eradication programmes in Europe

Europe is attempting to contain or, in some regions, to eradicate the invading and maize destroying western corn rootworm (WCR). Eradication and containment measures include crop rotation and insecticide treatments within different types of buffer zones surrounding new introduction points. However, quantitative estimates of the relationship between the probability of adult dispersal and distance from an introduction point have not been used to determine the width of buffer zones. We address this by fitting dispersal models of the negative exponential and negative power law families in logarithmic and non-logarithmic form to recapture data from nine mark-release-recapture experiments of marked WCR adults from habitats as typically found in the vicinity of airports in southern Hungary in 2003 and 2004. After each release of 4000–6300 marked WCR, recaptures were recorded three times using non-baited yellow sticky traps at 30–305 m from the release point and sex pheromone-baited transparent sticky traps placed at 500–3500 m. Both the negative exponential and negative power law models in non-log form presented the best overall fit to the numbers of recaptured adults (1% recapture rate). The negative exponential model in log form presented the best fit to the data in the tail. The models suggested that half of the dispersing WCR adults travelling along a given bearing will have travelled between 117 and 425 m and 1% of the adults between 775 and 8250 m after 1 day. An individual-based model of dispersal and mortality over a generation of WCR adults indicated that 9.7–45.3% of the adults would escape a focus zone (where maize is only grown once in 3 consecutive years) of 1 km radius and 0.6–21% a safety zone (where maize is only grown once in 2 consecutive years) of 5 km radius and consequently current European Commission (EC) measures are inadequate for the eradication of WCR in Europe. Although buffer zones large enough to allow eradication would be economically unpalatable, an increase of the minimum width of the focus zone from 1 to 5 km and the safety zone from 5 to 50 km would improve the management of local dispersal.     

The effects of altitude,aspect, grazing and time on the proportion of cyanogenics in neighbouring populations of Trifolium repens L. (white clover)

The proportion of cyanogenic individuals of white clover amongst 200 individuals in each of 32 neighbouring populations in Northumberland, UK were recorded. Sites differed for four altitude zones, two aspects, and were either sheep pasture or ungrazed meadow. The proportion of cyanogenics showed a striking reduction with increasing altitude. Below 100 m, north-facing sites contained more cyanogenics than south-facing sites, but aspect did not affect higher sites. Grassland management had no effect on the proportion of cyanogenics. A 24-year study of one population showed highly significant changes in the proportion of cyanogenics over time, suggesting that a significant turnover of individuals occurs. In some cases, different size class cohorts varied for the proportion of cyanogenics within a year, and the same cohort varied between years. We conclude that environment at birth may determine the proportion of cyanogenics for that cohort, so that this proportion persists in that cohort as it matures. Comparisons of the proportion of cyanogenics with mean monthly averages for January minimum temperature, July maximum temperature and August rainfall showed a significant association only with mean January minima 2 1/2 years previously. We hypothesise that the 2 to 3-year cohort may predominate in this population. We suggest that winter cold and summer drought may both select against cyanogenics. Grazing by large herbivores does not favour cyanogenesis, but some invertebrate herbivory may do so. Most selection probably occurs at birth and will be greatest in populations with a high turnover.     

Structure and function of wildfire and mountain pine beetle forest boundaries

Landscape boundaries, in particular those created by natural disturbances, are fundamental structures in landscape functioning. At the stand scale, forest boundaries show a wide range of characteristics varying from sharp to diffuse, wavy to straight, enclosed areas (patches) to open ones; all of these have different effects of forest vegetation. The objectives of this study were 1) to characterize the structure of forest boundaries (width, steepness, heterogeneity) and 2) to investigate forest vegetation functional response in the boundary zones created by wildfires and mountain pine beetle (MPB) outbreaks. We studied 11 mountain pine beetle and 7 wildfire boundary zones (4–7 y since disturbance) using field‐based two‐dimensional grids in southern central British Columbia (Canada). Boundary zone delineation was determined through spatially constrained clustering algorithms at three sampling unit resolutions (5×5 m, 10×10 m, and 20×20 m). Then, to characterize boundary width and shape, we developed two new boundary indexes (maximized and minimized boundary zones). The identified boundary widths ranged from 0 to 127 m with a mean width of 51 m at the 20×20 m resolution for both fire and MPB. Although the widths were comparable between disturbance types, fires generally had steeper boundaries (more pronounced) than MPB, largely due to higher peak tree mortality within the disturbances (89 vs 43%). Most of the forest vegetation response variables (understory vegetation diversity, plot‐level species richness, evenness, and multivariate community measures) in the boundary zones tended not to be intermediate in value between the intact forest and disturbance area, in spite of intermediate tree mortality. Tree mortality heterogeneity in the boundary zones was often highest in fires and was equal to the internal heterogeneity in MPB disturbances. Using historical natural disturbance patterns as a conservation strategy, this study proposes that forest management should create boundary complexity (width and shape), thereby creating landscape heterogeneity similar to landscapes influenced primarily by natural disturbances.     

An update on the nutrition of dairy sheep grazing Mediterranean pastures

In the light of recent findings in sheep nutrition and feeding behaviour, the diets of grazing dairy sheep should be based on forages encompassing a variety of complementary nutritional values and containing moderate levels of diverse plant secondary metabolites, until recently regarded as “anti-nutritional”. In lactating sheep, pastures of tannin-containing legumes like sulla (Hedysarum coronarium) and chicory (Cichorium intybus) can be integrated with annual grasses for establishing artificial pastures under rainfed conditions. Diets based on these forages, while ensuring high milking performance, can mitigate the unbalance of CP to energy ratio of grazing sheep. By grazing sulla and Italian ryegrass (50:50 by area) as spatially adjacent monocultures or in timely sequence (complementary grazing) sheep eat more and perform better than by grazing the ryegrass pasture only. Concentrate supplementation of lactating sheep should be preferably based on sources rich in digestible plant fiber (soyhulls or beet pulps), particularly from mid-lactation onwards and when supplementation levels are high. Milk urea concentration is confirmed as a useful monitoring tool to balance protein nutrition and curb the waste of N at animal and system level. Finally, challenging tasks for future research on dairy sheep grazing management and nutrition are on-farm application of recent technological advances, such as image-based estimation of pasture biomass and quality, evaluation of sheep dietary quality by faecal Near Infrared Reflectance Spectrometry, and establishment of remote control systems.     

The role of zoobenthos in energy flow in deep,oligotrophic Lake Thingvallavatn,Iceland

Macrozoobenthos in Thingvallavatn is dominated by 42 taxa. The vertical distribution delimits 5 communities: (1) the surf zone community from 0–2 m, (2) the upper stony littoral community from 2–6 m, (3) the lower stony littoral community from 6–10 m, (4) the Nitella zone community from 10–20 m, and (5) the profundal zone community from 20–114 m. Total mean lakewide production was 78 kJ m^–2 yr^–1. Herbivores, detritivores, and carnivores contributed 59%, 38% and 3%, respectively. Respiration and ingestion were estimated according to the literature. Net production efficiency averaged 0.50. Ingestion was dominated by herbivores in the littoral zones (46–81%), while detritivores made up 93% in the profundal zone. Total zoobenthic production averaged 6% of estimated available food with a range from 10–11% in the three upper littoral zones to only 2% in the Nitella zone. The profundal fauna converted 6% of the estimated sedimentation of organic matter to secondary production. On a lakewide basis the zoobenthis utilized one third of the estimated potential food resources. Zoobenthic production made up 32% of total secondary production.     

子囊菌交配型基因MAT1-1的系统发育

子囊菌具有无性态与有性态的复杂性,以及人们对其系统发育和亲缘关系了解的局限性,进而导致菌物学家对子囊菌分类尚持不同意见。子囊菌的交配型基因（MAT）进化保守,且编码的蛋白质调控子囊菌的有性生殖过程。核盘菌Sclerotinia sclerotiorum (Lib.) de Bary隶属于子囊菌门Ascomycota、盘菌纲Discomycete,是一种典型丝状同宗配合真菌,控制该菌有性生殖的交配型基因MAT1-1和MAT1-2紧密连锁,且该菌并无有性态与无性态的复杂性。故此,本文根据所克隆的核盘菌交配型基因MAT1-1,利用PAUP*软件将82种含有Alpha-box交配型基因的子囊菌进行了系统进化分析,通过核苷酸及氨基酸水平的系统发育分析,并结合Ainsworth（1973）分类系统及最新的Deep Hyphae（2006）分类系统的对比研究,发现所构建的系统进化树与传统分类所表现的进化关系基本一致,且核盘菌交配型基因MAT1-1在进化过程中功能相对保守,该分析结果有助于对其他子囊菌交配型基因的克隆、系统分类与进化研究,同时对核盘菌的亲缘关系、病害预测及防治等具有重要意义。     

羊尿对典型草原不同生活型草地植物生长特性的影响

连续2a研究了施尿量(4,2,1L/m2和0 L/m2)和施尿期(营养期和生殖期)对典型草原多年生密丛型禾本科植物长芒草(Stipa bungeana)、多年生轴根型菊科植物茵陈蒿(Artemisia capillaries)和多年生半灌木豆科植物胡枝子(Lespedeza davurica)生长特性的影响.结果表明,不同植物对畜尿沉积的响应不同,并受施尿量和施尿时期的作用.畜尿对草地植物具短期(4周内)灼烧作用,灼烧主要发生于尿斑中心;畜尿对长芒草生长具长期正效应(4周后),对茵陈蒿和胡枝子生长具持续负效应,此效应持续至少2a且随施尿量降低而降低.一般尿斑中心(4 L/m2)所有植物伤害,尿斑中心至边缘圈植物局部器官(嫩枝叶)伤害(2～4 L/m2),尿斑外渗区域(1～2 L/m2)所有植物无显著伤害.高施尿量(2～4 L/m2)下,长芒草具较高的年均分蘖数和地上生物量,而胡枝子和茵陈蒿与之相反.尿斑处3种植物具较高的分蘖(枝)死亡率和死物质率.茵陈蒿对各时期施尿均反应敏感,胡枝子和长芒草对生殖期施尿更敏感.尿斑处禾草枯黄期延迟,返青期提前.     

Use of white clover as an alternative to nitrogen fertiliser for dairy pastures in nitrate vulnerable zones in the UK: productivity, environmental impact and economic considerations

Perennial ryegrass and perennial ryegrass/white clover permanent dairy pastures are compared with respect to productivity, environmental impact and financial costs in nitrate vulnerable zones (NVZ) in the UK. With appropriate management, and utilisation of recommended perennial ryegrass and white clover cultivars, white clover is likely to stabilise at around 20% of total dry matter production in a mixed pasture. Plant dry matter production and milk production from a perennial ryegrass/white clover pasture are likely to be similar to that from a perennial ryegrass pasture receiving 200 kg N ha⁻¹ annum⁻¹ and around 70% of that obtained with perennial ryegrass supplied with 350–400 kg N ha⁻¹ annum⁻¹. Nitrate, phosphorus and methane losses from the system and decreases in biodiversity relative to a grazed indigenous sward are likely to be similar for a perennial ryegrass/white clover pasture and a perennial ryegrass pasture receiving 200 kg N ha⁻¹ annum⁻¹: nitrate leachate from both systems is likely to comply with European legislation. Greenhouse gas emissions resulting from nitrogen (N) fertiliser production would be avoided with the perennial ryegrass/white clover pasture. Within NVZ stocking rate restrictions, white clover can provide the N required by a pasture at a lower financial cost than that incurred by the application of N fertiliser.     

阿尔泰山西伯利亚落叶松径向生长对气候变化的分异响应

在全球气候变暖的背景下, 北半球中高纬度地区出现了树轮径向生长对气候变化的分异响应现象, 但是阿尔泰山优势针叶树种对气候因子响应的稳定性还存在不确定性。该研究选择阿尔泰山中段高海拔西伯利亚落叶松(Larix sibirica)样本建立了树轮宽度年表, 并对年表特征及树木径向生长-气候的动态关系进行了分析。结果表明: 生长季初期和中期的气温是研究区树木生长的主控气候因子; 树木径向生长与当年4月的气温显著负相关, 与当年6-7月的气温显著正相关; 研究区西伯利亚落叶松径向生长与当年4月和6-7月的气温发生了分异现象, 表现为随着气候变化, 树木径向生长对生长季初期由高温引起的干旱的响应敏感性越来越强, 而对生长季中期气温的敏感性表现出先减弱再增强的趋势。阿尔泰山西伯利亚落叶松径向生长对气候变化的响应比较敏感, 适合开展树木生长-气候变化的研究; 检验树木径向生长对气候变化分异响应为该区域基于树木年轮开展历史气候重建和提高未来森林生态系统发展趋势预测的准确性提供了科学依据。     

Production, Survival and Evaluation of Liquid Culture-produced Inocula of Coniothyrium minitans Against Sclerotinia sclerotiorum

Growth of Coniothyrium minitans on potato dextrose broth was compared with that on an inexpensive molasses-yeast liquid medium at 18-22°C in static culture. Biomass and conidial production were, in general, similar, although the rate of biomass production was quicker and conidial production was slightly greater per unit volume of medium in the molasses-yeast medium. Air-dried biomass from molasses-yeast liquid culture containing mycelia, pycnidia and conidia of C. minitans was mixed (12%, w/w) with kaolin to give a kaolin-biomass dust. The ability of C. minitans to survive and subsequently infect and reduce the viability of sclerotia of Sclerotinia sclerotiorum from this kaolin-biomass dust was found to be little affected by storage for 48 weeks between 4 and 15°C but was decreased by higher storage temperatures. The kaolin-biomass dust preparation did not differ from a standard maizemeal-perlite inoculum of C. minitans in its ability to infect sclerotia of S. sclerotiorum or reduce their viability or carpogenic germination in glasshouse and field pot bioassays. Further, when either inoculum was applied once to glasshouse soil naturally infested with S. sclerotiorum prior to planting three successive crops of lettuce, the pattern of disease control, reduction of sclerotial numbers/ plot, infection of sclerotia, reduction of sclerotial viability and survival in soil were similar for both inocula. The potential for the commercial development of liquid-culture-produced inocula of C. minitans is discussed.     

青藏高原人工草地土壤可溶性氮组分与植被生产力动态变化过程

氮作为人工草地最为重要的限制性因子, 在时间、空间上分布不均匀, 且在形态上存在差异, 与种植方式及地上净初级生产力(ANPP)存在相关关系。该研究以青海省同德牧场的无芒雀麦(Bromus inermis)、老芒麦(Elymus sibiricus)、垂穗披碱草(E. nutans)、西北羊茅(Festuca ryloviana)、中华羊茅(F. sinensis)、青海扁茎早熟禾(Poa pratensis var. anceps ‘Qinghai’)、冷地早熟禾(P. crymophila)、星星草(Puccinellia tenuiflora) 8种牧草单播人工草地为研究对象, 分析人工草地土壤可溶性氮库季节和年际动态变化过程及与ANPP之间的相互关系。该人工草地种植于2013年, 在2014-2016年(二龄、三龄和四龄)生长季6-9月测定土壤铵态氮(NH₄⁺-N)、硝态氮(NO₃^--N)、可溶性有机氮(SON)和可溶性总氮(STN)含量, 每年9月初测定ANPP, 所有样地没有施肥, 每年9月中旬刈割, 留茬5 cm。研究发现: (1) 8种禾本科牧草的ANPP在329.67-794.67 g·m^-2之间, 其中垂穗披碱草为794.67 g·m^-2, 显著高于其他牧草。(2)在二至四龄人工草地中, 土壤NO₃^--N、SON和STN含量均显著下降, 但NH₄⁺-N含量却显著增加。(3)土壤可溶性氮以SON为主, 占STN的45.11%-88.76% (0-10 cm)和47.75%-88.18% (10-20 cm); 其次为NO₃^--N, 占STN的5.81%-34.85% (0-10 cm)和6.08%-40.42% (10-20 cm); NH₄⁺-N最少仅3.41%-22.18% (0-10 cm)和3.09%-19.56% (10-20 cm)。(4)非度量多维尺度分析(NMDS)结果显示, 随种植年限的增加, 不同禾本科牧草对0-10 cm土壤可溶性氮影响趋于离散, 而对10-20 cm土壤的影响则相反, 且牧草对土壤可溶性氮含量的影响程度与土壤深度有关。(5)相关性分析表明, 土壤SON、STN含量与人工草地ANPP呈正相关关系, 与无机氮(IN)含量呈负相关关系。综上所述, 三至四龄人工草地增施氮肥是维持草地生产力的关键因素。以上结果为更深入了解青藏高原人工草地土壤可溶性氮动态变化及维持人工草地生产力和稳定性提供了科学依据。