贵州石笔木种子萌发特性及幼苗生长规律的研究

为探索贵州石笔木(Tutcheria kweichowensis Chang et Y.K.Li)的种子特性及种苗繁育规律,对种子的生物学特征和贮藏方式对种子萌发的影响及幼苗年生长规律进行了研究。结果表明,贵州石笔木种子的千粒重、生活力、含水量分别为0.92 kg、66.17%、11.75%,吸水率最高可达15.62%。长期贮藏适宜采用低温湿沙层积方式,短期催芽适宜在25℃、相对湿度80%的湿沙层积贮藏40 d左右,种子萌发率可达80%以上。幼苗出土后1年的生长节律表现为"慢-快-慢",5-9月为生长盛期,这一时期的苗高、地径的生长量分别占全年的65.48%、42.02%。根据幼苗的生长特性,采取阶段性育苗措施,适时加强田间管理和水、肥定向供给,对提高苗木质量和生产效益具有重要意义。     

玉兰类观赏植物的秋季芽接

白玉兰、飞黄玉兰、红运玉兰、二乔玉兰、望春玉兰、紫玉兰等木兰科观赏植物，具有独特的树形，多样的开花习性，美丽的花果，而且对环境条件要求不苛，适应性较广，在我国园林观赏树种中占有较重要的地位。它们的繁殖方法多样，各地有所差异。传统的方法是种子繁殖或嫁接...     

濒危植物西康玉兰种子休眠、萌发及贮藏特性

研究了西康玉兰(Magnolia wilsonii)种胚的形态大小,温度、层积、硝酸钾、浸种处理和GA_3对种子休眠及萌发的影响.通过将种子脱水至不同含水量和在两种温度(4℃和一20℃)下贮藏100 d后测其生活力,分析各处理对西康玉兰种子活力的影响.结果表明:西康玉兰种子胚尚未分化完全,需经过低温层积完成生理后熟;低温层积和GA3可打破种子休眠.种子最适萌发温度为25/20℃.由此推测,西康玉兰种子具有形态生理休眠特性.西康玉兰种子当含水量降至5.39%,存活率为53.50%.不同含水量的种子贮藏在-20℃条件下,100 d后种子全部死亡;但在4℃下含水量为10.31%的种子存活力高达76%.因此,西康玉兰种子极可能属于中间性种子,其适宜贮藏环境为4℃下的干藏或湿藏.     

花生花器分化的解剖学观察研究

本文对四种花生的七个品种分别进行了成熟种子中侧芽发育状况,从种子萌动到出苗和从出苗到开花整个花器官分化过程的解剖学观察,通过观察研究,得出如下结果: 1.不同类型品种,其侧芽发育的状况有显著不同。珍珠豆型、多粒型两个连续开花类型的品种,已分化出第三次侧芽时;普通型、龙生型两个交替开花类型的品种,只见有很小的第二次侧芽。2.不同类型的品种,花器宫分化发育过程的时间早晚不同。连续开花类型的品种,在出苗之前花芽已经形成,出现了花萼原基;交替开花类型的品种是在出苗当天至第二天,幼苗主茎已展开二片真叶时,在第一对侧枝的第三节,花芽才开始形成,出现花芽原基。3.所有类型品种.所经历的各个时期是一致的,均经过九个连续的形态变化时期。对不同类型品种花器官分化的各个时期,结合植株的生育状况进行了观察研究,为制定科学的栽培管理技术措施,提供了理论依据。     

开花后水分调控对两个筋型冬小麦品种品质与产量的影响

 通过开花后不同水分处理研究了两个不同筋型冬小麦品种(‘豫麦34’和‘洛阳8716’)(Triticum aestivum cv. `Yumai 34' and `Luoyang 8716')的品质及产量变化。结果表明：随着灌水时间推迟,湿面筋含量、沉降值、面团形成时间、稳定时间、评价值和拉伸面积有提高的趋势,但是千粒重和产量下降;随着开花后灌水量的增加,上述品质数值又有减少,产量及千粒重增加;多次灌水处理与开花后灌1次水处理、开花后不灌水处理之间差异显著,开花后21 d和28 d灌水处理的多项品质指标都大于不灌水处理。两品种面团稳定时间（45%和15%）、沉降值（20%和12%）在不同水分处理下变异系数较大,吸水率、湿面筋、蛋白质含量变异系数（<10%和 <5%）较小。     

不同光照处理下青藏高原克隆植物黄帚橐吾(Ligulariavirgaurea)种子大小对其幼苗生长的影响

以高寒草甸克隆植物黄帚橐吾为实验材料,通过遮荫网模拟植被遮荫,研究种子大小与萌发及幼苗生长能力的关系和幼苗对光照条件的反应。结果表明：（1）在自然光照下,黄帚橐吾种子大小对种子萌发的影响显著,大种子的萌发率高于小种子。遮荫生境下,大、小种子萌发率有所降低,但遮荫对小种子萌发的影响比大种子显著。小种子的萌发率下降了近1/8,而大种子的萌发率仅下降了1/11。（2）黄帚橐吾种子大小对幼苗生物量积累影响显著,大种子幼苗总生物量（TB）大于小种子幼苗的。但生物量的分配与播种时间相关,播种后60 d,在自然光照条件下,大种子幼苗对根生物量的分配大于小种子幼苗,而对叶生物量的分配则正好相反。在遮荫环境中,大、小种子幼苗普遍对根的生物量分配增加,大种子幼苗根冠比（R/S）大于小种子幼苗。（3）黄帚橐吾种子大小对幼苗的生长也有明显影响。在自然光照下,小种子幼苗的相对生长速率（RGR）较大于大种子幼苗,但叶面积比率（LAR）、叶面积干质量比（SLA）、叶干质量（LWR）差别不明显。在遮荫条件下,幼苗的LAR、SLA、LWR显著增加,但大、小种子幼苗间差异不显著,幼苗的RGR减小,小种子幼苗的减小趋势大于大种子幼苗。     

不同生长阶段遮荫对番茄光合作用、干物质分配与叶N、P、K的影响

对番茄植株做了两种不同程度的遮荫处理,观测了夏季午间遮荫对光合速率,干物质积累量及其在根,茎,叶之间的分配,和叶N,P,K的含量以及经济产量的影响,发现不同时期遮荫影响不同。（1）遮荫增加三个阶段（开花早期,盛花期和开花后期）的气孔导度和胞间CO2浓度,显著降低开花早期中午的净化合速率,但盛花期中度遮荫（40%遮荫）使净光合速率随着时间的增加逐渐上升,在开花后期表现更加明显,平均净光合速率比对照高20%以上,蒸腾速率也增加较多。（2）开花早期和盛花期重度遮荫（如本实验中的75%遮荫）显著降低根,茎的干重,而开花后期中度遮荫的根,茎干重高于对照,但遮荫对叶干重的影响不明显。（3）开花早期和盛花期遮荫不明显影响叶片中N,P,K的含量,但开花后期中度遮荫使N,P,K含量增加,（4）开花早期两种遮荫对果实产量影响较小,但盛花期重度遮荫使产量降低,全部产量中无效部分所占的比例上升,开花后期中度遮荫的总产量和有效产量增加,单果重也增加,这些结果表明,在某些时期中度遮荫可以克服夏天辐射过强,气温过高对番茄的不良影响,对番茄生长,干物质积累和提高产量等有利,在生产上有意义。     

玉兰育种研究初报

玉兰育种工作在我国尚处在起步阶段,现所采用的育种方法有：（1）在栽培繁殖过程中选择天然优良变异品种,现已根据花色,花型,花期选出10多个新品种;（2）通过人工杂交育种,现已获得三批杂交实生苗;人工杂交主要需克服花期不遇的困难,在杂种实生苗的管理上采用适当多次移栽和嫁接的方法,使实生苗提早开花,缩短育种年限 ;（3）物理,化学诱变,遗传工程,生物技术在玉兰育种中运用的较少。     

番橄榄实生育苗技术初探

对番橄榄实生育苗技术进行初步研究。结果表明,番橄榄育苗不宜使用果实直接播种,应采用成熟种子进行容器袋育苗,这样既有利于提高种子发芽率,又可避免移栽时苗木受损伤;遮荫度30%、空气相对湿度80%~90%有利于种子发芽和幼苗生长。     

不同光照处理下青藏高原克隆植物黄帚橐吾(Ligulariavirgaurea)种子大小对其幼苗生长的影响

以高寒草甸克隆植物黄帚橐吾为实验材料,通过遮荫网模拟植被遮荫,研究种子大小与萌发及幼苗生长能力的关系和幼苗对光照条件的反应。结果表明:(1)在自然光照下,黄帚橐吾种子大小对种子萌发的影响显著,大种子的萌发率高于小种子。遮荫生境下,大、小种子萌发率有所降低,但遮荫对小种子萌发的影响比大种子显著。小种子的萌发率下降了近1/8,而大种子的萌发率仅下降了1/11。(2)黄帚橐吾种子大小对幼苗生物量积累影响显著,大种子幼苗总生物量(TB)大于小种子幼苗的。但生物量的分配与播种时间相关,播种后60d,在自然光照条件下,大种子幼苗对根生物量的分配大于小种子幼苗,而对叶生物量的分配则正好相反。在遮荫环境中,大、小种子幼苗普遍对根的生物量分配增加,大种子幼苗根冠比(R/S)大于小种子幼苗。(3)黄帚橐吾种子大小对幼苗的生长也有明显影响。在自然光照下,小种子幼苗的相对生长速率(RGR)较大于大种子幼苗,但叶面积比率(LAR)、叶面积干质量比(SLA)、叶干质量(LWR)差别不明显。在遮荫条件下,幼苗的LAR、SLA、LWR显著增加,但大、小种子幼苗间差异不显著,幼苗的RGR减小,小种子幼苗的减小趋势大于大种子幼苗。     

Mowing Reduces Exotic Annual Grasses but Increases Exotic Forbs in a Semiarid Grassland

Cheatgrass (Bromus tectorum) and other exotic winter‐active plants can be persistent invaders in native grasslands, growing earlier in the spring than native plants and pre‐empting soil resources. Effective management strategies are needed to reduce their abundance while encouraging the reestablishment of desirable native plants. In this 4‐year study, we investigated whether mowing and seeding with native perennial grasses could limit growth of exotic winter‐actives, and benefit growth of native plants in an invaded grassland in Colorado, United States. We established a split‐plot experiment in October 2008 with 3 mowing treatments: control, spring‐mowed, and spring/summer‐mowed (late spring, mid‐summer, and late summer), and 3 within‐plot seeding treatments: control, added B. tectorum seeds, and added native grass seeds. Cover of plant species and aboveground biomass were measured for 3 years. In March and June of 2010, 2011, and March of 2012, B. tectorum and other winter‐annual grasses were half as abundant in both mowing treatments as in control plots; however, cover of non‐native winter‐active forbs increased 2‐fold in spring‐mowed plots and almost 3‐fold in spring/summer‐mowed plots relative to controls. These patterns remained consistent 1 year after termination of treatments. Native cool‐season grasses were most abundant in spring‐mowed plots, and least abundant in control plots. There was higher cover of native warm‐season grasses in spring/summer‐mowed plots than in control plots in July 2011 and 2012. The timing of management can have strong effects on plant community dynamics in grasslands, and this experiment indicates that adaptive management can target the temporal niche of undesirable invasive species.     

Ecological Consequences of Shifting the Timing of Burning Tallgrass Prairie

In the Kansas Flint Hills, grassland burning is conducted during a relatively narrow window because management recommendations for the past 40 years have been to burn only in late spring. Widespread prescribed burning within this restricted time frame frequently creates smoke management issues downwind. A potential remedy for the concentrated smoke production in late spring is to expand burning to times earlier in the year. Yet, previous research suggested that burning in winter or early spring reduces plant productivity and cattle weight gain while increasing the proportion of undesirable plant species. In order to better understand the ecological consequences of burning at different times of the year, plant production and species abundance were measured for 20 years on ungrazed watersheds burned annually in autumn, winter, or spring. We found that there were no significant differences in total grass production among the burns on either upland or lowland topographic positions, although spring burned watersheds had higher grass culm production and lower forb biomass than autumn and winter burned watersheds. Burning in autumn or winter broadened the window of grass productivity response to precipitation, which reduces susceptibility to mid-season drought. Burning in autumn or winter also increased the phenological range of species by promoting cool-season graminoids without a concomitant decrease in warm-season grasses, potentially widening the seasonal window of high-quality forage. Incorporating autumn and winter burns into the overall portfolio of tallgrass prairie management should increase the flexibility in managing grasslands, promote biodiversity, and minimize air quality issues caused by en masse late-spring burning with little negative consequences for cattle production.     

THE INFESTATION OF WINTER LETTUCE BY APHIDS AND ITS CONTROL

Observations have been made on the infestation by aphids of winter lettuce at Imperial College Field Station, Slough, for the seasons 1947–8 and 1949–54. The effects of transplanting and of the use of insecticides have been studied.
Plants drilled in September where they were to mature were ready for cutting a little earlier than those transplanted in November, but in years when aphids were numerous the drilled lettuces were heavily infested and very few of them hearted.
The infestation of young crops varied from year to year; in some winters it fell to a low level, in others it increased rapidly and persisted with serious effect on the crop. In some years lettuce mosaic virus was also prevalent. The dominant aphid species was Nusonovia ribis-nigri (Mosley).
An early and persistent attack, even in the absence of virus disease, much reduced the number of hearted plants and their average weight. A late attack by winged aphids in early spring sometimes spoilt fully hearted lettuces.
Dipping the plants in nicotine solution at the time of transplanting in November reduced aphid infestation; dusting with benzene hexachloride proved more effective.
If transplanting was delayed until February or March a relatively clean crop could be produced by insecticide treatment, but losses from fungal disease were usually high.     

Comparative patterns of phenology and growth form diversity in two winter rainfall deserts: the Succulent Karoo and Mojave Desert ecosystems

A comparative study of community structure and seasonal growth dynamics in the arid winter rainfall regions of the Succulent Karoo in South Africa and the Mojave Desert of the United States suggests that remarkably divergent patterns of resource use and resultant growth form diversity exist in regions with outwardly similar climatic regimes. An understanding of these divergent patterns in the two winter rainfall deserts allows predictions to be made on vegetation response to global change. Above-ground plant growth in the Succulent Karoo begins with the first significant rains in late summer and continues through winter because moderate minimum temperatures allow continued growth. These communities have low structural diversity above-ground, but also below-ground, where root systems commonly do not exceed 20 cm in depth. These shallow root systems harvest water from upper soil horizons soon after rain falls, and growth declines as rainfall decreases in late spring. In contrast, low temperatures during winter inhibit growth in the Mojave Desert until early spring at a time when a mean 74% of the hydrologic year precipitation (July-June) has already occurred. Thus species in this structurally diverse system rely on deeper stores of water for growth in spring and early summer. A global change scenario of a 2 to 4°C increase in mean annual temperature and increased summer rainfall in the Mojave desert would be expected to produce similar conditions in the Mojave Desert to those that exist in the Succulent Karoo today. Assuming no genetic constraints on phenotypic plasticity, this would suggest increased species diversity and a decline in structural diversity in the Mojave Desert over evolutionary time. Increased summer rainfall in the Succulent Karoo would be expected to lead to invasions of grasses and thus increased competitive pressure reducing community diversity.     

Genetics of flowering time in bread wheat <Emphasis Type="Italic">Triticum aestivum</Emphasis>: complementary interaction between vernalization-insensitive and photoperiod-insensitive mutations imparts very early flowering habit to spring wheat

Time to flowering in the winter growth habit bread wheat is dependent on vernalization (exposure to cold conditions) and exposure to long days (photoperiod). Dominant Vrn-1 (Vrn-A1, Vrn-B1 and Vrn-D1) alleles are associated with vernalization independent spring growth habit. The semidominant Ppd-D1a mutation confers photoperiod-insensitivity or rapid flowering in wheat under short day and long day conditions. The objective of this study was to reveal the nature of interaction between Vrn-1 and Ppd-D1a mutations (active alleles of the respective genes vrn-1 and Ppd-D1b). Twelve Indian spring wheat cultivars and the spring wheat landrace Chinese Spring were characterized for their flowering times by seeding them every month for five years under natural field conditions in New Delhi. Near isogenic Vrn-1 Ppd-D1 and Vrn-1 Ppd-D1a lines constructed in two genetic backgrounds were also phenotyped for flowering time by seeding in two different seasons. The wheat lines of Vrn-A1a Vrn-B1 Vrn-D1 Ppd-D1a, Vrn-A1a Vrn-B1 Ppd-D1a and Vrn-A1a Vrn-D1 Ppd-D1a (or Vrn-1 Ppd-D1a) genotypes flowered several weeks earlier than that of Vrn-A1a Vrn-B1 Vrn-D1 Ppd-D1b, Vrn-A1b Ppd-D1b and Vrn-D1 Ppd-D1b (or Vrn-1 Ppd-D1b) genotypes. The flowering time phenotypes of the isogenic vernalization-insensitive lines confirmed that Ppd-D1a hastened flowering by several weeks. It was concluded that complementary interaction between Vrn-1 and Ppd-D1a active alleles imparted super/very-early flowering habit to spring wheats. The early and late flowering wheat varieties showed differences in flowering time between short day and long day conditions. The flowering time in Vrn-1 Ppd-D1a genotypes was hastened by higher temperatures under long day conditions. The ambient air temperature and photoperiod parameters for flowering in spring wheat were estimated at 25°C and 12 h, respectively.     

Sexual segregation in winter, spring dispersal and habitat use in the pheasant (Phasianus colchicus)

Sexual segregation, spring dispersal and late winter to spring habitat selection were studied in the pheasant Phasianus colchicus L. on two areas for which the proportions of different habitats were similar. On one of the sites (Damerham) hand-reared pheasants were released for shooting. On the other (Fulwell) no releasing or shooting took place.
The sex ratio of birds feeding in fields in autumn favoured males because females fed in groups within woods. Groups of birds were significantly segregated by sex during early to late winter periods, but by late March they were not. Male groups and solitary males in winter were more evenly dispersed than female groups.
At Fulwell, female winter groups consisted of regular group members (mainly adults) and transitory individuals called 'drifters' (mainly immatures).
Females in their first breeding attempt dispersed further from their winter range to their breeding range than did adult females and females dispersed further than males. Males gaining a territory for the first time moved significantly further than old territory owners. Territorial males moved less than non-territorial males between successive spring ranges.
During March June, habitat use by 33 radio-tagged females changed markedly from mixed and deciduous woodland to fields sown with winter and spring corn. The implications for management are outlined.     

Establishing Tallgrass Prairie on Grazed Permanent Pasture in the Upper Midwest

The goal of the study was to learn whether native prairie grasses and, eventually, a diverse mixture of native forbs could be incorporated in permanent pastures by means of rotational grazing by cattle. An experiment was established on a farm in northeastern Iowa on a pasture that had never been plowed but had been grazed since the 1880s. One treatment was protected from grazing to test for the presence of remnant vegetation. Andropogon gerardii, Sorghastrum nutans, Panicum virgatum, and Desmanthus illinoensis were introduced in plots first treated with glyphosate; seeds were either drilled (DR) or hand-broadcast and incorporated by controlled cattle trampling (BT). Seedling establishment and aboveground biomass were followed over 3 years. There was no evidence for remnant native plants on uplands, but seven species of native forbs and four native graminoids flowered in exclosures erected within waterways. D. illinoensis initially established up to 12 seedlings/m² but had disappeared from all but one plot by the third year. Variation in native grass establishment among replicate plots within treatments was very high, ranging initially from 0.2 to 9.9 plants/m². In August of the second year, native grasses made up only 8% of the available forage in DR plots and 1% of BT plots. One year later, however, native grasses made up 56% of the available forage in DR plots and 37% of BT plots, and these differences were significant (p = 0.05). A pilot study seeded in late winter (frost seeding) suggested that seeds spread after cattle trampling produced five times more seedlings (2.5/m²) than seeds spread before cattle trampling (0.5/m²). Frost seeding had advantages because it did not require herbicide for sod suppression or tractor access to the site. New plantings could be safely grazed in early spring and late fall, before and after most native grass growth, to offset the negative economic impact of protecting new plantings from burning during the growing season. But this practice precluded subsequent prescribed burning. I propose a strategy for incorporating native wildflowers into the pasture over time with minimum cost.     

Seasonal quality of forages used by moose in the aspen-dominated boreal forest, central Alberta

Forages used by moose, Alces alces , in the aspen-dominated boreal forest were studied to determine seasonal changes in digestibility (nylon bag technique) and chemical composition. Digestibility of all forage classes increased to 70% during spring and summer with the presence of new growth and declined to a low of 30% with plant maturation and dormancy. Mean protein contents during these periods were >20% and <7%, respectively. Nutritional quality of herbaceous forages peaked earlier and higher than that of woody plants in spring but quality declined earlier and reached slightly lower levels in late winter. Cell wall composition of grasses, sedge, and foliage varied seasonally and was correlated with forage digestibility. In multiple linear regression models, hemicellulose, cellulose, and lignin content of browse, grass, and sedge provided significant predictions of digestibility.     

Photorefractoriness and energy availability interact to permit facultative timing of spring breeding

In seasonally breeding mammals, vernal reproductive development is not directly triggered by increases in day length, rather, an endogenous program of photorefractoriness to short winter days initiates spontaneous development in advance of spring. The transition to the reproductive phenotype is energetically demanding. How food availability in late winter and early spring impacts the onset and expression of photorefractoriness is not known. In this study, male Siberian hamsters were born into a simulated natural photoperiod, and at the winter solstice, they were subjected to a restricted feeding protocol in which a daily food ration was provided in an amount equal to ad libitum (AL) intake during the weeks preceding the solstice. Over the next several months, AL-fed control hamsters exhibited spontaneous recrudescence or spontaneous development. In contrast, vernal reproductive development was abolished in most food-rationed hamsters. In food-rationed hamsters that did exhibit recrudescence, conspicuous delays in the onset of gonadal development and decreases in the magnitude of growth were evident. In all hamsters, the termination of food rationing triggered rapid gonadal development. The data indicate that late winter/early spring increases in environmental food availability are required for the normal manifestation of photorefractoriness-induced reproductive development and suggest that a function of photorefractoriness may be merely to disinhibit the reproductive axis from photoperiodic suppression. Vernal gonadal development or recrudescence appears to be strongly affected by proximate energy availability.     

How Early Can the Seeding Dates of Spring Wheat Be under Current and Future Climate in Saskatchewan,Canada?

Background

Shorter growing season and water stress near wheat maturity are the main factors that presumably limit the yield potential of spring wheat due to late seeding in Saskatchewan, Canada. Advancing seeding dates can be a strategy to help producers mitigate the impact of climate change on spring wheat. It is unknown, however, how early farmers can seed while minimizing the risk of spring frost damage and the soil and machinery constraints.

Methodology/principal findings

This paper explores early seeding dates of spring wheat on the Canadian Prairies under current and projected future climate. To achieve this, (i) weather records from 1961 to 1990 were gathered at three sites with different soil and climate conditions in Saskatchewan, Canada; (ii) four climate databases that included a baseline (treated as historic weather climate during the period of 1961–1990) and three climate change scenarios (2040–2069) developed by the Canadian global climate model (GCM) with the forcing of three greenhouse gas (GHG) emission scenarios (A2, A1B and B1); (iii) seeding dates of spring wheat (Triticum aestivum L.) under baseline and projected future climate were predicted. Compared with the historical record of seeding dates, the predicted seeding dates were advanced under baseline climate for all sites using our seeding date model. Driven by the predicted temperature increase of the scenarios compared with baseline climate, all climate change scenarios projected significantly earlier seeding dates than those currently used. Compared to the baseline conditions, there is no reduction in grain yield because precipitation increases during sensitive growth stages of wheat, suggesting that there is potential to shift seeding to an earlier date. The average advancement of seeding dates varied among sites and chosen scenarios. The Swift Current (south-west) site has the highest potential for earlier seeding (7 to 11 days) whereas such advancement was small in the Melfort (north-east, 2 to 4 days) region.

Conclusions/significance

The extent of projected climate change in Saskatchewan indicates that growers in this region have the potential of earlier seeding. The results obtained in this study may be used for adaptation assessments of seeding dates under possible climate change to mitigate the impact of potential warming.