舞草硬实种子的高活力性状研究

舞草种子硬实率高达90%左右,种子在吸水过程中显示出其硬实程度的差异.第1天吸胀的种子硬实程度最低,随着吸胀时间的延长,硬实程度逐渐增高,直至第5天取尚未吸胀的种子,将其作为本试验硬实程度最高的种子,并用80～90 ℃热水打破其休眠.测试显示硬实种子的发芽率、活力指数及抗逆性均高于对照种子,而电导率则低于对照种子.试验结果证明在舞草种子批中硬实种子的活力高于非硬实种子,其活力强度随硬实程度的增加而递增,因此硬实种子才是舞草种子批中的高活力种子.     

刺槐硬实成因概述及发芽技术试验

硬实在植物界是一种普遍存在的现象,其中最常见的是豆科植物种子。木本植物如刺槐、皂荚的种子,硬实占有很高的比率。据笔者在临沂大青山林场测定,硬实率最高达93％,最低为32％,平均为58.7％,这就大大影响其种用价值。 硬实从外部形态上如色泽浓淡和种粒大小等很难确定,一般是通过浸种检查其中不能吸胀的数目。但某些刺槐硬实却非常顽强,在40℃温水中浸泡一个多月,仍不能改变其不透水性。所以加速刺槐硬实     

NaCl和PEG胁迫对不同大小刺槐种子萌发和幼苗生长的影响

【目的】研究盐和干旱胁迫下不同大小刺槐种子的萌发规律,提出合适种子大小与胁迫程度的选配建议,为刺槐优良苗木的培育提供参考。【方法】利用土壤筛,将种子分为大粒、中粒和小粒3个等级,明确每个等级种子大小特征、千粒质量和吸胀率。用NaCl和PEG 6000模拟盐和干旱胁迫,配制不同渗透势(0、-0.05、-0.15、-0.30、-0.49 MPa)的NaCl、PEG溶液。将不同大小的种子放置在光照培养箱内进行萌发试验,分析种子的萌发特征、幼苗生物量和根系发育,并比较不同大小种子在萌发中的可塑性。【结果】1)大粒和中粒种子的吸胀率显著大于小粒种子,中粒与小粒种子的千粒质量对比大粒种子分别降低22.01%、61.72%。2)随胁迫程度的增加,发芽率、发芽指数、活力指数显著降低,平均发芽时间显著增加;幼苗含水量、生物量、根长、根表面积、比根长、比根表面积显著降低。盐胁迫处理比干旱胁迫有着高的发芽率、发芽指数、活力指数、幼苗含水量,但在根干重、根冠比、根长、根表面积、比根长、比根表面积上低于干旱胁迫的。在各个指标的胁迫指数上,盐胁迫高于干旱胁迫的。3)在整个萌发过程中,大粒和中粒种子与小粒种子相比,...     

刺槐属杂交亲和性及果实特性研究

以刺槐属20个优良无性系和1个品种多花刺槐为亲本进行杂交,采用离体培养法比较雄株的花粉活力,并统计各杂交组合的结实率、亲和指数及种子形态等,研究了刺槐属品种自交、种间杂交、种内杂交亲和性及种子特性。结果表明:刺槐花粉活力种间多花刺槐大于普通刺槐,而刺槐不同无性系花粉萌发率近似,刺槐花粉活力在低温下至少能够保持5d;多花刺槐自交不亲和,种内自交不亲和或较小;刺槐种间具有较高的杂交亲和性,22个杂交组合中,鲁刺152×多花刺槐亲和指数最高为2.833,其次是兴刺1×鲁刺68,亲和指数为2.719,杂交组合鲁刺57×兴刺15,亲和指数为2.148。种子饱满度以自然结实的普遍好于杂交的,杂交组合与母本自由授粉之间的种子形态差异不明显,有的几乎没有差异。     

人工老化对刺槐种子活力的影响

刺槐种子在高温、高湿模拟条件下人工加速老化1～6d,随着老化时间的延长,其生活力和活力指标均发生明显变化.老化5d后,种子丧失活力,发芽率为0.在老化过程中,电导率和过氧化物酶活性随老化程度的增大而明显增大.     

不同处理方法对马棘种子发芽的影响

采用不同温度、不同强度碱溶液和浓硫酸不同浸泡时间处理马棘种子.试验表明,不同处理方法对马棘种子发芽效果有显著影响,60～80℃的温度处理可显著提高马棘种子的发芽势、发芽指数和活力指数,超过一定温度(90℃)则远远不如对照(20℃);碱溶液处理以pH9处理效果最好,但碱溶液处理效果并不显著;浓硫酸处理以浸泡20min效果最好,其发芽率、发芽势、发芽指数、简化活力指数和活力指数均为各处理最高值.通过种子生活力和种子硬实率的测定,认为硬实是造成马棘种子发芽率低的主要原因.     

碳酸氢钠对绒毛白蜡种子萌发和幼苗生长的影响

NaHCO_3,溶液漫种能影响绒毛白蜡种子的吸胀和发芽质量,导致发芽率、发芽指数和活力指数下降;在NaHCO_3逆境下形成的幼苗,苗高减小,鲜重降低。具有一对真叶的幼苗在含有NaHCO_3的营养液中水培,NaHCO_3浓度越高;幼苗高生长量越小,苗木重量越轻;但浓度为0.2%的溶液可促进幼苗根系生长,使其根茎比上升。一对真叶的幼苗对NaHCO_3的抗性比2对真叶的幼苗强。     

三种野生豆科牧草引种试验初报

文章观察了来自俄罗斯乌兰乌德的黄花苜蓿、红三叶和来自伊尔库茨克地区的牧地山黧豆三种野生豆科牧草的种子萌发、幼苗生长发育及物候期。对硬实率、发芽率、发芽指数及幼苗的生长速度、干鲜重等进行了观测。结果表明:三种野生豆科牧草均具有较高的硬实特性;在种子萌发过程中黄花苜蓿发芽率和发芽指数均相对较高;三种牧草生育期均较长。     

不同植物生长调节剂处理对刺槐种子萌发的影响

为了比较不同植物生长调节剂对刺槐种子萌发的影响效果,开展了IAA(吲哚乙酸)、IBA(吲哚丁酸)、2,4-D、GA(赤霉素)4种植物生长调节剂处理下的刺槐处子萌发试验。结果表明:各植物生长调节剂对诱导刺槐种子提前萌芽的效果尽管不明显,但能够打破种子休眠状态,提高种子的萌发数;各种植物生长调节剂中,以2,4-D提高刺槐种子发芽率、发芽势、发芽指数的效果最佳,浓度宜选择50～70 mg L~(-1)。     

贮藏温度和贮藏时间对垂柳种子生活力的影响

以成熟的垂柳种子为材料,测定了不同贮藏温度和不同贮藏时间下垂柳种子发芽率、发芽势、活力指数等生活力指标的变化,以探索贮藏温度和贮藏时间对垂柳种子生活力的影响。结果表明:适当的低温-10℃、-5℃、4℃可以延缓垂柳种子的劣变,延长其贮藏时间;常温20℃与极低温-20℃条件下会降低种子的生活力,表现为活力指数降低;随贮藏天数的增加,发芽率、发芽势、发芽指数表现出先升高后降低的趋势,发芽速则是先降低后升高。常温20℃贮藏7天种子发芽率显著下降,在-5℃贮藏3天的条件下种子生活力最强,可应用于垂柳种子萌发及人工种苗培育的实践中。     

Growth of Phlebiopsis gigantea in wood of seven conifer species

Heterobasidion parviporum and Heterobasidion annosum are widely distributed root‐rot fungi that infect conifers throughout Europe. Infection of conifer stumps by spores of these pathogens can be controlled by treating fresh stumps with a competing non‐pathogenic fungus, Phlebiopsis gigantea. In this study, growth of three Latvian strains of P. gigantea and the biological control agent ‘Rotstop’ strain was evaluated in stem pieces of Norway spruce, Scots pine, lodgepole pine, Douglas‐fir, Weymouth pine, Siberian larch and Sitka spruce. The growth rates of one H. parviporum and one H. annosum isolate were also measured in the same stem pieces. The growth rate of P. gigantea varied greatly in wood of different conifer species. It was higher in the three pine species, lower in Norway spruce and lowest in Sitka spruce and Siberian larch, and in Douglas‐fir, this fungus did not grow. The largest area of wood occupied by P. gigantea was in lodgepole pine. Growth of Latvian isolates of P. gigantea in the wood of Pinus and Picea species was comparable to that of the Rotstop isolate. Consequently, stump treatment with local P. gigantea isolates should be recommended. However, our results suggest that Douglas‐fir stump treatment against Heterobasidion by P. gigantea may be ineffective and other stump treatment methods should be considered.     

Growth of Mixed Birch-Coniferous Stands in Relation to Pure Coniferous Stands at Similar Sites in South-eastern Norway

Mean age, mean and top heights and yield were studied in 20 mixed stands of birch ( Betula pubescens Ehrh. and B. pendula Roth) and Picea abies (L.) Karst. and nine mixed stands of birch and Pinus sylvestris L. in south-eastern Norway. Each mixed stand and the adjacent pure coniferous stand (control) were growing under the same site conditions and had not been commercially thinned. There were no significant differences in mean age at breast height or in top heights between birch and conifers in the mixed stands, while mean height was significantly higher for birch than for spruce. A growth index was calculated based on total volume and age at breast height. For the spruce sites the growth in young mixed stands (birch < 17 m) was superior to that of pure spruce, while the difference was insignificant in older stands. The growth index correlated positively with the ratio between generatively and vegetatively regenerated birch trees, and negatively with the age of the oldest species in the mixture and with site quality. For the pine sites there was no significant difference in the growth index between mixed birch-pine and pure pine stands. A mixture effect of birch on the volume yield of spruce or pine could not be demonstrated.     

Defoliation by the Needle-shortening Pine Gall Midge,Thecodiplosis brachyntera,on Pines in Central Sweden

An outbreak of the needle-shortening pine gall midge, Thecodiplosis brachyntera , occurred on Scots pine, Pinus sylvestris (L.) and lodgepole pine, P. contorta (Dougl.) in central Sweden during 1995-1998. The larval feeding of T. brachyntera kills current-year needles and heavy infestation causes severe defoliation. A pattern of fluctuating defoliation among years and sites was found on both pine species. Defoliation was evenly distributed in the crown of P. sylvestris during years of high as well as low infestation; apical whorls had as much defoliation as basal whorls. In P. contorta , however, there was a tendency for defoliation to be concentrated on branches in the most apical whorls. Growth ring increments on P. sylvestris with high levels of defoliation (71%) did not differ from trees with moderate levels (26%) of defoliation. Shoot lengths were significantly shorter, however, on heavily infested trees the year after defoliation.     

Decomposition and nutrient loss from prunings of different contour hedgerow species in tea plantations in the sloping highlands of Sri Lanka

Contour hedgerows of multipurpose tree species in the sloping tea lands of Sri Lanka are expected to reduce soil erosion and also add significant amounts of plant nutrients to the soil via periodic prunings. The objective of this experiment was to characterize the biomass decomposition pattern and quantify the amount of nutrients added through prunings of six tree species (Calliandra calothyrsus, Senna spectabilis, Euphatorium innulifolium, Flemingia congesta, Gliricidia sepium and Tithonia diversifolia) currently being used in hedgerows associated with tea. Withered leaf and stem prunings (50 g) were enclosed in 2-mm litter bags, placed at 5-cm depth and retrieved after one, three, six, nine and 12 weeks. Loss of initial dry weight, N, P and K was measured. Single exponential decay function adequately described both dry weight and nutrient loss. Tree species differed significantly in their rate of breakdown with decomposition constants (k) varying from 0.0299 to 0.2006 week⁻¹ for leaves and from 0.0225 to 0.0633 week⁻¹ for stems. Gliricidia showed the highest k for leaves with the rest in the following descending order: Senna > Tithonia ≥ Euphatorium > Calliandra > Flemingia. A similar pattern was observed for loss of all nutrients with Calliandra and Flemingia always having lower k values than the rest. Although N immobilization was not observed, immobilization of P and K was observed during the first week of incubation in some species, particularly in stem prunings. Annual biomass of prunings differed significantly between tree species in the following descending order: Calliandra > Senna > Flemingia > Tithonia > Gliricidia > Euphatorium. Calliandra added the greatest amount of nutrients annually to the soil with Euphatorium adding the least. Calliandra prunings provided the annual total K requirement and 49% of the N requirement of mature tea. However, none of the species provided more than 5% of the P requirement. It is concluded that among the tree species tested, Calliandra and Flemingia are the most suitable for contour hedgerows in tea plantations of this agroclimatic region because of their higher soil nutrient enrichment capacity and slower decomposition rates which would minimize leaching losses. This revised version was published online in June 2006 with corrections to the Cover Date.     

Effects of Seed Weight and Seed Type on Early Seedling Growth of Pinus sylvestris under Harsh and Optimal Conditions

The effects of seed weight and seed type on seedling growth of Pinus sylvestris (L.) were studied by seeding individually weighed orchard and stand seed in different mixtures under harsh (direct seeding in field) and optimal (seeding in nursery) conditions. In the nursery experiment an increase in the seed weight from 3 to 7 mg increased the seedling height by 10-27% and total weight by 27-113%, and decreased the height/diameter ratio by 5-6% after 2 yrs. With elimination of seed weight effects, orchard seedlings were 2% taller than stand seedlings in year 2. Without elimination of seed weight effects, orchard seedlings were 7-13% taller. In the field experiment an increase in the seed weight from 3 to 7 mg increased seedling height by 18-65%, stem volume by 81-274% and the number of top-buds by 23-34% in year 5. After elimination of seed weight effects, orchard seedlings were 7-13% taller than stand seedlings and without elimination of seed weight effects 20-21% taller after 5 yrs. Even after elimination of both seed weight and genetic effects orchard seedlings were 3-9% larger than stand seedlings in the field experiment. In conclusion, the influence of seed weight and seed type on growth traits and slenderness is highly significant and the influence seems to be greater in harsh conditions.     

Modelling of adequate pretwist for obtaining straight timber

Abstract

Wood in general and wooden studs in particular are often distorted owing to uneven shrinkage during the drying process in the sawmill. Twist is often the most detrimental of all types of distortion, and it is caused by spiral grain in combination with variations in moisture content. For sawmills, the objective is to produce dried, straight boards, and one method of dealing with boards with excessive spiral grain is to sort them out and then dry them in a pretwisted position to obtain straight boards after drying. A model using the finite element (FE) method for the simulation of drying twist distortions was first calibrated against laboratory experiments in which boards were dried with and without restraints and pretwists. After the calibration, the FE results were compared with industrial test results for boards that were dried without restraints or with restraints with zero pretwist, i.e. straight restraints. The FE model used an elastic–ideally plastic material model to obtain permanent deformations. The calibration was to set the yield stresses so that there was a good match between FE results and results from the laboratory experiments. The comparison between the industrial test results and the FE results showed that the FE model is capable of realistic simulations of drying boards with and without restraints and presumably also pretwists.     

Potential to harness superior nutritional qualities of exotic baobabs if local adaptation can be conferred through grafting

Baobab leaves form an important part of the local diet in Sahel countries and elsewhere in Africa. Existing leaf nutritional data and agroforestry performance information are based solely on Adansonia digitata L., the baobab of continental Africa. The introduction potential of Adansonia species from the center of diversity in Madagascar and from Australia remains untapped. To assess this potential, the mineral contents and B₁ and B₂ vitamin levels of dried baobab leaves were determined for five-year old trees of A. digitata, A. gibbosa (A. Cunn.) Guymer ex D. Baum, A. rubrostipa Jum. & H. Perrier (syn. A. fony Baill.), A. perrieri Capuron and A. za Baill. grown in an introduction trial in Mali. Nutritional data were evaluated against survival and vigor to identify promising germplasm. Leaf vitamin and crude protein contents were highest in the Madagascar species, especially A. rubrostipa (B₁ 88 mg 100 g⁻¹, B₂ 187 mg 100 g⁻¹, protein 20.7% dry weight). However, the local species far outperformed the introductions in survival, tree height, basal diameter and resistance to termites. We suggest grafting as a way of harnessing the vigor of well-adapted local baobab varieties to the superior nutritional profiles of A. rubrostipa and others. Cross-species grafting tests in Adansonia were successful, thus creating new agroforestry possibilities with different scion/rootstock combinations.     

Boron in forest trees and forest ecosystems

This review critically examines the role of boron (B) in forests in view of recent findings on B nutrition and the continuing occurrence of B deficiency. Many perceptions about the role of B in plants and its uptake and mobility have been altered since the last review on B in forest trees in 1990. Now there is evidence for a fundamental role of B in the formation of the pectic structure in primary cell walls in plants, and further roles in membrane function are being explored. In plants, channel-mediated B uptake, active B uptake and B uptake by mycorrhizas have been shown, B transporters have been identified, and B retranslocation has been shown. We explore these findings and their consequences on forest trees and on ecosystems that they dominate. Particular emphasis is placed on B retranslocation and B in mycorrhizal symbiosis, given their importance in trees.     

Survival and Growth of Picea abies Regeneration after Shelterwood Removal with Single- and Double-grip Harvester Systems

Three stands in Sweden were followed for 7 yrs to study the survival and growth of Norway spruce [Picea abies (L.) Karst.] regeneration after shelterwood removal with single- and double-grip harvester systems. The height of all seedlings within circular plots was recorded before and after final cutting. The tallest seedling and one randomly selected seedling on each circular plot were permanently marked and their annual height growth was measured each year during the period 1993-1999. No significant differences between single- and double-grip harvester systems were found with respect to their effects on regeneration density, survival or annual height growth. The annual height growth of the individual seedlings after shelterwood removal was significantly correlated with seedling height before shelterwood removal. Significant differences were found in annual height growth between seedlings with high and low vitality. Logging damage did not affect the annual height growth. Several practical conclusions were drawn. First, the choice of harvester system does not affect seedling height growth or survival after shelterwood removal. Secondly, the removal of a 200 m³ shelterwood with 200 stems ha^-1 does not seem to constitute a serious problem for seedling survival and growth. Finally, estimated vitality and seedling height both seem to be fairly good predictors of postrelease survival and growth.     

Development of Pinus sylvestris Main Stems Following Three Different Precommercial Thinning Methods in a Mixed Stand

Reducing competition by point cleaning may be an attractive alternative to conventional precommercial thinning in forestry. In this study, survival and development of main stems of Scots pine (Pinus sylvestris L.) following point cleaning were examined in a mixed stand of mainly Scots pine and birch (Betula pendula Roth and Betula pubescens Ehrh.) in northern Sweden. Treatments studied were: no precommercial thinning, conventional precommercial thinning, point cleaning of all secondary stems, and point cleaning of only the secondary stems that were higher than the main stem, within a radius of 0.8 m from the main stem, respectively. A randomised complete block design with three replicates was used. Measurements taken 13 growing seasons after these treatments showed that conventional precommercial thinning was the best treatment for retaining Scots pines as main stems. However, conventional precommercial thinning resulted in the poorest timber quality of the remaining Scots pines in terms of stem taper, thickest branch diameter and relative live crown height. In conclusion, point cleaning has to be followed by a complementary cleaning operation if the objective is to retain Scots pines as main stems in such mixed stands.