4种柳树苗木叶的PV水分参数对水分胁迫的响应

在温室内研究了瑞典能源柳C号、2号柳、4号柳和陕北红皮柳苗木的抗旱能力。对其盆栽苗木施行水分轻度胁迫、中度胁迫、重度胁迫及正常(供水)生长4种处理,应用压力室和PV技术测定4种柳树苗木在不同处理状态下的叶组织多项水分参数,以此对其苗木的耐旱能力作综合评定。结果表明,在水分胁迫条件下,2号柳苗木叶吸收水分的能力最强;4种柳树的苗木均有一定的渗透调节和保持膨压能力,4号柳、2号柳、红柳的苗木能通过增加叶束缚水的含量来实现渗透调节,但其依靠改变苗木叶束缚水的含量来实现渗透调节的作用有限,红柳、4号柳苗木在土壤相对含水量降至61%时,2号柳苗木在土壤相对含水量降至46%时,其叶由束缚水含量所引起的渗透调节作用消失;在水分胁迫条件下,红柳、4号柳苗木通过改变叶组织细胞壁的弹性来保持其的膨压,2号柳、能源柳C号的苗木主要靠叶渗透调节来维持其的膨压。水分胁迫能增强红柳、能源柳C号、4号柳苗木保持最大膨压的能力,而降低2号柳苗木维持最大膨压的能力;4号柳能通过提高苗木叶细胞原生质忍耐脱水的能力来适应干旱,能源柳C号、红柳苗木叶细胞原生质耐脱水能力对水分胁迫的适应性差,在水分胁迫条件下其耐脱水能力减弱。通过对4种柳树苗木叶组织渗透调节和维持膨压能力的综合比较,其抗旱能力由强至弱依次为能源柳C号、2号柳、红柳和4号柳。     

利用PV曲线水分参数评价16种植物抗旱性

利用PV技术测定沙柳、乌柳、杠柳、沙枣、匙叶小檗等16种植物的饱和含水时的渗透势(Ψ_(ssat))、膨压为0时的渗透势(Ψ_(stlp))、相对水含量(RWC~(tlp))、相对渗透水含量(ROWC~(tlp))及最大弹性模量(ε_(max))5个水分参数。研究结果表明,16种植物对干旱的适应性各不相同,利用Ψ_(stlp)评价抗旱性具有可行性;依据PV水分参数,结合16种植物种的自然分布特征,将其分为3大类型,第Ⅰ类霸王、杠柳、匙叶小檗、小叶锦鸡儿、柠条锦鸡儿和乌头叶蛇葡萄为抗旱性强的植物,第Ⅱ类蒙古莸、沙木蓼、油蒿、沙枣和蒙古岩黄芪为中等抗旱植物,第Ⅲ类沙柳、黄柳、乌柳、小红柳和籽蒿为抗旱性弱的植物。     

不同家系马尾松对持续干旱的响应及抗旱性

【目的】了解持续干旱对不同家系马尾松幼苗生长和生理特征的影响,初步揭示马尾松的抗旱机制及抗旱遗传效应,比较不同家系的抗旱能力,为马尾松抗旱优良家系选育提供理论依据。【方法】以3个来自广西和贵州的2年生马尾松家系(GX01、GX02和GZ01)幼苗为试验材料,采用随机区组设计,温室土培盆栽模拟干旱环境,研究持续干旱胁迫对马尾松幼苗生长、渗透调节和抗氧化系统的影响。【结果】随干旱胁迫程度的加重,3个家系马尾松的SOD活性均呈先升后降趋势,各家系在胁迫0~10天存在显著差异(P0.05);POD活性亦呈先升后降趋势,但家系间差异不显著(P0.05);MDA含量变化中GX01呈先升后降趋势,GX02和GZ01呈先降后升趋势,各家系在胁迫5~20天以及第30天存在显著差异(P0.05);脯氨酸含量变化中GZ01呈持续上升趋势,GX02和GX01呈先升后降又再升高的趋势,各家系在胁迫20~30天存在显著差异(P0.05)。连续干旱限制马尾松苗期的生长,3个家系马尾松的苗高和地径的生长以及干物质积累均受到抑制,家系间的苗高生长、地径生长、干物质积累等均存在显著差异(P0.05);连续干旱导致GX01和GX02的根冠比显著高于对照,GZ01亦高于对照,但差异不显著。隶属函数分析得出3个马尾松家系幼苗抗旱性GX01GX02GZ01;灰色关联分析发现,根冠比、苗高与抗旱性关联度最大,其次为MDA和脯氨酸含量,可作为评价抗旱性的主要指标。【结论】马尾松幼苗在轻度干旱胁迫下通过增加保护酶活性抵御干旱;在中、重度干旱胁迫下通过增加渗透调节物质抵御干旱逆境伤害;极重度干旱胁迫下,保护酶活性显著下降,MDA含量显著上升,膜质过氧化伤害严重。干旱胁迫下,马尾松幼苗通过增加地下部分生长、减少地上部分生长以适应干旱逆境。马尾松抗旱性受遗传因素控制,不同家系间抗旱性的差异可能与其不同地理环境长期驯化所形成的遗传差异有关。     

应用PV技术对北方4种阔叶树抗旱性的研究

在温室内用盆栽法研究茶条碱（Acer ginnala)。山荆子（Malus baccata)，山桃（Prunus davidiana)和山梨（Pyrus ussuriensis)的抗旱能力。设置4种土壤水分处理（土壤相对含水量75%，61%，46%，35%）。应用压力室和PV技术测定4个树种多项水分参数，并对4树种耐旱能力进行综合评定。结果表明，在干旱胁迫条件下，山梨吸收水分能力最强；4树种均有一定的渗透调节和保持膨压能力。茶条槭，山梨，山桃能通过增加束缚水含量来实现渗透调节，但其依靠改变束缚水含量来实现渗透调节作用有限，山桃，茶条槭在土壤相对含水量降至61%时，山梨在土壤相对含水量降至46%时，由束缚水含量所引起的渗透调节作用消失；在干旱胁迫条件下，山桃，茶条槭通过改变细胞壁弹性来保持膨压，山梨，山荆孔子主要靠渗透调节来维持膨压，干旱胁迫能增强山桃，山荆子，茶条槭保持最大膨压的能力。而降低山梨维持最大膨压的能力；茶条槭能通过提高原生质忍耐脱水能力来适应干旱，山荆子，山桃原生质耐脱水能力对干旱胁迫的适应性差。在干旱胁迫条件下其耐脱水能力减弱。通过对4树种渗透调节和维持膨压能力进行综合比较。4种种抗旱能力由强至弱依次为山荆子，山梨，山桃和茶条槭。     

干旱胁迫对臭柏水分特性的影响

运用PV技术 ,从天然臭柏群落和在室内干旱胁迫处理的臭柏扦插苗中分别取样 ,测定了干旱胁迫下臭柏的水分参数。天然臭柏群落选自毛乌素沙地土壤水分条件不同的沙丘上部和沙丘下部。室内干旱胁迫处理是将臭柏插穗带往日本冈山大学扦插 ,生根扦插苗移植于砾耕栽培装置中 ,设置对照区、弱干旱胁迫区、强干旱胁迫区 (培养液渗透势分别为 0 0、- 0 1、- 0 3MPa) 3种处理进行长期干旱胁迫室内模拟试验。结果表明 ,毛乌素沙地生长的臭柏 ,在不同的立地条件下 ,小枝的水分特性不同 ,在较干旱的沙丘上部 ,与较湿润的沙丘下部相比 ,膨压为 0时的渗透势 (ψs)、水饱和状态下的水势 (ψw)值减小 ,最大体积弹性模量 (ε)、细胞内的束缚水含量 (VP VO)值增大 ;干旱胁迫模拟试验条件下 ,随着干旱胁迫的增强 ,ψs 和 ψw 值减小 ,ε和VP VO 值增大 ;在干旱胁迫下 ,臭柏渗透调节能力发生了变化 ,从而证明臭柏是耐旱性可变的树种 ,通过抗旱锻炼 ,可提高其耐旱性。此外 ,还讨论了毛乌素沙地沙丘不同部位生长的臭柏小枝水势的日变化规律及干旱胁迫下培养液渗透势与水分特征参数的相关性。     

马尾松不同家系苗期耐旱性分析

选取70个马尾松(Pinus massoniana)初级种子园半同胞家系为试验材料,结合反复干旱胁迫试验和大田试验,测定苗木萎蔫度和死亡率,离体针叶失水率,大田实验保存率,利用隶属函数法初步评价筛选出抗旱性较强的家系。结果表明:干旱胁迫下各家系苗木死亡率与萎蔫度存在极显著正相关性,评价结果具有较好的一致性;各家系苗木反复干旱胁迫死亡率变异系数为0.317,大于萎蔫度和离体针叶失水率变异系数,离散程度高,同时能体现苗木复水后的恢复能力,该评价指标具有更好的代表性和分辨能力。综合评价认为,在70个马尾松家系中,N-68号和N-28号家系苗木具有较强的抗旱性。     

水分胁迫条件下臭柏匍匐茎的蒸腾和吸水特性

在臭柏长期室内石砾土栽培条件下,通过培养液中加入PEG以调节溶液渗透势,设置对照区(pF值3.0)、水分胁迫区(pF值2.3)2种处理,并分别从匍匐茎中部人工培养不定根,测定有不定根和无不定根匍匐茎小枝的蒸腾速率、气孔导度及其水势的日变化和叶片水分特性.结果表明:1)在水分胁迫条件下,匍匐茎先端小枝通过降低正午水势提高吸水能力;基部小枝通过控制蒸腾,维持枝条水势防止失水.2)有不定根的匍匐茎通过降低质壁分离时的水势(ψwtlp)和充分吸水时的渗透势(ψ,ssat)提高吸水能力,而且增加细胞弹性率,迅速降低膨压保证失水时能尽快关闭气孔;而无不定根匍匐茎虽然吸水能力较差,但细胞壁柔软,即使蒸腾失水,也能在较长时间内维持膨压,保证生命活动进行.     

干旱胁迫对不同种源马尾松苗木生长的影响

对广东信宜、浙江江山、湖南汝城、重庆黔江和湖北大悟5个种源马尾松容器苗进行不同程度干旱周期性胁迫处理,测定和分析干旱胁迫对各种源马尾松苗木生长的影响。结果表明:干旱胁迫下,各种源马尾松苗木生长均受到抑制,中度胁迫和重度胁迫下的苗高增长量、地上部分干重、地下部分干重、总干重均低于对照。胁迫后期,各种源生长指标的变化幅度不一致。综合分析得出:湖南、湖北、广东种源较为耐旱;浙江、重庆种源耐旱能力较弱。     

干旱胁迫对马尾松菌根化苗木水分生理和光合特性的影响

以马尾松Pinus massoniana 1年生苗为材料,采用双因素随机区组试验设计,6个接种处理,分别为牛肝菌7 Suillus luteus,牛肝菌1,鸡油菌Cantharellus cibarius,彩色豆马勃Pisolithus tinctorius Strain Pt 715,土生空团菌Cenococcum geophilum Strain Cg SIV和对照(不接种);4个水分处理,土壤相对含水量分别为正常(65±5)%、轻度胁迫(50±5)%、中度胁迫(35±5)%和重度胁迫(25±5)%,比较分析马尾松菌根化及非菌根化苗木,在干旱胁迫下水分生理和光合特性的差异。结果表明,外生菌根真菌通过提高叶片相对含水量,增加束缚水含量,降低苗木水势、自由水和水分饱和亏缺,从而改善苗木水分状况,增强苗木保水能力;外生菌根真菌增加了苗木叶绿素含量,提高了苗木光合速率,各处理间差异显著(P 0.05)。较高的叶绿素含量使菌根化苗木的光合速率增强,气孔导度、胞间CO2浓度和资源利用效率也提高,从而降低蒸腾速率、气孔限制值和光合耗氧量,减少气孔对水分的阻力,提高菌根化苗木的含水量;马尾松菌根化苗木主要是通过提高光合利用效率来适应干旱环境,其抗旱能力由强到弱为:牛肝菌1土生空团菌牛肝菌7鸡油菌彩色豆马勃对照。     

四种常见针叶树种种子发芽对水分胁迫的响应

本文通过用PEG(聚乙二醇)配制不同浓度溶液,模拟不同土壤水势梯度,达到不同水分胁迫水平,进行柳杉、杉木、马尾松、侧柏等树种种子发芽水分胁迫实验。研究结果表明;水势在0～-0.6Mpa,除马尾松外,其余三种树种随水势下降,种子发芽率、发芽指数、苗长、活力指数均呈下降趋势。水势降至-0.86 Mpa时,各树种种子发芽均受完全抑制。其中侧柏在水势降至-0.6Mpa时,种子发芽已受完全抑制。综合比较,各树种种子的耐旱能力大小依次为:马尾松>杉木>柳杉>侧柏。     

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.