Phosphate Availability Alters Lateral Root Anatomy and Root Architecture of Fraxinus mandshurica Rupr. Seedlings

Abstract: Plants have evolved some mechanisms to maximize the efficiency of phosphorus acquisition. Changes in root architecture are one such mechanism. When Fraxinus mandshurica Rupr. seedlings were grown under conditions of low phosphorus availability, the length of cells in the meristem zone of the lateral roots was longer, but the length of cells in the elongation and mature zones of the lateral roots was shorter, compared with seedlings grown under conditions of high phosphorus availability. The elongation rates of primary roots increased as phosphorus availability increased, but the elongation rates of the branched zones of the primary roots decreased. The number of lateral root primordia and the length of the lateral roots decreased as phosphorus availability increased. The topological index (altitude slope) decreased as phosphorus availability increased, suggesting that root architecture tended to be herringbone-like when seedlings were grown under conditions of low phosphate availability. Herringbone-like root systems exploit nutrients more efficiently, but they have higher construction costs than root systems with a branching pattern.

Control of Negative Gravitropism and Tension Wood Formation by Gibberellic Acid and Indole Acetic Acid in Fraxinus mandshurica Rupr. var. japonica Maxim Seedlings

In the present study, we Investigated the role of glbberelllc acid （GA3） and Indole acetic acid （IAA） In the gravity response of stems and tension wood formation using two-year-old stems of Fraxinus mandshurica Rupr. var. Japonica Maxim seedlings. Forty-five seedlings were used and divided Into nine groups that Included five seedlings In each group. Seedlings were treated with applications of GA3 alone at concentrations of 2.89×10^-8 and 2.89×10^-7 μmol/L, IAA alone at concentrations of 5.71×10^-8 and 5.71×10^-7 μmol/L, or their combination to the apical bud of the stem using a mlcroplpette. Seedlings were positioned horizontally after the first treatment. The same treatments were repeated six times per week. At the end of the experiment, all seedlings were harvested. Then, stem segments were cut under a light microscope. Application of exogenous GA3 at the higher concentration stimulated the upward bending of stems, whereas exogenous IAA had no effect. A synergistic effect of GA3 and IAA on upward stem bending was observed following application of the two combinations of GA3 and IAA. Moreover, application of exogenous GA3 at the higher dose stimulated wood formation on both the upper and lower sides of the stems, whereas the mixture of GA3 and IAA had a synerglstic effect on wood formation In horizontal stems. Application of exogenous IAA alone at the lower concentration （5.71×10^-8 μmol/L） or application of a mixture of the higher concentrations of GA3 （2.89×10^-7 μmol/L） and IAA （5.71×10^-7 μmol/L） Inhibited the development of gelatinous fibers （the G-layer） of tension wood on the upper side of the horizontal stems. The differentiation of gelatinous fibers of tension wood was not Inhibited by GA3 when It was applied alone, whereas the development of the gelatinous fibers of tension wood was strongly affected by the application of IAA. The findings of the present study suggest that the development of the G-layer Is not related to the dose of GA3, but needs a relatively lower concentration of IAA.

Role of GA_3,GA_4 and Uniconazole-P in Controlling Gravitropism and Tension Wood Formation in Fraxinus mandshurica Rupr. var. japonica Maxim. Seedlings

GA3 and GA4 （gibberellins） play an important role in controlling gravitropism and tension wood formation in woody angiosperms. In order to improve our understanding of the role of GA3 and GA4 on xylem cell formation and the G-layer, we studied the effect of GA3 and GA4 and uniconazole-P, which is an inhibitor of GA biosynthesis, on tension wood formation by gravity in Fraxinus mandshurica Rupr. var. japonica Maxim. seedlings. Forty seedlings were divided into two groups; one group was placed upright and the other tilted. Each group was further divided into four sub-groups subjected to the following treatments： 3.43 x 10-9 lunol acetone as control, 5.78 x 10-8 lunol gibberellic acid （GA3）, 6.21 x 10-8 lunol GA4, and 6.86 x 10-8 lunol uniconazole-P. During the experimental period, GAs-treated seedlings exhibited negative gravitropism, whereas application of uniconazole-P inhibited negative gravitropic stem bending. GA3 and GA4 promoted wood fibers that possessed a gelatinous layer on the upper side, whereas uniconazole-P inhibited wood formation but did not inhibit the differentiation of the gelatinous layer in wood fibers on the upper side. These results suggest that： （i） both the formation of gelatinous fibers and the quantity of xylem production are important for the negative gravitropism in horizontally-positioned seedlings; （ii） GA3 and GA4 affect wood production more than differentiation of the gelatinous layer in wood fibers; G-layer development may be regulated by other hormones via the indirect-role of GA3 and GA4 in horizontally-positioned F. mandshurica seedlings rather than the direct effect of GAs; and （iii） the mechanism for upward wood stem bending is different to the newly developed shoot bending in reaction to gravity in this species.

Study on the variation in and selection of Fraxinus mandshurica provenances and families in northeast China

Fraxinus mandshurica Rupr.is one of the main afforestation species in northeast China,and there is great demand for improved F.mandshurica varieties.The results of an investigation into and analysis of the growth traits of F.mandshurica provenances and families showed that there were significant differences in different periods.However,variations in growth traits decreased year by year.There was a significant negative correlation between tree heights of the provenances and sunshine hours in their areas of origin.The provenances of Xinglong,Hailin and Wuchang were selected based on the volume of 18-year-old trees.The average genetic gain from the selection of fast-growing provenances was 19.4%.Ten superior fast-growing families were selected.The average volume of the selected families was22.6%,higher than that of all families.The correlation coefficient between heights at 6-year-old and at 18a was 0.838for provenances,and between heights at 4-year-old and at 18-year-old was 0.303 for families.These results indicate that early selection for height in provenances or families could be performed at 6 years or 4 years,respectively.Early selection for DBH and volume in families could start at 8 years.

ENDOGENOUS INHIBITORS IN SEED OF FRAXINUS MANDSHURICA RUPR AND THEIR EFFECT ON GERMINATION AND REGENERATION

Bioassay and GC-MS determination indicated that inhibitors of seeds of Fraxinus mandshurica Rupr were distributed mainly in zones of β-inhibitors (including ABA) and of high and low Rf value. The inhibitory activity of outer seed coat of the dormant seed (control treatment) was higher than that of seeds with only the inner coat attached e.g. ABA was 114 and 54ng/g fresh weight respectively. The inhibitory effect of No. 12 zone was even higher than ABA. The inhibitory activity of all the zones decreased after stratification (St) and burying (AO) treatment, especially that of the outer seed coat, whose ABA content decreased to 7(St) and 11(AO) ng / g(fw). However, the decrease in inhibition of root growth lagged bchind'thc decrease in germination. It is concluded that burial is advantageous to regeneration. Inhibitors of the outer seed coat and seeds were mostly destroyed under the adverse conditions of natural dissemination (Di treatment) indicating that Di was not conducive to regeneration. MS analysis revealed that the largest peaks of No. 6, 7 and 12 zones were linoleic acid, olcic acid and 17-C, 18-C, and 20-C long chain fatty acids. Several coumarins were found in No. 6 and 7 zones, and cadincncs, farncsol and scsquitcrpcncs were found in No. 6 and 12 zones having common bioorigins with ABA.

Ethylene Evolution Changes in Tilted Fraxinus mandshurica Rupr. var. japonica Maxim.Seedlings in Relation to Tension Wood Formation

The effects of ethylene on tension wood formation were studied in 3-year-old Fraxinus mandshurica Rupr. var. japonica Maxim. seedlings in two separate experiments. In experiment 1, ethylene evolution of buds and stems was measured using gas chromatography after 0, 2, 4, 7, 14, and 21 d of treatment; in experiment 2, both aminoethoxyvinylglycine （AVG） and AgNO3 were applied to the horizontally-placed stems, and the cell numbers on sites of applications were measured after 40 d. Ethylene evolution from buds was found to be much greater in tilted seedlings than in upright ones. The cell numbers of wood fibers in shoots and 1-year-old stems were reduced in treatments with 12.5×10^-7μmol/L AVG, 12.5×10^-8μmol/L AVG, and 11.8×10^-8μmol/Lmol/L AgNO3; whereas the horizontal and vertical diameters were reduced by treatment of 12.5×10^-7μmol/L AVG. Ethylene evolutions of shoots and 1-year-old stems were inhibited greatly in comparison with the control by applying 12.5×10^-7μmol/L AVG. The formation of a gelatinous layer of wood fibers was affected by neither AVG nor AgNO3 application. These results suggest that ethylene regulates the quantity of wood production, but does not affect G-layer formation in F. mandshurica Rupr. var.japonica Maxim. seedlings.

不同供氮水平下水曲柳(Fraxinus mandushurica Rupr.)幼苗根系呼吸季节动态

根呼吸是林木根系获得吸收养分和水分所需能量的重要生理活动。为了探讨林木根系呼吸速率的季节变化及其影响因素,采用离体根系法（Li-6400-06叶室连接到Li-6400便携式CO2/H2O分析系统）研究了水曲柳（Fraxinus mandushuricaRupr.）苗木各径级根呼吸速率在不同供氮水平下季节变化规律。结果表明：水曲柳苗木根呼吸速率表现出明显的季节动态,且与气温的季节变化规律相同,其中比根呼吸速率在0.5732μmolCO.2g-.1s-1（直径≤2 mm,10月份）~7.1861μmolCO.2g-.1s-1（直径≤2 mm,7月份）之间变化,表面积呼吸速率也是7月份最高,达到0.6848μmolCO.2cm-.2s-1（直径〉5 mm）,10月份最低,仅为0.0132μmolCO.2cm-.2s-1（直径≤2 mm）;比根呼吸速率随根直径变大而降低,表面积呼吸速率变化规律则完全相反。供氮水平对水曲柳苗木根呼吸速率的影响随气温升高明显增强,其在6~8月份各径级根系中均达到显著水平（0.0007〈P〈0.0424）。水曲柳苗木根呼吸速率与地下10cm土壤温度表现出明显的指数关系（R2=0.779~0.981）;细根（直径≤2mm）呼吸温度系数Q10值在3.45~8.48之间,而粗根（直径〉2mm）Q10值范围为2.07~2.96,Q10值随根系径级增大而降低的现象表明水曲柳苗木细根对温度变化反应更为敏感;细根Q10值在供氮水平间差异显著（P=0.0392〈0.05）,粗根则不明显,表明土壤供氮水平主要影响细根的Q10值变化。

Molecular cloning and expression under abiotic stresses and hormones of the ethylene response factor Ⅶ gene FmRAP2.12 from Fraxinus mandshurica

RELATED TO AP2.12(RAP2.12)is one of the Ethylene Response Factors(ERF)transcription factor and plays a key role in controlling plant root bending and responding to multiple abiotic stresses including hypoxia stress.In this study,FmRAP2.12 gene was isolated and characterized from Fraxinus mandshurica Rupr.The open reading frame(ORF)of FmRAP2.12 was 1170 bp and encoded a protein of 389 amino acids.The conserved domains,three-dimensional phylogenetic relationship of FmRAP2.12 was also investigated.Quantitative real-time(qRT-PCR)analyzed the expression of FmRAP2.12 in different tissues.The expression level of FmRAP2.12 was highest in roots followed by leaves,and lowest in male flowers.Abiotic stress and hormone signal-induced expression was established using qRT-PCR.Salt stress induced FmRAP2.12 to a double peak pattern:the first peak value was at 6 h and the second at 72 h.Drought stress also induced FmRAP2.12 to a double peak pattern:the first at6 h and the second at 48 h.FmRAP2.12 was up-regulated after initiation of gibberellic acid(GA3)treatment,with a one peak pattern at 24 h.FmRAP2.12 may not respond to cold stress and Abscisic acid(ABA)treatment.The transient overexpression of FmRAP2.12 caused the up-expression of downstream key genes of abiotic stress response and gibberellin pathway.Our research reveals the molecular characteristic and expression patterns under abiotic stress and hormone condition of FmRAP2.12,providing support for the genetic improvement of F.mandshurica at a molecular level.

Definition of fine roots on the basis of the root anatomy, diameter,and branch orders of one-year old Fraxinus mandshurica seedlings

Fine roots are important in root absorption of nutrient and water,and in root turnover.Accurate definition of fine roots is a prerequisite to improved estimation of the physiological and ecological functions of forest ecosystems.Root development and physiological functions are reflections of root anatomical structure.In this study,the anatomical structures of different root orders were analyzed by examining paraffin sections of one-year old Fraxinus mandshurica seedlings.One-year-old F.mandshurica seedlings had over five root orders.The root anatomical structures of all orders showed more differences.First and second order roots consisted of four sections： the epidermis,cortex,pericycle,and vascular bundles.Fourth and fifth order roots were mainly composed of the skin and peripheral vascular bundles（including the xylem and phloem）.Third order roots had root epidermal and cortical structures,but the quantity and integrity of the cortical cells were inferior to those of the first and second order roots,and superior to those of the fourth and fifth order roots.All the first and second order roots and some third order roots with discontinuous cork layer（〈0.4 mm in diameter）,but not the fourth and fifth order roots,were the fine roots of one-year old F.mandshurica seedlings.Although they had similar diameters,different portions of root systems had different anatomical structures and therefore,vary in capacity to absorb water and nutrients.Fine roots were accurately defined by root diameter,branch orders,and anatomical structural features of one-year old F.mandshurica seedlings.

Growth and photosynthetic responses of Fraxinus mandshurica seedlings to various light environments

To determine light requirement and adaptability of Fraxinus mandshurica seedlings, the seasonal variations of photosynthetic variables were measured in 3-year-old seedlings grown under four light levels （100%, 60%, 30%, and 15% of full sunlight） with a LI-6400 portable photosynthesis system. The leaf chlorophyll content, special leaf weight, annual height and basal diameter increment of seedlings were also observed. The maximum and minimum values of net photosynthetic rate, maximum rate of carboxylation, and maximum rate of electron transport of F. mandshurica seedlings were detected with 60% and 15% of full sunlight treatments, respectively. With the decrease of light level, both light saturation point and special leaf weight significantly declined （p 0.05）, but leaf chlorophyll content significantly increased （p 0.05）. Annual height and basal diameter increments of seedlings grown under 60% of full sunlight treatment were significantly greater than those of seedlings under other treatments （p 0.05）. It was concluded that F. mandshurica seedlings can adapt to a wide range of light environments from 15% to 100% of full sunlight by adjusting light saturation point, leaf chlorophyll content and special leaf weight. According to the maximum of relative growth, 60% of full sunlight treatment is the optimum light level for the growth of 3-year-old F. mandshurica seedlings.

Indirect somatic embryogenesis and regeneration of Fraxinus mandshurica plants via callus tissue

Somatic embryogenesis of Fraxinus mandshurica has the problems of low somatic embryo(SE) yield,unsynchronized SE development,and a high percentage of deformed SEs.We aimed to improve F.mandshurica SE production by synchronizing SE development,improving SE quality,and inducing root formation to obtain complete regenerated plants.Cotyledons of immature zygotic embryos of F.mandshurica were induced to form callus and then SEs.The SE induction percentage from explants differed among 32 mother trees,and the one with the highest SE induction percentage(29.8%) was used for further experiments.The highest callus induction percentage was94.2% on 1/2-strength Murashige and Skoog medium(MS1/2)supplemented with 0.15 mg·L^(-1) naphthalene acetic acid.The highest callus proliferation coefficient(240.5) was obtained on McCown's Woody Plant Medium containing 0.1 mg·L^(-1)6-benzyl adenine and 0.15 mg·L^(-1) 2,4-dichlorophenoxyacetic acid.The highest number of SEs(1020.5 g~(-1) fresh weight) was obtained on MS1/2 medium supplemented with1 mg·L^(-1) 6-benzyladenine.The highest number of cotyledon embryos(397/g fresh weight) was obtained by incubating materials on medium containing 1 mg·L^(-1) abscisic acid and then applying a drying treatment.The cotyledon embryos were milky white,uniformly sized(average length 4.7 mm),and 80% of them were normal.The SE rooting percentage on 1/2 MS medium containing 0.01 mg·L^(-1) NAA was 37.5%.Overall,the germination percentage of SEs was 26.4%,and complete regenerated plants were obtained after transplanting and acclimation.These results provide more possibilities for the preservation and breeding of F.mandshurica.

Nutrient retranslocation from the fine roots of Fraxinus mandshurica and Larix olgensis in northeastern China

Nutrient retranslocation in trees is important in nutrient budgets and energy flows in forest ecosystems. We investigated nutrient retranslocation in the fine roots of a Manchurian Ash （Fraxinus mandshurica） and a Larch （Larix olgensis） plantation in northeastern China. Nutrient retranslocation in the fine roots was investigated using three methods, specifically, nutrient concentration, the ratio of Ca to other elements （Ca/other elements ratio） and nutrient content. The method based on nutrient content proved most suitable when investigating nutrient retranslocation from fine roots of the two species. The nutrient-content-based method showed that there were retranslocations of N, P, K and Mg from the fine roots of Manchurian Ash, with retranslocation efficiencies of 13, 25, 65, and 38 %, respectively, whereas there were no Ca retranslocations. There were retranslocations of N, P, K, Ca and Mg from the fine roots of Larch, with retranslocation efficiencies of 31, 40, 52, 23 and 25 %, respectively.

Relationship between H_(2)O_(2) accumulation and NO synthesis during osmotic stress:promoted somatic embryogenesis of Fraxinus mandshurica

Osmotic stress promotes somatic embryogenesis of Fraxinus mandshurica,which leads to accumulation of reactive oxygen species(ROS).The single pieces of cotyledons of F.mandshurica were used as explants to induce somatic embryogenesis in osmotic-stress medium.Furthermore,the hydrogen peroxide H_(2)O_(2) content of explanted cells was varied by adding exogenous H_(2)O_(2) or catalase solution to assess the effects of the exogenous H_(2)O_(2)on somatic embryogenesis,intracellular H_(2)O_(2)accumulation,and the relationship between signaling mediated by ROS or reactive nitrogen species.The results revealed that exogenous H_(2)O_(2)(100?300μmol L^(–1))increased the number of somatic embryos.On 60th day of exogenous H_(2)O_(2)(200μmol L^(–1))treatment,the number of somatic embryos of explants treated,which was 136.54%,was higher than the control.Moreover,exogenous H_(2)O_(2)(100μmol L^(–1))significantly increased the intracellular H_(2)O_(2)content and enhanced the activities of superoxidase dismutase and peroxidase.Finally,exogenous H_(2)O_(2)(100μmol L^(–1))activated the intracellular non-enzymatic pathway for nitric oxide(NO)synthesis.The somatic embryogenesis in broadleaf trees increases with the change of endogenic ROS content,and depends on the upregulation of antioxidant enzymes.Both H_(2)O_(2)and NO,as signaling molecules,were found to be involved in the process of somatic embryogenesis in broadleaf trees.In the process of exogenous H_(2)O_(2)promoting somatic embryogenesis,NO synthesis depended on non-enzymatic reactions.These results provide a scientific basis for resolving the mechanism by which ROS levels are regulated during somatic embryogenesis of broadleaf trees and establish a reasonable and efficient technology system for regulating somatic embryogenesis of trees.

Progeny Test on the Natural Populations and Selection of Excellent Populations from Fraxinus Mandshurica

Fraxinus mandshurica is one of the ancient relict flora species originated from the Tertiary period, which is mainly produced in the eastern mountains in Northeast China. It has an important scientific value for studying the Tertiary flora and the Quaternary glacial climate. In order to make rational use of the natural genetic resources of F. mandshurica , and to increase the scientific and technological added value of improved varieties, this study used the method of positional observation of fixed standard fields to discuss the genetic variations of tree height and DBH of the natural populations and its open-pollinated progenies, systematically analyze the heritability and genetic gains in growth characters based on the analysis of progeny test, growth dynamic and heredity effects. The populations with good growth, stress resistance and adaptability were selected. The results showed that there were extremely significant difference in the growth characters among the natural populations, and the coefficients of variance for tree height （22.99%） were smaller, while the coefficients of variance for DBH （41.37%） were larger. On the other hand, there were extremely significant differences in the growth characters among the open-pollinated progenies, and the interaction between these progenies and the blocks was significant. Meanwhile, the growth characters had strong heritability, high genetic gain, and remarkable heredity effects. The heritability of tree height and DBH were 0.825 and 0.781, and the genetic gains were 15.16% and 25.85%, respectively. Therefore, Shanhetun （SHT） and Xinglong （XIL） were determined to be excellent natural populations both in the growth, resistance and adaptation with growth traits as the main evaluation index, which could be widely applied in the advanced generation improvement breeding.

不同针叶树混交对水曲柳吸收根和运输根形态与生物量垂直分布的影响

为研究树种之间根系的相互作用,以黑龙江省东北林业大学帽儿山地区的水曲柳(Fraxinus mandshurica)纯林和水曲柳与兴安落叶松(Larix gmelinii)、红松(Pinus koraiensis)、红皮云杉(Picea koraiensis)的混交林为研究对象,采用根钻法,研究了不同针叶树混交对水曲柳吸收根和运输根形态与生物量的垂直分布特征的影响。结果表明:在土壤表层(0<土壤深度(d)≤10 cm)和亚表层(10 cm<d≤20 cm),水曲柳红松混交林、水曲柳兴安落叶松混交林内,水曲柳吸收根生物量显著高于水曲柳纯林。4种林型内,水曲柳吸收根和运输根生物量均随土壤深度加深呈现下降的趋势,其中,45.79%~53.76%的吸收根和39.63%~49.39%的运输根位于土壤表层。在土壤表层,水曲柳云杉混交的运输根比根长显著降低,根平均直径显著增加。在土壤亚表层,水曲柳云杉混交的吸收根和运输根组织密度及吸收根平均直径显著低于纯林,而吸收根比根长显著高于纯林。水曲柳吸收根和运输根平均直径随土壤深度增加整体呈现增加的趋势,且在运输根表现更加明显。吸收根生物量和比根长均与土壤全氮质量分数存在显著正相关。因此,水曲柳与红松、落叶松混交在一定程度上提高了目的树种水曲柳的吸收根生物量,增强了水曲柳对土壤资源的获取能力。

光照强度对不同苗龄水曲柳裸根苗和容器苗生长的影响

分析不同苗龄水曲柳裸根苗和容器苗在不同光照强度下的适应能力,可为水曲柳苗木精准造林提供科学依据。以水曲柳1年生裸根苗、1年生容器苗、2年生裸根苗和2年生容器苗为试验材料,观察大田遮阴设置的100%、75%、50%和25%光照强度下水曲柳各类型苗木生长情况。结果显示,容器苗的苗高增长量和地径增长量分别比裸根苗显著高出58.74%、60.27%,4种苗木的地径增长量和根生物量积累量均在25%光照强度下为最低。在50%光照强度下,1年生容器苗的苗高增长量、地径增长量、叶面积和细根数量分别比1年生裸根苗高出39.51%、28.80%、35.27%、28.73%,2年生容器苗的苗高增长量、地径增长量、叶面积和细根数量分别比2年生裸根苗高出96.03%、94.06%、28.45%、40.69%,1年生裸根苗的苗高增长量和地径增长量分别比2年生裸根苗高出59.56%、85.57%。研究表明,4种水曲柳苗木在25%光照条件下生长均较差,1年生裸根苗比2年生裸根苗在弱光(50%)条件下生长更优,容器苗比裸根苗具有更强的弱光(50%)适应性。

不同气候情景下小兴安岭3个珍稀易危树种的潜在分布预测

【目的】水曲柳、黄菠萝和紫椴为小兴安岭地区亚顶极群落主要建群树种,分析水曲柳、黄菠萝和紫椴在全球气候变化的背景下的潜在分布区,揭示气候变化对植物分布格局影响,进而为森林质量精准提升和国家储备林建设提供依据。【方法】基于19个气候因子、土壤以及海拔数据,运用MaxEnt模型预测了小兴安岭地区3个珍稀易危树种当前、未来(2021—2040年、2041—2060年、2061—2080年和2081—2100年)4种气候变化情景(ssp126、ssp245、ssp370和ssp585)下潜在分布情况。【结果】1)MaxEnt模型拟合效果良好,AUC值均大于0.7;2)水曲柳重要环境因子依次为年降水量、最热季度的平均温度、最湿月份降水;黄菠萝重要环境因子依次为年降水量、最冷季度的平均温度、最冷季降水;紫椴重要环境因子依次为年平均温度、年降水量、最冷季度的平均温度;3)未来气候变化条件下,水曲柳适生区面积波动较大;黄菠萝在ssp370气候情景下,适生区面积缩减程度最大,其他情况适生区面积趋于平稳;紫椴适生区面积为21 769.87~25 579.46 km^(2),变化范围小,适生区面积有减小趋势。4种气候变化下3个树种核心区中心海拔升高31~222 m。【结论】为使小兴安岭地区森林质量提升,以适地适树为原则,可在伊春市大力种植黄菠萝,在黑河市南部和伊春市北部大力种植紫椴。气候变化对水曲柳影响较大,适生区存在面积小,并且适生区等级降低面积大,建议加大对水曲柳保护力度。

不同生境水曲柳种子的形态结构及抗旱性分析

为选育水曲柳耐干旱品种提供理论依据,选取不同生境水曲柳(Fraxinus mandshurica)种子为试验材料,对比分析不同生境下水曲柳种子的形态结构特征和吸水特性,采用不同质量浓度的聚乙二醇(Polyethylene glycol,PEG)溶液对水曲柳种子进行干旱胁迫,比较分析不同生境水曲柳种子在干旱环境下的萌发表现。研究结果显示,1)半干旱生境水曲柳的种子和种翅大小、千粒质量及种皮厚度等形态结构均显著大于适生生境种子;2)半干旱生境种子萌发时的吸水率显著低于适生生境种子7.75%;3)当PEG溶液质量浓度为10%时,半干旱生境水曲柳种子的发芽率、发芽指数、活力指数以及胚根长度开始显著高于适生生境种子。对发芽率进行线性回归,半干旱生境水曲柳种子的耐旱极限质量浓度是适生生境种子的1.23倍,具有更强的耐旱能力;4)干旱胁迫下,两生境水曲柳种子的过氧化氢酶、过氧化物酶、超氧化物歧化酶活性均表现出先上升后下降的趋势,且半干旱生境种子的酶活性始终高于适生生境。此研究结果表明在干旱环境造林选种时,可优先选用半干旱生境水曲柳种子作为造林种源,以提高种子萌发率和苗木成活率,为水曲柳资源扩大提供保障。