白刺光合生理特性对人工模拟增雨的响应

在乌兰布和沙漠东缘即内蒙古磴口县,利用Li-6400xt便携式光合测定系统分析仪测定不同增雨处理(4个增雨处理的增雨量分别是当地年降水量的25％、50％、75％和100％)条件下,典型荒漠植物白刺的光响应曲线,采用非直角双曲线模型对曲线进行拟合,计算最大净光合速率(Amax)、表观量子效率(AQY)、暗呼吸速率(Rd)、光补偿点(LCP)以及光饱和点(LSP)等生理参数,研究白刺光合生理特性对人工模拟增雨的响应.结果表明:对照的Amax、AQY、Rd、LCP和LSP分别为13.41 μmol·m-2·s-1、0.029 mol·mol-1、0.61 μmol·m-2·s-1、20.63 μmol·m-2·s-1和481.85 μmol· m-2·s-1.增雨使白刺的净光合速率(Pn)、蒸腾速率(Tr)、气孔导度(Gs)、Amax、AQY和Rd升高,使水分利用效率(WUE)降低.增雨处理在一定程度上改变白刺的光合生理特性,提高白刺的光合生产能力.对胞间CO2浓度和气孔限制值的变化分析表明:气孔因素是限制光饱和阶段光合速率的主要因素.     

遮荫对中华蚊母树苗期生长及光合特性的影响

【目的】探讨不同遮荫环境对中华蚊母树苗期生长及光合特性的影响,分析苗期中华蚊母树对不同遮荫环境的适应性,为城市园林建设中合理进行乔、灌木布置提供科学依据。【方法】采用遮荫网,设置全光CK、中度遮荫L1(25%全光)和重度遮荫L2(7%全光)3种光环境,测定不同光环境下苗期中华蚊母树生长、光合以及叶绿素荧光参数。【结果】经过60天的遮荫处理,L1和L2植株基径增量和比叶质量显著低于CK植株,而L1和L2植株叶长和最大叶宽显著高于CK植株;受遮荫影响,L1植株株高增量显著高于CK植株,而L2植株株高增量与CK植株差异不显著;遮荫导致了苗期中华蚊母树叶片最大净光合速率、暗呼吸速率、光补偿点以及光饱和点等光合指标降低,且随着遮荫程度增加,这些光合指标的降低程度也逐渐增加,L1植株叶片最大净光合速率、暗呼吸速率、光补偿点以及光饱和点分别比CK植株降低了11.8%,46.3%,48.6和15.5%,L2植株叶片最大净光合速率、暗呼吸速率、光补偿点以及光饱和点分别比CK植株降低了35.2%,65.7%,64.2%和20.4%;遮荫对苗期中华蚊母树叶片表观量子效率的影响并不明显,经过60天遮荫处理,L1和L2植株叶片表观量子效率均与CK植株差异不显著;遮荫使苗期中华蚊母树叶片最大光化学效率有所增加,其中L1植株叶片最大光化学效率显著高于CK植株,而L2植株叶片最大光化学效率与CK植株差异不显著;遮荫降低了苗期中华蚊母树叶片光化学猝灭和电子传递速率,L1植株叶片光化学猝灭和电子传递速率均显著低于CK植株,L2植株叶片光化学猝灭显著低于CK植株,但叶片电子传递速率与CK植株差异不显著;遮荫虽然降低了苗期中华蚊母树叶片的非光化学猝灭,但L1和L2植株叶片非光化学猝灭均与CK植株差异不显著。【结论】苗期中华蚊母树具有很强的耐荫能力,遮荫可使其对自身形态结构进行调整,如增加株高、叶长和叶宽和降低比叶质量等,以及叶片光合生理的调整,如降低叶片光补偿点和光饱和点、维持较高的表观量子效率和最大光化学效率等,来尽可能多地捕获光能及提高对弱光的利用率,同时也能使其减少对基径生长的能量分配以及降低叶片暗呼吸速率来减少对光合产物的消耗。因此,在进行城市园林建设时,可以尝试将中华蚊母树作为一种耐荫景观树种与乔木进行复合搭配栽植。     

人工模拟增雨对乌兰布和沙漠白刺生物量分配的影响

【目的】研究人工模拟增雨对白刺枝条生长速率、地上生物量及叶枝比的影响,揭示不同增雨条件下白刺光合产物的分配特征及其对水分条件变化的适应性。【方法】以乌兰布和沙漠东缘地区典型荒漠植物白刺为研究对象,在内蒙古磴口设置试验样地,对自然生长的白刺沙包进行人工模拟增雨(分别增加年均降水量的0%,25%,50%,75%和100%),增雨试验在2008—2014年连续进行。分析不同增雨条件下白刺的地上生物量、叶枝比、生殖枝和营养枝的生长速率及其季节内分配。【结果】1)2013年,75%和100%增雨对生殖枝和营养枝的干质量有显著影响;2014年,100%增雨对生殖枝和营养枝的干质量有显著影响。增雨使白刺生长季前期生殖枝和营养枝的相对生长量和相对生长速率增加,说明在增雨条件下白刺生殖枝和营养枝的生长速度加快,使其在群落中能够捕获更多的光能和吸收更多的CO_2。2)2013年生长季内,随着增雨量的增加,营养枝增加的速率以及生殖枝降低的速率逐渐增加,说明增雨使白刺在生长季前期对生殖生长以及生长季后期对营养生长的投入增加。2014年生长季内,随着增雨量的增加,营养枝增加的速率以及生殖枝降低的速率逐渐降低,主要是由于该年生长季前期自然降雨极少,而模拟增雨减缓了生殖枝生物量降低的缘故。在面对不同的增雨量时对光合产物表现出不同的分配策略,说明白刺对水分条件的变化有一定的调节能力,在适应降水增加的过程中已经具备较强的适应性。3)2013年,增雨使白刺地上生物量增加63.70%～ 151.60%,使叶枝比增加18.61%～ 48.83%;2014年,增雨使白刺地上生物量增加72.32%～ 134.28%,使叶枝比增加40.87%～ 140.56%。地上生物量和叶枝比随着增雨量的增加呈逐渐上升的趋势,说明在增雨量较大时,白刺将生物量干质量相对多地分配到地上部分的同时,分配更多的光合产物来促进叶片的生长。【结论】在未来全球气候变化条件下,白刺将通过提高枝条生长速率、调整干物质量在生殖枝和营养枝之间的累积以及增大光合产物对叶片的分配等一系列措施来积极应对降水的增加。     

叶片黄化对'赤霞珠'葡萄光合及叶绿素荧光特性的影响

【目的】研究黄化对‘赤霞珠’葡萄光合及叶绿素荧光特性的影响情况,为了解黄化对酿酒葡萄的伤害机制提供参考依据。【方法】以出现黄化现象的‘赤霞珠’葡萄植株为材料,分析Ⅰ、Ⅱ、Ⅲ、Ⅳ级黄化等级葡萄叶片的光合色素、光合作用气体交换参数及叶绿素荧光参数的变化特点。【结果】‘赤霞珠’葡萄因受土壤高pH值、低养分等因素的影响发生了叶片黄化现象;与正常植株(CK)相比,黄化等级分别为Ⅰ、Ⅱ、Ⅲ、Ⅳ级的葡萄叶片中的叶绿素总量分别降低了63.91%、70.43%、73.91%、76.52%,而黄化叶片中的类胡萝卜素在色素组成中的比例有所增高;叶片黄化迫使葡萄叶片净光合速率(P_n)、气孔导度(G_s)、蒸腾速率(T_r)均显著降低,Ⅳ级黄化叶片的P_n较对照显著下降85.08%;黄化叶片的叶绿素荧光动力曲线出现明显K点(300μs),ΔV_t和ΔW_t曲线上在100 ms处均出现了明显的凹峰;叶绿素荧光参数PSⅡ最大光化学效率(F_v/F_m)、结构性能指标(PI_(ABS))、原初光化学产额(ψ_o)、用于电子传递量子比率(φ_(Eo))等参数值均显著低于对照,而最小荧光强度(F_o)、单位反应中心吸收光能(ABS/RC)等值均显著高于对照,其PSⅡ潜在的光化学效率、光合电子传递速率、量子效率均显著低于对照。【结论】光合色素的减少,致使葡萄植株叶片黄化,影响了叶片的光合作用,导致叶片受到光抑制与光氧化,致使植株的代谢能力减弱。     

遮荫对掌叶半夏光合生理特性及产量的影响

该文研究了遮荫处理对掌叶半夏光合生理、产量和生物量的影响。结果表明:在全光和20%遮荫下条件下,掌叶半夏净光合速率Pn出现"光合午休"现象;与全光照相比,遮荫后叶片光补偿点(LCP)、光饱和点(LSP)、暗呼吸速率(Rd)等光合指标降低,而表观量子效率(AQY)上升;荧光参数PSⅡ最大光能转换效率(Fv/Fm)升高;随遮荫程度的增加,叶绿素含量增加,叶绿素a/b值减小;在0~60%遮荫下,产量和生物量增加。     

夏季遮荫改善大田牡丹叶片光合功能的研究

利用气体交换和叶绿素荧光分析技术,研究大田牡丹叶片在自然光照和夏季遮荫处理下光合作用日变化.结果表明:自然光下夏季牡丹叶片的净光合速率(Pn)明显低于春季,2个生长季节Pn日变化差异明显,即春季的Pn日变化呈"单峰型"曲线,夏季的Pn日变化为"双峰型"曲线,有明显的光合"午休";羧化效率(CE)变化趋势与Pn相似;表观量子效率(AQY)中午降低,下午逐渐回升;光系统Ⅱ(PSⅡ)最大光化学效率Fv/Fm和最大荧光Fm日变化为倒"单峰型"曲线,中午明显降低;与夏季自然光下相比,夏季遮荫处理(遮光50%)的牡丹叶片Pn、AQY、CE升高;气孔限制值(Ls)和叶温(t1)降低;Fv/Fm和Fm中午下降幅度显著减小.这些结果说明:夏季晴天中午高温、强光下,牡丹叶片PSⅡ反应中心发生了可逆失活,PSⅡ功能下调,光合作用的光抑制明显发生,遮荫可减轻光抑制,改善光合功能以增加光合产物积累.     

不同光照时间对欧美杨幼苗生长和光合特性的影响

【目的】研究不同光照时间下欧美杨生长过程中长势及生理适应性,为其优良高光效品种的早期选育及推广栽培提供一定的理论依据。【方法】以16个欧美杨无性系幼苗为研究对象,全遮光条件下,采用LED-100 W全光谱植物生长灯进行人工控光试验,探讨不同光照时间(11、12、13、14和15 h)对欧美杨幼苗生长、生物量、叶绿素相对含量及光合特性等的影响。【结果】1)光照14 h和15 h下幼苗的苗高地径相对增长率、叶生物量显著高于其他光照下(P0.01),而根冠比和叶片SPAD值相对较低,且幼苗光响应曲线走势基本一致,随光合有效辐射(PAR)增加,叶片净光合速率(P_n)先迅速增加,达光饱和点后曲线开始趋于平缓,直角双曲线拟合效果良好(相关系数R~(2 )≥0.948); 2)叶片最大净光合速率(P_(max))随光照时间的延长而增大,其中光照15 h比11 h高104.53%。光照15 h叶片表观量子效率(AQY)、暗呼吸速率(R_d)和光补偿点(LCP)最高,光照14 h光饱和点(LSP)较高,仅次于13 h,而LCP和R_d均低于其他光照时间; 3)叶绿素荧光参数显示,光照11 h幼苗的初始荧光(F_o)最大,最大荧光(F_m)总体差异未达极显著水平(P 0.01),可变荧光(F_v)在光照13 h相对较高。随光照时间延长PSⅡ反应中心原初光能转化效率(F_v/F_m)及潜在光化学活性(F_v/F_o)逐渐增大,且F_v/F_m均在0.83～0.85之间。【结论】随光照时间的延长,欧美杨幼苗的P_(max)、F_m、F_v、F_v/F_o和F_v/F_m均逐渐增大,F_o和根冠比逐渐减小,此外SPAD值、AQY、LSP、LCP和R_d对光照时间也存在不同程度的响应。此结果可作为早期估测欧美杨生长量和生态适应性的参考依据之一,也可作为欧美杨新品种选育、良种推广应用及生产实践过程的重要参考。     

模拟增雨对荒漠灌木白刺枝叶生长的促进作用

根据年均降水量,分别在乌兰布和沙漠东北缘(内蒙古磴口,年均降水145 mm)和巴丹吉林沙漠东南缘(甘肃民勤,年均降水115 mm)对天然白刺灌丛进行不同梯度的增雨实验(年均降水量的0％、25％、50％、75％、100％).结果表明:增雨的比例越大,白刺形态特征的变化越明显;100％增雨对磴口和民勤白刺形态特征的影响最明显,能够显著增加白刺标记枝的长度、直径和干质量,但是对成熟叶片和新叶片数的影响不显著;增雨还显著增加了9月磴口和民勤白刺枝叶的干质量和鲜质量;在较干旱的民勤地区,较大的增雨量才能促进白刺枝条生长;50％增雨即可促进夏末磴口白刺枝条生物量增加,75％增雨才能促进夏末民勤白刺枝条生物量增加.     

去遮荫后东北红豆杉幼苗和幼树光合特性对比

【目的】对比去遮荫后东北红豆杉幼苗和幼树叶片光合与荧光特性,揭示人工培养东北红豆杉幼苗在强光下发生光抑制的原因,为东北红豆杉人工栽培提供理论依据。【方法】以生长在遮荫条件下的东北红豆杉幼苗和幼树为试验材料(遮荫后光强为自然光强的40%),去除遮荫使幼苗和幼树暴露在自然强光条件下28天后,测定幼苗和幼树叶绿素含量、光合速率特性和叶绿素荧光特性。【结果】去遮荫后幼苗和幼树叶绿素含量无显著差异,幼树类胡萝卜素含量显著高于幼苗叶片,而幼树Chl/Cars低于幼苗叶片。幼苗叶片最大光合速率仅为幼树叶片的70%,幼苗具有较低的光补偿点和光饱和点,但表观量子效率(AQY)较高。幼苗叶片处于自然光照条件,叶片的羧化效率(CE)、CO2和光强均饱和下的最大光合速率(Amax)和Ru BP再生速率相对较低。强光诱导下,幼树叶片光合速率在25 min左右达到最大值,而幼苗叶片则需要为50 min,幼苗暗反应启动较慢。叶绿素荧光诱导曲线表明,在强光条件下,幼树叶片的实际光化学效率(ΦPSⅡ)和非光化学猝灭(NPQ)在较短时间内即可达到最大值,而幼苗叶片则需要相对较长的时间。荧光对不同光强相应曲线表明,幼苗叶片的ΦPSⅡ随光强增加而迅速降低,而幼树叶片则下降较慢。幼树叶片的NPQ随着光强增加而增加,而幼苗叶片的NPQ则在相对较低光强水平就达到最大值,幼苗叶片热耗散能力较低。【结论】幼苗叶片较低的光合速率产生相对较多的过剩能量,同时其叶片在高光强下的热耗散能力较低,这是幼苗与幼树相比不适应自然强光和产生光抑制的主要原因。     

不同遮荫水平下香榧苗期光合作用及氮分配的响应机制

【目的】通过比较不同遮荫水平下香榧苗期的生长指标、气体交换参数、光合色素含量和叶氮含量的差异,初步探讨不同遮荫水平下香榧苗期光合作用及氮分配的响应机制。【方法】以2年生香榧苗为材料,测定不同遮荫水平(0,50%,75%和90%遮荫水平)下香榧苗的苗高、地径、生物量及叶片的光响应、二氧化碳(CO_2)响应曲线、叶绿素和叶氮含量等指标。【结果】随遮荫水平的增加,香榧苗叶色逐渐增绿;地径增量和生物量均呈先增加后降低的趋势,其中50%和75%遮荫水平下的地径增量最高,分别为0遮荫下的215.2%和233.6%(P0.05),为90%遮荫下的161.4%和175.2%(P0.05);75%遮荫水平下的生物量最高,分别为0,50%,90%遮荫下的141.0%,111.5%和114.0%(P0.05)。随遮荫水平的增加,香榧苗的根冠比逐渐降低,但其叶片的叶绿素a(Chla)、叶绿素b(Chlb)和类胡萝卜素(Car)含量均呈逐渐升高的趋势。随遮荫水平的增加,香榧苗期叶片的光饱和点(LSP)、光补偿点(LCP)呈逐渐下降的趋势;其表观量子效率(AQY)呈逐渐升高的趋势;其最大净光合速率(P_(max))、最大Ru BP羧化速率(V_(cmax))及Ru BP再生的光合电子传递速率(J_(max))均呈先升高后降低的趋势,且这些参数在50%和75%遮荫水平下最高;但其单位面积上的叶氮含量(N_a)呈逐渐降低的趋势。随遮荫水平的增加,分配到羧化作用的N素(N_c)、能量代谢的N素(N_B)、捕光色素的N素(N_L)、光合氮素利用效率(PNUE)均呈先增加后降低的趋势,除N_L外其他参数均在75%遮荫水平下最高。【结论】遮荫处理能有效地促进香榧苗的生长;有效加强香榧苗对早晨或傍晚弱光的利用,这有利于植物体的生长发育。而过度遮荫(90%遮荫水平)的香榧苗P_(max)显著降低,这可能与其为了捕获更多的光能,将更多资源用于捕光蛋白上,而导致光合能力下降有关。与50%遮荫水平相比,75%遮荫水平的香榧苗将更多的氮素分配到光合机构(Nc和N_B)中,从而显著提高PNUE。综上所述,前期苗木培育中,给予香榧苗75%遮荫水平有利于其生长发育。     

Browsing Damage on Pine (Pinus sylvestris and P. contorta) by a migrating moose (Alces alces) Population in Winter: Relation to Habitat Composition and Road Barriers

In Scandinavia, moose (Alces alces L.) sometimes cause severe browsing damage to economically-important pine. Moose-vehicle accidents have spurred construction of fences along roads, and these may interfere with moose migration between summer and winter ranges, or the road alone may be a barrier. If this happens and moose build up along roads, landowners may suffer economically. Therefore, this study investigated whether roads, fences or other factors influence the use of young pine stands by moose. Eighty stands along roads in northern Sweden were evaluated in which individually-browsed branches were counted on 9972 pines. Moose browsing was not significantly related to birch (Betula pendula Roth, B. pubescens Ehrh.) density, nor did it differ between pines (Pinus contorta Douglas or P. sylvestris L.). However, increased pine density, site productivity and proximity to a highway were associated with increased browsing. Further large-scale studies are needed to understand moose habitat selection and the effects of roads.     

Effects of Root Freezing on the Physiology and Growth of Picea glauca,Picea mariana and Pinus banksiana Seedlings Under Different Soil Moisture Regimes

The root systems of 2-yr-old Picea glauca, Picea mariana and Pinus banksiana seedlings were submitted to various frost temperatures during an artificial frost to induce different levels of root damage. Frost-damaged and control seedlings were placed in a greenhouse under high and low soil moisture regimes. Seedling growth and physiology were evaluated periodically. Seedling survival was reduced when root damage reached levels of 60-80%. Root systems of all three species showed partial to total recovery by the end of the experiment. In general, root freezing damage caused reductions in seedling growth, with these reductions becoming less significant over time. Root damage had little to no effect on black spruce and jack pine seedling physiology, while white spruce CO 2 uptake decreased with increasing root damage. Shoot nitrogen content of all three species decreased slightly with increasing root damage.     

Stand Structure in Pine,Spruce and Deciduous Forests: A Comparison Between Finnish and Russian Karelia

This study investigated the stand structure in pine, spruce and deciduous forests in the border district of Finland and Russia. A total of 46 mature forest stands was selected as pairs, the members of each pair being as similar as possible with respect to their forest site type, age, moisture and topography. The stands were then compared between the two countries by means of basal areas and number of stems. The proportions of dominating tree species were 2-12% lower, and correspondingly the proportions of secondary tree species higher, in Russian forests. The density of the forest stock was also higher in each forest type in Russia. The forests in the two countries differed most radically in terms of the abundance of dead trees. The amount was two to four times higher in Russian deciduous and spruce forests, and in pine forests the difference was 10-fold. The stand structures indicated that Russian coniferous stands, in particular, were more heterogeneous than intensively managed pine and spruce stands in Finland.     

Growth and Terminal Bud Formation in Picea abies Seedlings Grown with Alternating Diurnal Temperature and Different Light Qualities

The root collar diameter and the height:diameter ratio are of particular importance in container-grown seedlings where a high density in the containers may produce spindly seedlings. Temperature regimes and light quality are known to affect plant growth. The aim of this study was to identify responses in Picea abies (L.) Karst. seedlings grown with light providing different red:far-red ratios and under temperature regimes with alternating day (DT) and night temperature (NT) from negative (DT < NT) to positive (DT > NT) difference (DIF) between DT and NT. Experiments were conducted in controlled environment chambers and in a daylight phytotron. Only limited thermoperiodic responses appeared in P . abies seedlings with respect to seedling height and dry weight accumulation. The formation of terminal buds, however, was clearly delayed in seedlings grown at negative DIF. The results indicate a requirement for day extension light that is high in far-red, to prevent terminal bud formation under natural short-day conditions. An extended study should be conducted to clarify the minimum level of light intensity and the optimal light quality needed to prevent terminal bud formation under natural short-day conditions.     

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.     

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.     

CAD与建筑设计的关系

本文分析了CAD在设计中引起的正面和负面影响,并进行了系统的阐述,从而使设计者在应用中能够保持客观的态度。     

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.     

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.