Acorn production is linked to secondary growth but not to declining carbohydrate concentrations in current-year shoots of two oak species

In trees, reproduction constitutes an important resource investment which may compete with growth for resources. However, detailed analyses on how growth and fruit production interact at the shoot level are scarce. Primary canopy growth depends on the development of current-year shoots and their secondary growth might also influence the number and size of fruits supported by them. We hypothesise that an enhanced thickening of current-year shoots is linked positively to acorn production in oaks. We analysed the effect of acorn production on shoot growth of two co-occurring Mediterranean oak species with contrasting leaf habit (Quercus ilex, Quercus faginea). Length and cross-sectional area of current-year shoots, apical bud mass, number of leaves and acorns, xylem and conductive area, number of vessels of acorn-bearing and non-bearing shoots were measured in summer and autumn. Nitrogen and carbohydrates analyses were also performed in stems and leaves of both shoot types. Stem cross-sectional area increased in acorn-bearing shoots when compared with non-bearing shoots for both species and such surplus secondary growth was observed since summer. In bearing shoots, the total transversal area occupied by vessels decreased significantly from basal to apical positions along the stem as did the xylem area and the number of vessels. Leaves of bearing shoots showed lower nitrogen concentration than those of non-bearing shoots. Carbohydrate concentrations did not differ in stems and leaves as a function of the presence of acorns. Such results suggest that carbohydrates may preferentially be allocated towards reproductive shoots, possibly through enhanced secondary growth, satisfying all their carbon demands for growth and reproduction. Our findings indicate that acorn production in the two studied oaks depends on shoot secondary growth.     

武夷山不同海拔植物水分利用效率的变化及其与养分变化的关系

以武夷山不同海拔(600、900、1300、1500、1800、2000和2100 m)的乔木、灌木和草本3种生活型植物为研究对象,观测其水分利用效率和叶片氮、磷养分浓度随海拔的变化趋势,旨在探索海拔梯度间水分、养分变化与植物水分利用效率变化的关系.结果表明: 植物水分利用效率随海拔的增加呈显著上升趋势,乔木叶片δ¹⁸O随海拔变化不显著.总体上看,叶片氮浓度未观测到规律性的变化,高海拔地区的叶片磷浓度显著高于低海拔地区.水分利用效率与叶片磷浓度呈显著正相关,而与叶片氮浓度相关性不显著.不同海拔植物水分利用效率变化主要由光合速率的变化引起,水分状况对植物水分利用效率的影响不显著.海拔梯度间植物叶片磷浓度的差异对光合速率影响显著,进而影响水分利用效率.     

Effect of controlled carbon dioxide on in vitro shoot multiplication in Feronia limonia (L.) Swingle

The effect of controlled carbon dioxide environment on in vitro shoot growth and multiplication in Feronia limonia (a tropical fruit plant, Family- Rutaceae) was studied. Carbon dioxide available in the ambient air of the growth room was insufficient for in vitro growth of the shoots alone. Also, the presence of sucrose only as the C-source in the medium (without CO₂), was found to be inadequate for sustainable growth and multiplication of shoots. The carbon dioxide enrichment promoted shoot multiplication and overall growth. The promotory effect of CO₂ was independent of the presence of sucrose in the medium. In the presence of both CO₂ and sucrose, an additive effect was observed producing maximum shoot growth. In the absence of sucrose a higher concentration of CO₂ (10.0)g m⁻³ was required to achieve photoautotrophic shoot multiplication comparable to ambient air controls. Highest leaf area per shoot cluster promoting shoot growth and multiplication was recorded under this treatment. Shoots growing on sucrose containing medium under controlled CO₂ environment of 0.6 g m⁻³ concentration evoked better response than ambient air controls (shoots growing on sucrose containing medium) in growth room. This treatment produced the overall best response. The present study highlighted the possibility of photoautotrophic multiplication which might prove useful for successful hardening and acclimatization in tissue culture plants.     

星斗山常绿落叶阔叶混交林木本植物叶功能性状及其多样性特征分析

为探究亚热带常绿落叶阔叶混交林中木本植物叶功能性状的变异特征,以及群落功能多样性在海拔梯度下的响应规律。该研究以鄂西南地区的星斗山国家级自然保护区海拔1 200～1 700 m的常绿落叶阔叶混交林为研究对象,对群落内木本植物的叶面积(LA)、比叶面积(SLA)、叶干物质含量(LDMC)、叶厚度(LT)、叶氮含量(LNC)、叶磷含量(LPC)6种叶功能性状的变异特征进行了分析,并分析了群落水平下木本植物叶功能性状和功能多样性对海拔变化的响应。结果表明:(1)星斗山保护区内木本植物叶面积、比叶面积、叶干物质含量、叶厚度、叶氮含量和叶磷含量平均值分别为151.49 cm~2、247.98 cm~2/g、34.08%、0.21 mm、16.59 mg/g和0.04 mg/g,其变异幅度依次为206.96%、57.00%、28.15%、52.38%、24.83%和76.92%。(2)在植物科、叶习性、生活型和树高4个因素中,科类群对6种叶功能性状的影响最大,其次为叶习性。(3)海拔对叶面积、叶干物质含量、叶磷含量影响极显著(P0.001),但对比叶面积、叶厚度和叶氮含量无显著影响(P0.05)。(4)不同海拔梯度上群落生物承载量、功能丰富度、功能分离度和功能离散度均达到显著差异(P0.05),仅功能均匀度在海拔梯度上差异不显著。     

Preformation and neoformation in shoots of Nothofagus antarctica (G. Forster) Oerst. (Nothofagaceae) shrubs from northern Patagonia

The size (length and diameter) and number of leaf primordia of winter buds of Nothofagus antarctica (G. Forster) Oerst. shrubs were compared with the size and number of leaves of shoots derived from buds in equivalent positions. Buds developed in two successive years were compared in terms of size and number of leaf primordia. Bud size and the number of leaf primordia per bud were greater for distal than for proximally positioned buds. Shoots that developed in the five positions closest to the distal end of their parent shoots had significantly more leaves than more proximally positioned shoots of the same parent shoots. The positive relationship between the size of a shoot and that of its parent shoot was stronger for proximal than for distal positions on the parent shoots. For each bud position on the parent shoots there were differences in the number of leaf primordia per bud between consecutive years. The correlations between the number of leaf primordia per bud and bud size, bud position and parent shoot size varied between years. Only shoots produced close to the distal end of a parent shoot developed neoformed leaves; more proximal sibling shoots consisted entirely of preformed leaves. Leaf neoformation, a process usually linked with high shoot vigour in woody plants, seems to be widespread among the relatively small shoots developed in N. antarctica shrubs, which may relate to the species' opportunistic response to disturbance.     

壳斗科五树种幼苗叶片结构型性状及其相关关系

通过种子的人工采集、低温沙藏和温室培育后,将幼苗移栽到环境条件相同的同质园中自然生长,研究了中亚热带壳斗科丝栗栲(Castanopsis fargesii)、苦槠(C.sclerophylla)、锥栗(Castanea henryi)、板栗(C.mollissima)和麻栎(Quercus acutissima)2年生幼苗生长季节的叶面积、叶厚度、比叶面积、叶干物质含量、叶氮浓度、叶磷浓度和叶氮磷比7种结构型性状的差异及其相关关系。结果表明:(1)在5树种幼苗中,锥栗幼苗的叶面积和比叶面积最大、叶氮浓度最高,其叶干物质含量最低;丝栗栲幼苗的叶面积最小、叶氮浓度和叶磷浓度最低;苦槠幼苗的叶厚度和比叶面积最小,其叶干物质含量最高;板栗幼苗则是叶厚度最小;同时5树种幼苗叶片的氮磷比均无显著差异(P0.1)。(2)Pearson相关和线性回归分析表明,壳斗科5树种幼苗的叶面积与叶氮浓度极显著正相关(P0.01),并与比叶面积显著正相关(P0.05);叶厚度与比叶面积极显著负相关(P0.01),其与叶干物质含量显著正相关(P0.05);比叶面积与叶干物质含量极显著负相关(P0.01),并与叶氮浓度极显著正相关(P0.01),同时与叶磷浓度显著负相关(P0.05);叶氮浓度与叶干物质含量、叶磷浓度分别为显著负相关(P0.05)和显著正相关(P0.05)。该研究结果表明壳斗科5树种幼苗叶片的7种结构型性状表现出了一定的种间差异性,但同一结构型性状的大小顺序和种间差异的显著性不同;同时所有树种幼苗叶片各结构型性状间的相关性及其显著程度不同。     

Light,leaf age,and leaf nitrogen concentration in a tropical vine

Summary Tropical vines in the Araceae family commonly exhibit alternating periods of upward and downward growth, decoupling the usual relationship between decreasing light environment with increasing age among the leaves on a shoot. In this study I examined patterns of light, leaf specific mass, and leaf nitrogen concentration in relation to leaf position, a measure of developmental age, in field collected shoots of Syngonium podophyllum. These data were analyzed to test the hypothesis that nitrogen allocation parallels within-shoot gradients of light availability, regardless of the relationship between light and leaf age. I found that leaf nitrogen concentration, on a mass basis, was weakly correlated with leaf level light environment. However, leaf specific mass, and consequently nitrogen per unit leaf area, were positively correlated with gradients of light within the shoot, and either increased or decreased with leaf age, providing support for the hypothesis that nitrogen allocation parallels gradients of light availability.     

井冈山鹿角杜鹃群落灌木层植物叶功能性状对海拔梯度的响应

为揭示鹿角杜鹃(Rhododendron latoucheae)群落灌木层植物叶功能性状及其对环境变化的响应趋势,对分布于井冈山不同海拔梯度鹿角杜鹃群落灌木层植物的叶功能性状进行了研究。结果表明,海拔梯度对灌木植物的叶功能性状有显著影响。随海拔的升高,叶片的干物质含量(LDMC)、厚度(LT)、氮含量(LNC)、磷含量(LPC)呈显著上升趋势,比叶面积(SLA)和N/P呈显著下降趋势,而叶大小(LS)呈先上升后下降的变化趋势;灌木植物叶片的LDMC与SLA、LS呈负相关,与LT、LNC、LPC呈正相关;SLA与LT、LNC呈负相关;LS与LT呈负相关;LNC与LPC呈正相关;N/P与LPC呈负相关;环境因子对灌木植物叶功能性状有重要影响,除受海拔的影响外,LPC、N/P还受坡位的影响,LS、LNC则分别还受到坡向和坡度的影响。因此,井冈山地区鹿角杜鹃群落灌木层植物通过改变叶功能性状来适应海拔和其它环境因子的变化。     

Survival of Tillers and Distribution of Dry Matter between Ear and Shoot of Barley Varieties

Plants of Plumage Archer barley grown in pots produced moreshoots than did Proctor, but had fewer ears at maturity, becausesome shoots died about 7 days before ear emergence. The numberand position on the plant of the shoots that died were consistentfor particular growing conditions. Shoots that died were notalways the last to be produced. There were no consistent differencesin dry weight, leaf area, nitrogen content, or apex developmentbetween shoots that did and did not survive; nor did removingthree developing ears on older shoots affect the survival ofother shoots. Growth of Plumage Archer plants was not checkedby death of shoots; dry matter, nitrogen, and leaf area wereredistributed so that increase in surviving shoots compensatedfor losses in the dead shoots. The dry-weight ratio of ear to shoot was smaller for Proctorthan for Plumage Archer at ear emergence and anthesis, but atmaturity it was greater for Proctor, both when ears were shadedto prevent them photosynthesizing and when they were unshaded.The varietal difference in ear: shoot dry-weight ratio was reversedbecause the relative growth-rate of ears of Proctor was greaterand because more dry matter was lost from its shoots. Both changesmay have been caused by translocation to the ear of a greaterproportion of the assimilate from the shoots of Proctor thanof Plumage Archer. Leaves of Proctor appeared to be more efficientin producing dry matter for the ear than those of Plumage Archer.     

Idiosyncratic phenomenon of regeneration from cotyledons in the idiot fruit tree,Idiospermum australiense

Idiospermum australiense (Diels) S. T. Blake, is a rare species that produces very large diaspores (up to 225 g) comprising 2–6 cotyledons. Anecdotal evidence suggested that each cotyledon within the diaspore could develop an independent root/shoot axis in natural populations and under glasshouse conditions. To investigate this potential, 13 diaspores were collected. Six diaspores were kept intact and cotyledons in the remaining seven were separated, planted into soil and scored for germination. All shoots were allowed to grow for 12 weeks. To test for differences in growth response from seedlings emerging from intact diaspores and single cotyledons, plant height, shoot mass, stem mass, leaf mass and total leaf area were compared between groups using both absolute values and values standardized to initial reserve mass. To examine the effects of reserve mass in more detail, height to stem mass, leaf mass to stem mass and specific leaf area was also compared between groups. All intact cotyledons and 24 of the 27 single cotyledons produced a functional root/shoot system. Time to germination was not different between groups. Shoot mass, stem mass and leaf mass were significantly greater in intact diaspores than in single cotyledons, although no difference was found in any parameter when standardized to initial reserve mass. Shoots arising from individual cotyledons were significantly taller per gram initial weight, because of a significantly greater relationship between height and stem mass. Shoots arising from single cotyledons also had a significantly greater investment in leaf mass per unit stem mass, even though there was no difference in specific leaf area between groups. Thus, seedlings arising from individual cotyledons grew relatively taller and produced a greater area of leaf tissue relative to stem than those arising from intact diaspores.     

Fitness implications of late bud break and time of burning in Lannea edulis (Sond.) Engl. (Anacardiaceae)

Many woody plants of savannas have massive underground parts (“lignotubers”) and diminutive aboveground parts with phenologies that are triggered by fire. Lannea edulis (Anacardiaceae) represents this life form and is widely distributed in south central Africa. The phenology of L. edulis was monitored on 42 permanently marked shoots over a 3-year period, from 2002 to 2004, and under three fire treatments (early and middle dry season burning, and fire protection) to determine whether (i) fire affected time of bud break and (ii) time of fruit ripening affected seed germination. Statistical analyses revealed that shoot reproductive status and fire treatments significantly affected time of bud break and the lag between bud break and leaf production. Shoot reproductive status explained 27% (P<0.001) while the interaction between reproductive status and fire treatments explained 34% (P<0.0001) of the variation in time at bud break. The appearance of the first leaf was delayed by 4 weeks in reproductive shoots compared with vegetative shoots. Shoot reproductive status explained 28% (P<0.0001) of the variation in the lag between bud break and appearance of the first leaf suggesting the existence of resource competition between reproduction and vegetative growth. However, reproductive status and fire treatments did not affect shoot size and leaves produced because replacement shoots after dieback due to fire were as long as shoots surviving from previous years due to insignificant annual shoot extension among the latter. There was high autocorrelation in the germination rate of seed-lots with seeds from fruits ripening early having a significantly higher germination rate (47% in 2002 and 89% in 2004) than those from fruits ripening later (3% in 2002 and 53% in 2004). Since time at bud break and fruit ripening were linked, it is proposed that late bud break results in reduced fitness in L. edulis because of reduced seed germination rate. Early and late dry season fires that delay bud break and destroy reproductive structures, respectively, also reduce this measure of fitness.     

Different responses of biomass allocation and leaf traits of Dodonaea viscosa to concentrations of nitrogen and phosphorus

调整叶性状和生物量分配格局是植物适应环境变化的主要途径, 研究车桑子(Dodonaea viscosa)幼苗生物量分配与叶性状对氮磷浓度的响应对认识车桑子在氮磷浓度变化下的适应策略具有重要意义。该研究通过砂培法, 测定不同氮浓度(3、5、15、30 mmol·L^-1)与不同磷浓度(0.25、0.5、1、2 mmol·L^-1)下车桑子幼苗的生长、生物量分配、叶性状的响应特征及其相互关系。结果表明: 高浓度氮(30 mmol·L^-1)促进了车桑子幼苗生长、叶片氮含量和生物量积累, 其余氮添加条件(3、5、15 mmol·L^-1)下车桑子幼苗各性状无显著差异, 但相比高氮水平, 其生物量积累和叶片氮含量显著降低, 根冠比和氮利用效率显著增加。随着磷添加浓度的增加, 车桑子幼苗生物量显著增加, 低磷条件(0.25、0.5 mmol·L^-1)限制了车桑子幼苗生长和生物量积累, 其根冠比和磷利用效率均没有发生显著变化, 但比叶面积和叶/茎生物量比例显著增加, 叶干物质含量显著降低。氮处理下, 叶片氮含量与根冠比显著负相关; 磷处理下, 叶片氮含量与比叶面积显著正相关。同时, 氮处理下, 车桑子幼苗株高、基径、总生物量等生长性状均与根冠比显著负相关, 与叶片氮含量显著正相关, 表明根冠比和叶片氮含量的调整在车桑子适应氮限制中发挥重要作用; 而磷处理下, 株高、基径、总生物量与比叶面积显著负相关, 与叶干物质含量显著正相关, 表明叶片结构性状的调整在车桑子适应低磷环境中具有重要意义。该研究表明, 车桑子幼苗生物量分配和叶性状及性状间的权衡策略对氮、磷的响应具有明显差异性, 在今后的研究中, 应关注氮和磷对植物性状影响的差异性。     

车桑子幼苗生物量分配与叶性状对氮磷浓度的响应差异

调整叶性状和生物量分配格局是植物适应环境变化的主要途径, 研究车桑子(Dodonaea viscosa)幼苗生物量分配与叶性状对氮磷浓度的响应对认识车桑子在氮磷浓度变化下的适应策略具有重要意义。该研究通过砂培法, 测定不同氮浓度(3、5、15、30 mmol·L^-1)与不同磷浓度(0.25、0.5、1、2 mmol·L^-1)下车桑子幼苗的生长、生物量分配、叶性状的响应特征及其相互关系。结果表明: 高浓度氮(30 mmol·L^-1)促进了车桑子幼苗生长、叶片氮含量和生物量积累, 其余氮添加条件(3、5、15 mmol·L^-1)下车桑子幼苗各性状无显著差异, 但相比高氮水平, 其生物量积累和叶片氮含量显著降低, 根冠比和氮利用效率显著增加。随着磷添加浓度的增加, 车桑子幼苗生物量显著增加, 低磷条件(0.25、0.5 mmol·L^-1)限制了车桑子幼苗生长和生物量积累, 其根冠比和磷利用效率均没有发生显著变化, 但比叶面积和叶/茎生物量比例显著增加, 叶干物质含量显著降低。氮处理下, 叶片氮含量与根冠比显著负相关; 磷处理下, 叶片氮含量与比叶面积显著正相关。同时, 氮处理下, 车桑子幼苗株高、基径、总生物量等生长性状均与根冠比显著负相关, 与叶片氮含量显著正相关, 表明根冠比和叶片氮含量的调整在车桑子适应氮限制中发挥重要作用; 而磷处理下, 株高、基径、总生物量与比叶面积显著负相关, 与叶干物质含量显著正相关, 表明叶片结构性状的调整在车桑子适应低磷环境中具有重要意义。该研究表明, 车桑子幼苗生物量分配和叶性状及性状间的权衡策略对氮、磷的响应具有明显差异性, 在今后的研究中, 应关注氮和磷对植物性状影响的差异性。     

The effects of a rust infection on fitness components in a natural population of Tolumnia variegata (Orchidaceae)

The effects of a rust infection (Sphenosphora saphena, Basidiomycetes) on several fitness components of the orchid Tolumnia (Oncidium) variegata were quantified in a subtropical moist forest of Puerto Rico. Infected and uninfected plants of two size categories were observed and manipulated by increasing natural levels of fruit production to determine the effects of infection on short and long-term sexual reproduction, subsequent vegetative and reproductive growth, and mortality. Under artificially high levels of fruit production, infection had no effect on short or long-term reproduction through male or female function except for a modest decline in seed viability in small plants. Under natural levels of fruit production, infection was only related to a reduction in the number of leaves per shoot. At artificially high levels of fruit production, infection reduced leaf length, leaf width, and the number of live shoots. Survival was not associated with rust occurrence. The rust appears to have minor ecological impact on this orchid population.     

Leaf position,light levels,and nitrogen allocation in five species of rain forest pioneer trees

We used path analysis to ask whether leaf position or leaf light level was a better predictor of within-plant variation in leaf nitrogen concentration in five species of rain forest pioneer trees (Cecropia obtusifolia, Ficus insipida, Heliocarpus appendiculatus, Piper auritum, and Urera caracasana) from the Los Tuxtlas Biological Station, Veracruz, Mexico. Three hundred seventy-five leaves on 28 plants of the five species were analyzed for leaf nitrogen concentration, leaf mass per area, and leaf light interception at different positions (= nodes) along a shoot. Mean values of leaf nitrogen concentration ranged from 0.697 to 0.993 g/m² in the five species, and varied by as much as 2.24 g/m² among leaves on individual plants. Leaf position on the shoot explained significantly more of the within-plant variation in leaf nitrogen concentration than did leaf light level in four of the five species: Cecropia obtusifolia, Heliocarpus appendiculatus, Piper auritum (branch leaves only), and Urera caracasana. However, individual species differed considerably in the patterns of nitrogen allocation and leaf mass per area among leaves on a shoot. These results suggest that leaf nitrogen deployment in these plants is, in part, developmentally constrained and related to the predictability of canopy light distribution associated with plant growth form.     

干热河谷石漠化区顶坛花椒叶片功能性状的海拔分异规律

为阐明顶坛花椒人工林叶片功能性状的海拔分异规律,探讨顶坛花椒对不同海拔生境的适应策略,该研究测定了叶片厚度、比叶面积、叶全氮含量等9个功能性状和土壤有机碳、全氮、全磷等8个环境因子,揭示了顶坛花椒人工林叶片功能性状的内在关联及其随海拔的分异规律。结果表明:(1)随海拔升高,顶坛花椒比叶面积、叶全磷、叶全钾含量先升高后降低,叶干物质含量、叶全氮含量先降低后逐渐升高,叶片厚度、叶面积及叶片含水率逐渐增大。(2)顶坛花椒叶片功能性状间具有显著的相关性,叶全氮与叶全磷呈显著负相关,与叶片厚度的关系则相反;叶干物质含量与比叶面积、叶片含水率呈显著的抑制效应。(3)土壤因子对顶坛花椒叶片的影响表现为速效氮速效钾有机碳,其他土壤因子的影响较小。研究显示顶坛花椒主要通过增强防御功能性状、协调叶片养分含量的生存策略来提高获取资源和抵御外界环境胁迫的能力,对土壤养分具有强烈的依赖性,其干旱适应属性为干旱避免,该研究为顶坛花椒人工林复壮、高产与稳定,及喀斯特石漠化区生态修复提供科学依据。     

Interspecific and intraspecific differences in shoot and leaf lifespan of four Carex species which differ in maximum dry matter production

The effect of N supply on shoot and leaf lifespan was investigated in established stands of four herbaceous Carex species which differed in maximum dry matter production. These species were, in rank order of increasing maximum dry matter production (per unit ground area): Carex diandraC. rostrata. The observed patterns of shoot and leaf turnover were compared with data on leaf characteristics and nitrogen use efficiency indices of these species. There was no consistent difference in shoot production (number of shoots produced per unit ground area) between species with low production and those with high production: Carex diandra (low production) and C. lasiocarpa (high production) had high shoot production, while shoot production in c. rostrata (low production) and C. acutiformis (high production) was much lower. The rank order of the mean lifespan of shoots was: C. diandra. Thus, the lifespan of shoots increased with increasing maximum dry matter production of these Carex species. In all species, increased N supply led to a significant reduction in shoot lifespan. The reduction of shoot lifespans in response to enhanced N supply will result in increased nutrient turnover rates in these species. There was no consistent difference in the number of leaves produced per shoot between low-production and high-production species. C. diandra and C. lasiocarpa had relatively low leaf production, while C. rostrata and C. acutiformis had relatively high leaf production per shoot. Thus, this pattern is opposite to the pattern in shoot production. The rank order of the mean lifespan of leaves was: C. diandra. This implies that the high-production species had longer mean leaf lifespans than the low-production species. Mean leaf lifespan was not significantly affected by enhanced N supply, except in C. diandra, where leaf lifespan decreased in response to enhanced N supply. Shoot lifespans did not show any significant relation with the specific leaf area (SLA, leaf area per unit leaf mass) or the leaf area ratio (LAR, leaf area per unit plant mass) of the species under study. There was, however, a negative relation (r ²=0.71) with the nitrogen concentration in the leaves. Shoot lifespans were positively related (r ²=0.79) with whole-plant nitrogen use efficiency (NUE, dry matter production per unit N-loss) and with the mean residence time of nitrogen (MRT, the average time-span during which a unit of nitrogen is present in the plant) (r ²=0.78), but not with the nitrogen productivity (A, annual dry matter production per unit N in the plant). Leaf lifespan was positively related with the mean residence time of nitrogen in the plants (r ²–0.70). For all the other parameters, there were no significant relations with leaf lifespan. From these results we conclude that: (1) at the stand level, shoot and leaf lifespans are positively related with maximum dry matter production; and (2) shoot and leaf lifespan are important determinants of whole-plant nitrogen economy.     

Ecophysiological studies on the shrub Vaccinium myrtillus L. taken from a wide altitudinal range

Summary Observations have been made on the gas exchange and morphology of Vaccinium myrtillus taken from altitudes of 200 m, 610 m and 1,100 m along an altitudinal gradient in central Scotland. Under saturating irradiance, optimum temperatures and a range of vapour pressure deficits, photosynthetic rate and stomatal conductance increased with the altitude of origin of the populations. Correlated with these increases was an increase in the adaxial stomatal density with altitude. This response to altitude could be simulated in controlled conditions, by growing plants in a CO₂ concentration below ambient, similar to that expected at altitude.Plant height decreased with altitude, a feature which was maintained in cultivation. Stem rigidity declined with altitude, in a manner which is predicted to limit the reproductive capacity of the population from 1,100 m in high wind speeds.Total leaf nitrogen increased with altitude. The nitrogen economy of the shoot is discussed in terms of nitrogen availability for stems and leaves and its control over maximum rates of photosynthesis, competitive ability and reproductive capacity.     

Variation of growth and functional traits of invasive knotweeds (<Emphasis Type="Italic">Fallopia</Emphasis> spp.) in Belgium

Three invasive Fallopia taxa are present in Belgium: F. japonica (FJ), F. sachalinensis (FS) and their hybrid F. × bohemica (FB). FS is the least invasive of the three taxa. In this study, we compared the taxa, in sites where they co-occur, for differences in functional traits that might influence their competitive ability and invasiveness—shoot height and ramification, leaf size, specific leaf area (SLA) and foliar nitrogen (N) concentration. The three taxa exhibited similar growth kinetics and similar SLA. However, FS differed in its architecture and allocation of leaf area, having less ramified shoots and a steeper gradient of decreasing leaf size along the main shoot. Also, FS had greater foliar N and less efficient N resorption from senescing leaves. These traits values may result in lower competitive ability of FS for light and nitrogen. For the same traits, FB was generally intermediate between FS and FJ, but often closer to the latter. FB was more variable than FS and FJ, possibly due to larger genetic variation. SLA and ramification varied greatly amongst sites for all taxa, due in part to plastic response to contrasting light regimes. Variation in functional traits values may in part explain the variation in invasiveness amongst the members of the Fallopia complex in Belgium.     

Factors influencing shoot multiplication of lotus (<Emphasis Type="Italic">Nelumbo nucifera</Emphasis>)

Effect of plant growth regulators, explant size, season of explant collection, temperature (20, 25 and 30 °C) and photoperiod on in vitro lotus (Nelumbo nucifera Gaertn.) shoot formation and growth were examined. Shoots formation was greatly influenced by growth regulators, explant size and season of explant collection. The maximum number of shoots were induced from bud explants on Murashige and Skoog (MS) medium containing 4.44 μM benzyladenine (BA) + 0.54 μM α-naphthalene acetic acid (NAA). Explants formed by bud of one expanded and one unexpanded leaf, which was collected in spring gave encouraging results of shoot production. Higher temperature favoured shoot induction and subsequent growth was much better at 25 °C compared to that at 20 and 30 °C.