Size structure of current-year shoots in mature crowns

Characteristics of current-year shoot populations were examined for three mature trees of each of three deciduous broad-leaved species. For first-order branches (branches emerging from the vertical trunk) of the trees examined, lengths or diameters of all current-year shoots were measured. Total leaf mass and total current-year stem mass of first-order branches were estimated using an allometric relationship between leaf or stem mass and length or diameter of current-year stems. For each tree, the number of current-year shoots on a first-order branch was proportional to the basal stem cross-sectional area of the branch. On the other hand, first-order branches had shoot populations with size structures similar to each other. As a result, the leaf mass of a first-order branch was proportional to the basal stem cross-sectional area of the branch, being compatible with the pipe-model relationship. All current-year shoot populations had positively skewed size structures. Because small shoots have a larger ratio of leaf mass to stem mass than large shoots, first-order branches had an extremely large ratio of leaf mass to current-year stem mass. This biased mass allocation will reduce costs for current stem production, respiration and future radial growth, and is beneficial to mature trees with a huge accumulation of non- photosynthetic organs. The allometric relationships between leaf mass and basal stem diameter and that between leaf mass and current-year stem mass of first-order branches were each similar across the trees examined. Characteristics of shoot populations tended to offset inter-species diversity of shoot allometry so that branch allometry shows inter-species convergence.     

Assessing allometric models to predict vegetative growth of mango (Mangifera indica; Anacardiaceae) at the current-year branch scale

? Premise of the study: Accurate and reliable predictive models are necessary to estimate nondestructively key variables for plant growth studies such as leaf area and leaf, stem, and total biomass. Predictive models are lacking at the current-year branch scale despite the importance of this scale in plant science. ? Methods: We calibrated allometric models to estimate leaf area and stem and branch (leaves + stem) mass of current-year branches, i.e., branches several months old studied at the end of the vegetative growth season, of four mango cultivars on the basis of their basal cross-sectional area. The effects of year, site, and cultivar were tested. Models were validated with independent data and prediction accuracy was evaluated with the appropriate statistics. ? Key results: Models revealed a positive allometry between dependent and independent variables, whose y-intercept but not the slope, was affected by the cultivar. The effects of year and site were negligible. For each branch characteristic, cultivar-specific models were more accurate than common models built with pooled data from the four cultivars. Prediction quality was satisfactory but with data dispersion around the models, particularly for large values. ? Conclusions: Leaf area and stem and branch mass of mango current-year branches could be satisfactorily estimated on the basis of branch basal cross-sectional area with cultivar-specific allometric models. The results suggested that, in addition to the heteroscedastic behavior of the variables studied, model accuracy was probably related to the functional plasticity of branches in relation to the light environment and/or to the number of growth units composing the branches.     

Effect of stem length to stem slender ratio of current-year twigs on the leaf display efficiency in evergreen and deciduous broadleaved trees

Aims Branches and leaves are the two main structural units of tree crown composition. Among the adaptive strategies of plants, the functional traits of branches and the relationships between branch traits and leaf traits determine the capacity of trees to access light and space. In this study, our objective is to test the hypothesis that leaf display efficiency is affected by the stem length to stem slender ratio within current-year twigs.Methods The stem length to stem slender ratios of current-year twigs were used as the proxy of stem structure traits. Leaf area ratio (total leaf area per stem mass), leaf density (leaf number per stem length) and leaf/stem mass ratio (total leaf mass per stem mass) were used as the proxies of leaf display efficiency. The relationship between stem structure traits and leaf display efficiency within current-year twigs were studied for 25 evergreen and 60 deciduous broadleaved woody species in Qingliang Mountain, Zhejiang, China. The standardized major axis estimation method was used to examine the scaling relationship between stem structural traits and leaf display efficiency within current-year twigs.Important findings The proxies of leaf display efficiency, measured by leaf area ratio, leaf density or leaf/stem mass ratio, were all significantly and negative correlated with stem length to stem slender ratio within current-year twigs in both evergreen and deciduous broadleaved woody species. This suggested that leaf display efficiency decreased with stem length to stem slender ratios within current-year twigs, which may reflect the role of mechanical safety and light within twigs. The slope of the relationship between leaf display efficiency and stem long-dimension structure traits in evergreen species was not significantly different from the one in deciduous species. In contrast, the y-intercept of the relationship between leaf density and stem long-dimension structure traits was significantly larger in evergreen species than in deciduous species, i.e. the leafing intensity of evergreen species was higher than that of deciduous species. Individual leaf area and specific leaf area were smaller in evergreen species than in deciduous species, which resulted in deciduous species have a larger leaf area per stem mass and leaf mass per stem mass at a given stem length to stem slender ratio compared to evergreen species. It may reflect the conservative adaptive strategy of high consumption and slow benefit in evergreen species. Our results demonstrated that leaf display efficiency could be affected by stem length, and would change with leaf life-span (deciduous versus evergreen).     

Changes in crown development patterns and current-year shoot structure with light environment and tree height in Fagus crenata (Fagaceae)

The relative effects of light and tree height on the architecture of leader crowns (i.e., the leading section of the main trunk, 100 cm in length) and current-year shoots for a canopy species, Fagus crenata, occupying both the ridge top and the valley bottom in a cool-temperate forest in Japan were investigated. For leader crowns, the number of current-year shoots and leaves increased with increasing tree height, whereas the mean length of current-year shoots increased with increasing relative photon flux density (PFD). The leader crown area decreased, and the depth and leaf area index of leader crowns increased, with increasing relative PFD. The mass of current-year shoots increased with relative PFD. However, this total mass was allocated differently between stems and leaves depending on tree height, such that the relative allocation to stems increased with increasing tree height. Furthermore, stem structures within current-year shoots also changed with height, such that taller trees produced thicker and shorter stems of the same volume. In contrast, leaf structure and leaf biomass allocations changed with relative PFD. Specific leaf area decreased with increasing relative PFD. In addition, leaf number increased more rapidly with increasing individual leaf mass for trees exposed to greater relative PFD. Consequently, the total leaf area supported by a stem of a given diameter decreased with increasing tree height and relative PFD. Thus, the architecture of leader crowns and current-year shoots were related differently to light and tree height, which are considered important for efficient light capture and the growth of small and tall trees in different environments.     

水淹深度、持续时间及发生频率对扬子狐尾藻早期生长的影响

研究了水淹扰动包括不同的深度(0,10,60 cm)、持续时间(1周、2周)和发生频率(1次、2次)对扬子狐尾藻(Myriophyllum oguraense Miki subsp.yangtzense Wang)早期生长的影响。结果表明,湿生状态下未经过水淹处理的植株的总生物量最大、所产生的分枝数最多、株高最小;在经过水淹处理后,植株的总生物量、植株所产生的分枝数显著减少,而株高则显著增加。随着水淹深度的增大和持续时间的增加,植株的总生物量、分枝数显著减小,而株高则在浅水位处理下(10 cm)随着水淹持续时间的增加而增加,在深水位处理下(60 cm)随着水淹持续时间的增加而减小。总生物量在较长时间持续于浅水位下(2周,10 cm)和较短时间持续于深水位下(1周,60 cm)时随水淹发生频率的增高而增大,分枝数也呈增多趋势。随着水淹发生频率的增高,深水位(60 cm)显著促进株高的增加。此外,水淹处理后,茎生物量比增大,而根生物量比、叶生物量比、分枝生物量比则呈减小趋势。这些研究结果表明水淹扰动是影响扬子狐尾藻早期生长和克隆繁殖的重要因子之一,同时也说明扬子狐尾藻对不同的水淹扰动有不同的生长和克隆繁殖对策。     

攀援植物绞股蓝幼苗对光照强度的形态和生长反应

 利用遮阳网产生光照强度梯度,以研究攀援植物绞股蓝(Gynostemma pentaphyllum)幼苗对光梯度的形态和生长反应。结果表明：1)相对生长速率、净同化速率和总生物量随光照强度减弱而降低,总叶面积、比茎长、株高、分枝角度、叶面积率和比叶面积却增加;2)株高生长与相对生长速率成负相关;3)幼苗生物量分配对光梯度的反应不敏感。这些结果意味着绞股蓝幼苗的形态和生长反应对不同光环境具有可塑性,比茎长和株高随光照减弱而增加有利于绞股蓝幼苗“寻找”到外界支持物。     

Phenotypic plasticity of lianas in response to altered light environment

The growth, morphology and biomass allocation of 11 liana species (six light-demanding and five shade-tolerant) were investigated by growing plants in three contrasting light environments (i.e., field, forest edge and forest interior). Our objectives were to determine: (1) changes in plant traits at the species level; and (2) differences in light-demanding and shade-tolerant species in response to altered light environment. We found that all seedlings of liana species increased in total biomass, total leaf area, relative growth rate (RGR), net assimilation rate (NAR), height, basal diameter, root length, leaf number, root mass/total plant mass (RMR) and root-to-shoot dry biomass (R/S ratio), and decreased in leaf area ratio (LAR), specific leaf area (SLA), leaf size, stem mass-to-total plant mass ratio (SMR) and leaf mass-to-total plant mass ratio (LMR) with increasing light availability. Under the three light environments, the two types of species differed significantly in total biomass, total leaf area, RGR, NAR, LAR, SLA and leaf number, and not in leaf area. Only light-demanding species differed significantly in height, root length, basal diameter, RMR, SMR, LMR and R/S ratio. The mean plasticity index of growth and biomass allocation were relatively higher than the morphological variables, with significant differences between the two groups. Our results showed that liana species respond differently to changing light environments and that light-demanding species exhibit higher plasticity. Such differences may affect the relative success of liana species in forest dynamics.     

Hydraulic and mechanical stem properties affect leaf-stem allometry in mango cultivars

Leaf size-stem size allometric relationships are important features of biomass allocation in plants and are affected by biological functions linking the two organs. They have been studied at specific and supraspecific levels, but not at the infraspecific level. It was hypothesized that allometric relationships link leaf size and stem size at the cultivar level, and are cultivar-specific in relation to distinctive functional stem traits: hydraulic conductivity and mechanical strength. Allometric relationships between leaf size and stem size were established for 3 yr, using the standardized major axis method, on current-year branches, composed of one to 16 growth units, for four mango (Mangifera indica) cultivars characterized by contrasting growth habits. The hydraulic and mechanical stem properties of these cultivars were also measured. The slopes of the relationships were similar among cultivars, but not the y-intercepts. Different y-intercepts in the stem mass vs branch cross-sectional area relationship and in the leaf mass vs stem mass relationship were related to mechanical and to hydraulic stem properties, respectively. These results showed that leaf-stem allometry in mango cultivars was shaped by hydraulic and mechanical stem properties, supporting a functional interpretation of the relationship between leaf and stem dimensions.     

SURFACE AREA RELATIONS OF WOODY PLANTS AND FOREST COMMUNITIES

Surface area of wood and bark is an important dimension of forests, with implications for respiration rate, energy exchange, and water and mineral budgets. Surface area of stem wood and bark can be estimated effectively from linear regressions on conic surface (one-half basal circumference times tree height) or from regressions of the logarithm of area on the logarithm of diameter at breast height. Branch surface can be estimated from a formula using branch basal diameter, length, and number of current twigs, and from logarithmic regressions of branch bark surface on basal diameter of branches and breast-height diameter of trees. In temperate deciduous forests several square meters of plant surface occur above each square meter of ground surface; these plant surfaces include 0.3–0.6 m² of stem bark, 1.2–2.2 m² of branch bark, and 3.0–6.0 m² of leaf blades. Branch bark surface increases more rapidly than leaf surface with increasing size of branches and trees. Growth and aging of trees, and maturation of forests, imply increasing ratios of bark (and wood) surface to the photosynthetic leaf surface which supports its growth and respiration.     

Long-term growth dynamics of natural forests in Hokkaido,northern Japan

Abstract. The long-term growth dynamics of natural forest stands on the island of Hokkaido were described on the basis of an analysis of data from 38 permanent plots spanning 15–22 yr. Stand structure was characterized by basal area, stem density and tree size variability. To detect trends in stand structure, regression models for recruitment rate (per ha per yr), mortality rate and the rate of change in stem density and tree size variability were developed by a stepwise method using initial basal area, stem density, tree size variability, species composition summarized by LNMDS ordination, altitude, annual mean temperature, annual precipitation, type of understorey vegetation, topography and slope aspect as candidates for predictor variables. The same analyses were conducted for basal area increment (net growth) and its components: survivor growth = basal area gain by growth of surviving individuals and mortality = basal area loss by death of individuals. Stem density remained generally unchanged; recruitment was relatively low even in very sparse stands. Stand basal area generally increased as survivor growth was approximately double the mortality. Recruitment rate was strongly affected by the presence of dwarf bamboo (Sasa spp.) vegetation on the forest floor which inhibited tree regeneration. Mortality rate was density-dependent; dense stands had higher mortality than sparse stands. Density change rate (recruitment rate - mortality rate) was, therefore, determined by both the type of understorey vegetation and stem density. Survivor growth was high in stands with high stem density and basal area. Mortality was dependent on basal area and altitude. Net basal area increment (net growth) was dependent only on stem density with other factors that influenced survivor growth and mortality omitted. Tree size variability decreased in stands with high tree size variability whereas it increased in stands with low size variability. Based on the obtained models for density change rate and net basal area increment, trajectories of stands were illustrated on a log-log diagram of stem density and basal area. The predicted differences in trajectories as affected by the understorey vegetation type indicated the importance of dwarf bamboo vegetation for forest dynamics on Hokkaido.     

Relationships between branch spacing, growth rate and light in tropical forest saplings

1. The spacing of branches along central stems was related to growth rate and light level in forest saplings and trees in tropical moist forest on Barro Colorado Island (BCI), Panama. The study included 14 species with tiers of plagiotropic branches (having planar leaf arrangements) and four species with continuous distributions of plagiotropic branches.
2. All species showed increases in branch spacing with increasing light and growth rate of diameter, similar to the patterns in leaf spacing noted previously in species which initially bear large leaves on unbranched stems.
3. Non-tiered species had shorter internodes than tiered species but because the latter bear more branches per node, both groups had similar numbers of branches per unit stem length, when compared at similar growth rates.
4. Differences in the relationship between internode length and growth rate among tiered species were related to demographic characteristics, suggesting that tree architecture may influence forest composition.
5. The strong correlation observed between branch spacing and growth rate suggests that branch spacing may be used to estimate past growth histories of forest tree species with plagiotropic branches.     

基于空间变异性的树冠非结构性碳含量估算：以胡桃楸和春榆为例

以胡桃楸和春榆为例,采用枝解析法测定不同基径枝条的非结构性碳水化合物（NSC）浓度的变异,进而估算并评价不同取样方法对树冠NSC含量估算的误差.结果表明： 器官对两种树种树冠NSC浓度的影响显著,叶、新枝、老枝和死枝的可溶性糖与淀粉的总和（TNC）的平均浓度分别为17.6%、12.6%、5.7%和2.9%.叶和新枝的NSC浓度随枝基径、枝龄、枝长和枝相对高度的变异多不显著,但老枝的NSC浓度随枝基径、枝龄和枝长增大而降低,而随枝相对高度增加而增加,其中枝基径是老枝NSC浓度的最佳预测变量（R²在0.87~0.95）.两树种叶、新枝和老枝平均TNC含量分别占其树冠TNC含量的28%、2%和70%.分析树冠枝NSC的空间变异性对树冠NSC含量估算误差的影响发现,采用新枝和直径约3 cm老枝枝段的NSC浓度估算冠层NSC含量是较简易而精确的方法.     

胡杨叶片大小与叶数量的权衡关系对地下水埋深的响应

本文以胡杨(Populus euphratica Oliv.)为研究对象,采用标准化主轴回归估计(SMA)方法探讨了种群叶片大小(单叶面积、单叶质量)与出叶强度(基于小枝质量、茎质量、茎体积)的异速生长关系对地下水埋深梯度(Groundwater depth,GWD)的响应及其变化规律.结果显示:随GWD增加,胡杨当年...     

太白红杉种内和种间竞争研究

采用逐步扩大范围的方法确定影响对象木 (Objectivetree) 的最佳竞争范围, 利用单木竞争指数的改进模型对太白红杉 (Larixchinensis) 种内和种间竞争强度进行了定量分析, 并讨论了不同竞争强度下太白红杉的形态变化。结果表明 :随对象木胸径的增大, 由于太白红杉种群自然稀疏过程中密度调节作用, 植株距离增加, 种内竞争强度降低 ;太白红杉主要分布于亚高山地段, 群落内其它物种较少, 个体普遍较小, 结果种间竞争相对较弱, 种内与种间竞争关系顺序为 :太白红杉 太白红杉 >巴山冷杉 (Abiesfargesii) 太白红杉 >牛皮桦 (Betulaplatyphylla) 太白红杉 >其它树种 太白红杉 ;竞争强度和对象木胸径的关系服从幂函数关系 (CI =AD-B), 当太白红杉胸径达到 35cm以上时, 竞争强度几乎没有变化, 所得的预测模型能很好地预测太白红杉种内和种间的竞争强度 ;不同竞争强度下, 太白红杉主茎各层的分枝角度、总分枝数、当年生枝条长、平均枝长和活枝数均表现出显著的差异。表明采用逐步扩大范围的方法能有效地确定竞争木范围, 较好地反应太白红杉种内和种间的竞争关系。同时, 太白红杉通过自身形态变化, 提高了对光的截获能力和对不同竞争强度的适应能力。     

Spatial variation in sapwood area to leaf area ratio and specific leaf area within a crown of silver birch

Spatial variation in sapwood area to leaf area ratio (Huber value, HV) and specific leaf area (SLA) was examined in branches of closed-canopy trees of silver birch (Betula pendula Roth). HV increased basipetally within a crown and decreased with increasing branch order, but exhibited no significant radial trend along a primary branch. HV was primarily determined by branch position in a crown and branch diameter at the sampling point, being independent of the size of the tree and branch. Greater HV in the lower-crown branches is considered a means to mitigate differences in hydraulic transport capacity between the branches located in different canopy layers. Beside branch position and sampling location on a branch, SLA depended significantly on several other variables characterising tree and branch size. SLA increased basipetally within a crown and along a primary branch, but exhibited no significant trend with branch orders. Because height caused leaf area (A_L) to diminish more rapidly than leaf dry weight, A_L primarily determined the vertical variation in SLA.     

Stem diameter growth rates in a fire‐prone savanna correlate with photosynthetic rate and branch‐scale biomass allocation,but not specific leaf area

Plant growth rates strongly determine ecosystem productivity and are a central element of plant ecological strategies. For laboratory and glasshouse‐grown seedlings, specific leaf area (SLA; ratio of leaf area to mass) is a key driver of interspecific variation in growth rate (GR). Consequently, SLA is often assumed to drive GR variation in field‐grown adult plants. However, there is an increasing evidence that this is not the general case. This suggests that GR – SLA relationships (and perhaps those for other traits) may vary depending on the age or size of the plants being studied. Here we investigated GR – trait relationships and their size dependence among 17 woody species from an open‐canopy, fire‐prone savanna in northern Australia. We tested the predictions that SLA and stem diameter growth rate would be positively correlated in saplings but unrelated in adults while, in both age classes, faster‐GR species would have higher light‐saturated photosynthetic rate (A_sat), higher leaf nutrient concentrations, higher branch‐scale biomass allocation to leaf versus stem tissues and lower wood density (WD). SLA showed no relationship to stem diameter GR, even in saplings, and the same was true of leaf N and P concentrations, and WD. However, branch‐scale leaf:stem allocation was strongly related to GR in both age groups, as was A_sat. Together, these two traits accounted for up to 80% of interspecific variation in adult GR, and 41% of sapling GR. A_sat is rarely measured in field‐based GR studies, and this is the first report of branch‐scale leaf:stem allocation (analogous to a benefit:cost ratio) in relation to plant growth rate. Our results suggest that we may yet find general trait‐drivers of field growth rates, but SLA will not be one.     

不同密度下沙地樟子松碳、氮、磷化学计量及养分重吸收特征

以樟子松纯林为对象,研究了6种密度(490、750、1110、1550、1930、2560株.hm-2)下不同器官(当年生叶、一年生叶、当年生枝、一年生枝和细根)的C、N、P化学计量特征及叶片N、P重吸收效率.结果表明:随着林分密度增加,当年生和一年生叶C含量及当年生和一年生枝P含量呈降低趋势(1550株.hm-2除外...     

Development of biomass proportions in Norway spruce (Picea abies [L.] Karst.)

This study tests the hypotheses that (1) the above-ground structure of Norway spruce (Picea abies [L] Karst.) is derivable from the functional balance theory, and that (2) crown ratio is a key source of structural variation in trees of different age and social position. Twenty-nine trees were measured in three stands (young, middle-aged, and mature), with three thinning treatments (unthinned, normal, and intensive) in the two older stands. There was a strong linear relationship between the total cross-sectional area of branches and that of stem at crown base. Foliage mass was linearly related with stem basal area at crown base. Also an allometric relationship was found between foliage mass and crown length. The mean length (weighted by basal area) of branches obeyed an exponential function of crown length. The parameters of most of these relationships were independent of slenderness (tree height/breast height diameter) and tree age However, total branch cross-sectional area per stem cross-sectional area in the young trees was greater than in the older trees. The young trees also had slightly shorter branches than predicted by the mean branch length equation. This was probably caused by branch senescence which had not yet started in the young stand. The older trees had a relatively long lower crown segment which was growing slowly and senescing. It was proposed that a segmented crown structure is characteristic of shade tolerant tree species, and that the structural model could be further developed by making the two segments explicit.     

胡杨当年生小枝茎构型对展叶效率的影响

枝叶异速生长关系对理解荒漠植物生物量分配和生活史策略具有重要意义。该研究以小枝茎长度、茎纤细率和茎体积表征茎构型, 以叶密度(单位茎长度的叶数量)、叶面积比(单位小枝茎干质量的总叶面积)和叶茎质量比(单位小枝茎干质量的总叶干质量)表征展叶效率, 采用标准化主轴回归(SMA)方法研究胡杨(Populus euphratica)当年生小枝茎构型对展叶效率的影响及二者沿地下水埋深(GWD)梯度的权衡策略。结果显示, 胡杨当年生小枝茎直径、展叶效率和比叶面积、叶大小随GWD增加而降低, 小枝茎长度、茎纤细率及其上的叶数量则增大。小枝茎构型性状均与展叶效率呈显著负相关关系, 即随小枝茎长度、茎纤细率和茎体积的增加, 展叶效率逐渐降低, 这可能是枝叶大小、水分传导与机械支撑间的权衡结果。小枝茎构型与展叶效率的异速生长指数(斜率)随GWD增加而增大, 是由于单位小枝茎投资获得的叶面积或者叶质量降低所致, 反映出随GWD增加胡杨采取了高消耗低收益的保守型策略。胡杨应对环境压力时, 倾向于在长枝上着生数量较多的小叶, 短枝上着生数量较少的大叶, 体现出胡杨小枝的资源利用策略与枝叶大小的权衡机制。综上所述, GWD显著影响胡杨小枝茎构型-展叶效率的权衡关系, 低展叶效率是胡杨应对日益旱化荒漠环境的适应策略。     

水分因素对沙地柏实生苗水分和生长特征的影响

为探讨未来降雨变化对半干旱气候区毛乌素沙地常绿优势灌木沙地柏(Sabina vulgaris)实生苗水分和生长特征的可能影响，在鄂尔多斯沙地草地生态站开展了模拟降雨变化的实验。水分饱和亏缺和组织密度随土壤水分含量提高而降低，失水系数却相反，这表明沙地柏实生苗的保水抗旱性随模拟降雨量增加而降低。水分梯度对枝茎面积比无显著影响，叶质量茎面积比和叶质量枝面积比随土壤水分含量增大而降低，这意味着实生苗分枝的供水潜力随水分可利用性提高而降低。水分变化显著影响生物量分配，而对形态和植冠生产力指数均无显著影响；生物量、株高和基茎增量的变化反映了沙地柏生长的缓慢性。根系对水分变化的敏感性高于叶和茎，地下部分生物量投资随水分可利用性提高而增大，这暗示沙地柏实生苗可能通过节约利用水分方式适应自然生境中的水分胁迫。