不同光环境下紫椴幼树树冠结构的可塑性响应

从冠形、侧枝和叶片在树冠中的空间分布角度对天然更新紫椴幼树的树冠结构进行了论述,认为紫椴幼树树冠对光照条件的变化有显著的可塑性响应.强光通过抑制主干的生长促进了侧枝的分化,庇荫则通过抑制1级侧枝的生长促进了侧枝的再分枝.随着光照水平的降低,紫椴幼树的数量叶片密度显著降低,且叶片逐渐集中于冠上层.林冠下的紫椴幼树通过这种侧枝和叶片的分布格局,在形态上提高其对光的截获能力在适度庇荫环境中,紫椴幼树垂直生长采取演替先锋种的"避荫”对策,侧枝生长采取中等耐荫种的"掠光”对策;在弱光环境中,紫椴幼树则采取典型的忍耐适应行为.这种树冠结构的变化是提高紫椴幼树对光的截获能力的一种有益适应.     

樟子松人工林分枝结构的分析

基于对6块樟子松(Pinus sylvestris var. mongolica)人工林固定标准地中的30株样木枝解析调查数据,通过分析不同林分、不同大小林木1级枝和2级枝的分枝概率、分枝格局和分枝角度,揭示了樟子松人工林树冠的分枝结构特点。研究结果表明：樟子松人工林1级枝和2级枝的平均分枝数量分别为3.84个和2.80个,两者分枝概率均呈正态分布;1级和2级枝条在光照条件好的几个区间（方位角46°～225°）分布较多,1级枝条的水平分布遵从均匀分布,而2级枝条则不遵从均匀分布;树冠上层枝条的分枝角度略小于树冠中、下层,上层平均分枝角度为45.6°,而中下层平均分枝角度都为49.4°。不同大小林木的1级枝分枝结构规律表明：Ⅰ级木和Ⅴ级木的每轮平均分枝数非常接近,分别为3.89和3.94个,比Ⅲ级木每轮分枝数大0.5个左右;1级枝水平分布在各区间内(45°间隔)相差在0.24%～2.81%之间,方差分析结果表明枝条水平分布与林木大小无关;不同大小林木的分枝角度有所差别,Ⅰ级木、Ⅲ级木和Ⅴ级木的平均分枝角度分别为48.5°、42.2°和50.7°。     

Irradiance heterogeneity within crown affects photosynthetic capacity and nitrogen distribution of leaves in Cedrela sinensis

Because light conditions in the forest understory are highly heterogeneous, photosynthetic acclimation to spatially variable irradiance within a crown is important for crown‐level carbon assimilation. The effect of variation in irradiance within the crown on leaf nitrogen content and photosynthetic rate was examined for pinnate compound leaves in saplings of Cedrela sinensis, a pioneer deciduous tree. Five shading treatments, in which 0, 25, 50, 75 and 100% of leaves were shaded, were established by artificial heavy shading using shade screen umbrellas with 25% transmittance. Although the nitrogen content of leaves was constant regardless of shading treatment, ribulose 1·5‐bisphosphate carboxylase/oxygenase (Rubisco) content and light‐saturated photosynthetic capacity were lower in shade leaves within partially shaded crowns than within fully shaded crowns. Shade leaves within partially shaded crowns contained higher amount of amino acids. Most shade leaves died in partially shaded crowns, whereas more than half of shade leaves survived in totally shaded crowns. Assumptions on photosynthetic acclimation to local light conditions cannot explain why shade leaves have different photosynthetic capacities and survival rates in between partially and totally shaded crowns. Irradiance heterogeneity within the crown causes a distinct variation in photosynthetic activity between sun and shaded leaves within the crown.     

Relationship between respiratory depletion of sugars and loss of cold hardiness in coniferous seedlings over-wintering at raised temperatures: indications of different sensitivities of spruce and pine

Long-term effects of elevated winter temperatures on cold hardiness were investigated for Norway spruce (Picea abies L. Karst.), lodgepole pine (Pinus contorta Dougl.) and Scots pine (Pinus sylvestris L.). Two-year-old seedlings with the same pre-history of growth and cold hardening in the field were maintained from early December to late March at two field sites in northern Sweden and in a cold room. The temperatures at these locations averaged –13·5, –8·9 and 5·5°C, respectively. Following treatments, carbohydrate contents and cold tolerances were assessed. Needle respiration was also analysed during the 5·5°C treatment. Cold tolerance of lodgepole pine and Scots pine was much reduced following the 5·5°C treatment. Cold tolerance was somewhat reduced in lodgepole pine following the –8·9 °C treatment, but was essentially maintained in spruce throughout all treatments. The cold tolerance of needles was strongly correlated with their soluble sugar contents. Spruce maintained cold hardiness by having larger reserves of sugars and lower rates of respiration which decreased more rapidly as sugars were depleted. Tolerance of lodgepole pine to frost desiccation was also much reduced following the 5·5°C treatment.     

Differential selection of North American and Scandinavian conifer browse by northwestern moose (Alces alces andersoni) in winter

Scandinavian moose (Alces alces) eat Scots pine (Pinus sylvestris) in winter. Although North American moose are known to eat conifers such as true firs (Abies spp.) in winter, substantial consumption of pine by moose in North America has not been documented. Here, we document short-term winter preferences of human-habituated northwestern moose (Alces alces andersoni) for branches of mature North American and European conifer species as determined by a cafeteria-style feeding trial. Moose selected for species such as Douglas fir (Pseudotsuga menziesii; from which they took the smallest bite diameters) while avoiding species such as lodgepole pine (Pinus contorta; from which they took the largest bites) and hybrid white spruce (Picea glauca × engelmanii). The amount of species-specific biomass consumed by moose was negatively correlated with bite diameters taken from branches of those species and did not appear to be significantly influenced by differences in twig morphology between species. Our trial suggests that northwestern moose readily consume conifers in winter and, from the species we tested, prefer Douglas fir. While no clear preference existed between Scots pine and lodgepole pine, moose avoided lodgepole pine, but not Scots pine, relative to Douglas fir. Our trial suggests that northwestern moose are more likely to feed on the branches of Douglas fir than pine, which may be of interest to foresters managing conifers within the North American range of moose, particularly where Scots pine are being considered for planting.     

Spacial distribution of photosynthetic capacity and performance in a mountain spruce forest of Northern Germany

Summary Biomass distribution and diurnal CO₂ uptake under natural conditions were investigated on Picea abies in a mountainous climate (Solling, Northwest Germany). Spruce has a remarkable variability in leaf characteristics. Even on a single branch in the lower sun crown, needle dry weight and surface area change considerably from the branch base to the tip and accoring to exposure. Only about 18% of the total biomass of the tree was current year's growth, about 40% of the needles were 4 years and older reaching a maximal age of 12 years. The main growing zone was at the border of upper shade and lower sun crown and the main accumulation of dry weight was at a greater tree height than was observed for maximal growth of needle numbers or surface area. The annual, new growth shifted toward the upper sun crown. Maximal daily CO₂ uptake was highest in the lower sun crown on days with variable cloud cover when temperatures were moderate and water vapor pressure deficits were low. Also the annual CO₂ uptake was highest in the lower sun crown, where 4-year-old and older needles contributed about 35% to the annual CO₂ uptake of the tree. Current year growth contributed about 15% of the total CO₂ gain. The upper and lower sun crowns produce about 70% of the total carbon gain. The carbon balance of spruce and the distribution of the production process in relation to needle age and crown level are discussed.     

Branch architecture,light interception and crown development in saplings of a plagiotropically branching tropical tree,Polyalthia jenkinsii (Annonaceae)

To investigate crown development patterns, branch architecture, branch-level light interception, and leaf and branch dynamics were studied in saplings of a plagiotropically branching tree species, Polyalthia jenkinsii Hk. f. & Thoms. (Annonaceae) in a Malaysian rain forest. Lengths of branches and parts of the branches lacking leaves ('bare' branches) were smaller in upper branches than in lower branches within crowns, whereas lengths of 'leafy' parts and the number of leaves per branch were larger in intermediate than in upper and lower branches. Maximum diffuse light absorption (DLA) of individual leaves was not related to sapling height or branch position within crowns, whereas minimum DLA was lower in tall saplings. Accordingly, branch-level light interception was higher in intermediate than in upper and lower branches. The leaf production rate was higher and leaf loss rate was smaller in upper than in intermediate and lower branches. Moreover, the branch production rate of new first-order branches was larger in the upper crowns. Thus, leaf and branch dynamics do not correspond to branch-level light interception in the different canopy zones. As a result of architectural constraints, branches at different vertical positions experience predictable light microenvironments in plagiotropic species. Accordingly, this pattern of carbon allocation among branches might be particularly important for growth and crown development in plagiotropic species.     

Mining conifers’ mega-genome using rapid and efficient multiplexed high-throughput genotyping-by-sequencing (GBS) SNP discovery platform

Next-generation sequencing (NGS) technologies are revolutionizing both medical and biological research through generation of massive SNP data sets for identifying heritable genome variation underlying key traits, from rare human diseases to important agronomic phenotypes in crop species. We evaluated the performance of genotyping-by-sequencing (GBS), one of the emerging NGS-based platforms, for genotyping two economically important conifer species, lodgepole pine (Pinus contorta) and white spruce (Picea glauca). Both species have very large genomes (>20,000 Mbp), are highly heterozygous, and lack reference sequences. From a small set (six accessions each) of independent replicated DNA samples and a 48-plex read depth, we obtained ~60,000 SNPs per species. After stringent filtering, we obtained 17,765 and 17,845 high-coverage SNPs without missing data for lodgepole pine and white spruce, respectively. Our results demonstrated that GBS is a robust and suitable method for genotyping conifers. The application of GBS to forest tree breeding and genomic selection is discussed.     

Competitive strategies in adult beech and spruce: space-related foliar carbon investment versus carbon gain

In Central Europe, Fagus sylvatica and Picea abies represent contrasting extremes in foliage type, crown structure and length of growing season. In order to examine the competitive strategies of these two co-occurring species, we tested the following hypotheses: (1) the space occupied by the foliage of sun branches is characterized by greater foliar mass investment compared to shade branches, (2) the carbon (C) gain per unit of occupied space is greater in sun than in shade branches, and (3) annual C and water costs of the foliage for sustaining the occupied space are low, wherever C gain per unit of occupied space is low. These were investigated in a mature forest in Southern Germany. The examination was based on the annual assessment of space-related resource investments and gains of the foliage. The foliated space around branches was regarded as the relevant volume with respect to aboveground resource availability. Occupied crown space per standing foliage mass was higher in shade compared to sun branches of beech, whereas no difference existed in crown volume per foliage mass between sun and shade branches of spruce (hypothesis 1 accepted for beech but rejected for spruce). However, beech occupied more space per foliage mass than spruce. The C gain per occupied crown volume was greater in sun than in shade branches (hypothesis 2 accepted) but did not differ between species. The amount of occupied space per respiratory and transpiratory costs did not differ between species or between sun and shade branches. In beech and spruce, the proportion of foliage investment in the annual C balance of sun and shade branches remained rather stable, whereas respiratory costs distinctly increased in shade foliage. Hence, shade branches were costly structures to occupy space, achieving only low and even negative C balances (rejection of hypothesis 3), which conflicts with the claimed C autonomy of branches. Our findings suggest that competitiveness is determined by the standing foliage mass and the annual branch volume increment rather than annual investments in foliage. Expressing competitiveness in terms of space-related resource investments versus returns, as demonstrated here, has the potential of promoting mechanistic understanding of plant–plant interactions.     

Regenerative and age dynamic of spruce population in pine plantations under conditions typical for spruce development

We have studied the natural regeneration of spruce (Picea abies L.) under a canopy of pine (Pinus sylvestris L.) on loamy soils. Spruce survival and growth depend on the duration of the regeneration period from the creation of the plantation and the local conditions formed as a result of uneven thinning of pine and spruce canopy. The formation of spruce population is mainly determined by trees that regenerated upon intensive thinning of 20- to 40-year-old pine trees. Spruce regeneration may be enhanced by timely cleaning cutting in pine plantations. The first one, done at the age of 15–20 years, favors pine growth and spruce regeneration. At the normal reproduction of spruce population under the canopy of 80-year-old pine plantations, the second spruce layer is formed. Trunk reserve in this layer is 20–25% of the reserves of the first layer. After its formation, the light regime in the forest depends greatly on the space volume occupied by spruce crowns. Their percentage is especially high at the relative height equal to 0.4–0.7 of the mean spruce height in the second layer. Smaller spruce trees may exist for a long time period, but their development is slowed down and they die at the undergrowth stage. When the plantation is 150 years old, the reserves of spruce trees regenerated under the canopy of pine comprise one-third of the total reserves of the plantation. If the growing conditions are favorable for spruce (C₃), the stability and productivity of pine-spruce plantations exceed those of the pure spruce plantations. The reasonability of natural spruce regeneration for the creation of pine-spruce plantations under C₃ conditions should be substantiated with the consideration of their designation, ages of cuttings, and the possibility of plantation creation and sanitary cuttings according to the valid regulations.     

Selection of shade trees in forest restoration plantings should not be based on crown tree architecture alone

The planting of tree seedlings is a common restoration technique in the tropics, and using large‐crowned, fast‐growing shade species is recommended to suppress invasive grasses and accelerate forest succession. We analyzed the effectiveness of shade species in shading the forest floor during the rainy and dry seasons at young forest restoration sites, whether shade changes according to site for a given species, and whether crown architecture can predict the shade level. We measured the photosynthetically active radiation (PAR) intercepted by the tree crowns of 14 species in two 3‐year‐old restoration plantings. The ability to predict shade based on crown architecture traits was evaluated using multiple linear regressions. The interception of PAR varied according to species, site, and season for seven species and was generally higher during the rainy season. Low values of tree and first branch height and high values of trunk diameter and mean area of a leaf predicted greater light interception. For the dry season, the ability to predict PAR interception was weaker than that for the rainy season and affected by a shorter tree height and a greater crown area. The crown architecture of shade species did not completely predict their shading ability, and the preselection of shade species for forest restoration purposes based only on crown architecture traits is not effective. Therefore, it is important to consider other factors, such as how long trees retain their leaves throughout the year and the soil and management conditions of the sites undergoing restoration, during the selection of species.     

Asynchrony in larval development of the pine beauty moth, Panolis flammea, on an introduced host plant may affect parasitoid efficacy

In the United Kingdom, Panolis flammea (Den. and Schiff.) (Lepidoptera: Noctuidae) is an important pest species of the introduced lodgepole pine but not of its natural host Scots pine. The timing of P. flammea larval growth must be synchronized with its host tree if the larvae are to succeed. We collected field data during 1990 which revealed that the phenological window starts earlier in Scots pine and is shorter than that observed in lodgepole pine. The larvae are found in the field earlier and within a narrower time frame within a Scots pine forest than in a lodgepole pine forest. The larval developmental period is significantly longer on lodgepole pine than on Scots pine. The synchrony/asynchrony of P. flammea to its natural host (Scots pine) and an introduced tree (lodgepole pine) results in the parasitoids having a different impact on the larvae of the two hosts. At any one time, the host plant, caterpillars and parasitoids are more synchronous on the ancestral Scots pine than on lodgepole pine, resulting in a higher percentage of larvae in the optimal instar for parasitism at that time. In lodgepole pine, the percentage of suitable instars available to parasitoids is lower at any given time. The information presented here furthers our understanding of the possible mechanisms for the observed differential population dynamics of the insect on Scots pine and lodgepole pine in the UK. Handling editor: Robert Glinwood.     

Performance of the tree‐killing bark beetles Ips typographus and Pityogenes chalcographus in non‐indigenous lodgepole pine and their historical host Norway spruce

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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.     

Changes in cold hardiness of introduced and native interior Alaskan evergreens in relation to water and lipid content during spring dehardening

Needle hardiness of introduced yellow pine, Pinus banksiana Lamb., lodgepole pine, P. contorta Dougl, and native white spruce, Picea glauca (Moench) Voss, were assessed by the effective prefreezing temperature method. Yellow pine needles were less hardy than lodgepole pine or white spruce needles in Alaska on each date measured. Although hardiness decreased in springtime in all species, decreases in hardiness in yellow pine began before temperatures were above ?20°C, apparently in response to day length, while decreases in hardiness in lodgepole pine and white spruce began only when mean temperatures were above 0°C. Hardiness was increased by decreasing the water content of yellow pine and spruce needles. However, only the latter increased its field hardiness by decreased water contents, and only to a small degree. Large decreases in phospholipid occurred during the dehardening period, indicating the presence of major membrane-associated changes. However, changes in hardiness did not closely parallel those in phospholipid; hardiness decreased before phospholipid did in spruce and after phospholipid did in lodgepole pine. In yellow pine, changes in hardiness were more closely related to changes in phospholipid content. Decreases in phospholipid appeared to be correlated with the day length in all species.     

Effect of shade stress on growth,morphology, and carbon dynamics of loblolly pine branches

Summary Shade treatments were applied to the terminal portions of branches in loblolly pine trees to test whether portions of branches were autonomous with respect to carbohydrates. The shade treatments reduced light by 50% and 72% compared with full sun conditions resulting in significant reductions in net photosynthesis. Branch growth (branch diameter and length, branch and needle biomass) decreased significantly within the shaded portion of the branch. Branch and needle morphology were also affected by shading. Lateral branches subtending terminal shoots were labelled with ¹⁴C 2 times during the growing season. No movement of ¹⁴C into the terminal portions of the branch was evident during the first growth flush. However, during the second flush of growth small but statistically significant amounts of ¹⁴C were imported into the terminal portion of the shaded branches from subtending laterals. It was concluded that loblolly pine shoots were usually autonomous with respect to carbohydrate supply, but that carbohydrate movement into the terminal shoot from subtending foliage could occur under conditions of very high stress.     

Concentrative nitrogen allocation to sun-lit branches and the effects on whole-plant growth under heterogeneous light environments

We investigated the nitrogen and carbohydrate allocation patterns of trees under heterogeneous light environments using saplings of the devil maple tree (Acer diabolicum) with Y-shaped branches. Different branch groups were created: all branches of a sapling exposed to full light (L-branches), all branches exposed to full shade (S-branches), and half of the branches of a sapling exposed to light (HL-branches) and the other half exposed to shade (HS-branches). Throughout the growth period, nitrogen was preferentially allocated to HL-branches, whereas nitrogen allocation to HS-branches was suppressed compared to L- and S-branches. HL-branches with the highest leaf nitrogen content (N_area) also had the highest rates of growth, and HS-branches with the lowest N_area had the lowest observed growth rates. In addition, net nitrogen assimilation, estimated using a photosynthesis model, was strongly correlated with branch growth and whole-plant growth. In contrast, patterns of photosynthate allocation to branches and roots were not affected by the light conditions of the other branch. These observations suggest that tree canopies develop as a result of resource allocation patterns, where the growth of sun-lit branches is favoured over shaded branches, which leads to enhanced whole-plant growth in heterogeneous light environments. Our results indicate that whole-plant growth is enhanced by the resource allocation patterns created for saplings in heterogeneous light environments.     

Drought induces lagged tree mortality in a subalpine forest in the Rocky Mountains

Extreme climatic events are key factors in initiating gradual or sudden changes in forest ecosystems through the promotion of severe, tree-killing disturbances such as fire, blowdown, and widespread insect outbreaks. In contrast to these climatically-incited disturbances, little is known about the more direct effect of drought on tree mortality, especially in high-elevation forests. Therefore projections of drought-induced mortality under future climatic conditions remain uncertain. For a subalpine forest landscape in the Rocky Mountains of northern Colorado (USA), we quantified lag effects of drought on mortality of Engelmann spruce Picea engelmannii , subalpine fir Abies lasiocarpa , and lodgepole pine Pinus contorta . For the period 1910–2004, we related death dates of 164 crossdated dead trees to early-season and late-season droughts. Following early-season droughts, spruce mortality increased over five years and fir mortality increased sharply over 11 years. Following late-season droughts, spruce showed a small increase in mortality within one year, whereas fir showed a consistent period of increased mortality over two years. Pine mortality was not affected by drought. Low pre-drought radial growth rates predisposed spruce and fir to drought-related mortality. Spruce and fir trees that died during a recent drought (2000–2004) had significantly lower pre-drought growth rates than live neighbour trees. Overall, we found large interspecific differences in drought-related mortality with fir showing the strongest effect followed by spruce and pine. This direct influence of climatic variability on differential tree mortality has the potential for driving large-scale changes in subalpine forests of the Rocky Mountains.     

Differential shading of branches or whole trees: survival, growth, and reproduction

This study compared the effects of shading individual branches or whole trees on the survival, growth and reproduction of branches of mountain birch [Betula pubescens ssp. czerepanovii (Orlova) Hämet-Ahti]. When a single branch was shaded its performance decreased drastically, while individual branches performed relatively well if the whole tree was shaded. For instance, after two summers 90% of the individually shaded branches were dead, while none of the study branches died following shading of entire trees. These results indicate that the fate of a branch depended more on shading-induced asymmetric competition among branches than on the shading itself. Furthermore, the increased growth of non-shaded branches in the trees where only two branches were shaded suggests that resources were preferentially allocated to branches in more favorable positions. Branch autonomy may promote environmental screening and growth towards favorable directions, optimizing the use of available light resources. In addition, branch autonomy may buffer the genet against environmental hazards, thus increasing the fitness of the genet at the cost of an increased mortality for individual modules.     

Comparisons of mountain pine beetle (Dendroctonus ponderosae Hopkins) reproduction within a novel and traditional host: effects of insect natal history,colonized host species and competitors

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