A method for estimating light interception by a conifer shoot

We present an operational method for estimating the amount of PAR intercepted by a coniferous shoot. Interception of PAR by a shoot is divided into three components: the amount of radiation coming from the sky, the transmission of radiation through the surrounding vegetation, and the shoot' s silhouette area facing the direction of the incoming radiation. All three components usually vary with direction. Radiation incident from the sky consists of direct and diffuse radiation. The well-known equation of motion for the sun and Beer' s Law for atmospheric transmittance are used to simulate the directional distribution of direct sunlight for any given period of time. The diffuse component is assumed to be uniform. Meteorological field measurements are used to calibrate the absolute amounts of the direct and diffuse components. The gap fraction (proportion of visible sky) in different directions around a shoot is measured by analyzing a hemispherical fish-eye photograph, taken at the location of the shoot, with an image processing program. Similarly, the shoot silhouette area (SSA) is measured by photographing the shoot from many different directions. The measurements of SSA are interpolated by a method called trigonometric interpolation to obtain the directional distribution of SSA over the entire hemisphere. This distribution is then rotated according to the shoot' s position in the canopy. Multiplying incoming PAR, canopy gap fraction and SSA in different directions, and summing over all directions, gives an estimate of PAR intercepted by the shoot during the chosen period of time. The method is described step by step, and applied, as an example, to a shoot from a Scots pine (Pinus sylvestris L.) stand in central Finland. Differences in radiation interception properties between sun and shade shoots and their relevance to canopy-scale models are discussed.     

Structural scaling of light interception efficiency in Picea engelmannii and Abies lasiocarpa

Sunlight interception efficiency was compared at the leaf, shoot, branch and crown levels for Picea engelmannii (Parry) and Abies lasiocarpa ((Hook.) Nutt.), dominant tree species of the central Rocky Mountains, USA. The ratio of silhouette to total leaf area (STAR) was used to quantify the efficiency of direct-beam sunlight interception at each structural scale. Total mean reductions in STAR from the leaf to the crown level were 0.39 to 0.06 in P. engelmannii and 0.46 to 0.02 in A. lasiocarpa. These reductions in STAR occurred for both species as structural scale increased due to a more upright leaf inclination, increased leaf twisting and curvature, or greater mutual shading among plant structures. A steeper leaf inclination between the leaf and shoot level accounted for 26 +/- 19% (95% C.I.) of the total leaf-to-crown STAR reduction; mutual shading among leaves on shoots caused a 14 +/- 7% reduction, whereas leaf curvature and twisting accounted for 22 +/- 3% for a total reduction of 62 +/- 8%. The STAR varied slightly from the shoot to the branch level (+/- 7%) except for a 26% reduction in shade shoots of A. lasiocarpa as a result of increased mutual shading among leaves at lateral nodes. Another substantial reduction in STAR occurred from the branch to the crown level (35 +/- 3% of total) as a result of shading of one branch layer by another within the crown. Thus, light interception efficiency decreased as structural scale increased in both species, especially from the leaf to the shoot level and from the branch to the crown level.     

Summary models for light interception and light-use efficiency of non-homogeneous canopies

The application of detailed models of canopy photosynthesis rely on the estimation of attenuation of light in the canopy. This attenuation is readily estimated with the Lambert-Beer law when the canopy is homogeneous. In reality, forest canopies are far from homogeneous, and this has led to the use of detailed light extinction models that account for grouping of foliage between and within trees. Because such models require detailed parameterization and fine resolution inputs, they are impractical in larger-scale applications. Thus, there is interest in simplified models that can be readily parameterized. We developed two equations that can be used to estimate mean annual light interception by single unshaded trees and by stands of Poisson distributed trees. Interception by single trees is a function of crown surface area, the ratio of leaf area to crown surface area, the extinction coefficient in a homogeneous canopy--which can be determined separately--and one empirical parameter that depends on the mean solar angle. The summary model was tested against a detailed model of interception, and showed good agreement, although with slight bias. The results showed that crown surface area is a good summary variable for crown size and shape, because errors are independent of crown shape (ellipsoids, cones and height:width ratios). We also tested whether canopy photosynthesis is proportional to light interception across canopies differing in structure and leaf area index, and found that light-use efficiency is influenced by canopy structure. The model is useful in larger-scale applications because it can be parameterized with available data without the need for additional empirical parameters. It can also be used to study the effect of stand structure on mean annual light interception and productivity.     

Photosynthetic nitrogen-use efficiency in evergreen broad-leaved woody species coexisting in a warm-temperate forest

Photosynthetic nitrogen-use efficiency (PNUE, photosynthetic capacity per unit leaf nitrogen) varies among species from different habitats and correlates with several ecological characteristics such as leaf life span and leaf mass per area. We investigated eight evergreen broad-leaved woody species with different leaf life spans that coexist in a warm-temperate forest. We determined photosynthetic capacity at ambient CO(2) concentration in saturated light, nitrogen concentration, and the concentration of ribulose-1,5-bisphosphate carboxylase (RuBPCase), a key enzyme of photosynthesis and the largest sink of nitrogen in leaves. Each species showed a strong correlation between photosynthetic capacity and RuBPCase concentration, and between RuBPCase concentration and nitrogen concentration. Photosynthetic capacity of leaves decreased with increasing leaf life span, whereas PNUE did not correlate significantly with leaf life span. There was a twofold variation in PNUE among species. This relatively small variation in PNUE is consistent with the argument that species that coexist in a single habitat maintain a similar PNUE. The two components of PNUE-photosynthetic rate per unit RuBPCase and RuBPCase per unit leaf nitrogen-were not significantly correlated with other leaf characteristics such as leaf life span and leaf mass per area. We conclude that differences in PNUE are relatively small among coexisting species and that differences in absolute amounts of photosynthetic proteins lead to differences in photosynthetic productivity among species.     

Physiological responses to water stress and waterlogging in Nothofagus species

Gas exchange and water relations were investigated in Nothofagus solandri var. cliffortioides (Hook. f.) Poole (mountain beech) and Nothofagus menziesii (Hook. f.) Oerst (silver beech) seedlings in response to water stress and waterlogging. At soil matric potentials (Psi(soil)) above -0.005 MPa, N. solandri had significantly higher photosynthetic rates (A), and stomatal and residual conductances (g(sw) and g(rc)), and lower predawn xylem water potentials (Psi(predawn)) than N. menziesii. The relative tolerance of plants to water stress was defined in terms of critical soil matric potential (Psi(cri)) and lethal xylem water potential (Psi(lethal)). The estimated values of Psi(cri) and Psi(lethal) were -1.2 and -7 MPa, respectively, for N. solandri, and -0.7 and -4 MPa, respectively, for N. menziesii. Photosynthesis was sustained to a xylem water potential (Psi(xylem)) of -7 MPa in N. solandri compared with -4 MPa in N. menziesii. Following rewatering, both A and Psi(xylem) recovered quickly in N. solandri, whereas the two variables recovered more slowly in N. menziesii. During the development of water stress, nonstomatal inhibition significantly affected A in both N. solandri and N. menziesii. Nothofagus menziesii was more susceptible to inhibition of A by waterlogging than N. solandri. However, the tolerance of N. solandri to severe waterlogging was also limited as a result of a failure to form adventitious roots, suggesting a lack of adaptation to these conditions. The differences in tolerance to water stress and waterlogging between the two species are consistent with the distribution patterns of N. solandri and N. menziesii in New Zealand.     

Petiole length and biomass investment in support modify light interception efficiency in dense poplar plantations

Leaf architecture, stand leaf area index and canopy light interception were studied in 13 poplar clones growing in a second rotation of a coppice plantation, to determine the role of leaf architectural attributes on canopy light-harvesting efficiency and to assess biomass investment in leaf support tissue. Stand leaf area index (L) varied from 2.89 to 6.99, but L was only weakly associated with canopy transmittance (TC). The weak relationship between TC and L was a result of a higher degree of foliage aggregation at larger values of L, leading to lower light-interception efficiency in stands with greater total leaf area. We observed a strong increase in leaf aggregation and a decrease in light-harvesting efficiency with decreasing mean leaf petiole length (PL) but not with leaf size, possibly because, in cordate or deltoid poplar leaves, most of the leaf area is located close to the petiole attachment to the lamina. Although PL was the key leaf characteristic of light-harvesting efficiency, clones with longer petioles had larger biomass investments in petioles, and there was a negative relationship between PL and L, demonstrating that enhanced light harvesting may lead to an overall decline in photosynthesizing leaf surface. Upper-canopy leaves were generally larger and had greater dry mass (MA) and nitrogen per unit area (NA) than lower-canopy leaves. Canopy plasticity in MA and NA was higher in clones with higher foliar biomass investment in midrib, and lower in clones with relatively longer petioles. These relationships suggest that there is a trade-off between photosynthetic plasticity and biomass investment in support, and also that high light-harvesting efficiency may be associated with lower photosynthetic plasticity. Our results demonstrate important clonal differences in leaf aggregation that are linked to leaf structure and biomass allocation patterns within the leaf.     

An analysis of light effects on foliar morphology,physiology, and light interception in temperate deciduous woody species of contrasting shade tolerance

Maximum Rubisco activities (V(cmax)), rates of photosynthetic electron transport (J(max)), and leaf nitrogen and chlorophyll concentrations were studied along a light gradient in the canopies of four temperate deciduous species differing in shade tolerance according to the ranking: Populus tremula L. < Fraxinus excelsior L. < Tilia cordata Mill. = Corylus avellana L. Long-term light environment at the canopy sampling locations was characterized by the fractional penetration of irradiance in the photosynthetically active spectral region (I(sum)). We used a process-based model to distinguish among photosynthesis limitations resulting from variability in fractional nitrogen investments in Rubisco (P(R)), bioenergetics (P(B), N in rate-limiting proteins of photosynthetic electron transport) and light harvesting machinery (P(L), N in chlorophyll and thylakoid chlorophyll-protein complexes). On an area basis, V(cmax) and J(max) (V(a) (cmax) and J(a) (max)) increased with increasing growth irradiance in all species, and the span of variation within species ranged from two (T. cordata) to ten times (C. avellana). Examination of mass-based V(cmax) and J(max) (V(m) (cmax) and J(m) (max)) demonstrated that the positive relationships between area-based quantities and relative irradiance mostly resulted from the scaling of leaf dry mass per area (M(A)) with irradiance. Although V(m) (cmax) and J(m) (max) were positively related to growth irradiance in C. avellana, and J(m) (max) was positively related to irradiance in P. tremula, the variation range was only a factor of two. Moreover, V(m) (cmax) and J(m) (max) were negatively correlated with relative irradiance in T. cordata. Rubisco activity in crude leaf extracts generally paralleled the gas-exchange data, but it was independent of light in T. cordata, suggesting that declining V(m) (cmax) with increasing relative irradiance was related to increasing diffusive resistances from the intercellular air spaces to the sites of carboxylation in this species. Because irradiance had little effect on foliar nitrogen concentration, the relationships of P(B) and P(R) with irradiance were similar to those of V(m) (cmax) and J(m) (max). Shade-intolerant species tended to have greater P(B) and P(R) and also larger V(a) (cmax) and J(a) (max) than more shade-tolerant species. However, for the whole material, P(B) and P(R) varied only about 50%, whereas V(a) (cmax) and J(a) (max) varied more than 15-fold, further emphasizing the importance of leaf anatomical plasticity in determining photosynthetic acclimation to high irradiance. Leaf chlorophyll concentrations and fractional nitrogen investments in light harvesting increased hyperbolically with decreasing irradiance to improve quantum use efficiency for incident irradiance. The effect of irradiance on P(L) was of the same order as its effect in the opposite direction on M(A), leading to either a constant model estimate of leaf absorptance with I(sum) or a slightly positive correlation. We conclude that leaf morphological plasticity is a more relevant determinant of foliage adaptation to high irradiance than foliage biochemical properties, whereas biochemical adaptation to low irradiance is of the same magnitude as the anatomical adjustments. Although shade-tolerant species did not have greater chlorophyll concentrations and P(L) than shade-intolerant species, they possessed lower M(A), and could maintain a more extensive foliar display for light capture with constant biomass investment in leaves.     

Root architecture in relation to tree-soil-crop interactions and shoot pruning in agroforestry

Desirable root architecture for trees differs between sequential and simultaneous agroforestry systems. In sequential systems extensive tree root development may enhance nutrient capture and transfer to subsequent crops via organic pools. In simultaneous systems tree root development in the crop root zone leads to competition for resources.Fractal branching models provide relationships between proximal root diameter, close to the tree stem, and total root length or surface area. The main assumption is that a root branching proportionality factor is independent of root diameter. This was tested in a survey of 18 multipurpose trees growing on an acid soil in Lampung (Indonesia). The assumption appeared valid for all trees tested, for stems as well as roots. The proportionality factor showed a larger variability in roots than in stems and the effects of this variabilily should be further investigated. A simple index of tree root shallowness is proposed as indicator of tree root competitiveness, based on superficial roots and stem diameter.Pruning trees is a major way to benefit from tree products and at the same time reduce above-ground competition between trees and crops. It may have negative effects, however, on root distribution and enhance below-ground competition. In an experiment with five tree species, a lower height of stem pruning led to a larger number of superficial roots of smaller diameter, but had no effect on shoot:root ratios or the relative importance of the tap root.     

Differential photosynthetic and survival responses to soil drought in two evergreen Nothofagus species

We asked if differences in distribution between Nothofagus nitida and N. dombeyi were associated with differences in drought tolerance. Survival, gas exchange and chlorophyll fluorescence were measured on seedlings subjected to a gradual drought. At a predawn leaf water potential (Ψ_m) of ?2.7 MPa, survival of N. nitida was 50%, compared to 100% in N. dombeyi. Under well-watered conditions, the two species displayed similar stomatal conductance (g _w ) and transpiration (E), but net photosynthesis (A) and instantaneous water-use efficiency (WUE _i ) were slightly higher in N. nitida. A, E and g _w declined in N. nitida along the gradual drought but increased in N. dombeyi at a Ψ_m between ?1.5 and ?2.5 MPa, and declined then drastically at a Ψ_m below < ?2.5 MPa. As N. dombeyi was able to maintain A at higher levels despite declining g _w , this species displayed significantly increased WUE _i at Ψ_m below ?2.5 MPa. Photochemical efficiency of PSII in the light (ΔF/Fmr) and photochemical quenching (qP) were always lower in N. nitida and along with the photochemical efficiency in the dark (Fv/Fm) they declined in both species. Non-photochemical quenching (NPQ) increased slowly in N. dombeyi along with the gradual drought, whilst it decreased in N. nitida. These results show that differences in drought tolerance are in agreement with sorting of Nothofagus species along moisture gradients in south-central Chile.     

Estimation of light interception properties of conifer shoots by an improved photographic method and a 3D model of shoot structure

The spherical mean of the shoot silhouette-to-total leaf area ratio (STAR) and the shoot transmission coefficient (c) are two key structural parameters in radiative transfer models for calculating canopy photosynthesis and leaf area index. The standard optical method for estimating these parameters might introduce errors in the estimates for species with flexible shoots and needles by changing shoot inclination relative to its inclination in situ. We devised and tested two methods to address this problem. First, we modified the standard optical method by designing an apparatus that allows shoots to be photographed in their original orientation. Second, we developed a faster, model-based approach to replace photography and tested the results against the established approach. We used shoots of three pine species, Pinus echinata Mill. (needle length ~50 mm), P. taeda L. (~150 mm) and P. palustris Mill. (~300 mm). Values of the parameters simulated by the model were similar to those measured from the photographs. In our data, STAR varied about twofold among the pine species and was ~40% higher in shade shoots than in sun shoots of P. taeda. The transmission coefficient for P. taeda shade shoots was also ~40% higher than that of sun shoots of all three species. We tested the versatility of the model by employing it on shoots of two other pine species (P. strobus L. and P. thumbergiana Parl.) as well as on shoots of Tsuga canadensis L. Carr. and Picea pungens Engelm. Regardless of shoot characteristics, the model generated values of shoot structural parameters similar to those estimated with the optical method. Although species-specific and vertical gradients in parameter values are best for modeling radiative transfer in conifer canopies, our results suggest that, in the absence of adequate data, STAR can be approximated as 0.16 for a wide range of shoot structures. For applications requiring angle-dependent parameterization, our new model facilitates rapid generation of these radiative transfer parameters.     

Colonization of Two Nothofagus species by Lepidoptera in Southern Britain

Between 1975 and 1982 a study was made of the invertebrate faunacolonizing two deciduous species of southern beech, Nothofagusobliqua and N. procera, introduced into Britain from South America.Special attention was paid to the folivorous larvae of Lepidopterawhich were sampled at 15 localities in southern England, mostlyin Forestry Commission trial plots and arboreta in Gloucestershire. The literature describing the native insect fauna of Nothofagusin Chile and Argentina is briefly reviewed. Mention is alsomade of the few previous records of lepidopterous larvae observedfeeding on Nothofagus in Britain. The larvae of 81 species Lepidoptera are recorded from Nothofagus.Seventy-eight of these were feeding on the foliage, of which73 were found on N. procera and 62 on N. obliqua, although approximately62 per cent of all the larvae collected were from N. obliqua.Faunal differences between the sites studied are briefly described.Two additional species of cutworm larvae are also reported attackingthe roots of Nothofagus seedlings. The changing lepidopterous fauna on Nothofagus from May untilSeptember is described and discussed. Spring-feeding larvaeof Operophtera brumata (L.), Agriopis aurantiaria (Hübn.)and Erannis defoliaria (Clerck) comprised 55 per cent of alllarvae collected on the two hosts, and represented between 68per cent and 87 per cent of those larvae in beating samplescollected in late May and early June. Most of the larvae collected were reared to adult in the laboratoryon a diet of Nothofagus leaves. The majority of these are regardedas polyphagus species although 64 are known to have one of thetwo native Quercus as a host-plant, while 24 have been recordedas feeding on Fagus sylvatica. The relevance of these two generaas sources for the Lepidoptera fauna colonizing Nothofagus isdiscussed. Nothofagus obliqua and N. procera are shown to have acquireda substantial lepidopterous fauna since their introduction intoBritain near the beginning of this century, although most ofthe trees sampled were less than 25 years old. These two speciesof Nothofagus may be vulnerable to defoliation by several speciesof caterpillar, especially if planted as monocultures in areaswhere oak and beech are plentiful. However, their surprisinglylarge insect fauna may be seen to have some value for natureconservation purposes.     

油茶截枝复壮产量效益评价

为研究老龄化油茶截枝复壮产量效益,以'赣州油'系列50 a树龄油茶为研究对象,分年度和品种进行主干100～120 cm处截枝处理,截口涂抹林木长效保护剂和凡士林进行防病保水,以未截枝作对照组.连续跟踪调查截枝组和未截枝组产量,记录投入和产出数据,2020年测定截枝组和未截枝组单果特征.截枝后3 a开始有收成,鲜果产量达228.80 kg·667m-2,与未截枝处理相当,截枝后5年进入盛产.截枝对油茶果实性状影响比较明显,截枝后果实性状明显高于未截枝油茶;不同品种的果实性状对截枝的反映效果基本一致,'GLS赣州油1号'赣州油1号'和'赣州油7号'的单果鲜重、果实横径、出籽率、出油率等均比未截枝处理高;截枝后树体病虫害发生率下降;截枝后第4年回本,第5年进入高产,收入保持在4000元·667m-2以上.截枝复壮是一项切实有效的油茶低产林改造技术,能够短期内提高油茶产量和茶果质量,并且改造投入不高,后期收益可观.     

Explaining growth of individual trees: Light interception and efficiency of light use by Eucalyptus at four sites in Brazil

The growth of wood in trees and forests depends on the acquisition of resources (light, water, and nutrients), the efficiency of using resources for photosynthesis, and subsequent partitioning to woody tissues. Patterns of efficiency over time for individual trees, or between trees at one time, result from changes in rates photosynthesis and shifts in the relative partitioning to wood. We measured the production ecology (stem growth, light interception, and light use efficiency) to explain patterns of growth among trees within plots through stand development, and tested three hypotheses: (1) dominant trees have higher light use efficiency than subordinate trees; (2) lower variation in the size distribution of trees within plots allows higher light use efficiency; and (3) uniform stand structure and high light use efficiency reduce the age-related decline in tree growth. The experiment used clonal plantations of Eucalyptus at four locations in eastern Brazil. Irrigation and fertilization treatments ensured the major resource limitation for tree growth would be light supply. The influence of variation in the sizes of trees within plots was tested by comparing plots with all trees planted in a single day (uniform treatment) with plots where planting was spread over 80 days (heterogeneous treatment). Light interception per tree was simulated with the MAESTRA model. Across sites, treatments and whole-rotation stand development, dominant trees showed higher rates of stem growth, light interception, and light use efficiency than subordinate trees (supporting the first hypothesis). For example, dominant trees (80th percentile rank) at the end of the rotation grew four-times faster than suppressed trees (20th percentile rank), as a result of 2.1-fold greater light interception, and 1.8-fold greater stem growth per unit of light interception. In some cases, greater variation among tree sizes within plots led to lower efficiency of light use by average-size trees, providing mixed evidence for the second hypothesis. Greater uniformity of sizes of trees within plots did not substantially mitigate the decline in stem growth from mid-rotation to the end of the rotation, refuting the third hypothesis. The high efficiency of dominant trees underscores the marginal contribution of subordinate trees to total stand growth, and should spur further work on thinning to increase growth and lengthen rotations for dominant trees.     

燕山北部山地人工针叶林及天然阔叶林植被层的降水截留量研究

为了比较人工针叶林及天然阔叶林对降水的调控作用,利用泡枝法对燕山北部山地落叶松人工林及天然次生杨桦林植被层对降水的截留量进行了比较。研究结果表明:在各个年龄阶段,落叶松乔木林冠截留量都高于天然次生杨桦林。落叶松人工林幼龄林、中龄林、近熟林乔木林冠截留量分别为0.44mm、0.74mm、0.69mm,杨桦林则分别为0.25mm、0.33mm、0.49mm;但落叶松人工林灌木的截留量低于天然次生杨桦林;华北落叶松人工林植被层总截留量高于天然次生杨桦林,分别是0.48mm、0.78mm、0.74mm。随着林龄的增加,杨桦林林冠截留量有逐渐增加的趋势,幼龄林、中龄林、近熟林分别为0.41 mm、0.38 mm、0.76mm;但落叶松林到达近熟林时林冠截留量却有所下降。     

Changes during early development in photosynthetic light acclimation capacity explain the shade to sun transition in Nothofagus nitida

Nothofagus nitida (Phil.) Krasser, an emergent tree of the Chilean evergreen forest, regenerates under the canopy. Nonetheless, it is common to find older saplings in clear areas. We hypothesized that this transition from shade to sun during the early developmental stages is made possible by an ontogenetic increase in the light acclimation capacity of photosynthesis. To test our hypothesis, we studied photosynthetic performance and photoprotection in N. nitida saplings at different developmental stages corresponding with three different height classes (short: 16.2 cm; medium-height: 48.0 cm; and tall: 73.7 cm) grown under contrasting light conditions (photosynthetic photon flux (PPF) of 20, 300 or 600 micromol m(-2) s(-1)) until newly expanded leaves had developed. Light-saturated CO(2) assimilation rate and light compensation and saturation points increased with increasing PPF. Medium-height and tall saplings acclimated to high light had higher electron transport rates and higher proportions of open Photosystem II reaction centers than shorter plants acclimated to high light. Short saplings showed higher thermal dissipation and contents of xanthophylls than taller saplings. Only medium-height and tall saplings acclimated to high light recovered after photoinhibition. State transitions were higher in short plants growing in low light, and decreased with plant height and growth irradiance. Thus, during development, N. nitida changes the balance of light energy utilization and photoprotective mechanisms, supporting a phenotypic transition from shade to sun during its early ontogeny.     

The trade-off between safety and efficiency in hydraulic architecture in 31 woody species in a karst area

Karst topography is a special landscape shaped by the dissolution of one or more layers of soluble bedrock, usually carbonate rock such as limestone or dolomite. Due to subterranean drainage, overland flow, extraction of water by plants and evapotranspiration, there may be very limited surface water. The hydraulic architecture that plants use to adapt to karst topography is very interesting, but few systematic reports exist. The karst area in southwestern China is unique when compared with other karst areas at similar latitudes, because of its abundant precipitation, with rainfall concentrated in the growing season. In theory, resistance to water-stress-induced cavitation via air seeding should be accompanied by decreased pore hydraulic conductivity and stem hydraulic conductivity. However, evidence for such trade-offs across species is ambiguous. We measured the hydraulic structure and foliar stable carbon isotope ratios of 31 karst woody plants at three locations in Guizhou Province, China, to evaluate the functional coordination between resistance to cavitation and specific conductivity. We also applied phylogenetically independent contrast (PIC) analysis in situations where the inter-species correlations of functional traits may be biased on the potential similarity of closely related species. The average xylem tension measurement, at which 50% of hydraulic conductivity of the plants was lost (Ψ(50)), was only -1.27 MPa. Stem Ψ(50) was positively associated with specific conductance (K(s)) (P?相似文献   

9个阔叶树种在桂中地区的适应性调查与分析

为筛选适合广西桂中地区种植的阔叶树,选择9个阔叶树种在桂中地区开展种植试验研究,4年生时测定其树高、胸径、冠幅、保存率等生长指标.结果表明:不同树种的保存率存在显著性差异,黑金丝柚木、交趾黄檀、鸡翅木和黑木相思4种树种的保存率较高,对试验区的环境适应能力较强;小叶红豆、灰木莲保存率较低,适应能力较差.不同树种的树高、胸径、冠幅、保存率存在极显著性差异,通过系统聚类分析,可分为3个类群,A类群包含大花序桉、黑木相思和鸡翅木,生长较为迅速;B类群包含交趾黄檀、大果紫檀、白桂木、灰木莲和黑金丝柚木,生长速度中等;C类群包含小叶红豆,生长较为缓慢.综合评价:黑木相思生长速度快、保存率高、适应性强,适合在桂中地区推广种植;小叶红豆生长速度较慢、适应性较差,不宜大面积推广种植.     

Low light acclimation in five temperate broad-leaved tree species of different successional status: the significance of a shade canopy

?Context

Tree species differ largely in their capability to produce characteristic shade leaves with effective morphological and physiological acclimation to low light.

?Aims

By examining the sun/shade leaf differentiation in leaf morphology, foliar nitrogen and photosynthetic capacity in five temperate tree species of different successional status, we aimed at identifying those leaf traits that determine the development of a typical shade crown with low light-acclimated leaves.

?Methods

Leaf morphology, foliar N content, photosynthetic capacity (V _cmax, J _max and A _max) and leaf dark respiration (R _d) were measured in the canopies of 26 adult trees of Fraxinus, Acer, Carpinus, Tilia and Fagus species.

?Results

Six traits (the sun/shade leaf differentiation in specific leaf area, leaf size, A _max per leaf area or per mass, photosynthetic N use efficiency and R _d) were found to characterise best the degree of low light acclimation in shade leaves. All five species exhibited certain modifications in leaf morphology and/or physiology in response to low light; Fagus sylvatica showed the highest and Fraxinus excelsior the lowest shade leaf acclimation.

?Conclusions

Our results indicate that the five early/mid- to late-successional species have developed species-specific low light acclimation strategies in their shade crowns which differ in terms of the relative importance of leaf morphological and physiological acclimation.     

Vessel length distribution in the stems of three New Zealand species of Nothofagus

Summary A modification of the Zimmermann and Jeje (1981) latex paint infusion technique was utilized to determine vessel length distributions in N. fusca (Hook.f.) Oerst., N. menziesii (Hook.f.) Oerst. and N. solandri var. cliffortioides (Hock.f.) Poole. In all thirty trees examined, the majority of vessels were less than 2 cm long; with 97% of the vessels shorter than 6 cm in N. menziesii and N. solandri, with the same percentage being shorter than 8 cm in N. fusca. The longest individual vessels recorded were 24 cm for N. menziesii, 22 cm for N. solandri and 33 cm for N. fusca. The longest vessels in all three species occurred in the earlywood and also exhibited the largest diameters.     

9个阔叶树种在桂中地区的适应性调查与分析

为筛选适合广西桂中地区种植的阔叶树,选择9个阔叶树种在桂中地区开展种植试验研究,4年生时测定其树高、胸径、冠幅、保存率等生长指标.结果表明:不同树种的保存率存在显著性差异,黑金丝柚木、交趾黄檀、鸡翅木和黑木相思4种树种的保存率较高,对试验区的环境适应能力较强;小叶红豆、灰木莲保存率较低,适应能力较差.不同树种的树高、胸径、冠幅、保存率存在极显著性差异,通过系统聚类分析,可分为3个类群,A类群包含大花序桉、黑木相思和鸡翅木,生长较为迅速;B类群包含交趾黄檀、大果紫檀、白桂木、灰木莲和黑金丝柚木,生长速度中等;C类群包含小叶红豆,生长较为缓慢.综合评价:黑木相思生长速度快、保存率高、适应性强,适合在桂中地区推广种植;小叶红豆生长速度较慢、适应性较差,不宜大面积推广种植.