Assessing forest structure and function from spectral transmittance measurements: a case study in a Mediterranean holm oak forest

Annual changes in structural attributes and seasonal dynamics in water content, photosynthetic rate and light-use efficiency (LUE) were assessed by spectral transmittance for 4 years (1999-2003) in six stands of a Mediterranean holm oak forest. Green biomass, total biomass and leaf area index (LAI) were determined. In 1999, seasonal dynamics of net carbon dioxide (CO2) exchange and water content were measured. We recorded photosynthetically active radiation (PAR) transmittance and hyperspectral transmittance in the 400-1100 nm region and derived reflectance-based vegetation indices. Transmittance over the PAR region derived from either ceptometer or spectroradiometer measurements (PART and TPAR, respectively) was related to green and total biomass. Both PART and TPAR were also related to LAI (r=0.79 and r=0.70, respectively, P <0.001) and were appropriate for comparison among stands, whereas subtle changes in LAI within a stand were better assessed by the transmittance amplitude in the red edge region (TRE) (within a stand, r=0.77-0.99, P <0.001). Spectral transmittance-based indices successfully captured physiological processes that occurred on temporal (seasonal) and spatial scales. The transmittance-based water index (TWI) was related to both foliage and canopy water content (r=0.69, P <0.001). Estimates of foliage and canopy water content improved in dense (closed) stands (r=0.84 and r=0.87, respectively, P <0.001) compared with low-density stands. Under non-drought conditions, transmittance-based photochemical reflectance index (TPRI) was related to LUE (r=0.58, P <0.05) and net CO2 exchange (r=0.72, P <0.01), and the combined TPAR x TPRI index greatly improved these relationships (r=0.93 and r=0.84, respectively, P <0.01), indicating that both structural and physiological adjustments modified CO2 fixation capacity in these forest stands. Our novel approach to the study of transmitted radiation provides a tool for estimating structural and functional variables such as LAI, LUE and water content, which are key determinants of terrestrial productivity.     

Estimating above-ground biomass by fusion of LiDAR and multispectral data in subtropical woody plant communities in topographically complex terrain in North-eastern Australia

We investigated a strategy to improve predicting capacity of plot-scale above-ground biomass （AGB） by fusion of LiDAR and Land- sat5 TM derived biophysical variables for subtropical rainforest and eucalypts dominated forest in topographically complex landscapes in North-eastern Australia. Investigation was carried out in two study areas separately and in combination. From each plot of both study areas, LiDAR derived structural parameters of vegetation and reflectance of all Landsat bands, vegetation indices were employed. The regression analysis was carded out separately for LiDAR and Landsat derived variables indi- vidually and in combination. Strong relationships were found with LiDAR alone for eucalypts dominated forest and combined sites compared to the accuracy of AGB estimates by Landsat data. Fusing LiDAR with Landsat5 TM derived variables increased overall performance for the eucalypt forest and combined sites data by describing extra variation （3% for eucalypt forest and 2% combined sites） of field estimated plot-scale above-ground biomass. In contrast, separate LiDAR and imagery data, andfusion of LiDAR and Landsat data performed poorly across structurally complex closed canopy subtropical minforest. These findings reinforced that obtaining accurate estimates of above ground biomass using remotely sensed data is a function of the complexity of horizontal and vertical structural diversity of vegetation.     

A theoretical analysis of the influence of heterogeneity in chlorophyll distribution on leaf reflectance

Attempts to determine the vitality of vegetation and to detect vegetation stress from remotely sensed data have focused on chlorophyll concentration, because it influences the reflectance of vegetation and tends to correlate with vegetation health and stress. Pollution, pathogens and pests can cause localized regions of chlorosis and necrosis across a leaf surface, but the extent to which these patches influence the overall reflectance and spectral signature of the leaf and canopy has not been tested. A conifer leaf model (LIBERTY), which simulates the influence of leaf biochemical concentrations of chlorophyll, water, lignin, cellulose and protein on the reflectance of leaves from 400 to 2500 nm, was used to determine the effect of patches of chlorosis on leaf reflectance. A fraction of the leaf f is assumed to be chlorotic with a chlorophyll concentration C(1). The remainder of the leaf has chlorophyll concentration C(2) such that mean leaf chlorophyll concentration, C(mean) = fC(1) + (1 - f)C(2), is constant for a range of f and C(1) values. LIBERTY can be used to estimate the reflectance of a leaf with a particular chlorophyll concentration at a particular wavelength R(lambda,C) (assuming other leaf properties remain constant), thus we can estimate the reflectance of the chlorotic leaf as fR(lambda,C(1))+ (1 - f)R(lambda,C(2)). The model indicated that small areas of chlorosis have a disproportionately large influence on overall leaf reflectance. For example, a leaf with 25% of its area chlorotic can have the same reflectance (400-700 nm) as a homogeneous leaf with 60% less chlorophyll. Thus, determination of chlorophyll concentration from remotely sensed data is prone to underestimation when chlorophyll is nonuniformly distributed. Hence, attempts to model leaf and canopy reflectance using radiative transfer models will need to consider how to incorporate nonuniform chlorophyll distribution.     

Shoot biomass growth is related to the vertical leaf nitrogen gradient in Salix canopies

Plant canopy optimization models predict that leaf nitrogen (N) distribution in the canopy will parallel the vertical light gradient, and numerous studies with many species have confirmed this prediction. Further, it is predicted that for a given canopy leaf area, a low vertical light extinction coefficient will promote rapid growth. Therefore, the ideal canopy of fast-growing plants should combine high leaf area index with a low light extinction coefficient; the latter being reflected in a flat vertical leaf N gradient throughout the canopy. Based on data from an experimental Salix stand (six varieties) grown on agricultural land in central Sweden, we tested the hypothesis that shoot growth is correlated with vertical leaf N gradient in canopies of hybrid willows bred for biomass production, which could have implications for Salix breeding. Tree improvement research requires screening of growth-related traits in large numbers of plants, but assessment of canopy leaf N gradients by chemical analysis is expensive, time-consuming and destructive. An alternative to analytical methods is to estimate leaf N gradients nondestructively with an optical chlorophyll meter (SPAD method). Here we provide a specific calibration for interpreting SPAD data measured in hybrid willows grown in biomass plantations on fertile agricultural land. Based on SPAD measurements, a significant and inverse relationship (r(2) = 0.88) was found between shoot biomass growth and vertical leaf N gradient across canopies of six Salix varieties.     

Imaging spectroscopy of foliar biochemistry in forestry environments

Remote sensing estimates of leaf biochemicals provide valuable information on ecosystem functioning, vitality and state at local to global spatial scales. This paper aims to give an overview of the state of the art of foliar biochemistry assessment in general and, where possible, attention is given to: (1) Eucalyptus forest environments, (2) use of hyperspectral remote sensing or imaging spectroscopy, and (3) the challenges towards operational application of such assessments. Estimation of foliar biochemicals has improved significantly from early broad-band sensor attempts, given the advent of hand-held, airborne and space-borne spectrometers. These instruments provide sensing in contiguous, narrow spectral bands in the visible to shortwave infrared, as compared to the small number of broad spectral bands provided by multispectral sensors. Chlorophyll, nitrogen, cellulose and lignin represent a sample of biochemicals that have been assessed successfully, particularly at leaf level and with varying success at the canopy scale. A major challenge is scaling of predictions of biochemicals from ground to airborne and ultimately space-borne levels. This entails development of algorithms that minimise the contributions of canopy structure, atmospheric conditions, sensor/illumination geometry and leaf water content variations. Some advances have been made in this direction including the derivation of new vegetation indices and the use of spectral transformations such as derivative analysis and continuum removal. Other studies have focused on developing physically based models, e.g. radiative transfer models (RTMs), which appear to be more robust when compared to statistical models. However, the application of RTMs needs to progress beyond the estimation of only chlorophyll and biochemicals in monoculture environments to other nutrients and adapted for more complex canopies. Furthermore, inversion techniques of these models need to be improved.     

Improving predictions of forest growth using the 3-PGS model with observations made by remote sensing

Measurements made by remote sensing can characterize the leaf area density and nitrogen/chlorophyll content of forest canopies, as well as maximum photosynthetic capacity and above-ground structure and biomass. Combining these with climate data estimated from relationships based on temperature measurements and using an appropriate process-based model, it is possible to calculate, with useful accuracy, carbon sequestration and wood production by different forest types covering large land areas. To broaden its application and reduce the need for detailed information on stand characteristics, a satellite-driven version of the model 3-PG, was developed. The 3-PGS model incorporates the major first-order physiological processes that determine forest growth, and the biophysical factors that affect and govern those processes. It incorporates remotely sensed estimates of seasonal variation in canopy light interception (fPAR) and includes physiological variables (stomatal conductance and canopy quantum efficiency) that can be estimated by remote-sensing measurements of factors that influence those variables. 3-PGS therefore provides a useful framework within which to evaluate how data from the array of airborne and satellite-borne sensors now available might be used to initialize, drive, and test process-based growth models across regions with diverse soils and climates. We address the question: to what extent might additional remote-sensing techniques improve 3-PGS predictions?Sensitivity analyses indicate that model accuracy would be most improved through better estimates of seasonal changes in canopy photosynthetic capacity (α) and canopy conductance (G_c). Canopy photosynthetic capacity depends on the amount of light absorbed by the canopy, estimated as a fraction of photosynthetically active radiation (fPAR), and on foliage nitrogen or chlorophyll content, which can be estimated using multi-spectral imagery. G_c depends on canopy leaf area index (L) and stomatal conductance of the foliage (g_s), which is affected by the vapor pressure deficit of the air and soil water content. The onset and effects of drought can be determined from changes in canopy reflectance and fPAR identified from sequential measurements; the same measurements, coupled with calculations of evapotranspiration using climatic data and standard formulae, provide estimates of total available water in forest root zones. Periodic surveys with Light Detection and Ranging (LiDAR) and interferometric RADAR may serve to validate model predictions of above-ground growth (NPP_A), while progressive reduction in light-use efficiency (NPP_A/APAR) may identify forests with declining vigor that are likely to succumb to attack from insects and pathogens.     

3种木兰科植物叶片SPAD值的分布特征及其与叶绿素含量的关系

为探讨3种木兰科植物灰木莲Manglietia glauca、醉香含笑Michelia macclurei和乐昌含笑Michelia chapensis叶片SPAD值的分布特征及其与叶绿素含量之间的关系,采用SPAD叶绿素计和分光光度法分别测定了三者叶片SPAD值和叶绿素含量.结果表明:3种植物叶片SPAD值的差异主要...     

Conceptual Development of a Eucalypt Canopy Condition Index Using High Resolution Spatial and Spectral Remote Sensing Imagery

Abstract

Recent advances in remote sensing technologies and image analysis provide a realistic opportunity to develop a reliable, robust indicator of forest health for Australian eucalypt forests. Using these technologies we present the development of a conceptual framework for a new indicator based on eucalypt canopy condition. The indicator, termed the Eucalypt Canopy Condition Index (ECCI), is derived from an assumed hierarchy of canopy decline symptoms, both physiological and structural. Our objective is to identify and discuss possible combinations of spectral, radiometric and spatial (scale) features from remotely sensed data that theoretically and practically correlate with each hierarchical phase of severity in canopy decline. Some of the issues associated with the development and application of the ECCI are discussed, and finally, how the ECCI could be integrated into existing or future operational systems is illustrated.     

Use of thermal imaging to determine leaf conductance along a canopy gradient in European beech (Fagus sylvatica)

Using an infrared camera, we measured the leaf temperature across different canopy positions of a 23-m-tall deciduous forest tree (Fagus sylvatica L.) including typical sun and shade leaves as well as intermediate leaf forms, which differed significantly in specific leaf area (SLA). We calculated a temperature index (I(G)) and a crop water stress index (CWSI) using the surface temperatures of wet and dry reference leaves. Additional indices were computed using air temperature plus 5 °C (I(G)?+?5, CWSI?+?5) as dry references. The minimum temperature of the wet leaf and the maximum temperature of the dry leaf proved to be most suitable as reference values. We correlated the temperature indices with leaf area-related conductance to water vapor (g(L)) using porometry at the leaf level and using xylem sap flow at the branch level. At the leaf and at the branch level, I(G) and CWSI were equally well suited as proxies of g(L), whereas the relationships of I(G)?+?5 and CWSI?+?5 with g(L) were only weak or even insignificant. At the leaf level, the correlations of I(G) and CWSI with g(L) were significant in all parts of the crown. The slopes of g(L) vs. I(G) and CWSI did not differ significantly among the crown parts; this indicates that they were not influenced by SLA or irradiance. At the branch level, close correlations (r?>?0.8) were found between temperature indices and g(L) across the crown. These results demonstrate that satisfactory relationships between temperature indices and g(L) can be established in tall trees even in those canopy parts that are exposed to relatively low levels of irradiance and exhibit relatively low values of g(L).     

A model-based performance test for forest classifiers on remote-sensing imagery

Ambiguity between forest types on remote-sensing imagery is a major cause of errors found in accuracy assessments of forest inventory maps. This paper presents a methodology, based on forest plot inventory, ground measurements and simulated imagery, for systematically quantifying these ambiguities in the sense of the minimum distance (MD), maximum likelihood (ML), and frequency-based (FB) classifiers. The method is tested with multi-spectral IKONOS images acquired on areas containing six major communities (oak, pine, fir, primary and secondary high tropical forests, and avocado plantation) of the National Forest Inventory (NFI) map in Mexico. A structural record of the canopy and optical measurements (leaf area index and soil reflectance) were performed on one plot of each class. Intra-class signal variation was modelled using the Discrete Anisotropic Radiative Transfer (DART) simulator of remote-sensing images. Atmospheric conditions were inferred from ground measurements on reference surfaces and leaf optical properties of each forest type were derived from the IKONOS forest signal. Next, all forest types were simulated, using a common environmental configuration, in order to quantify similarity among all forest types, according to MD, ML and FB classifiers. Classes were considered ambiguous when their dissimilarity was smaller than intra-class signal variation.     

Morphological and physiological adjustment to N and P fertilization in nutrient-limited Metrosideros polymorpha canopy trees in Hawaii

Leaf-level studies of Metrosideros polymorpha Gaud. (Myrtaceae) canopy trees at both ends of a substrate age gradient in the Hawaiian Islands pointed to differential patterns of adjustment to both nutrient limitation and removal of this limitation by long-term (8-14 years) nitrogen (N), phosphorus (P) and N + P fertilizations. The two study sites were located at the same elevation, had similar annual precipitation, and supported forests dominated by M. polymorpha, but differed in the age of the underlying volcanic substrate, and in soil nutrient availability, with relatively low N at the young site (300 years, Thurston, Hawaii) and relatively low P at the oldest site (4,100,000 years, Kokee, Kauai). Within each site, responses to N and P fertilization were similar, regardless of the difference in soil N and P availability between sites. At the young substrate site, nutrient addition led to a larger mean leaf size (about 7.4 versus 4.8 cm2), resulting in a larger canopy leaf surface area. Differences in foliar N and P content, chlorophyll concentrations and carboxylation capacity between the fertilized and control plots were small. At the old substrate site, nutrient addition led to an increase in photosynthetic rate per unit leaf surface area from 4.5 to 7.6 micromol m(-2) s(-1), without a concomitant change in leaf size. At this site, leaves had substantially greater nutrient concentrations, chlorophyll content and carboxylation capacity in the fertilized plots than in the control plots. These contrasting acclimation responses to fertilization at the young and old sites led to significant increases in total carbon gain of M. polymorpha canopy trees at both sites. At the young substrate site, acclimation to fertilization was morphological, resulting in larger leaves, whereas at the old substrate site, physiological acclimation resulted in higher leaf carboxylation capacity and chlorophyll content.     

Effect of livestock grazing and human uses on herbaceous species diversity in oriental beech （Fagus orientalis Lipsky） forests,Guilan, Masal,northern Iran

Plant diversity plays key ecological roles in forest ecosystems, including influencing succession, resilience and nutrient cycling. This study was conducted to investigate the effect of livestock grazing and human uses on herbaceous species diversity. We surveyed 50 ha of protected area and 50 ha of unprotected area to evaluate herbaceous species diversity in oriental beech （Fagus orientalis Lipsky） forests in northern Iran. We calculated and compared three indices each of diversity and evenness, and species richness between the two areas. Herbaceous cover was higher in the unprotected area while leaf litter depth and tree canopy cover were higher in the protected area. The diversity indices, H （Shan- non-Wiener index ）, N~ （McArthur index）, N2 （Hill＇s index）, EQ （Modified Nee index）, E,ar （Smith-Wilson index）, E5 （modified index of Hill） and R=S （species richness） and species richness R=S were greater in the protected area than in the unprotected area, suggesting that protection from grazing results in increased numbers of plants and species. The effect of land protection on plant diversity was more pronounced for evenness than for species richness and the positive correlation between diversity and evenness indices was higher than that between diversity and richness.     

Leaf photosynthetic properties in a willow (Salix viminalis and Salix dasyclados) plantation in response to fertilization

Specific leaf area (SLA), nitrogen and chlorophyll concentrations and photosynthetic characteristics were studied in upper and lower canopy leaves of Salix viminalis and S. dasyclados grown at two nutrition levels. Fertilization increased SLA and leaf mass-based nitrogen concentration in most cases. Positive effects of fertilization on leaf light-saturated photosynthetic rate (A _max ^A ) and maximum carboxylation rate (V _cmax) were not detected. Significant differences between the leaves from upper and lower canopy layers in area-based nitrogen, A _max ^A , SLA, mass-based chlorophyll, V _cmax and stomatal conductance were found for most plots. We attempted to estimate the fraction of non-photosynthetic nitrogen and found that it tended to be higher due to fertilization. Thus, the insensitivity of leaf photosynthesis to fertilization could be caused by higher proportion of non-photosynthetic nitrogen in the leaves of fertilized plots. Though leaf-level photosynthesis was not increased by fertilization, considerably higher leaf area index of fertilized plots still resulted in increased canopy carbon gain.     

毛竹及其变种叶功能性状与影响因素

以毛竹、黄槽毛竹、花毛竹、厚壁毛竹、金丝毛竹为研究对象,分析比较其不同年龄立竹间叶功能性状特征,筛选主要叶功能性状指标,并探究影响毛竹及其变种叶功能性状的主要影响因子。结果表明:不同年龄毛竹及其变种叶功能性状存在差异,而竹种比年龄(1、3、5 a)对叶功能性状的影响程度大;主成分分析表明,影响毛竹及其变种叶功能性状的主要指标为叶全氮、叶全磷、叶绿素a、叶绿素b含量、叶绿素总量、比叶面积、叶含水量;叶全碳、叶全氮、叶全磷、叶绿素a、叶绿素b含量、叶绿素总量、叶面积、叶厚度、比叶面积、叶干物质含量、叶含水量、叶组织密度均与土壤养分呈显著相关。毛竹及其变种叶功能性状受土壤有效磷、全磷、碱解氮、有机质、全钾、速效钾含量的共同影响,其中有效磷、全磷、碱解氮含量是影响其叶功能性状的主要因子。叶养分元素(全氮、全磷)、叶绿素、叶形态性状(比叶面积、叶含水量)可作为毛竹及其变种筛选的主要叶功能性状指标,毛竹及其变种通过多性状间的功能协调形成最佳功能组合进而使其自身适应环境变化。     

黄金枸骨变色期的叶色与叶片光合色素含量关系研究

为研究黄金枸骨叶色在遮荫下变色的问题,通过盆栽试验,利用人工遮荫使叶色变化,观测叶色转变期的色素变化。结果表明:叶色由黄变绿的过程中,叶色参数L,a,b值显著下降(P<0.05),花色素苷含量呈显著上升的趋势(P<0.05);叶色、叶绿素a、叶绿素b、总叶绿素和花色素苷之间呈显著正相关性(P<0.05),类胡萝卜素与其他指标为负相关性,说明这些指标的变化最终决定或影响了叶色的变化。通过分析各生理指标的变化情况,发现黄金枸骨叶色转变的根本原因是叶绿素与类胡萝卜素比值的变化,叶片中叶绿素含量增多,提高了叶绿素与类胡萝卜素的比值,使叶色变绿。     

Why does leaf nitrogen decline within tree canopies less rapidly than light? An explanation from optimization subject to a lower bound on leaf mass per area

A long-established theoretical result states that, for a given total canopy nitrogen (N) content, canopy photosynthesis is maximized when the within-canopy gradient in leaf N per unit area (N(a)) is equal to the light gradient. However, it is widely observed that N(a) declines less rapidly than light in real plant canopies. Here we show that this general observation can be explained by optimal leaf acclimation to light subject to a lower-bound constraint on the leaf mass per area (m(a)). Using a simple model of the carbon-nitrogen (C-N) balance of trees with a steady-state canopy, we implement this constraint within the framework of the MAXX optimization hypothesis that maximizes net canopy C export. Virtually all canopy traits predicted by MAXX (leaf N gradient, leaf N concentration, leaf photosynthetic capacity, canopy N content, leaf-area index) are in close agreement with the values observed in a mature stand of Norway spruce trees (Picea abies L. Karst.). An alternative upper-bound constraint on leaf photosynthetic capacity (A(sat)) does not reproduce the canopy traits of this stand. MAXX subject to a lower bound on m(a) is also qualitatively consistent with co-variations in leaf N gradient, m(a) and A(sat) observed across a range of temperate and tropical tree species. Our study highlights the key role of constraints in optimization models of plant function.     

Differentiation among effects of nitrogen fertilization treatments on conifer seedlings by foliar reflectance: a comparison of methods

Analysis of reflectance can be used to estimate foliar concentrations of photosynthetic pigments, thus providing information on the physiological status of green plants. We compared several methods of reflectance analysis for the capacity to differentiate among effects of fertilization treatments across different irradiances on seedlings of Engelmann spruce (Picea engelmanii Parry ex Engelm.). Seedlings were grown in two light treatments (0 and 60% shade) and three nitrogen (N) treatments (10, 25 and 100 mg N l-1) for one growing season, after which foliar reflectance of the needles was measured. Five indices were tested: R550 (% reflectance at 550 nm); red edge position; the ratio R698:R760; the structure independent pigment index (SIPI); and the photochemical reflectance index (PRI). Both the light and nutrient treatments significantly affected foliar chlorophyll a and b and carotenoid concentrations. Among the indices tested, R550, red edge position and R698:R760 ratio were related to chlorophyll concentration, and were significantly affected by both light and N treatments. Both SIPI and PRI were related to chlorophyll and carotenoid concentrations. Among these relationships, PRI was affected by both treatments, whereas SIPI was sensitive to N treatment but not to light treatment. All five indices were weakly but significantly correlated with growth as measured by dry weight.     

Leaf distribution in large trees and stands of the floodplain forest in southern Moravia

Vertical distributions of leaf dry mass (M(d)) and leaf area (A(f)) were related to relative irradiance (I(r); I(r) above the stand = 1) in closed-canopy, old-growth stands of the floodplain forest in southern Moravia composed largely of Quercus, Fraxinus and Tilia species. Foliage area and mass at any given canopy height were converted to solar equivalent leaf area (A(s)) and mass (M(s)) by multiplying actual values at a given level in the canopy by the relative irradiance at that position. Stand leaf area index (LAI) was 5 (7 including shrub and herb layer), and solar equivalent parameters reached about 25% of that amount. In all species, vertical profiles of both relative irradiance and leaf dry mass to area ratio (LMA) were sigmoidal and the two variables were linearly related. The dominant, upper canopy species had a larger proportion of solar equivalent foliage than suppressed understory species. For individual trees of all species, the upper canopy had a larger proportion of solar equivalent foliage than the lower canopy. Light compensation points at both the leaf and whole-tree level were defined according to leaf or tree position, size and structure. I conclude that optimization of A(s) for forest stands may be used as a basis for determining thinning schedules and evaluating tree survival after damage to tree crowns by various factors.     

Photosynthetic capacity in a central Amazonian rain forest

The vertical profile in leaf photosynthetic capacity was investigated in a terra firme rain forest in central Amazonia. Measurements of photosynthesis were made on leaves at five levels in the canopy, and a model was fitted to describe photosynthetic capacity for each level. In addition, vertical profiles of photosynthetic photon flux density, leaf nitrogen concentration and specific leaf area were measured. The derived parameters for maximum rate of electron transport (J(max)) and maximum rate of carboxylation by Rubisco (V(cmax)) increased significantly with canopy height (P < 0.05). The highest J(max) for a single canopy level was measured at the penultimate canopy level (20 m) and was 103.9 &mgr;mol m(-2) s(-1) +/- 24.2 (SE). The highest V(cmax) per canopy height was recorded at the top canopy level (24 m) and was 42.8 +/- 5.9 &mgr;mol m(-2) s(-1). Values of J(max) and V(cmax) at ground level were 35.8 +/- 3.3 and 20.5 +/- 1.3 &mgr;mol m(-2) s(-1), espectively. The increase in photosynthetic capacity with increasing canopy height was strongly correlated with leaf nitrogen concentration when examined on a leaf area basis, but was only weakly correlated on a mass basis. The correlation on an area basis can be largely explained by the concomitant decrease in specific leaf area with increasing height. Apparent daytime leaf respiration, on an area basis, also increased significantly with canopy height (P < 0.05). We conclude that canopy photosynthetic capacity can be represented as an average vertical profile, perturbations of which may be explained by variations in the environmental variables driving photosynthesis.     

楸树无性系叶绿素荧光特性及其性状研究

对29个楸树无性系的生长性状(树高、胸径)、叶片性状(比叶重、叶片含水量)和叶绿素荧光参数(F(r)/Fm)等5个指标进行测定.结果表明:29个楸树无性系树高、胸径的平均值分别为6.12 m、6.48 cm;叶片比叶重为92.6 g/m2,含水量为0.7％;F(r)/Fm平均值为0.816.方差分析结果表明:5个指标在...