Canopy Photosynthesis Model Research Articles

Maximization of Daily Canopy Photosynthesis: Effects of Herbivory on Optimal Nitrogen Distribution

Recent models have shown that higher leaf nitrogen concentration per unit area maximizes nitrogen use efficiency with increasing light intensity. As a result, total canopy photosynthesis is maximized when nitrogen concentrations are higher towards the top of a canopy. Expanding upon this previous work, a model of daily canopy photosynthesis was constructed based on distributions of light, leaf nitrogen, and folivory. The model indicates that the optimal distribution of nitrogen depends significantly upon both the severity and location of folivory. Relative to nitrogen distributions that maximized daily canopy photosynthesis without herbivory, the optimal nitrogen distribution shifted towards either more uniform or skewed distributions when herbivores fed on high nitrogen foliage at the top of the canopy or on low nitrogen foliage towards the bottom of the canopy, respectively. These results suggest that, because foliar losses are balanced by increased irradiance of remaining leaves, plants' nitrogen allocation patterns should depend on how severe defoliation is and whether damage is concentrated towards the top or bottom of a canopy. Moreover, the critical importance of nitrogen distribution to photosynthesis implies that plants should not necessarily minimize loss of leaf area to folivores, but should protect the ratio of total nitrogen to leaf area and the distribution of nitrogen within the canopy. As a corollary to the nutrient stress hypothesis of plant defense theory, the model suggests that plants may need to translocate nutrients to maintain an optimal distribution in the canopy following herbivory. The model reinforces the point that leaf area loss alone is a poor indicator of loss of photosynthetic capacity when nitrogen is non-uniformly distributed among leaves. To accurately assess damage to a plant, one must consider not only what resources have been removed, but what resources remain.

Canopy development, photosynthesis and radiation-use efficiency in sunflower in response to nitrogen

Abstract Sunflower (Helianthus annuus L.) was sown at two densities (5.7 and 2.9 plants m−2) at Cordoba, Spain (lat. 38°N) on May 4, 1992 on a site of low nitrogen status. A high nitrogen comparison was established with 25 g m−2 applied in a split dressing of 15 and 10 g m−2 at 15 and 65 days after sowing (das). The growth of the four treatments (2 densities × 2 N levels) was measured on three occasions, 41 and 56 das and finally at flowering 71 das, as above-ground biomass in laminae and in stems plus petioles. Leaf nitrogen concentration was measured on every third leaf in those canopies. The areas of all leaves on 4 plants per plot was measured every 10 days from 33 das. On those days and many intervening occasions, canopy light interception was measured at noon and on some occasions integrated values were obtained over periods of several days. Frequent measurements of leaf photosynthesis were made in response to irradiance and leaf nitrogen content. Over the experimental period to 71 das, nitrogen promoted growth from 200 to 800 g m−2. This response was almost equally the result of doubling interception (1.9) and radiation-use efficiency (2.1). In the first stage of growth, up to 41 das, interception increased more (2.5) than did RUE (1.6). Maximum leaf photosynthesis (at high irradiance) increased from 10 to 40 μmol m−2 s−1 over the range of specific leaf nitrogen concentration from 1.0 to 2.8 g N m−2. Analyses with a simulation model of canopy photosynthesis showed that only a small part (14%) of the observed response in RUE could be attributed to greater photosynthesis resulting from greater N content and its distribution in the canopies. The major part therefore comprised undefined responses of partitioning of biomass to roots and to losses by respiration.

Effects of Physiological and Environmental Variations on Size-Structure Dynamics in Plant Populations

Sensitivity analysis was conducted, based on the canopy photosynthesis and continuity equation models which were developed in a previous paper (Yokozawa and Hara, 1992), to investigate effects of variation in physiological parameters (maximal photosynthetic rate per unit leaf area, respiration rate per unit leaf area, maintenance respiration rate per unit weight, growth respiration rate per unit weight, light extinction coefficient of the canopy, etc.) on the size-structure dynamics in plant populations. As the degree of asymmetry in competition between individuals increased, effects of variation in physiological parameters diminished. Therefore, a population undergoing one-sided competition (most asymmetric competition) is a stable system, little affected by temporal and spatial variations in the environmental conditions which lead to variation in physiological parameters, whereas a population undergoing symmetric two-sided competition is sensitive to these fluctuations. It was also shown by simulation that the degree of asymmetry in competition decreases (through effects on canopy photosynthesis) as nutrient level in the soil is reduced. It is suggested that symmetric two-sided competition is associated with non-transitivity of competition between species (i.e. frequent reversals of rank order of species), and hence with species diversity. Several other ecological phenomena are discussed in relation to allometry (i.e. allocation-growth pattern) and the degree of asymmetry in competition.

Canopy photosynthetic production in a Japanese larch forest. II. Estimation of the canopy photosynthetic production

Seasonal changes and yearly gross canopy photosynthetic production were estimated for an 18 year old Japanese larch (Larix leptolepis) forest between 1982 and 1984. A canopy photosynthesis model was applied for the estimation, which took into account the effect of light interception by the non-photosynthetic organs. Seasonal changes in photosynthetic ability, amount of canopy leaf area and light environment within the canopy were also taken into account. Amount of leaf area was estimated by the leaf area growth of a single leaf. The change of light environment within the canopy during the growing season was estimated with a light penetration model and the leaf increment within the canopy. Canopy respiration and surplus production were calculated as seasonal and yearly values for the three years studied. Mean yearly estimates of canopy photosynthesis, canopy respiration and surplus production were 37, 13 and 23 tCO2 ha−1 year−1, respectively. Vertical trend, seasonal changes and yearly values of the estimates were analyzed in relation to environmental and stand factors.

Mode of Competition and Size‐structure Dynamics in Plant Communities

Abstract Competition between individual plants is defined as a mathematical function for the mean growth rate of individuals in a vertically mono‐layered crowded stand as compared with growth of an isolated individual of the same size. The degree of competitive asymmetry can be described mathematically by using this definition. A canopy photosynthesis model for individual growth in a mono‐layered stand shows that physiological and environmental variations have little effects on the size‐structure dynamics of plant populations undergoing strongly asymmetric competition. These variations affect greatly the size‐structure dynamics under symmetric competition. It has also been shown that one‐sided competition (the most asymmetric competition) is never realised in a mono‐layered stand. A spatial competition model shows that variation in the spatial distribution pattern of individuals greatly affects the size‐structure dynamics of populations undergoing symmetric competition, whilst it has little effect on populations undergoing strongly asymmetric competition. Therefore, it can be concluded that a population undergoing strongly asymmetric competition is a stable system little affected by variations in various factors and that a population undergoing symmetric competition is an unstable system greatly affected by these variations.Based on these theoretical results, the relationships between the mode of competition, species diversity and community stability are discussed and a hypothesis on these processes and mechanisms is proposed for grassland and forest plant communities. One‐sided competition is associated with the stability of community structure, and this type of competition works as a structuring force for plant communities. Symmetric competition is associated with species diversity, and this type of competition cannot be a structuring force of plant communities, i.e. symmetric competition is irrelevant to the deterministic community dynamics. Distinctly multi‐layered forests show “apparent” one‐sided competition between layers (i.e. little direct interactions between canopies in different layers, but higher‐layer trees suppress lower‐layer trees one‐sidedly), bringing about structural stability, but trees in each layer undergo symmetric competition, bringing about species diversity. Mono‐layered grassland shows symmetric competition, bringing about small‐scale spatio‐temporal changes in species' abundance and hence species diversity. The real world lies between the two extreme types of competition, one‐sided and completely symmetric, and each plant community has its own position in this continuous spectrum of the competition mode.

Temporal expression of effects of varying nitrogen supply on canopy growth, photosynthesis and fruit production for Actinidia deliciosa vines in the field

The effects of varying nitrogen supply on canopy leaf area, response of leaf net photosynthesis (An) to quantum flux density (Q), and fruit yields of kiwifruit vines (Actinidia deliciosa var. deliciosa) were examined in a two‐year field experiment. Vines were grown with 0, 250 or 750 kg N ha−1 year−1. The responses to nitrogen supply were compared with responses to shade, to examine the impact of reduced carbon assimilation on canopy leaf area and fruit yields. Nitrogen supply did not affect significantly any of the measured variables during the first season of the experiment. In the second season, canopy leaf area was reduced significantly where nitrogen supply was limited. The quantum efficiency of photosynthesis (φq) increased from 0. 03 mol CO2 mol−1 Q soon after leaf emergence to more than 0. 05 mol CO2 mol−1 Q during the middle of the growing season. The quantum saturated rate of An (Asat) also increased during the season, from 7–10 μmol CO2 m−2 s−1 soon after leaf emergence, to 15–20 (μmol CO2 m−2 s−1 during the middle of the growing season. φq and Asat increased significantly with nitrogen supply at all measurement times during the second season. For vines with high nitrogen, fruit yields in both seasons were similar, averaging 3. 05 kg m−2. Fruit yields in the second season were reduced significantly where nitrogen supply was limited, due to reduced fruit numbers. The relative effects of reduced leaf area and reduced leaf photosynthesis for carbon assimilation by nitrogen deficient vines were examined using a mathematical model of canopy photosynthesis for kiwifruit vines. Simulations of canopy photosynthesis indicated that effects on leaf area and on leaf photosynthesis were of similar importance in the overall effects of nitrogen deficiency on carbon assimilation. The effects of nitrogen supply on fruit numbers (i. e. flower development) preceded the measured effects on carbon assimilation, indicating that the nitrogen supply affected carbon partitioning to reserves in the first season.

Use of Interactive Computer Graphics for Simulation of Radiation Interception and Photosynthesis for Canopies of Kiwifruit Vines with Heterogeneous surface Shape and Leaf Area Distribution

A method incorporating interactive computer graphics to simulate spatially variable interception and canopy photosynthesis is described. The method presents a graphical interface to a conventional model of radiation interception and canopy photosynthesis. Included is the capacity to consider a large number of positions within the canopy, thus providing a rapid and convenient representation of the dynamics of photosynthesis while also overcoming limitations of one-dimensional models applied to complex plant canopies. The method was applied to examine spatial variability of photosynthesis within canopies of kiwifruit (Actinidia deliciosa) vines growing on two trellis types. The diurnal integral of simulated canopy photosynthesis, assuming sunny conditions, for a vine trained on a horizontal 'Pergola' trellis was 14% higher than that for a vine with similar leaf area distribution trained on a 'T-bar' trellis with inclined surfaces. Simulations of photosynthesis for vines on a T-bar trellis, assuming spatially variable leaf area distributions as measured under filed conditions, indicated disproportionate contributions from different regions of the canopy. Canopy regions inclined to the east or the west were usually the major sites for photosynthesis immediately after sunrise and before sunset respectively, while regions near the cordon were the most important overall. For any day, the maximum simulated photosynthetic rate generally declined with distance from the cordon and, at any distance from the cordon, increased with leaf index. For a vine with an average leaf area index of 2·7, diurnal integrals of photosynthesis on a sunny day in late summer ranged from 1·0 mol CO2 m-2 near the cordon to 0·5 mol CO2 m-2 at 1·5 m from the cordon. Within-canopy shading was more important on sunny days than on cloudy days, while the spatial distribution of leaf area was especially important on cloudy days. Comparison of simulations with direct measurements of canopy photosynthesis indicated that a numerical integral of simulated photosynthesis, based on a large number of canopy positions, provided a reasonable estimate of total canopy photosynthesis.

A Canopy Photosynthesis Model for the Dynamics of Size Structure and the Competition Mode in Plant Populations

A dynamic model for growth and mortality of individual plants in a stand is developed, based on the process of canopy photosynthesis, and assuming an allometric relationship between plant height and weight, i.e. an allocation-growth pattern of plant height and stem diameter. The following were shown by simulation: (i) competition between individuals in a crowded stand is never completely one-sided but always asymmetrically two-sided, even though competition is only for light; (ii) plants of the ‘height-growth’ type exhibit a greater asymmetry in competition than plants of the ‘diameter-growth’ type; (iii) the competition mode between plants of the ‘height-growth’ type becomes more asymmetric with increasing photosynthetic ability than with plants of the ‘diameter-growth’ type. These results can explain recent empirical results obtained from several natural plant communities.

A Canopy Photosynthesis Model for the Dynamics of Size Structure and Self-thinning in Plant Populations

A dynamic model for growth and mortality of individual plants in a stand was developed, based on the process of canopy photosynthesis, and assuming an allometric relationship between plant height and weight, i.e. allocation-growth pattern of plant height and stem diameter. Functions G(t,x), for the mean growth rate of individuals of size x at time t, and M(t,x), for the mortality rate of individuals of size x at time t, were developed from this used in simulations. The dynamics of size structure were simulated, combining the continuity equation model, a simple version of the diffusion model, with these functions

A model of canopy photosynthesis and water use incorporating a mechanistic formulation of leaf CO 2 exchange

A model of the carbon uptake and water balance of forest stands is described where leaf photosynthesis is represented by a mechanistic model of photosynthesis by C 3 plants. Data are presented to support an empirical relationship linking stomatal conductance, photosynthesis, relative humidity and ambient CO 2 concentration. The model was applied to stands of Pinus radiata subject to extremes of water and nutrient availability. Simulated water storage in the root zone agreed with measurements conducted over a 5 year period. Simulated and measured seasonal patterns of water use reached maximum rates of approximately 7 mm day −1 in summer for irrigated stands with projected leaf area indices of approximately 8. Simulated annual net photosynthesis (net of photorespiration and day-time foliar respiration) ranged from approximately 17 Mg C ha −1 year −1 for control stands to approximately 45 Mg C ha −1 year −1 for irrigated and fertilised stands.

Experimental and Modelling Studies of Competition for Light in Roadside Grasses

Summary Equiproportional mixtures and monocultures of two roadside grass species (Elymus repens (L.) Gould and Puccinellia distans (L.) Pari.) were grown in experimental field plots under non-limiting water and nutrient conditions. During the course of the season, E. repens increasingly overgrew and shaded plants of P. distans which eventually died. A multispecies canopy photosynthesis model was parameterized using measurements of structural and physiological characteristics from three different stages of canopy development. Results of simulations clearly revealed that canopy photosynthesis of P. distans was highly dependent on the degree of light competition caused by E. repens. Since P. distans has recently invaded stands of roadside vegetation throughout Central Europe where it has replaced the native and highly competitive E. repens, it is hypothesized that this success is due to disturbance factors that keep E. repens from growing tall and shading P. distans.

Variation in Interception of the Direct Solar Beam by Top Canopy Layers

Leaves that show paraheliotropic movement are inclined at a shallow angle with respect to the horizontal near dawn and dusk, and at a steep angle near solar noon. However, the mean inclination angle is only a first approximation to the distribution of leaf angles, and, as such, is not a good measure of the complexity of the underlying distribution. In order to ascertain the accuracies of statistical summaries of angular data used to measure the orientation of plant leaves for intercepting light, I used cellulation plots to analyze the distribution of leaf angles or cosines of the angle of incidence. Examination of these plots shows that inclinations of leaves in the top canopy layer of individual heliotropic plants are distributed over a wide range of angles during a period of several hours before and after solar noon, but that there is a sharp lower limit to this distribution of angles. Experimental observations show that near midday leaves are inclined at least at some minimum angle with respect to the horizontal. In order to interpret these data, I used a simple model of plant canopy photosynthesis and optimized the distribution of leaf angles to maximize total canopy photosynthesis. The results of this model suggest that the existence of a limit angle may be a function primarily of stress factors, and that the distribution of leaf angles more vertical than the limit angle may be important primarily for maximization of whole—plant photosynthesis.

A Functional Model Describing Sapling Growth Under a Tropical Forest Canopy

The consequence of the trade-off between trunk growth and crown growth in understorey saplings is examined using a simple growth model. The model is based on published findings of interspecific variation in allometric relationships of saplings of shade-tolerant trees, their physiological parameters, and the light environment under forest canopy in south-east Asian tropical rain forests. All interspecific differences in allometries are described to reflect the difference in the allocation of dry weight between trunk stem and branch stem. In the model, branchdeveloping saplings have greater above-ground weight, larger trunk diameter, wider crown area and lower leaf area density at the same height than trunk-developing saplings. The model calculates the architecture-specific sapling growth rate, applying a classic canopy photosynthesis model to express crown photosynthesis, taking into account the self-shading within the sapling crown. Results show that the optimal allocation which maximizes sapling height growth rate for the understorey light environment is within the observed range of allocation in saplings of shade-tolerant tree species. It is proposed that fluctuation of the understorey light condition in time and space brings about the allometric variation among coexisting saplings. Key-words: Allocation, allometry, branching architecture, growth model, light environment, saplings, simulation, tropical rain forest

Effect of light interception by non‐photosynthetic organs on canopy photosynthetic production

AbstractA canopy photosynthesis model was derived on the assumption that the light diminution within a canopy is caused by both leaves and non‐photosynthetic organs. The light diminution by leaves and that by non‐photosynthetic organs were taken into account separately in the Lambert‐Beer equation of light extinction. The light flux density on the leaf surface at each depth was evaluated from the leaf's share of light. The light flux density on the leaf surface thus obtained was incorporated into the Monsi‐Saeki model of canopy photosynthesis. The proposed model was applied for estimating gross canopy photosynthesis in a 19‐year‐old Larix leptolepis plantation where 38% of the light diminution was due to non‐photosynthetic organs. The daily canopy photosynthesis on one summer day calculated using the present model was about 22% less than that calculated by the conventional Monsi‐Saeki model, in which light interception by non‐photosynthetic organs is neglected. The degree of such reduction in canopy photosynthesis through shading by non‐photosynthetic organs was assessed in relation to parameters affecting light extinction, leaf photosynthetic characteristics, and light regime above the canopy.

Leaf age structure and canopy photosynthesis in rotationally and continuously grazed swards

AbstractThe leafage structure of ryegrass canopies and its role in canopy photosynthesis were compared under continuous and rotational grazing by sheep. Under continuous grazing, an increase in the intensity of grazing increased the proportion (by leaf area) of young leaves in the sward. A mechanistic mathematical model was used to demonstrate how this may have arisen, even though it would largely have been the young leaves that were eaten.However, the observations do not confirm the hypothesis that continuously grazed swards have a characteristically greater proportion of young leaves, and so a greater photosynthetic potential, than rotationally grazed ones. The proportion of young leaves increased during regrowth following severe rotational grazing (residual LAI < 05) and the photosynthetic potential of the canopy became greater than under continuous grazing.A model of canopy photosynthesis was used to demonstrate that the observed difference in the proportion of young leaves alone was unlikely to account for all the differences in canopy photosynthesis between managements, and further differences in canopy structure were evaluated. Despite the delay in the restoration of leaf area following severe grazing in a rotation, the total photosynthetic uptake of a system involving some 12–13 days regrowth and 3 days grazing exceeded that of a well‐utilized continuously grazed sward. Re growths of longer duration led to progressively greater total photosynthetic uptake, though this was not considered synonymous with greater yield.

Maximizing daily canopy photosynthesis with respect to the leaf nitrogen allocation pattern in the canopy.

A model of daily canopy photosynthesis was constructed taking light and leaf nitrogen distribution in the canopy into consideration. It was applied to a canopy of Solidago altissima. Both irradiance and nitrogen concentration per unit leaf area decreased exponentially with increasing cumulative leaf area from the top of the canopy. The photosynthetic capacity of a single leaf was evaluated in relation to irradiance and nitrogen concentration. By integration, daily canopy photosynthesis was calculated for various canopy architectures and nitrogen allocation patterns. The optimal pattern of nitrogen distribution that maximizes the canopy photosynthesis was determined. Actual distribution of leaf nitrogen in the canopy was more uniform than the optimal one, but it realized over 20% more photosynthesis than that under uniform distribution and 4.7% less photosynthesis than that under the optimal distribution. Redeployment of leaf nitrogen to the top of the canopy with ageing should be more effective in increasing total canopy photosynthesis in a stand with a dense canopy than in a stand with an open canopy.

An estimate of the photosynthetic production of individual trees in a Chamaecyparis obtusa plantation.

A Weibull function was used to model the vertical distribution of leaf area of individual trees in a 25-year-old Chamaecyparis obtusa (Siebold & Zucc.) Endl. plantation. The parameter representing the shape of the leaf distribution was independent of tree size. A scale parameter tended to decrease with tree size suggesting a critical minimum height for retention of foliage by trees. On the basis of leaf distribution, the photosynthetic production of individual trees was estimated from the canopy photosynthetic production, which was determined from a model of canopy photosynthesis. The data indicated that the photosynthesis of a tree was proportional to the corresponding tree weight to the power of 1.84. Furthermore, the photosynthetic production varied as the 3/2nd power of total leaf area of the tree. Thus, it was concluded that the photosynthetic production per unit of leaf area, that is, the mean photosynthetic activity of a tree, is proportional to the stem girth at clear length, or the square root of the leaf area of the tree.

Effects of Density and Extinction Coefficient on Size Variability in Plant Populations

The effects of density and extinction coefficient on size variability, as measured by the coefficient of variation of plant weight in even-aged monocultures, were investigated theoretically using a diffusion model of growth and size distribution and a canopy photosynthesis model over the range of densities at which self-thinning (size-dependent mortality) does not occur. Size inequality (the coefficient of variation of plant weight) increases with increasing density or leaf area index at each growth stage. Plants with erect leaves are prone to lower size inequality than plants with horizontal leaves. These results agree well with existing observations on even-aged plant monocultures and suggest that competition between plants is mainly one-sided (competition for light). One sided competition affects size variability through a G(t, x) function (mean growth of plants of size x at time t per unit time). Two-sided competition (including competition for nutrients) affects size variability through a D(t, x) function (variance of growth of plants of size x at time t per unit time). In this case, size inequality decreases with increasing density. The importance of studying size variability is emphasized.

Response of sunflower to strategies of irrigation III. Crop photosynthesis and transpiration

Connor, D.J., Patta, J.A. and Jones, T.R., 1985. Response of sunflower to strategies of irrigation. III. Crop photosynthesis and transpiration. Field Crops Res., 12: 281--293. The diurnal photosynthesis and transpiration of sunflower (cv. Sungold) subjected to three water regimes were measured on 29 days over one crop cycle using open-system field assimilation chambers. TWo treatments were irrigated at weekly and 2-weekly intervals respectively and the third treatment was rainfed. The data define the high photosynthetic potential of the sunflower crop, which at LAI = 2.5 reached 9 g CO s m -2 h -~ at global flux density of 800 W m -s, and its response to water shortage. Photosynthesis and transpiration were markedly restricted by low water supply but this response was dominated by the adjustment to LAI rather than to leaf conductance and photosynthetic rate. Wilting of stressed crops contributed more to the depression of their afternoon photosynthesis than did stomatal closure. A published model of canopy photosynthesis was able to describe the diurnal photosynthetic response of non-wilting crops to irradiance. Daily photosynthesis was highly correlated with intercepted radiation (5.24 g CO2 MJ -~) and with the ratio of daily transpiration to mean daily saturation vapour pressure deficit (119 mg CO 2 (g H20) -~ mbar -1). There was no effect of treatment upon daily transpiration/photosynthesis ratio.

Daily photosynthesis totals calculated from solar radiation histograms

Histograms of the number of hours in the day in which the photosynthetic photon flux density (PPFD) of solar radiation was within 5 preset bands, were constructed from readings made with a miniature battery-operated millivolt histogram recorder, connected to a photon sensor. The number of histograms showing a bimodal distribution was much fewer than was expected from a review of the literature, even in a site shaded by trees. This was attributed to smoothing of the data over a whole day, compared with published data which were mostly taken near noon. Bimodal distributions were found in a greenhouse under clear or partly cloudy conditions. The histograms were combined with published data for the instantaneous gross photosynthetic responses to PPFD of two bermudagrass swards, one of low leaf area index (LAI) and highly non-linear response, and the other of high LAI and more linear response. The daily photosynthesis totals of the swards were calculated by summing the products of the number of hours accumulated in each band by the photosynthetic rate in the center of the band. Because of the non-linearity of response, the photosynthesis total in the greenhouse was 75–82% of that calculated for an open site on a clear day, while the daily photon total was only 70% of the open site value. Also, for the same daily photon total, the daily photosynthesis total of each sward on the open site was greater on a day of light clouds (moderate PPFD) than on a day of sunshine alternating with heavy clouds (bimodal histogram of PPFDs). The difference between the two days was greater for the sward with the more non-linear response. These interactions between non-linearity of photosynthetic response and type of radiation histogram were in the expected direction, however, the differences were not very large (+ 10% for the sites and responses studied). The histogram recorder provides an inexpensive and convenient means of obtaining solar radiation data that can be used to calculate daily photosynthesis totals, either from experimental photosynthesis data or from canopy photosynthesis models. Because the response of photosynthesis is non-linear, linear integrals of solar irradiance do not provide sufficient information for such photosynthesis studies.