Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

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Different biomechanical design and ecophysiological strategies in juveniles of two liana species with contrasting growth habit
Chen, Y.J. ; Bongers, F. ; Zhang, J.L. ; Liu, J.Y. ; Cao, K.F. - \ 2014
American Journal of Botany 101 (2014)6. - ISSN 0002-9122 - p. 925 - 934.
vine ipomoea-purpurea - seasonal rain-forest - support availability - tropical forest - hydraulic conductivity - phenotypic responses - aboveground biomass - light interception - climbing plants - wood density
Premise of the study: Lianas constitute a major functional type in tropical zones. While some liana species start climbing immediately after germination (shade-avoidance), others have a long self-supporting phase (shade-tolerance). The morphophysiological characteristics of these two growth habits are unknown. Methods: We quantified growth traits, biomass allocation, mechanics, anatomy, and hydraulics for saplings of Ventilago calyculata (an immediate obligate climber) and Ziziphus attopensis (having a long self-supporting phase), both in the family Rhamnaceae. The mechanics, anatomy, and hydraulics for the mature individuals of the two species were also evaluated. Key results: In the juvenile stage, V. calyculata had a higher slenderness ratio, height growth rate, and photosynthetic rate but similar biomass growth rate compared with Z. attopensis. In contrast, Z. attopensis had a higher leaf area growth rate, specific leaf area, and leaf mass fraction. Ziziphus attopensis had stiffer, but less conductive stems than V. calyculata. Stem rigidity of saplings decreased from base to apex in Z. attopensis, but increased in V. calyculata. Both species had similar resistance to xylem embolism. However, the leaves of V. calyculata were able to resist greater water deficits. At the mature stage, wider and longer vessels emerged in the xylem, and both species increased stem specific conductivity and drought resistance in stems and leaves. Ventilago calyculata had significantly higher specific conductivity and was more drought tolerant than Z. attopensis. Conclusions: The two lianas differed significantly in growth, biomass allocation, anatomy, mechanics, ecophysiology, and hydraulic properties in line with their growth habits and shade adaptation strategies.
Stimulating seedling growth in early stages of secondary forest succession: a modeling approach to guide tree liberation
Kuijk, M. ; Anten, N.P.R. ; Oomen, R.J. ; Schieving, F. - \ 2014
Frontiers in Plant Science 5 (2014). - ISSN 1664-462X - 13 p.
natural regeneration - rain-forest - light interception - south kalimantan - carbon gain - costa-rica - canopy photosynthesis - subtropical forests - dipterocarp forest - tropical pasture
Excessive growth of non-woody plants and shrubs on degraded lands can strongly hamper tree growth and thus secondary forest succession. A common method to accelerate succession, called liberation, involves opening up the vegetation canopy around young target trees. This can increase growth of target trees by reducing competition for light with neighboring plants. However, liberation has not always had the desired effect, likely due to differences in light requirement between tree species. Here we present a 3D-model, which calculates photosynthetic rate of individual trees in a vegetation stand. It enables us to examine how stature, crown structure, and physiological traits of target trees and characteristics of the surrounding vegetation together determine effects of light on tree growth. The model was applied to a liberation experiment conducted with three pioneer species in a young secondary forest in Vietnam. Species responded differently to the treatment depending on their height, crown structure and their shade-tolerance level. Model simulations revealed practical thresholds over which the tree growth response is heavily influenced by the height and density of surrounding vegetation and gap radius. There were strong correlations between calculated photosynthetic rates and observed growth: the model was well able to predict growth of trees in young forests and the effects of liberation there upon. Thus, our model serves as a useful tool to analyze light competition between young trees and surrounding vegetation and may help assess the potential effect of tree liberation.
Simulation of water-limited growth of the forage shrub saltbush (Atriplex nummularia Lindl.) in a low-rainfall environment of southern Australia
Descheemaeker, K.K.E. ; Smith, A.P. ; Robertson, M.J. ; Whitbread, A. ; Huth, N.I. ; Davoren, W. ; Emms, J. ; Llewellyn, R. - \ 2014
Crop and Pasture Science 65 (2014)10. - ISSN 1836-0947 - p. 1068 - 1083.
medicago-sativa l. - western-australia - farming systems - light interception - discharge areas - use efficiency - model - soil - agroforestry - crops
Old man saltbush (Atriplex nummularia Lindl.) is a useful forage shrub for livestock in the low-rainfall areas of the world, and particularly in Australia. In these semi-arid and arid environments, saltbush is valuable for increasing the production from otherwise marginal areas of the farm and during drought periods when there are few feed alternatives. The ability to predict the growth and development of perennial forages such as old man saltbush in response to rainfall, soils and farm management is necessary for farming system planning and design purposes. A field experiment was conducted at Waikerie, South Australia, to inform the development of a new forage shrub model for use in the APSIM framework. The model takes into account the common setup of saltbush plantations in alley systems, by simulating light interception and water uptake for interacting shrub and inter-row zones separately. This is done by modelling the canopy and root system development. Field data across three soil types along a landscape catena showed that the model was able to satisfactorily predict daily biomass accumulation, partitioning into leaf and woody biomass, and regrowth after grazing. The model was sensitive to properties associated with the root system, and with limited parameterisation can be tailored to simulate different clonal cultivars. The model can now be used in the APSIM framework to assess temporal and spatial dynamics of forage systems combining shrubs with herbaceous pasture components.
Crown depth as a result of evolutionary games: decreasing solar angle should lead to shallower, not deeper crowns
Vermeulen, P.J. - \ 2014
New Phytologist 202 (2014)4. - ISSN 0028-646X - p. 1249 - 1256.
nitrogen-use efficiency - carbon allocation - adaptive significance - plant monocultures - light interception - height growth - fagus-crenata - tree height - rain-forest - canopy
There is a general notion in the literature that, with increasing latitude, trees have deeper crowns as a result of a lower solar elevation angle. However, these predictions are based on models that did not include the effects of competition for light between individuals. Here, I argue that there should be selection for trees to increase the height of the crown base, as this decreases shading by neighbouring trees, leading to an evolutionarily stable strategy (ESS). Because the level of between-tree shading increases with decreasing solar angle, the predicted ESS will shift to higher crown base height. This argument is supported by a simulation model to check for the effects of crown shape and the change of light intensity that occurs with changing solar angle on model outcomes. So, the lower solar angle at higher latitudes would tend to select for shallower, and not deeper, crowns. This casts doubt on the common belief that a decreasing solar angle increases crown depth. More importantly, it shows that different assumptions about what should be optimized can lead to different predictions, not just for absolute trait values, but for the direction of selection itself.
Optimizing illumination in the greenhouse using a 3D model of tomato and a ray tracer
Visser, P.H.B. de; Buck-Sorlin, G.H. ; Heijden, G.W.A.M. van der - \ 2014
Frontiers in Plant Science 5 (2014). - ISSN 1664-462X - 7 p.
structural plant-model - light interception - cucumber canopies - photosynthesis - simulation - environment - absorption
Reduction of energy use for assimilation lighting is one of the most urgent goals of current greenhouse horticulture in the Netherlands. In recent years numerous lighting systems have been tested in greenhouses, yet their efficiency has been very difficult to measure in practice. This simulation study evaluated a number of lighting strategies using a 3D light model for natural and artificial light in combination with a 3D model of tomato. The modeling platform GroIMP was used for the simulation study. The crop was represented by 3D virtual plants of tomato with fixed architecture. Detailed data on greenhouse architecture and lamp emission patterns of different light sources were incorporated in the model. A number of illumination strategies were modeled with the calibrated model. Results were compared to the standard configuration. Moreover, adaptation of leaf angles was incorporated for testing their effect on light use efficiency (LUE). A Farquhar photosynthesis model was used to translate the absorbed light for each leaf into a produced amount of carbohydrates. The carbohydrates produced by the crop per unit emitted light from sun or high pressure sodium lamps was the highest for horizontal leaf angles or slightly downward pointing leaves, and was less for more upward leaf orientations. The simulated leaf angles did not affect light absorption from inter-lighting LED modules, but the scenario with LEDs shining slightly upward (20°) increased light absorption and LUE relative to default horizontal beaming LEDs. Furthermore, the model showed that leaf orientation more perpendicular to the string of LEDs increased LED light interception. The combination of a ray tracer and a 3D crop model could compute optimal lighting of leaves by quantification of light fluxes and illustration by rendered lighting patterns. Results indicate that illumination efficiency increases when the lamp light is directed at most to leaves that have a high photosynthetic potential. - See more at: http://journal.frontiersin.org/Journal/10.3389/fpls.2014.00048/abstract#sthash.oZ0vUtYM.dpuf
Early competition shapes maize whole-plant development in mixed stands
Zhu, J. ; Vos, J. ; Werf, W. van der; Putten, P.E.L. van der; Evers, J.B. - \ 2014
Journal of Experimental Botany 65 (2014)2. - ISSN 0022-0957 - p. 641 - 653.
zea-mays l. - perennial ryegrass - leaf appearance - intercropping systems - light interception - resource capture - modular concept - growth-stages - spring wheat - sheath tube
Mixed cropping is practised widely in developing countries and is gaining increasing interest for sustainable agriculture in developed countries. Plants in intercrops grow differently from plants in single crops, due to interspecific plant interactions, but adaptive plant morphological responses to competition in mixed stands have not been studied in detail. Here the maize (Zea mays) response to mixed cultivation with wheat (Triticum aestivum) is described. Evidence is provided that early responses of maize to the modified light environment in mixed stands propagate throughout maize development, resulting in different phenotypes compared with pure stands. Photosynthetically active radiation (PAR), red:far-red ratio (R:FR), leaf development, and final organ sizes of maize grown in three cultivation systems were compared: pure maize, an intercrop with a small distance (25 cm) between maize and wheat plants, and an intercop with a large distance (44 cm) between the maize and the wheat. Compared with maize in pure stands, maize in the mixed stands had lower leaf and collar appearance rates, increased blade and sheath lengths at low ranks and smaller sizes at high ranks, increased blade elongation duration, and decreased R:FR and PAR at the plant base during early development. Effects were strongest in the treatment with a short distance between wheat and maize strips. The data suggest a feedback between leaf initiation and leaf emergence at the plant level and coordination between blade and sheath growth at the phytomer level. A conceptual model, based on coordination rules, is proposed to explain the development of the maize plant in pure and mixed stands.
Model-based evaluation of maturity type of potato using a diverse set of standard cultivars and a segregating diploid population
Khan, M.S. ; Eck, H.J. van; Struik, P.C. - \ 2013
Potato Research 56 (2013)2. - ISSN 0014-3065 - p. 127 - 146.
solanum-tuberosum - competitive ability - light interception - path coefficient - leaf appearance - rapd markers - late blight - crop - growth - l.
The objective of this paper is to evaluate the performance of the conventional system of classifying maturity type in potato and to provide a concept of maturity type based on crop physiology. We present an approach in which physiological traits are used to quantify and assess maturity type unambiguously for a set of varieties covering a wide range of maturity classes and a diploid F1 population separating for maturity and well-adapted to Dutch growing conditions, both grown in six environments. We defined physiological maturity based on four traits: the duration of maximum green canopy, the area under the green canopy cover progress curve, and the rate and duration of tuber bulking. The results indicated that physiological maturity type criteria tended to define maturity classes less ambiguously than the conventional criterion. Moreover, the conventional criterion was subject to more random noise and lacked stability and/or repeatability compared with the physiological traits. The physiological maturity criteria also illustrated the physiological trade-offs that existed between the selected traits and underlined the subtle complexities in classifying maturity type. This study highlighted the capabilities of different maturity type criteria in discriminating between different maturity classes among the large set of genotypes. Our new approach involving key physiological traits could be beneficial in offering physiology-based criteria to re-define maturity type. An improved criterion based on important physiological traits would allow relating the maturity to crop phenology and physiology. These new criteria may be amenable to further genetic analysis and could help in designing strategies for potato ideotype breeding for genotypes with specific maturity types
Meristem temperature substantially deviates from air temperature, even in moderate environments: Is the magnitude of this deviation species-specific?
Savvides, A. ; Ieperen, W. van; Dieleman, J.A. ; Marcelis, L.F.M. - \ 2013
Plant, Cell & Environment 36 (2013)1. - ISSN 0140-7791 - p. 1950 - 1960.
shoot-tip temperature - climate-change - leaf development - effective thickness - light interception - boundary-layers - heat-transfer - crop yields - maize apex - plant
Meristem temperature (Tmeristem) drives plant development but is hardly ever quantified. Instead, air temperature (Tair) is usually used as its approximation. Meristems are enclosed within apical buds. Bud structure and function may differ across species. Therefore, Tmeristem may deviate from Tair in a species-specific way. Environmental variables (air temperature, vapour pressure deficit, radiation, and wind speed) were systematically varied to quantify the response of Tmeristem. This response was related to observations of bud structure and transpiration. Tomato and cucumber plants were used as model plants as they are morphologically distinct and usually growing in similar environments. Tmeristem substantially deviated from Tair in a species-specific manner under moderate environments. This deviation ranged between -2.6 and 3.8¿°C in tomato and between -4.1 and 3.0¿°C in cucumber. The lower Tmeristem observed in cucumber was linked with the higher transpiration of the bud foliage sheltering the meristem when compared with tomato plants. We here indicate that for properly linking growth and development of plants to temperature in future applications, for instance in climate change scenarios studies, Tmeristem should be used instead of Tair, as a species-specific trait highly reliant on various environmental factors
The relative importance of above- versus belowground competition for tree growth and survival during early succession of a tropical moist forest
Breugel, M. van; Breugel, P. van; Jansen, P.A. ; Martinez-Ramos, M. ; Bongers, F. - \ 2012
Plant Ecology 213 (2012)1. - ISSN 1385-0237 - p. 25 - 34.
plant-populations - rain-forests - asymmetric competition - secondary succession - local interference - biomass allocation - light interception - size asymmetry - life-history - dry forest
Competition between neighboring plants plays a major role in the population dynamics of tree species in the early phases of humid tropical forest succession. We evaluated the relative importance of above- versus below-ground competition during the first years of old-field succession on soil with low fertility in Southern Mexico, using the premise that competition for light is size-asymmetric, unlike competition for nutrients. Plant growth is thus expected to be disproportionally impeded by larger neighbors. We studied how growth and survival of 3.5–5.5 m tall saplings of Cecropia peltata and Trichospermum mexicanum, two pioneer species that dominate the secondary forests in the study region, varied with the abundance and size of neighboring trees in 1–2 year old secondary vegetation. We found that local neighborhood basal area varied 10-fold (3 to 30 cm2 m-2) and explained most of the variation in diameter and height growth of the target saplings. Most growth variables were strongly affected by the neighbors bigger than the focal trees with no significant additive effect of the smaller neighbors, indicating asymmetric competition. Smaller neighbors did have a small but significant additive effect on the diameter growth of Cecropia saplings and stem slenderness of Trichospermum saplings. We conclude that competition for light was more important than belowground competition in this initial phase of moist tropical forest successional, despite the low soil fertility
Limited Edge Effects Along a Burned-Unburned Bornean Forest Boundary Seven Years after Disturbance
Slik, J.W.F. ; Beek, M. van; Bernard, C. ; Bongers, F. ; Breman, F.C. ; Cannon, C.H. ; Sidiyasa, K. - \ 2011
Biotropica 43 (2011)3. - ISSN 0006-3606 - p. 288 - 298.
tropical rain-forest - lowland dipterocarp forest - amazonian forest - wood density - seed-size - ecological attributes - natural regeneration - aboveground biomass - neotropical forests - light interception
Large parts of the everwet tropics have been burned, leaving many unburned–burned forest edges. Here we studied a Bornean forest edge to determine: (1) how unburned and burned forest differ in vegetation structure, diversity, composition and plant functional traits 7 yr after fire, and (2) if these variables showed significant edge effects. Environmental and inventory data from 120 plots (0.01 ha each), covering both sides of a ~1.3 km forest boundary were sampled. Differences in vegetation structure, diversity, composition and plant functional traits were analyzed in relation to disturbance type (Mann–Whitney tests) and edge distance (partial correlation analysis that controlled for confounding effects of elevation, slope and fire intensity). Seven years after fire, burned forest differed significantly from unburned forest in most measured variables while few significant edge effects were detected, i.e., there existed a sharp delimitation between the two forest types. The regeneration of the burned forest depended almost entirely on in situ recruitment with little input of late successional species from the neighboring old growth forest. On the other hand, old growth forest showed few signs of edge degradation. A possible explanation for these results might be related to the absence of a mast fruiting event during these first 7 yr of forest recovery, resulting in low levels of late successional species seed input into the burned forest, combined with the quick development of a closed canopy in the burned forest by early successional species that shielded the unburned forest from adverse edge effects
A system identification approach for developing and parameterising an agroforestry system model under constrained availability of data
Keesman, K.J. ; Graves, A. ; Werf, W. van der; Burgess, P.J. ; Palma, J. ; Dupraz, C. ; Keulen, H. van - \ 2011
Environmental Modelling & Software (2011). - ISSN 1364-8152
land equivalent ratio - light interception - silvoarable agroforestry - production ecology - plant-growth - yield-safe - trees - europe - canopy - forest
This paper introduces a system identification approach to overcome the problem of insufficient data when developing and parameterising an agroforestry system model. Typically, for these complex systems the number of available data points from actual systems is less than the number of parameters in a (process-based) model. In this paper, we follow a constrained parameter optimization approach, in which the constraints are found from literature or are given by experts. Given the limited a priori systems knowledge and very limited data sets, after decomposition of the parameter estimation problem and after model adaptation, we were able to produce an acceptable correspondence with validation data from a real-world agroforestry experiment
Functional-structural plant modelling: a new versatile tool in crop science
Vos, J. ; Evers, J.B. ; Buck-Sorlin, G.H. ; Andrieu, B. ; Chelle, M. ; Visser, P.H.B. de - \ 2010
Journal of Experimental Botany 61 (2010)8. - ISSN 0022-0957 - p. 2101 - 2115.
wheat triticum-aestivum - hordeum-vulgare l. - far-red ratio - leaf nitrogen economy - zea-mays l. - light interception - spring wheat - architectural model - photosynthetic capacity - cellular interactions
Plants react to their environment and to management interventions by adjusting physiological functions and structure. Functional–structural plant models (FSPM), combine the representation of three-dimensional (3D) plant structure with selected physiological functions. An FSPM consists of an architectural part (plant structure) and a process part (plant functioning). The first deals with (i) the types of organs that are initiated and the way these are connected (topology), (ii) co-ordination in organ expansion dynamics, and (iii) geometrical variables (e.g. leaf angles, leaf curvature). The process part may include any physiological or physical process that affects plant growth and development (e.g. photosynthesis, carbon allocation). This paper addresses the following questions: (i) how are FSPM constructed, and (ii) for what purposes are they useful? Static, architectural models are distinguished from dynamic models. Static models are useful in order to study the significance of plant structure, such as light distribution in the canopy, gas exchange, remote sensing, pesticide spraying studies, and interactions between plants and biotic agents. Dynamic models serve quantitatively to integrate knowledge on plant functions and morphology as modulated by environment. Applications are in the domain of plant sciences, for example the study of plant plasticity as related to changes in the red:far red ratio of light in the canopy. With increasing availability of genetic information, FSPM will play a role in the assessment of the significance towards plant performance of variation in genetic traits across environments. In many crops, growers actively manipulate plant structure. FSPM is a promising tool to explore divergent management strategies.
Recruitment and attrition of associated plants under a shading crop canopy: Model selection and calibration
Stilma, E.S.C. ; Keesman, K.J. ; Werf, W. van der - \ 2009
Ecological Modelling 220 (2009)8. - ISSN 0304-3800 - p. 1113 - 1125.
agri-environment schemes - population-dynamics - agricultural landscapes - light interception - arable weeds - biodiversity - germination - management - growth - yield
Associated plant and animal diversity provides ecosystem services within crop production systems. The importance of the maintenance or restoration of diversity is therefore increasingly acknowledged. Here we study the population dynamics of associated annual plants (`weeds¿) during the growth of a crop in a season and introduce a minimal model to characterize the recruitment and attrition of the associated plants under the influence of shading by the crop. A mechanistically based, logistic, light interception model was parameterized with light interception measurements in two single crops (barley and rye) and in mixtures of these cereals with peas. Population dynamics data were collected for the annuals Papaver rhoeas, Centaurea cyanus, Chrysanthemum segetum, and Misopates orontium. A minimal population dynamics model was identified for each annual plant species, using system identification techniques as model selection and calibration. For three of the four species, a two-parameter model consisting of light-dependent recruitment in combination with a constant death rate, explained 75¿96% of the variation in plant densities over the season. Model fit for P. rhoeas improved when a germination delay of 200 °Cd after sowing was included, resulting in a three-parameter model. The developed models have a simple yet biologically meaningful structure and the values of the parameters give a useful summary of the population dynamics of an annual plant population under the influence of the dynamic leaf cover of a shading crop. Further development of these models can contribute to systems design for maintaining plant diversity in crop systems.
Relationships among ecologically important dimensions of plant trait variation in seven neotropical forests
Wright, I.J. ; Ackerly, D.D. ; Bongers, F.J.J.M. ; Harms, K.E. ; Ibarra-Manriquez, G. ; Martinez-Ramos, M. ; Mazer, S.J. ; Muller-Landau, H.C. ; Paz, H. ; Pitman, N.C.A. ; Poorter, L. ; Silman, M.R. ; Vriesendorp, C.F. ; Webb, C.O. ; Westoby, M. ; Wright, S.J. - \ 2007
Annals of Botany 99 (2007)5. - ISSN 0305-7364 - p. 1003 - 1015.
lowland rain-forest - leaf life-span - seed size - wood density - functional convergence - light interception - water transport - tree height - los-tuxtlas - canopy
Background and Aims When ecologically important plant traits are correlated they may be said to constitute an ecological 'strategy' dimension. Through identifying these dimensions and understanding their inter-relationships we gain insight into why particular trait combinations are favoured over others and into the implications of trait differences among species. Here we investigated relationships among several traits, and thus the strategy dimensions they represented, across 2134 woody species from seven Neotropical forests. Methods Six traits were studied: specific leaf area (SLA), the average size of leaves, seed and fruit, typical maximum plant height, and wood density (WD). Trait relationships were quantified across species at each individual forest as well as across the dataset as a whole. 'Phylogenetic' analyses were used to test for correlations among evolutionary trait-divergences and to ascertain whether interspecific relationships were biased by strong taxonomic patterning in the traits. Results The interspecific and phylogenetic analyses yielded congruent results. Seed and fruit size were expected, and confirmed, to be tightly related. As expected, plant height was correlated with each of seed and fruit size, albeit weakly. Weak support was found for an expected positive relationship between leaf and fruit size. The prediction that SLA and WD would be negatively correlated was not supported. Otherwise the traits were predicted to be largely unrelated, being representatives of putatively independent strategy dimensions. This was indeed the case, although WD was consistently, negatively related to leaf size. Conclusions The dimensions represented by SLA, seed/fruit size and leaf size were essentially independent and thus conveyed largely independent information about plant strategies. To a lesser extent the same was true for plant height and WD. Our tentative explanation for negative WD-leaf size relationships, now also known from other habitats, is that the traits are indirectly linked via plant hydraulics.
Using the expolinear growth equation for modelling crop growth in year-round cut chrysanthemum
Lee, J.H. ; Goudriaan, J. ; Challa, H. - \ 2003
Annals of Botany 92 (2003)5. - ISSN 0305-7364 - p. 697 - 708.
oleracea l. botrytis - intercepted radiation - light interception - solar-radiation - use efficiency - young tomato - plant-growth - 3 densities - temperature - irradiance
The aim of this study was to predict crop growth of year-round cut chrysanthemum (Chrysanthemum morifolium Ramat.) based on an empirical model of potential crop growth rate as a function of daily incident photosynthetically active radiation (PAR, MJ m¿2 d¿1), using generalized estimated parameters of the expolinear growth equation. For development of the model, chrysanthemum crops were grown in four experiments at different plant densities (32, 48, 64 and 80 plants m¿2), during different seasons (planting in January, May¿June and September) and under different light regimes [natural light, shading to 66 and 43 % of natural light, and supplementary assimilation light (ASS, 40¿48 µmol m¿2 s¿1)]. The expolinear growth equation as a function of time (EXPOT) or as a function of incident PAR integral (EXPOPAR) effectively described periodically measured total dry mass of shoot (R2 > 0·98). However, growth parameter estimates for the fitted EXPOPAR were more suitable as they were not correlated to each other. Coefficients of EXPOPAR characterized the relative growth rate per incident PAR integral [rm,i (MJ m¿2)¿1] and light use efficiency (LUE, g MJ¿1) at closed canopy. In all four experiments, no interaction effects between treatments on crop growth parameters were found. rm,i and LUE were not different between ASS and natural light treatments, but were increased significantly when light levels were reduced by shading in the summer experiments. There was no consistent effect of plant density on growth parameters. rm,i and LUE showed hyperbolic relationships to average daily incident PAR averaged over 10-d periods after planting (rm,i) or before final harvest (LUE). Based on those relationships, maximum relative growth rate (rm, g g¿1 d¿1) and maximum crop growth rate (cm, g m¿2 d¿1) were described successfully by rectangular hyperbolic relationships to daily incident PAR. In model validation, total dry mass of shoot (Wshoot, g m¿2) simulated over time was in good agreement with measured ones in three independent experiments, using daily incident PAR and leaf area index as inputs. Based on these results, it is concluded that the expolinear growth equation is a useful tool for quantifying cut chrysanthemum growth parameters and comparing growth parameter values between different treatments, especially when light is the growth-limiting factor. Under controlled environmental conditions the regression model worked satisfactorily, hence the model may be applied as a simple tool for understanding crop growth behaviour under seasonal variation in daily light integral, and for planning cropping systems of year-round cut chrysanthemum. However, further research on leaf area development in cut chrysanthemum is required to advance chrysanthemum crop growth prediction
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