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1.
The growth of spring cabbage (Brassica oleracea var. capitataL.) and carrot (Daucus carota L.) in mixed species stands iscompared with growth curves predicted by two forms of a dynamiccompetition model, which uses a conductance relationship (Aikmanand Scaife, 1993) to allow for the constraints on growth froma set of environmental variables. While a plant is isolated,light interception is assumed to occur within a zone whose areais a function of plant weight. Lateral foliage expansion isconstricted when the available space is filled. One form ofthe model assumes that all plants are of similar height (Aikmanand Benjamin, 1994). The second form assumes the crown zonesare in separate vertical layers, allowing greater lateral expansionin each layer but imposing shading on the underlayer. Parameter values of the model were estimated from the growthwithin even-aged monocrops. The first form of the model gavethe best prediction of growth in the intercrops, often producinga close agreement between observed and predicted weights. Onlyat the highest density used, 0·05 m spacing, did thedifferent height form of model give a better prediction of growth. Many mixed species stands may be approximated by one or otherof the forms of the model, and the relevant form can easilybe calibrated from the growth observed in monocrops. Hence,simple models may be sufficiently accurate to predict growthin mixed species systems such as intercrops, or crops and weeds.Copyright1995, 1999 Academic Press Cabbage, carrot, competition, intercrop, light, mechanistic model, temperature, canopy architecture 相似文献
2.
When inducing simultaneously β-galactosidase and tryptophanase in a batch culture either the synthesis of tryptophanase or
of both enzymes is decreased due to an insufficient cAMP concentration. The addition of this nucleotide can overcome this
decrease. In a continuous culture both enzymes are synthesized at the maximum rate, as the amount of cAMP produced during
carbon limitation of growth is probably sufficient for the simultaneous synthesis of both enzymes. In the β-galactosidase
hyperproduction mutant cultivated continuously the level of β-galactosidase markedly decreases when tryptophanase is simultaneously
induced. Also this decrease is caused by cAMP insufficiency and can be overcome by increasing its concentration. cAMP is thus
an important regulatory factor of both enzymes and becomes a limiting factor in their simultaneous synthesis; a competition
for this regulatory compound apparently occurs and probably also a different mutual affinity of the regulatory complex with
the promoter site of the enzyme opérons is involved. 相似文献
3.
Improving grasslands: the influence of soil moisture and nitrogen fertilization on the establishment of seedlings 总被引:3,自引:1,他引:2
1. In order to investigate the factors influencing the establishment of seedlings in permanent grassland, the influence of soil moisture and nitrogen fertilization on competition between established plants of Lolium perenne and seedlings of Phleum pratense or Trifolium pratense was studied in two experiments under greenhouse conditions using the 'split-box'-technique.
2. There was no difference in the production of plant dry matter of P. pratense or T. pratense between 30% volumetric soil water content (−0·005 MPa) and 22% (−0·04 MPa), but 15% soil moisture (−0·33 MPa) reduced plant growth. L. perenne yields were linearly reduced by reduced soil moisture content.
3. Shoot competition from L. perenne reduced the plant dry matter yield of P. pratense and T. pratense more than did root competition in these experiments. When shoot competition was present, differences between moisture contents were not detected, indicating that light was probably the limiting resource under such conditions. No significant interaction between root competition and soil moisture was observed for plant weight.
4. Root competition was not prevented even though sufficient water and nitrogen were supplied. This indicated either that some other growth factor was limiting or the plants competed for resources at the root hair level even though sufficient resources were supplied at the pot or field scale. Therefore, in the situation of direct drilling of species during grassland renovation, it may be difficult to alleviate competition by adequate provision of water and nitrogen. 相似文献
2. There was no difference in the production of plant dry matter of P. pratense or T. pratense between 30% volumetric soil water content (−0·005 MPa) and 22% (−0·04 MPa), but 15% soil moisture (−0·33 MPa) reduced plant growth. L. perenne yields were linearly reduced by reduced soil moisture content.
3. Shoot competition from L. perenne reduced the plant dry matter yield of P. pratense and T. pratense more than did root competition in these experiments. When shoot competition was present, differences between moisture contents were not detected, indicating that light was probably the limiting resource under such conditions. No significant interaction between root competition and soil moisture was observed for plant weight.
4. Root competition was not prevented even though sufficient water and nitrogen were supplied. This indicated either that some other growth factor was limiting or the plants competed for resources at the root hair level even though sufficient resources were supplied at the pot or field scale. Therefore, in the situation of direct drilling of species during grassland renovation, it may be difficult to alleviate competition by adequate provision of water and nitrogen. 相似文献
4.
Representation of vegetation dynamics in the modelling of terrestrial ecosystems: comparing two contrasting approaches within European climate space 总被引:10,自引:0,他引:10
Benjamin Smith I. Colin Prentice Martin T. Sykes 《Global Ecology and Biogeography》2001,10(6):621-637
- 1 Advances in dynamic ecosystem modelling have made a number of different approaches to vegetation dynamics possible. Here we compare two models representing contrasting degrees of abstraction of the processes governing dynamics in real vegetation.
- 2 Model (a) (GUESS) simulates explicitly growth and competition among individual plants. Differences in crown structure (height, depth, area and LAI) influence relative light uptake by neighbours. Assimilated carbon is allocated individually by each plant to its leaf, fine root and sapwood tissues. Carbon allocation and turnover of sapwood to heartwood in turn govern height and diameter growth.
- 3 Model (b) (LPJ) incorporates a ‘dynamic global vegetation model’ (DGVM) architecture, simulating growth of populations of plant functional types (PFTs) over a grid cell, integrating individual‐level processes over the proportional area (foliar projective cover, FPC) occupied by each PFT. Individual plants are not simulated, but are replaced by explicit parameterizations of their growth and interactions.
- 4 The models are identical in their representation of core physiological and biogeochemical processes. Both also use the same set of PFTs, corresponding to the major woody plant groups in Europe, plus a grass type.
- 5 When applied at a range of locations, broadly spanning climatic variation within Europe, both models successfully predicted PFT composition and succession within modern natural vegetation. However, the individual‐based model performed better in areas where deciduous and evergreen types coincide, and in areas subject to pronounced seasonal water deficits, which would tend to favour grasses over drought‐intolerant trees.
- 6 Differences in model performance could be traced to their treatment of individual‐level processes, in particular light competition and stress‐induced mortality.
- 7 Our results suggest that an explicit individual‐based approach to vegetation dynamics may be an advantage in modelling of ecosystem structure and function at the resolution required for regional‐ to continental‐scale studies.
5.
The aim of this study was to find out whether the low plant production under a canopy of Heracleum laciniatum Horn was due to competition for water, nutrients or light or to chemical inhibitors produced by H. laciniatum .
The main conclusion is that the low plant production observed under the canopy is due to competition for light. There were also indications that the competition for nutrition was larger in the soil under H. laciniatum than in the meadow outside the stand, but it has not been shown that nutrient supply limits the plant growth under the canopy. There were no indications that competition for water was a limiting factor. Water percolated through pots with H. laciniatum plants slightly inhibited growth of Poa pratensis and Phleum pratense , but had no effect on H. laciniatum . In soil samples collected from mid of June to late October seeds of Phleum pratense germinated better in meadow-soil than in soil collected under H. laciniatum . Allelopathy is suggested to account for a minor part only of the suppressed plant production under a H. laciniatum canopy. 相似文献
The main conclusion is that the low plant production observed under the canopy is due to competition for light. There were also indications that the competition for nutrition was larger in the soil under H. laciniatum than in the meadow outside the stand, but it has not been shown that nutrient supply limits the plant growth under the canopy. There were no indications that competition for water was a limiting factor. Water percolated through pots with H. laciniatum plants slightly inhibited growth of Poa pratensis and Phleum pratense , but had no effect on H. laciniatum . In soil samples collected from mid of June to late October seeds of Phleum pratense germinated better in meadow-soil than in soil collected under H. laciniatum . Allelopathy is suggested to account for a minor part only of the suppressed plant production under a H. laciniatum canopy. 相似文献
6.
A plant's morphology is both strongly influenced by local light availability and, simultaneously, strongly influences this local light availability. This reciprocal relationship is complex, but lies at the heart of understanding plant growth and competition. Here, we develop a sub-individual-based simulation model, cast at the level of interacting plant components. The model explicitly simulates growth, development and competition for light at the level of leaves, branches, etc., located in 3D space. In this way, we are able to explore the manner in which the low-level processes governing plant growth and development give rise to individual-, cohort-, and community-level phenomena. In particular, we show that individual-level trade-offs between growing up and growing out arise naturally in the model, and robustly give rise to cohort-level phenomena such as self-thinning, and community processes such as the effect of ecological disturbance on the maintenance of biodiversity. We conclude with a note on our methodology and how to interpret the results of simulation models such as this one. 相似文献
7.
García-Barrios L Mayer-Foulkes D Franco M Urquijo-Vásquez G Franco-Pérez J 《Bulletin of mathematical biology》2001,63(3):507-526
Spatial disposition of plants in intercrops, and differences in sowing time between species, can strongly affect their ecological
interactions and, in consequence, the system’s viability and performance. Empirical exploration of a wide range of spatial
and temporal plant arrangements is costly and time-consuming. Modelling the growth of mixed crops is a tool which, combined
with empirical tests, can greatly reduce the time and investment required for this task. Spatially explicit, individual-based
dynamic models seem well suited for this purpose; their exploration and experimental validation for the case of simple, two-species,
artificial plant communities, can also provide further insight as to how the spatial and temporal scales of a plant’s multispecific
neighbourhood affect its growth and performance. The aim of this investigation was to further develop a published spatially
explicit individual-based mixed crop growth model [Vandermeer, J. H. (1989). The Ecology of Intercropping, Cambridge, U.K.: Cambridge University Press, p. 237], and to validate it experimentally. With this purpose in mind: (1)
computer programs to simulate individual plant growth and to perform statistical analysis of both deterministic and stochastic
versions of the model were developed; (2) the model was parametrized using a complex experimental diculture with several cohorts
and spatial arrangements; (3) the predictive capacity of the model was tested using independent spatio-temporal experimental
arrangements; (4) a modified version of the model was written, which abandons the assumption of linearity of the neighbourhood
index at the cost of increasing the number of parameters; (5) The performance of stochastic versions of both Vandermeer’s
and our modified model were compared, employing a non-parametric measure of goodness of fit. We conclude that this approach
to modelling plant growth subject to intra and interspecific competition is a remarkably efficient, general, conceptually
elegant, heuristic tool whose predictive power can be further improved when nonlinear terms are introduced into the neighbourhood
competition index, as done in our modified version of Vandermeer’s model. 相似文献
8.
An ecosystem model of the phytoplankton competition in the East China Sea, as based on field experiments 总被引:1,自引:0,他引:1
Yanbin Li Xiulin Wang Xiurong Han Keqiang Li Xixi Zhao Xiaoyong Shi 《Hydrobiologia》2008,600(1):283-296
An ecological dynamic model for the simulation of two pelagic phytoplankton groups is developed in this article. Model parameters
were adjusted and validated based on the light-limited field culture experiments and the mesocosm experiments in the East
China Sea (ECS). The calculation comparisons from the proposed model, along with field experiment observations, show that
the model simulate the datasets very well, qualitatively and quantitatively. The parameters’ sensitivity analysis indicates
that the competition between the diatoms and dinoflagellates is most sensitive to the photosynthetic process, followed by
the exudation process of the phytoplankton, while the autolysis and respiration processes of phytoplankton and the grazing
and exudation processes of zooplankton can also influence this competition to some extent. The sensitive parameters include:
the photosynthetic optimal specific rate; the optimal irradiance and optimal temperature for phytoplankton growth; and the
half-saturation constant for limiting nutrients, etc. Results of the sensitivity analysis also indicate that light, temperature
and limiting nutrients are the controlling environmental factors for the competition between the diatoms and dinoflagellates
in the ECS. In order to explore the effects of light and nutrients on the phytoplankton competition, simulations were carried
out with varying light and nutrient conditions. Model simulations suggest that the diatoms favor higher irradiance, lower
DIN/PO4–P ratios, higher SiO4–Si/DIN ratios and higher nutrient concentrations, as compared to the dinoflagellates. These results support the speculation
that the increase in the DIN/PO4−P ratio and the decrease in the SiO4–Si/DIN ratio in the ECS may be responsible for the composition change in the functional Harmful Algal Bloom (HAB) groups
from the diatom to the dinoflagellate communities over the last two decades.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.
Handling editor: L. Naselli-Flores 相似文献
9.
A Canopy Photosynthesis Model for the Dynamics of Size Structure and Self-thinning in Plant Populations 总被引:8,自引:2,他引:6
A dynamic model for growth and mortality of individual plantsin a stand was developed, based on the process of canopy photosynthesis,and assuming an allometric relationship between plant heightand weight, i.e. allocation growth pattern of plant height andstem diameter. Functions G(t, x), for the mean growth rate ofindividuals of size x at time t, and M(t,x), for the mortalityrate of individuals of size x at time t, were developed fromthis model and used in simulations. The dynamics of size structurewere simulated, combining the continuity equation model, a simpleversion of the diffusion model, with these functions. Simulationsreproduced several well-documented phenomena: (1) size variabilityin terms of coefficient of variation and skewness of plant weightincreases at first with stand development and then stabilisesor decreases with an onset of intensive self-thinning; (2) duringthe course of self-thinning, there is a power relationship betweendensity and biomass per unit ground area, irrespective of theinitial density and of the allocation-growth pattern in termsof the allometric parameter relating plant height and weight.The following were further shown by simulation: (a) competitionbetween individuals in a crowded stand is never completely one-sidedbut always asymmetrically two-sided, even though competitionis only for light; (b) plants of height-growthtype exhibit a greater asymmetry in competition than plantsof diameter-growth type, (c) the effect of competitionon the growth of individuals in a crowded stand converges toa stationary state, even when the stand structure still changesgreatly. All of these theoretical results can explain recentempirical results obtained from several natural plant communities.Finally, a new, general functional form for G(t, x) in a crowdedstand is proposed based on these theoretical results, insteadof a priori or empirical growth and competition functions. Canopy photosynthesis, competition mode, continuity equation, self-thinning, simulation, size distribution 相似文献
10.
Aims We present an improved model for the growth of individuals in plant populations experiencing competition.Methods Individuals grow sigmoidally according to the Birch model, which is similar to the more commonly used Richards model, but has the advantage that initial plant growth is always exponential. The individual plant growth models are coupled so that there is a maximum total biomass for the population. The effects of size-asymmetric competition are modeled with a parameter that reflects the size advantage that larger individual have over smaller individuals. We fit the model to data on individual growth in crowded populations of Chenopodium album .Important findings When individual plant growth curves were not coupled, there was a negative or no correlation between initial growth rate and final size, suggesting that competitive interactions were more important in determining final plant size than were plants' initial growth rates. The coupled growth equations fit the data better than individual, uncoupled growth models, even though the number of estimated parameters in the coupled competitive growth model was far fewer, indicating the importance of modeling competition and the degree of size-asymmetric growth explicitly. A quantitative understanding of stand development in terms of the growth of individuals, as altered by competition, is within reach. 相似文献
11.
Background and Aims
There is increasing interest in the development of plant growth models representing the complex system of interactions between the different determinants of plant development. These approaches are particularly relevant for grapevine organogenesis, which is a highly plastic process dependent on temperature, solar radiation, soil water deficit and trophic competition.Methods
The extent to which three plant growth models were able to deal with the observed plasticity of axis organogenesis was assessed. In the first model, axis organogenesis was dependent solely on temperature, through thermal time. In the second model, axis organogenesis was modelled through functional relationships linking meristem activity and trophic competition. In the last model, the rate of phytomer appearence on each axis was modelled as a function of both the trophic status of the plant and the direct effect of soil water content on potential meristem activity.Key Results
The model including relationships between trophic competition and meristem behaviour involved a decrease in the root mean squared error (RMSE) for the simulations of organogenesis by a factor nine compared with the thermal time-based model. Compared with the model in which axis organogenesis was driven only by trophic competition, the implementation of relationships between water deficit and meristem behaviour improved organogenesis simulation results, resulting in a three times divided RMSE. The resulting model can be seen as a first attempt to build a comprehensive complete plant growth model simulating the development of the whole plant in fluctuating conditions of temperature, solar radiation and soil water content.Conclusions
We propose a new hypothesis concerning the effects of the different determinants of axis organogenesis. The rate of phytomer appearance according to thermal time was strongly affected by the plant trophic status and soil water deficit. Futhermore, the decrease in meristem activity when soil water is depleted does not result from source/sink imbalances. 相似文献12.
Changes in Individual Allometry Can Lead to Species Coexistence without Niche Separation 总被引:1,自引:0,他引:1
The principle of competitive exclusion is a fundamental tenet of ecology. Commonly used competition models predict that at
most only one species per limiting resource can coexist in the same environment at steady state; hence, the upper limit to
species diversity depends only on the number of limiting resources and not on the rates of resource supply. We demonstrate
that such model behavior is the result of both the growth and biomass turnover functions being proportional to the population
biomass. We argue that at least the growth function should be a nonlinear, concave downward function of biomass. This form
for the growth function should arise simply because of changes in the allometry of individuals in the population. With this
change in model structure, we show that any number of species can coexist at an asymptotically stable steady state, even where
there is only one limiting resource. Furthermore, if growth increases nonlinearly with biomass, the steady-state resource
concentration and hence the potential for biodiversity increases as the resource supply rate increases.
Received 31 August 2001; accepted 10 April 2002. 相似文献
13.
14.
The optimal allocation theory predicts that growth is allocated between the shoot and the roots so that the uptake of the
most limiting resource is increased. Allocation is dynamic due to resource depletion, interaction with competitors, and the
allometry of growth. We assessed the effects of intra- and inter-specific competition on growth and resource allocation of
the meadow species Ranunculus acris and Agrostis capillaris, grown in environments with high (+) or low (−) availability of light (L) and nutrients (N). We took samples twice a week
over the 7 weeks experiment, to follow the changes in root-to-shoot ratios in plants of different sizes, and carried out a
larger scale harvest at the end of the experiment. Of all the tested factors, availability of nutrients had the largest effect
on the growth rate and shoot-to-root allocation in both species, although both competition and light had significant effects
as well. The highest root-to-shoot ratios were measured from the L+N− treatment, and the lowest from the L−N+ treatment, as
predicted by the optimal allocation theory. Competition changed resource allocation, but not always toward acquiring the resource
that is most limiting to growth. We thus conclude that the greatest variation in shoot-to-root allocation was due to the resource
availability and the effects of competition were small, probably due to low density of plants in the experiment. 相似文献
15.
Searching for a model for use in vegetation analysis 总被引:8,自引:0,他引:8
M. P. Austin 《Plant Ecology》1980,42(1-3):11-21
Summary Indirect gradient analysis methods require an explicit vegetation model which must be based on direct gradient analysis studies. Various vegetation models are reviewed. Field evidence for the models is discussed. Experimental studies of species response to environmental gradients are reviewed and discussed. Three types of gradient are recognized as important for development of models: indirect environmental gradients where the environmental factor has no direct physiological influence on plant growth e.g. elevation; direct environmental gradients where the factor has a direct physiological effect on growth but is not an essential resource, e.g. pH; resource gradients where the factor is an essential resource for plant growth. The behaviour of the ecological carrying capacity and the role of competition along such gradients are shown to be important for developing vegetation models. 相似文献
16.
Damgaard C 《Comptes rendus biologies》2004,327(3):255-260
Neighbouring plants generally compete for the limiting resources in order to grow and reproduce. Some resources, e.g., sun light, may be monopolised by the larger plants and this may lead to asymmetric competition where a plant, which is twice as large, grows more than twice as fast. A previously published individual-based Richards growth model that describes the asymmetric growth of individual plants is here generalised with respect to a variable mean plant density and an explicit spatial setting. 相似文献
17.
Resource competition and suppression of plants colonizing early successional old fields 总被引:3,自引:0,他引:3
Early colonizing annual plants are rapidly suppressed in secondary succession on fertile midwestern old fields, while later
colonizing perennials persist. Differences in competitive ability for above- and belowground resources may be partly responsible
for differences in species persistence during succession, as both light and nutrient availability may change rapidly. We found
that, although both above- and belowground competition suppress growth of colonizing plants, belowground competition was the
dominant factor in the suppression of the annual Ambrosia artemisiifolia in 2nd-year-old fields near the W.K. Kellogg Biological Station in southwestern Michigan. Despite an ability to persist in
later successional fields, seedling transplants of the perennial Achillea millefolium were also suppressed by above- and belowground competition, with belowground competition having the strongest effect. As
in many old fields, nitrogen availability is the primary factor limiting plant productivity. There was no clear difference
between the species in ability to compete for 15N from an enriched patch, although there was an indication of greater precision of foraging by Achillea. Life history differences between these species and consequent differences in the phenology of root growth relative to other
old-field plants are likely to play a large role in the persistence of Achillea in successional fields where Ambrosia is suppressed.
Received: 8 January 1998 / Accepted: 16 September 1998 相似文献
18.
19.
Metal complexes increase uptake of Zn and Cu by plants: implications for uptake and deficiency studies in chelator-buffered solutions 总被引:1,自引:0,他引:1
The allocation of resources among roots and shoots represents the largest flux of resources within a plant and therefore should have been selected to maximize benefits to plants. Yet, it is unclear why some species like temperate grasses have such high root length density (RLD). Either the slow rate of diffusion of inorganic N in soils or interplant competition could explain the high RLD of temperate grasses. Using a fine-scale model of nutrient dynamics in the soil and plant growth, a cost–benefit approach was used to assess optimal allocation rates for plants that accounted for value of both carbon and nitrogen. In the absence of interplant competition, resource benefits are maximized with very little root length except in extremely dry soils for ammonium. In the presence of a competitor, optimal allocation of N to roots is much greater and increases as ability of competitors to produce root length increase. Competition for inorganic nitrogen generates a classic aspect of the tragedy of the commons, the “race for fish”, where plants must allocate more resources to acquisition of the limiting resource than is optimal for plants in the absence of competition. As such, nutrient competition needs to be directly addressed when understanding plant- and ecosystem-level resource fluxes as well as the evolution of root systems. 相似文献
20.
Sebastian J. Schreiber 《Journal of mathematical biology》1997,36(2):133-148
General dynamic models of systems with two prey and one or two predators are considered. After rescaling the equations so
that both prey have the same intrinsic rate of growth, it is shown that there exists a generalist predator that can mediate
permanence if and only if there is a population density of a prey at which its per-capita growth rate is positive yet less
than its competitor’s invasion rate. In particular, this result implies that if the outcome of competition between the prey
is independent of initial conditions, then there exists a generalist predator that mediates permanence. On the other hand,
if the outcome of competition is contingent upon initial conditions (i.e., the prey are bistable), then there may not exist
a suitable generalist predator. For example, bistable prey modeled by the Ayala–Gilpin (θ-Logistic) equations can be stabilized
if and only if θ<1 for one of the prey. It is also shown that two specialist predators always can mediate permanence between
bistable prey by creating a repelling heteroclinic cycle consisting of fixed points and limit cycles.
Received 10 August 1996; received in revised form 21 March 1997 相似文献