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Silva Fennica vol. 36 no. 3 | 2002

Special issue: Optimality Approach in Plant Ecology

Category : Research article

article id 533, category Research article

Anna Liisa Ruotsalainen, Juha Tuomi, Henry Väre. (2002). A model for optimal mycorrhizal colonization along altitudinal gradients. Silva Fennica vol. 36 no. 3 article id 533. https://doi.org/10.14214/sf.533

Keywords: alpine gradient; mycorrhiza; nutrient uptake kinetics; photosynthetic nutrient use efficiency

Abstract | View details | Full text in PDF | Author Info

Mycorrhizal associations are generally favourable for vascular plants in nutrient-poor conditions. Still, non-mycorrhizal plants are common in high arctic and alpine areas, which are often poor in nitrogen and phosphorus. The relative proportion of mycorrhizal plants has been found to decrease along with increasing altitude, suggesting that the advantage of the mycorrhizal symbiosis may change along an altitudinal gradient. This may be related to the environmental factors that possibly constrain the amount of photosynthesized carbon to be shared with mycorrhizal fungi. We propose a simple optimization model for root colonization by fungal symbionts and analyze the advantages of mycorrhizas in relation to the nutrient use efficiency of photosynthesis (PNUE), the kinetics of nutrient uptake and the soil nutrient levels. Our model suggests that mycorrhizas are not usually favoured at low PNUE values. At low nutrient levels, mycorrhizas may be advantageous if they have a lower threshold concentration of nutrient uptake (xmin) compared to non-mycorrhizal roots. If mycorrhizal roots have a higher maximum capacity of nutrient uptake (Vmax), mycorrhizas can be favourable for the host plant even at relatively low nutrient concentrations and at relatively low PNUE. Consequently, the possible patterns along altitudinal gradients essentially depend on PNUE. If the soil nutrient concentration is constant and PNUE decreases, the advantage of mycorrhizal symbiosis declines independently of the nutrient uptake kinetics. If PNUE remains constant and the soil nutrient concentration decreases along with increasing altitude, the emerging colonization pattern (either increasing, decreasing or intermediate) depends on the nutrient uptake kinetics. Additionally, if both PNUE and the soil nutrient concentration decrease, several patterns may emerge, depending on the nutrient uptake kinetics.

Ruotsalainen, Department of Biology, Botanical Museum, Box 3000, FIN-90014 University of Oulu, Finland E-mail: annu.ruotsalainen@oulu.fi
Tuomi, Department of Biology, Box 3000, FIN-90014 University of Oulu, Finland E-mail: jt@nn.fi
Väre, Botanical Museum, Finnish Museum of Natural History, Box 7, FIN-00014 University of Helsinki, Finland E-mail: hv@nn.fi

article id 532, category Research article

Pedro J. Aphalo, Anna W. Schoettle, Tarja Lehto. (2002). Leaf life span and the mobility of “non-mobile” mineral nutrients – the case of boron in conifers. Silva Fennica vol. 36 no. 3 article id 532. https://doi.org/10.14214/sf.532

Keywords: needle age; conifers; model; boron; leaf life span; nutrient mobility; toxicity

Abstract | View details | Full text in PDF | Author Info

Nutrient conservation is considered important for the adaptation of plants to infertile environments. The importance of leaf life spans in controlling mean residence time of nutrients in plants has usually been analyzed in relation to nutrients that can be retranslocated within the plant. Longer leaf life spans increase the mean residence time of all mineral nutrients, but for non-mobile nutrients long leaf life spans concurrently cause concentrations in tissues to increase with leaf age, and consequently may reduce non-mobile nutrient use efficiency. Here we analyze how the role of leaf life span is related to the mobility of nutrients within the plant. We use optimality concepts to derive testable hypotheses, and preliminarily test them for boron (B), a nutrient for which mobility varies among plant species. We review published and unpublished data and use a simple model to assess the quantitative importance of B retranslocation for the B budget of mature conifer forests and as a mechanism for avoiding toxicity.

Aphalo, Faculty of Forestry, University of Joensuu, P.O. Box 111, FIN-80101 Joensuu, Finland; Current address Department of Biological and Environmental Science, University of Jyväskylä, P.O. Box 35, FIN-40351 Jyväskylä, Finland. E-mail: pedro.aphalo@jyu.fi
Schoettle, Rocky Mountain Research Station, 240 West Prospect Road, Fort Collins, CO 80526, USA E-mail: aws@nn.us
Lehto, Faculty of Forestry, University of Joensuu, P.O. Box 111, FIN-80101 Joensuu, Finland E-mail: tl@nn.fi

article id 531, category Research article

Thomas N. Buckley, Jeffrey M. Miller, Graham D. Farquhar. (2002). The mathematics of linked optimisation for water and nitrogen use in a canopy. Silva Fennica vol. 36 no. 3 article id 531. https://doi.org/10.14214/sf.531

Keywords: stomatal conductance; optimality theory; nitrogen allocation; NUE; WUE

Abstract | View details | Full text in PDF | Author Info

We develop, and discuss the implementation of, a mathematical framework for inferring optimal patterns of water and nitrogen use. Our analysis is limited to a time scale of one day and a spatial scale consisting of the green canopy of one plant, and we assume that this canopy has fixed quantities of nitrogen and water available for use in photosynthesis. The efficiencies of water and nitrogen use, and the interactions between the two, are strongly affected by physiological and physical properties that can be modeled in different ways. The thrust of this study is therefore to discuss these properties and how they affect the efficiencies of nitrogen and water use, and to demonstrate, qualitatively, the effects of different model assumptions on inferred optimal strategies. Preliminary simulations suggest that the linked optimisation of nitrogen and water use is particularly sensitive to the level of detail in canopy light penetration models (e.g., whether sunlit and shaded fractions are pooled or considered independently), and to assumptions regarding nitrogen and irradiance gradients within leaves (which determine how whole-leaf potential electron transport rate is calculated from leaf nitrogen content and incident irradiance).

Buckley, Environmental Biology Group, Research School of Biological Sciences, The Australian National University, GPO Box 475, Canberra City, ACT 2601, Australia and Cooperative Research Centre for Greenhouse Accounting, RSBS, ANU E-mail: tom_buckley@alumni.jmu.edu
Miller, Environmental Biology Group, Research School of Biological Sciences, The Australian National University, GPO Box 475, Canberra City, ACT 2601, Australia E-mail: jmm@nn.au
Farquhar, Environmental Biology Group, Research School of Biological Sciences, The Australian National University, GPO Box 475, Canberra City, ACT 2601, Australia and Cooperative Research Centre for Greenhouse Accounting, RSBS, ANU E-mail: gdf@nn.au

article id 530, category Research article

Graham D. Farquhar, Thomas N. Buckley, Jeffrey M. Miller. (2002). Optimal stomatal control in relation to leaf area and nitrogen content. Silva Fennica vol. 36 no. 3 article id 530. https://doi.org/10.14214/sf.530

Keywords: stomatal conductance; optimal leaf area; optimality theory; resource substitution

Abstract | View details | Full text in PDF | Author Info

We introduce the simultaneous optimisation of water-use efficiency and nitrogen-use efficiency of canopy photosynthesis. As a vehicle for this idea we consider the optimal leaf area for a plant in which there is no self-shading among leaves. An emergent result is that canopy assimilation over a day is a scaled sum of daily water use and of photosynthetic nitrogen display. The respective scaling factors are the marginal carbon benefits of extra transpiration and extra such nitrogen, respectively. The simple approach successfully predicts that as available water increases, or evaporative demand decreases, the leaf area should increase, with a concomitant reduction in nitrogen per unit leaf area. The changes in stomatal conductance are therefore less than would occur if leaf area were not to change. As irradiance increases, the modelled leaf area decreases, and nitrogen/leaf area increases. As total available nitrogen increases, leaf area also increases. In all the examples examined, the sharing by leaf area and properties per unit leaf area means that predicted changes in either are less than if predicted in isolation. We suggest that were plant density to be included, it too would further share the response, further diminishing the changes required per unit leaf area.

Farquhar, Cooperative Research Centre for Greenhouse Accounting and Environmental Biology Group, Research School of Biological Sciences, Australian National University, ACT 2601, Australia E-mail: farquhar@rsbs.anu.edu.au
Buckley, Cooperative Research Centre for Greenhouse Accounting and Environmental Biology Group, Research School of Biological Sciences, Australian National University, ACT 2601, Australia E-mail: tnb@nn.au
Miller, Research School of Biological Sciences, Australian National University, ACT 2601, Australia E-mail: jmm@nn.au

article id 529, category Research article

Tuula Aalto, Pertti Hari, Timo Vesala. (2002). Comparison of an optimal stomatal regulation model and a biochemical model in explaining CO2 exchange in field conditions. Silva Fennica vol. 36 no. 3 article id 529. https://doi.org/10.14214/sf.529

Keywords: photosynthesis; Scots pine; optimization; Pinus sylvestris L.; CO2 exchange; biochemical model

Abstract | View details | Full text in PDF | Author Info

Gas exchange of Pinus sylvestris L. was studied in subarctic field conditions. Aspects on optimal control of the gas exchange were examined using approach by Hari et al. (Tree Phys. 2: 169–175, 1986). Biochemical model by Farquhar et al. (Planta 149: 78–90, 1980) was utilized to describe the photosynthetic production rate of needles. The model parameters were determined from field measurements. The results from the optimization approach and biochemical model were compared and their performance was found quite similar in terms of R2 calculated using measured exchange rates (0.89 for optimization model and 0.85 for biochemical model). Minor differences were found in relation to responses to intercellular carbon dioxide concentration and temperature.

Aalto, Finnish Meteorological Institute, Air Quality Research, Sahaajankatu 20 E, FIN-00810 Helsinki, Finland E-mail: tuula.aalto@fmi.fi
Hari, University of Helsinki, Dept. of Forest Ecology, P.O. Box 27, FIN-00014 University of Helsinki, Finland E-mail: ph@nn.fi
Vesala, University of Helsinki, Dept. of Physics, P.O. Box 64, FIN-00014 University of Helsinki, Finland E-mail: tv@nn.fi

Category : Review article

article id 535, category Review article

Thomas J. Givnish. (2002). Adaptive significance of evergreen vs. deciduous leaves: solving the triple paradox. Silva Fennica vol. 36 no. 3 article id 535. https://doi.org/10.14214/sf.535

Keywords: deciduous trees; phenology; evergreens; optimality models; leaf longevity

Abstract | View details | Full text in PDF | Author Info

Givnish, Dept of Botany, University of Wisconsin, Madison, WI 53706, USA E-mail: givnish@facstaff.wisc.edu

Category : Research note

article id 534, category Research note

Ilkka Leinonen, Heikki Hänninen. (2002). Adaptation of the timing of bud burst of Norway spruce to temperate and boreal climates. Silva Fennica vol. 36 no. 3 article id 534. https://doi.org/10.14214/sf.534

Keywords: adaptation; modelling; frost damage; bud burst; phenology; stabilizing selection

Abstract | View details | Full text in PDF | Author Info

The adaptation of the annual cycle of development of boreal and temperate trees to climatic conditions has been seen as a result of stabilizing selection caused by two opposite driving forces of natural selection, i.e. the tolerance of unfavorable conditions during the frost exposed season (survival adaptation) and the effective use of growth resources during the growing season (capacity adaptation). In this study, two theories of the effects of climate on the adaptation of the timing of bud burst of trees were evaluated. This was done with computer simulations by applying a temperature sum model for predicting the timing of bud burst of different Norway spruce genotypes on the basis of air temperature data from various climatic conditions. High geographical variation in the temperature response of bud burst, typical for Norway spruce, was included in the theoretical analyses. The average timing of bud burst and the corresponding risk of occurrence of damaging frost during the susceptible period after bud burst were calculated for each genotype in each climate. Two contrasting theories of the stabilizing selection were evaluated, i.e. the overall adaptedness of each genotype was evaluated either 1) by assuming a fixed threshold for the risk of frost damage, or 2) by assuming a tradeoff between the risk of frost damage and the length of the growing season. The tradeoff assumption produced predictions of between provenance variation in bud burst which correspond more closely with empirical observations available in literature, compared to the fixed threshold assumption.

Leinonen, University of Oklahoma, Department of Botany and Microbiology, Norman, OK 73019, USA E-mail: leinonen@ou.edu
Hänninen, University of Helsinki, Department of Ecology and Systematics, FIN-00014 Helsinki, Finland E-mail: hh@nn.fi

Category : Discussion article

article id 536, category Discussion article

Ian Cowan. (2002). Fit, fitter, fittest; where does optimisation fit in? Silva Fennica vol. 36 no. 3 article id 536. https://doi.org/10.14214/sf.536

Keywords: survival; optimisation; growth; assimilation; nitrogen-use; water-use

View details | Full text in PDF | Author Info

Cowan, Research School of Biological Sciences, Australian National University, Canberra, ACT 0200, Australia E-mail: iancowan@bigpond.com.au

Category : Commentary

article id 528, category Commentary

Annikki Mäkelä, Thomas J. Givnish, Frank Berninger, Thomas N. Buckley, Graham D. Farquhar, Pertti Hari. (2002). Challenges and opportunities of the optimality approach in plant ecology. Silva Fennica vol. 36 no. 3 article id 528. https://doi.org/10.14214/sf.528

Keywords: models; acclimation; adaptation; optimisation; evolution; hypotheses; evaluation

Abstract | View details | Full text in PDF | Author Info

A meeting was held in Hyytiälä, Finland 10–12 April 2000 to assess critically the current challenges and limitations of the optimality approach in plant ecophysiology and botany. This article summarises the general discussions and views of the participants on the use of optimisation models as tools in plant ecophysiological research. A general framework of the evolutionary optimisation problem is sketched with a review of applications, typically involved with balanced regulation between parallel processes. The usefulness and limitations of the approach are discussed in terms of published examples, with special reference to model testing. We conclude that, regardless of inevitable problems of model formulation, wider application of the optimality approach could provide a step forward in plant ecophysiology. A major role of evolutionary theory in this process is simply the formulation of testable hypotheses, the evaluation of which can lead to important advances in our ecophysiological understanding and predictive ability.

Mäkelä, University of Helsinki, Dept. of Forest Ecology, P.O. Box 27, FIN-00014 University of Helsinki, Finland E-mail: annikki.makela@helsinki.fi
Givnish, University of Wisconsin, Department of Botany, Madison, WI 53706 USA E-mail: tjg@nn.us
Berninger, University of Helsinki, Dept. of Forest Ecology, P.O. Box 27, FIN-00014 University of Helsinki, Finland E-mail: fb@nn.fi
Buckley, Cooperative Research Centre for Greenhouse Accounting and Environmental Biology Group, and Research School of Biological Sciences, Australian National University, ACT 2601, Australia E-mail: tnb@nn.au
Farquhar, Cooperative Research Centre for Greenhouse Accounting and Environmental Biology Group, and Research School of Biological Sciences, Australian National University, ACT 2601, Australia E-mail: gdf@nn.au
Hari, University of Helsinki, Dept. of Forest Ecology, P.O. Box 27, FIN-00014 University of Helsinki, Finland E-mail: ph@nn.fi

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