Modelling Canopy Production. III. Canopy Light-Utilisation Efficiency and Its Sensitivity to Physiological and Environmental Variables

A previously published model which predicts daily canopy photosynthesis from standard daily meteorological data and parameters of the single-leaf photosynthetic light-response curve is extended to predict annual canopy photosynthesis. The model is based on biologically plausible assumptions about canopy structure and assumes the single-leaf light response is a non-rectangular hyperbola of arbitrary shape. It uses simple algorithms for taking diurnal variation of temperature, and seasonal temperature acclimation of photosynthesis, into account. The model provides theoretical support for the observation that production by a canopy is proportional to irradiance intercepted or absorbed by the canopy. The model is used to explore the sensitivity of annual photosynthesis to parameters of the single-leaf light response. It is shown how the sensitivity of annual canopy photosynthesis to various factors can be determined from the sensitivity of parameters of the light response to the same factors. In particular, annual photosynthesis is shown to be sensitive to the effects of nutrition and temperature on light-saturated photosynthetic rate, and to seasonal temperature acclimation of photosynthesis. It is important that the variation with temperature, nutrition and season of parameters of the single-leaf light-response function be determined.

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Modelling Canopy Production. II. From Single-Leaf Photosynthesis Parameters to Daily Canopy Photosynthesis

Functional Plant Biology ◽

10.1071/pp9950603 ◽

1995 ◽

Vol 22 (4) ◽

pp. 603 ◽

Cited By ~ 60

Author(s):

PJ Sands

Keyword(s):

Simple Algorithm ◽

Light Response ◽

Daily Maximum ◽

Canopy Photosynthesis ◽

Leaf Photosynthesis ◽

Daily Production ◽

Area Index ◽

Single Leaf ◽

Diurnal Temperature Variation ◽

Analytical Expressions

This paper presents a simple algorithm for calculating daily canopy photosynthesis given parameters of the single-leaf light response, the canopy extinction coefficient, canopy leaf area index, daylength, daily solar irradiance and daily maximum and minimum temperatures. Analytical expressions are derived for total daily production by a canopy of leaves whose light response is either a rectangular hyperbola or a Blackman response. An expression which gives an excellent approximation to canopy photosynthesis for an arbitrary hyperbolic light response is then derived. These expressions assume photosynthetically active radiation (PAR) within the canopy follows Beer's law, light-saturated photosynthetic rate at any point in the canopy is proportional to the ratio of local PAR to full-sun PAR, diurnal variation of PAR is sinusoidal, and parameters of the single-leaf photosynthetic light response do not vary diurnally. It is shown how these expressions can be used to accommodate diurnal temperature variation of photosynthesis in a simple manner. The accuracy of the approximation to the basic integral of leaf photosynthesis over the canopy and over time is illustrated by applying the algorithm to compute the seasonal variation of daily canopy photosynthesis and comparing these data with corresponding values obtained by numerical integration.

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Changes in the photosynthetic light response curve during leaf development of field grown maize with implications for modelling canopy photosynthesis

Photosynthesis Research ◽

10.1007/bf00018264 ◽

1994 ◽

Vol 42 (3) ◽

pp. 217-225 ◽

Cited By ~ 22

Author(s):

C. M. Stirling ◽

C. Aguilera ◽

N. R. Baker ◽

S. P. Long

Keyword(s):

Leaf Development ◽

Response Curve ◽

Light Response ◽

Canopy Photosynthesis ◽

Light Response Curve

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A model of frost impacts on seasonal photosynthesis of Eucalyptus pauciflora

Functional Plant Biology ◽

10.1071/pp97098 ◽

1998 ◽

Vol 25 (1) ◽

pp. 27 ◽

Cited By ~ 17

Author(s):

David A. King ◽

Marilyn C. Ball

Keyword(s):

Response Curve ◽

Time Course ◽

Light Response ◽

Initial Slope ◽

Canopy Photosynthesis ◽

Light Response Curve ◽

Plant Sensitivity ◽

Highly Nonlinear ◽

Short And Long Term

A model of the time course of frost impacts on seasonal photosynthesis of Eucalyptus pauciflora Sieb. ex Spreng. was constructed, incorporating seasonal shifts in frost hardiness and both short- and long-term impacts on the initial slope and saturated level of the photosynthetic light response curve. The approach is an extension of Sands’ model (Australian Journal of Plant Physiology, 1995, 22, 603–614) which calculates daily canopy photosynthesis as a function of daily irradiance and temperatures without the impacts of cold nights. Modelled effects of frost on cumulative photosynthesis over 8 months were highly nonlinear and rather sensitive to the temporal sequence of minimum temperatures and extent of frost hardening. Most of the effects were associated with long-term damage caused by a few severe or unseasonal frosts. Shifting either plant sensitivity or minimum temperatures by several degrees had large impacts on predicted outcomes. These results are consistent with other observations that the increase in frost severity associated with land clearing is impeding eucalypt regeneration in interior Australia and may be applicable to other frost-prone areas.

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Modelling Canopy Production. I. Optimal Distribution of Photosynthetic Resources

Functional Plant Biology ◽

10.1071/pp9950593 ◽

1995 ◽

Vol 22 (4) ◽

pp. 593 ◽

Cited By ~ 38

Author(s):

PJ Sands

Keyword(s):

Photosynthetic Rate ◽

Homogeneous Function ◽

Nitrogen Concentration ◽

Light Response ◽

Leaf Nitrogen ◽

Optimal Distribution ◽

Canopy Photosynthesis ◽

Area Index ◽

Single Leaf ◽

Canopy Nitrogen

On the basis of detailed numerical simulations, Field (1983. Oecologia 56, 341-347) stated that total canopy photosynthesis will be a maximum for a fixed total canopy leaf nitrogen provided the derivative δA/δN, where A is photosynthetic rate and N is leaf nitrogen concentration, has the same value throughout the canopy. This paper uses the calculus of variations to formally prove Field's assertion. It shows that if the single-leaf light response is a first-degree homogeneous function of both light-saturated photosynthetic rate Amax and intensity I of photosynthetically active radiation and if Amax is linearly related to N, then the optimal distribution of leaf nitrogen is linearly related to the decline in I with canopy depth, and Amax is proportional to this decline. The nature of photosynthetic gains due to optimisation of canopy nitrogen distribution is illustrated numerically for a simple model canopy. It is found that, for canopies with fixed mean leaf nitrogen, canopy photosynthesis is approximately proportional to canopy leaf area index (LAI), and the gain due to canopy optimisation compared with a uniform canopy is small for shallow canopies but pronounced for deep canopies. It is also found that, for canopies with fixed total leaf nitrogen, there is a canopy LAI which maximises canopy photosynthesis, and that this LAI and the corresponding canopy photosynthesis are approximately proportional to total canopy nitrogen.

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