Institute of Horticultural Production Systems Vegetable Systems Modelling Hartmut Stützel and Tsu-Wei Chen Plant canopies under drought stress– structures, functions, (genes) and models

2 Plant canopies: structural and functional properties  Leaf area index  Inclination of leaves  Leaf angle distribution  Leaf curvature  Optical properties  Light extinction coefficient  Gap fraction  Internode length  Canopy photosynthesis  CO 2 transport (stomatal, mesophyll resistance)  Biochemical conversion (Rubisco, light)  Transpiration Canopies under stress Light intensity, light quality and availability of water

3 Canopies under stress How are these functional and structural properties influenced by stress? How can we quantify stress effects on function and structure?

4 Morphological traits of wheat as related to water supply Canopies under stress after data fom Zhang et al. 2011

5 Simulated diurnal time course of net canopy photosynthesis for a maize crop having leaf area index (L) of 2, 4, or 8 and average leaf inclination from the horizontal of (a) 40°or (b) 80°. Simulation conducted for Day 180 of the year at Johnston, IA (41°40′ N lat) Hammer et al Canopies under stress

6 Simulated effects of increasing and decreasing leaf angle by 30 % on light extinction coefficient and Light interception of tomato canopies Canopy light interception: 78% Light extinction coefficient: 0.60 ± 0.02 Canopy light interception: 49% Light extinction coefficient 0.27 ± 0.01 Canopies under stress Chen et al. 2014, J. exp. Bot., accepted 130% 70%

7 Response of net photosynthetic CO 2 assimilation (PN) to intercellular CO 2 concentration (c i ) of barley plants grown at ambient (A) and elevated (B) [CO 2 ] and subjected to well-watered conditions (circles) or 9 (squares), 13 (triangles) and 16 d (diamonds) of water stress. Canopies under stress Robredo et al. 2010

8 Generalized response of net photosynthesis (A N ) and several parameters related to photosynthetic capacity to water stress when using daily maximum leaf stomatal conductance (g s ) content as the reference for stress intensity Flexas et al Canopies under stress

9 Modelling canopy processes  Big leaf models: treat the canopy as an extended leaf (or a small set of large leaves), map the properties of a whole canopy onto a single leaf (or a few leaves, Amthor, 1994)  Sunlit-shade models: divide the (big leaf) canopy and leaf nitrogen between sunlit and shaded leaves (de Pury and Farquhar 1997)  Multi-layer models: canopy is divided into layers, each with different light level, predicted by Beer’s law, and differentiation into sunlit and shade leaves (including a sunfleck penetration), a coupled scheme of leaf photosynthesis and stomatal conductance (Clark et al., 2011) → no precise prediction of the spatial and temporal hetero- geneities of light inside a canopy Canopies under stress

10 Diurnal canopy CO 2 uptake rate (A c ) of a rice canopy calculated with average photosynthetic photon flux density (PPFD) at different layers of a canopy (average light) compared with A c calculated using the detailed PPFD of each individual facet in the canopy (detailed light). Song et al Canopies under stress

11 Functions StructureEnvironment Spatially explicit models of canopies: Functional- structural plant models (FSPM)  Simulate plant growth and development based on individual organs  Explicitly allow for feedbacks between plant structure and plant function  Interactions between organs  Canopies are constructed as assemblies of plants  Static  Dynamic Canopies under stress

12 Functions StructureEnvironment Dynamic cucumber architecture model Canopies under stress

13 The virtual 2 m cucumber canopy with 18 plants, constructed using digitized data in GroIMP, in top view (A) and side view (B). Chen et al. 2014; doi: /aob/mcu100 Canopies under stress

14 An example of dynamic functional-structural plant model (L-Peach, Allen, Prusinkiewicz and DeJong, 2005)

15 Functional-structural models: research questions  Spatial integration of processes  Effects of physiological limitations on canopy performance  Effects of light direction (e.g. direct/diffuse) on growth  Disentangling physiological from morphological effects  Influence of canopy architecture modifications: row width, plant density etc.  Assessment of plant traits: breeding, pruning …. Canopies under stress

16 Simulated leaf photosynthesis rate under 100 % direct light and 100 % diffuse light in a cucumber canopy Chen et al. 2014; doi: /aob/mcu100 Canopies under stress

17 Analysis of limitations to productivity:  Physiological limitations  Photosynthesis  CO 2 diffusion  Biochemical apparatus  Light  Structural limitations  Leaf area  Leaf area distribution  Leaf exposition: leaf angle, azimuth angle Canopies under stress

18 Reference photosynthesis rate Current photosynthesis rate Diffusional limitation Biochemical limitation Light limitation Current CO 2 conc. Calculation of photosynthetic limitations due to biochemical, light and diffusional factors Canopies under stress

19 Changes of (A)stomatal, (B) mesophyll, (C) diffusional (stomatal + mesophyll), (D) biochemical, (E) light and (F) total (diffusional + biochemical + light) limitations with leaf rank (counted from bottom to top) and light conditions above the canopy (79 % direct light and 21 % diffuse light) Chen et al. 2014; doi: /aob/mcu100 Canopies under stress

20 Canopies under stress Chen et al. 2014; doi: /aob/mcu100

21 Simulated relationships between water potential in the root zone and photosynthetic limitations of a cucumber leaf on day 15 after leaf appearance. The environmental conditions were: ambient CO 2 concentration = 380 ppm, water vapour deficit = 0.87 kPa, leaf absorbed light intensity = 800 µmol m -2 s -1, and leaf temperature = 25°C. Canopies under stress

22 Simulated effects of drought stress (soil water potential MPa) on photo- synthesis rates at different positions in a cucumber canopy Canopies under stress

23 Simulated effects of drought stress (soil water potential MPa) on light use efficiencies at different positions in a cucumber canopy Canopies under stress

24 Canopy part upper middle- upper middle- lower lower whole plant Maximum A c (µmol plant -1 s -1 ) Non-stress Drought Maximum LUE c (µmol CO 2 /µmol PAR) Non-stress Drought I c for maximum LUE c (µmol plant -1 s -1 ) Non-stress Drought Influence of drought stress (water potential Ψs = -0.4 MPa in the root zone) on canopy photosynthesis and light use efficiency in different positions of the canopy Canopies under stress

25 Light interception Osmotic stress Ionic stress (ion accumulation) Organ size red. Stom. conduct. red. Photosynthesis Transpiration Ion accumulation What happens under salinity? Toxic Biochemical capacity Light use efficiency Non-architectural effects Architectural effects Canopies under stress

26 y = x R 2 = 0.99 y = x R 2 = 0.91 Effect of salinity on shoot dry mass on day 77 after the first leaf appearance under 22/18°C (low temperature) and 32/28°C (high temperature) day/night temperature conditions Canopies under stress

27 Relative light use efficiency at three salinity levels under low (LT, 22/18°C) and high (HT, 32/28°C) day/night temperature conditions 40 mM60 mM80 mM Day LTHTLTHTLTHT Canopies under stress

28 Total and architectural effects of salinity on shoot dry mass on day 77 after the first leaf appearance under 22/18°C (low temperature) and 32/28°C (high temperature) day/night temperature conditions Canopies under stress

29 Conclusions  A canopy is more than a big leaf  Canopy structure has strong impact on productivity and resource use → optimization  Systematic analysis of architectural effects on productivity and resource use is just at the beginning  FSPM are models Canopies under stress

30 Thank you! Canopies under stress