The architecture of plants is linked to a wide variety of functions. Such functions include efficient water transport, light interception, soil resource acquisition, and the maintenance of a mechanically stable structure. From an ecological/evolutionary perspective, plants are supposed to establish an architecture that allows them to optimize such functions. Plants are however not static, because they develop their architecture gradually over their life, and in response to changes in environmental conditions. Some concepts of plant architecture therefore include plant development too.
Plant architecture can be regarded at different scales, and has been manipulated by people for several purposes (Turnbull et al. 2005). In this section, we will focus on plant architecture at the whole plant level and individual branch level, since the lower levels of organization are covered elsewhere (e.g. Anatomy and Microscopy, Morphology ).
Halle, Oldeman and Tomlinson (1978) provided a protocol to classify the modular structure and development of woody plants. These protocols have been refined later. The protocols distinguish between different growth processes, branching processes, morphological differentiation of branches, and the position of reproductive organs. While originally the protocols provided descriptions of the “potential” development and architecture of plants (Sterck 2005), i.e. plants without severe environmental stress, the descriptions are also used to interpret underlying physiological processes and plastic responses (Barthelemy and Caraglio 2007).
3D architectural simulation for light interception efficiency
The 3D distribution of leaves and stem segments has been formalized for using the plant model YPlant (Pearcy and Yang 1996). The modeling approach is based on a protocol for measuring sizes, form and orientation of different plant components, i.e. the stem segments between leaves and the individual leaves. The model provides a number of functional properties, including the efficiency of light interception, water balance, and mechanical stability (Pearcy et al. 2005, Tyree & Zimmermann 2002).
Above ground woody plant size and form
The above ground plant size and form express how plants compete for space and light, and how they balance the form for, for example, water transport and transpiration, leaf display and stability, and reproduction (Sterck 2005). When size/form are considered for different ages or reference sizes, they can show major size and form changes during plant life (Poorter et al. 2007). Size and form traits are also critical for estimating the biomass accumulation and the carbon reserves in vegetations, particularly in forests (Chaves et al. 2005).
Clonal plant architecture
In contrast to woody plants, clonal plants mainly forage in horizontal direction for resources, and develop a completely different architecture than unitary plants. For clonal plants, apical dominance, branching (or “spacer”) angles and lengths are strong drivers of the spatial architecture and resource use by clonal plants (Callaghan et al. 1990, de Kroon & Schieving 1991).
Leaf area index
Leaf area index can be considered at the vegetation and individual plant level. For an individual plant, leaf area index is defined as the amount of leaf area per unit ground area of the horizontally projected crown. It provides information on light interception per unit crown area, which determines on the one hand the light acquisition by a plant and the shade it casts on its shorter neighbors. It can be measured precisely for small individual plants, and estimated non-destructively for larger plants/trees. Because of its obvious relationship with productivity, leaf area index is a central component in productivity models for plants (Horn 1971, Sterck & Schieving 2007), vegetations (Monsi & Saeki 195, Anten 2005) and globe (Zhao & Running 2010).
Water balance traits
The leaf area to sapwood area expresses a balance between transpiration and stem water supply. It can be determined at whole plant level (Shinozaki et al 1964) and branch level (e.g. Martinez-Villalta et al. 2009). Water balance traits can be refined by taking the specific hydraulic conductivity of the functional wood into account, and is often referred to as leaf specific conductivity (Tyree and Zimmermann 2002). Branch specific conductivity is considered a more physiological trait by itself, and covered in the Water relations section.
Root size and form
The mass and length distribution of roots can be determined at the vegetation level, and from average rooting depth can be determined, and for example the 95% quantile rooting depth as a proxy for maximum rooting depth.
The fine root mass fraction gives the mass distributed in acquisitive roots versus the total mass of roots, including the larger transporting parts. Also see Soils and Rhizosphere and Morphology sections.
Anten NPR. 2005. Optimal photosynthetic characteristics of individual plants in vegetation stands and implications for species coexistence. Annals of Botany 95: 495-506.
Barthelemy D, Caraglio Y. (2007) Plant architecture: a dynamic, multilevel and comprehensive approach to plant form, structure and ontogeny. Annals of Botany 99: 375-407.
Callaghan TV et al. 1990. Models of clonal plant growth based on population dynamics and architecture. Oikos 57: 257-269.
Chave et al. 2005. Tree allometry and improved estimation of carbon stocks and balance in tropical forests. Oecologia 145: 87-99.
De Kroon H, Schieving F. 1991. Resource allocation patterns as a function of clonal morphology: a general model applied to a foraging clonal plant. Journal of Ecology 79: 519-530.
Halle F, Oldeman RAA, Tomlinson PB (1978) Tropical trees and forests. Berlin, Springer-Verlag.
Horn HS. 1971. The adaptive geometry of plants. Princeton University Press, USA.
Martinez-Vilalta et al. (2009). Hydraulic adjustment of Scots pine across Europe. New Phytologist 184: 353-364.
Monsi M, Saeki T. 1953. Uber der Lichtfactor in den Pflanzengesellschaften und seine Bedeutung für die Stoffproduktion. Japanese Journal of Botany 14: 22-52.
Shinozaki K, Yoda K, Hozumi K, Kira T (1964) A quantitative analysis of plant form: the pipe model theory I. basic analyses. Japanese Journal of Ecology 14(3): 97-105.
Pearcy RW, Yang W (1996) A three-dimensional crown architectural model for assessment of light capture and carbon gain by understorey plants. Oecologia 108: 1-12.
Pearcy RW, Muraoka H, Valladares, F. 2005. Crown architecture in sun and shade environments: assessing function and trade-offs with a three-dimensional simulation model. New Phytologist 166(3): 791-800.
Poorter, L., Bongers L, Bongers F. 2007. Architecture of 54 moist-forest tree species: traits, trade-offs, and functional groups. Ecology 87(5): 1289-1301.
Sterck FJ. 2005 Woody tree architecture. In: Plant architecture and its manipulation. Annual Plant Reviews, Turnbull CGN, ed. Volume 7. Blackwell Publishing, Oxford.
Sterck FJ, Schieving F. 2007. 3-D Growth patterns of trees: effects of carbon economy, meristem activity, and selection. Ecological Monographs 77(3): 405-420.
Turnbull, CGN. 2005. Plant architecture and its manipulation. Annual Plant Reviews, Volume 7. Blackwell Publishing, Oxford.
Tyree MT, Zimmermann MH (2002) Xylem structure and the ascent of sap. Ed. Timel TE. Springer-Verlag, Berlin.
Zhao M, Running SW. 2010. Drought-reduced reduction in global terrestrial net primary production from 2000 through 2009. Science 329 (5994): 940-943.