Effects of Plant Morphology and Emergence Time on Size Hierarchy Formation in Experimental Populations of Two Varieties of Cultivated Peas (Pisum Sativum)

Abstract

The effects of plant form and emergence time on size hierarchy formation in populations of two morphologically and genetically distinct varieties of peas (leafless and leafed) were studied. There were no significant differences in germinability between the two varieties, although leafless peas imbibed more rapidly than the leafed ones did. Monocultures of leafed and leafless peas were established at two densities: plants grown alone in small pots and plants grown at 576 m ‐. Time emergence was noted, and plant shape, biomass and seed production were measured at two‐week intervals for ten weeks. Seedlings emerged continually over an eight‐day period, and two cohorts of seedlings were distinguished (seedlings emerging 6–7 days after planting, and seedlings emerging > 7 days after planting). Dominance and suppression were observed in the high‐density populations, and early‐emerging plants had less hierarchical biomass distributions than did late‐emerging ones. Although leafless peas were larger and suffered less mortality than leafed ones did at identical densities, there were no differences in the degree of size inequality between the two genotypes (emergence cohorts pooled), or within emergence cohorts between genotypes. The degree of size inequality increased with time among dominant individuals and decreased with time among suppressed individuals. These results broadly support Weiner and Thomas's (1986) hypothesis that plant form may affect the extent but not the existence of competitive asymmetry in plant populations.

Density Effects on Plant Height Growth and Inequality in Sunflower Populations

“…The plasticity of plant growth forms in response to light competition has been a focus of plant intraspecific competition studies (Franco 1985;Ellison 1987;Ellison and Rabinowitz 1989;Geber 1989;Holbrook and Putz 1989;Weiner 1990;Weiner et al 1990;Weiner and Thomas 1992;Weiner and Fishman 1994;Nagashime et al 1995;Wang and Zhang 1997;Henry and Aarssen 1999;Arenas et al 2002;Li et al 2006). Because light is a directional and pre-emptable resource (Schwinning and Weiner 1998), plant height plays an important role in determining light interception and, hence, height may become a primary determinant of individual success in dense plant stands (Weiner and Fishman 1994).…”

Branching and competitive hierarchies in populations of <i>Galium aparine</i>

“…Previous studies have suggested that the absence of competitive hierarchy development in some crowded populations of plants is typical of plant species in which branching is limited and shade casting by leaves is inherently low, as in grasses and small-leafed or leafless species (Turner and Rabinowitz 1983;Ellison 1989;Ellison and Rabinowitz 1989;Geber 1989). In view of the present results, it could be suggested, alternatively, that the development of competitive hierarchies would be restricted whenever plant-plant interactions prevent height differences among neighbours to increase.…”

“…Intraspecific plant-plant interactions usually increase size inequality among neighbours compared with that among noncompeting plants (e.g., Lomnicki 1988;Weiner and Thomas 1986;Weiner 1990). Although differences in seed size and emergence time are known to increase size inequalities (Stanton 1985;Miller 1987;Ellison and Rabinowitz 1989), growth inequalities caused by unequal resource capture are believed to play a key role in the development of size inequalities among crowded plants (Weiner and Thomas 1986). The development of competitive hierarchies in crowded populations is also evidenced by size-related differences in plant shape and by a permanent position of neighbour plants on a size-ranking scale (Franco and Harper 1988;Geber 1989;Thomas and Weiner 1989;Bazzaz 1993, 1995;Weiner and Thomas 1992;Weiner and Fishman 1994;Aibo and Kohyama 1996).…”

Size Hierarchy and Stability in Competitive Plant Populations

“…The degree of asymmetry of competition between individuals is primarily determined by individual plant characteristics such as vertical foliage profile, growth pattern (plant height growth vs stem diameter growth), biomass allocation pattern between leaves, stems and roots, physiological parameters (photosynthetic rate, nutrients absorption rate, etc.) and underground fungal networks in relation to resources for which plants compete [e.g., Hara (1988); Ellison and Rabinowitz (1989); Weiner (1990); Yokozawa and Hara (1995) and Schwinning and Weiner (1998)]. In particular, it has been shown both theoretically and by field data analysis that conifers tend to show asymmetric competition while broad-leaved trees show symmetric competition (Hara et al, 1991;Lundqvist, 1994;Stoll et al, 1994;Yokozawa and Hara, 1995;Kikuzawa and Umeki, 1996).…”