Density Effects on Plant Height Growth and Inequality in Sunflower Populations

Abstract

Comparisons between competing and non-competing sunflower (Helianthus annuus L.) populations demonstrate pronounced effects of density on plant height growth, height-to-crown width ratio, and a population's height inequality. In the present study, non-destructive measurements of height and the projected crown area of sunflower plants were taken at seven times from emergence to fruit maturation in even-aged monospecific stands with initial densities of 1, 4, 16, and 64 plants/m 2 . The mean height of populations increased and then decreased with increasing population density; the height inequalities of uncrowded populations decreased during stand growth, whereas the height inequalities of crowded populations decreased first and then increased during stand development. The interindividual relationships between the relative height growth rate and height within uncrowded populations became significantly negative during population growth, whereas these relationships were negative first and then became positive during the development of crowded populations. In the uncrowded populations, the static interindividual relationship between height-to-crown width ratio and volume was positive, whereas for the crowded population these relationships became negative with increasing competition for light. The data suggest that the plastic responses of plant height and height-to-crown width ratio to light competition will become more intense with increasing competition intensity. The results of the present study argue strongly for the importance of size-dependent individual-level plastic responses due to size-asymmetric light competition in generating the variations in population height inequality.

Effect of Planting Density on the Growth and Yield of Sunflower under Mulched Drip Irrigation

“…The maximum stem thickness and flower diameter were obtained for plants at a spacing of 50 cm, while the plant height reached its highest value at a plant spacing of 30 cm (Table 6). Accompanied by an increase in plant density, the maximum value of stem thickness and flower diameter decreased, while the maximum value of plant height increased, which was in agreement with the research of Xiao el al (2006) [25], who indicated that the average plant height increased with an increase in plant density (lower than 16 plants/m 2 ). However, there was no significant difference between the designed treatments on the maximum value of plant height, stem thickness, and head diameter.…”

Positive interactions can increase size inequality in plant populations

“…1). The effect of facilitation was particularly evident under low to medium population densities, but was not observed at high densities: the lowest size inequality occurred at intermediate densities, not at the lowest densities, as observed in most studies on competition (such as Weiner & Thomas 1986;Weiner et al 2001;Xiao et al 2006). This pattern is consistent with our previous results , which suggest that positive interactions dominate population behaviour at low to medium densities, while competition dominates in high-density populations (see also Dickie et al 2005;Leslie 2005).…”

“…The effect of facilitation was particularly evident under low to medium population densities, but was not observed at high densities: the lowest size inequality occurred at intermediate densities, not at the lowest densities, as observed in most studies on competition (such as Weiner & Thomas 1986; Weiner et al. 2001; Xiao et al. 2006).…”

Population Dynamics and Life History Response to Precipitation Changes for a Desert Ephemeral Plant With Biseasonal Germination

“…Adequate water not only benefits individual plant growth but also increases the density of the population. The productivity and available resources of ecosystems are limited, and a high population density intensifies competition for water, nutrients, and space among plants in a community ( Enquist et al, 1998 ; Xiao et al, 2006 ). In summary, transient fluctuations in precipitation levels can affect plant survival, thereby determining the density of plants and population expansion without affecting population structure.…”