Differential effects of light quality, provided by different grass neighbours, on the growth and morphology of Trifolium repens L. (white clover)

Abstract

The ability to respond in a specific manner to different light conditions imposed by different species of grass is a major factor contributing to white clover persistence in pastures. Gaps in a pasture provide light with a higher red:far-red ratio (R:FR) and higher photosynthetic photon flux density (PPFD) than the light filtered through neighbours. White clover (Trifolium repens L.) was grown under different light conditions in ways that tried to simulate as closely as possible some of the light conditions experienced in a natural field situation, being partially shaded and receiving light reflected from neighbouring grasses. The objective was to determine specifically if the mere presence of neighbouring grasses could influence the growth and morphology of white clover individuals without physically contacting them, and thereby send a signal of impending competition. In the first experiment, white clover was subjected to shading cast from three different grass species. There were differences in both the quantity and quality of light received under the various grass canopies. The canopies reduced overall growth and branching of clones, while increasing the length of and biomass allocation to petioles. Lolium perenne L. canopy shade had different effects compared to Holcus lanatus L. or Dactylis glomerata L., but between the latter two species, no differences were detected. In the second experiment, light reflected from grass neighbours was provided simultaneously with direct light. There was a strong increase in FR and a resulting decrease in the R:FR due to neighbouring D. glomerata, but few consistent effects on white clover growth and morphology; there was evidence of phototropic movement by the leaves. We show that plants must experience partial shading, and not just reflected light, in order to alter their morphology in response to the presence of different species of grass neighbours.

Species richness and identity affect the use of aboveground space in experimental grasslands

“…Gradients of light availability (photon flux density) and spectral light quality are developed within closed canopies (Monsi and Saeki, 1953;Jones, 1992). Changes in light quality perceived by phytochrome may control the activity of axillary buds, tillering and the formation of reproductive shoots in grass species (Deregibus et al, 1985;Casal et al, 1986 and Harper, 1987;Thompson and Harper, 1988;Markuvitz and Turkington, 2000) and other stoloniferous species (Schmid, 1986) and would consequently lead to decreased abundances of such species. Thus, light quality does not only induce shade-avoidance reactions.…”

Morphological plasticity of white clover (Trifolium repens L.) in response to spatial and temporal resource heterogeneity

“…Individuals possess a spreading architecture, with each clone (the product of a given genet) being composed of many ramets connected by stolons. Resource heterogeneity is an important determinant of ramet morphology Marcuvitz and Turkington 2000), and the occupation of favorable microsites may be important to the long-term survival of a clone (Snaydon 1962;Chapman 1983;Harris 1987;Parish 1987). Clover growth is usually suppressed by competition with grasses (Turkington and Harper 1979;Turkington 1989;Bülow-Olsen et al 1984); however, microsites favorable to growth occur naturally in these pastures due to variation in soil factors, (Snaydon 1962), or from animal activity (dung pats, mole hills, and urine spots ;Weeda 1976;Parish andTurkington 1990a, 1990b).…”

Variation in petiole and internode length affects plant performance in Trifolium repens under opposing selection regimes

“…Factors contributing to temporal and spatial heterogeneity in pastures are variation in soil conditions, irregular disturbance due to herbivory and human activity such as mowing (Farley and Fitter 1999;Jackson and Caldwell 1993;Waite 1994). Herbaceous vegetations can be characterized as dynamic mosaics of different microhabitats ranging from sites with low levels of disturbance, and severe competition for light, to more open spots with low above ground competition resulting from high levels of canopy disturbance by grazing or mowing (Evans and Turkington 1988;Marcuvitz and Turkington 2000).…”