The regulation of clover shoot growing points density and morphology during short-term clover decline in mixed swards

Abstract The spring growth of infrequently cut mixed swards, with or without inorganic fertilizer nitrogen applied, was studied at two sites. During regrowth, a decline in the sward clover content to 20–30 per cent of the initial clover content was observed in some situations (in N-fertilized swards, or during early spring growth). Changes in the density and in the morphology of clover shoot growing points were analysed during this decline in clover content. After 40 to 50 days of regrowth, the mean density of clover shoot growing points declined by 35 to 67 per cent. The mean number of growing points per branch was reduced by 17 to 69 per cent and the mean branch density by 21 to 55 per cent. The mean biomass per a clover shoot growing point was negatively correlated with growing point density and the decline in the mean growing point density was accompanied by a 200 to 300 per cent increase in the mean biomass per growing point, which indicated an asymmetrical mortality of clover shoot growing points. Clover leaf area per unit shoot weight was negatively correlated with the mean size of a growing point and, accordingly, clover leaf area ratio declined after approximately 30 days of regrowth. The links between the asymmetrical mortality of clover growing points, competition for light and the short-term decline of white clover within mixed swards allowed to regrow to a high leaf area index, are discussed.

[1]  J. Woledge,et al.  The Effect of Nitrogenous Fertilizer on the Photosynthesis and Growth of White Clover/Perennial Ryegrass Swards , 1985 .

[2]  F. Gastal,et al.  Photomorphogenesis of white clover (Trifolium repens L.) phytochrome mediated effects on 14C-assimilate partitioning , 1992 .

[3]  S. Kays,et al.  The regulation of plant and tiller density in a grass sward , 1974 .

[4]  J. Simon,et al.  Compétition pour la lumière et morphologie du trèfle blanc (Trifolium repens L.) : émission des feuilles et des ramifications , 1989 .

[5]  J. Woledge,et al.  The effect of nitrogen in spring on shoot number and leaf area of white clover in mixtures , 1987 .

[6]  J. Frame,et al.  Agronomy of White Clover , 1986 .

[7]  Jane Woledge,et al.  Growth and photosynthesis of tall and short cultivars of white clover with tall and short grasses , 1992 .

[8]  A. Laidlaw.  The effects of nitrogen fertilizer applied in spring on swards of ryegrass sown with four cultivars of white clover , 1980 .

[9]  D. Chapman.  GROWTH AND DEMOGRAPHY OF TRIFOLIUM REPENS STOLONS IN GRAZED HILL PASTURES , 1983 .

[10]  R. Turkington,et al.  Integration among ramets of Trifolium repens , 1991 .

[11]  C. Donald,et al.  Light relationships in grass-clover swards , 1962 .

[12]  C. Körner.  Some Often Overlooked Plant Characteristics as Determinants of Plant Growth: A Reconsideration , 1991 .

[13]  M. Robson,et al.  Effect of Nitrogen Supply on the Grass and Clover Components of Simulated Mixed Swards Grown under Favourable Environmental Conditions I. Carbon Assimilation and Utilization , 1985 .

[14]  J. Woledge.  Competition between grass and clover in spring as affected by nitrogen fertiliser , 1988 .

[15]  A. Davies,et al.  Effects of spring defoliation and fertilizer nitrogen on the growth of white clover in ryegrass/clover swards , 1990 .

[16]  G. Lemaire,et al.  Structure of a Lucerne Population (Medicago sativa L.) and Dynamics of Stem Competition for Light During Regrowth , 1988 .

[17]  A. Parsons,et al.  PLANT-ANIMAL INTERACTIONS IN A CONTINUOUSLY GRAZED MIXTURE. II. THE ROLE OF DIFFERENCES IN THE PHYSIOLOGY OF PLANT GROWTH AND OF SELECTIVE GRAZING ON THE PERFORMANCE AND STABILITY OF SPECIES IN A MIXTURE , 1991 .

[18]  R. Haynes.  Competitive Aspects of the Grass-Legume Association , 1980 .

[19]  K. Mitchell,et al.  Growth of pasture species under controlled environment: III. Growth at various levels of constant temperature with 8 and 16 hours of uniform light per day , 1962 .

[20]  A. Parsons,et al.  Plant−animal interactions in a continuously grazed mixture. I, Differences in the physiology of leaf expansion and the fate of leaves of grass and clover , 1991 .

[21]  C. Marshall,et al.  The effect of local shading and darkening on branch growth, development and survival in Trifolium repens and galium aparine , 1992 .

[22]  M. Hutchings,et al.  An Investigation of Shoot Interactions in Mercurialis Perennis L., A Rhizomatous Perennial Herb , 1976 .

[23]  G. Beinhart.  Effects of Environment on Meristematic Development, Leaf Area, and Growth of White Clover 1 , 1963 .

[24]  H. Kroon,et al.  Size hierarchies of shoots and clones in clonal herb monocultures: do clonal and non-clonal plants compete differently? , 1992 .

[25]  H. Harvey.  Patterns of assimilate translocation in Trifolium repens. , 1970 .

[26]  L. Thompson.  The Influence of Natural Canopy Density on the Growth of White Clover, Trifolium repens , 1993 .