title: Cotyledon damage affects seed number through final plant size in the annual grassland species Medicago lupulina.
abstract: OBJECTIVE
  The effects of cotyledon damage on seedling growth and survival are relatively well established, but little is known about the effects on aspects of plant fitness such as seed number and size. Here the direct and indirect mechanisms linking cotyledon damage and plant fitness in the annual species Medicago lupulina are examined.
  
  
  METHODS
  Growth and reproductive traits, including mature plant size, time to first flowering, flower number, seed number and individual seed mass were monitored in M. lupulina plants when zero, one or two cotyledons were removed at 7 d old. Structural equation modelling (SEM) was used to examine the mechanisms linking cotyledon damage to seed number and seed mass.
  
  
  RESULTS
  Cotyledon damage reduced seed number but not individual seed mass. The primary mechanism was a reduction in plant biomass with cotyledon damage that in turn reduced seed number primarily through a reduction in flower numbers. Although cotyledon damage delayed flower initiation, it had little effect on seed number. Individual seed mass was not affected by cotyledon removal, but there was a trade-off between seed number and seed mass.
  
  
  CONCLUSIONS
  It is shown how a network of indirect mechanisms link damage to cotyledons and fitness in M. lupulina. Cotyledon damage had strong direct effects on both plant size and flowering phenology, but an analysis of the causal relationships among plant traits and fitness components showed that a reduction in plant size associated with cotyledon damage was an important mechanism influencing fitness.
authors.affiliation: Institute of Ecology, Key Laboratory of Arid and Grassland Agroecology of the Ministry of Education, Lanzhou University, Lanzhou, China.
authors.forename: Shiting
authors.initials: S
authors.lastname: Zhang
authors.forename: Chuan
authors.initials: C
authors.lastname: Zhao
authors.forename: Eric G
authors.initials: EG
authors.lastname: Lamb
mesh_terms: D018548:Cotyledon / Q000502:physiology*; D029902:Medicago / Q000254:growth & development* / Q000502:physiology; D008954:Models, Biological; D012098:Reproduction; D036226:Seedlings / Q000254:growth & development*