Evidence that the negative relationship between seed mass and relative growth rate is not physiological but linked to species
identity: a within-family analysis of Scots pine
Jorge Castro (1, 2), Peter B. Reich (3), Ángela Sánchez-Miranda (1) and Juan D. Guerrero (1)
1. Grupo de Ecología Terrestre, Departamento de Ecología, Facultad de Ciencias, Universidad de Granada, E-18071 Granada, Spain / 2. Corresponding author () / 3. Department of Forest Resources, University of Minnesota, 1530 N. Cleveland Avenue, St. Paul, MN 55108, USA / Received July 6, 2007; accepted October 4, 2007; published online May 1, 2008
Summary
Seed mass and relative growth rate (RGR) are important determinants of early seedling growth, and hence seedling establishment.
Although a positive interspecific relationship between seed mass and seedling dry mass is well established, much less is known
about the relationships among seed mass, seedling mass and RGR within species. We examined relationships among seed mass,
seedling mass and RGR within and among maternal plant lines of Scots pine (Pinus sylvestris L.). To assess the effects of seed mass and maternal origin on RGR, individual seeds from two seed crops (years 2004 and
2005) of ten maternal plants growing under nursery conditions were weighed and then germinated. Seed mass was strongly determined
by maternal plant, and seedling mass was largely determined by seed mass, with a positive correlation between these variables
both across and within maternal plants. In contrast, RGR was weakly related to seed mass, with no consistent pattern in the
sign of the relationship. It is well known that species differ in RGR and that RGR is related to seed mass across species.
Lack of consistent evidence for this relationship within maternal lines, and for Scots pine overall, suggests that the relationship
is not directly causal, but reflects consistent evolutionary covariation in these two physiologically independent traits.
