Data from: Biomass partitioning in response to intraspecific competition depends on nutrients and species characteristics: a study of 43 plant species

Competition simultaneously limits the availability of above- and
below-ground resources for plants. How plants respond to density with
changes in patterns of biomass allocation is poorly understood. Previous
studies had inconsistent results, but emphasised increased biomass
allocation to stems in response to density. However, the response of
plants to density may depend on environmental conditions and on
characteristics of the species. We grew 43 herbaceous plant species at
three densities (1, 8, and 64 individuals per pot) and two nutrient levels
in a common garden and measured biomass allocation to roots (RMF), leaves
(LMF) and stems (SMF), and specific root (SRL) and shoot length (SSL). The
species differed in functional group (grasses, forbs and legumes),
lifespan and realised niche with respect to nutrients (Ellenberg's
nutrient indicator value). Intraspecific competition and self-thinning
increased with nutrient supply. Overall, plants increased their RMF with
density independent of nutrient level, indicating that competition was
mainly for below-ground resources. However, characteristics of the species
influenced their responses to density and nutrients in terms of biomass
allocation, SRL and SSL. At high densities, legumes were more productive
than the other functional groups and hardly changed their allocation
patterns, suggesting that they were less nutrient-limited due to their
mutualism with nitrogen-fixing rhizobia. The SRL of perennials was lower
and their RMF was higher and increased more strongly in response to
density than that of annuals, which could be interpreted as mechanisms to
increase survival. The realised niche of species with respect to nutrients
influenced the response to density and nutrients in terms of SMF, LMF, SRL
and SSL in line with adaptations to both nutrient availability and
competition for light in the typical habitats. Synthesis. We found that
intraspecific competition was mainly for below-ground resources, which may
be typical for many species growing in moderately nutrient-rich but
high-light habitats. Our results show that growth conditions, species
characteristics and their interactions influence patterns of biomass
allocation and plant morphology.