Population rules can apply to individual plants and affect their architecture. An evaluation on the cushion plant Mulinum spinosum (Apiaceae)

JAVIER PUNTIERI; MARÍA DAMASCOS; YANINA LLANCAQUEO; MAYA SVRIZ

AoB Plants

Oxford Journals

Lugar: Oxford; Año: 2010 vol. 2010 p. 1 - 10

2041-2851

Background and aims. Plants are regarded as populations of modules such as axes and growth units (GUs, i.e. seasonally produced axis segments). Due to their dense arrays of GUs, cushion plants mayresemble crowded plant populations in the way the number of components (GUs in plants,individuals in populations) relates to their individual sizes.Methodology The morphological differentiation of GUs and its relationship with biomass accumulation andplant size were studied for the cushion subshrub Mulinum spinosum (Apiaceae), a widespreadspecies in dry areas of Patagonia. In 2009, GUs were sampled from one-quarter of each of 24adult plants. Within- and between-plant variations in GU length, diameter, number of nodesand biomass were analysed and related to whole-plant size.Principal results Each year, an M. spinosum cushion develops flowering GUs and vegetative GUs. Flowering GUsare larger, twice as numerous and contain two to four times more dry mass (excluding reproductive structures) than vegetative GUs. The hemispherical area of the cushions was positivelycorrelated with the biomass of last-year GUs. The biomass of flowering GUs was negativelycorrelated with the density of GUs. Mulinum spinosum plants exhibited a notable differentiation between flowering and vegetative GUs, but their axes, i.e. the sequences of GUs,were not differentiated throughout the plants. Flowering GUs comprised a major proportionof each plant’s photosynthetic tissues.Conclusions A decrease in the size of flowering GUs and in their number relative to the total number of GUsper plant, parallel to an increase in GU density, is predicted as M. spinosum plants age overyears. The assimilative role of vegetative GUs is expected to increase in summer because oftheir less exposed position in the cushion. These GUs would therefore gain more fromwarm and dry conditions than flowering GUs