Meristem Growth, Phenology, and Architecture in Chamaephytes of the Iberian Peninsula: Insights into a Largely Neglected Life Form

Abstract

Protection of resting buds and timing of shoot development are crucial morphological traits of plants growing in a seasonal climate. For eight species of Iberian chamaephytes with contrasting morphology and ecology, we explored the different growth stages within the morphogenetic cycle of the shoot (including the initiation, morphogenesis and maturation of vegetative and reproductive structures), the seasonality of these growth stages and their relationship with the general climate of the species distribution area. We evaluated the implications of morphogenetic cycles on the phenology, architecture and distribution of each species, and tried to identify good descriptors of these cycles for their inclusion in databases of functional plant traits. The morphology, activity and growth of meristems and the expansion of shoots were assessed periodically by dissecting buds under stereomicroscope. Plant phenology was recorded monthly for a minimum of 13 months on 15 marked plants of six out of the eight study species. All species showed naked buds, with meristems protected by leaf primordia and surrounding young leaves. We identified five stages of growth that summarize the processes of organogenesis and expansion of primordia in study species. Depending on the temporal arrangement of these stages and the type of structures subtending renewal meristems, we identified two types of morphogenetic cycles in study species: naked buds formed on brachyblasts (short branches) that extend for a relatively long time by neoformation; and naked buds on little shoot primordia that remain concealed by part of subtending leaves and extend rapidly in spring (preformed growth) sometimes followed by a period of slow expansion by neoformation. These morphogenetic cycles seem to be related to the general climate where study species grow: species with brachyblasts grow preferentially in areas with dry summers and not very cold winters, while species with shoot primordia protected by leaf structures tend to grow in areas with cold winters and not very dry summers. Some traits like the type and size of buds, or the type of morphogenetic cycle are quite easy to measure and provide important ecological information. These traits are good candidates to be included in plant trait databases.