The effects of rooting frequency and position of rooted ramets on plasticity and yield in a clonal species: an experimental study with Glechoma hederacea

Clonal plants produce numerous ramets that can be distributed over a considerable area. Resources are translocated between ramets, especially when they occupy microsites of different quality, or places where leaves or roots cannot be deployed. It is common for a proportion of the ramets of clones and clonal fragments to lack roots. We conducted a greenhouse study using clonal fragments of Glechoma hederacea to examine the effects of differences in the number and position of rooted ramets on yield and plasticity of clonal fragments. We hypothesized that (1) mass of roots and root mass ratio would increase as the number of rooted ramets decreased, (2) plasticity in rooted ramets would buffer the clonal fragment against reduction in yield as the number of rooted ramets declined, (3) ramet plasticity in response to the absence of rooting, and the beneficial effects of this plasticity, would be greater when older ramets were rooted. The same yield was achieved in clonal fragments with only one out of four ramets rooted as in clonal fragments with all four of their ramets rooted, regardless of whether rooting was confined to older or younger ramets. Plasticity in biomass allocated to roots was greater in older rooted ramets succeeded by unrooted ramets than in younger rooted ramets preceded by unrooted ramets. Modular plasticity, involving both direct responses to local conditions, and indirect responses to the conditions experienced by connected modules, buffered performance against variation in rooting ability, enabling clonal fragments to maintain their yield and lateral expansion even when a high proportion of their ramets lacked roots.