Fitness Implications of Clonal Integration and Leaf Dynamics in a Stoloniferous Herb, Nelsonia canescens (Lam.) Spreng (Nelsoniaceae)

Abstract

Very little has been published on the life-history significance of clonal plants inhabiting southern African savanna environments. This study investigated the fitness implications of clonal integration, resprouting behaviour and growth phenology in a stoloniferous herb, Nelsonia canescens (blue pussyleaf) at a savanna site in Zambia, central Africa. Census data on growth and survival were obtained regularly on permanently marked ramets over a 4-year period, from 2001 to 2005, and analyzed to assess how physiological integration and module demography contribute to fitness in Nelsonia. Above ground and below ground growth occurred during the dry and rainy seasons, respectively. Dry season growth was characterized by resprouting and production of stolons that bore small pubescent leaves with high mortality (30–80% month−1). Deep roots and high leaf turnover appear to contribute to sustained growth during the dry season when topsoil moisture and nutrient availability are low. The interaction between maximum temperature and precipitation explained a significant proportion (59%, p<0.01) of the monthly variation in leaf size and increasing evapo-transpiration levels appeared to trigger the shift in leaf size from a large wet season type to a small dry season one. During the dry season Nelsonia resprouted from dormant buds buried at the time of root development in daughter ramets in the rainy season. Temporal integration significantly (p<0.05) enhanced survival of daughter ramets. However, daughter ramets with severed mother–daughter ramet inter-connectors experienced high initial mortality that was caused by both early stolon severing and drought stress during the root development phase. The majority of ramets lived for 5–10 months and 25% were still alive at the age of 3.5 years. The study showed that although the growth phenology of Nelsonia has serious ecological implications for accessing scarce resources during the dry season, the species utilizes a number of strategies to overcome resource limitations in a seasonally heterogenous environment.