Seasonal Course of Total Non-Structural Carbohydrates in the Lignotuberous Mediterranean-Type Shrub Erica australis

Lignotuberous plants are frequently dominant in Mediterranean-type shrublands, and total non-structural carbohydrates (TNC) stored in the lignotuber are assumed to play an important role in resprouting after fire. However, seasonal variations in TNC in this organ and other plant parts have not been properly evaluated, particularly in relation to periods of fire risk, during which lignotuber TNC concentrations should be highest. We document the seasonal course of TNC concentrations in the stems, lignotubers and roots of 13 populations of the Mediterranean-type, lignotuberous, resprouter shrub Erica australis from central Spain. Plant water potentials were measured in parallel to correlate seasonal variations in water availability with fluctuations in TNC concentrations. Mean TNC concentrations in stems, lignotubers and roots throughout the year were 55, 73 and 120 mg g-1dry weight, respectively. Roots contained highest TNC concentrations, which were maximal in late spring. Starch concentrations decreased in all plant parts during spring, when plants were actively growing and reproducing. Lignotuber TNC concentrations were lowest in early summer, and remained relatively low during the period of maximum fire risk. Monosaccharide concentrations increased significantly in all plant parts during the summer, coinciding with a reduction in plant water potential. We conclude that seasonal fluctuations of TNC in E. australis are related to periods of plant growth and reproduction, and also occur in response to stressful conditions. No evidence was obtained supporting the idea that seasonal fluctuations of TNC may be a response to ensure highest TNC content in the lignotuber during periods with maximum fire risk.