Investigations on plant functional traits, epidermal structures and the ecophysiology of the novel bioenergy species Sida hermaphrodita Rusby and Silphium perfoliatum L.

Abstract

A growth experiment was performed with different accessions of the novel bioenergy species Sida hermaphrodita Rusby (Fanpetals, Malvaceae) and Silphium perfoliatum L. (Cup Plant, Asteraceae) to study differences between the perennial shrubs and the variation among biotypes. Non-destructive assessments (phenology, leaf numbers, height, SPAD and gas exchange) and several harvests were conducted to examine growth, allometry and the quality of shoot material (C:N, raw ash, protein, fibre, fat, calorific value and leafδ¹³C). In addition to the functional analyses, epidermal structures of two widely used accessions were addressed to give insight into anatomical properties of the species.

In the establishment phase, productivity was higher on average in S. hermaphrodita than in S. perfoliatum since latter remains in the rosette stage in the first year. While the accessions of S. hermaphrodita did not significantly differ in growth, functional traits and forage quality, S. perfoliatum showed large biotypic variation. Leaf water and ash contents, raw protein and fat levels were higher in latter species, while raw fibre contentswere twice as highin S. hermaphrodita. At the end of the season, the calorific value of senesced stems of S. hermaphrodita proved to be higher than that of senesced leaves of S. perfoliatum pointing to its suitability of as a solid fuel.

Despite the shorter longevity, lower SPAD and smaller size, the delicate leaves of S. hermaphrodita had more stomata, higher photosynthetic rates and higher stomatal conductances than the robust leaves of S. perfoliatum. Less negative δ¹³C signatures in S. perfoliatum (-27.3 ‰) compared to S. hermaphrodita (-30.24 ‰), point to the potentially higher water use efficiency of S. perfoliatum. Further investigations on the relationships between leaf properties, carbon acquisition and stomatal conductance under dry conditions may serve to select productive lines of the bioenergy species on marginal land thus avoiding conflicts with the farming of food crops.