Mechanics and growth form of the moss Hylocomium splendens

Abstract

The moss Hylocomium splendens has two different growth forms. Sympodial growth occurs where the apical meristem ceases activity annually and growth is continued by a lateral bud. Sympodial plants are vertical and self-supporting. Monopodial growth occurs when the apex continues growth. Monopodial plants are prostrate. The aims of the study were to examine stem mechanics of the different growth forms and to compare mechanical properties along stems. Stems of annual segments were subjected to three point bending tests. In sympodial plants the stiffness of the stem material increased significantly with segment age. Flexural rigidity increased significantly with age in segments from 1 to 4 years old, and then declined. Segment diameter decreased significantly with age in sympodial plants. Monopodial plants showed no significant effects of segment age on the diameter, material stiffness or flexural rigidity of stems. Sympodial segments were significantly wider, stronger, more rigid and composed of stiffer material with a higher stress at yield than monopodial segments, but did not have a larger proportion of strengthening material. Sympodial stems had significantly more cellulose than monopodial stems. The moss Hylocomium splendens shows a range of mechanical adaptations, as a self-supporting or a prostrate plant, which suit it to life in very different environments.