Effects of Maternal Nutrient Environment and Maturation Position on Seed Heteromorphism, Germination, and Seedling Growth in Triplasis purpurea (Poaceae)

Abstract

The annual dunegrass Triplasis purpurea exhibits a position-dependent seed heteromorphism. From the lower to the upper nodes along a tiller of an individual there is an increase in the number of seeds set on leaf sheath-enclosed axillary panicles and a decrease in seed mass. Between individuals, seed number and mass are most affected by microenvironmental conditions. The interactive effects of maturation position and maternal nutrient environment on seed heteromorphism, germination, and seedling growth were investigated. Field-collected seedlings from two populations on Staten Island, N.Y., were grown in the greenhouse and subjected to three maternal environments: (1) high nutrients (3 g/L fertilizer every 2 wk), (2) medium nutrients (1.5 g/L every 2 wk), and (3) low nutrients (tap water). The seed number at each tiller node was recorded and mature tillers with sheath-enclosed, intact seeds were separated into fragments by node and subjected to a germination trial. For one population, seeds were also removed from leaf sheaths. The effects of node position and maternal environment on seedling growth were also studied. High soil nutrients resulted in significant enhancement of germination. For one population, germination increased with increasing node position. Seeds from emergent, terminal panicles showed the greatest germination. Removal of the leaf sheath increased the speed of germination. Root and shoot dry mass was greatest for seedlings from seeds of maternal parents in the high-nutrient environment. Shoot dry mass was also greater for seedlings from heavier, lower-node seeds (relative to lighter, upper-node seeds). In the heterogeneous dune habitat, fitness for this annual species, expressed as seed mass and seed production by an individual, may be influenced by soil that is relatively higher in nutrients in a way that increases the likelihood of successful seedling establishment the following year.