The influence of local environment and population origin on some reproductive traits of Nardus stricta (Poaceae) in the Scottish Highlands

Abstract Nardus stricta L is widespread in species-poor grassland on acidic soils throughout Scotland. Its wide altitudinal, latitudinal and longitudinal range enables a study of how plant reproductive performance is influenced by variation in the climatic environment. The aim of this study was to establish whether any such changes in reproductive performance are attributable to direct environmental effects or to genetic differentiation between populations. The investigation involved field observations, germination tests with seeds of diverse provenance, and the transplantation of tillers sourced from low (<500 m) and high (>900 m) altitudes into planting sites located at low and at high altitude. Geographic variation in fecundity was evident, with seed germinability declining markedly with increasing altitude and oceanicity of origin. Reciprocal transplantation showed that the number of flowering spikes, spike maturation, seed germinability, and seed production per plant were all strongly influenced by the growing environment. Transplantation also showed that plants were adapted to their altitude of origin in that they exhibited significant home-site advantages. Hence, at the low-altitude planting site, the fecundity of transplants from low altitude greatly exceeded that of those from high altitude. At the high-altitude site, the high-altitude transplants flowered better and matured earlier than did their low-altitude counterparts. Yet their fecundity did not differ because infertility was prevalent in the plants sourced from high altitude. This, coupled with the established agamospermy of N. stricta, suggests that gene exchange in high-altitude populations may be very restricted, thus constraining the plant’s ability to adapt to environmental change.