Effects of Soil Nutrient Availability on the Role of Sexual Reproduction in an Alaskan Tundra Plant Community

In a warming climate, sexual reproduction may play an important role in plant community composition in arctic tundra. As temperatures increase and currently immobilized soil nutrients become available, flowering, fruiting, and germination conditions will likely improve. We examined how experimentally adding soil nutrients for 13 and 20 years affected species composition, flower and fruit production, seed dispersal, composition of the seed bank, and seedling establishment in a dry heath plant community in northern Alaska. Fertilizer addition significantly shifted adult community composition by decreasing lichens and evergreen shrubs and increasing abundance of a bunchgrass, Hierochloe alpina, and dwarf birch, Betula nana. More seeds were dispersed adjacent to nutrient amended plots, particularly of B. nana, and soil seed banks differed significantly between control and fertilized soils reflecting the adult communities in the field. Few seedlings were observed in any field plots. However, seeds of H. alpina likely played a role in the community shift because this species has few, small individuals in control plots, yet is densely packed in fertilized plots. B. nana, on the other hand, appears to be increasing in relative abundance via vegetative growth of existing individuals. Therefore, although sexual reproduction leading to seedling establishment is rare currently, as nutrients become more available in a warming climate, individuals may recruit from seed more often as long as space is available.