Current and Future Costs of Reproduction in Oxytropis sericea, a Perennial Plant from the Colorado Rocky Mountains, U.S.A.

Abstract

We studied tradeoffs among current reproduction, vegetative growth, and resource storage, and the consequences of such tradeoffs for future growth and reproduction in an alpine tundra population of long-lived iteroparous herb, Oxytropis sericea from the Colorado Rocky Mountains. When plant reproductive effort was manipulated through the removal of inflorescence buds, branching and leaf production increased significantly in the year of treatment but the end-of-season nonstructural carbohydrate content in storage organs (taproots and branches) was not affected. In contrast, plants from which buds were removed, accumulated more nitrogen and phosphorus in their perennial branches (although not in taproots), compared to controls. Bud removal in 1996 and in 1997 led to greater vegetative growth in the following summer, with potential consequences for long term reproductive effort. Addition of mineral fertilizer to flowering individuals in 1996 stimulated some aspects of vegetative growth and reproduction in 1997 indicating that growth in these plants was nutrient-limited. Leaf photosynthetic rates were not affected by the removal of inflorescence buds, inflorescences or infructescences during 1996, but were significantly lower in plants prevented from fruiting in 1997, showing limited evidence for photosynthetic compensation of reproductive effort. We suggest that mineral nutrients, rather than photosynthate, constitute the currency underlying the future costs of reproduction in O. sericea.