PARENT SESSION
Tuesday, August 8, 5:00-6:30 pm
Poster Session 12 - Plant population and reproductive ecology
Exhibit Hall, Ballroom Level, Cook Convention Center

Nitrogen addition alters ramet demography and reproductive allocation in two casepistose grass species of tallgrass prairie.

Dalgleish, Harmony¹, Kula, Abigail^*,1, Hartnett, David¹, Sandercock, Brett¹, ¹ Kansas State University, Manhattan, KS, USA

ABSTRACT- Because of their rapid turnover rates, ramet populations of clonal plants may have a great capacity to respond to global environmental change such as increased nitrogen deposition, precipitation changes and exotic species invasions. We developed matrix models of ramet (bud and tiller) populations for two species of caespitose grasses on Konza prairie (Sporobolous heterolepis and Koeleria macrantha) over two years that had been either fertilized (10g N m^-2) or left untreated to test the hypothesis that plants would respond to a nutrient pulse through altered tiller demography rather than altered tiller size. Tillers of both species exhibited shifts in reproductive allocation in response to N fertilization by increasing the probability of flowering in both years, (S. heterolepis, by 43% in 2004, 7% in 2005; K. macrantha, by 50% in 2005) and, in 2005, significantly decreasing vegetative bud production in S. heterolipis (fertilized: 3.26 ± 0.05 buds/tiller, unfertilized 3.53 ± 0.05 buds/tiller). Tiller emergence rates were consistently higher in fertilized populations of both species, as were tiller population growth rates (). Tiller size did not significantly increase in response to N addition (P > 0.4). Using both prospective (elasticity, loop analysis) and retrospective (Life Table Response Experiment) analyses, we demonstrate that tiller reproduction (bud-tiller transition) and vegetative tiller emergence have the largest influence on . This study elucidates underlying demographic mechanisms driving responses to nutrient pulses and has implications for the genet population dynamics of both species. In addition, these demographic mechanisms have the potential to influence community and ecosystem processes, such as species composition and productivity. This study represents a vital step to obtaining a better mechanistic and predictive understanding of grassland responses to global change phenomena.

Key words: demography, plant population ecology, grassland ecology