Variation in the maternal environment can produce individual variability in offspring dispersal if maternal traits are environmentally variable and linked to an offspring’s movement ability. We were interested in understanding how the maternal environment, namely the available soil resources, had the potential to alter the dispersal ability of plant offspring if those resource additions influence maternal traits related to seed dispersal. While there is ample evidence for fertilization effects on plant productivity and diversity, little work has focused on the effects of nutrient additions and the ratio of these additions (i.e., stoichiometry) on the structural and reproductive traits related to dispersal in plants coexisting in natural communities. In this study, we combined empirical and theoretical approaches to understand how nutrient additions influences dispersal ability in grassland plants. In three sites across the Midwestern United States, we added all combinations of nitrogen, phosphorus, and potassium to existing communities of grassland plants and measured three traits related to dispersal at the individual level (including the height at seed release, the seed mass, and the number of seeds produced), on all species in the flowering community in the fall of 2012. These trait values were used to parameterize an experimentally validated dispersal model that incorporates wind stochasticity and ecological plant traits, to create dispersal probabilities for all species in all nutrient treatments.
We found that plant traits related to dispersal were strongly influenced by nutrient additions. Nitrogen addition significantly influenced seed release height, but this depended on species. Higher order nitrogen additions (e.g., plots with both nitrogen and phosphorus, nitrogen and potassium, or all three nutrients) drove significant increases in the number of seeds produced per individual, indicating the importance of nitrogen for reproduction, but only when in combination with other limiting nutrients. Seed mass was less responsive to nutrient additions, but there was some evidence that the addition of both nitrogen and phosphorus together played an important role in altering seed size. When these traits were used to parameterize the dispersal model, we show that the stoichiometric environment can also change the probability of long-distance dispersal. In an era of global nutrient change, this work indicates the importance of further understanding of how resource-drive dispersal influences long-term coexistence and spatial patterning of plants.