Nutrient addition into ecosystems is increasing at an unprecedented rate.  Nutrient addition is known to affect plant growth but little is known about the long term effects of nutrients on population dynamics. In this study, we grew experimental plant populations under a range of nutrient conditions to 1) determine whether the dynamics in the experimental populations match the qualitative predictions based on non-linear density dependence models and 2) test whether increases in reproduction caused by nutrient enrichment cause plant populations to undergo cycles. The experimental populations were designed to meet key assumptions of theoretical models (discrete generations) that are ecologically appropriate for annual plants, but also contain features of plant population dynamics (e.g. spatially local interactions, modular growth form) that violate theoretical assumptions. Replicate experimental populations of the weed, Cardamine pensylvanica were grown in three nutrient treatments over 17 generations under constant conditions in growth chambers.  

Results/Conclusions

Average population size differed among treatment (mean 27, 48,67 for low, medium and high nutrient populations respectively). Long-term dynamics differed among treatments with low nutrient populations achieving stable dynamics, medium nutrient populations cycling and high nutrient populations undergoing longer and more irregular cycles. Our results have implications for the management of weeds in agroecosystems. Weeds grown within high input agriculture may experience greater peaks and troughs in dynamics making them harder to manage over the long term.  In terms of natural ecosystems, the instability created by high inputs of nutrients can cause plant populations to undergo longer, less predictable cycles and this inherent instability created by high nutrient additions may ultimately lead to higher potential extinction rates.