Nutrient availability and atmospheric CO2 partial pressure modulate the effects of nutrient heterogeneity on the size structure of populations in grassland species

Background and Aims: Size-asymmetric competition occurs when larger plants have a disproportionate advantage in competition with smaller plants. It has been hypothesized that nutrient heterogeneity may promote it. Experiments testing this hypothesis are inconclusive, and in most cases have evaluated the effects of nutrient heterogeneity separately from other environmental factors. The aim of this study was to test, using populations of Lolium perenne, Plantago lanceolata and Holcus lanatus, two hypotheses: (a) nutrient heterogeneity promotes size-asymmetric competition; and (b) nutrient heterogeneity interacts with both atmospheric CO2 partial pressure (PCO2) and nutrient availability to determine the magnitude of this response. Methods: Microcosms consisting of monocultures of the three species were grown for 90 d in a factorial experiment with the following treatments: PCO2 (37 5 and 70 Pa) and nutrient availability (NA; 40 and 120 mg of N added as organic material) combined with diff...