Initial richness, consumer pressure and soil resources jointly affect plant diversity and resource strategies during a successional field experiment

Abstract

Abstract Plant community succession is structured by initial richness, plant consumer pressure and soil resource supply. These drivers influence species' trait trade‐offs that underlie temporal changes in plant community diversity. Importantly, how these drivers interact with each other and through time and whether they act on different facets of plant community diversity by promoting different plant trade‐off strategies remains poorly understood. We experimentally manipulated initial plant richness, consumer pressure via pesticide spraying and soil resource supply via fertilization across 4 years of old field succession. We then allowed natural colonization and extinction to occur and examined how the three drivers influenced succession. Specifically, we examined changes in temporal dynamics by conducting yearly taxonomic cover surveys and measuring light penetration to the ground. In the third year, we measured vegetative height and specific leaf area (SLA), and investigated seed mass using a trait database. Higher initial richness, lower consumer pressure and increased soil resource supply all decreased colonizing species richness and light availability and variably altered species evenness. These effects generally acted additively rather than interactively in driving community diversity during succession. However, soil resource supply suppressed consumer pressure effects on species richness and light availability, while consumer pressure and soil resource supply modified initial richness effects on light availability. Treatments acted on different trait identities, revealing different mechanisms underlying taxonomic responses. Initial richness effects on seed mass of colonizing species were modified by soil resource supply. Decreased consumer pressure increased intraspecific community height and decreased interspecific SLA. Increased soil resource supply increased community height, SLA and seed mass. Synthesis. Our results suggest species' resource strategies underlie plant diversity responses to consumer pressure and soil resource supply. Resource addition promoted resource‐acquisitive species; consumer pressure disadvantaged resource‐conservative species. Meanwhile, initial richness altered subsequent community composition primarily through persistence of early residents. We show that community responses to drivers of succession depend on underlying trait trade‐offs of resident species, and these trade‐offs influence community diversity across succession.