Search

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.

Plant responses to major environmental drivers like precipitation can influence important aspects of carbon (C) cycling like soil CO2 efflux ( urn:x-wiley:00220477:media:jec13382:jec13382-math-0001 ). These responses may be predicted by two independent classes of drivers: plant size—larger plants respire more and produce a larger quantity of labile C, and plant economics—plants possessing more acquisitive plant economics strategies (i.e. high metabolic rate and tissue nutrient content) produce higher‐quality tissue that respires rapidly and decomposes quickly. At two sites in central Texas, USA with similar climates and differing soil characteristics, we examined the response of eight Panicum virgatum genotypes to three annual precipitation levels defined by the driest, average and wettest years from each site's precipitation history. We evaluated the individual and joint influence of plant genotypes and precipitation on urn:x-wiley:00220477:media:jec13382:jec13382-math-0002 and traits related to plant economics and plant size. We then used confirmatory path analysis to evaluate whether effects of precipitation on urn:x-wiley:00220477:media:jec13382:jec13382-math-0003 were in part related to effects of precipitation on plant economics traits or size (‘mediated’ effects). These genotypes exhibited variation in plant economics traits and above‐ground net primary productivity (ANPP), an above‐ground measure of plant size. Increasing precipitation increased urn:x-wiley:00220477:media:jec13382:jec13382-math-0004 and ANPP more than plant economics traits. At both sites, ANPP was the best predictor of urn:x-wiley:00220477:media:jec13382:jec13382-math-0005 . Moreover, the sites differed in the ways that plant size and plant economics traits combined with precipitation to influence urn:x-wiley:00220477:media:jec13382:jec13382-math-0006 . At the Austin site, the positive effect of precipitation on urn:x-wiley:00220477:media:jec13382:jec13382-math-0007 was mediated primarily by ANPP, offset by a smaller effect of leaf nitrogen content; no direct precipitation effect was detected. At the Temple site, increasing precipitation had positive direct and ANPP‐mediated effects on urn:x-wiley:00220477:media:jec13382:jec13382-math-0008 . This suggests that greater water limitation at Austin may strengthen the links between plant size and urn:x-wiley:00220477:media:jec13382:jec13382-math-0009 . Synthesis. Estimates of C cycling can be improved by accounting for mediation of precipitation effects on urn:x-wiley:00220477:media:jec13382:jec13382-math-0010 by plant economics traits and plant size in resource‐limited environments.