Responses of plant-arthropod communities to nutrient enrichment in hyper-arid and semi-arid zones

Excessive nutrient loading in coastal wetlands is threatening biodiversity and altering ecosystem functioning worldwide. Nonetheless, fertilization studies have focused mainly on temperate, continental and humid climates, while little is known about the effects of nutrient enrichment in more arid environments.This study examines the responses of salt marsh plants and two dominant arthropod communities (Isopoda and Coleoptera) to short-term nutrient addition in hyper-arid (HA) and semi-arid (SA) zones of Chile. We experi-mentally increased nitrogen (N) and phosphorous (P) to examine how enrichment alters primary producers and consumer taxonomic and non-taxonomic (size-based) structure. Both N and P increased plant biomass in the HA, while in the SA, N addition increased biomass but P addition had no significant effects. N and P addition affected arthropod community and size structure differentially in HA and SA. N addition changed Coleoptera composition in HA, while P addition had large contrasting effect sizes on Isopoda and Coloeptera size evenness. In SA, N addition had large and negative effect sizes on Isopoda size evenness and Coleoptera mean body size, while P addition had large, positive effect sizes on total arthropod abundance and changed the composition of both Coleoptera and Isopoda. Although nutrient additions did not significantly affect arthropod productivity, struc-tural equation models suggested that increases in vegetation biomass with fertilization in HA could mediate positively the effects of fertilization on arthropod biomass, but not in SA where Coleoptera body size reduced. In conclusion, this study revealed that over a short time frame the effects of nutrient additions flow through the food webs more disproportionately in SA than in HA.