Stronger effects of long-term P enrichment on soil biota than plants in grasslands

Abstract

Although some researchers have assessed the influences of the plant community on phosphorus (P) enrichment, we lack a comprehensive understanding of whether P limits the abundance and diversity of soil micro-food webs (hereafter SMFWs) components. After establishing a multigradient P-enrichment experiment in a semiarid grassland in 1999, we collected data of the diversity and structure of the SMFWs (including bacteria, fungi, and nematodes) as well as of soil abiotic and plant variables in 2010 and 2017 (after 11 and 18 years of enrichment, respectively). We found that both 11 and 18 years of P enrichment had minor influences on the plant biomass and diversity of plant alpha and beta. However, both 11 and 18 years of P enrichment decreased the biomass (or abundance) and alpha diversity and changed the beta diversity of components in the SMFWs, with stronger effects on bacteria and fungi than on nematodes for alpha diversity and stronger effects on soil fungi and nematodes than bacteria for beta diversity. In addition, we also found that 18 years of P enrichment had stronger effects on the alpha diversity of components in the SMFWs than 11 years of P addition. Structure equation model showed that the decrease in the biomass/abundance and alpha diversity of components in the SMFWs were mainly associated with P-related variables for 11 years of P enrichment but with soil pH for 18 years of P enrichment. The Mantel test showed that the variations in beta diversity were caused by soil abiotic variables for bacteria and fungi but by soil abiotic variables and fungi for nematodes. Overall, our results suggested that P enrichment had strong negative effects on the SMFWs but had minor effects on plants in a grassland ecosystem, and therefore long-term P enrichment may decouple the relationship between plants and SMFWs in global drylands.