Prolonged drought causes negative plant-soil feedbacks in grassland species under field conditions

Abstract

Climate change has been shown to alter plant-soil feedbacks (PSFs, the impacts of plants on future communities via their impacts on soil biotic and abiotic properties), with implications for plant community dynamics. However, few studies have assessed effects on PSFs under field conditions or the mechanisms involved. We assessed drought effects on PSFs of four common grassland species (Lolium multiflorum, Medicago sativa, Plantago lanceolata, and Trifolium repens) in situ in a mesic grassland under ambient rainfall and prolonged drought conditions using a long-term rainfall manipulation system. The four species were first grown in monocultures in sub-plots of each of six ambient and drought plots to condition the soils. Then, each species was grown in a sub-plot conditioned by the same species (‘home’) and a sub-plot conditioned by each of the other three species (‘away’). We found that three species (L. multiflorum, M. sativa and T. repens) produced higher biomass in their ‘home’ soil than away soil under ambient rainfall while they consistently grew better in away soil under drought conditions, indicating drought-induced negative shifts in PSFs. There were strong interaction effects of rainfall treatment and conditioning species on several phospholipid-derived fatty acids markers, including a marker associated with arbuscular mycorrhizal fungi (AMF). We found a significant positive correlation between PSFs and the AMF marker across all treatment combinations, indicating that PSFs were driven by changes in positive plant-soil biotic interactions. Furthermore, drought increased plant parasitic nematode abundances. We found a strong significant negative correlation between PSFs and plant parasitic nematodes across all treatment combinations, indicating that the drought-induced shifts to more negative PSFs were driven by increased negative plant-soil biotic interactions. Drought may therefore negatively impact common grassland species due to stronger negative PSFs but at the same time promote species co-existence by reducing the abundance of competitive species.