Nitrogen enrichment suppresses revegetated shrub growth under increased precipitation via herb-induced topsoil water limitation in a desert ecosystem in northern China

Abstract

Revegetated woody plant communities are widely distributed in degraded drylands, and they are expected to be intrinsically sensitive to precipitation change and nitrogen enrichment. However, the interactive effects of precipitation and nitrogen on them remain largely unknown. This study aimed to examine how revegetated plant community responds to an increase in precipitation and nitrogen enrichment. We conducted a field experiment over three years in a revegetated Artemisia ordosica shrubland in the Mu Us Desert of northern China, and investigated the effects of water and nitrogen addition on plant growth and soil resource availability. Increased precipitation and nitrogen enrichment dramatically promoted herb growth. Increased precipitation significantly increased shrub productivity without fertilization, whereas nitrogen enrichment weakened shrub growth under increased precipitation. Nitrogen enrichment significantly reduced topsoil moisture and offset water stress alleviation under increased precipitation. Structural equation modeling revealed that nitrogen-enhanced herb growth caused topsoil moisture to decline, potentially weakening shrub growth under increased precipitation. The results suggest that nitrogen enrichment tends to suppress shrub growth under increased precipitation due to herb-induced topsoil water limitation. Our findings provide empirical evidence that water competition from herbaceous plants negatively affect shrub growth under nitrogen enrichment, and highlight the plant-water interaction underlying the responses of desert shrubland to global environmental changes.