Vegetation–soil–microbiota dynamics across a 50-year grassland chronosequence: implications for desertified land restoration in the loess hilly region of China

Abstract

Abstract Purpose Alfalfa (Medicago sativa L.) establishment is an effective strategy for restoring degraded grasslands. However, the mechanisms underlying ecological restoration in reconstructed grasslands following alfalfa establishment are still poorly understood. This study investigated vegetation community, soil quality and rhizosphere microbiota dynamics across a reconstructed grassland chronosequence in the loess region of Northwest China. Methods A space-for-time substitution method was used to evaluate vegetation coverage and alfalfa production performance in grassland stands with different ages (1–50 years old). High-throughput sequencing was conducted to characterise microbial communities in rhizosphere soils. Results The plant heights, yields and stem-to-leaf ratios of alfalfa all peaked in the seven-year-old stand and then decreased in older stands, with Stipa bungeana replacing alfalfa as the dominant species in the 50-year-old stand. Soil bulk density and major nutrient contents were highest in the artificial grassland (1–10 years). Soil enzyme activities (e.g., urease and sucrase) were enhanced in the transitional grassland (10–30 years), accompanied by enrichment of potentially beneficial microorganisms (e.g., Actinobacteria and Mortierella) and functional fungi (e.g., saprotrophs and symbiotrophs). Soil water content, total porosity and microbial diversity reached their maximum levels in the natural grassland (> 30 years). Conclusions The results indicated that alfalfa establishment altered soil structure and nutrient status over the short term, subsequently creating an optimal rhizosphere micro-environment. The improved soil conditions and rhizosphere microbiota were favourable for establishment of native grass species, leading to the formation of a stable natural ecosystem.