Root traits and mineral nutrients in the rhizosphere and shoot biomass of African dryland grasses

Abstract

Seed-based ecological restoration through reseeding perennial grasses has been successfully used to combat desertification in Africa. However, studies to investigate the relationship between root traits of the native grasses and mineral nutrients in rhizosphere and plant biomass remain limited. This has limited our understand of the relationship between belowground processes and ecological restoration outcomes, especially in nutrient poor African dryland environments. This study was conducted in a long-term ecological restoration site in typical semi-arid African dryland to elucidate the relationship between root traits and mineral nutrients in the rhizosphere and shoot biomass of native perennial grasses used for seed-based ecological restoration i.e. Cenchrus ciliaris, Enteropogon macrostachyus and Eragrostis superba. Cenchrus ciliaris exhibited superior root characteristics than E. macrostachyus and E. superba in all the measured traits expect for specific root length (SRL) and root tissue density (RTD). Root trait relationships of the root economic spectrum were largely not supported. A significant negative correlation between RTD and SRL was only found in E. superba (r2 = 0.92, P = 0.03). Calcium and potassium mineral concentrations in soil displayed a regular pattern where E. macrostachyus consistently had the highest concentrations. Total phosphorus concentrations were highest in C. ciliaris. Shoot biomass total calcium and phosphorus concentrations were highest in E. superba while total magnesium and potassium concentrations were highest in C. ciliaris. Correlation analysis revealed only a few significant relationships between root traits and mineral concentrations in soil and shoot biomass. African grasses used for seed-based ecological programs exhibit varying root traits and mineral nutrient concentrations in the rhizosphere and shoot biomass, underpinning their significant role in modulating soil fertility and nutrient cycling in reseeded African drylands. Integrating root traits and mineral nutrient concentrations in rhizosphere and shoot biomass can deepen our holistic understanding of the ecological restoration process using perennial grasses. This will better inform the selection of appropriate species to successfully restore degraded landscapes and support positive outcomes for future sustainability of African drylands in a changing global environment.