Abstract
Rhizosphere processes are critical for nutrient cycling, maintaining soil quality and sustaining plant growth and productivity. However, our understanding of the interplay between plant roots and other soil ecosystem engineers such as earthworms is still limited. Our objective was to determine the influence of Pontoscolex corethrurus, a common endogeic earthworm, on the bulk and rhizosphere soil chemical properties and on the growth of two economically important coffee species. A six-month mesocosm experiment was implemented to grow Coffea arabica and C. canephora with and without earthworms. We measured plant growth variables (height, stem thickness, number of leaves, leaf area, biomass and chemical composition) and soil physico-chemical parameters in both the rhizosphere and bulk soils. We found that soil properties significantly differed among soil zones (bulk vs. rhizosphere). Contents of total P, H, Ca, C/N ratio and CEC were consistently larger in the bulk soil than in the rhizosphere, while C, N and Mg contents were highest in the rhizosphere soil. Although the presence of earthworms had little effect on plant growth, their influence on plant and soil nutrient contents was stronger and highly dependent on coffee species. In C. arabica, earthworms reduced the depletion of Na and Ca in the rhizosphere, but promoted the accumulation of available P and possibly accelerated plant N uptake in that of C. canephora. These differences may be explained by the indirect effect of earthworms on nutrient dynamics, likely mediated by induced shifts in the rhizosphere microbial community. Our findings contribute to the understanding of nutrient dynamics in the rhizosphere of two coffee species, revealing a complex influence of earthworms in rhizosphere processes, and call for a further understanding of the microbe-mediated impact of earthworms in the rhizosphere of C. arabica and C. canephora.