Do plant species of different resource qualities form dissimilar energy channels below-ground?

Abstract

This study aimed at examining whether plant species of varying resource quality give rise to a fungal- or bacterial-based energy channel in the plants’ rhizosphere, when planted in soil, in which the plant species naturally occur. In an 18-month large-scale laboratory mesocosm experiment, two plant species ( Holcus lanatus and Lotus corniculatus) producing labile litter and two plant species ( Picea abies and Calluna vulgaris) producing recalcitrant litter were placed in the same mesocosm. This allowed the decomposer biota (microbes, protozoa, nematodes, collembolans, and enchytraeid worms) to freely choose their preferred plant rhizosphere. Because a fungal-based energy channel is in theory regarded to retain nutrients better in the soil than a bacterial-based energy channel, water was collected underneath the plant species and analyzed for its nutrient (N and P) content. In general, the number of soil biota groups responding significantly to the plant treatment increased with time. Soil microbes were the first group to react, but the ability of the plants to boost a clearly fungal- or bacterial-based energy channel was generally weak. However, at the end of the study, a higher fungal-to-bacterial biomass ratio was found beneath Calluna than beneath the other plant treatments. Of the secondary consumers, nematodes were the most responsive group, with total number and especially plant parasites being more abundant beneath Lotus than beneath Picea and Calluna indicating a root-based energy channel to persist under the legume. Protozoa, enchytraeid worms and collembolans responded weakly and inconsistently to plant treatment. Liberation of plant-available nutrients was plant-dependent. Towards the end of the study, less nitrate and phosphate leached through the Picea soils than through the control, which indicates a more effective nutrient retention to take place under this plant species. We found that plant species can, in a relatively short time, modify the composition of the soil decomposer community. However, no consistent evidence for the plant–soil systems developing to separated detritus energy channels emerged, we found a clearly separated root energy channel under the legume L. corniculatus.