Seasonal Evolution of the Rhizosphere Effect on Major and Trace Elements in Soil Solutions of Norway Spruce (<i>Picea abies Karst</i>) and Beech (<i>Fagus sylvatica</i>) in an Acidic Forest Soil

Abstract

In low-nutrient ecosystems such as forests developed on acidic soil, the main limiting factor for plant growth is the availability of soil nutrients. The aim of this study was to investigate in a temperate forest: 1) the influence of the rhizosphere processes on the availability of nutrients and trace elements during one year period and 2) the seasonal evolution of this rhizosphere effect. Bulk soil and rhizosphere were collected in organo-mineral and mineral horizons of an acidic soil during autumn, winter, and spring under Norway spruce ( Picea abies Karst) and beech ( Fagus sylvatica ). Soil solutions were extracted by soil centrifugation. Rhizosphere solutions were enriched in K, and in Ca, Mg, and Na (principally in spring) compared to those of the bulk soil. Our study reveals seasonal variations of the rhizosphere effect for Ca, Mg, and Na under both species, i.e. , higher enrichment of the rhizosphere solution in spring as compared with that in autumn and winter. An enrichment of the rhizosphere solutions was also observed for trace elements regardless of the season under both species in the mineral horizon, only. In contrast, seasonal variations of the rhizosphere effect for the trace elements were observed in the solutions of the organomineral horizon under beech, i.e. , enrichment in autumn and depletion in winter. This study demonstrates that rhizosphere biological activities significantly increase nutrient bioavailability during the growth period. These complex interactions between roots, microbial communities and soils are a key-process that supports tree nutrition in nutrient-poor forest soils. This research also reveals that rhizosphere processes a) occur throughout the year, even in winter, and b) influence differently the dynamics of nutrients and trace elements in the root vicinity of the organo-mineral horizon.