Species effects and seasonal trends on plant efflux quantity and quality in a spruce swamp forest

Abstract

We aimed to compare seasonal exudate quality and quantity between Sphagnum moss, Eriophorum vaginatum (graminoid) and Vaccinium myrtillus (ericoid shrub). Exudates were collected in May, July and September 2014 using a culture-based method and characterized by total organic carbon (TOC) and nitrogen (TN) contents with exudation fluxes expressed on a root-mass basis. Organic acids, sugars and amino acids in the exudates were identified by ion exchange chromatography. C and N exudate fluxes, in situ exudation fluxes and exudate contribution to soil dissolved organic matter (DOM) were estimated. Differences in exudate biodegradability were assessed by 13C pulse labeling. E. vaginatum had the largest exudation fluxes, Sphagnum the lowest, and V. myrtillus intermediate, being the greatest in July. All species mostly exuded organic acids except Sphagnum in September when sugars (allose, xylose) and amino acids (cystine) dominated. Sphagnum exudates were more C-rich and less degradable than the vascular species exudates, which released both organic and inorganic N forms. E. vaginatum exudates were richer in amino acids and citrate especially in July. Exudates contributed up to 20% to soil DOM. Plant species composition greatly affects exudate quantity, quality and timing. Plant exudates represent considerable contributions to soil DOM.