Quantitative analysis of soluble exudates produced by ectomycorrhizal roots as a response to ambient and elevated CO 2

Abstract

Despite its potential impact on soil carbon flow, few studies have attempted to quantify the effects of elevated carbon dioxide (CO 2) on production of exudates by mycorrhizal plants. In this study we quantified low molecular weight (LMW) organic compounds exuded by non-mycorrhizal (NM) and ectomycorrhizal (ECM) plants in relation to exposure to elevated CO 2. Scots pine seedlings, either colonized by one of eight different ECM fungi or non-mycorrhizal (NM), were exposed to either ambient (350 ppm) or elevated (700 ppm) concentrations of CO 2. Exudation of LMW organic acids (LMWOAs), amino acids, dissolved monosaccharides and total dissolved organic carbon (DOC) was determined and exudation rates were calculated per g root and fungal dry mass. CO 2 had a significant impact on exudation. Under elevated CO 2, exudation of total LMWOAs increased by 120–160%, amino acids by 250%, dissolved monosaccharides by 130–270% and DOC by 180–220% compared to ambient CO 2 treatment. Net CO 2 assimilation rates increased significantly by 41–47% for seedlings exposed to elevated CO 2. Exuded C calculated as a percentage of assimilated CO 2 increased by 41–88% in the elevated CO 2 treatment compared to ambient CO 2 treatment.