Quantitative analysis of soluble exudates produced by ectomycorrhizal roots as a response to ambient and elevated CO2

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.