Fine roots and ectomycorrhizal colonization in black spruce subjected to reductions in soil moisture

Abstract

Growth and survival of boreal tree species depends on fungal symbionts, namely mycorrhizas. Owing to their rapid turnover, fine roots and their symbionts can be prompt and sensitive indicators of the effects of environmental changes on forest ecosystems. We investigated how a reduction in soil moisture influences the fine roots and ectomycorrhizas (ECM) of black spruce [Picea mariana (Mill.) BSP] after 3 years of rain exclusion in four mature stands of the boreal forest of Quebec, Canada. Rain was excluded with transparent plastic under-canopy covers installed during the growing seasons 2010–2012. Soil moisture was strongly affected by the treatment, with water content being reduced from 40% to 21% on average. As expected, the experimental trees showed a decrease in the proportion of vital root tips and ECM with respect to controls. The proportion of vital ECM was also globally reduced from 73.8% to 68.6%, but the effects of the treatment were only significant in two sites. The expected drier conditions due to current warming will likely influence the presence of mycorrhizas, with potential consequences on the root vitality of boreal tree species.