Increased air humidity and understory composition shape short root traits and the colonizing ectomycorrhizal fungal community in silver birch stands

Abstract

Climate change is predicted to bring about a rise in precipitation and air humidity at northern latitudes, which could have considerable impact on forest management. This paper investigates the effect of increased air humidity and understory composition on short root morphology and on the relative abundance of colonizing ectomycorrhizal (EcM) fungal associates in silver birch (Betula pendula Roth.) stands.Short root morphological traits of silver birch were analyzed at increased humidity and ambient conditions for two different understories (early-successional grasses and diverse “forest” understory) in three consecutive years (2009–2011). The fungal community was determined in 2010 (after three seasons of misting) using molecular methods. The study was conducted on the Free Air Humidity Manipulation (FAHM) experimental facility established in Estonia.Silver birches responded to the rise in air humidity by forming longer and thinner short roots, which can be interpreted as a morphological adaptation leading to an increase in the absorptive area. The response was stronger when humidification concurred with the species-poor understory of pioneer grasses. The inter- and intra-treatment variation in short root morphological parameters decreased by the third year. Using molecular methods, overall 64 EcM taxonomic units were distinguished. Hydrophilic fungal morphotypes dominated significantly in humidified plots, hydrophobic morphotypes in control plots.Our results suggest that rising air humidity causes a morphological stress response in EcM short roots. Young trees show the ability to adapt to climate change with great plasticity by modifying short root length, diameter and specific root length (SRL). Humidification leads to a shift in the fungal colonizers towards the dominance of hydrophilic taxa, which may alter ecosystem functioning.