Long-term experimental warming and fertilization have opposing effects on ectomycorrhizal root enzyme activity and fungal community composition in Arctic tundra

摘要

As the Arctic rapidly warms, deciduous ectomycorrhizal (EcM) shrubs are expanding across the tundra. While we know how EcM host plants respond to warming and the associated nutrient release predicted for a future Arctic, considerably less is known about how EcM function will respond, despite their important role in plant nutrient acquisition in the nutrient-limited tundra. To explore how EcM-associated nutrient cycling may change, we characterized EcM-associated root enzyme activity and community in a 28-year full factorial warming and fertilization experiment in Arctic tundra. We measured activity at the individual root tip-level (pmol.min(-1).mm(-2) root) and used EcM root tip abundance to scale to community-level activity ((pmol.min(-1).cm(-3) soil). We then Sanger sequenced fungi on the same root tips to pair identity with function. Linear mixed effects models and multivariate analysis showed warming and fertilization generally had opposing, and sometimes interacting, effects on EcM root-associated activity. Responses also differed depending on the scale. Fertilization decreased activity on both scales while warming dampened the effect of fertilization. Additionally, warming increased EcM mot tip abundance, and therefore community-level enzyme activity. Ectomycorrhizal root tip communities changed with fertilization, but not with warming. Changes in enzyme activity were moderately correlated with both changes in fungal community and soil inorganic nitrogen concentrations. The contrast in responses of mot tip-level activity and community-level activity point to a potential shift in allocation to EcM function: whereas the production of degradative enzymes may become less important for nutrient acquisition, the exploration of the soil environment through increased number of EcM mot tips may become more important. Furthermore, the future role of EcM in a warmer Arctic likely depends on the magnitude of nutrient release that comes with warming. While warming may increase the importance of EcM-associated nutrient cycling if nutrient availability remains low, it has the potential to decrease their importance if nutrient availability greatly increases.