Differences in soil type drive the intraspecific variation in the responses of an earthworm species and, consequently, tree growth to warming

The magnitude of the change in tree growth caused by climate warming can be highly dependent on biological context, including factors such as the presence of associated decomposers and their behaviors. We test the hypothesis that 1) the presence of earthworms modifies the response of soil inorganic N and tree growth to warming via the change of cast production; and furthermore 2) the type of soil as food for earthworm differentiate the earthworm response and its effects on the plant-soil system. We conducted a microcosm experiment rearing a geophageous earthworm species (Aporrectodea rosea) and birch (Betula ermanii) seedlings with two types of soil (sedimentary soil and serpentine soil) under two temperature regimes (ambient and ambient +3.3 °C). While the warming increased the cast production by the earthworms in the serpentine soil, it did not influence cast production in the sedimentary soil. The net nitrogen mineralization rate and the net inorganic N production showed similar dynamics to cast production under the warmer conditions, although the net nitrification rate did not. A significant increase in tree height from warming was observed only in the serpentine soil with earthworms, and the tree height was positively correlated with inorganic N production. The context-dependent change of soil N dynamics to warming could be caused by differential feeding activity of earthworm, and it results in the modification of the growth characteristics of birch seedlings.