Figure 1.

Experimental design of the study. At time 0 (indicated by the asterisk), reference temperate soil (0–20 cm depth from surface) was homogenized and divided among fifteen 1 l glass mesocosms that were maintained at ambient moisture through the experiment. Nondestructive sampling of each mesocosm proceeded from week 4 onwards as indicated by the x-axis. Unwarmed Control mesocosms (solid gold line, n = 6) were maintained at 14°C, which was ambient soil temperature at the time of collection. Disturbed mesocosms (dashed blue line, n = 9, including Disturbance and Disturbance + Immigration groups) were acclimated for four weeks at 14°C, increased to 60°C over two weeks, maintained at 60°C as a thermal press disturbance for eight weeks, then decreased back to 14°C over two weeks, and finally maintained for a total of 45 weeks. Four of the disturbance mesocosms received homogenized soil slurry from Control mesocosms as a dispersal event at week 17, after the thermal press was released (Disturbance + Immigration treatment; see methods). Note the break in the x-axis time scale between weeks 20 and 45.