Answer:
The heat they generate
Step-by-step explanation:
These geothermal vents have been known to release pressures that have been built up over time I'm the form of steam and really hot water. The article from which this question was drawn, goes on to say that the temperature of the ground around areas with the vents can go up to more than 150 degrees fahrenheit. The heat condition of this place was what made Rusty Rodriguez to wonder how plants were still able to survive in the soil.
So the answer is the heat they generate, since these vents generate great heat which normally would have made it difficult for plants to survive.