Preheat oven to 450 degrees F. Cut potatoes and celery root into 1/2-inch thick matchsticks. In a small bowl, mix together cayenne, paprika, 5-spice powder, garlic powder, black pepper and salt. Spread matchsticks evenly on 2 sheet trays and toss with oil and spice mixture. Roast until golden brown, about 40 minutes, shaking pan occasionally. Serve immediately.