To make dressing, in mini food processor, pulse capers with vinegar, mustard, salt and pepper. Add oil and pulse until creamy. Set aside.
Combine celery root and carrot in bowl; toss with 3 tbsp (45 mL) dressing. Toss beets, separately, with remaining dressing. Divide arugula among 4 salad plates. Top arugula with celery root mixture and beet mixture. Garnish with radishes.