You decide to perform a simple experiment to determine whether nitrogen or phosphorus is a more limiting nutrient in a pond in your backyard. Using a curtain that does not allow water, nutrients, or organisms to pass through, you divide your pond into four equal-sized quadrats (like a pie with four pieces). You randomly apply one of the following treatments to each quadrat: no nutrients (control), nitrogen only, phosphorus only, nitrogen and phosphorus. After 10 days, you measure net primary productivity (NPP) in each quadrat of your pond. You find the following results: Control NPP = 1.2 g C/m2/d; nitrogen only NPP = 1.3 g C/m2/d; phosphorus only NPP = 2.8 g C/m2/d; nitrogen and phosphorus added NPP = 2.8 g C/m2/d. Which is true about nutrient limitation in your pond? Group of answer choices Nitrogen is the only limiting nutrient Neither nutrient is limiting Phosphorus is the only limiting nutrient Nitrogen and phosphorus are both limiting nutrients