Which are the two macronutrients that usually play the most important role in limiting plant growth globally?

Explanation

**Step-by-Step Solution:**

1. **Understanding Macronutrients**: Begin by defining macronutrients. These are essential nutrients that plants require in large amounts for their growth and development. Examples of macronutrients include carbon, hydrogen, oxygen, nitrogen, phosphorus, potassium, magnesium, calcium, and sulfur.

2. **Identifying Limiting Nutrients**: Next, consider which macronutrients are most commonly associated with limiting plant growth. Limiting nutrients are those that, when in short supply, can hinder plant growth and development.

3. **Focus on Magnesium and Calcium**: Among the macronutrients, magnesium and calcium are particularly important. Magnesium is a crucial component of chlorophyll, the pigment responsible for photosynthesis. Without sufficient magnesium, plants cannot effectively carry out photosynthesis, which is vital for their growth.

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