The International Treaty on Plant Genetic Resources for Food and Agriculture focuses on ensuring the conservation and sustainable use of plant genetic resources for food and agriculture. This directly impacts biodiversity as it aims to protect the variety of plant species crucial for food security and ecosystem health.

The United Nations Convention to Combat Desertification addresses land degradation in arid, semi-arid, and dry sub-humid areas. Desertification can significantly reduce biodiversity by destroying habitats and reducing plant and animal life. By working to combat desertification, this convention indirectly protects biodiversity.

The World Heritage Convention focuses on preserving cultural and natural heritage sites. Conservation natural heritage sites may contribute to biodiversity conservation. Thus 'D' is the correct answer.