The compound that provides the reducing power for Calvin cycle reactions is NADPH.

Here's why:

* Calvin cycle is the light-independent stage of photosynthesis, where carbon dioxide is converted into glucose.

* Reducing power is the ability to donate electrons, leading to the reduction of a molecule.

* NADPH (nicotinamide adenine dinucleotide phosphate) is a reduced electron carrier produced during the light-dependent reactions of photosynthesis. It carries high-energy electrons.

* In the Calvin cycle, NADPH is used to reduce 1,3-bisphosphoglycerate (1,3-BPG) to glyceraldehyde-3-phosphate (G3P), a key step in the production of glucose.

So, NADPH acts as the crucial source of reducing power, allowing the Calvin cycle to fix carbon dioxide and synthesize carbohydrates.