The study looked at how nitrogen and calcium levels affect the growth and photosynthesis of nectarine trees in protected cultivation. They found that increasing calcium levels initially boosted chlorophyll content and photosynthesis, but then had diminishing returns. The best results were seen with 4 mmol/L calcium at low nitrogen levels and 8 mmol/L calcium at high nitrogen levels. This shows that the interaction between nitrogen and calcium plays a crucial role in the photosynthetic performance of nectarine trees.