Interactive Effects of CO2 Enrichment and Nitrogen Levels on Leaf Gas Exchange Capacities of Sweet Potato

Abstract

Different nitrogen (N) doses may stimulate the photosynthetic responses of sweet potato under CO₂-enriched environment (ECO₂). The photosynthetic responses of two varieties, Sree Arun and Sree Kanaka, were adjudicated under varying nitrogen levels (0%, 25%, 50%, 100%, and 125% of the recommended N dose), exposed to ambient CO₂ (400 ppm) and elevated CO₂ (600 and 800 ppm). The results indicated that, compared to ambient CO₂, the net photosynthetic rate (P_n) and intercellular CO₂ (C_i) were significantly increased at ECO₂, while stomatal conductance (g_s) and transpiration (E) were significantly exacerbated. This resulted in an improved intrinsic (P_n/g_s) and instantaneous water use efficiency (P_n/E). Relative humidity and vapour pressure deficit during the time of measurements remained at 73%–85% and ~0.95–1.42 kPa, respectively, at 28°C ± 2°C leaf temperature. Furthermore, the results demonstrated that higher N doses increased photosynthesis and improved plant water relations by modulating stomatal conductance and transpiration rate. Overall, the responses of sweet potato plants to ECO₂ and N supply were genotypic-dependent, and nitrogen application could play an important role in modulating these responses under ECO₂. The findings from this study provide valuable insights for tailoring nitrogen-based management practices for sweet potato in a carbon-enriched environment.