Disentangling the interactions between leaf water, nitrogen, carbon status, and photosynthesis using high throughput phenotyping and statistical models: A study of fungi tolerant grapevine varieties

In the context of climate change and the need to reduce inputs, optimising photosynthesis and grapevine performance requires a better understanding of the interactions between water status, nitrogen availability, and source-sink relationships. This study investigates the combined effects of leaf water potential (Ψpd), leaf nitrogen content (LN), and leaf-to-fruit ratio (L:F) on the photosynthetic activity of three fungus-tolerant grapevine varieties (ARTABAN, 3159-B, and G5). The experiment was conducted over two years in an experimental vineyard subjected to different agronomic practices that modified water and nitrogen availability (cover cropping, irrigation, fertilisation) and source-sink balance (winter and summer pruning). High-throughput phenotyping methods, including Near InfraRed Spectrometry (NIRS) and chlorophyll fluorescence, were used to rapidly estimate leaf nitrogen and non-structural carbohydrate contents, as well as photosynthetic activity. Our results show that, among the monitored variables, Ψpd was the main determinant of photosynthesis, while L:F and LN had a moderate influence. ARTABAN maintained higher photosynthetic activity for a given intensity of water deficit than G5, likely due to its lower L:F. Structural equation modelling revealed causal relationships for the three genotypes between Ψpd and LN, between Ψpd and L:F, between L:F and LN, and lastly between Ψpd and photosynthesis (An). In addition, our results showed that leaf non-structural carbohydrate content was driven by both sink demand and maximum CO2 assimilation rate (Amax), rather than by water or nitrogen availability. These findings highlight the importance of integrating water management and canopy structure optimisation to maintain carbon assimilation under limiting conditions, thus providing new perspectives for improving vineyard resilience to climate change.