Phloem carbon isotopic signature as a valuable tool to assess physiological adjustments among European grapevine varieties under a Mediterranean climate

Abstract

Wine production is being threatened by climate change, particularly in the Mediterranean region. Thus, more knowledge on vineyards’ well-functioning and adjustments to drought conditions is essential. We aimed to understand how grapevine varieties from different European origins, under the same climatic context, respond to water stress and whether the climatic origin plays a role in their water-use efficiency (WUE). With that in mind, we assessed the carbon isotopic signatures (δ13C) in berry juice and phloem of 172 white and red grapevine varieties grown in Herdade do Esporão (Alentejo, Portugal) from five different climatic origins in two different rainfed water treatments: with full and no irrigation. Our findings indicate that there is a 13C enrichment in both berry juice and phloem under water stress, regardless of the climatic origin of the grapevine varieties. This suggests that the plants exhibited greater stomatal regulation and tighter control over water loss during drought conditions. Also, we found a positive correlation between berry juice and phloem δ13C signatures that is maintained under limited water conditions (i.e., non-irrigated rainfed condition: NI-rf). Six clusters, based on δ13C patterns in NI-rf, were obtained and the varieties that showed the higher WUE listed. The patterns of δ13C drought-adjustments (differences among water-treatments) were dependent on specific varieties capacity to acclimate, and the varieties that were grouped as the ones with high WUE in NI-rf also showed greater δ13C drought-adjustments. These results highlight a range of WUE adjustments, revealed through phloem isotopic analysis, being phloem δ13C signature a complementary and promising proxy to assess grapevine varieties’ drought acclimation capacity. Our study reinforces vineyard plasticity and great adaptative ability, transversal to several grapevine varieties with different climatic origins. The results provided might be a complementary support to identify the varieties that are potentially more physiologically equipped under drought, and to further explore their vitality and grape quality under sustainable water-management scenarios.