Adaptation and resilience of scions and rootstocks to water constraint? It’s complicated and requires an integrated approach

Abstract

The ability, and the underlying mechanisms of grapevines to cope with and adapt to recurring water constraints, are the focuses of this study. It is an important topic given the growing climate extremes, droughts and water-scarce conditions experienced in the vineyards of the world. Our approach relies on integrative analyses where relationships between a plant’s environment, its intrinsic responses to stressful conditions, and extrinsic biotic factors such as microbial populations are interrogated. Experiments were first conducted in a potted vineyard containing scions (Cabernet Sauvignon, Merlot, Pinotage, Petit Verdot, and Shiraz) and rootstocks (Ramsey, 110 Richter, 101-14 Mgt, and USVIT 8-7) on their own roots, as well as in grafted combinations. This allows control over when, how long, to what level and how many recurring events of water constraint are applied, using active drying workflows. Profiles of the responses of the scions, rootstocks and their grafted combinations as water constraints increase and relax were achieved. The plasticity in responses, specifically linked to stomatal conductance and transpiration (day and night) is strongly influenced by the scion/rootstock combinations, with evidence of adapted responses with recurring drying events. The contribution of intrinsic (morphological, physiological and epigenetic) and extrinsic (rootzone microbial community) factors to water stress resilience were investigated in a second vineyard resource, a validated model vineyard where three scion cultivars (Pinotage, Shiraz, and Cabernet Sauvignon) on two rootstocks (Richter 110 and USVIT8-7) grow under dryland and well-watered scenarios. Profiling of the site, soil, atmospheric conditions, plants, and their physiological responses provide contextual data for a diurnal transpiration analysis, as well as an epigenetic and soil microbiomics evaluation. On the latter, we will show that each cultivar is surrounded by different microbial communities, but of similar traits. For example, a mixture of genera that can tolerate extreme environments in the soil was found under dryland conditions, whereas the well-watered plants were surrounded by saprobes and decomposers, suggesting that each cultivar has a different pool of genera from which to recruit microorganisms to the rhizosphere under different irrigation levels. The combined data provides insight into the adaptability of grapevines and confirms the value of the approach to investigate resilience.