Source-sink manipulations through shading, crop load and water deficit affect plant morphogenesis and carbon sink priorities leading to contrasted plant carbon status in grapevine

Backgrounds and aims: Shading, water deficit, and crop load shape plant development in a very plastic way. They directly influence the plant's carbon supply and demand to and from the different organs via metabolic, hydraulic and hormonal mechanisms. However, how the multiple environmental factors combine through these mechanisms and how they interplay with carbon status, vegetative and reproductive development and carbon assimilation of the plant needs to be investigated in the context of current climatic and technological constraints.

Methods: With this aim, two experiments were conducted on potted grapevines, subjected to ten combinations of treatments. Axis organogenesis, berry characteristics at harvest (weight, number and total soluble content) and a series of leaf traits (gas exchanges, non-structural carbohydrate contents, water potential and SPAD values) were measured.

Key results: Grapevine development showed different responses corresponding to different sink priorities: under shade, vegetative development was maintained at the expense of berries, whereas under high crop load and water deficit, berry growth was the priority sink. These responses were accompanied by changes in the specific leaf area in agreement with the shade avoidance syndrome. These different strategies affected the plant carbon status as estimated through the starch content in leaves. Leaf starch content was not affected by shade, while it decreased under water deficit and crop load conditions. Carbon assimilation was decreased under water deficit, low crop load and shading conditions. Hydraulic properties and leaf nitrogen content correlated withthis decrease while plant carbon status has a very low impact. Finally, no major interaction between the different types of constraints were observed both on morphological and functional variables.

Conclusions: Depending on the type of abiotic constraints, grapevine exhibits specific morphogenetic responses at plant and leaf levels. The absence of interaction between the different constraints showed that grapevine is able to exhibit independent responses to shade and water deficit. This result is of major importance to further design new agricultural systems facing multiple abiotic constraints, such as those in agroforestery and agrivolatic system.