Carbohydrate reserves play a critical role in the grapevine growth cycle by providing a carbon source to support root and shoot growth after bud break. Research results suggest that the amount of reserves stored over winter can influence reproductive development and shoot growth for the next season. In this article, we discuss various determinants of carbohydrate reserves and a new study that weighs the roles of these determinants.
Determinants of carbohydrate reserve dynamics
Carbohydrate reserve dynamics in the perennial tissues of grapevines are primarily determined by the growth and maintenance requirements and how well those requirements are balanced by the supply of carbohydrates from photosynthesis.
This balance between carbon supply and demand is in turn influenced by factors:
- related to climatic conditions (season duration, temperature, etc..) which affect photosynthesis and carbon assimilation.
- related to management such as yield, canopy size, water supply.
Differences due to climate versus agricultural practices
How do changes in climate patterns affect nutrient uptake and what are their consequences on fruit quality?
To understand the magnitude of changes caused by climatic variations and their effect on vineyard production, you can take a look at our vintage conferences videos. We also previously reported in our blog how changes in precipitation patterns will cause sudden “spurts” of nitrogen to be released. Consequently a drought during the winter is expected to lower nitrogen uptake, whereas a wet winter can increase nitrogen uptake. Such variations in climatic conditions directly affect nutrient dynamics and consequently carbon assimilation.
What about changes caused by agricultural practices? Do they impose similar effects or larger effects than seasonal variations on vineyard performances? Let’s take 2 examples to illustrate why this is not an easy question to address.
- Crop load adjustment, like crop thinning, can alter carbohydrates reserve storage. Fruit removal modifies the relationship between carbon sinks and sources during maturation. Such practice can reduce the time required for sugar or color accumulation in the fruit and lead to an increase of carbohydrate reserves stored into the perennial organs. By contrast, heavily cropped vines show symptoms of delayed maturation and a reduction in the amount of winter carbohydrate reserves.
- Irrigation management : to control shoot growth and enhance fruit composition a common strategy consists of imposing a period of water stress between fruit set and veraison. When comparing vines grown under full irrigation with vines grown under deficit irrigation, researchers have reported a reduction in starch concentration in wood tissues.
The relative impact of climate and agricultural practices
With this context in mind, an interesting study led by Holzapfel and Smith in Australia, assessed the relative impact of vineyard practices versus climatic factors on carbohydrate reserves dynamics.
The authors found that:
- Carbohydrate reserve mobilization and storage patterns can vary significantly across seasons.
- Seasonal climatic variations play a larger role than agricultural practices in determining these patterns (like hedging, cluster thinning or irrigation)
Consequently, in the short term, seasonal climatic factors have a stronger influence on carbohydrate storage with direct implications on vine reproductive potential. However, changes in agricultural practices are more suitable for making long-term productivity adjustments. In that sense, the effects of vineyard management operations can be compared to maneuvering a very large boat: it takes time to change the direction where the vineyard is going….
Those results on carbohydrates dynamics variations justify the value of monitoring wood biomass to anticipate seasonal variations on vine productivity. It is also useful to better control long-term effects of agricultural practices on vineyard production.
Take-away: Keep in mind that manipulation of reserve accumulation through agricultural practices may create long term adjustment of vine productivity, as opposed to short term yield fluctuation which are more likely to reflect seasonal variations.
With Physiocap you could map the long term effects of your agricultural practices in terms of modifying the wood structure and the vineyard spatial structure.