Partitioning of dry matter, carbon, nitrogen and inorganic ions of grapevines: effective partial rootzone drying and relationship with restricted spring growth

Abstract

A reduced shoot growth and greatly increased WUE is a characteristic of partial rootzone drying (PRD), but little is known about the effect of PRD on partitioning of C, N and inorganic ions such as K. Our experiments with field-grown Cabernet Sauvignon, where the PRD grapevines were irrigated at half the control rate, and Shiraz where the PRD grapevines were irrigated at same rate as controls, have confirmed that PRD is not simply an irrigation strategy that applies less water—rather it alters the way in which the plant responds to its environment, e.g. PRD alters the sensitivity of the stomatal response to atmospheric conditions and significantly influences enzymes that regulate nutrient accumulation and partitioning. PRD did not change the total amount of carbon and nitrogen on a whole plant basis. However, it caused a significant partitioning of carbon and nitrogen towards the trunk, roots and fruit at the expense of shoot growth. This change in partitioning occurred as a result of altered activity of the enzymes controlling the assimilation of carbon and nitrogen. This hypothesis was reinforced by the fact that berries showed significantly higher levels of hexose early in the season.

Although PRD had no significant effect on berry characteristics at harvest such as Brix and pH, it reduced per berry K+ content and increased total amino acid concentration that may lead to positive outcomes for wine quality.

Restricted spring growth (RSG) is a disorder with sporadic occurrence in mostly the dry inland areas of Australia. Various groups have speculated that RSG is a result of a combination of factors such as climate, cultural and pathological disruptions on nutrient accumulation leaving grapevines vulnerable to unfavourable external conditions. Field experiments included the exposure of young Cabernet Sauvignon to a range of cultural disruptions on carbon and nitrogen status to induce the RSG disorder in a closely monitored environment. Although field experiments had significant effects on shoot growth and nutrient status, no classical RSG disorders could be achieved. However, RSG symptoms encountered in commercial vineyards were associated with an increase in the C/N nutrient status. Similar observations were made in field experiments where vines were exposed to low soil moisture conditions during the winter months.

Summary

Confirmed that PRD is not simply an irrigation strategy that applies less water, it alters the way in which the vine responds to its environment. PRD does not change the amount of C and N but it partitioned nutrients and dry matter away from vegetative and towards permanent structure of the vine.