Heat waves: effect on budbreak date, shoot growth and xylem vessels of Vitis vinifera cv. Malbec

Abstract

We tested the hypotheses that heat waves occurring before budbreak advance budbreak date and increase shoot growth rate due to greater density and size of xylem vessels in irrigated Malbec vines (Vitis vinifera L.) in Mendoza, Argentina. We compared field grown vines heated to 2 ºC above the 90th percentile of the monthly distribution of the maximum temperature for three consecutive days before budbreak (HT3) with unheated vines (BL3). In 2012, we repeated this experiment and added another treatment, vines at ambient temperature (A3). In the same season we also conducted another experiment with a longer heating period (fifteen consecutive days before budbreak; HT15), unheated vines (BL15) and vines at ambient temperature (A15). Vines were heated by an active heating system especially design and built to increase day and night temperatures. HT3, BL3, HT15 and BL15 vines were into individual transparent polyethylene tents and received equal air flow from blowers. A3 and A15 vines were not into the plastic tents.

Maximum air temperature in HT3 treatments reached 35 ºC in 2011 (6 ºC above ambient), and 38 ºC in 2012 (10 ºC above ambient), however, maximum bud temperature reached 40 ºC in 2011, and 42 ºC in 2012 (5 ºC above air temperature in both seasons). Budbreak date was advanced in the HT15 treatment; nevertheless no other phenological changes were detected. Shoot growth rate was increased in heated treatments both seasons. Higher rates of leaf and laterals appearance were also recorded. Greater density and size of primary xylem vessels were observed in shoots from heated vines (13 vessels mm^-2, 0.18 mm²) compared to those unheated (10 vessels.mm^-2, 0.14 mm²). Second xylem vessels were not affected by heating treatment. Heat temperatures before budbreak did not affect yield or its components.

Heat waves that occurred close to budbreak permanently affected some shoot morphological features and growth responses. Increases of primary xylem vessels density and size may later affect hydraulic conductivity, vulnerability to xylem cavitation and vine transpiration.