Text Box 1

Isohydric and anisohydric winegrape varieties and stomatal response to water availability

Joelle Bou Harb and Markus Keller, WSU IAREC Introduction A mild to moderate soil water stress is desirable for production: The decrease in leaf water potential Ѱ allows for canopy reduction through cell elongation inhibition

A beneficial reduction in stomatal conductance (gs) leading to an increase in the vine water use efficiency General guidelines: Mild water stress is usually accompanied by a drop of several bars from well-watered conditions Moderate water stress by a drop of more than several bars but less than 12 Bars (or 1.2 MPa) from well-watered conditions

For example: Well-watered conditions Ѱmidday = -0.6 MPa. A good target would be between -1.1 to -1.6 MPa (!!!)

Shoot elongation decreases linearly with declining Ѱ and stops completely at Ѱ=-1.2 MPa differences So far 2 main categories of response to water stress have been characterized: ISOHYDRIC and ANISOHYDRIC ISOHYDRIC ANISOHYDRIC  Ѱmidday is the same in stressed plants  Ѱmidday is lower in stressed plants than in and in well-watered plants well-watered plants

 Stomata sensitive to soil moisture drop  Stomata less sensitive to soil moisture drop and gs drops early and gs remains high

 Risk of photosynthesis inhibition  Lower risk of photosynthesis inhibition

 Model variety:  Model variety: gs Isohydric Isohydric Ѱ midday Anisohydric Anisohydric

Soil moisture Soil moisture Hypothesis Instead of 2 extremes, there is a continuum of responses to water availability within vinifera. More categories can arise showing groups of varieties that can be managed differently in the same Objectives To compare 18 different varieties grown under the same conditions in Eastern State and depict different pattern of responses over a full range of soil moisture such as Ѱmidday pattern Materials and Methods Dry down/recovery cycles for 2015, 2016 2017 at the ROZA experimental vineyard Measurement of Ѱmidday (Pressure chamber) and stomatal conductance (Porometer) Measurement of soil moisture (Neutron probe) for each replicate 18

16 18 varieties studied at the ROZA vineyard 14 Red varieties White varieties 12 Cabernet Soil moisture (%) 10 Mean Sauvignon Mean±SE 8 9-Jun 26-Jun 16-Jul 21-Jul 24-Jul 30-Jul 1-Aug 12-Aug 19-Jun 9-Jul 18-Jul 23-Jul 29-Jul 31-Jul 3-Aug 18-Aug Date 18 Grenache Semillon

16 Pinot Gris 14 Petit verdot Auxerrois 12 Nebbiolo Muscat Blanc

Soil moisture (%) 10 Mean Mean±SE Lemberger 8 1-Jun 4-Jun 5-Jun 9-Jun 3-Jun 2-Aug 4-Aug 8-Aug 23-Jul 24-Jul 27-Jul

17-Jun 21-Jun 23-Jun 29-Jun 30-Jun Gewurztraminer 10-Aug 11-Aug 16-Aug 17-Aug 21-Aug 23-Aug 24-Aug 25-Aug 29-Aug 30-Aug 20-Sep 21-Sep 23-Sep 28-Sep 29-Sep Date Soil moisture evolution 2015 (Top) Albarino and 2016 (Bottom) Results 3 categories of Ѱmidday behavior to water availability have been depicted Category 1: Linear drop or near-anisohydric varieties

-0.4 -0.4 -0.6 -0.6 -0.8 -0.8 -1.0 -1.0 -1.2 -1.2

(MPa) -1.4

(MPa) -1.4 -1.6 -1.6 -1.8 2015 -1.8 2015 2016 2016

Midday water potential leaf -2.0 Midday water potential leaf -2.0 2017 2017 -2.2 -2.2 8 10 12 14 16 18 20 22 24 6 8 10 12 14 16 18 20 22 24 Soil moisture (%) Soil moisture (%) Semillon Cabernet franc Ѱmidday drops to low levels

Mild to moderate water stress can occur anywhere between 64% of field capacity (FC) and 44% of FC

Varieties: , Cabernet franc, Pinot gris, Pinot noir, Auxerrois, Semillon, Albarino, Sauvignon blanc

Category 1: Linear drop or midday

Ѱ near-anisohydric varieties

Soil moisture Category 2: Linear drop after a threshold of soil moisture

-0.4 -0.4 -0.6 -0.6 -0.8 -0.8 -1.0 -1.0 -1.2 -1.2 (MPa) (MPa) -1.4 -1.4 2015 -1.6 -1.6 2015 2016 2016 -1.8

Midday water potential leaf -1.8 2017 Midday water potential leaf 2017 -2.0 -2.0 6 8 10 12 14 16 18 20 22 6 8 10 12 14 16 18 20 22 24 26 Soil moisture (%) Soil moisture (%) Grenache Petit Verdot  These are more conservative varieties that do not on average allow for Category 2: Linear Ѱmidday to drop to low values as soil drop after a moisture declines threshold of soil moisture Moderate water stress is barely attained

Mild water stress to moderate water midday stress can occur at lower soil moisture Ѱ of 56% til Permanent Wilting Point PWP (40% FC in Sandy loam soil) Soil moisture  Varieties: Merlot, Grenache, Petit Verdot, Nebbiolo, Malbec, Gewurztraminer Category 3: Near-isohydric varieties

-0.4 -0.4 -0.6 -0.6 -0.8 -0.8 -1.0 -1.0 -1.2 -1.2 (MPa) (MPa) -1.4 -1.4 -1.6 -1.6 2015 2015 -1.8 2016 2016 Midday water potential leaf

Midday leaf water potential -1.8 2017 2017 -2.0 -2.0 6 8 10 12 14 16 18 20 22 24 6 8 10 12 14 16 18 20 22 24 26 Soil moisture (%) Soil moisture (%) Lemberger Riesling A plateau of Ѱmidday values occur over a large range of declining soil moisture Category 3: values Near-isohydric varieties Ѱmidday remains high despite soil drought midday It is difficult to attain a moderate stress Ѱ

Mild water stress can occur at soil moisture of 64% til below Permanent Soil moisture Wilting Point PWP (40% FC in Sandy loam soil), which is a very wide range

 Varieties: Lemberger, Riesling and Muscat blanc Stomatal conductance and its sensitivity to soil moisture depletion

Variety Ѱmidday Ѱmidday gs sensitivity to pattern sensitivity to soil moisture (R soil moisture (R value) value)

Semillon Category 1 0.82 0.87 Cabernet franc Category 1 0.78 0.76 Chardonnay Category 1 0.58 0.61 Gewurztraminer Category 2 0.53 0.79 Merlot Category 2 0.51 0.78 Petit Verdot Category 2 0.59 0.47 Riesling Category 3 0.33 0.56 Muscat blanc Category 3 0.46 0.53 Lemberger Category 3 0.52 0.25  Unlike what is reported, all varieties in Category 1 did not have insensitive stomata to soil moisture 1000 Cabernet Franc (Categ 1)  Allowing soil moisture to drop to Lemberger (Categ 2) moderate levels of water stress is to 800 Petit Verdot(Categ 3) be done carefully for such varieties in order to keep the photosynthesis 600 unaffected 400 Unlike what is reported, the

varieties that maintain their water gs (mmol.m-2.s-1) 200 status do not have more insensitive stomata for eg. Category 3 (and 0 some of the varieties in category 2) 6 8 10 12 14 16 18 20 22 24 Soil moisture (%) Allowing soil moisture to enter a mild stress mode can be more safely done for those varieties Other factors affecting the response: Vapor pressure deficit VPD

-0.4 -0.4 -0.6 -0.6 -0.8 -0.8 -1.0 -1.0 -1.2 -1.2 -1.4 -1.4 -1.6 -1.6 -1.8 VPD status: High -1.8 VPD status: High VPD status: Low VPD status: Low -2.0 -2.0 Midday water potential (MPa) leaf 10 12 14 16 18 20 22 24 Midday water potential (MPa) leaf 8 10 12 14 16 18 20 22 24 Soil moisture (%) Soil moisture (%)

VPD can be an additional factor affecting the Ѱmidday in some varieties. In Malbec (Left), Ѱmidday decreased even under high soil moisture when VPD was high recorded compared to a low VPD. This was not seen in Grenache (Right) Take home messages  There are 3 patterns of Ѱmidday over the full range of soil moisture that can be depicted among winegrape varieties

Some varieties can reach desired moderate water stress state at higher soil moisture than others. Some varieties will have hard time to reach a moderate stress stage Varieties that can lower their Ѱmidday do not always have insensitive stomata neither do the varieties that maintain Ѱmidday always have the most sensitive stomata. This lead to further attention to a photosynthesis inhibition risk VPD is a factor than can affect the response of vines and explain some variability in measurements Funding: Washington State and Wine Research Program WSU

Acknowledgements: Advisor: Markus Keller

Labmates: Alan Kawakami Lynn Mills, Yun Zhang, Natasha Shcherbatyuk, Ben-Min Chang