Water relations and horticulture HORT 301: Plant Physiology Mike Mickelbart

Lecture outline Who cares about water? Review water movement in plants Examples of water relations in horticulture 2

Drought 3

Franklin, Tennessee, Aug 27, 2007. <0 Franklin, Tennessee, Aug 27, 2007. <0.1” rain in Aug, >14 days with temperatures at or above 100°F, Water restrictions currently in effect. Photo courtesy of Jordan Gerth. 4

Drought Local 6

Drought Global Scarce water and population boom leads California to 'perfect drought' Jun 25 2007 · No rain forecast in south of state until September · Sprinklers and car washing could be stopped Turkey rations water as cities hit by drought Aug 3 2007 Turkey's two major cities are grappling with water shortages after record low levels of snow and rain in the winter and searing summer temperatures. Darfur conflict heralds era of wars triggered by climate change, UN report warns Jun 23 2007 · Drought and advancing desert blamed for tensions · Chad and southern Africa also at risk from warming Source: Guardian Unlimited 7

The main question How does water move into and out of plants? 8

The main question How does water move into and out of plants? Driving force = water potential 9

The main question How does water move into and out of plants? Driving force = water potential w w w 10

The main question How does water move into and out of plants? Driving force = water potential w = p + s + g \figures\ch04\pp04161.jpg

The main question How does water move into and out of plants? Driving force = water potential Series of resistances Leaf Xylem Root Soil 12

Transplant shock w = p + s + g + ? Soil water potential gradient 13

 = cell wall extensibility Fruit growth Turgor essential for fruit growth fruit create water stress in trees excessive turgor leads to splitting Splitting in fruits Changes in turgor Cell wall elasticity ©Ed Hume Enterprises Turgor potential drives growth (1/V)(dV/dt) = (P-Y) V = volume  = cell wall extensibility P = turgor pressure Y = yield threshold w = p + s + g + m

The main question How does water move into and out of plants? Driving force = water potential w = p + s + g \figures\ch04\pp04161.jpg

w = p + s + g + m w w 16

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Poinsettia bract edge burn 18

The main question How does water move into and out of plants? Driving force = water potential Series of resistances Leaf Xylem Root Soil 19

Boundary layer 20

Greenhouse management Leaf-air gradient Water uptake Plant cooling Nutrient uptake Air flow Boundary layer 21

ABA and water loss 22

Partial root zone drying 23

Partial root zone drying 24

Partial root zone drying 25

Partial root zone drying Yield and water use of winegrapes Variety Variable Control PRD Shiraz Yield (t/ha) Water (Ml/ha) Yield/water 22.6 1.4 16.1 21.5 0.7 30.7 Cabernet sauvignon 15.2 10.9 15.4 22.0 Riesling 29.1 4.5 6.4 28.9 2.4 11.9 30.6 5.2 5.9 28.7 2.6 McCarthy, 2000 26

Partial root zone drying 27

Mass merchandising (box stores) Handle large quantities of ornamentals Home Depot Garden Centers 1990 $3.8 billion 1994 $12.5 billion 2006 >$25 billion

Mass merchandising (box stores) Handle large quantities of ornamentals Home Depot Garden Centers 1990 $3.8 billion 1994 $12.5 billion 2006 >$25 billion

ABA and water loss ABA causes stomata to close Driving force = water potential Series of resistances Leaf Xylem Root Soil 30

Indiana Field Trial for ConTego Supertunia ‘Citrus’ Control ConTego™ 1000 ppm Photograph taken 10 days after withholding water R. Lopez, Purdue Univ.

Indiana Field Trial for ConTego Coleus ‘Versa Crimson Gold’ Control ConTego™ 1000 ppm Photograph taken 10 days after withholding water R. Lopez, Purdue Univ.

Indiana Field Trial for ConTego Gerbera ‘Revolution’ Control ConTego™ 1000 ppm Photograph taken 8 days after withholding water R. Lopez, Purdue Univ.

Indiana Field Trial for ConTego Impatiens hawkeri Control ConTego™ 1000 ppm Photograph taken 10 days after withholding water R. Lopez, Purdue Univ.

Indiana Field Trial for ConTego Coleus ‘Versa Crimson Gold’ Plants were irrigated after the drought stress and planted in the Purdue Trial Gardens for evaluation. Photo is 44 d after treatment. Treated Control R. Lopez, Purdue Univ.

Water relations and horticulture Water movement Water potential gradients Resistances to water movement Gradients in horticulture Soil gradients Organ gradients (fruit/stem/leaves) Leaf to air gradients (RH) Resistances in horticulture Stomatal resistance ABA 36