1. Water relations and horticulture HORT 301: Plant Physiology Mike Mickelbart

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

3. Drought U.S.

4. The Kettleman Hills near the town of Kettleman City, California, along I-5, May 2007. Normally, the hills would be green at this time, but less than 1 inch of rain has fallen since January 1, and no annual grasses grew this year.

5. Barren River Lake, Barren Co, Kentucky, June 16, 2007. Reservoir 7.5 feet below summer pool, due to inadequate precipitation throughout the winter and spring seasons. Photo courtesy of Stu Foster.

6. Franklin, Tennessee, Aug 27, 2007. 14 days with temperatures at or above 100°F, Water restrictions currently in effect. Photo courtesy of Jordan Gerth.

7. Drought

8. Source: Tucson Weekly

9. Drought Global Recent articles 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

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

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

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

13. The main question How does water move into and out of plants? –Driving force = water potential –Series of resistances

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

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

16. Examples of water relations in horticulture Irrigation scheduling Fruit production Greenhouse management Stress monitoring in vineyards Evaporative cooling Transplant shock Partial root zone drying Saline irrigation water Water use efficiency

17. Fruit growth “The importance of water to horticultural crops is particularly great because most horticultural produce is sold by weight, with water being the major component, so there is often a marked premium in ensuring that water content is optimized, often through precise control of irrigation.” Jones and Tardieu. 1998. Modelling water relations of horticultural crops: a review. Sci. Hort. 74:21-46.

18. Fruit growth Maintenance of turgor is essential for –biochemical processes –growth Turgor essential for fruit growth –fruit create water stress in trees –excessive turgor leads to splitting Can be maintained by osmotic adjustment Cell wall elasticity is important Turgor potential drives growth (1/V)(dV/dt) =  (P-Y) V = volume  = cell wall extensibility P = turgor pressure Y = yield threshold

19. Greenhouse management Relative humidity –Water uptake –Plant cooling –Nutrient uptake Air flow

20. Greenhouse management Relative humidity –Water uptake –Plant cooling –Nutrient uptake Air flow –Boundary layer

21. Vineyard stress monitoring

23. Evaporative cooling Average temps for parts of apple tree during 156 h overhead sprinkling Mean temp Irrigationairbarkleaffruit Overtree29.625.626.127.6 Undertree30.429.830.932.6 Nonirrigated31.631.931.234.8

24. Transplant shock Soil differences

25. Partial root zone drying

28. Water use efficiency (WUE) Irrigation efficiency Crop/landscape WUE Plant WUE

31. Irrigation Irrigation efficiencies –Ea –Eu Irrigation application considerations –ET –Uniformity –Timing –Crop requirements

32. Irrigation Irrigation application considerations –Crop requirements (Et crop ) Species Climate/weather Production practices Stage of growth –Developing a water budget

33. Water use efficiency Plant WUE –Species

34. Water use efficiency Plant WUE –Within species P. deltoides x P. maximowicziiP. nigra x P. maximowiczii

35. Examples of water relations in horticulture Irrigation scheduling Fruit production Greenhouse management Stress monitoring in vineyards Evaporative cooling Transplant shock Partial root zone drying Saline irrigation water Water use efficiency