Plant Environment: Water

1. Plant Environment: Water • Water makes up 80-90% of herbaceous and 50% of woody plants • Water is important to plants • Water critical for plant growth (photosynthesis: 6CO2 + 6H2O ---> C6H12O6 + 6O2) • Water needed to obtain nutrients from soil (nutrients dissolved in water) • Water needed for cell elongation, one way plant tissues increase in size

2. Plant Environment: Water • From soil into root cells • Water enters root hairs (projections of cells above root tip) • How does water move through plants? • Root hairs greatly increase surface area for water entry • Root cells ‘pump’ minerals into cells (using ATP energy) • High concentration of minerals inside roots creates osmotic gradient (difference in water concentration) • Water moves from high to low water concentration • Adding minerals into roots decreases the concentration of water in roots causing water to enter by osmosis

3. Plant Environment: Water • From root cells to xylem in roots • Water (and minerals) move between or through cells of cortex • How does water move through plants? • Casparian strips blocks water, force it through membranes of endodermal cells • Endodermal cells selects nutrients that enter xylem

4. Plant Environment: Water • Xylem is dead, hollow, tubular cells • How does water move through plants?

5. Plant Environment: Water • From xylem upward to leaves • Water molecules ‘clings’ to xylem and to each other • How does water move through plants? • Water in xylem is unbroken ‘column’ • Water evaporates from leaves ‘pulling’ water up xylem • Evaporative water loss through stomates of leaves is transpiration • 90% of water ‘absorbed’ by roots lost via transpiration in leaves

6. Plant Environment: Water • Cooling turf or greenhouse (by evaporative cooling) • Frost protection • Other uses of water in horticulture • Modify local environment • Irrigation

7. Plant Environment: Water • Slight water stress causes stomates to close; photosynthesis reduced • Water deficiency in plants • Reduction in growth • Smaller leaves • Shorter internodes • Smaller plants • Slight water stress can effectively prevent fast, leggy growth

8. Plant Environment: Water • Severe water deficiency • wilting • Water deficiency in plants • Dry leaf tips or margins • Yellowing of older leaves • Abscission of leaves, flowers, fruit • Same symptoms can occur because of prolonged, excess water

9. Plant Environment: Water • Container plants • Saturate soil with water; let dry before next watering • Proper watering of plants • Watering completely encourages root growth throughout container • Always use pots with drainage holes • Water until some water trickles out of drainage holes • Overwatering occurs from watering too frequently not too much at one time

10. Plant Environment: Water • garden plants • Garden plants need regular water • Proper watering of plants • Deficits followed by excess water during particular growth stages reduces quality of vegetable • beans with large air pockets • Ruptures in tomato skin • Growth cracks in carrots

11. Plant Environment: Water • Soluble salt problems result from: • High levels of salt in soil • Soluble salt problems: • High level of salt in irrigation water • Excessive use of fertilizers • Symptoms include: • Wilting • Drying of tips of margins of leaves • Abscission of leaves, flower, fruit (Symptoms same as lack of water…why?) • Problem solved by flushing plant with water