Keseimbangan Air pada Tumbuhan air dalam tanah, penyerapan air oleh akar, transpor air dan nutrien melalui xilem, transpirasi Retno Mastuti Semester Genap 2015 ‐ 2016
Water Potential Measure of the energy state of water.
This concept is important in plant physiology because it determines the direction and movement of water.
B. Equation for water potential Ψw = Ψp + Ψs + Ψm + Ψg Water potential is the sum of the contributions of the various factors that influence water potential • Ψw = water potential • Ψp = pressure potential • Ψs = solute or osmotic potential • Ψm = matrix potential, and • Ψg = gravity potential
Pressure (Pressure Potential; Ψp)
a a large positive pressure pressure potential potential of zero
• • •
Due to the pressure build up in cells against to the wall. It is usually positive, although may be negative (tension) as in the xylem. Pressure can be measured with an osmometer.
Solute (or osmotic) potential (Ψs) • This is the contribution due to dissolved solutes. • Solutes always decrease the free energy of water, thus there contribution is always negative. • The solute potential of a solution can be calculated with the van’t Hoff equation: Ψs = ‐ miRT where,
m = molality (moles/1000 g); i = ionization constant (often 1.0); R = gas constant (0.0083 liter x MPa/mol) T = temperature (K).
Matric potential (Ψm) • This is the contribution to water potential due to the force of attraction of water for colloidal, charged surfaces. • It is negative because it reduces the ability of water to move. • In large volumes of water it is very small and usually ignored. • However, it can be very important in the soil, especially when referring to the root/soil interface.
Gravity (Ψg) • The gravitiational potential increases about 0.1 MegaPascal per 10 meters in height • Contributions due to gravity which is usually ignored unless referring to the tops of tall trees.
Ψw = Ψp + Ψs
A. Air Dalam Tanah Tabel 1. Beberapa tipe tanah, ukuran partikelnya dan luas permukaan/g tanah Tipe tanah
Ukuran partikel (µm)
Pasir: kasar (coarse sand)
2000 – 200
Area (luas) permukaan/g < 1 ‐ 10
200 – 20
< 1 ‐ 10
20 – 2
10‐100
< 2
100 ‐ 1000
halus (fine sand) Lumpur (silt) Lempung (clay)
Ketersediaan dan pergerakan air pada tipe tanah yang berbeda
Gambar 2. Proses penyimpanan air di dalam tanah
• When soil moisture is at field capacity, plant roots are able to obtain water with less effort, and water is thus rapidly available to them • As the soil water is reduced by soil moisture utilization the plants must exert greater effort to extract the same amount of moisture
B. Pergerakan air tanah‐akar There are two major ways to move molecules:
A. Diffusion : spontaneous, random movement of molecules from an area of high free energy (higher concentration) to one of low free energy (lower concentra on) → concentration gradient. Does not require energy (exergonic). Net diffusion stops when concentration on both sides equal (if crossing a membrane) or when there is a uniform distribution of particles. When equilibrium is reached : Molecules continue to move, but no net change in concentration. B. Osmosis: water diffusion through selective permeable membrane C. Bulk (or Mass) Flow. : mass movement of molecules in response to a pressure gradient, from high to low pressure, following a pressure gradient.
B. Penyerapan air di tanah oleh akar
B. Penyerapan air di tanah oleh akar
C. Transpor Air dan Mineral di Batang melalui Pembuluh xilem
Capillarity
Water rises up narrow tubes due to the adhesive forces between the water molecules and the wall of the tube
Xylem vessels are very narrow
Water rises higher in narrower tubes
D. Evaporasi Air di Daun ‐ Transpirasi
Appendices
Keseimbangan Air pada Tumbuhan + ‐
transpirasi
transpor air dan nutrien melalui xilem, transpirasi
air dalam tanah, penyerapan air oleh akar ‐‐
