Water and Plants Strategies for Drought PDF
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York University
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Summary
This document covers water loss in terrestrial environments and strategies plants employ to cope with drought. It discusses factors impacting water potential and presents different plant adaptations, including avoiding drought conditions and tolerating them. For example, different plant types such as ephemerals and CAM adaptations are presented.
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Water Water is the medium in which all biochemical reactions necessary for life occur Availability in a terrestrial environment may be limited NOT FOR SALE OR DISTRIBUTION PROPERTY OF YORK UNIVERSITY Water loss in the terrestrial environment Water flows from an...
Water Water is the medium in which all biochemical reactions necessary for life occur Availability in a terrestrial environment may be limited NOT FOR SALE OR DISTRIBUTION PROPERTY OF YORK UNIVERSITY Water loss in the terrestrial environment Water flows from an area of higher pressure to lower (pressure or turgor potential). Atmospheric water potential is related to relative humidity. If less than 98%, water potential is low relative to organisms → water loss! NOT FOR SALE OR DISTRIBUTION PROPERTY OF YORK UNIVERSITY Barriers to reduce water loss Terrestrial organisms must have barriers or resistance to water loss. E.g. skin, and waxy cuticles of insects and plants. Terrestrial plants must take up water from the soil to replace water lost to the atmosphere. Plants lose water by transpiration when stomates are open for CO2 uptake. NOT FOR SALE OR DISTRIBUTION PROPERTY OF YORK UNIVERSITY Plants & water loss Terrestrial plants must take up water from the soil to replace water lost to the atmosphere. Plants lose water by transpiration when stomata are open for CO2 uptake. NOT FOR SALE OR DISTRIBUTION PROPERTY OF YORK UNIVERSITY Water potential = water pressure in a plant or soil Symbol: (psi); units = megapascals (MPa) Water flows from region of higher to region of lower pressure → Pure water flows into a plant root or dry soil In a plant, water potential: = p + + m, where – p = hydrostatic pressure (pressure potential) – = osmotic potential (solutes --> ) – m = matric potential (surface area --> m) soil > root > leaf > air 5 NOT FOR SALE OR DISTRIBUTION PROPERTY OF YORK UNIVERSITY Stomata Carbon dioxide enters Water vapour lost Guard cells shrink --> closure; conserves water – At night – During drought 10 Strategies for drought i. Avoiders Ephemerals – Short lifespan – Wet season only – Seeds survive drought Drought deciduous species – Leaves shed in dry season 12 Strategies for drought ii. Tolerators Leaves transpire slowly Sunken stomata – E.g. pines – Cost: slower photosynthesis More efficient photosynthesis E.g. C4 --> reduces photorespiration E.g. CAM --> stomata open at night 13
