Adaptations of flowering plants to differing water availability

Adaptations of flowering plants to differing water availability

Plants can be classified depending on the prevailing water supply. Mesophytes are plants living in conditions of adequate water supplies. Xerophytes are plants that live in conditions where water is scarce. Hydrophytes are water plants.

Mesophytes

Most land plants growing in temperate regions are mesophyes. They have an adequate water supply and although they lose a lot of water, it's readily replaced by uptake from the soil, so they don't require any special means of conserving it. If such a plant loses too much water, it will wilt and the leaves droop. The stomata close and the leaf surface area available for absorbing light is reduced so photosynthesis becomes less efficient.

Most crop plants are mesophytes, they're adapted to grow best in well-drained soils and moderately dry air. Water uptake during the night replaces the water lost during the day. Excessive water loss is prevented because stomata generally close at night when it's dark.

Mesophyes must survive unfavourable times of the year, particularly when the ground is frozen and liquid water isn't available:

• Many shed their leaves before winter, so they don't lose water by transpiraton, when liquid water may be scarce.
• The aerial parts of many non-woody plants die off in winter, they aren't exposed to rost or cold winds, but their underground organs, such as bulbs and corms, survive.
• Most annual mesophyes over-winter as dormant seeds, with such a low metabolic rate that almost no water is required.

Xerophyes

Xerophytes ar eplants with xeromorphic characteristics. They've adapted to living with low water availability and have modified structures which prevent excessive water loss. They may live in hot, dry desert regions, cold regions where the soil water is frozen for much of the year or exposed, windy locations.

Marram grass which colonises sand dunes, is a xerophyte. There's no soil and rainwater drives away rapidly, there's high wind speeds, salt spray and a lack of shade from the sun. It has the following modifications:

• Rolled leaves - large…