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42 Transpiration

Part 4. Hydrometeorology

  1. John Roberts

Published Online: 15 APR 2006

DOI: 10.1002/0470848944.hsa045

Encyclopedia of Hydrological Sciences

Encyclopedia of Hydrological Sciences

How to Cite

Roberts, J. 2006. Transpiration. Encyclopedia of Hydrological Sciences. 4:42.

Author Information

  1. Centre for Ecology and Hydrology, Wallingford, Oxfordshire, UK

Publication History

  1. Published Online: 15 APR 2006

Abstract

The transpiration process is the uptake of water by plant roots, transport through the plant and evaporation from the leaf through pores called stomata. Evaporation of water from the leaf is determined by atmospheric conditions such as radiation, temperature and humidity deficit but the plant can limit transpiration by partial or complete stomatal closure. Generally stomata open in response to increasing radiation but tend to close with increasing air humidity deficit and reduced availability of soil moisture. Because the stomata have to be open in daylight for the entry of carbon dioxide into the leaf for the photosynthesis process, water loss is an inevitable consequence. Nevertheless transpiration itself has important roles. Nutrients are brought into the plant when water is taken up from the soil and evaporation of transpired water prevents leaf temperature reaching supra-optimal levels. There are numerous ways that transpiration might be measured. These include measurements of soil water changes below vegetation or changes in atmospheric humidity above vegetation. Alternatively measurements can be made on individual plants or leaves. In most circumstances the source of water for transpiration is the soil and principally the surface soil layers where most roots are found. In the future, increased levels of atmospheric CO2 are expected to reduce transpiration through reduction in stomatal aperture.

Keywords:

  • water movement;
  • stomata;
  • gas exchange;
  • cooling;
  • nutrient uptake;
  • measurement;
  • sources;
  • climate change