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33 - Photosynthetic water-use efficiency
- Edited by Jaume Flexas, Universitat de les Illes Balears, Palma de Mallorca, Francesco Loreto, Hipólito Medrano, Universitat de les Illes Balears, Palma de Mallorca
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- Book:
- Terrestrial Photosynthesis in a Changing Environment
- Published online:
- 05 March 2013
- Print publication:
- 19 July 2012, pp 523-536
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Summary
Introduction
Gas exchange is tightly coupled to evaporation in all living organisms (Woods and Smith, 2010). Photosynthesis of terrestrial plants is associated with water loss because the CO2 needed to be fixed into carbohydrates enters the leaf through stomata with the consequent loss of water from the sub-stomatal cavity to the atmosphere. Leaf-to-air water-vapour gradient is about 100 times larger than the CO2 gradient. Consequently, plants have to tightly regulate stomatal opening in order to avoid leaf dehydration. This causes a wide variation of the ratio between the rate of CO2 uptake (photosynthesis) and the rate of water-vapour loss (transpiration). This ratio expresses the efficiency of the carbon gain with respect to water loss, i.e., water-use efficiency (WUE).
Plant growth and biomass production are thus largely conditioned by the water resources, which are extremely variable in time and space around the globe, therefore water availability along the growing season is a determinant factor for plant-biome distribution and GPP. In general, it is widely established that ecosystem or crop production is closely dependent on soil-water availability (Beer et al., 2007).
Figure 33.1 shows a list of the main biological determinants, related with plant photosynthesis and transpiration characteristics, as well as the main environmental conditions that determine the specific values of WUE and its wide range of variation.
20 - Photosynthesis under water deficits, flooding and salinity
- Edited by Jaume Flexas, Universitat de les Illes Balears, Palma de Mallorca, Francesco Loreto, Hipólito Medrano, Universitat de les Illes Balears, Palma de Mallorca
-
- Book:
- Terrestrial Photosynthesis in a Changing Environment
- Published online:
- 05 March 2013
- Print publication:
- 19 July 2012, pp 299-311
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- Chapter
- Export citation
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Summary
Introduction
Drought, salinity and flooding are among the most important abiotic stresses affecting plant growth and survival in large areas of the globe. They affect natural ecosystems, plantations and croplands, therefore posing large problems to nature conservation and to farmers and foresters. Drought is a major concern not only in the arid and semi-arid zones, but is also increasingly affecting temperate regions that are now subjected to occasional severe drought spells (IPCC2007 www.ipcc.ch). Alternatively, the same IPCC report indicates an increased occurrence of heavy precipitation and tropical cyclone activity, leading to more frequent flooding events. Salinity and flooding are often secondary stresses following years of incorrect and unsustainable irrigation practices, leading to increased soil salinity and the rise of phreatic soil-water. Flooding can have catastrophic impacts on the productivity of arable farmland, as most crops are intolerant to excess water (Voesenek et al., 2006). Moreover, drought and salt stresses are commonly accompanied by high temperatures and high irradiances that exacerbate the negative impact of each stress acting in isolation (Mittler, 2006).
The primary effects of drought and salinity are similar, as salinity in the soil reduces osmotic potential, making it harder for roots to extract water (Munns, 2002; Munns and Tester, 2008). On the contrary, under flooding water availability is high but O2 availability for root respiration is restricted owing to its slow diffusion in water, limiting root growth (Blom and Voesenek, 1996; Bailey Serres and Voesenek, 2008).