Photosynthesis: Ecology

Abstract

Photosynthesis is the process by which plants convert light energy into chemical energy for use in growth and cellular repair. The ability of plants to capture light energy, carry out photosynthesis and grow is affected by many environmental factors including temperature, water and nutrient supply. Plants living in natural environments are also subject to competition and shading from other plants and have a number of biochemical and morphological adaptations to increase the efficiency of light absorption, whilst avoiding light stress. Various adaptations of photosynthesis exist that allow plants to tolerate extreme environmental conditions. Ultimately, the overall net photosynthetic rate of ecosystems has a major impact on the global carbon budget. These impacts may be significantly altered by global warming and subsequent climate change.

Key Concepts:

  • Photosynthesis requires the efficient capture of light whilst avoiding the absorption of damaging excess energy.

  • Light absorption can be optimised by plant growth, the movement of leaves and the movement of chloroplasts within leaves.

  • To grow optimally, plants must achieve a balance between the capture of light and the uptake of other resources.

  • Plants living in shaded conditions have adaptations to efficiently capture light including increased shoot:root ratios, thin leaves and high chlorophyll concentrations.

  • Two adaptations to C3 photosynthesis exist to optimise water use efficiency: C4 photosynthesis and crassalucean acid metabolism (CAM).

  • Both C4 and CAM involve a separation of CO2 absorption and fixation: C4 spatially and CAM temporally.

  • If a plant is to survive, grow and reproduce, it must make a net gain in carbon, that is, carbon gained through photosynthesis must be greater than carbon lost through respiration.

  • Photosynthesis makes a significant contribution to carbon uptake from the atmosphere and may go some way to offsetting atmospheric increases due to human activity.

  • Understanding the effects of global warming on photosynthesis is complex but necessary to fully understand the consequences of climate change.

Keywords: adaptation; C3; C4; CAM; transpiration

Figure 1.

Summary of the different photosynthetic pathways. C3 plants fix CO2 directly, using the enzyme ribulose bisphosphate carboxylase oxygenase (Rubisco), reaction CO2 with ribulose bisphosphate (RuBP) to form PGA in the chloroplasts of the mesophyll. C4 plants react PEP carboxylase to react CO2 with phosphoenolpyruvate (PEP) to form oxaloacetic acid, which is in turn converted to malate. This is transferred to the bundle sheath, where malate is broken down to release CO2, which is used by Rubisco. CAM plants use PEP carboxylase to fix CO2 at night and then break down the malate so produced during the day to provide CO2 for Rubisco.

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Further Reading

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Dyson, Beth, and Johnson, Giles(May 2014) Photosynthesis: Ecology. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0003198.pub2]