Journal ArticleDOI
Solar radiation and productivity in tropical ecosystems
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TLDR
Conventional estimates of efficiency in terms of the amount of solar radiation incident at the earth's surface provide ecologists and agronomists with a method for comparing plant productivity under different systems of land use and management and in different * Opening paper read at IBP/UNESCO Meeting on Productivity of Tropical Ecosystems.Abstract:
In thermodynamic terms, ecosystems are machines supplied with energy from an external source, usually the sun. When the input of energy to an ecosystem is exactly equal to its total output of energy, the state of equilibrium which exists is a special case of the First Law of Thermodynamics. The Second Law is relevant too. It implies that in every spontaneous process, physical or chemical, the production of 'useful' energy, which could be harnessed in a form such as mechanical work, must be accompanied by a simultaneous 'waste' of heat. No biological system can break or evade this law. The heat produced by a respiring cell is an inescapable component of cellular metabolism, the cost which Nature has to pay for creating biological order out of physical chaos in the environment of plants and animals. Dividing the useful energy of a thermodynamic process by the total energy involved gives a figure for the efficiency of the process, and this procedure has been widely used to analyse the flow of energy in ecosystems. For example, the efficiency with which a stand of plants produces dry matter by photosynthesis can be defined as the ratio of chemical energy stored in the assimilates to radiant energy absorbed by foliage during the period of assimilation. The choice of absorbed energy as a base for calculating efficiency is convenient but arbitrary. To derive an efficiency depending on the environment of a particular site as well as oil the nature of the vegetation, dry matter production can be related to the receipt of solar energy at the top of the earth's atmosphere. This exercise was attempted by Professor William Thomson, later Lord Kelvin, in 1852. 'The author estimates the mechanical value of the solar heat which, were none of it absorbed by the atmosphere, would fall annually on each square foot of land, at 530 000 000 foot pounds; and infers that probably a good deal more, 1/1000 of the solar heat, which actually falls on growing plants, is converted into mechanical effect.' Outside the earth's atmosphere, a surface kept at right angles to the sun's rays receives energy at a mean rate of 1360 W m-2 or 1f36 kJ m-2 s-1, a figure known as the solar constant. As the energy stored by plants is about 17 kJ per gram of dry matter, the solar constant is equivalent to the production of dry matter at a rate of about 1 g m-2 every 12 s, 7 kg m-2 per day, or 2 6 t m-2 year-'. The annual yield of agricultural crops ranges from a maximum of 30-60 t ha-' in field experiments to less than I t ha-' in some forms of subsistence farming. When these rates are expressed as a fraction of the integrated solar constant, the efficiencies of agricultural systems lie between 0-2 and 0 004%, a range including Kelvin's estimate of 0-1%. Conventional estimates of efficiency in terms of the amount of solar radiation incident at the earth's surface provide ecologists and agronomists with a method for comparing plant productivity under different systems of land use and management and in different * Opening paper read at IBP/UNESCO Meeting on Productivity of Tropical Ecosystems, Makerere University, Uganda, September 1970.read more
Citations
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Journal ArticleDOI
Primary Production of the Biosphere: Integrating Terrestrial and Oceanic Components
TL;DR: Integrating conceptually similar models of the growth of marine and terrestrial primary producers yielded an estimated global net primary production of 104.9 petagrams of carbon per year, with roughly equal contributions from land and oceans.
Journal ArticleDOI
Climate and the efficiency of crop production in Britain
TL;DR: The efficiency of crop production is defined in thermodynamic terms as the ratio of energy output (carbohydrate) to energy input (solar radiation). Temperature and water supply are the main climatic constraints on efficiency as mentioned in this paper.
Journal ArticleDOI
Terrestrial ecosystem production: A process model based on global satellite and surface data
Christopher S. Potter,James T. Randerson,Christopher B. Field,Pamela A. Matson,Peter M. Vitousek,Harold A. Mooney,Steven Klooster +6 more
TL;DR: In this paper, the authors present a modeling approach aimed at seasonal resolution of global climatic and edaphic controls on patterns of terrestrial ecosystem production and soil microbial respiration using satellite imagery (Advanced Very High Resolution Radiometer and International Satellite Cloud Climatology Project solar radiation), along with historical climate (monthly temperature and precipitation) and soil attributes (texture, C and N contents) from global (1°) data sets as model inputs.
Journal ArticleDOI
Terrestrial Gross Carbon Dioxide Uptake: Global Distribution and Covariation with Climate
Christian Beer,Markus Reichstein,Enrico Tomelleri,Philippe Ciais,Martin Jung,Nuno Carvalhais,Christian Rödenbeck,M. Altaf Arain,Dennis D. Baldocchi,Gordon B. Bonan,Alberte Bondeau,Alessandro Cescatti,Gitta Lasslop,Anders Lindroth,Mark R. Lomas,Sebastiaan Luyssaert,Hank A. Margolis,Keith W. Oleson,Olivier Roupsard,Elmar Veenendaal,Nicolas Viovy,Christopher M. Williams,F. Ian Woodward,Dario Papale +23 more
TL;DR: Estimates of spatially distributed GPP and its covariation with climate can help improve coupled climate–carbon cycle process models.
Journal ArticleDOI
A Continuous Satellite-Derived Measure of Global Terrestrial Primary Production
Steven W. Running,Ramakrishna R. Nemani,Faith Ann Heinsch,Maosheng Zhao,Matthew C. Reeves,Hirofumi Hashimoto +5 more
TL;DR: A new satellite-driven monitor of the global biosphere that regularly computes daily gross primary production and annual net primary production at 1-kilometer (km) resolution over 109,782,756 km2 of vegetated land surface is introduced.
References
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Journal ArticleDOI
Comparisons of plant productivity
TL;DR: The principles of comparative productivity and the net primary productivity of different types of plant community are discussed, which help clarify the role of waste and energy in the productivity of a plant community.
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