Modelling O-18(2) and O-16(2) unidirectional fluxes in plants: I. Regulation of pre-industrial atmosphere

作者：Andre Marcel J^*

来源：Biosystems, 2011, 103(2): 239-251.

DOI：10.1016/j.biosystems.2010.10.004

• Rubisco coevolution
• Palaeoatmosphere
• Pre-industrial atmosphere
• Oxygen compensation point
• Role of C3 plants
• Atmospheric regulation

In closed systems, the O-2 compensation point (Gamma(0)) was previously defined as the upper limit of O-2 level, at a given CO2 level, above which plants cannot have positive carbon balance and survive. Studies with O-18(2) measure the actual O-2 uptake by photorespiration due to the dual function of Rubisco, the enzyme that fixes CO2 and takes O-2 as an alternative substrate. One-step modelling of CO2 and O-2 uptakes allows calculating a plant specificity factor (Sp) as the sum of the biochemical specificity of Rubisco and a biophysical specificity, function of the resistance to CO2 transfer from the atmosphere to Rubisco. The crossing points (Cx, Ox) are defined as CO2 and O-2 concentrations for which O-2 and CO2 uptakes are equal. It is observed that: (1) under the preindustrial atmosphere, photorespiration of C3 plants uses as much photochemical energy as photosynthesis, i.e. the Cx and Ox are equal or near the CO2 and O-2 concentrations of that epoch; (2) contrarily to Gamma(c), a Gamma(0) does not practically limit the plant growth, i.e. the plant net CO2 balance is positive up to very high O-2 levels; (3) however, in a closed biosystem, Gamma(0) exists; it is not the limit of plant growth, but the equilibrium point between photosynthesis and he opposite respiratory processes; (4) a reciprocal relationship exists between Gamma(0) and Gamma(c), as unique functions of the respective CO2 and O-2 concentrations and of Sp, this invalidates some results showing two different functions for Gamma(0) and Gamma(c), and, consequently, the associated analyses related to greenhouse effects in the past; (5) the pre-industrial atmosphere levels of O-2 and CO2 are the Gamma(0) and Gamma(c) of the global bio-system. They are equal to or near the values of Cx and Ox of C3 plants, the majority of land plants in preindustrial period. We assume that the crossing points represent favourable feedback conditions for the biosphere-atmosphere equilibrium and could result from co-evolution of plants-atmosphere-climate. We suggest that the evolution of Rubisco and associated pathways is directed by an optimisation between photosynthesis and photorespiration.

• 出版日期2011-2
• 单位中国地震局