Photosynthesis: Temperate and Tropical Characteristics within a Single Grass Genus

There ought to be an equation for that

An overriding interest in photosynthesis has propelled my wanderings from chemist to biochemist to plant physiologist and on to global topics. Equations and models have been organizing principles along the way. This fascination started as a reaction to difficulties with written communication, but it has proven to be quite useful in moving across different levels of organization. I conclude with some discussion of the importance of Earth system models for understanding and predicting how human activities may influence the climate, environment, and biota in the future, and some ideas about how disciplinary science might make larger contributions to this interdisciplinary problem.

The distribution of C3 and C4 grasses in Australia in relation to climate

All but four of 833 native and 292 naturalised Australian grasses (Poaceae) have been assigned as having the C₄ or C₄ photosynthetic pathway. In conjunction with comprehensive species composition data for 75 geographic subdivisions Australiawide, this has permitted the construction of distribution maps for C₃ and C₄ grasses. C₃ and C₄ grass distributions have been considered (i) independently, using subdivisional native species numbers; and (ii) relatively, using 'subdivisional % C₄'. C₃ species are most numerous in the Southern Tablelands (New South Wales), the QZ subdivision (Victoria), and Tasmania; C₄ species in the northern Northern Territory and northern Queensland, including the Cook subdivision where 54% of Australia's native C₄ grasses can be found. C₃ species predominate only in south-west Western Australia, parts of southern South Australia, the Tablelands, central and south coast, and south western slopes of New South Wales, Victoria and Tasmania. C₄ species predominate over 80-85% of the continental area. For 16 temperature and rainfall variables, subdivisional area-weighted means were calculated, and correlation analyses performed. C₃ species number correlates most highly with January average maximum temperature (-ve) and spring rainfall (+ve); C₄ species number with October average minimum temperature (+ve) and February median rainfall (+ve); '%C₄' with January average minimum temperature (+ve). Predictive multiple linear regression equations were generated using climatic variables. In general, C₄ grass species, like C₃ species, increase in number with increasing rainfall, in their preferred temperature regime. C₄ species are most numerous where the summer is hot and wet; C₃ species where the spring is cool and wet. C₄ species numbers decline with decreasing temperature and/or decreasing summer rainfall; C₃ species numbers decline with increasing temperature and/or decreasing spring rainfall. Results are also considered in relation to the taxonomic and physiological heterogeneity of grasses and to Australia's geobotanic history.

Carbon dioxide compensation points in related plant species

Both high and low C0(2) compensation concentrations were found in the plant genera-Panicum, Cyperus, and Euphorbia. Within each genus, however, high and low compensations were found in different subgenera. Thus, they may not be genetically closely related. No significant differences in CO(2) compensation were found among 100 genetic lines of Triticum aestivum L. or among 20 lines of Hordeum vulgare L.