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Arundo donax has attracted interest as a potential bioenergy crop due to a high apparent productivity. It uses C3 photosynthesis yet appears competitive with C4 grass biomass feedstock’s and grows in warm conditions where C4 species might be expected to be that productive. Despite this there has been no systematic study of leaf photosynthetic properties. This study determines photosynthetic and photorespiratory parameters for leaves in a natural stand of A. donax growing in southern Portugal. We hypothesise that A. donax has a high photosynthetic potential in high and low light, stomatal limitation to be small and intrinsic water use efficiency unusually low. High photosynthetic rates in A. donax resulted from a high capacity for both maximum Rubisco (Vc,max 117 μmol CO2 m−2 s−1) and ribulose-1:5-bisphosphate limited carboxylation rate (Jmax 213 μmol CO2 m−2 s−1) under light-saturated conditions. Maximum quantum yield for light-limited CO2 assimilation was also high relative to other C3 species. Photorespiratory losses were similar to other C3 species under the conditions of measurement (25%), while stomatal limitation was high (0.25) resulting in a high intrinsic water use efficiency. Overall the photosynthetic capacity of A. donax is high compared to other C3 species, and comparable to C4 bioenergy grasses.

This paper presents the first micrometeorological-based measurements of methane (CH4) emissions from Asian rice paddies of which we are aware. The research features the tunable diode laser trace gas analyzer system (TGAS) recently developed at the University of Guelph. CH 4 fluxes were measured between March 9 and 24, 1992, from an irrigated rice paddy field at the International Rice Research Institute (IRRI), the Philippines. The daytime CH 4 flux averaged 6.0/xg m -2 s -1 . The CH 4 fluxes displayed a diurnal trend similar to daily soil temperature curves, with peak emissions of about 8/xg m -2 s -1 in the early afternoon. A tenfold increase in CH 4 emissions (to about 70/xg m -2 s -1) during a brief weeding experiment resulted from soil disturbance. Up to 25/xg m -2 s -1 of CH 4 were released during a drying of the field, after which unsuitable soil redox potentials apparently suppressed methanogenesis. The CH 4 flux was also arrested when the field was flooded with oxygen-rich water during a heavy rainstorm. where Fme flux of CH 4 (/xg m -2 s-l); K eddy diffusivity (m2 s -•); ACme change in CH 4 concentration (/xg m-3); Az (m) vertical height difference. TGAS measurements were used to determine a finite CH 4 concentration difference ACme. Three estimates of the eddy diffusivity K were inferred using micrometeorological tech-SIMPSON ET AL.' TUNABLE DIODE LASER MEASUREMENT OF METHANE FLUXES 7285 OF METHANE FLUXES 7289

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