Tropospheric ozone (O 3 ) decreases photosynthesis, growth, and yield of crop plants, while elevated carbon dioxide (CO 2 ) has the opposite effect. The net photosynthetic rate (P N ), dark respiration rate (R D ), and ascorbic acid content of rice leaves were examined under combinations of O 3 (0, 0.1, or 0.3 cm 3 m -3 , expressed as O 0 , O 0.1 , O 0.3 , respectively) and CO 2 (400 or 800 cm 3 m -3 , expressed as C 400 or C 800 , respectively). The P N declined immediately after O 3 fumigation, and was larger under O 0.3 than under O 0.1 . When C 800 was combined with the O 3 , P N was unaffected by O 0.1 and there was an approximately 20 % decrease when the rice leaves were exposed to O 0.3 for 3 h. The depression of stomatal conductance (g s ) observed under O 0.1 was accelerated by C 800 , and that under O 0.3 did not change because the decline under O 0.3 was too large. . Excluding the stomatal effect, the mesophyll P N was suppressed only by O 0.3 , but was substantially ameliorated when C 800 was combined. Ozone fumigation boosted the R D value, whereas C 800 suppressed it. An appreciable reduction of ascorbic acid occurred when the leaves were fumigated with O 0.3 , but the reduction was partially ameliorated by C 800 . The degree of visible leaf symptoms coincided with the effect of the interaction between O 3 and CO 2 on P N . The amelioration of O 3 injury by elevated CO 2 was largely attributed to the restriction of O 3 intake by the leaves with stomatal closure, and partly to the maintenance of the scavenge system for reactive oxygen species that entered the leaf mesophyll, as well as the promotion of the P N .

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Earthquake swarms, often interpreted to result from fluids invading the brittle seismogenic zone, have seismicity patterns that are significantly different from an aftershock sequence. Following the M w 9.0 Tohoku-Oki earthquake, an unusual, shallow normal-faulting swarm sequence occurred near the Pacific coast in the southeast Tohoku district. An integrated approach combining geophysical and geochemical methods was utilized to establish the presence of aqueous fluids around the seismic source region and their derivation. Magnetotelluric inversion defined an anomalous conductor with a width of 20 km and clearly visible to depths of more than 20 km, extending to the base of the crust. Independent geophysical observations, including seismic, strongly support the suggestion that fluid-filled porous materials and fluids associated with slab dehydration are present in the convergent plate boundary. In order to provide geochemical constraints on the source of the fluids triggering the swarm activity, new helium isotope data were acquired from gas and water samples around the seismic source region. The observed 3 He/ 4 He ratios in these samples are significantly lower than the atmospheric value of 1.4 × 10 À6 , indicating that the mantle helium contribution is less than 10% of the total helium. Assuming the fluid-triggered swarm activity, the plausible explanations for the generation of fluids are limited to the following: (1) sediment porosity reduction and from smectite-illite and opal-quartz reactions in the subducting deep sea sediments, (2) metamorphism of fore-arc basin sediments, sedimentary, and/or volcanic rocks detached from the plate, or (3) dehydration reactions in the subducted oceanic crust and/or hydrated mantle below the fore-arc mantle wedge. Geophysical and geochemical findings suggest metamorphic fluids produced by isothermal decompression of altered sediments accompanying uplift and exhumation. Owing to continued fluid production at depths of~20 km, the fluids migrate into the seismic source region. The swarm sequence would have been triggered by stress changes associated with the Tohoku-Oki earthquake, enhanced by vertical metamorphic fluid expulsion from the reaction zone.

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