Nitrate reductase activity in field-grown Pueraria lobata (Kudzu) in southeastern Brazil

Abstract

Although Pueraria lobata (Willd.) Ohwi (P. thunbergiana) (Sieb. & Zucc.) Benth.) is thus ecologically and economically important in much of the world, its physiological ecology and other factors contributing to its invasive growth are not well understood. Nitrate reductase activity (NRA) measurements have long been used to indicate the effect of changes in the environment on a plant's capacity to assimilate nitrate nitrogen. The objective of this paper was to describe how naturally occurring changes in air temperature (T_a) and solar radiation flux density (S_t), affect the in vivo nitrate reductase activity in field-grown P. lobata and consequently the ability of this species to assimilate nitrate nitrogen in non-native areas. A meteorological thermometer and a thermocouple pyranometer were used to measure changes in the air temperature and the solar radiation flux density, respectively. The highest nitrate reductase activity found in this study [5.8 μmol NO₂ h^-1 (g FW)^-1] was observed when T_a was 27.4^oC. A significant reduction in nitrate reductase activity was observed with T_a below 21.8^oC or above 33.6^oC. Nitrate reductase activity was linear and positively related to S_t. A 12% increase in nitrate reductase activity was observed when S_t rose from 531 to 852 W m^-2. These results suggest that P. lobata can be a successful competitor in regions located at the transition between subtropical and tropical biomes.