Evaluation of an optimal extraction method for measuring d-ribulose-1,5-bisphosphate carboxylase/oxygenase (RubisCO) in agricultural soils and its association with soil microbial CO2 assimilation.

Assimilating atmospheric carbon (C) into terrestrial ecosystems is recognized as a primary measure to mitigate global warming. Ribulose-1,5-bisphosphate carboxylase/oxygenase (RubisCO) is the dominant enzyme by which terrestrial autotrophic bacteria and plants fix CO 2 . To investigate the possibility of using RubisCO activity as an indicator of microbial CO 2 fixation potential, a valid and efficient method for extracting soil proteins is needed. We examined three methods commonly used for total soil protein extraction. A simple sonication method for extracting soil protein was more efficient than bead beating or freeze–thaw methods. Total soil protein, RubisCO activity, and microbial fixation of CO 2 in different agricultural soils were quantified in an incubation experiment using 14 C-CO 2 as a tracer. The soil samples showed significant differences in protein content and RubisCO activity, defined as nmol CO 2 fixed g −1 soil min −1 . RubisCO activities ranged from 10.68 to 68.07 nmol CO 2 kg −1 soil min −1 , which were closely related to the abundance of cbbL genes ( r = 0.900, P = 0.0140) and the rates of microbial CO 2 assimilation ( r = 0.949, P = 0.0038). This suggests that RubisCO activity can be used as an indicator of soil microbial assimilation of atmospheric CO 2 . [ABSTRACT FROM AUTHOR]