Methods for the continuous measurement of O2 consumption and H2 production by nodulated legume root systems

Two examples are provided of the use of these detectors together with the soyabean/USDA16 symThe details of two systems for measuring O 2 uptake biosis in a flow-through system furnished with and H 2 production in flow-through gas systems used an infrared gas analyser (IRGA) to measure CO 2 to study nodule physiology and biochemistry are pre- production. sented here. Both are constructed from commercially available fuel cells. Oxygen uptake measurements are Key words: Root nodules, nitrogen fixation, hydrogen based upon the differential signal from paired production, oxygen uptake, respiratory quotient. detectors exposed to sample and blank gas streams. Because of the very small signal5background ratio needed to detect O 2 uptake against atmospheric O 2 Introduction concentration, these detectors were mounted in ther- The measurement of gaseous inputs and outputs from mally controlled aluminium blocks designed to avoid nodulated legume roots represents a valuable non-invasive changes in back pressure. Also to avoid apparent con- tool for studying nodule physiology and biochemistry. To centration differences arising because of pressure dif- facilitate such studies open-ended flow-through systems ferences at the detectors it is important that sample, have been developed in which gas streams of defined control and calibration gas flow rates are the same. composition can be passed over the nodulated roots of Hydrogen detectors were mounted in an aluminium intact undisturbed plants sealed into appropriate conblock similar to that used for O 2 , although the require- tainers (Minchin et al., 1983; Layzell et al., 1989). The ments for temperature and back pressure control are eZuent gas from these containers can be analysed for much less stringent for this application. respiratory CO 2 production, H 2 evolution and O 2 uptake. The limit for differential detection of O 2 uptake in A brief overview of the significance of these measureair was about 25 ppm (1 mmol l’1) and for H 2 production ments, of previous analytical problems and of the design, 1 ppm (0.04 mmol l’1). Linearity checks for the two construction and function of two detector systems for detectors over the range 4‐90% O 2 and 15‐750 ppm measuring H 2 production and O 2 uptake is presented here.