Document: LYD-3-60-7

Can liquid chloroform be used for microbial biomass N and P assays?

OLANDER, L.P.* and P.M.VITOUSEK

Stanford University, Stanford CA 94305-5020 ¹

Abstract:
One accepted method for determining microbial biomass N and P is the chloroform fumigation-extraction technique. In this method moist soils are fumigated with chloroform vapor, which lyses microbial cells and releases their internal N and P. An alternative method used in the past was to add liquid chloroform directly to a soil suspension and shake it. The advantages of this technique are that it requires less time and it can easily be used with time staggered samples. However, chloroform can dissolve organic matter raising concerns that the non-living organic N and P could be solubilized along with microbial. Previous studies of the fumigation method suggested some release of C, but little release of N and P. We tested the chloroform fumigation and liquid methods in a series of Hawaiian soils that vary greatly in mineralogy, organic matter content, and how that organic matter is held. We generated a chloroform response curve by increasing concentrations of chloroform added to soil suspensions and then compared the results to that of the typical fumigation method for each soil type. The amount of N and P released from soils with increasing concentrations of liquid chloroform quickly reached saturation at 0.2 ml chloroform in a 30ml:1gDWE soil suspension, at a level very similar to that observed in the typical fumigation method. These results suggest that liquid chloroform techniques release no more N and P from non-living organic matter than do fumigation techniques.

Keywords: soil, microbial biomass, nitrogen, phosphorus

This abstract is being presented at: 11:00 AM in session:
Oral Session #71: Soil Microbial Biomass and Soil Respiration.