Table 2.

Comparison of DNA and RNA co-extraction methods and kits, tested on soils FH (high pH peat, pH 7.39), FL (low pH peat, pH 3.65), and Å (low pH clay soil, pH 5.5).

Method/Kit	Nicolaisen’s methoda			MPb		PMb		PS + AKb			Optimized method
TNA purification prior to digestc	-			+		-		+			+
Soils tested	FH	FL	Å	FH	FL	FH	FL	FH	FL	Å	FH	FL	Å
Amplifiable DNAd	+	+	+	+	+	+	+	+	±f	+	+	+	+
Complete removal of DNA after 1st digestiond,e	+	-	-	+	-	+	-	+	-	-	+	+	-
Complete removal of DNA after 2nd digestiond,e	+	-	-	+	±f	+	-	+	-	+	+	+	+
cDNA synthesis	+	NT	NT	+	±f	+	NT	+	NT	+	+	+	+

^aMethod from Nicolaisen et al. (2008).

^bSee Table 1 for list of kit abbreviations.

^cTNA purification with the OPIR kit.

^dSee text for details on DNA amplification and removal assessment.

^eDNA was digested with TURBO DNase, and RCC kit was used for purification after each digestion.

^fResults from replicates varied, likely due to the presence of inhibitory compounds.

gDNA, genomic DNA; NT, not tested because of residual gDNA.