The mineralization rate of black soil carbon in the deep layers of Japanese volcanic ash soil may be easily accelerated by labile carbon supply

Figures & data

Table 1. Characteristics of the soil used in this study.

	pH
Depth (cm)	(H2O)	(KCl)	(NaF)	T-C (g kg^−1)	C:N Ratio	δ^13C (‰)	MI^a	^14C age^b (YrBP)
40–50	5.1	4.3	11.5	89.4	16.0	–19.8	1.64	4764–5082

^aThe melanic index of soil humus.

^bThe ¹⁴C age of soil samples from 40–45 cm and 45–50 cm, respectively.

Figure 1. Cumulative total CO₂ emissions from each treatment. S, soil only (control); SN, soil with mineral N; SC, soil with glucose; SCN, soil with glucose plus mineral N. Bars indicate the standard error of the mean (n = 3). Asterisks (***) indicate significant differences at P < 0.001 by a one-way analysis of variance (ANOVA).

Figure 2. Cumulative soil-derived CO₂ (gray), glucose-derived CO₂ (blank), and PEs (data above the bars) in each treatment. (a) days 7, (b) days 14, and (c) days 21. S, soil only (control); SN, soil with mineral N; SC, soil with glucose; SCN, soil with glucose plus mineral N. The number in parentheses (%) indicates the relative magnitude of PE. Bars indicate the standard error of the mean (n = 3). Values with different letters are significantly different (P < 0.05) by Tukey’s HSD post hoc test. Capital letters indicate glucose-derived CO₂, and small letters indicate soil-derived CO₂ and the PEs.

Figure 3. Microbial biomass in each treatment. S, soil only (control); SN, soil with mineral N; SC, soil with glucose; SCN, soil with glucose plus mineral N. Bars indicate the standard error of the mean (n = 3).

Figure 4. Linear correlation coefficients (Pearson’s correlation coefficient) between microbial biomass C and cumulative soil-derived CO₂ emission during the 21-day incubation period for each treatment (n = 12). Asterisks(**) indicates significance level at P < 0.01.