Threshold concentrations of glucose to increase the ratio of respiration to assimilation in a Japanese arable soil and a strongly acidic Japanese forest soil

Figures & data

Table 1 Physicochemical and microbial properties of the soils

Soil	pH (H2O)	Soil organic C (mg C g^−1 soil)	Total N (mg N g^−1 soil)	Clay content (%)	Biomass C (μg C g^−1 soil)
Japanese arable soil	7.0	31	1.8	8.0	253
Japanese forest soil	4.4	155	9.6	44.5	1601

Figure 1 Respiration rates as a function of time after the addition of various concentrations of glucose for Japanese arable (a,b) and forest (c, d) soils. The numbers in the key show the concentrations of added glucose (μg C g−1 soil). Error bars indicate standard errors (n = 3).

Figure 2 K2SO4-extractable C as a function of time after the addition of various concentrations of glucose for Japanese arable (a) and forest (b,c) soils. The numbers in the key show the concentrations of added glucose (μg C g−1 soil). Error bars indicate standard errors (n = 3). Significant differences between extractable-C with and without the addition of glucose at *P = 0.05.

Table 2 Respiration profiles, time taken until all glucose was utilized (h) and the ratio of extra C respired to utilized glucose C (%) after the addition of various concentrations of glucose to the Japanese arable and forest soils

Soil	Added glucose (μg C g^−1)	Added glucose to biomass ratio (%)	Added glucose (mmol L^−1)	Respiration profile	Time taken until all glucose was utilized (h)	Respired to utilized glucose ratio (%)
Japanese arable soil	30	11.8	10.0	Z	6	21.3 (1.91)
	40	15.7	13.3	Z	6	21.9 (2.04)
	50	19.7	16.7	Z	6	20.7 (1.49)
	60	23.6	20.0	Z	6	20.8 (1.37)
	85	33.4	28.3	G	9	24.3 (0.72)
	250	98.3	83.3	G	15	26.3 (0.47)
	1000	393.1	333.3	G	18	28.5 (0.17)
Japanese forest soil	100	6.2	6.1	Z	12	20.5 (2.50)
	150	9.4	9.1	Z	12	20.1 (2.47)
	200	12.5	12.2	Z	12	21.1 (1.60)
	250	15.6	15.2	Z	12	20.0 (1.50)
	300	18.7	18.2	Z	12	20.2 (0.67)
	500	31.2	30.4	G	12	24.9 (1.15)
	1000	62.5	60.8	G	15	27.7 (1.75)
	2000	125.0	121.6	G	21	29.2 (0.66)
	4000	249.9	243.1	G	24	28.8 (0.67)
Values represent mean and standard error (n = 3). G, growth associated respiration type; Z, zero-order respiration type.

Figure 3 Chloroform-labile C (♦) and substrate-induced respiration rates (▀) plotted against the concentrations of added glucose at 6 and 12 h after the addition of various concentrations of glucose for Japanese arable (a) and forest (b) soils, respectively. Error bars indicate standard errors (n = 3). Significant differences between chloroform-labile C or substrate-induced respiration rates with and without the addition of glucose at *P = 0.05. G, growth-associated respiration type; Z, zero-order respiration type.

Figure 4 Ratio of respired to utilized glucose C plotted on a logarithmic scale of the concentrations of added glucose C to biomass C (%). Error bars indicate standard errors (n = 3). Data for the Kazakh soil are from Sawada et al. (2008).

Figure 5 Respiration rates divided by biomass C as a function of time after the addition of the highest concentrations of glucose. Error bars indicate standard errors (n = 3). Data for the Kazakh soil were obtained by recalculating the respiration rate after the addition of the highest concentration of glucose in fig. 1b in Sawada et al. (2008).

Table 3 Threshold concentrations of glucose and microbial properties of the soils studied

Soil	Threshold ratio of glucose to biomass (%)	Threshold concentration of glucose (mmol L^–1)	SIR (μg C g^−1 h^−1)	SIR to biomass C ratio (h^−1)	Specific respiration increment (h^−1)	Lag period (h)
Japanese arable soil	23.6–33.4	20.0–28.3	4.96 (0.05)	0.0195 (0.0008)	0.371 (0.004)	3.49 (0.09)
Japanese forest soil	18.7–31.2	18.2–30.4	17.4 (0.4)	0.0091 (0.0003)	0.143 (0.003)	6.77 (0.39)
Kazakh forest soil	46.7–77.8	40.5–67.4	27.4 (0.5)	0.0213 (0.0004)	0.140 (0.018)	6.67 (0.41)
Values represent mean and standard error (n = 3). Values in the Kazakh forest soil are cited and recalculated from Sawada et al. (2008).

Sawada , K , Funakawa , S and Kosaki , T . 2008 . Soil microorganisms have a threshold concentration of glucose to increase the ratio of respiration to assimilation . Soil Sci. Plant Nutr. , 54 : 216 – 223 .

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