In situ short-term dynamics of CO₂ flux and microbial biomass after simulated rainfall in dry croplands in four tropical and continental ecosystems

Figures & data

Table 1 Description of the climate and surface soil properties (0–5 cm) at each experimental site.

Name	Averaged air temp. (^oC)	Precipitation (mm yr^–1)	Crop	Soil pH (H20)	Particle size distributions (%)			Total C (g C kg soil^–1)	Total N (g N kg soil^–1)	C:N ratio	EMC^a (mg C kg soil^–1)
					Clay	Silt	Sand
TH	25.0	2080	Maize	4.9	35.4	14.3	50.3	16.0	1.1	14.2	294.1
TZ	24.5	920	Maize	5.8	32.0	15.8	52.2	15.2	1.1	14.3	289.8
KZ	2.8	340	Fallow	8.3	38.2	37.8	24.0	28.9	1.8	16.2	782.7
HG	10.9	530	Wheat	6.6	42.2	32.6	25.2	23.2	2.0	11.7	459.9

a: EMC = Easiliy mineralizable carbon, that was evaluated by incubation for 28 days (25^oC, water holding capacity 60%). C: Carbon; N: Nitrogen.

Figure 1 Trends in air and soil temperature (5 cm depth; a, b, e, f) and volumetric moisture content of soil (0–15 cm depth; c, d, g, h) at the Thailand, Tanzania, Kazakhstan and Hungary sites. At the Hungary site, volumetric moisture content was measured at a depth of 5 cm in W plot, because of the limited species found with the logger sensor. Also, a small amount of rainfall (2.0 mm) was observed during the experiments (after 11 h). The data for Thailand (TH) were revised from Sugihara et al. (2010b). C plot: Control plot; W plot: Water treatment plot.

Figure 2 Fluctuations in soil carbon dioxide (CO₂) efflux* at each experimental site; Thailand (TH), Tanzania (TZ), Kazakhstan (KZ) and Hungary (HG). Bars indicate the standard error. Sugihara et al. (2010b) provided the figures for the TH site. *The soil CO₂ efflux rate was converted to that expected at 25°C based on the Q10 relationship (Fang and Moncrieff 2001). C plot: Control plot; W plot: Water treatment plot; WG plot: water and glucose treatment plot.

Figure 3 Fluctuations in in situ microbial biomass at each experimental site: Thailand (TH), Tanzania (TZ), Kazakhstan (KZ) and Hungary (HG). Bars indicate the standard error. Sugihara et al. (2010b) provided the figure for the TH site. The values for in situ microbial biomass were measured and calculated according to the adapted SIR. C plot: Control plot; W plot: Water treatment plot; WG plot: water and glucose treatment plot.

Figure 4 Fluctuations in in situ microbial activity (qCO₂) at each experimental site: Thailand (TH), Tanzania (TZ), Kazakhstan (KZ) and Hungary (HG). Bars indicate the standard error. Sugihara et al. (2010b) provided the figure for the TH site. Values for in situ microbial activity were measured and calculated according to the adapted SIR. C plot: Control plot; W plot: Water treatment plot; WG plot: water and glucose treatment plot.

Figure 5 Fluctuations in the ratio of the WG plot to the C plot for in situ microbial biomass. The horizontal gray dotted line indicates a value of 1. Bars indicate the standard error. W plot data was used as an alternative for C plot only for the Hungary site. Values for in situ microbial biomass were measured and calculated according to the adapted SIR. * indicates the significant difference between the sites at each similar sampling time, based on ANOVA and post hoc Tukey test analysis (P < 0.05). TH: Thailand; TZ: Tanzania; KZ: Kazakhstan; HG: Hungary; C plot: Control plot; W plot: Water treatment plot; WG plot: water and glucose treatment plot.

Table 2 Cumulative soil CO₂ efflux in the initial 100 h, and its ratio to easily mineralizable carbon, total carbon and added glucose.

	CC100 ^a	CW100 ^a	CWG100 ^a	(CW100–Cc100)/EMC^b (%)	(CW100–Cc100)/TC^c (%)	(CWG100–Cc100)/glucose^d (%)
TH	1.5	2.8	12.8	8.2	0.15	15.0
TZ	0.9	1.8	8.2	4.9	0.09	9.7
KZ	2.1	3.5	7.0	2.9	0.08	6.4
HG	1.2	1.5	3.7	1.1	0.02	3.4

a: C_C100, C_W100, C_WG100 = cumulative soil CO₂ efflux at the C, W and WG plots, respectively (g C m⁻² 100 h⁻¹). Cumulative soil CO₂ efflux was estimated by integrating the areas in Figure 2 for the initial 100 h. We integrated the areas for 71 h at only the HG site, because the experiment was finished at 71 h. Because the C flush in HG site was completely finished within 24 h, the difference between C_W100 and C_C100, and that between C_WG100 and C_C100, was not affected by this procedure.

b: EMC = easily mineralizable carbon, which was evaluated by incubation for 28 days (25°C, Water holding capacity 60%), (g C m⁻²: 5 cm soil depth).

c: TC = total carbon of soil (g C m⁻²: 5 cm soil depth).

d: Glucose = added glucose (75 g C m⁻²) in the WG plot.

Sugihara S , Funakawa S , Kosaki T 2010b: In situ short-term carbon and nitrogen dynamics in relation to microbial dynamics after a simulated rainfall in croplands of different soil texture in Thailand. Soil Sci. Plant Nutr., 56, 813–823. doi:10.1111/j.1747-0765.2010.00516.x

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Fang C , Moncrieff JB 2001: The dependence of soil CO2 efflux on temperature. Soil Biol. Biochem., 33, 155–165. doi:10.1016/S0038-0717(00)00125-5

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