Net nitrogen mineralization and nitrification of different landscape positions in a lowland subtropical rainforest in Taiwan

Figures & data

Figure 1 Geographical location of the long-term ecological research site in Nanjenshan Mountain in southern Taiwan.

Figure 2 Monthly mean rainfall, temperature and wind velocity at the Nanjenshan Nature Reserve. Windward data were obtained from the meteorological observatory at nearby Nanjen Lake. Leeward data were obtained from the meteorological observatory close to the footslope position of the transect site.

Table 1 Gravimetric soil moisture (moisture; w/w%), volumetric soil moisture (TDR; v/v%), air temperature and soil temperature at a depth of 15 cm for each sampling date at the Nanjenshan transect site

	January 2006				August 2006
	Moisture (%)	TDR (%)	Air temperature (°C)	Soil temperature (°C)	Moisture (%)	TDR (%)	Air temperature (°C)	Soil temperature (°C)
	19 January 2006				22 August 2006
F	31.1 ± 2.2^b	32.2 ± 2.2^a	22.1 ± 0.5^a	19.1 ± 0.1^a	29.9 ± 2.7^b	31.7 ± 0.4^a	26.7 ± 0.2^a	25.6 ± 0.1^a
S	42.2 ± 3.7^a	32.8 ± 3.8^a	20.6 ± 0.1^b	17.9 ± 0.4^b	42.0 ± 3.2^a	35.7 ± 1.4^a	26.7 ± 0.4^a	24.5 ± 0.1^b
	26 January 2006 (0 mm)^†				29 August 2006 (22.5 mm)
F	31.2 ± 1.6^b	30.9 ± 1.1^a	19.2 ± 1.2^a	17.4 ± 0.3^a	30.1 ± 3.2^b	–	29.2 ± 0.3^a	25.3 ± 0.2^a
S	42.7 ± 2.4^a	31.4 ± 1.5^a	17.3 ± 1.0^a	16.8 ± 0.2^b	41.2 ± 2.2^a	36.2 ± 2.7	26.5 ± 0.4^b	24.4 ± 0.3^b
	3 February 2006 (1.5 mm)				4 September 2006 (10.5 mm)
F	32.2 ± 1.8^b	37.2 ± 0.9^a	19.0 ± 0.2^a	17.7 ± 0.2^a	27.8 ± 3.3^b	–	27.1 ± 0.2^a	25.2 ± 0.1^a
S	43.7 ± 2.7^a	34.8 ± 1.9^a	17.1 ± 0.2^a	16.9 ± 0.2^b	39.2 ± 0.9^a	–	27.1 ± 0.2^a	24.3 ± 0.1^b
	9 February 2006 (1.5 mm)				12 September 2006 (87.5 mm)
F	32.4 ± 1.7^b	38.4 ± 1.6^a	15.5 ± 0.4^a	16.8 ± 0.6^a	30.9 ± 2.4^b	–	26.3 ± 0.3^a	24.1 ± 0.0^a
S	44.5 ± 0.9^a	37.9 ± 1.2^a	13.3 ± 0.1^b	16.2 ± 0.3^a	40.0 ± 2.1^a	–	25.3 ± 0.6^a	23.8 ± 1.0^a
	16 February 2006 (0.2 mm)				19 September 2006 (43.0 mm)
F	33.4 ± 2.8^b	36.9 ± 1.0^a	22.7 ± 1.5^a	18.0 ± 0.3^a	30.2 ± 2.5^b	35.1 ± 1.5^a	24.7 ± 0.5^a	22.8 ± 0.1^a
S	45.7 ± 2.6^a	35.3 ± 1.5^a	21.5 ± 0.5^a	16.6 ± 0.3^b	42.9 ± 3.7^a	34.5 ± 2.5^a	22.7 ± 0.3^b	22.0 ± 0.1^b
^†Data in parentheses are cumulative rainfall between two sampling dates. Values are mean ± standard deviation (n = 3). Data with different letters between landscape positions are statistically significant at P < 0.05 (Student’s t-test). F, footslope; S, summit; –, data not available.

Table 2 Organic carbon and total nitrogen of the soil and litter properties for the different landscape positions before incubation

	January 2006		August 2006
	Footslope	Summit	Footslope	Summit
Soil
OC (g kg^−1)	12.3 ± 1.71^b	23.4 ± 3.88^a	13.2 ± 0.78^b	27.1 ± 2.46^a
TN (g kg^−1)	1.11 ± 0.15^b	1.61 ± 0.34^a	0.95 ± 0.09^b	1.84 ± 0.20^a
C:N ratio	10.5 ± 1.7^b	14.7 ± 1.3^a	13.9 ± 1.7^a	14.8 ± 0.4^a
Litter
C (g kg^−1)	376 ± 99^a	417 ± 16^a	402 ± 31^a	418 ± 63^a
N (g kg^−1)	12.8 ± 2.4^a	10.7 ± 0.5^a	10.2 ± 1.9^a	11.0 ± 0.8^a
C:N ratio	29.3 ± 4.5^b	39.2 ± 0.7^a	40.1 ± 5.2^a	38.3 ± 8.0^a
P (g kg^−1)	0.62 ± 0.06^a	0.48 ± 0.02^b	0.47 ± 0.08^a	0.43 ± 0.01^a
K (g kg^−1)	5.15 ± 1.05^a	4.93 ± 0.72^a	5.90 ± 0.99^a	4.58 ± 0.86^a
Ca (g kg^−1)	4.56 ± 2.50^a	3.67 ± 0.74^a	6.17 ± 1.44^a	4.57 ± 1.19^a
Mg (g kg^−1)	3.13 ± 0.25^a	2.90 ± 0.08^a	3.08 ± 0.52^a	2.67 ± 0.31^a
Values are mean ± standard deviation (n = 3). Data with different letters between footslope and summit are statistically significant at P < 0.05 (Student’s t test). OC, organic carbon; TN, total nitrogen.

Table 3 Comparisons of soil microbial properties at the beginning and end of the in-situ core incubation

	January 2006			August 2006
	Beginning	End		Beginning	End
	0 day	28 day (open)	28 day (capped)	0 day	28 day (open)	28 day (capped)
Cmic (mg CO2-C kg^−1)
Footslope	863 ± 130^b	906 ± 174^a	861 ± 210^a	962 ± 67^b	925 ± 36^b	1012 ± 219^a
Summit	1158 ± 46^a	1106 ± 213^a	1061 ± 189^a	1259 ± 80^a	1349 ± 127^a	1321 ± 70^a
Nmic (mg N kg^−1)
Footslope	32 ± 14^b	43 ± 17^b	44 ± 18^b	71 ± 9^a	32 ± 7^b	50 ± 21^b
Summit	102 ± 14^a	123 ± 22^a	119 ± 25^a	140 ± 28^a	90 ± 20^a	95 ± 16^a
Cmic : Nmic ratio
Footslope	29.3 ± 8.8^a	22.6 ± 4.5^a	20.8 ± 4.6^a	13.7 ± 1.2^a	29.6 ± 4.6^a	22.0 ± 5.7^a
Summit	11.6 ± 1.4^a	9.0 ± 1.1^b	9.0 ± 1.8^b	9.2 ± 1.4^b	15.4 ± 2.2^a	14.2 ± 1.6^a
Cmic : OC (%)
Footslope	7.0 ± 1.1^a	7.4 ± 1.4^a	7.0 ± 1.7^a	7.3 ± 0.5^a	7.0 ± 0.3^a	7.7 ± 1.7^a
Summit	4.9 ± 0.2^a	4.7 ± 0.9^a	4.5 ± 0.8^a	4.6 ± 0.3^b	5.0 ± 0.5^b	4.9 ± 0.3^a
Nmic : TN (%)
Footslope	2.9 ± 1.3^b	3.8 ± 1.6^b	4.0 ± 1.6^a	7.5 ± 0.9^a	3.4 ± 0.7^a	5.2 ± 2.2^a
Summit	6.3 ± 0.9^a	7.7 ± 1.4^a	7.4 ± 1.6^a	7.6 ± 1.5^a	4.9 ± 1.1^a	5.1 ± 0.9^a
Values are mean ± standard deviation (n = 3). Data with different letters between landscape positions are statistically significant at P < 0.05 (Student’s t test). OC, organic carbon; TN, total nitrogen.

Figure 3 Concentrations of soil ammonium-N (NH4+-N), mineral N and nitrate-N (NO3−-N) during in situ incubation in January 2006 at the Nanjenshan transect site. Error bars are the standard deviation (n = 3); where no bars are shown only one data point (core) is available.

Table 4 Statistical analysis using the general linear model procedure for soil nitrogen concentrations during in situ incubation periods at the transect site in January and August 2006

Source of variation	January 2006						August 2006
	NH4 ^+-N		(NH4 ^++NO3 ^−)		NO3 ^−-N		NH4 ^+-N		(NH4 ^++NO3 ^−)		NO3 ^−-N
	F	P > F	F	P > F	F	P > F	F	P > F	F	P > F	F	P > F
Week 0
Land	0.04	0.84	0.16	0.71	0.58	0.49	5.78	0.047	0.16	0.70	1.15	0.32
Core	0.40	0.56	0.23	0.66	0.52	0.51	0.09	0.77	0.03	0.87	0.07	0.81
Land × Core	0.53	0.51	1.33	0.31	0.07	0.80	0.09	0.77	0.03	0.87	0.07	0.81
Week 1
Land	3.47	0.14	6.91	0.06	4.99	0.09	7.93	0.026	3.29	0.11	0.04	0.85
Core	22.50	0.009	11.57	0.03	2.65	0.18	0.96	0.36	0.79	0.40	0.09	0.77
Land × Core	8.80	0.04	3.35	0.14	0.43	0.55	1.19	0.31	0.11	0.75	0.39	0.55
Week 2
Land	1.64	0.27	0.81	0.42	0.06	0.81	14.17	0.007	2.90	0.13	0.86	0.39
Core	0.11	0.75	0.64	0.47	0.88	0.40	0.62	0.46	0.04	0.84	0.25	0.63
Land × Core	1.04	0.37	0.00	0.97	0.22	0.67	0.57	0.47	0.28	0.62	0.17	0.69
Week 3
Land	2.53	0.19	2.49	0.19	0.60	0.48	7.28	0.03	0.60	0.46	0.56	0.48
Core	0.24	0.65	0.00	0.99	0.03	0.87	1.50	0.26	18.55	0.003	10.97	0.01
Land × Core	3.87	0.12	0.08	0.79	0.20	0.68	0.65	0.45	2.76	0.14	3.88	0.09
Week 4
Land	0.00	0.98	0.10	0.76	0.22	0.67	2.84	0.14	0.92	0.37	0.01	0.93
Core	0.03	0.88	0.43	0.55	1.23	0.33	0.01	0.91	6.04	0.04	14.96	0.006
Land × Core	1.20	0.34	0.00	0.96	1.12	0.35	0.13	0.73	0.14	0.72	0.06	0.81
Values in bold are significant.

Table 5 Repeated-measures multivariate ANOVA of landscape position (landscape), core method (core) and in-situ incubation period (time) on soil nitrogen concentrations at the transect site in January and August 2006

Source of variation	df		P values
			NH4 ^+-N	(NH4 ^++ NO3 ^−)-N	NO3 ^−-N
			January 2006
Between-subject effect
Landscape	1		0.75	0.54	0.64
Core	1		0.24	0.42	0.81
Landscape × core	1		0.06	0.60	0.58
Error	4
Within-subject effect	Num. df	Den. df
Time	4	1	0.47	0.14	0.29
Time × landscape	4	1	0.43	0.43	0.77
Time × core	4	1	0.65	0.38	0.42
Time × landscape × core	4	1	0.89	0.49	0.88
			August 2006
Between-subject effect
Landscape	1		0.003**	0.14	0.94
Core	1		0.65	0.06	0.04*
Landscape × core	1		0.48	0.76	0.49
Error	7
Within-subject effect	Num. df	Den. df
Time	4	4	0.56	0.12	0.03*
Time × landscape	4	4	0.19	0.47	0.69
Time × core	4	4	0.50	0.03*	0.04*
Time × landscape × core	4	4	0.40	0.42	0.47
Values in bold are significant. *P < 0.05; **P < 0.01 ; df, degrees of freedom.

Figure 4 Concentrations of soil ammonium-N (NH4+-N), mineral N and nitrate-N (NO3−-N) during in situ incubation in August 2006 at the Nanjenshan transect site. Error bars are the standard deviation (n = 3).

Table 6 Net rates and amounts of mineralization and nitrification at the Nanjenshan transect site

	January 2006		August 2006
	Footslope	Summit	Footslope	Summit
Net amount of N mineralization
(mg N m^−2 28 day^−1)	844	868	1130	1990
Net rate of N mineralization
(mg N m^−2 day^−1)	30.1	31.0	40.2	71.3
(mg N g C^−1 day^−1)	0.018	0.010	0.023	0.019
(mg N g N^−1 day^−1)	0.201	0.143	0.313	0.287
Net amount of nitrification
(mg N m^−2 28 day^−1)	691	737	1440	1810
Net rate of nitrification
(mg N m^−2 day^−1)	24.7	26.3	51.5	64.6
(mg N g C^−1 day^−1)	0.015	0.008	0.029	0.018
(mg N g N^−1 day^−1)	0.165	0.121	0.402	0.260
Net rates and amounts of mineralization and nitrification were calculated from differences in the mean concentrations between the beginning and end of the in situ incubation.