Effects of nitrogen-fixing and non-nitrogen-fixing tree species on soil properties and nitrogen transformation during forest restoration in southern China

Figures & data

Figure 1 Map of study site (Heshan station).

Figure 2 Monthly mean soil temperature (measured at a soil depth of 5 cm) and rainfall amount at Heshan station in 2007.

Table 1 Vegetation description of the six forest types (including a shrubland) at Heshan Station

Forest type	Main species	Height (m)	Coverage (%)	d.b.h. (cm)
AM	Acacia mangium	20.3	90	23.2
AA	Acacia auriculiformis	19.4	80	22.5
EU	Eucalyptus citriodora	25.4	90	18.5
SS	Schima superba	12.1	80	14.3
MX	Schima wallichii	12.3	80	13.6
	Castanopsis hystrix	11.2		12.7
SL	Litsea cubeba	3.3	60	–
	Evodia lepta	5.6		–
Data were collected in October 2007, 23 years after the initial planting. AA, Acacia auriculiformis; AM, Acacia mangium; d.b.h., diameter at breast height; EU, Eucalyptus citriodora; MX, native species mixture; SL, secondary shrubland; SS, Schima superba.

Table 2 General soil properties in the 0–5 cm and 5–10 cm soils of the six forest types at Heshan station in 2007

Variables	Soil layer	AM	AA	EU	SS	MX	SL	Ft	Sd	Ft × Sd
SOM (g kg^−1)	0–5 cm	78.9^c ± 3.78	73.4^b ± 7.68	50.2^a ± 4.42	49.4^a ± 6.55	46.3^a ± 9.89	52.0^ab ± 2.69	<0.01	<0.001	ns
	5–10 cm	32.6 ± 4.03	28.5 ± 4.55	30.2 ± 9.17	23.5 ± 3.80	17.6 ± 3.28	29.1 ± 2.17
TN (g kg^−1)	0–5 cm	1.39^c ± 0.08	1.13^b ± 0.10	0.91^a ± 0.01	0.84^a ± 0.01	0.88^a ± 0.07	0.98^ab ± 0.05	<0.01	<0.001	<0.01
	5–10 cm	0.68 ± 0.03	0.71 ± 0.07	0.73 ± 0.11	0.64 ± 0.10	0.73 ± 0.06	0.66 ± 0.05
C/N	0–5 cm	33.2 ± 2.33	37.4 ± 4.97	32.1 ± 2.72	33.8 ± 4.27	30.5 ± 4.26	30.7 ± 0.09	ns	<0.001	ns
	5–10 cm	27.7 ± 2.38	23.1 ± 2.02	26.5 ± 10.3	21.4 ± 5.05	15.4 ± 1.71	26.0 ± 2.00
BD (g cm^−3)	0–5 cm	0.88 ± 0.03	1.04 ± 0.07	0.91 ± 0.04	1.01 ± 0.03	0.98 ± 0.07	0.99 ± 0.05	<0.05	<0.001	ns
	5–10 cm	1.16^ab ± 0.02	1.31^c ± 0.02	1.27^bc ± 0.02	1.17^abc ± 0.06	1.04^a ± 0.09	1.25^bc ± 0.04
Soil pH	0–5 cm	3.81 ± 0.02	3.85 ± 0.03	3.88 ± 0.04	3.87 ± 0.04	3.88 ± 0.03	3.85 ± 0.02	<0.05	<0.05	ns
	5–10 cm	3.81 ± 0.06	3.92 ± 0.02	3.94 ± 0.02	3.96 ± 0.04	3.97 ± 0.03	3.85 ± 0.03
AA, Acacia auriculiformis; AM, Acacia mangium; BD, bulk density; EU, Eucalyptus citriodora; Ft, forest types effects; MX, native species mixture; Sd, soil depth effects; SL, secondary shrubland; SOM, soil organic matter; SS, Schima superba; TN, total nitrogen. Data are mean ± standard error (n = 3). In each layer, a one-way anova was used to detect differences among forest types; means sharing the same superscript were not significantly different at P = 0.05 (least significant difference).

Table 3 Pearson’s correlation analysis of soil pH, soil organic matter, total nitrogen and exchangeable K, Na, Ca and Mg

	pH	K	Na	Ca	Mg	SOM
K	−0.016	1
Na	−0.046	−0.166	1
Ca	−0.107	−0.324	0.550*	1
Mg	−0.535*	0.005	0.267	0.478*	1
SOM	−0.720**	0.050	0.507*	0.199	0.660**
TN	−0.511*	−0.097	0.567*	0.447	0.674**	0.732**
Significant correlations are indicated as follows: *P < 0.05, **P < 0.01. Sample sizes are 18 for all variables. This analysis was based on the average values of these variables in the 0–5 cm and 5–10 cm soils. SOM, soil organic matter; TN, total nitrogen.

Figure 3 Soil exchangeable (a) K+, (b) Na+, (c) Ca2+ and (d) Mg2+ in the 0–5 cm and 5–10 cm soils under the six forest types at Heshan station (mean ± standard error, n = 3). AA, Acacia auriculiformis; AM, Acacia mangium; EU, Eucalyptus citriodora; MX, native species mixture; SL, secondary shrubland; SS, Schima superba. Bars sharing the same superscript letter are not significantly different at P = 0.05 (least significant difference).

Figure 4 (a, b) Soil extractable ammonium, (c, d) nitrate and (e, f) available P in the rainy season (a,c,e) and (b,d,f) dry season of 2007 in the six forest types at Heshan station (mean ± standard error, n = 3). AA, Acacia auriculiformis; AM, Acacia mangium; EU, Eucalyptus citriodora; MX, native species mixture; SL, secondary shrubland; SS, Schima superba. Bars sharing the same superscript letter are not significantly different at P = 0.05 (least significant difference).

Table 4 Net nitrogen mineralization and nitrification rates (data were combined in the 0–10 cm soils) in the six forest types at Heshan station in 2007

Forest type	Nitrogen mineralization (kg N ha^−1 month^−1)		Nitrification (kg N ha^−1 month^−1)
	Rainy	Dry	Rainy	Dry
AM	11.0 ± 1.62	−1.46 ± 1.93	14.51 ± 1.85	0.37 ± 0.54
AA	10.9 ± 2.08	0.93 ± 0.92	14.67 ± 1.40	4.09 ± 0.35
EU	8.56 ± 3.24	−2.46 ± 0.86	11.04 ± 2.95	1.27 ± 0.94
SS	11.3 ± 2.96	−2.01 ± 0.81	14.25 ± 2.24	1.44 ± 1.62
MX	7.41 ± 1.09	−0.78 ± 0.90	10.36 ± 1.12	1.79 ± 0.2
SL	8.03 ± 1.99	1.68 ± 3.14	10.30 ± 2.10	1.82 ± 0.41
P-value	ns	ns	ns	ns
AA, Acacia auriculiformis; AM, Acacia mangium; EU, Eucalyptus citriodora; MX, native species mixture; SL, secondary shrubland; SS, Schima superba. Data are mean ± standard error (n = 3).