Effect of stand age on the temporal dynamics of soil active carbon and nitrogen in Chinese cypress artificial forests

Figures & data

Table 1. Characteristics of sampling sites

Sampling code	Stand age (yr)	Forest stage	Elevation (m)	Aspect	Slope (°)	Mean tree height (m)	Mean DBH (cm)	Canopy density (%)	Stand density (Trees ha^−1)	Soil depth (cm)
25a	25	Middle	400	South	15	7.2	7.62	85	4400	28 ~ 33
35a	35	Near-mature	410	Southwest	12	8.7	9.04	80	4000	33 ~ 35
45a	45	Mature	370	Southwest	18	10.7	13.75	90	2600	33 ~ 39
55a	55	Mature	415	Southeast	10	12.2	15.29	90	2400	34 ~ 45
65a	65	Overripe	400	Southwest	13	14.0	19.43	95	1900	38 ~ 45

DHB, diameter at breast height.

Figure 1. Principal component analysis (PCA) for the response of soil active C and N contents to stand age, temporal dynamic and soil layer. MBC, microbial biomass C; MBN, microbial biomass N; DOC, dissolved organic C; DON, dissolved organic N; 25a, middle forest stage (25 years old); 35a, near-mature forest stage (35 years old); 45a and 55a, mature forest stage (45 and 55 years old); 65a, overripe forest stage (65 years old); SA, TD and SL reprsent stand age, temporal dynamic and soil layer, respectively.     

Figure 2. Temporal dynamics of soil microbial biomass C (MBC) (a) and microbial biomass N (MBN) (b) in Chinese cypress artificial forest with five stand ages. 25a, middle forest stage (25 years old); 35a, near-mature forest stage (35 years old); 45a and 55a, mature forest stage (45 and 55 years old); 65a, overripe forest stage (65 years old).

Figure 3. Temporal dynamics of soil dissolved organic C (DOC) (a) and dissolved organic N (DON) (b) in Chinese cypress artificial forest with five stand ages. 25a, middle forest stage (25 years old); 35a, near-mature forest stage (35 years old); 45a and 55a, mature forest stage (45 and 55 years old); 65a, overripe forest stage (65 years old).

Figure 4. Temporal dynamics of soil ammonium-N (NH₄⁺-N) (a) and nitrate-N (NO₃⁻-N) (b) in Chinese cypress artificial forest with five stand ages. 25a, middle forest stage (25 years old); 35a, near-mature forest stage (35 years old); 45a and 55a, mature forest stage (45 and 55 years old); 65a, overripe forest stage (65 years old).

Table 2. Pearson correlation coefficients between soil active C, N components, and soil properties (n = 180)

Variable	Bacteria	Fungi	Actinomycete	TC	TN	AP	AK	pH	SWC	Clay	Silt	Sand	LAN	LAP	LAK	LB	LWC
MBC	0.430**	0.283**	0.267**	0.420**	0.496**	0.191*	0.056	0.114	0.402**	0.228**	0.296**	−0.294**	0.258**	−0.319**	0.014	0.433**	0.190*
MBN	0.293**	0.242**	0.160*	0.360**	0.406**	0.257**	0.004	0.197**	0.268**	0.232**	0.286**	−0.284**	.262**	−0.335**	−0.054	0.357**	0.074
DOC	0.459**	0.357**	0.156*	0.470**	0.631**	0.412**	0.219**	0.098	0.304**	0.161*	0.219**	−0.217**	0.295**	−0.431**	−0.056	0.456**	0.060
DON	0.565**	0.725**	−0.292**	0.221**	0.778**	0.300**	0.113	0.029	0.373**	0.411**	0.364**	−0.368**	0.127	−0.186*	0.052	0.219**	−0.099
NH4^+-N	0.137	0.139	−0.176*	0.267**	0.553**	0.217**	0.131	−0.094	0.114	0.089	0.064	−0.065	0.066	−0.130	0.019	0.309**	−0.280**
NO3^−-N	0.387**	0.419**	0.110	0.473**	0.839**	0.279**	0.134	0.195**	0.201**	0.162*	0.238**	−0.236**	0.452**	−0.524**	−0.002	0.516**	−0.138

*, P < 0.05; **, P < 0.01. MBC, microbial biomass C; MBN, microbial biomass N; DOC, dissolved organic C; DON, dissolved organic N; NH₄⁺-N, ammonium-N; NO₃⁻-N, nitrate-N. Bacteria, the number of bacteria communities; Fungi, the number of fungi communities; Actinomycete, the number of actinomycete communities; TC, total C; TN, total N; AP, available phosphorus; AK, available potassium, SWC, soil water content; Clay, soil clay volume fraction; Silt, soil silt volume fraction; Sand, soil sand volume fraction; LAN, litter available N content; LAP, litter available phosphorus content; LAK, litter available potassium content; LB, litter biomass; LWC, litter water content.

Table 3. Multiple regression models for the relationship between soil active C and N components as well as soil properties (n = 180)

Equation	Adjusted R^2	P
Y1 = 2.607X1 + 0.060X2 + 2.866X3 + 0.071X4 − 52.661	0.381	0.009
Y2 = 0.243X1 + 0.007X2 + 1.730X5 + 7.026	0.213	0.039
Y3 = 0.363X1 + 0.008X2 + 4.111X6 + 15.172	0.466	0.004
Y4 = 0.209X1 + 0.009X7 + 0.027X8 − 0.004X4 + 3.292X9 − 0.012X2 + 1.450X6 − 4.637	0.813	0.028
Y5 = 0.113X1 − 0.022X10 − 0.057X3 + 0.529X6 + 0.981	0.422	0.007
Y6 = 0.733X1 − 0.029X8 + 0.017X2 + 3.591X11 − 2.557X9 − 31.183	0.841	0.002

Y₁, microbial biomass C (MBC); Y₂, microbial biomass N (MBN); Y₃, dissolved organic C (DOC); Y₄, dissolved organic N (DON); Y₅, ammonium-N (NH₄⁺-N); Y₆, nitrate-N (NO₃⁻-N). X₁, total N (TN); X₂, the number of actinomycete communities (Actinomycete); X₃, litter water content (LWC); X₄, litter biomass (LB); X₅, total C (TC); X₆, available phosphorus (AP); X₇, available potassium (AK); X₈, the number of bacteria communities (Bacteria); X₉, soil clay volume fraction (Clay); X₁₀, the number of fungi communities (Fungi); X₁₁, pH.

Table 4. Main litter properties in Chinese cypress artificial forests with five stand ages

Sampling code	LWC (%)	LB (kg ha^−1 yr^−1)	LAN (g ha^−1 yr^−1)	LAP (g ha^−1 yr^−1)	LAK (g ha^−1 yr^−1)
25a	37.4 ± 5.11 a	782 ± 75.7 b	160 ± 8.49 c	9.27 ± 0.08 c	512 ± 14.5 d
35a	25.4 ± 3.06 bc	2060 ± 397 a	461 ± 17.1 a	17.8 ± 1.95 ab	1788 ± 19.2 a
45a	23.1 ± 7.36 c	1848 ± 346 a	492 ± 14.0 a	14.3 ± 2.34 b	992 ± 15.8 b
55a	30.5 ± 1.99 abc	1861 ± 83.8 a	397 ± 15.6 b	19.5 ± 1.61 a	769 ± 20.5 c
65a	35.3 ± 4.62 ab	888 ± 218 b	191 ± 9.51 c	8.10 ± 0.19 d	494 ± 5.33 d

Values are mean ± standard error (n = 3). The different lowercase in the same column refer to significant differences among the five stand ages (P < 0.05). LWC, litter water content; LB, litter biomass; LAN, litter available N content; LAP, litter available phosphorus content; LAK, litter available potassium content.