Effects of nitrogen and phosphorus additions on the stability of soil aggregates and their carbon and nitrogen contents in evergreen broadleaf forests

doi:10.17521/cjpe.2024.0417

Abstract

Abstract:

Aims Ecosystem reactive nitrogen (N) and phosphorus (P) inputs induced by recent industrial and agricultural development can modify soil carbon (C) storage capacity by affecting soil aggregate structure and stabilization. However, observational studies on modeling the effects of N and P deposition on soil aggregates are still lacking in subtropical regions, with research on P-N interactions being comparatively scarce.

Methods In order to investigate how ecosystem N enrichment and its interactions with P deposition affect C sequestration mechanisms in soil aggregates, N and P addition experiments were conducted for 7 consecutive years in a subtropical forest in southern China. Sample plots of four N addition types were established (control: CK, 0 kg N·hm^-2·a^-1; low N addition: LN, 50 kg N·hm^-2·a^-1; N addition: NA, 100 kg N·hm^-2·a^-1; N and P addition: N+P, 100 kg N·hm^-2·a^-1 + 50 kg P·hm^-2·a^-1). Soil properties, soil aggregates and their C, N contents, and C, N stable isotopes composition of aggregates at each aggregate level were determined.

Important findings Evergreen broadleaf forest macroaggregates (diameter > 250 μm) were the dominant soil aggregate size, accounting for 83%-87% of the total soil mass, and LN treatment increased macroaggregate formation, mean mass diameter and mean geometric diameter, while NA and N+P treatments marginally reduced soil aggregate stability. N enrichment in this region primarily increased the C and N contents of aggregate, attributable on an increase in the concentration of these elements at each grain level. The added organic matter was predominantly enriched in macroaggregates, which were characterized by a high C to N ratio and rich ¹³C abundance. Conversely, excessive N input was detrimental to the stabilization of soil aggregate structure and C sequestration, in comparison with low N addition. The addition of P did not significantly alter the stability of local aggregates or their C and N components. The total soil C, N, and P contents of evergreen broadleaf forests under N addition did not promote soil aggregate formation, and the decrease in pH significantly promoted the increase of C and N contents of aggregates. The results of this study enhance our understanding of the mechanisms of aggregate change, and thus represent important references for predicting the potential of soil C sinks in evergreen broadleaf forests and other areas with similar conditions under future N and P deposition.

Key words: nitrogen and phosphorus addition, evergreen broadleaf forest, soil aggregates, carbon content, nitrogen content, stable isotope

DAI Yun-Ze, YAO Liang-Jin, CHEN Miao, XU Xiao-Niu. Effects of nitrogen and phosphorus additions on the stability of soil aggregates and their carbon and nitrogen contents in evergreen broadleaf forests[J]. Chin J Plant Ecol, 2026, 50(1): 55-69.

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URL: https://www.plant-ecology.com/EN/10.17521/cjpe.2024.0417

https://www.plant-ecology.com/EN/Y2026/V50/I1/55

Figures/Tables 9

Fig. 1 Soil physicochemical properties under nitrogen and phosphorus addition (mean ± SD). Different lowercase letters indicate significant differences between treatments (p < 0.05). CK, control check; LN, low nitrogen addition; NA, nitrogen addition; N+P, nitrogen and phosphorus addition. DOC, dissolved organic carbon content; DON, dissolved organic nitrogen content; MBC, soil microbial biomass carbon content; MBN, soil microbial biomass nitrogen content; SOC, soil organic carbon content; STN, soil total nitrogen content; TP, soil total phosphorus content.

Table 1 ANOVA of soil aggregate fractions

指标 Index	LN		NA		N+P
指标 Index	F	p	F	p	F	p
大团聚体质量百分比 Macroaggregate mass percentage	1.29	0.27	0.21	0.65	0.33	0.57
微团聚体质量百分比 Microaggregate mass percentage	1.04	0.32	0.11	0.75	0.02	0.89
粉黏粒质量百分比 Silt + clay mass percentage	1.24	0.28	0.40	0.54	0.91	0.36
MWD	1.30	0.27	0.21	0.65	0.34	0.57
GMD	0.98	0.34	0.22	0.65	0.52	0.48
大团聚体碳(C)浓度 Macroaggregate carbon concentration	18.95	<0.01^**	10.12	<0.01^**	4.28	0.06
微团聚体C浓度 Microaggregate carbon concentration	19.24	<0.01^**	16.34	<0.01^**	4.43	0.05
粉黏粒C浓度 Silt + clay carbon concentration	12.12	<0.01^**	6.07	0.03^*	5.21	0.04^*
大团聚体氮(N)浓度 Macroaggregate nitrogen concentration	10.15	<0.01^**	4.70	0.04^*	2.37	0.14
微团聚体N浓度 Microaggregate nitrogen concentration	13.71	<0.01^**	5.33	0.03^*	2.69	0.12
粉黏粒N浓度 Silt + clay nitrogen concentration	7.60	0.01^*	1.78	0.20	3.79	0.07
大团聚体SOC:STN Macroaggregate SOC:STN	9.42	<0.01^**	31.80	<0.01^**	6.59	0.02^*
微团聚体SOC:STN Microaggregate SOC:STN	0.72	0.41	7.20	0.02^*	2.48	0.14
粉黏粒SOC:STN Silt + clay SOC:STN	0	0.99	2.40	0.14	0.69	0.42
大团聚体C含量 Macroaggregate carbon content	21.48	<0.01^**	13.84	<0.01^**	4.05	0.06
微团聚体C含量 Microaggregate carbon content	2.02	0.17	3.74	0.07	2.94	0.11
粉黏粒C含量 Silt + clay carbon content	1.59	0.23	4.34	0.05	3.80	0.07
大团聚体N含量 Macroaggregate nitrogen content	11.82	<0.01^**	5.93	0.03	1.96	0.18
微团聚体N含量 Microaggregate nitrogen content	1.28	0.28	2.02	0.18	1.92	0.19
粉黏粒N含量 Silt + clay nitrogen content	1.10	0.31	2.66	0.12	3.53	0.08
大团聚体δ¹³C Macroaggregate δ¹³C	1.98	0.14	1.98	0.14	1.98	0.14
微团聚体δ¹³C Microaggregate δ¹³C	6.84	<0.01^**	6.84	<0.01^**	6.84	<0.01^**
粉黏粒δ¹³C Silt + clay δ¹³C	2.92	0.04^*	2.92	0.04^*	2.92	0.04^*
大团聚体δ¹⁵N Macroaggregate δ¹⁵N	13.89	<0.01^**	13.89	<0.01^**	13.89	<0.01^**
微团聚体δ¹⁵N Microaggregate δ¹⁵N	1.70	0.19	1.70	0.19	1.70	0.19
粉黏粒δ¹⁵N Silt + clay δ¹⁵N	4.72	<0.01^**	4.72	<0.01^**	4.72	<0.01^**

Table 1 ANOVA of soil aggregate fractions

指标 Index	LN		NA		N+P
指标 Index	F	p	F	p	F	p
大团聚体质量百分比 Macroaggregate mass percentage	1.29	0.27	0.21	0.65	0.33	0.57
微团聚体质量百分比 Microaggregate mass percentage	1.04	0.32	0.11	0.75	0.02	0.89
粉黏粒质量百分比 Silt + clay mass percentage	1.24	0.28	0.40	0.54	0.91	0.36
MWD	1.30	0.27	0.21	0.65	0.34	0.57
GMD	0.98	0.34	0.22	0.65	0.52	0.48
大团聚体碳(C)浓度 Macroaggregate carbon concentration	18.95	<0.01^**	10.12	<0.01^**	4.28	0.06
微团聚体C浓度 Microaggregate carbon concentration	19.24	<0.01^**	16.34	<0.01^**	4.43	0.05
粉黏粒C浓度 Silt + clay carbon concentration	12.12	<0.01^**	6.07	0.03^*	5.21	0.04^*
大团聚体氮(N)浓度 Macroaggregate nitrogen concentration	10.15	<0.01^**	4.70	0.04^*	2.37	0.14
微团聚体N浓度 Microaggregate nitrogen concentration	13.71	<0.01^**	5.33	0.03^*	2.69	0.12
粉黏粒N浓度 Silt + clay nitrogen concentration	7.60	0.01^*	1.78	0.20	3.79	0.07
大团聚体SOC:STN Macroaggregate SOC:STN	9.42	<0.01^**	31.80	<0.01^**	6.59	0.02^*
微团聚体SOC:STN Microaggregate SOC:STN	0.72	0.41	7.20	0.02^*	2.48	0.14
粉黏粒SOC:STN Silt + clay SOC:STN	0	0.99	2.40	0.14	0.69	0.42
大团聚体C含量 Macroaggregate carbon content	21.48	<0.01^**	13.84	<0.01^**	4.05	0.06
微团聚体C含量 Microaggregate carbon content	2.02	0.17	3.74	0.07	2.94	0.11
粉黏粒C含量 Silt + clay carbon content	1.59	0.23	4.34	0.05	3.80	0.07
大团聚体N含量 Macroaggregate nitrogen content	11.82	<0.01^**	5.93	0.03	1.96	0.18
微团聚体N含量 Microaggregate nitrogen content	1.28	0.28	2.02	0.18	1.92	0.19
粉黏粒N含量 Silt + clay nitrogen content	1.10	0.31	2.66	0.12	3.53	0.08
大团聚体δ¹³C Macroaggregate δ¹³C	1.98	0.14	1.98	0.14	1.98	0.14
微团聚体δ¹³C Microaggregate δ¹³C	6.84	<0.01^**	6.84	<0.01^**	6.84	<0.01^**
粉黏粒δ¹³C Silt + clay δ¹³C	2.92	0.04^*	2.92	0.04^*	2.92	0.04^*
大团聚体δ¹⁵N Macroaggregate δ¹⁵N	13.89	<0.01^**	13.89	<0.01^**	13.89	<0.01^**
微团聚体δ¹⁵N Microaggregate δ¹⁵N	1.70	0.19	1.70	0.19	1.70	0.19
粉黏粒δ¹⁵N Silt + clay δ¹⁵N	4.72	<0.01^**	4.72	<0.01^**	4.72	<0.01^**

Fig. 2 Changes in the distribution of soil aggregates under nitrogen and phosphorus addition (mean ± SD). CK, control check; LN, low nitrogen addition; NA, nitrogen addition; N+P, nitrogen and phosphorus addition. Different lowercase letters indicate significant differences between treatments (p < 0.05).

Fig. 3 Effect of nitrogen and phosphorus addition on mean weight diameter (MWD) and geometric mean diameter (GMD) of soil aggregates (mean ± SD). CK, control check; LN, low nitrogen addition; NA, nitrogen addition; N+P, nitrogen and phosphorus addition. Different lowercase letters indicate significant differences between treatments (p < 0.05).

Fig. 4 Changes in carbon and nitrogen concentrations in soil aggregates under nitrogen and phosphorus addition (mean ± SD). CK, control check; LN, low nitrogen addition; NA, nitrogen addition; N+P, nitrogen and phosphorus addition. Different lowercase letters indicate significant differences between treatments (p < 0.05).

Fig. 5 Changes in carbon to nitrogen ratio of soil aggregates under nitrogen and phosphorus addition (mean ± SD). CK, control check; LN, low nitrogen addition; NA, nitrogen addition; N+P, nitrogen and phosphorus addition. SOC, soil organic carbon content; STN, soil total nitrogen content. Different lowercase letters indicate significant differences between treatments (p < 0.05).

Fig. 6 Changes in carbon and nitrogen content of soil aggregates under nitrogen and phosphorus addition (mean ± SD). CK, control check; LN, low nitrogen addition; NA, nitrogen addition; N+P, nitrogen and phosphorus addition. Different lowercase letters indicate significant differences between treatments (p < 0.05).

Table 2 Isotopic changes in soil aggregates under nitrogen and phosphorus addition (mean ± SD, ‰)

处理 Treatment	大团聚体δ¹³C Macroaggregate δ¹³C	微团聚体δ¹³C Microaggregate δ¹³C	粉黏粒δ¹³C Silt + clay δ¹³C	大团聚体δ¹⁵N Macroaggregate δ¹⁵N	微团聚体δ¹⁵N Microaggregate δ¹⁵N	粉黏粒δ¹⁵N Silt + clay δ¹⁵N
CK	-27.71 ± 1.92^b	-27.85 ± 0.04^a	-30.80 ± 4.47^a	-24.65 ± 10.18^a	-10.96 ± 4.84^a	-5.19 ± 0.86^a
LN	-26.27 ± 0.46^a	-31.11 ± 1.68^b	-34.16 ± 6.37^a	-47.04 ± 5.67^c	-11.33 ± 5.55^a	-5.73 ± 0.64^b
NA	-26.88 ± 1.80^ab	-29.65 ± 1.37^b	-54.83 ± 37.96^b	-33.55 ± 9.85^b	-8.88 ± 1.15^a	-4.67 ± 0.43^a
N+P	-26.46 ± 0.52^ab	-30.85 ± 2.63^b	-33.65 ± 3.82^a	-41.03 ± 3.13^c	-7.79 ± 2.12^a	-5.19 ± 0.30^ab

Fig. 7 Correlation analysis between soil aggregate fractions and environmental factors (A), and effect of soil aggregate distribution and its carbon, nitrogen concentration changes on soil carbon and nitrogen stability (B). DOC, dissolved organic carbon content; DON, dissolved organic nitrogen content; GMD, geometric mean diameter; MBC, soil microbial biomass carbon content; MBN, soil microbial biomass nitrogen content; MAC-δ13C, macroaggregate 13C isotope ratio (δ13C); MAC-δ15N, macroaggregate 15N isotope ratio (δ15N); MAC-content, macroaggregate content; MAC-SOC:STN, macroaggregate SOC:STN; MACC-concentration, macroaggregate carbon concentration; MACC-content, macroaggregate carbon content; MANC-concentration, macroaggregate nitrogen concentration; MANC-content, macroaggregate nitrogen content; MIC-δ13C, microaggregate δ13C; MIC-δ15N, microaggregate δ15N; MIC-content, microaggregate content; MIC-SOC:STN, microaggregate SOC:STN; MICC-concentration, microaggregate carbon concentration; MICC-content, microaggregate carbon content; MINC-concentration, microaggregate nitrogen concentration; MINC-content, microaggregate nitrogen content; MWD, mean weight diameter; SC-δ13C, silt + clay δ13C; SC-δ15N, silt + clay δ15N; SC-content, silt + clay content; SC-SOC:STN, silt + clay SOC:STN; SCC-concentration, silt + clay carbon concentration; SCC-content, silt + clay carbon content; SMC, soil moisture content; SNC-concentration, silt + clay nitrogen concentration; SNC-content, silt + clay nitrogen content; SOC, soil organic carbon content; STN, soil total nitrogen content; TP, soil total phosphorus content. *, p < 0.05; **, p < 0.01; ***, p < 0.001.

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