Response of aboveground and belowground carbon storage to nitrogen addition and precipitation change in an alpine meadow ecosystem

doi:10.17521/cjpe.2024.0243

Abstract

Abstract:

Aims Alpine grassland ecosystems store vast amounts of organic carbon while are fragile. Understanding the responses of the ecosystem carbon storage to the synchronous atmospheric nitrogen deposition and changing precipitation regimes is critical to project the fate of ecosystem carbon budgets under the context of global change.
Methods Based on a manipulation field experiment of nitrogen addition (10 g·m^-2·a^-1) and precipitation change (precipitation reduction by 50% and increase by 50%) in an alpine meadow on the northeastern Qing-zang Plateau in 2017, the plant biomass, soil organic carbon content (SOCC) and its fractions were observed from 2022 to 2023, in order to explore the response of ecosystem carbon storage to the changes in nitrogen and precipitation.
Important findings The results showed that there were little interaction effects of nitrogen addition and precipitation change on vegetation aboveground biomass (AGB). The response of vegetation AGB to the changes in nitrogen and precipitation was functional group-dependent. Nitrogen addition treatment increased the AGB of graminoid and sedge. Decreased precipitation treatment reduced AGB by 27% while increased precipitation treatment impacted AGB insignificantly. Except for sedge, the proportion of functional group AGB against community AGB changed undetectably. The responses of 0-40 cm belowground biomass (BGB) and SOCC to the changes in nitrogen and precipitation were weak and depth- and year-dependent. The root/shoot ratio reduced by 31% in nitrogen addition treatment and increased by 83% in decreased precipitation treatment, respectively. Nitrogen addition treatment increased soil surface (0-10 cm) mineral-associated organic carbon (MAOC) content by 31%. The response ratio (RR) of vegetation AGB was positively related to graminoid. The RR of 0-40 cm BGB was determined by soil surface and deep (20-40 cm) BGB positively. The RR of 0-40 cm SOCC was equivalently regulated by each layer SOCC. Soil surface BGB directly impacted the surface particulate organic carbon (POC) content positively and indirectly impacted the surface MAOC content via POC content negatively. The vegetation AGB affected the deep MAOC content positively and the deep POC content negatively. The main effects, rather than the interaction effects of the changes in nitrogen and precipitation, affect AGB significantly while BGB and SOCC undetectably. The differential effects of plant biomass on soil organic carbon fractions are depth-dependent.

Key words: alpine meadow, biomass, soil organic carbon, particulate organic carbon, mineral-associated organic carbon, nitrogen addition, precipitation change

ZHANG Fa-Wei, LI Hong-Qin, ZHU Jing-Bin, FAN Bo, ZHOU Hua-Kun, LI Ying-Nian, LIANG Nai-Shen. Response of aboveground and belowground carbon storage to nitrogen addition and precipitation change in an alpine meadow ecosystem[J]. Chin J Plant Ecol, 2025, 49(9): 1399-1409.

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URL: https://www.plant-ecology.com/EN/10.17521/cjpe.2024.0243

https://www.plant-ecology.com/EN/Y2025/V49/I9/1399

Figures/Tables 5

Table 1 F values of linear mixed-effect models of plant biomass, root/shoot ratio (R/S), and soil properties to precipitation change (Rain), nitrogen addition (N), and functional groups (FG) or soil depths (SD)

变量 Variables	地上生物量 AGB	地下生物量 BGB	根冠比 R/S	土壤全氮含量 SNC	土壤全磷含量 SPC	土壤碱解氮含量 SNaC	土壤速效磷含量 SPaC	土壤pH Soil pH	土壤有机碳含量 SOCC	颗粒态有机碳含量 POC content	矿物结合态有机碳含量 MAOC content
降水改变 Rain	3.79^*	1.46	4.07^*	2.01	0.68	0.30	1.13	18.10^***	4.10^*	0.16	0.33
氮添加 N	0.57	0.44	11.03^**	1.32	0.95	7.25^**	0.15	0.10	1.30	1.49	5.73^*
土壤深度(功能群) SD (FG)	86.55^***	319.71^***	−	660.93^***	25.29^***	176.22^***	177.46^***	638.30^***	434.59^***	119.47^***	213.64^***
年份 Y	0.07	8.40^**	3.34	48.48^***	1.16	114.86^***	42.28^***	5.00^*	38.82^***	−	−
Rain × N	2.88	0.29	0.65	1.08	1.22	1.25	3.17^*	0.70	1.49	0.14	1.22
Rain × SD (FG)	1.16	0.36	−	0.33	0.50	0.05	2.53^*	9.80^***	0.48	0.06	0.27
Rain × Y	0.07	1.21	0.18	0.97	0.34	0.07	1.00	5.00^*	2.63	−	−
N × SD (FG)	14.85^***	0.59	−	1.04	3.97	6.40^**	0.55	25.80^***	0.76	0.36	0.01
N × Y	0.07	0.55	0.42	5.64^*	0.70	3.75	4.89^*	2.40	14.58^**	−	−
Y × SD (FG)	0.02	2.76	−	9.08^**	6.98^**	39.03^**	18.27^***	63.70^***	22.76^***	−	−

Fig. 1 Responses of aboveground biomass (A), belowground biomass (B), soil organic carbon content (C), and content of soil organic carbon fractions (D) to the changes in nitrogen and precipitation (mean ± SD). CK, control; CK+50%, increased precipitation; CK-50%, decreased precipitation; N, nitrogen addition; N+50%, nitrogen addition with increased precipitation; N-50%, nitrogen addition with decreased precipitation. MAOC, mineral-associated organic carbon; POC, particulate organic carbon.

Fig. 2 Response ratio of aboveground biomass (AGB), 0-40 cm belowground biomass (BGB), root/shoot ratio (R/S), and 0-40 cm soil organic carbon content (SOCC) to the changes in nitrogen and precipitation (mean ± SD). ***, **, and * are p < 0.001, p < 0.01, and p < 0.05, respectively. CK, control; CK+50%, increased precipitation; CK-50%, decreased precipitation; N, nitrogen addition; N+50%, nitrogen addition with increased precipitation; N-50%, nitrogen addition with decreased precipitation.

Fig. 3 Pearson correlations among the response ratio of aboveground biomass (AGB), belowground biomass (BGB), soil organic carbon content (SOCC), and key variables’ response ratio. The number is the correlation coefficient. ×, p > 0.05. AGBG, AGBF, AGBL, AGBS, and AGBA, AGB of graminoid, forb, legume, sedge and community; BGB0-10, BGB10-20, BGB20-40, and BGB0-40, BGB of 0-10 cm, 10-20 cm, 20-40 cm, and 0-40 cm soil; Coverage, vegetation coverage; Height, maximal height; SOCC0-10, SOCC10-20, SOCC20-40, and SOCC0-40, SOCC of 0-10 cm, 10-20 cm, 20-40 cm, and 0-40 cm soil.

Fig. 4 Structural equation models for the response ratio (RR) of 0-10 cm and 20-40 cm soil organic carbon fractions and soil organic carbon content. Solid, dashed, and dotted lines showed positive, negative and insignificant relationships. The numbers that annotate the arrows were the standardized path coefficients. R2 suggested that explanatory power of the models to responses. *** and * are p < 0.001, and p < 0.05, respectively. AGB, aboveground biomass; BGB, belowground biomass; MAOC, mineral-associated organic carbon; POC, particulate organic carbon; SOCC, soil organic carbon content.

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