Soil organic carbon and its easily decomposed components under precipitation change and nitrogen addition in a desert steppe in northwest China

doi:10.17521/cjpe.2023.0229

Abstract

Abstract:

Aims Soil organic carbon (C) pool plays an important role in regulating terrestrial C cycle and global climate, etc. The purpose of this study is to furnish data that will facilitate the scientific prediction of the C sink function of the grasslands in semi-arid regions under global change.

Methods Based on a two-factor field experiment of precipitation change (-50%, -30%, natural, +30%, +50%) and nitrogen (N) addition (0 and 5 g·m^-2·a^-1) established in 2017 in a desert steppe in Ningxia, we explored the response patterns and driving factors of soil organic C characteristics (content, storage, and components) in 0-60 cm soils after 4 years of treatments.

Important findings N addition had little effects on soil organic C characteristics. In contrast, precipitation exerted a significant influence on soil organic C characteristics, with the magnitude of the effect contingent up on the N level and soil depth. In the absence of N addition, both increasing and decreasing precipitation had a minimal impact on organic C characteristics across the whole 0-60 cm depth. In contrast, a 30% reduction in precipitation led to a significant increase in the content of easily oxidized organic C and dissolved organic C, while a 30% increase in precipitation resulted in a significant increase in the content of particulate organic C and light fraction organic C under 5 g·m^-2·a^-1 N addition. The content of soil organic C and its storage were positively correlated with soil water content, cellobiohydrolase activity and alkaline phosphatase activity. Conversely, they were negatively correlated with soil NO₃^--N. The content of easily oxidized organic C, particulate organic C and light fraction organic C was found to be positively correlated with soil leucine aminopeptidase activity and the Simpson dominance index, while negatively correlated with microbial biomass N content. Dissolved organic C and microbial biomass C content showed the opposite relationship with the three indices above. These findings indicate that alterations in precipitation levels exert minimal influence on soil organic C content and its storage in the context of N addition. However, moderate increases and decreases in precipitation will diminish soil organic C stability by influencing soil water content, N availability, enzyme activity and plant community dominance, which may, in turn, elevate the risk of soil C emission in desert steppes.

Key words: semi-arid region, precipitation pattern, nitrogen deposition, soil carbon emission, soil carbon stability

MA Xu-Han, HUANG Ju-Ying, YU Hai-Long, HAN Cui, LI Bing. Soil organic carbon and its easily decomposed components under precipitation change and nitrogen addition in a desert steppe in northwest China[J]. Chin J Plant Ecol, 2024, 48(8): 1065-1077.

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https://www.plant-ecology.com/EN/Y2024/V48/I8/1065

Figures/Tables 11

Fig. 1 Monthly dynamics of meteorological factors in Yanchi County, Ningxia during 2018-2022. The meteorological data are obtained from China Meteorological Data Network (https://data.cma.cn/).

Fig. 2 Precipitation change and nitrogen addition experiment layout in Yanchi County, Ningxia. (random block split zone design). See abbreviations in Table 1.

Table 1 Experimental treatments and their abbreviations in the text in Yanchi County, Ningxia

氮添加处理 Nitrogen addition treatment (N·m^-2·a^-1)	降水量减少50% 50% reduction in precipitation	降水量减少30% 30% reduction in precipitation	自然降水量 Natural precipitation	降水量增加30% 30% increase in precipitation	降水量增加50% 50% increase in precipitation
0	W1N0	W2N0	W3N0	W4N0	W5N0
5	W1N5	W2N5	W3N5	W4N5	W5N5

Table 2 Effects of precipitation (α), nitrogen addition (β) and soil depth (γ) on soil organic carbon and its components in desert steppe of Yanchi County, Ningxia

变异来源 Source of variation	自由度 Degree of freedom (df)	SOC	EOC	DOC	POC	LFOC	MBC	SOCS
α	4	1.033^*	4.864	4.566	2.669^**	5.009	5.800^**	2.428
β	1	2.832	1.174	0.010	9.313	5.411	14.317	2.923
γ	3/1/2¹⁾	114.396^**	35.593^**	265.927^*	24.062^*	19.692^*	1 861.216^*	48.817^*
α × β	4	1.838	19.222^*	4.555^*	6.332	0.200	5.107	0.773
α × γ	12/4/8¹⁾	2.001	7.463	5.117	10.147^*	10.809	2.406	3.042
β × γ	3/1/2¹⁾	6.961	4.411	21.818^*	2.376	0.168	84.427^*	36.539^**
α × β × γ	12/4/8¹⁾	4.980	12.955^*	5.835	7.800^*	0.924	4.033	1.730

Fig. 3 Effects of precipitation and nitrogen addition on 0-60 cm soil organic carbon content in desert steppe of Yanchi County, Ningxia (mean ± SE). See abbreviations in Table 1. Different uppercase and lowercase letters indicate significant differences among the precipitation treatments under 0 and 5 g N·m-2·a-1 (p < 0.05), respectively. * represents significant differences between nitrogen treatments under the same precipitation condition (p < 0.05).

Fig. 4 Effects of precipitation and nitrogen addition on 0-60 cm soil organic carbon (C) and its components contents in desert steppe of Yanchi County, Ningxia (mean ± SE). See abbreviations in Table 1. Different uppercase and lowercase letters indicate significant differences among the precipitation treatments under 0 and 5 g N·m-2·a-1 (p < 0.05), respectively. * represents significant differences between nitrogen treatments under the same precipitation condition (p < 0.05).

Fig. 5 Effects of precipitation and nitrogen addition on 0-60 cm soil organic carbon (C) storage in desert steppe of Yanchi County, Ningxia (mean ± SE). See abbreviations in Table 1. Different uppercase and lowercase letters indicate significant differences among the precipitation treatments under 0 and 5 g N·m-2·a-1 (p < 0.05), respectively. * represents significant differences between nitrogen treatments under the same precipitation condition (p < 0.05).

Table 3 Conditional effects of environmental factors in redundancy analysis of soil organic carbon content and its storage in desert steppe of Yanchi County, Ningxia

因子 Factor	NO₃^--N	CBH	AKP	STP	SWC	NH₄⁺-N	MBP	EC	BG	NAG
贡献率 Contribution (%)	40.7	25.7	21.3	20.2	16.1	14.7	7.7	7.6	5.9	5.6
F	14.600	7.800	6.100	5.700	4.400	4.000	2.000	1.900	1.500	1.400
p	0.004*	0.016*	0.008*	0.030*	0.042*	0.064	0.146	0.154	0.258	0.262

Fig. 6 Redundancy analysis of soil organic carbon and its storage and environmental factors under precipitation change and nitrogen addition in desert steppe of Yanchi County, Ningxia. AKP, soil alkaline phosphatase activity; CBH, soil cellobiohydrolase activity; NO3--N, soil nitrate nitrogen content; SOC, soil organic carbon content; SOCS, soil organic carbon storage; STP, soil total porosity; SWC, soil water content.

Table 4 Conditional effects of environmental factors in redundancy analysis of soil organic carbon components in desert steppe of Yanchi County, Ningxia

因子 Factor	MBN	LAP	D	NH₄⁺-N	EC	E	ST	MBP	R	SWC
贡献率 Contribution (%)	26.9	20.9	15.7	9.2	7.5	7.0	5.8	2.4	2.2	1.9
F	8.400	6.100	4.300	2.400	1.900	1.800	1.500	0.600	0.500	0.500
p	0.006*	0.014*	0.034*	0.118	0.170	0.192	0.264	0.496	0.484	0.518

Fig. 7 Redundancy analysis of soil organic carbon components and environmental factors under precipitation change and nitrogen addition in desert steppe of Yanchi County, Ningxia. D, Simpson dominance index; DOC, soil dissolved organic carbon content; EOC, soil easily oxidized organic carbon content; LAP, soil leucine aminopeptidase activity; LFOC, soil light group organic carbon content; MBC, microbial biomass carbon content; MBN, microbial biomass nitrogen content; POC, soil particulate organic carbon content.

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