The Impact and Mechanism of land reclamation and retirement on the coupling relationship between soil carbon and nitrogen in Karst areas

doi:10.13745/j.esf.sf.2024.11.76

Abstract

Abstract:

During the process of ecological restoration in karst areas, most of the retired croplands were reclaimed in the past and subjected to deep tillage. But this has received relatively little attention, and there is a lack of understanding of whether it causes changes in the soil carbon-nitrogen coupling relationship. In this paper, typical reclaimed croplands were selected within the demonstration area for ecological restoration of rocky desertification, with traditional croplands as a comparison. A total of 39 soil samples were collected from the surface to the bedrock, and the soil organic carbon content (SOC), total nitrogen content (TN), the natural abundance of soil stable isotope ¹³C (δ¹³C_SOC), and the carbon-to-nitrogen ratio (C/N) were analyzed. Correlation analysis and principal component analysis were used to study the soil carbon-nitrogen coupling relationship and its mechanism. The study shows that the soil carbon and nitrogen of traditional croplands exhibit coupled changes, mainly regulated by the input of vegetation-derived carbon and the degree of microbial decomposition of carbon. As soil depth increases, the input of carbon and nitrogen from vegetation sources gradually decreases, and microbial carbon decomposition activities are limited by the insufficient supply of carbon and nitrogen (known as “carbon-nitrogen limitation”). This is consistent with general patterns. In contrast, the mean contents of SOC and TN in the reclaimed slope croplands were 2.23%±0.33% and 0.25%±0.03%, respectively, which were 74.2% and 66.7% higher than those in the traditional croplands. There was no correlation between SOC and TN contents, and a positive correlation between δ¹³C_SOC and SOC, showing a clear “decoupling” characteristic of soil carbon and nitrogen. The main reason is that land reclamation led to the replacement of surface and deep soils. Deep, originally nitrogen-poor soils receive additional atmospheric nitrogen deposition and nitrogen from rocks in the surface layer, while the originally nitrogen-rich surface soils replenish the nitrogen in the deeper soils. This lifted the “nitrogen limitation”. And the decomposition rate of the originally carbon-rich surface soil decreases after being buried at a depth of 45 to 65cm, lifting the “carbon limitation”. These findings of this study enrich the theory of soil carbon-nitrogen coupling in karst areas and provide an important reference for the evaluation of carbon and nitrogen distribution and storage under ecological restoration in karst rocky mountainous areas.

Key words: Karst, land reclamation and conversion, soil organic carbon, total nitrogen, ¹³C stable isotope, C/N

CLC Number:

WU Zeyan, LI Qiang, ZHANG Cheng, JIANG Zhongcheng, LUO Weiqun, HU Zhaoxin, TU Chun. The Impact and Mechanism of land reclamation and retirement on the coupling relationship between soil carbon and nitrogen in Karst areas[J]. Earth Science Frontiers, 2025, 32(5): 524-533.

Figures/Tables 10

Fig.1 Distribution of soil sampling sites in the study area

Table 1 Statistics of carbon and nitrogen indicators in RRF and CF soil profile

样地	指标	最大值	最小值	平均值	标准差	变异系数^*
RRF	SOC含量/%	2.71	1.51	2.23	0.33	0.15
	δ¹³C_SOC值/‰	-16.14	-20.28	-18.50	1.30	-0.07
	TN含量/%	0.30	0.21	0.25	0.03	0.15
	C/N值	13.14	6.86	8.85	1.66	0.19
CF	SOC含量/%	1.92	0.96	1.28	0.22	0.17
	δ¹³C_SOC值/‰	-15.87	-20.83	-17.84	1.42	-0.08
	TN含量/%	0.22	0.11	0.15	0.03	0.11
	C/N值	11.04	6.71	8.40	1.37	0.16

Table 2 Correlation between carbon and nitrogen indicators in RRF soil profile

指标	SOC含量	TN含量	δ¹³C_SOC值	C/N值
SOC含量	1
TN含量	0.190	1
δ¹³C_SOC值	0.563^*	-0.254	1
C/N值	0.739^**	-0.506^*	0.619^*	1

Table 3 Correlation between carbon and nitrogen indicators in CF soil profile

指标	SOC含量	TN含量	δ¹³C_SOC值	C/N值
SOC含量	1
TN含量	0.642^**	1
δ¹³C_SOC值	-0.486^*	-0.944^**	1
C/N值	0.251	-0.569^*	0.685^**	1

Fig.2 Curves of various carbon and nitrogen indicators in the soil profile of CF sites

Fig.3 Factor loading of two principal components and sample scores of CF site

Fig.4 Scatter plot of soil SOC,δ13CSOC, and TN in CF site

Fig.5 Factor loading of two principal components and sample scores of RRF site

Fig.6 Curves of various carbon and nitrogen indicators in the soil profile of RRF plot

Fig.7 Scatter plot of soil SOC,δ13CSOC, and TN in RRF site

References 36

[1]	WANG J X, LAN J C, LONG Q X, et al. Soil organic carbon transfer in aggregates subjected to afforestation in Karst region as indicated by ¹³C natural abundance[J]. Forest Ecology and Management, 2023, 531: 120798.
[2]	YU P J, LI Y X, LIU S W, et al. Afforestation influences soil organic carbon and its fractions associated with aggregates in a Karst region of Southwest China[J]. Science of the Total Environment, 2022, 814: 152710.
[3]	李发东, 栗照鑫, 乔云峰, 等. 土壤有机碳同位素组成在农田生态系统碳循环中的应用进展[J]. 中国生态农业学报(中英文), 2023, 31(2): 194-205.
[4]	HU P L, LIU S J, YE Y Y, et al. Soil carbon and nitrogen accumulation following agricultural abandonment in a subtropical Karst region[J]. Applied Soil Ecology, 2018, 132: 169-178.
[5]	QIN C Q, LI S L, YU G H, et al. Vertical variations of soil carbon under different land uses in a Karst critical zone observatory (CZO), SW China[J]. Geoderma, 2022, 412: 115741.
[6]	LAN J C, HU N, FU W L. Soil carbon-nitrogen coupled accumulation following the natural vegetation restoration of abandoned farmlands in a Karst rocky desertification region[J]. Ecological Engineering, 2020, 158: 106033.
[7]	LI S L, LIU C Q, CHEN J N, et al. Karst ecosystem and environment: characteristics, evolution processes, and sustainable development[J]. Agriculture, Ecosystems & Environment, 2021, 306: 107173.
[8]	JIANG Z C, LIAN Y Q, QIN X Q. Rocky desertification in Southwest China: impacts, causes, and restoration[J]. Earth-Science Reviews, 2014, 132: 1-12.
[9]	蒋忠诚, 罗为群, 童立强, 等. 21世纪西南岩溶石漠化演变特点及影响因素[J]. 中国岩溶, 2016, 35(5): 461-468.
[10]	YUE Y M, QI X K, WANG K L, et al. Large scale rocky desertification reversal in South China Karst[J]. Progress in Physical Geography: Earth and Environment, 2022, 46(5): 661-675.
[11]	LV Y, ZHANG L, LI P, et al. Ecological restoration projects enhanced terrestrial carbon sequestration in the Karst region of Southwest China[J]. Frontiers in Ecology and Evolution, 2023, 11: 1179608.
[12]	SCHIEDUNG M, TREGURTHA C S, BEARE M H, et al. Deep soil flipping increases carbon stocks of New Zealand grasslands[J]. Global Change Biology, 2019, 25(7): 2296-2309.
[13]	ALCÁNTARA V, DON A, WELL R, et al. Deepploughing increases agricultural soil organic matter stocks[J]. Global Change Biology, 2016, 22(8): 2939-2956.
[14]	KIRSCHBAUM M U F, DON A, BEARE M H, et al. Sequestration of soil carbon by burying it deeper within the profile: a theoretical exploration of three possible mechanisms[J]. Soil Biology and Biochemistry, 2021, 163: 108432.
[15]	BURGER D J, SCHNEIDER F, BAUKE S L, et al. Fifty years after deep-ploughing: effects on yield, roots, nutrient stocks and soil structure[J]. European Journal of Soil Science, 2023, 74(6): e13426.
[16]	刘娅. 喀斯特小流域土壤碳氮耦合与沉积有机质来源研究[D]. 贵阳: 贵州师范大学, 2023.
[17]	HAN G L, TANG Y, LIU M, et al. Carbon-nitrogen isotope coupling of soil organic matter in a Karst region under land use change, Southwest China[J]. Agriculture, Ecosystems & Environment, 2020, 301: 107027.
[18]	POAGE M A, FENG X H. A theoretical analysis of steady state δ¹³C profiles of soil organic matter[J]. Global Biogeochemical Cycles, 2004, 18(2): GB2016.
[19]	景建生, 刘子琦, 罗鼎, 等. 喀斯特洼地土壤有机碳分布特征及影响因素[J]. 森林与环境学报, 2020, 40(2): 133-139.
[20]	ABDALLA K, MUTEMA M, HILL T. Soil and organic carbon losses from varying land uses: a global meta-analysis[J]. Geographical Research, 2020, 58(2): 167-185.
[21]	LI C F, WANG Z C, LI Z W, et al. Soil erosion impacts on nutrient deposition in a typical Karst watershed[J]. Agriculture, Ecosystems & Environment, 2021, 322: 107649.
[22]	李强. 岩溶土壤有机碳库分配、更新及其维持的微生物机制[J]. 微生物学报, 2022, 62(6): 2188-2197.
[23]	PUENTE M E, LI C Y, BASHAN Y. Rock-degrading endophytic bacteria in cacti[J]. Environmental and Experimental Botany, 2009, 66(3): 389-401.
[24]	LOPEZ-LOZANO N E, CARCAÑO-MONTIEL M G, BASHAN Y. Using native trees and cacti to improve soil potential nitrogen fixation during long-term restoration of arid lands[J]. Plant and Soil, 2016, 403(1): 317-329.
[25]	PIOTROWSKA-DŁUGOSZ A, DŁUGOSZ J, FRĄC M, et al. Enzymatic activity and functional diversity of soil microorganisms along the soil profile: a matter of soil depth and soil-forming processes[J]. Geoderma, 2022, 416: 115779.
[26]	LIAO C, CHANG K K, WU B Y, et al. Divergence in soil particulate and mineral-associated organic carbon reshapes carbon stabilization along an elevational gradient[J]. Catena, 2024, 235: 107682.
[27]	HICKS PRIES C E, RYALS R, ZHU B, et al. The deep soil organic carbon response to global change[J]. Annual Review of Ecology, Evolution, and Systematics, 2023, 54: 375-401.
[28]	崔雅如, 牟长城, 姬文慧, 等. 长白山月亮湾亚高山湿地生态系统碳氮储量沿水分梯度空间分异规律及机制[J]. 生态学报, 2024, 44(18): 7977-7990.
[29]	MAYER S, KÜHNEL A, BURMEISTER J, et al. Controlling factors of organic carbon stocks in agricultural topsoils and subsoils of Bavaria[J]. Soil and Tillage Research, 2019, 192: 22-32.
[30]	ALCÁNTARA V, DON A, VESTERDAL L, et al. Stability of buried carbon in deep-ploughed forest and cropland soils: implications for carbon stocks[J]. Scientific Reports, 2017, 7(1): 5511.
[31]	CHAOPRICHA N T, MARÍN-SPIOTTA E. Soil burial contributes to deep soil organic carbon storage[J]. Soil Biology and Biochemistry, 2014, 69: 251-264.
[32]	HICKS PRIES C E, SULMAN B N, WEST C, et al. Root litter decomposition slows with soil depth[J]. Soil Biology and Biochemistry, 2018, 125: 103-114.
[33]	KRÜGER N, FINN D R, DON A. Soil depth gradients of organic carbon-13: a review on drivers and processes[J]. Plant and Soil, 2024, 495(1): 113-136.
[34]	HU L N, LI Q, YAN J H, et al. Vegetation restoration facilitates below ground microbial network complexity and recalcitrant soil organic carbon storage in Southwest China Karst region[J]. Science of the Total Environment, 2022, 820: 153137.
[35]	HOULTON B Z, MORFORD S L, DAHLGREN R A. Convergent evidence for widespread rock nitrogen sources in Earth’s surface environment[J]. Science, 2018, 360(6384): 58-62.
[36]	MORFORD S L, HOULTON B Z, DAHLGREN R A. Direct quantification of long-term rock nitrogen inputs to temperate forest ecosystems[J]. Ecology, 2016, 97(1): 54-64.