Enriching particulate nitrogen fraction enhances the bioavailability of soil mineral nitrogen in a grazing hillslope grassland

Abstract

Although grazing and topography jointly regulate grassland ecosystem processes, the interactive influence of their effects on the spatial distribution of soil nitrogen (N) fractions and bioavailability remains unclear. Here, we sampled soils along three topographical positions (i.e., upper, middle, and down slope) in grazing and paired-adjacent enclosed (ungrazed) sites, respectively, in an Inner Mongolia hillslope grassland, and we measured N contents of particulate organic matter (POM-N) and mineral associated organic matter, and potential net N mineralization (Nm). Results showed that POM-N and Nm were, respectively, 174% and 1114% greater in the grazing site than in the enclosed grazing site in the 0–10 cm soil layer at the downslope position. Across the landscape of the grazing sites, POM-N and Nm were 1.79–2.03 and 2.82–6.83 times higher, respectively, in the downslope than in the upper and middle slope positions. Furthermore, POM-N showed a significantly positive correlation with the Nm. The results of this study indicate that grazing and erosion interactively drives the redistribution of POM along the slope by promoting plant residue fragmentation and soil materials movement, thereby reshaping the pattern of soil nitrogen cycling at the landscape scale.

Graphical abstract

Keywords

livestock grazing / soil nitrogen fractions / soil nitrogen cycling / soil erosion

Highlight

	● Effects of grazing and topography on soil N fractions and availability were identified.
	● Downslope at grazing sites enriched particulate organic N.
	● Downslope at grazing sites exhibited the highest net N mineralization.
	● The particulate organic N was positively correlated with the N bioavailability.

References

[1] Bai, Y.F., Cotrufo, M.F., 2022. Grassland soil carbon sequestration: current understanding, challenges, and solutions. Science377, 603–608.

[2] Cotrufo, M.F., Haddix, M.L., Kroeger, M.E., Stewart, C.E., 2022. The role of plant input physical-chemical properties, and microbial and soil chemical diversity on the formation of particulate and mineral-associated organic matter. Soil Biology and Biochemistry168, 108648.

[3] Cotrufo, M.F., Ranalli, M.G., Haddix, M.L., Six, J., Lugato, E., 2019. Soil carbon storage informed by particulate and mineral-associated organic matter. Nature Geoscience12, 989–994.

[4] Dai, L.C., Fu, R.Y., Guo, X.W., Du, Y.G., Lin, L., Zhang, F.W., Li, Y.K., Cao, G.M., 2021. Long-term grazing exclusion greatly improve carbon and nitrogen store in an alpine meadow on the northern Qinghai-Tibet Plateau. CATENA197, 104955.

[5] Donovan, M., Monaghan, R., 2021. Impacts of grazing on ground cover, soil physical properties and soil loss via surface erosion: a novel geospatial modelling approach. Journal of Environmental Management287, 112206.

[6] Fu, H.M., Duan, Y.H., Zhu, P., Gao, H.J., Xu, M.G., Yang, X.M., 2021. Potential N mineralization and availability to maize in black soils in response to soil fertility improvement in Northeast China. Journal of Soils and Sediments21, 905–913.

[7] Kraaij, T., Milton, S.J., 2006. Vegetation changes (1995–2004) in semi-arid Karoo shrubland, South Africa: effects of rainfall, wild herbivores and change in land use. Journal of Arid Environments64, 174–192.

[8] Kristensen, J.A., Svenning, J.C., Georgiou, K., Malhi, Y., 2022. Can large herbivores enhance ecosystem carbon persistence. Trends in Ecology & Evolution37, 117–128.

[9] Lavallee, J.M., Soong, J.L., Cotrufo, M.F., 2020. Conceptualizing soil organic matter into particulate and mineral-associated forms to address global change in the 21st century. Global Change Biology26, 261–273.

[10] Lehmann, J., Kleber, M., 2015. The contentious nature of soil organic matter. Nature528, 60–68.

[11] McSherry, M.E., Ritchie, M.E., 2013. Effects of grazing on grassland soil carbon: a global review. Global Change Biology19, 1347–1357.

[12] Nie, X.D., Li, Z.W., He, J.J., Huang, J.Q., Zhang, Y., Huang, B., Ma, W.M., Lu, Y.M., Zeng, G.M., 2015. Enrichment of organic carbon in sediment under field simulated rainfall experiments. Environmental Earth Sciences74, 5417–5425.

[13] Niu, W.L., Ding, J.Y., Fu, B.J., Zhao, W.W., Eldridge, D., 2025. Global effects of livestock grazing on ecosystem functions vary with grazing management and environment. Agriculture, Ecosystems & Environment378, 109296.

[14] Pan, S.L., Shi, J., Peng, Y.M., Wang, Z., Wang, X., 2023. Soil organic carbon pool distribution and stability with grazing and topography in a Mongolian grassland. Agriculture, Ecosystems & Environment348, 108431.

[15] Qiu, L.P., Zhu, H.S., Liu, J., Yao, Y.F., Wang, X., Rong, G.H., Zhao, X.N., Shao, M.G., Wei, X.R., 2021. Soil erosion significantly reduces organic carbon and nitrogen mineralization in a simulated experiment. Agriculture, Ecosystems & Environment307, 107232.

[16] Quinton, J.N., Govers, G., Van Oost, K., Bardgett, R.D., 2010. The impact of agricultural soil erosion on biogeochemical cycling. Nature Geoscience3, 311–314.

[17] Schiettecatte, W., Gabriels, D., Cornelis, W.M. and Hofman, G., 2008. Impact of deposition on the enrichment of organic carbon in eroded sediment. CATENA72, 340–347.

[18] Stanley, P.L., Wilson, C., Patterson, E., Machmuller, M.B., Cotrufo, M.F., 2024. Ruminating on soil carbon: applying current understanding to inform grazing management. Global Change Biology30, e17223.

[19] Wang, X., Cammeraat, E.L.H., Kalbitz, K., 2020. Erosional effects on distribution and bioavailability of soil nitrogen fractions in Belgian Loess Belt. Geoderma365, 114231.

[20] Witzgall, K., Vidal, A., Schubert, D.I., Höschen, C., Schweizer, S.A., Buegger, F., Pouteau, V., Chenu, C., Mueller, C.W., 2021. Particulate organic matter as a functional soil component for persistent soil organic carbon. Nature Communications12, 4115.

[21] Xie, Z.J., Chen, T.W., Potapov, M., Zhang, F., Wu, D.H., Scheu, S., Sun, X., 2022. Ecological and evolutionary processes shape below‐ground springtail communities along an elevational gradient. Journal of Biogeography49, 469–482.

[22] Yu, W.J., Huang, W.J., Weintraub-Leff, S.R., Hall, S.J., 2022. Where and why do particulate organic matter (POM) and mineral-associated organic matter (MAOM) differ among diverse soils. Soil Biology and Biochemistry172, 108756.

[23] Zhang, M.N., Delgado-Baquerizo, M., Li, G.Y., Isbell, F., Wang, Y., Hautier, Y., Wang, Y., Xiao, Y.L., Cai, J.T., Pan, X.B., Wang, L., 2023. Experimental impacts of grazing on grassland biodiversity and function are explained by aridity. Nature Communications14, 5040.

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