Nano zero-valent iron-modified biochar regulates soil carbon mineralization and stability across aggregates in alpine degraded grassland

Abstract

Nano-engineered amendments, such as nano zero-valent iron-modified biochar (nZVI-BC), offer promising potential for restoring degraded soils; however, their role in regulating soil carbon cycling, particularly under climate warming conditions, remains insufficiently understood. This study evaluates the effects of nZVI-BC and yak dung biochar (BC), applied at 1% and 5% (w/w), on soil organic carbon (SOC) dynamics in degraded alpine grasslands. Biochar was incorporated into three soil aggregate size fractions (< 0.25 mm, 0.25–2 mm, and >2 mm), and soils incubated at 5 °C and 15 °C for 28 days to measure SOC mineralization, priming effect, and temperature sensitivity (Q₁₀). When the temperature increased from 5 °C to 15 °C, SOC mineralization in all soil aggregate sizes significantly increased, with priming effects showing a positive enhancement and peaking under the 5% nZVI-BC treatment. Both types of biochar effectively enhanced SOC mineralization across most aggregate sizes and generally increased Q₁₀ values; however, in large macroaggregates, mineralization under the 5% nZVI-BC treatment was no longer at its peak, and its Q₁₀ value markedly decreased relative to the control. The study indicates that the effect of biochar on SOC mineralization is regulated by the interaction between aggregate size and temperature, with large macroaggregates being crucial for SOC sequestration. This highlights the potential of nZVI-BC in modulating soil carbon cycling and aggregate stability in cold-region soils. Leveraging the high reactivity of nZVI, future research could explore the co-benefits of nZVI-BC in synergistically enhancing soil carbon sequestration and remediating soil pollutants, thereby optimizing its ecological value and sustainable application in alpine ecosystems.

Graphical abstract

Keywords

temperature sensitivity (Q₁₀) / soil aggregates / soil carbon mineralization / priming effect / biochar

Highlight

	● The addition of nano zero-valent iron biochar accelerated SOC mineralization in alpine degraded grassland.
	● Biochar amendments generally increased temperature sensitivity ( Q 10) of SOC decomposition, but nZVI-BC decreased Q 10 in large aggregates.
	● Stronger positive priming effects were observed under 5% biochar, especially at 15 °C.
	● Priming effect was correlated positively with the amount of biochar added.

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