Global grassland degradation, driven by human disturbances and climate change, affects nearly 80% of desertified regions worldwide. Restoration efforts often employ either active methods, like targeted seeding, or passive methods, such as removing livestock grazing. A key concern is how exogenous carbon inputs, like biocharBiochar is a carbon-rich material created from biomass decomposition in low-oxygen conditions. It has important applications in environmental remediation, soil improvement, agriculture, carbon sequestration, energy storage, and sustainable materials, promoting efficiency and reducing waste in various contexts while addressing climate change challenges. More, interact with these long-term restoration strategies, particularly regarding soil organic carbon (SOC) dynamics and the priming effect (PE)—the accelerated decomposition of native SOM by fresh carbon input. A study published by Zhou et al. in Ecological Indicators investigated the long-term effects of yak dung biochar on SOC mineralization and the priming effect in alpine grasslands on the Qinghai-Tibetan Plateau (QTP) that had undergone a decade of active or passive restoration.

The research demonstrated a critical distinction in how biochar affected soil carbon dynamics across the two restoration pathways. Active restoration (AR), which involves interventions like seeding, resulted in a strong positive priming effect (PE) in both soil depths, indicating accelerated native SOC decomposition. The magnitude of this positive priming was substantial, ranging from 120.5%−297.0% in the topsoil and 157.2%−287.3% in the subsoil. This positive PE is likely linked to the improved soil structure, elevated organic carbon content, and stimulated microbial activity characteristic of actively restored soils. Biochar addition in AR soils significantly increased SOC mineralization rates compared to both degraded and passively restored grasslands.

In sharp contrast, passive restoration (PR), which relies only on natural recovery, showed a dual-directional effect. The priming effect was positive in the topsoil (ranging from 34.7%−80.9%) but shifted to negative in the subsoil (ranging from −67.1% to 47.7%). This shift to negative priming in the subsoil is hypothesized to be due to biochar promoting the physical protection and sorption of native organic matter or preferential utilization of its labile C by oligotrophic microbes. Overall, biochar addition did not statistically alter the SOC mineralization rates in passively restored grasslands. In the heavily degraded grasslands, biochar induced a slight negative priming effect, reducing mineralization rates at 5∘C and 15∘C in the topsoil by 58.0% and 54.5%, respectively.

The primary environmental factor driving the priming effect differed significantly between the two restoration approaches. In active restoration (AR), soil pHpH is a measure of how acidic or alkaline a substance is. A pH of 7 is neutral, while lower pH values indicate acidity and higher values indicate alkalinity. Biochars are normally alkaline and can influence soil pH, often increasing it, which can be beneficial More was the key driver, collectively accounting for 87% of the variation when combined with SOC and ammonium nitrogen (NH4+​-N). The biochar-induced rise in pH in AR soils likely led to altered mineral-organic interactions and microbial community restructuring that accelerated SOC decomposition. Conversely, in passive restoration (PR), phospholipid fatty acids (PLFA), a measure of viable microbial biomassBiomass is a complex biological organic or non-organic solid product derived from living or recently living organism and available naturally. Various types of wastes such as animal manure, waste paper, sludge and many industrial wastes are also treated as biomass because like natural biomass these More, were the dominant drivers, collectively explaining 67% of the variation when combined with SOC and available phosphorus (AP). In these resource-limited PR conditions, microbial activity is strongly coupled to substrate supply, meaning that the readily available carbon from the biochar triggered rapid growth and metabolism by dormant microbes, which then primed the native SOM decomposition.

The temperature sensitivity coefficient (Q10​) of SOC mineralization, which quantifies the increase in mineralization rate for every 10∘C rise, was generally unaffected by either restoration approach or biochar addition across all temperatures tested. However, biochar addition did significantly increase the Q10​ (measured at 25/15∘C) in the topsoil. Mantel tests indicated that soil moisture content (SMC), SOC, and PLFA influenced Q10​ in passive restoration, while only SMC was influential in active restoration. This study highlights that biochar application must be context-dependent, with its effects on soil carbon cycling tied directly to the chosen grassland restoration strategy. The findings provide useful recommendations for developing sustainable ecological restoration and soil management strategies on the Qinghai-Tibetan Plateau.

Source: Zhou, S., Xiu, Y., Wu, J., Gong, J., Kausar, T., Degen, A. A., Sun, F., Ma, Z., Xue, R., & Bai, Y. (2025). Decade-long active restoration induced positive priming effects on soil organic carbon in desertified grassland: The amplifying effect of biochar. Ecological Indicators, 179, 114250.